WO2012056501A1

WO2012056501A1 - Step-down chopper device

Info

Publication number: WO2012056501A1
Application number: PCT/JP2010/006411
Authority: WO
Inventors: 村田一大; 崎村紘子
Original assignee: パナソニック株式会社
Priority date: 2010-10-29
Filing date: 2010-10-29
Publication date: 2012-05-03
Also published as: TW201232807A

Abstract

A switching element (SW) is disposed on a first current path between an input node (Nin1) and an intermediate node (N1). An inductor (L1) is disposed in series with a load element (RD) on a second current path between the intermediate node (N1) and an input node (N2). A reflux element (D1) is disposed on a third current path between the intermediate node (N1) and an input node (Nin2), and returns current to the second and third current paths in periods when the switching element (SW) is off. A control circuit (11) switches the switching element (SW) on and off in such a manner that the instantaneous current value of a switching current (iSW) approaches a target current value (iTG) when the time that elapses from when the switching element turns on equals a first time ratio with respect to the duration from when the switching element turns on to when the switching element turns off.

Description

Step-down chopper device

This invention relates to a step-down chopper device.

Conventionally, there is known a step-down chopper device that controls a load current flowing through a load element by controlling on / off of the switching element. In such a step-down chopper device, the time variation gradient of the inductor current flowing through the inductor (inductor) due to variations in the input voltage of the step-down chopper device, the voltage between the terminals of the load element, and the inductance value of the inductor connected in series with the load element. The current value rises or falls) varies. In addition, the average current value of the inductor current may fluctuate due to variations in the time-varying gradient of the inductor current. In this case, the current value of the load current also varies. For example, when the turn-on period and the turn-off period of the switching element are constant, the maximum current value (current value at turn-off) and / or the minimum current value (current at turn-on) due to variations in the time variation gradient of the inductor current Value) fluctuates, and as a result, the average current value of the inductor current fluctuates.

Therefore, Patent Document 1 describes the following step-down chopper device. That is, the step-down chopper device described in Patent Document 1 switches the switching element from OFF to ON when the current value of the inductor current reaches “0”, and the current value of the inductor current reaches a predetermined maximum current value. Then, the switching element is switched from on to off. As described above, when the step-down chopper device operates in the critical mode, the average current value of the inductor current can be maintained at a desired value regardless of variations in the gradient of the inductor current over time.

Special table 2008-539565 gazette

However, since the step-down chopper device described in Patent Document 1 can operate only in the critical mode, the average current value of the inductor current cannot be set to a current value higher than ½ of the maximum current value of the inductor current. . That is, when the step-down chopper device operates in the critical mode, the minimum current value of the inductor current is “0”, so the average current value of the inductor current (the average value of the maximum current value and the minimum current value) is the inductor current. 1/2 of the maximum current value. For this reason, it is difficult to increase the average current value of the inductor current.

Also, since the step-down chopper device described in Patent Document 1 can only operate in the critical mode, the conduction loss of the switching element (for example, power loss due to on-resistance) is larger than that in the case of operating in the continuous mode. That is, when the average current value of the inductor current is the same, the power loss in the switching element is higher when operating in the critical mode than when operating in the continuous mode. Therefore, it is difficult to reduce power loss in the switching element.

Accordingly, an object of the present invention is to provide a step-down chopper device that can suppress fluctuations in the average current value of the inductor current due to variations in the time-varying gradient of the inductor current and can operate not only in the critical mode but also in the continuous mode. To do.

According to one aspect of the present invention, a step-down chopper device is a step-down chopper device that controls a load current flowing through a load element, and includes a first input node and a second input node to which an input voltage is applied. A switching element provided in a first current path between the first input node and the intermediate node; and a load element in a second current path between the intermediate node and the second input node; The second and third current paths are provided in a third current path between the inductor provided in series and the intermediate node and the second input node, and the switching element is in an off state. A return element that circulates current to the switching element, and an elapsed time from turn-on of the switching element to a first duration with respect to a duration from turn-on to turn-off of the switching element. So as to approach the target current value instantaneous current value is a predetermined switching current flowing through the switching element when the time becomes ratio, and a control circuit for controlling the on / off the switching element.

In the step-down chopper device, the average current value of the inductor current can be brought close to a desired value by bringing the instantaneous current value of the switching element close to the target current value. In addition, the instantaneous current value of the switching current (when the elapsed time from the turn-on of the switching element becomes the first time ratio with respect to the duration from the turn-on to the turn-off of the switching element) with respect to the variation in the time change gradient of the inductor current Current value of the switching current) can be made difficult to fluctuate, so that fluctuations in the average current value of the inductor current due to variations in the time-varying gradient of the inductor current can be suppressed. Furthermore, since the operation is possible not only in the critical mode but also in the continuous mode, the average current value of the inductor current can be increased as compared with the case of operating only in the critical mode, and the power loss in the switching element can be reduced.

The control circuit detects the instantaneous current value of the switching current when the elapsed time from the turn-on of the switching element becomes the first time ratio with respect to the duration from the turn-on to turn-off of the switching element. Then, the turn-on cycle of the switching element may be controlled according to the difference between the instantaneous current value of the switching current and the target current value.

Further, in the step-down chopper device, the control circuit detects a switching current detection unit that detects a current value of the switching current and a turn-on elapsed time corresponding to an elapsed time from the turn-on of the switching element. The current of the switching current detected by the switching current detector when the time has reached a first time ratio with respect to a predetermined on-duration that defines the duration from the turn-on to the turn-off of the switching element A turn-on cycle adjusting unit that detects a value as an instantaneous current value of the switching current and adjusts a turn-on cycle of the switching element according to a difference between the instantaneous current value of the switching current and the target current value; and the turn-on cycle adjustment Turn-on lap adjusted by the department The switching element is turned on, turn the elapsed time detected by the turn-on cycle adjusting unit may include a switching controller to turn off the switching element when it reaches to the ON duration based on.

In the step-down chopper device, it is not necessary to detect the inductor current (or load current) in order to perform feedback control of the average current value of the inductor current, so that the power loss accompanying the detection of the inductor current (or load current) is reduced. Does not occur. Therefore, the power loss in the step-down chopper device can be reduced as compared with the case where on / off of the switching element is controlled based on the detection result of the inductor current (or load current). Further, since the turn-on cycle becomes longer as the input voltage becomes higher, the number of times of switching per unit time of the switching element is reduced. Therefore, it is possible to suppress an increase in switching loss (power loss that occurs during switching) due to an increase in input voltage.

Alternatively, in the step-down chopper device, the control circuit detects a current value of the switching current and a turn-on elapsed time corresponding to an elapsed time from the turn-on of the switching element, and the switching element Detected by the switching current detection unit when the turn-on elapsed time corresponding to the turn-on to turn-off time is equal to the first time ratio with respect to the turn-on elapsed time. A turn-on cycle adjusting unit that detects a current value of the switching current as an instantaneous current value of the switching current and adjusts a turn-on cycle of the switching element according to a difference between the instantaneous current value of the switching current and the target current value; Adjusted by the turn-on cycle adjuster Switching control for turning on the switching element based on the turn-on cycle and turning off the switching element when the current value of the switching current detected by the switching current detection unit reaches a predetermined maximum current value. May be included.

In the step-down chopper device, it is not necessary to detect the inductor current (or load current) in order to perform feedback control of the average current value of the inductor current, so that the power loss accompanying the detection of the inductor current (or load current) is reduced. Does not occur. Therefore, the power loss in the step-down chopper device can be reduced as compared with the case where on / off of the switching element is controlled based on the detection result of the inductor current (or load current). In addition, since the current value of the switching current is controlled so as not to exceed the predetermined maximum current value, the maximum current value of the switching current is limited so that the current value of the switching current does not exceed the rated current value of the switching element. it can. Thereby, selection of a switching element can be made easy.

In the step-down chopper device, the control circuit has a current value of the return current flowing through the second and third current paths lower than a predetermined current value during a period from the turn-off to the turn-on of the switching element. The turn-on cycle adjusting unit further includes a discontinuous state detecting unit that detects a discontinuous state, and the turn-on period adjusting unit continues the turn-on elapsed time when the discontinuous state is not detected by the discontinuous state detecting unit. The turn-on cycle of the switching element is adjusted according to the difference between the instantaneous current value of the switching current and the target current value when the first time ratio with respect to time is reached, and the discontinuous state detection unit When the discontinuous state is detected, the turn-on period of the switching element is set to the turn-on time of the switching element. The time ratio obtained by dividing by the current continuous time corresponding to the elapsed time until detection by the discontinuous state detecting unit becomes the first time ratio with respect to the turn-on elapsed time with respect to the ON duration time. The turn-on period of the switching element may be adjusted so as to approach the current ratio obtained by dividing the instantaneous current value of the switching current at that time by the target current value.

In the step-down chopper device, the average current value of the inductor current can be maintained at a desired value not only in the critical mode and the continuous mode but also in the discontinuous mode.

Alternatively, in the step-down chopper device, the control circuit continues from the turn-on of the switching element to the turn-off after the switching element is turned on until the current value of the switching current reaches the target current value. You may control the continuation time from the turn-on of the said switching element to the turn-off so that it may become the said 1st time ratio with respect to time.

In the step-down chopper device, the current value of the switching current when the elapsed time from the turn-on of the switching element becomes the first time ratio with respect to the duration from the turn-on to the turn-off of the switching element is brought close to the target current value. become.

In the step-down chopper device, the control circuit includes a switching current detection unit that detects a current value of the switching current, and a current of the switching current that is detected by the switching current detection unit after the switching element is turned on. The ON duration time is set so that the arrival time until the value reaches the target current value becomes the first time ratio with respect to the ON duration time that defines the duration time from the turn-on to the turn-off of the switching element. The ON duration adjusting unit to adjust, and the switching element is turned on based on a predetermined turn-on period, and the ON duration time adjusted by the ON duration adjusting unit elapses after the switching element is turned on. Switching to turn off the switching element It may include a control unit.

In the step-down chopper device, it is not necessary to detect the inductor current (or load current) in order to perform feedback control of the average current value of the inductor current, so that the power loss accompanying the detection of the inductor current (or load current) is reduced. Does not occur. Therefore, the power loss in the step-down chopper device can be reduced as compared with the case where on / off of the switching element is controlled based on the detection result of the inductor current (or load current).

In the step-down chopper device, the control circuit has a current value of a return current flowing through the second and third current paths lower than a predetermined current value during a period from the turn-off to the turn-on of the switching element. The switching control unit may further include a discontinuous state detecting unit that detects a discontinuous state, and the switching control unit may turn on the switching element when the discontinuous state is detected by the discontinuous state detecting unit.

The above step-down chopper device can prevent the transition from the continuous mode to the discontinuous mode.

Alternatively, in the step-down chopper device, the control circuit includes a switching current detection unit that detects a current value of the switching current, an inductor current detection unit that detects a current value of an inductor current flowing in the inductor, and the switching element. The time required for the switching current detected by the switching current detector to reach the target current value after the turn-on is determined to be an ON duration that defines the duration from the turn-on to the turn-off of the switching element. An on-duration adjusting unit that adjusts the on-duration so as to be the first time ratio, and a current value of the inductor current detected by the inductor current detecting unit after the switching element is turned off. Reached until the target current value is reached An off duration adjusting unit for adjusting the off duration so that the interval is a second time ratio with respect to an off duration defining a duration from turn-off to turn-on of the switching element; After the turn-on, the switching element is turned off when the on-duration adjusted by the on-duration adjusting unit has elapsed, and the off-adjusted by the off-duration adjusting unit after the switching element is turned off. And a switching control unit that turns on the switching element when the duration time elapses.

In the above step-down chopper device, the transition from the continuous mode to the discontinuous mode can be prevented by adjusting the OFF duration.

Note that the first time ratio is 1 / 2.22 or more and may be 1 / 1.82 or less. By setting in this way, the fluctuation amount of the average current value of the inductor current with respect to the fluctuation of the input voltage can be kept within the allowable range.

The second time ratio is 1 / 2.22 or more and may be 1 / 1.82 or less. By setting in this way, the fluctuation amount of the average current value of the inductor current with respect to the fluctuation of the input voltage can be kept within the allowable range.

As described above, it is possible to suppress fluctuations in the average current value of the inductor current due to variations in the time change gradient of the inductor current. Further, since the operation is possible not only in the critical mode but also in the continuous mode, the average current value of the inductor current can be increased and the power loss in the switching element can be reduced as compared with the case of operating only in the critical mode.

FIG. 3 is a diagram illustrating a configuration example of a step-down chopper device according to the first embodiment. The figure which shows the structural example of the turn-on period adjustment part shown in FIG. The figure which shows the structural example of the switching control part shown in FIG. The timing chart for demonstrating the operation | movement by the pressure | voltage fall chopper apparatus shown in FIG. The timing chart for demonstrating the case where the raise gradient of an inductor electric current becomes steep in the pressure | voltage fall chopper apparatus shown in FIG. The timing chart for demonstrating the case where the fall gradient of an inductor electric current becomes steep in the pressure | voltage fall chopper apparatus shown in FIG. The figure which shows the structural example of the pressure | voltage fall chopper apparatus by Embodiment 2. FIG. The figure which shows the structural example of the turn-on period adjustment part shown in FIG. The figure which shows the structural example of the switching control part shown in FIG. The timing chart for demonstrating the operation | movement by the pressure | voltage fall chopper apparatus shown in FIG. FIG. 8 is a timing chart for explaining a case where the rising gradient of the inductor current becomes steep in the step-down chopper device shown in FIG. 7. The timing chart for demonstrating the case where the fall gradient of an inductor current becomes steep in the step-down chopper device shown in FIG. FIG. 6 is a diagram illustrating a configuration example of a step-down chopper device according to a third embodiment. The figure which shows the structural example of the non-continuous state detection part shown in FIG. The figure which shows the structural example of the turn-on period adjustment part shown in FIG. FIG. 14 is a diagram illustrating a configuration example of a switching control unit illustrated in FIG. 13. 14 is a timing chart for explaining the operation (continuous mode) by the step-down chopper device shown in FIG. 13. The timing chart for demonstrating the operation | movement (discontinuous mode) by the pressure | voltage fall chopper apparatus shown in FIG. The figure which shows the modification of the pressure | voltage fall chopper apparatus shown in FIG. The figure which shows the structural example of the turn-on period adjustment part shown in FIG. The figure which shows the structural example of the switching control part shown in FIG. The figure which shows the modification of a period control part. The figure which shows the modification of a discontinuous state detection part. FIG. 10 is a diagram illustrating a configuration example of a step-down chopper device according to a fourth embodiment. The figure which shows the structural example of the ON continuation time adjustment part shown in FIG. The figure which shows the structural example of the switching control part shown in FIG. The timing chart for demonstrating the operation | movement by the pressure | voltage fall chopper apparatus shown in FIG. The timing chart for demonstrating the case where the raise gradient of an inductor electric current becomes steep in the pressure | voltage fall chopper apparatus shown in FIG. The timing chart for demonstrating the case where the fall gradient of an inductor current becomes steep in the pressure | voltage fall chopper apparatus shown in FIG. FIG. 10 is a diagram illustrating a configuration example of a step-down chopper device according to a fifth embodiment. The figure which shows the structural example of the discontinuous state detection part shown in FIG. The figure which shows the structural example of the switching control part shown in FIG. The timing chart for demonstrating the operation | movement (continuous mode) by the pressure | voltage fall chopper apparatus shown in FIG. The timing chart for demonstrating the operation | movement (discontinuous mode prevention) by the pressure | voltage fall chopper apparatus shown in FIG. FIG. 10 is a diagram illustrating a configuration example of a step-down chopper device according to a sixth embodiment. The figure which shows the structural example of the OFF continuation time adjustment part shown in FIG. The figure which shows the structural example of the switching control part shown in FIG. The timing chart for demonstrating the operation | movement by the pressure | voltage fall chopper apparatus shown in FIG. The timing chart for demonstrating the case where the rising gradient of an inductor current becomes steep in the step-down chopper device shown in FIG. The timing chart for demonstrating the case where the fall gradient of an inductor current becomes steep in the pressure | voltage fall chopper apparatus shown in FIG. The graph for demonstrating the setting range of a time ratio. The figure for demonstrating the modification (low side type) of a pressure | voltage fall chopper apparatus. The figure which shows the structural example of the image display apparatus provided with the pressure | voltage fall chopper apparatus as a light source drive device.

Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 shows a configuration example of a step-down chopper device 1 according to a first embodiment. The step-down chopper device 1 controls a load current iRD flowing through the load element RD, and includes a switching element SW, an inductor L1, a freewheeling diode D1 (freewheeling element), and a control circuit 11.

[Switching element, inductor, freewheeling diode]
The switching element SW is provided in a current path (first current path) between the input node Nin1 and the intermediate node N1, and switches on / off in response to the switching control signal SWG. An input voltage Vin is applied between the input nodes Nin1 and Nin2. Inductor L1 is provided in series with load element RD in the current path (second current path) between intermediate node N1 and input node Nin2. The free-wheeling diode D1 is provided in a current path (third current path) between the intermediate node N1 and the input node Nin2. Further, the freewheeling diode D1 recirculates the current to the second and third current paths (a closed circuit path constituted by the inductor L1, the load element RD, and the freewheeling diode) during a period in which the switching element SW is in the off state. Here, a capacitor CC is connected in parallel to the load element RD. That is, the load current iRD is a direct current corresponding to the average current value of the inductor current iL flowing through the inductor L1. Note that the capacitor CC may not be connected in parallel to the load element RD. In this case, the load current iRD is the same current as the inductor current iL.

[Control circuit]
The control circuit 11 switches the switching current flowing in the switching element SW when the elapsed time from the turn-on of the switching element SW becomes the first time ratio (1 / a) with respect to the duration from the turn-on to the turn-off of the switching element SW. The switching element SW is turned on / off so that the instantaneous current value of iSW approaches a predetermined target current value iTG. Here, the control circuit 11 determines the switching current iSW when the elapsed time from the turn-on of the switching element SW becomes the first time ratio (1 / a) with respect to the duration from the turn-on to the turn-off of the switching element SW. The instantaneous current value is detected, and the turn-on cycle of the switching element SW is controlled according to the difference between the instantaneous current value of the switching current iSW and the target current value iTG. The control circuit 11 may include a switching current detection unit 101, a turn-on cycle adjustment unit 102, a switching control unit 103, an on duration setting unit 104, and a target current value setting unit 105.

<ON duration setting section>
The ON duration setting unit 104 sets an ON duration TCon (here, a voltage corresponding to the ON duration TCon) that defines the duration from the turn-on to the turn-off of the switching element SW. The longer the ON duration time TCon, the higher the voltage corresponding to the ON duration time TCon. Note that the on duration setting unit 104 may change the on duration TCon in response to external control. That is, the ON duration time TCon may be a predetermined fixed value or a variable value that can be changed by external control.

<Target current value setting section>
The target current value setting unit 105 sets a target current value iTG (here, a voltage corresponding to the target current value iTG). The higher the target current value iTG, the higher the voltage corresponding to the target current value iTG. When the average current value of the inductor current iL is maintained at a desired value, the target current value iTG is equal to the first time with respect to the duration from the turn-on of the switching element SW to the turn-off. This corresponds to the current value of switching current iSW at the time ratio (1 / a) (ideal value of instantaneous current value). For example, when the first time ratio (1 / a) is “1/2”, the target current value iTG corresponds to a desired value of the average current value of the inductor current. Note that the target current value setting unit 105 may change the target current value iTG in response to external control. That is, the target current value iTG may be a predetermined fixed value or a variable value that can be changed by external control.

<Switching current detector>
The switching current detection unit 101 detects a current value (switching current value idSW) of the switching current iSW. Here, the switching current detection unit 101 detects a voltage (for example, the drain voltage of the switching element SW) corresponding to the switching current value idSW. The higher the switching current value idSW, the higher the voltage corresponding to the switching current value idSW.

<Turn-on cycle adjuster>
The turn-on cycle adjusting unit 102 detects a turn-on elapsed time TEon (here, a voltage corresponding to the turn-on elapsed time TEon) corresponding to the elapsed time from the turn-on of the switching element SW. The longer the turn-on elapsed time TEon, the higher the voltage corresponding to the turn-on elapsed time TEon. Further, the turn-on cycle adjusting unit 102 is a switching current detecting unit when the turn-on elapsed time TEon becomes the first time ratio (1 / a) with respect to the on-duration time TCon set by the on-duration setting unit 104. The switching current value idSW detected by 101 is detected as the instantaneous current value of the switching current iSW. Here, the turn-on cycle adjusting unit 102 detects a voltage corresponding to the instantaneous current value of the switching current iSW. The higher the instantaneous current value of the switching current iSW, the higher the voltage corresponding to the instantaneous current value of the switching current iSW. Further, the turn-on cycle adjusting unit 102 is a cycle control voltage that defines the turn-on cycle of the switching element SW according to the difference between the instantaneous current value of the switching current iSW and the target current value iTG set by the target current value setting unit 105. The turn-on cycle of the switching element SW is adjusted by raising or lowering CNT.

《Switching control unit》
The switching control unit 103 changes the signal level of the switching control signal SWG from the low level to the high level based on the turn-on cycle (turn-on cycle corresponding to the cycle control voltage CNT) adjusted by the turn-on cycle adjusting unit 102. The switching element SW is turned on (the switching element SW is changed from the off state to the on state). Further, the switching control unit 103 sets the signal level of the switching control signal SWG when the turn-on elapsed time TEon detected by the turn-on period adjusting unit 102 reaches the on-duration time TCon set by the on-duration setting unit 104. The switching element SW is turned off by changing from the high level to the low level (the switching element SW is changed from the on state to the off state).

[Configuration example of turn-on cycle adjuster]
As shown in FIG. 2, the turn-on cycle adjustment unit 102 may include a turn-on elapsed time detection unit 111, a time ratio detection unit 112, an instantaneous current value detection unit 113, and a cycle control unit 114.

<Turn-on elapsed time detector>
The turn-on elapsed time detector 111 detects the turn-on elapsed time TEon. For example, the turn-on elapsed time detector 111 may include a capacitor C1, a current source CS1, switching elements SW1 and SW2, and an inverter INV1. One end of the capacitor C1 is connected to a ground node (a node to which the ground voltage GND is applied). Current source CS1 and switching element SW1 are connected in series between a power supply node (a node to which power supply voltage VDD is applied) and the other end of capacitor C1. Switching element SW2 is connected between the other end of capacitor C1 and the ground node. The inverter INV1 inverts the switching control signal SWG. The switching elements SW1 and SW2 are turned on / off in response to the switching control signal SWG and the output signal of the inverter INV1, respectively.

When the signal level of the switching control signal SWG changes from the low level to the high level, the switching element SW1 is turned on and the switching element SW2 is turned off. Thereby, charging of the capacitor C1 by the current source CS1 is started, and the voltage of the capacitor C1 (voltage corresponding to the turn-on elapsed time TEon) gradually increases. When the signal level of the switching control signal SWG changes from the high level to the low level, the switching element SW1 is turned off and the switching element SW2 is turned on. Thereby, discharging of the capacitor C1 is started, and the voltage of the capacitor C1 is reset to an initial value (for example, 0V).

The time ratio detection unit 112 detects that the turn-on elapsed time TEon has reached the first time ratio (1 / a) with respect to the ON duration time TCon. For example, the time ratio detection unit 112 may include a time voltage generation unit VG1 and a comparator CMP1. The time voltage generation unit VG1 multiplies the voltage corresponding to the ON duration time TCon by 1 / a and outputs it as a voltage corresponding to the comparison time TXon (a time corresponding to 1 / a of the ON duration time TCon). For example, the time voltage generation unit VG1 may be a resistance divider circuit that multiplies the voltage corresponding to the ON duration time TCon by 1 / a. The comparator CMP1 compares the voltage corresponding to the comparison time TXon with the voltage corresponding to the turn-on elapsed time TEon. Here, when the turn-on elapsed time TEon reaches the comparison time TXon, the signal level of the output signal (timing signal TMG) of the comparator CMP1 changes from the high level to the low level.

In response to the detection by the time ratio detection unit 112, the instantaneous current value detection unit 113 uses the switching current value idSW detected by the switching current detection unit 101 as a first value for the turn-on elapsed time TEon with respect to the ON duration TCon. It is detected as an instantaneous current value (instantaneous current value iDET) of the switching current iSW at the time ratio (1 / a). For example, the instantaneous current value detection unit 113 may include a sample / hold circuit (S / H) SH1. The sample / hold circuit SH1 samples the voltage corresponding to the switching current value idSW in synchronization with the transition edge (here, the falling edge) of the timing signal TMG, and the sampled voltage corresponds to the instantaneous current value iDET. Hold as.

The cycle control unit 114 increases or decreases the cycle control voltage CNT for controlling the turn-on cycle of the switching element SW according to the difference between the instantaneous current value iDET and the target current value iTG. Here, the periodic control voltage CNT decreases as the instantaneous current value iDET increases with respect to the target current value iTG. For example, the cycle control unit 124 may include a comparator CMP2 and a resistance element R1. The comparator CMP2 compares the voltage corresponding to the instantaneous current value iDET with the voltage corresponding to the target current value iTG. The resistance element R1 feeds back the output signal of the comparator CMP2 to the inverting input terminal of the comparator CMP2.

[Configuration example of switching control unit]
As shown in FIG. 3, the switching control unit 103 may include an oscillator 115, a comparator 116, a pulse generator 117, and an SR latch 118.

The oscillator 115 periodically outputs a turn-on pulse Pon based on the turn-on period corresponding to the cycle control voltage CNT. Here, the lower the cycle control voltage CNT, the longer the turn-on cycle. The comparator 116 compares the voltage corresponding to the turn-on elapsed time TEon with the voltage corresponding to the on-duration time TCon. Here, when the turn-on elapsed time TEon reaches the ON duration TCon, the signal level of the output signal of the comparator 116 changes from the high level to the low level. The pulse generator 117 outputs a turn-off pulse Poff in synchronization with the output change of the comparator 116 (here, the falling edge of the output signal of the comparator 116). The SR latch 118 changes the signal level of the switching control signal SWG from the low level to the high level in response to the turn-on pulse Pon from the oscillator 115. In addition, the SR latch 118 changes the signal level of the switching control signal SWG from the high level to the low level in response to the turn-off pulse Poff from the pulse generator 117.

[Operation]
Next, the operation of the step-down chopper device 1 will be described with reference to FIG. Here, it is assumed that the first time ratio (1 / a) is “1/2”.

First, in the switching control unit 103, when the oscillator 115 outputs the nth turn-on pulse Pon (n is an arbitrary natural number), the SR latch 118 changes the signal level of the switching control signal SWG from the low level to the high level. Let Thereby, the switching element SW is turned on, and the inductor current iL (switching current value iSW) gradually increases.

Next, when the turn-on elapsed time TEon reaches the comparison time TXon (1/2 of the on-duration time TCon set by the on-duration time setting unit 104), in the turn-on period adjusting unit 102, the time ratio detecting unit 112 The signal level of the signal TMG is changed from a high level to a low level. The instantaneous current value detection unit 113 detects the switching current value idSW as the instantaneous current value iDET in response to the falling edge of the timing signal TMG. The cycle control unit 114 increases or decreases the cycle control voltage CNT according to the difference between the instantaneous current value iDET and the target current value iTG. As a result, the switching control unit 103 adjusts the output period of the turn-on pulse Pon in the oscillator 115 (that is, the turn-on period T of the switching element SW).

Next, when the turn-on elapsed time TEon reaches the ON duration TCon (ON duration TCon set by the ON duration setting unit 104), the signal level of the output signal of the comparator 116 is high in the switching control unit 103. The pulse generator 117 outputs a turn-off pulse Poff. The SR latch 118 changes the signal level of the switching control signal SWG from the high level to the low level in response to the turn-off pulse Poff. As a result, the switching element SW is turned off, and the inductor current iL gradually decreases.

Next, when a turn-on cycle T (turn-on cycle adjusted by the turn-on cycle adjusting unit 102) has elapsed since the generation of the n-th turn-on pulse Pon, the switching control unit 103 causes the oscillator 115 to switch the n + 1-th turn-on pulse Pon. Is output.

[Adjustment of turn-on cycle]
The turn-on period T of the switching element SW is adjusted according to the difference value (iDET−iTG) between the instantaneous current value iDET of the switching current and the target current value iTG. For example, as shown in FIG. 5, when the rising slope of the inductor current iL (switching current iSW) becomes steeper than in the case of FIG. 4 (for example, when the input voltage Vin increases), the instantaneous current value iDET of the switching current and the target current The difference value (iDET−iTG) from the value iTG is larger than in the case of FIG. 4, and the cycle control voltage CNT is lower than in the case of FIG. As a result, the turn-on period T of the switching element SW becomes longer than in the case of FIG. Further, as shown in FIG. 6, when the descending gradient of the inductor current iL becomes steeper than in the case of FIG. 4 (for example, when the voltage across the terminals of the load element RD becomes higher), the instantaneous current value iDET of the switching current and the target current value The difference value from iTG (iDET−iTG) is smaller than that in FIG. 4, and the cycle control voltage CNT is higher than that in FIG. As a result, the turn-on period T of the switching element SW is shorter than in the case of FIG.

As described above, by adjusting the turn-on cycle T of the switching element SW so that the instantaneous current value iDET of the switching current approaches the target current value iTG, the average current value iAVE of the inductor current can be brought close to a desired value. Here, as the amplification gain of the comparator CMP2 included in the cycle control unit 114 increases, the difference value between the instantaneous current value iDET of the switching current and the target current value iTG becomes closer to “0”. That is, the instantaneous current value iDET of the switching current can be brought close to the target current value iTG. In FIG. 4, for the sake of simplification, the difference value between the instantaneous current value iDET of the switching current and the target current value iTG is assumed to be “0”. Further, since the amount of change in the difference value between the instantaneous current value iDET of the switching current and the target current value iTG is minute relative to the amount of change in the turn-on cycle T of the switching element SW, FIG. 5 and FIG. For simplification, it is assumed that the amount of change in the difference value between the instantaneous current value iDET of the switching current and the target current value iTG is “0”.

[Variation of time gradient of inductor current]
4, 5, and 6, even if the time change gradient of the inductor current iL varies, the elapsed time from the turn-on of the switching element SW to the duration Ton from the turn-on to the turn-off of the switching element SW When the current becomes “½”, the current value of the inductor current iL (switching current iSW) becomes the average current value iAVE of the inductor current. Further, as the elapsed time from the turn-on of the switching element SW is closer to ½ of the elapsed time Ton from the turn-on to the turn-off of the switching element SW, the current value of the inductor current iL (switching current iSW) at that elapsed time becomes the inductor value. It becomes difficult for the current iL to fluctuate with respect to the variation of the time change gradient. That is, the switching current when the turn-on elapsed time TEon becomes the first time ratio (1 / a) with respect to the ON duration time TCon as the first time ratio (1 / a) becomes closer to “1/2”. The instantaneous current value iDET is less likely to fluctuate with respect to the variation in the time change gradient of the inductor current iL.

As described above, since the instantaneous current value iDET of the switching current can be made difficult to fluctuate with respect to the variation in the time variation gradient of the inductor current iL, the average of the inductor current caused by the variation in the time variation gradient of the inductor current iL. Variations in the current value iAVE can be suppressed.

When operating in the continuous mode and the critical mode, the average current value iAVE of the inductor current corresponds to the average value ((iP + iS) / 2) of the maximum current value iP and the minimum current value iS of the inductor current. Here, the minimum current value iS of the inductor current is “0” when operating in the critical mode, and is higher than “0” when operating in the continuous mode. Therefore, assuming that the maximum current value iP of the inductor current is the same value, the average current value iAVE of the inductor current is higher when operating in the continuous mode than when operating in the critical mode. That is, since the step-down chopper device 1 shown in FIG. 1 can operate not only in the critical mode but also in the continuous mode, the average current value iAVE of the inductor current can be made higher than when operating only in the critical mode. .

Also, assuming that the average current value of the inductor current is the same value, the power loss in the switching element SW is lower when operating in the continuous mode than when operating in the critical mode. That is, since the step-down chopper device 1 shown in FIG. 1 can operate not only in the critical mode but also in the continuous mode, the power loss in the switching element SW can be reduced as compared with the case of operating only in the critical mode.

In addition, in order to maintain the average current value of the inductor current at a desired value, the inductor current (or load current) is detected using a resistance element, and the average current value of the inductor current is controlled based on the detection result. (Feedback control) can be considered. With this method, power loss occurs when detecting the inductor current (or load current). On the other hand, in the step-down chopper device 1 shown in FIG. 1, the inductor current iL (or load current iRD) does not have to be detected in order to feedback control the average current value iAVE of the inductor current. , No power loss due to detection of the load current iRD) occurs. Therefore, power loss in the step-down chopper device can be reduced as compared with the case where on / off of switching element SW is controlled based on the detection result of inductor current iL (or load current iRD).

In general, the higher the input voltage Vin, the greater the switching loss (power loss generated during switching) per switching in the switching element SW. In the step-down chopper device 1 shown in FIG. 1, the higher the input voltage Vin, the longer the turn-on cycle T of the switching element SW, and the lower the number of switching times per unit time of the switching element SW. Therefore, an increase in switching loss accompanying an increase in the input voltage Vin can be suppressed.

(Embodiment 2)
FIG. 7 shows a configuration example of the step-down chopper device 2 according to the second embodiment. The step-down chopper device 2 includes a control circuit 21 instead of the control circuit 11 shown in FIG. The control circuit 21 replaces the turn-on cycle adjusting unit 102, the switching control unit 103, and the on duration setting unit 104 shown in FIG. 1 with a turn-on cycle adjusting unit 202, a switching control unit 203, and a maximum current value setting unit. 204. Other configurations may be the same as those in FIG.

<Maximum current value setting section>
The maximum current value setting unit 204 sets a maximum current value iMAX (here, a voltage corresponding to the maximum current value iMAX) that defines the maximum current value of the inductor current iL (switching current iSW). As the maximum current value iMAX increases, the voltage corresponding to the maximum current value iMAX increases. The maximum current value setting unit 204 may change the maximum current value iMAX in response to external control. That is, the maximum current value iMAX may be a predetermined fixed value or a variable value that can be changed by external control.

<Turn-on cycle adjuster>
The turn-on cycle adjusting unit 202 detects a turn-on elapsed time TEon (here, a voltage corresponding to the turn-on elapsed time TEon) corresponding to the elapsed time from the turn-on of the switching element SW. Further, the turn-on cycle adjusting unit 202 detects an on duration TCon (here, a voltage corresponding to the on duration TCon) corresponding to the duration from the turn-on to the turn-off of the switching element SW. Further, the turn-on cycle adjusting unit 202 detects the current of the switching current iSW detected by the switching current detecting unit 101 when the turn-on elapsed time TEon becomes the first time ratio (1 / a) with respect to the on-continuation time TCon. The value (switching current value idSW) is detected as the instantaneous current value (instantaneous current value iDET) of the switching current. Further, the turn-on cycle adjusting unit 202 increases the cycle control voltage CNT that defines the turn-on cycle of the switching element SW according to the difference between the instantaneous current value iDET and the target current value iTG set by the target current value setting unit 105. Alternatively, the turn-on cycle of the switching element SW is adjusted by lowering.

《Switching control unit》
The switching control unit 203 changes the signal level of the switching control signal SWG from the low level to the high level based on the turn-on cycle (turn-on cycle corresponding to the cycle control voltage CNT) adjusted by the turn-on cycle adjusting unit 202. The switching element SW is turned on. Further, the switching control unit 203, when the current value of the switching current iSW detected by the switching current detection unit 101 (switching current value idSW) reaches the maximum current value iMAX set by the maximum current value setting unit 204, The switching element SW is turned off by changing the signal level of the switching control signal SWG from the high level to the low level.

[Configuration example of turn-on cycle adjuster]
As shown in FIG. 8, the turn-on cycle adjusting unit 202 may include an on-duration detecting unit 211 in addition to the configuration example of the turn-on cycle adjusting unit 102 shown in FIG. 2. Based on the turn-on elapsed time TEon, the on-duration detection unit 211 detects an on-duration TCon corresponding to the duration from the turn-on of the switching element SW to the turn-off. For example, the ON duration detection unit 211 may include a peak / hold circuit (P / H) PH1, capacitors C2 and C3, switching elements SW3 and SW4, and an inverter INV2.

The peak / hold circuit PH1 detects and holds the maximum value of the voltage corresponding to the turn-on elapsed time TEon. One ends of the capacitors C2 and C3 are connected to the ground node. The switching element SW3 is connected between the peak / hold circuit PH1 and the other end of the capacitor C2. Switching element SW4 is connected between the other end of capacitor C2 and the other end of capacitor C3. The inverter INV2 inverts the switching control signal SWG. Switching elements SW3 and SW4 are turned on / off in response to the output signal of inverter INV2 and switching control signal SWG, respectively.

When the nth falling edge (change from high level to low level) of the switching control signal SWG occurs, the turn-on elapsed time detector 111 resets the voltage corresponding to the turn-on elapsed time TEon. Therefore, the voltage held in the peak / hold circuit PH1 can be said to be a voltage corresponding to the duration (n-th on-time) from the n-th turn-on of the switching element SW to the n-th turn-off. In response to the falling edge of the switching control signal SWG, the switching element SW3 is turned on and the switching element SW4 is turned off. As a result, the voltage held in the peak / hold circuit PH1 (that is, the voltage corresponding to the n-th on-time) is held in the capacitor C2.

Next, when the (n + 1) th rising edge (change from low level to high level) of the switching control signal SWG occurs, the voltage corresponding to the turn-on elapsed time TEon starts to rise in the turn-on elapsed time detection unit 111, and the peak The voltage held in the / hold circuit PH1 also gradually increases. In response to the rising edge of the switching control signal SWG, the switching element SW3 is turned off and the switching element SW4 is turned on. As a result, the voltage TCn held in the capacitor C2 (voltage corresponding to the n-th on-time) is applied to the capacitor C3. Therefore, the voltage held in the capacitor C3 can be said to be a voltage corresponding to the time corresponding to the first to n-th on times (for example, the average time of the first to n-th on times). . The voltage held in the capacitor C3 is supplied as a voltage corresponding to the ON duration TCon (ON duration detected by the ON duration detector 211).

Note that the ON duration detection unit 211 may further include a voltage correction circuit that corrects fluctuations in voltage corresponding to the ON duration TCon (voltage drop in the switching elements SW2 and SW3, etc.).

[Configuration example of switching control unit]
As illustrated in FIG. 9, the switching control unit 203 may include a comparator 216 instead of the comparator 116 illustrated in FIG. 3. Other configurations may be the same as those in FIG. The comparator 216 compares the voltage corresponding to the switching current value idSW with the voltage corresponding to the maximum current value iMAX. Here, when the switching current value idSW reaches the maximum current value iMAX, the signal level of the output signal of the comparator 216 changes from the high level to the low level. The pulse generator 117 outputs a turn-off pulse Poff in synchronization with the output change (here, falling edge) of the comparator 216.

[Operation]
Next, the operation of the step-down chopper device 2 will be described with reference to FIG. Here, it is assumed that the first time ratio (1 / a) is “1/2”. In FIG. 10, for the sake of simplification, the difference value between the instantaneous current value iDET and the target current value iTG is assumed to be “0”.

First, in the switching control unit 203, when the oscillator 115 outputs the nth turn-on pulse Pon, the SR latch 118 changes the signal level of the switching control signal SWG from the low level to the high level. Thereby, the switching element SW is turned on, and the inductor current iL (switching current value iSW) gradually increases.

Next, when the turn-on elapsed time TEon reaches the comparison time TXon (1/2 of the on-duration time TCon detected by the on-duration detection unit 211), in the turn-on cycle adjusting unit 202, the time ratio detection unit 112 The signal level of the signal TMG is changed from a high level to a low level. The instantaneous current value detection unit 113 detects the switching current value idSW as the instantaneous current value iDET in response to the falling edge of the timing signal TMG. The cycle control unit 114 increases or decreases the cycle control voltage CNT according to the difference between the instantaneous current value iDET and the target current value iTG. As a result, the switching control unit 203 adjusts the output period of the turn-on pulse Pon in the oscillator 115 (that is, the turn-on period T of the switching element SW).

Next, when the switching current value idSW reaches the maximum current value iMAX, in the switching control unit 203, the signal level of the output signal of the comparator 216 changes from high level to low level, and the pulse generator 117 turns off the turn-off pulse Poff. Is output. The SR latch 118 changes the signal level of the switching control signal SWG from the high level to the low level in response to the turn-off pulse Poff. As a result, the switching element SW is turned off, and the inductor current iL gradually decreases. Further, in the turn-on cycle adjusting unit 202, the on-duration detection unit 211 detects the on-duration time TCon based on the turn-on elapsed time TEon.

Next, when a turn-on cycle T (turn-on cycle adjusted by the turn-on cycle adjusting unit 202) has elapsed since the generation of the n-th turn-on pulse Pon, the switching control unit 103 causes the oscillator 115 to switch the n + 1-th turn-on pulse Pon. Is output.

[Adjustment of turn-on cycle]
The turn-on period T of the switching element SW is adjusted according to the difference value (iDET−iTG) between the instantaneous current value iDET of the switching current and the target current value iTG. For example, as shown in FIG. 11, when the rising gradient of the inductor current iL (switching current iSW) becomes steeper than in FIG. 10, the difference value (iDET−iTG) between the instantaneous current value iDET of the switching current and the target current value iTG. ) Is smaller than in the case of FIG. 10, and the cycle control voltage CNT is lower than in the case of FIG. As a result, the turn-on period T of the switching element SW becomes shorter than that in the case of FIG. Also, as shown in FIG. 12, when the drop gradient of the inductor current iL becomes steeper than in the case of FIG. 10, the difference value (iDET−iTG) between the instantaneous current value iDET of the switching current and the target current value iTG is shown in FIG. The period control voltage CNT becomes higher than in the case of FIG. As a result, the turn-on period T of the switching element SW becomes shorter than that in the case of FIG.

As described above, by adjusting the turn-on cycle T of the switching element SW so that the instantaneous current value iDET of the switching current approaches the target current value iTG, the average current value iAVE of the inductor current can be brought close to a desired value. Note that the amount of change in the difference value between the instantaneous current value iDET of the switching current and the target current value iTG is very small with respect to the amount of change in the turn-on cycle T of the switching element SW. For simplification, it is assumed that the amount of change in the difference value between the instantaneous current value iDET of the switching current and the target current value iTG is “0”.

[Variation of time gradient of inductor current]
Here, from FIG. 10, FIG. 11, and FIG. 12, the turn-on elapsed time TEon is the first time ratio with respect to the on-continuation time TCon as the first time ratio (1 / a) is closer to “1/2”. It can be seen that the instantaneous current value iDET of the switching current at (1 / a) is less likely to fluctuate with respect to the variation in the time change gradient of the inductor current iL.

As described above, since the instantaneous current value iDET of the switching current can be made difficult to fluctuate with respect to the variation in the time variation gradient of the inductor current iL, the average of the inductor current caused by the variation in the time variation gradient of the inductor current iL. Variations in the current value iAVE can be suppressed. Further, since the operation is possible not only in the critical mode but also in the continuous mode, the average current value iAVE of the inductor current can be increased and the power loss in the switching element SW can be reduced as compared with the case of operating only in the critical mode. .

Furthermore, since it is not necessary to detect the inductor current iL (or load current iRD) in order to perform feedback control of the average current value iAVE of the inductor current, it is based on the detection result of the inductor current iL (or load current iRD). The power loss in the step-down chopper device can be reduced as compared with the case where on / off of the switching element SW is controlled.

Further, since the current value of the switching current iSW is controlled so as not to exceed the predetermined maximum current value iMAX, the maximum switching current is set so that the current value of the switching current iSW does not exceed the rated current value of the switching element SW. The current value iP can be limited. Thereby, selection of switching element SW can be made easy.

(Embodiment 3)
FIG. 13 shows a configuration example of the step-down chopper device 3 according to the third embodiment. The step-down chopper device 3 includes a control circuit 31 instead of the control circuit 11 shown in FIG. The control circuit 31 includes a discontinuous state detection unit 301, a turn-on cycle adjustment unit 302, and a switching control unit 303 instead of the turn-on cycle adjustment unit 102 and the switching control unit 103 shown in FIG. Other configurations may be the same as those in FIG.

《Discontinuous state detector》
The discontinuous state detection unit 301 detects that a discontinuous state has occurred. The discontinuous state is a return current flowing through the second and third current paths (a closed circuit path formed by the inductor L1, the load element RD, and the return diode D1) during the period from the turn-off to the turn-on of the switching element SW. Is a state where the current value becomes lower than a predetermined current value (for example, around 0 A). Here, the discontinuous state detection unit 301 detects that a discontinuous state has occurred based on the difference between the voltages across the inductor L1 (the node voltage V1 at the intermediate node N1 and the node voltage V2 at the intermediate node N3). .

<Turn-on cycle adjuster>
When the discontinuous state detection unit 301 does not detect the discontinuous state, the turn-on period adjusting unit 302 determines the turn-on period T (() of the switching element SW according to the difference between the instantaneous current value iDET of the switching current and the target current value iTG. (Turn-on period corresponding to continuous mode or critical mode). On the other hand, when the discontinuous state is detected by the discontinuous state detecting unit 301, the turn-on period adjusting unit 302 sets the turn-on period T of the switching element SW to the current continuous time (from the turn-on of the switching element SW to the discontinuous state detecting unit 301. The time ratio (T / TDon) obtained by dividing by the elapsed time until the detection) is an instantaneous current value iDET of the switching current (the turn-on elapsed time TEon is equal to the first time ratio (1 / a) corresponding to the turn-on period T (discontinuous mode) of the switching element SW so as to approach the current ratio (iDET / iTG) obtained by dividing the switching current value idSW) at the time of a) by the target current value iTG. Adjust the turn-on cycle.

《Switching control unit》
Similar to the switching control unit 103 shown in FIG. 1, the switching control unit 303 turns on the switching element SW based on the turn-on cycle T adjusted by the turn-on cycle adjusting unit 302, and the turn-on elapsed time TEon is on duration. When TCon is reached, the switching element SW is turned off.

[Configuration example of non-continuous state detector]
As shown in FIG. 14, the discontinuous state detection unit 301 may include a comparator CMP3 and a logic circuit (LGC) LGC1. The comparator CMP3 compares the voltage across the inductor L1 (node voltages V1, V2). Here, when the node voltage V1 becomes higher than the node voltage V2 and when the node voltages V1 and V2 become equal to each other, the signal level of the output signal of the comparator CMP3 changes from the high level to the low level. When the signal level of the output signal of the comparator CMP3 changes from the high level to the low level during the period in which the switching control signal SWG is at the low level, the logic circuit LCG1 has the signal level of the discontinuous detection signal S301 (the output signal of the logic circuit LCG1). Is changed from the high level to the low level, and the signal level of the switching control signal SWG changes from the low level to the high level, the signal level of the discontinuous detection signal S301 is changed to the high level.

When the signal level of the switching control signal SWG is low level, the switching element SW is turned off, so that the return current is inducted in the closed circuit path constituted by the inductor L1, the load element RD, and the return diode D1. It will flow as iL. In this case, the node voltage V1 is lower than the node voltage V2. Therefore, the output signal of the comparator CMP3 is maintained at a high level, and the logic circuit LGC1 maintains the signal level of the discontinuous detection signal S301 at a high level. Here, when the current value of the return current reaches a predetermined current value (for example, 0 V), the node voltage V1 becomes equal to the node voltage V2. As a result, the signal level of the output signal of the comparator CMP3 changes from the high level to the low level. As a result, the logic circuit LGC1 changes the signal level of the discontinuous detection signal S301 from the high level to the low level. Thus, when a discontinuous state occurs, the signal level of the discontinuous detection signal S301 changes from a high level to a low level. Next, when the signal level of the switching control signal SWG changes from the low level to the high level, the logic circuit LGC1 changes the signal level of the discontinuous detection signal S301 from the low level to the high level.

Also, when a discontinuous state occurs, the voltage difference (V1−V2) between the node voltages V1 and V2 may ring around 0V. In this case, the signal level of the output signal of the comparator CMP3 goes back and forth between the high level and the low level. In the discontinuous state detection unit 301 shown in FIG. 14, the logic circuit LGC1 causes the switching control signal SWG to change from the low level after the signal level of the output signal of the comparator CMP3 changes from the high level to the low level. Until the signal level becomes high, the signal level of the discontinuous detection signal S301 is kept low. As a result, even if the voltage difference (V1−V2) between the node voltages V1 and V2 rings around 0 when a discontinuous state occurs, the signal level of the discontinuous detection signal S301 can be maintained at a low level (non-contiguous). Accurately detect that a continuous condition has occurred).

[Configuration example of turn-on cycle adjuster]
As illustrated in FIG. 15, the turn-on period adjusting unit 302 may include a turn-on elapsed time detecting unit 311 and a pulse control unit 312 instead of the turn-on elapsed time detecting unit 111 illustrated in FIG. 2. Other configurations may be the same as those in FIG.

<Turn-on elapsed time detector>
The turn-on elapsed time detector 311 detects the turn-on elapsed time TEon. For example, the turn-on elapsed time detector 311 includes a capacitor C4, current sources CS2 and CS3, switching elements SW5, SW6, and SW7, a differential amplifier (AMP) AMP1, a logic circuit (LGC) LGC2, and an inverter INV3. May be included.

One end of the capacitor C4 is connected to the ground node. Current source CS2 and switching element SW5 are connected in series between the power supply node and the other end of capacitor C4. Switching element SW6 is connected between the other end of capacitor C4 and the ground node. The differential amplifier AMP1 outputs a differential voltage between the voltage corresponding to the instantaneous current value iDET and the voltage corresponding to the target current value iTG. The current value of the current source CS3 changes according to the differential voltage (voltage corresponding to the difference between the instantaneous current value iDET and the target current value iTG) from the differential amplifier AMP1. Here, when the current value of the current source CS2 is “iCHG” and the current value of the current source CS3 is “iDCH”, the current value of the current source CS3 is iDCH = iCHG × iTG / (iDET−iTG). Adjusted to Current source CS3 and switching element SW7 are connected in series between the other end of capacitor C4 and the ground node. The logic circuit LGC2 turns on the switching element SW6 in synchronization with the rising edge of the switching control signal SWG. When the voltage of the capacitor C4 (voltage corresponding to the turn-on elapsed time TEon) reaches an initial value (for example, 0 V), the switching element SW6. To turn off. The inverter INV3 inverts the discontinuous detection signal S301. The switching elements SW5, SW6, and SW7 are turned on / off in response to the discontinuous detection signal S301, the output signal of the logic circuit LGC2, and the output signal of the inverter INV3, respectively.

When the signal level of the discontinuous detection signal S301 is high, the switching element SW5 is maintained in the on state, and the switching element SW7 is maintained in the off state. In this case, when the signal level of the switching control signal SWG changes from the low level to the high level, the switching element SW6 is turned on. As a result, the capacitor C4 is discharged, and the voltage of the capacitor C4 (voltage corresponding to the turn-on elapsed time TEon) is reset to an initial value (for example, 0 V). When the voltage of the capacitor C4 reaches the initial value, the switching element SW6 is turned off. Thereby, charging of the capacitor C4 by the current source CS2 is started, and the voltage of the capacitor C4 gradually increases. As described above, the voltage of the capacitor C4 increases as the turn-on elapsed time TEon increases.

Here, when the discontinuous state occurs and the signal level of the discontinuous detection signal S301 changes from the high level to the low level, the switching element SW5 is turned off and the switching element SW7 is turned on. Thereby, discharging of the capacitor C4 by the current source CS3 is started, and the voltage of the capacitor C4 gradually decreases. That is, the voltage rise time (charge time of the capacitor C4) corresponding to the turn-on elapsed time TEon corresponds to the elapsed time (current continuous time) from the turn-on of the switching element SW to the detection by the discontinuous state detection unit 301.

<Pulse control unit>
The pulse control unit 312 outputs a control signal P302 when the turn-on elapsed time TEon detected by the turn-on elapsed time detection unit 311 reaches the turn-on period T in the discontinuous mode. For example, the pulse control unit 312 may include a pulse generator PG1 and a logic circuit (LGC) LGC3. When the voltage corresponding to the turn-on elapsed time TEon reaches an initial value (for example, 0 V), the pulse generator PG1 outputs a control pulse. The logic circuit LGC3 allows the control pulse from the pulse generator PG1 to pass as the control pulse P302 during the period when the signal level of the switching control signal SWG is low, and during the period when the signal level of the switching control signal SWG is high. The control pulse from the pulse generator PG1 is not passed. That is, the voltage rise time corresponding to the turn-on elapsed time TEon and the total time of the fall time (discharge time of the capacitor C4) (the voltage corresponding to the turn-on elapsed time TEon rises from the initial value and then drops to the initial value again. (Elapsed time until) corresponds to the turn-on period T in the discontinuous mode of the switching element SW.

[Configuration example of switching control unit]
As illustrated in FIG. 16, the switching control unit 303 may include a selection unit 313 in addition to the configuration example of the switching control unit 103 illustrated in FIG. 3. When the signal level of the discontinuous detection signal S301 changes from the high level to the low level during the period in which the signal level of the switching control signal SWG is low, the selection unit 313 turns on the control pulse P302 from the turn-on cycle adjustment unit 302. Select as P303. In addition, the selection unit 313 generates a turn-on pulse Pon from the oscillator 115 when the signal level of the discontinuous detection signal S301 is maintained high during the period in which the signal level of the switching control signal SWG is low. The turn-on pulse P303 is selected. The SR latch 118 changes the signal level of the switching control signal SWG from the low level to the high level in response to the turn-on pulse P303 from the selection unit 313.

[Operation]
Next, the operation of the step-down chopper device 3 will be described with reference to FIGS. 17 and 18. Here, it is assumed that the first time ratio (1 / a) is “1/2”. In FIG. 17, for the sake of simplification, the difference value between the instantaneous current value iDET and the target current value iTG is assumed to be “0”.

As shown in FIG. 17, when the discontinuous state does not occur, the signal level of the discontinuous detection signal S301 is maintained at the high level, and the control pulse P302 is not generated. Therefore, in the switching control unit 303, the oscillator 115 outputs the turn-on pulse Pon based on the turn-on cycle (cycle according to the cycle control voltage CNT) adjusted by the turn-on cycle adjusting unit 302, and the selection unit 313 Is selected as the turn-on pulse P303 supplied to the SR latch 118. That is, the switching control unit 303 turns on the switching element SW based on the turn-on cycle T corresponding to the continuous mode.

On the other hand, as shown in FIG. 18, when the discontinuous state occurs, the voltages across the inductor L1 (node voltages V1 and V2) are equal to each other, so that the discontinuous state detecting unit 301 detects the signal level of the discontinuous detection signal S301. Is changed from high level to low level. In the turn-on elapsed time detecting unit 311 of the turn-on period adjusting unit 302, the discharge of the capacitor C4 by the current source CS3 is started, and the voltage corresponding to the turn-on elapsed time TEon gradually decreases. Next, when the voltage corresponding to the turn-on elapsed time TEon reaches an initial value (for example, 0 V), the pulse control unit 312 of the turn-on period adjusting unit 302 outputs a control pulse P302. In the switching control unit 303, the selection unit 313 selects the control pulse P302 as the turn-on pulse P303. That is, the switching control unit 303 turns on the switching element SW based on the turn-on period T corresponding to the discontinuous mode.

[Correspondence between time ratio and current ratio]
Next, the time ratio (T / TDon) obtained by dividing the turn-on period T by the current continuous time TDon (the elapsed time from the turn-on of the switching element SW to the detection by the discontinuous state detection unit 301) and the instantaneous current value iDET The correspondence relationship with the current ratio (iDET / iTG) obtained by dividing the current by the target current value iTG will be described.

In the turn-on elapsed time detector 311 of the turn-on period adjuster 302, if the current value of the current source CS2 is “iCHG” and the current value of the current source CS3 is “iDCH”, the current value of the current source CS3 is Is adjusted to hold.

iDCH = iCHG × iTG / (iDET-iTG)
iDCH / iCHG = iTG / (iDET-iTG) [Formula 1]
The voltage corresponding to the turn-on elapsed time TEon gradually increases according to the current value (charging current value) of the current source CS2 in the current continuous time TDon, and after the current continuous time TDon has elapsed, the current value of the current source CS3. Decreases gradually according to (discharge current value). Therefore, it can be expressed as:

TDon x iCHG = (T-TDon) x iDCH
(T-TDon) / TDon = iCHG / iDCH [Equation 2]
Substituting [Expression 1] into [Expression 2] yields the following expression.

(T-TDon) / TDon = (iDET-iTG) / iTG
T / TDon-1 = iDET / iTG-1
T / TDon = iDET / iTG [Formula 3]
As in [Equation 3], a time ratio (T / TDon) obtained by dividing the turn-on period T by the current continuous time TDon is a current ratio (iDET / D) obtained by dividing the instantaneous current value iDET by the target current value iTG. The turn-on period T is adjusted so as to approach iTG).

Further, the average current value iAVE of the inductor current can be maintained at a desired value not only in the critical mode and the continuous mode but also in the discontinuous mode.

(Modification of Embodiment 3)
FIG. 19 shows a configuration example of a step-down chopper device 3a according to a modification of the third embodiment. The step-down chopper device 3a includes a control circuit 31a instead of the control circuit 31 shown in FIG. The control circuit 31a replaces the ON duration setting unit 104, the turn-on cycle adjusting unit 302, and the switching control unit 303 shown in FIG. 13 with a maximum current value setting unit 204, a turn-on cycle adjusting unit 302a, and a switching control unit 303a. including. Other configurations are the same as those in FIG. As shown in FIG. 20, the turn-on cycle adjusting unit 302a includes a turn-on elapsed time detecting unit 111 and an on-duration detecting unit 211 shown in FIG. 8 in addition to the configuration example of the turn-on cycle adjusting unit 302 shown in FIG. . As shown in FIG. 21, the switching control unit 303a includes a comparator 216 shown in FIG. 9 instead of the comparator 116 shown in FIG. Other configurations are the same as those in FIG. Even in such a configuration, the average current value of the inductor current can be maintained at a desired value not only in the critical mode and the continuous mode but also in the discontinuous mode.

(Modification of cycle control unit)
Note that the turn-on

cycle adjusting units

103, 203, 303, and 303a may include the cycle control unit 114a illustrated in FIG. 22 instead of the cycle control unit 114. The cycle control unit 114a includes a sample / hold circuit SH2 and a differential amplifier AMP2 in addition to the configuration example of the cycle control unit 114 shown in FIG. The sample / hold circuit SH2 samples the cycle control voltage CNT (output signal of the comparator CMP2) in synchronization with the falling edge of the timing signal TMG and holds it as the cycle control voltage CNTp. The differential amplifier AMP2 increases or decreases the cycle control voltage CNTa according to the difference between the cycle control voltage CNT (ie, the current cycle control voltage) and the cycle control voltage CNTp (ie, the previous cycle control voltage). For example, as the cycle control voltage CNT becomes higher than the cycle control voltage CNTp, the cycle control voltage CNTa increases. Thus, the cycle control unit may be an error amplification type or a state machine type.

(Modification of discontinuous state detection unit)
Further, the

control circuits

31 and 31a may include the discontinuous state detection unit 301a illustrated in FIG. 23 instead of the discontinuous state detection unit 301. The discontinuous state detection unit 301a may include a resistance element R2, a differential amplifier AMP3, and a comparator CMP4. Resistance element R2 is inserted in the current path between intermediate node N1 and inductor L1. The differential amplifier AMP3 outputs an output voltage corresponding to the difference between the both-end voltages V4 and V5 of the resistance element R2. The comparator CMP4 compares the output voltage of the differential amplifier AMP3 with the reference voltage REF0. Here, the reference voltage REF0 is a voltage for determining whether the output voltage of the differential amplifier AMP3 is 0 V or less (for example, a voltage in the vicinity of 0 V), and the one-end voltage V4 of the resistance element R2 is the voltage of the resistance element R2. When the voltage at the other end is lower than V5, and when the one end voltage V4 and the other end voltage V5 of the resistance element R2 are equal to each other, the signal level of the output signal of the comparator CMP4 (discontinuous detection signal S301a) becomes a low level. When the one end voltage V4 of the resistance element R2 is higher than the other end voltage V5 of the resistance element R2, the signal level of the output signal of the comparator CMP4 becomes a high level.

When the signal level of the switching control signal SWG is low (when the switching element SW is in an off state), the return current is applied to the closed circuit path constituted by the inductor L1, the load element RD, and the return diode D1. It will flow as current iL. In this case, the one voltage V4 of the resistance element R2 is higher than the other end voltage V5 of the resistance element R2. Therefore, the comparator CMP4 maintains the signal level of the discontinuous detection signal S301a at a high level. Here, when the current value of the return current reaches a predetermined current value (for example, 0 V), the one end voltage V4 and the other end voltage V5 of the resistance element R2 become equal to each other. Thereby, the comparator CMP3 changes the signal level of the discontinuous detection signal S301a from the high level to the low level. That is, when a discontinuous state occurs, the signal level of the discontinuous detection signal S301a changes from a high level to a low level. As described above, the discontinuous state detection unit may detect that a discontinuous state has occurred based on the voltage between both ends of the resistance element R2 inserted between the intermediate node N1 and the inductor L1.

(Embodiment 4)
FIG. 24 shows a configuration example of the step-down chopper device 4 according to the fourth embodiment. The step-down chopper device 4 includes a control circuit 41 instead of the control circuit 11 shown in FIG. Other configurations may be the same as those in FIG. The control circuit 41 has a first time with respect to the duration from when the switching element SW is turned on to when the switching element SW is turned on until the current value of the switching current iSW reaches the target current value iTG. The duration from the turn-on to the turn-off of the switching element SW is controlled so that the ratio (1 / a) is obtained. The control circuit 41 may include a switching current detection unit 101, a target current value setting unit 105, an ON duration adjustment unit 401, and a switching control unit 402.

《On duration adjustment unit》
The ON duration adjustment unit 401 is a target current in which the current value (switching current value idSW) of the switching current iSW detected by the switching current detection unit 101 after the switching element SW is turned on is set by the target current value setting unit 105. The ON duration TCon so that the arrival time until reaching the value iTG is the first time ratio (1 / a) with respect to the ON duration TCon that defines the duration from the turn-on to the turn-off of the switching element SW. Adjust.

《Switching control unit》
The switching control unit 402 turns on the switching element SW by changing the signal level of the switching control signal SWG from the low level to the high level based on a predetermined turn-on cycle determined in advance. Further, the switching control unit 402 changes the signal level of the switching control signal SWG from the high level to the low level when the ON duration time TCon adjusted by the ON duration duration adjustment unit 401 elapses after the switching element SW is turned on. By changing, the switching element SW is turned off.

[Configuration example of ON duration adjustment unit]
As shown in FIG. 25, the ON duration adjustment unit 401 may include an ON arrival time detection unit 411 and an ON duration setting unit 412.

《On arrival time detection unit》
The on-arrival time detector 411 corresponds to an on-arrival time TRon (here, corresponding to the on-arrival time TRon) corresponding to the arrival time from when the switching element SW is turned on until the switching current value idSW reaches the target current value iTG. Voltage). The longer the on-arrival time TRon, the longer the high level time of the voltage corresponding to the on-arrival time TRon. For example, the on arrival time detection unit 411 may include a pulse generator PG21, a comparator CMP21, and an SR latch SR21.

The pulse generator PG21 outputs a set pulse in synchronization with the rising edge (change from low level to high level) of the switching control signal SWG. The comparator CMP21 compares the voltage corresponding to the switching current value idSW with the voltage corresponding to the target current value iTG. Here, when the switching current value idSW reaches the target current value iTG, the signal level of the output signal of the comparator CMP21 changes from the low level to the high level. In response to the set pulse from the pulse generator PG21, the SR latch SR21 changes the voltage level of the voltage corresponding to the ON arrival time TRon from the low level to the high level. In addition, the SR latch SR21 changes the voltage level of the voltage corresponding to the ON arrival time TRon from the high level to the low level in response to the output change (here, the rising edge) of the comparator CMP21.

<ON duration setting section>
The ON duration setting unit 412 is a time obtained by multiplying the ON arrival time TRon detected by the ON arrival time detection unit 411 by the reciprocal of the first time ratio (1 / a) (that is, the ON duration time TCon). The ON duration time TCon (here, the voltage corresponding to the ON duration time TCon) is set based on the ON arrival time TRon so as to be the on arrival time TRon. The longer the ON duration time TCon, the longer the voltage fluctuation time corresponding to the ON duration time TCon (the total time of the rise time and the fall time). For example, the ON duration setting unit 412 may include a capacitor C21, current sources CS21 and CS22, switching elements SW21 and SW22, and an inverter INV21.

One end of the capacitor C21 is connected to the ground node. Current source CS21 and switching element SW21 are connected in series between the power supply node and the other end of capacitor C21. Current source CS22 and switching element SW22 are connected in series between the other end of capacitor C21 and the ground node. The inverter INV21 inverts the voltage corresponding to the on arrival time TRon. Switching elements SW21 and SW22 are turned on / off in response to the voltage corresponding to on-arrival time TRon and the output signal of inverter INV21, respectively.

When the voltage level of the voltage corresponding to the ON arrival time TRon changes from the low level to the high level, the switching element SW21 is turned on and the switching element SW22 is turned off. Thereby, charging of the capacitor C21 by the current source CS21 is started, and the voltage of the capacitor C21 (voltage corresponding to the ON duration TCon) gradually increases. Next, when the voltage level of the voltage corresponding to the ON arrival time TRon changes from the high level to the low level, the switching element SW21 is turned off and the switching element SW22 is turned on. Thereby, discharging of the capacitor C21 by the current source CS22 is started, and the voltage of the capacitor C21 gradually decreases. Here, the current ratio between the current value of the current source CS21 (charge current value) and the current value of the current source CS22 (discharge current value) is set so that the ON duration TCon is a times the ON arrival time TRon. ing. For example, when the first time ratio (1 / a) is “1/2”, the current ratio between the current source CS21 and the current source CS22 is “1: 1”.

[Configuration example of switching control unit]
As shown in FIG. 26, the switching control unit 402 may include a comparator 413, a pulse generator 414, a pulse generator 415, and an SR latch 416.

The comparator 413 compares the voltage corresponding to the ON duration time TCon with the reference voltage REFon. Here, the reference voltage REFon is a voltage (for example, a voltage in the vicinity of 0V) for determining the rise start and fall end of the voltage corresponding to the ON duration time TCon, and the voltage corresponding to the ON duration time TCon has increased. When the voltage drops later and reaches the reference voltage REFon (that is, when the ON duration TCon elapses after the switching element SW is turned on), the signal level of the output signal of the comparator 413 changes from the high level to the low level. The pulse generator 414 outputs a turn-off pulse Poff in synchronization with the output change (here, falling edge) of the comparator 413. That is, the pulse generator 414 outputs the turn-off pulse Poff when the ON duration TCon elapses after the switching element SW is turned on.

The pulse generator 415 outputs a turn-on pulse Pon at a predetermined cycle. The SR latch 416 changes the signal level of the switching control signal SWG from the low level to the high level in response to the turn-on pulse Pon from the pulse generator 415. The SR latch 416 changes the signal level of the switching control signal SWG from the high level to the low level in response to the turn-off pulse Poff from the pulse generator 414.

[Operation]
Next, the operation of the step-down chopper device 4 will be described with reference to FIG. Here, it is assumed that the first time ratio (1 / a) is “1/2”.

First, in the switching control unit 402, when the pulse generator 415 outputs the n-th turn-on pulse Pon, the SR latch 416 changes the signal level of the switching control signal SWG from the low level to the high level. As a result, the switching element SW is turned on, and the inductor current iL (switching current value idSW) gradually increases. In the ON duration adjustment unit 401, the ON arrival time detection unit 411 changes the voltage level of the voltage corresponding to the ON arrival time TRon from a low level to a high level, and the ON duration setting unit 412 The voltage corresponding to TCon is gradually increased.

Next, when the switching current value idSW reaches the target current value iTG, in the ON duration adjustment unit 401, the ON arrival time detection unit 411 changes the voltage level of the voltage corresponding to the ON arrival time TRon from the high level to the low level. Change. Thereby, the ON duration setting unit 412 gradually decreases the voltage corresponding to the ON duration TCon.

Next, when the voltage corresponding to the on duration TCon reaches the reference voltage REFon, the on duration TCon has elapsed since the switching element SW is turned on. At this time, the pulse generator 414 outputs the nth turn-off pulse Poff. As a result, the switching element SW is turned off, and the inductor current iL gradually decreases.

Next, when a turn-on period T (predetermined turn-on period) has elapsed since the generation of the n-th turn-on pulse Pon, the pulse generator 415 outputs the (n + 1) -th turn-on pulse Pon in the switching control unit 402. .

[Adjustment of ON duration]
The ON duration TCon is the duration from when the switching element SW is turned on until the current value of the switching current iSW reaches the target current value iTG (ON arrival time TRon). It is adjusted so as to be the first time ratio (1 / a) with respect to (ON duration TCon). For example, as shown in FIG. 28, when the rising gradient of the inductor current iL (switching current iSW) becomes steeper than in the case of FIG. 27 (for example, when the input voltage Vin becomes high), as shown in FIG. Even when the descending gradient of the inductor current iL becomes steeper than in the case of FIG. 27 (for example, when the voltage between the terminals of the load element RD becomes high), the current of the switching current iSW after the switching element SW is turned on. From the turn-on of the switching element SW so that the arrival time until the value reaches the target current value iTG is the first time ratio (1 / a) with respect to the duration Ton from the turn-on of the switching element SW to the turn-off. The duration Ton until turn-off is adjusted.

Thus, by adjusting the ON duration time TCon so that the ON arrival time TRon becomes the first time ratio (1 / a) with respect to the ON duration time TCon, the elapsed time from the turn-on of the switching element SW is set. That is, the current value of the switching current iSW at the first time ratio (1 / a) with respect to the duration from the turn-on to the turn-off of the switching element SW is brought close to the target current value iTG. Thereby, the average current value iAVE of the inductor current can be brought close to a desired value.

[Variation of time gradient of inductor current]
Here, from FIG. 27, FIG. 28, and FIG. 29, even if the time change gradient of the inductor current iL fluctuates, the elapsed time from the turn-on of the switching element SW to the duration Ton from the turn-on to the turn-off of the switching element SW. When the current becomes “½”, the current value of the inductor current iL (switching current iSW) becomes the average current value iAVE of the inductor current. Further, as the elapsed time from the turn-on of the switching element SW approaches ½ of the duration Ton from the turn-on to the turn-off of the switching element SW, the current value of the inductor current iL (switching current iSW) at the elapsed time becomes the inductor value. It becomes difficult for the current iL to fluctuate with respect to the variation of the time change gradient. That is, as the first time ratio (1 / a) is closer to “1/2”, the average current value iAVE of the inductor current is less likely to vary with respect to the variation in the time change gradient of the inductor current iL.

As described above, it is possible to suppress fluctuations in the average current value iAVE of the inductor current due to variations in the time change gradient of the inductor current iL. Further, since the operation is possible not only in the critical mode but also in the continuous mode, the average current value iAVE of the inductor current can be increased and the power loss in the switching element SW can be reduced as compared with the case of operating only in the critical mode. .

(Embodiment 5)
FIG. 30 shows a configuration example of the step-down chopper device 5 according to the fifth embodiment. The step-down chopper device 5 includes a control circuit 51 instead of the control circuit 41 shown in FIG. The control circuit 51 may include a discontinuous state detection unit 501 and a switching control unit 502 instead of the switching control unit 402 shown in FIG. Other configurations may be the same as those in FIG.

《Discontinuous state detector》
The discontinuous state detection unit 501 is a discontinuous state (a state in which the current value of the return current flowing through the second and third current paths is lower than a predetermined current value during the period from the turn-off to the turn-on of the switching element SW). ) Is detected.

《Switching control unit》
Similar to the switching control unit 402, the switching control unit 502 turns on the switching element SW by changing the signal level of the switching control signal SWG from the low level to the high level based on a predetermined turn-on cycle. After the switching element SW is turned on, the switching control signal SWG is changed from the high level to the low level when the ON duration time TCon adjusted by the ON duration adjustment unit 401 elapses, thereby switching the switching element SW. To turn off. In addition, when the discontinuous state is detected by the discontinuous state detecting unit 501, the switching control unit 502 turns on the switching element SW by changing the signal level of the switching control signal SWG from the low level to the high level.

[Configuration example of non-continuous state detector]
As illustrated in FIG. 31, the discontinuous state detection unit 501 may include an inverter INV23 in addition to the comparator CMP3 and the logic circuit LGC1 illustrated in FIG. The inverter INV23 inverts the output signal of the logic circuit LGC1 (corresponding to the discontinuous detection signal S301) and outputs it as a control pulse P501.

When the signal level of the switching control signal SWG is a low level, the signal level of the output signal of the logic circuit LGC1 is maintained at a high level, so that the signal level of the output signal of the inverter INV23 is maintained at a low level. (In other words, the control pulse P501 is not generated). Here, when the current value of the return current reaches a predetermined current value (for example, 0 A), the signal level of the output signal of the logic circuit LGC1 changes from the high level to the low level, so that the signal level of the output signal of the inverter INV23 Changes from a low level to a high level (that is, the control pulse P501 is generated). Thus, when the discontinuous state occurs, the control pulse P501 is generated.

Note that the discontinuous state detection unit 501 may include the resistor element R2, the differential amplifier AMP3, and the comparator CMP4 shown in FIG. 23 instead of the comparator CMP3 and the logic circuit LGC1 shown in FIG. . In this case, the inverter INV23 inverts the output signal of the comparator CMP4 and outputs it as the control pulse P501.

[Configuration example of switching control unit]
As illustrated in FIG. 32, the switching control unit 502 may include an oscillator 511 and a selection unit 512 instead of the pulse generator 415 illustrated in FIG. 26. Other configurations may be the same as in FIG.

The oscillator 511 periodically outputs a control pulse P502 based on a predetermined turn-on cycle. The oscillator 511 starts the periodic output of the control pulse P502 in synchronization with the turn-on pulse P503. The selection unit 512 selects the control pulse P501 as the turn-on pulse P503 when the control pulse P501 is generated in a period in which the signal level of the switching control signal SWG is low. On the other hand, the selection unit 512 selects the control pulse P502 from the oscillator 511 as the turn-on pulse P503 when the control pulse P501 is not generated during the period when the signal level of the switching control signal SWG is low. The SR latch 416 changes the signal level of the switching control signal SWG from the low level to the high level in response to the turn-on pulse P503 from the selection unit 512.

[Operation]
Next, the operation of the step-down chopper device 5 will be described with reference to FIG. 33 and FIG. Here, it is assumed that the first time ratio (1 / a) is “1/2”.

As shown in FIG. 33, when the discontinuous state does not occur, the control pulse P501 does not occur. Therefore, in the switching control unit 502, the selection unit 512 selects the control pulse P502 from the oscillator 511 as the turn-on pulse P503. That is, the switching control unit 502 turns on the switching element SW based on a predetermined turn-on cycle T.

On the other hand, as shown in FIG. 34, when a discontinuous state occurs, the voltage across the inductor L1 (node voltages V1, V2) becomes equal to each other, and therefore the discontinuous state detection unit 501 outputs a control pulse P501. In the switching control unit 502, the selection unit 512 selects the control pulse P501 from the discontinuous state detection unit 501 as the turn-on pulse P503. The oscillator 511 restarts the periodic output of the control pulse P502 in synchronization with the turn-on pulse P503 (in this case, the control pulse P501).

As described above, it is possible to suppress fluctuations in the average current value iAVE of the inductor current due to variations in the time change gradient of the inductor current iL. Further, since the operation is possible not only in the critical mode but also in the continuous mode, the average current value iAVE of the inductor current can be increased and the power loss in the switching element SW can be reduced as compared with the case of operating only in the critical mode.

Also, when the discontinuous state occurs, the switching element SW is forcibly turned on, so that the transition from the continuous mode to the discontinuous mode can be prevented.

(Embodiment 6)
FIG. 35 shows a configuration example of the step-down chopper device 6 according to the sixth embodiment. The step-down chopper device 6 includes a control circuit 61 instead of the control circuit 41 shown in FIG. Other configurations may be the same as those in FIG. The control circuit 61 may include an inductor current detection unit 601, an off duration adjustment unit 602, and a switching control unit 603 instead of the switching control unit 402 shown in FIG.

<Inductor current detector>
The inductor current detection unit 601 detects the current value of the inductor current iL flowing through the inductor L1 (inductor current value idL). Here, the inductor current detection unit 601 detects a voltage corresponding to the inductor current value idL. The higher the inductor current value idL, the higher the voltage corresponding to the inductor current value idL.

《Off duration adjustment unit》
The off duration adjusting unit 602 is a target current in which the current value (inductor current value idL) of the inductor current iL detected by the inductor current detecting unit 601 after the switching element SW is turned off is set by the target current value setting unit 105. The off duration TCoff is such that the arrival time until reaching the value iTG is a second time ratio (1 / b) with respect to the off duration TCoff that defines the duration from the turn-off of the switching element SW to the turn-on. Adjust.

《Switching control unit》
The switching control unit 603 changes the signal level of the switching control signal SWG from the high level to the low level when the ON duration time TCon adjusted by the ON duration duration adjustment unit 401 elapses after the switching element SW is turned on. As a result, the switching element SW is turned off. Further, the switching control unit 603 changes the signal level of the switching control signal SWG from the low level to the high level when the ON duration time TCoff adjusted by the OFF duration adjusting unit 602 has elapsed after the switching element SW is turned off. By changing, the switching element SW is turned on.

[Configuration example of off duration adjustment unit]
As illustrated in FIG. 36, the off duration adjustment unit 602 may include an off arrival time detection unit 611 and an off duration setting unit 612.

《Off arrival time detection unit》
The off-arrival time detection unit 611 corresponds to an off-arrival time TRoff corresponding to the arrival time from when the switching element SW is turned off until the inductor current flow value idL reaches the target current value iTG (here, corresponding to the off-arrival time TRoff). Voltage). As the OFF arrival time TRoff increases, the high level time of the voltage corresponding to the OFF arrival time TRoff increases. For example, the off arrival time detection unit 611 may include a pulse generator PG22, a comparator CMP22, and an SR latch SR22.

The pulse generator PG22 outputs a set pulse in synchronization with the falling edge (change from high level to low level) of the switching control signal SWG. The comparator CMP22 compares the voltage corresponding to the inductor current value idL with the voltage corresponding to the target current value iTG. Here, when the inductor current value idL reaches the target current value iTG, the signal level of the output signal of the comparator CMP22 changes from the low level to the high level. In response to the set pulse from the pulse generator PG22, the SR latch SR22 changes the voltage level of the voltage corresponding to the OFF arrival time TRoff from the low level to the high level. In addition, the SR latch SR22 changes the voltage level of the voltage corresponding to the OFF arrival time TRoff from the high level to the low level in response to the output change (here, the rising edge) of the comparator CMP22.

《Off duration setting section》
The off duration setting unit 612 multiplies the off arrival time TRoff detected by the off arrival time detection unit 611 by the reciprocal of the second time ratio (1 / b) (that is, the off arrival time TRoff). The OFF duration time TCoff (here, the voltage corresponding to the OFF duration time TCoff) is set based on the OFF arrival time TRoff. The longer the OFF duration time TCoff, the longer the voltage fluctuation time corresponding to the OFF duration time TCoff (the total time of the rise time and the fall time). For example, the off duration setting unit 612 may include a capacitor C22, current sources CS23 and CS24, switching elements SW23 and SW24, and an inverter INV22.

One end of the capacitor C22 is connected to the ground node. Current source CS23 and switching element SW23 are connected in series between the power supply node and the other end of capacitor C22. Current source CS24 and switching element SW24 are connected in series between the other end of capacitor C22 and the ground node. The inverter INV22 inverts the voltage corresponding to the off arrival time TRoff. The switching elements SW23 and SW24 are turned on / off in response to the voltage corresponding to the off-arrival time TRoff and the output signal of the inverter INV22.

When the voltage level of the voltage corresponding to the OFF arrival time TRoff changes from the low level to the high level, the switching element SW23 is turned on and the switching element SW24 is turned off. Thereby, charging of the capacitor C22 by the current source CS23 is started, and the voltage of the capacitor C22 (voltage corresponding to the off duration time TCoff) gradually increases. Next, when the voltage level of the voltage corresponding to the OFF arrival time TRoff changes from the high level to the low level, the switching element SW23 is turned off and the switching element SW24 is turned on. Thereby, discharging of the capacitor C22 by the current source CS24 is started, and the voltage of the capacitor C22 gradually decreases. Here, the current ratio between the current value of the current source CS23 (charge current value) and the current value of the current source CS24 (discharge current value) is set so that the off duration time TCoff is b times the off arrival time TRoff. ing. For example, when the second time ratio (1 / b) is “1/2”, the current ratio between the current source CS23 and the current source CS24 is “1: 1”.

[Configuration example of switching control unit]
As shown in FIG. 37, the switching control unit 603 may include a comparator 613 and a pulse generator 614 instead of the pulse generator 415 shown in FIG. Other configurations may be the same as in FIG.

The comparator 613 compares the voltage corresponding to the off duration time TCoff with the reference voltage REFoff. Here, the reference voltage REFoff is a voltage (for example, a voltage in the vicinity of 0V) for determining the rise start and fall end of the voltage corresponding to the off duration TCoff, and the voltage corresponding to the off duration TCoff has increased. When the voltage subsequently drops and reaches the reference voltage REFoff (that is, when the OFF duration time TCoff elapses after the switching element SW is turned off), the signal level of the output signal of the comparator 613 changes from the high level to the low level. The pulse generator 614 outputs a turn-on pulse Pon in synchronization with a change in the output of the comparator 613 (here, a falling edge). That is, the pulse generator 614 outputs the turn-on pulse Pon when the OFF duration TCoff elapses after the switching element SW is turned off.

[Operation]
Next, the operation of the step-down chopper device 6 will be described with reference to FIG. Here, it is assumed that the first time ratio (1 / a) and the second time ratio (1 / b) are “1/2”.

First, in the switching control unit 603, when the pulse generator 614 outputs the n-th turn-on pulse Pon, the SR latch 416 changes the signal level of the switching control signal SWG from the low level to the high level. As a result, the switching element SW is turned on, and the inductor current iL (switching current value idSW) gradually increases. In the ON duration adjustment unit 401, the ON arrival time detection unit 411 changes the voltage level of the voltage corresponding to the ON arrival time TRon from a low level to a high level, and the ON duration setting unit 412 The voltage corresponding to TCon is gradually increased.

Next, when the voltage corresponding to the on duration TCon reaches the reference voltage REFon, the on duration TCon has elapsed since the switching element SW is turned on. At this time, the pulse generator 414 outputs the nth turn-off pulse Poff. As a result, the switching element SW is turned off, and the inductor current iL gradually decreases. Further, in the off duration adjustment unit 602, the off arrival time detection unit 611 changes the voltage level of the voltage corresponding to the off arrival time TRoff from the low level to the high level, and the off duration setting unit 612 The voltage corresponding to TCoff is gradually increased.

Next, when the inductor current value idL reaches the target current value iTG, in the off duration adjustment unit 602, the off arrival time detection unit 611 changes the voltage level of the voltage corresponding to the off arrival time TRoff from the high level to the low level. Change. Thereby, the off duration setting unit 612 gradually decreases the voltage corresponding to the off duration TCoff.

Next, when the voltage corresponding to the ON duration time TCoff reaches the reference voltage REFoff, the OFF duration time TCoff has elapsed since the switching element SW is turned off. At this time, the pulse generator 614 outputs the (n + 1) th turn-on pulse Pon.

[Adjustment of ON duration]
The ON duration TCon is the duration from when the switching element SW is turned on until the current value of the switching current iSW reaches the target current value iTG (ON arrival time TRon). It is adjusted so as to be the first time ratio (1 / a) with respect to (ON duration TCon). For example, as shown in FIG. 39, even when the rising gradient of the inductor current iL (switching current iSW) becomes steeper than in FIG. 38 (for example, when the input voltage Vin becomes high), the switching element SW is turned on. The time until the current value of the switching current iSW reaches the target current value iTG is set to the first time ratio (1 / a) with respect to the duration Ton from the turn-on to the turn-off of the switching element SW. Further, the duration Ton from the turn-on to the turn-off of the switching element SW is adjusted.

[Adjustment of OFF duration]
The off duration time TCoff is the duration time from when the switching element SW is turned off until the current value of the inductor current iL reaches the target current value iTG (off arrival time TRoff). It is adjusted to be the second time ratio (1 / b) with respect to (off duration TCoff). For example, as shown in FIG. 40, even when the descending gradient of the inductor current iL is steeper than in FIG. 38 (for example, when the voltage across the terminals of the load element RD is increased), the switching element SW is turned off. The arrival time until the current value of the inductor current iL reaches the target current value iTG is set to the second time ratio (1 / b) with respect to the duration Toff from the turn-off to the turn-on of the switching element SW. The duration Toff from turn-off to turn-on of the switching element SW is adjusted.

Thus, by adjusting the off duration time TCoff so that the off arrival time TRoff becomes the second time ratio (1 / b) with respect to the off duration time TCoff, the average current value iAVE of the inductor current is set to a desired value. Can be approached.

[Variation of time gradient of inductor current]
Here, from FIG. 38 and FIG. 39, even if the rising gradient of the inductor current iL fluctuates, the elapsed time from the turn-on of the switching element SW is “1 /” with respect to the duration Ton from the turn-on to the turn-off of the switching element SW. When 2 ″, the current value of the inductor current iL (switching current iSW) is found to be the average current value iAVE of the inductor current. Further, as the elapsed time from the turn-on of the switching element SW is closer to ½ of the duration Ton from the turn-on of the switching element SW to the turn-on / off, the current value of the inductor current iL (switching current iSW) at that elapsed time becomes the inductor value. It becomes difficult to fluctuate with respect to variations in the rising gradient of the current iL. That is, as the first time ratio (1 / a) is closer to “1/2”, the average current value iAVE of the inductor current is less likely to vary with respect to the variation in the rising gradient of the inductor current iL.

38 and 40, even if the descending gradient of the inductor current iL varies, the elapsed time from the turn-off of the switching element SW is “1/2” with respect to the duration Toff from the turn-off of the switching element SW to the turn-on. ”, The current value of the inductor current iL becomes the average current value iAVE of the inductor current. Further, as the elapsed time from the turn-off of the switching element SW is closer to ½ of the duration Toff from the turn-off to the turn-on of the switching element SW, the current value of the inductor current iL at the elapsed time becomes a descending gradient of the inductor current iL. It becomes difficult to fluctuate with respect to the variation of. That is, as the second time ratio (1 / b) is closer to “1/2”, the average current value iAVE of the inductor current is less likely to vary with respect to the variation in the descending gradient of the inductor current iL.

Further, the transition from the continuous mode to the non-continuous mode is prevented by adjusting the off duration time TCoff so that the off arrival time TRoff becomes the second time ratio (1 / b) with respect to the off duration time TCoff. it can.

(Other embodiments)
[First time ratio / Second time ratio]
In the above embodiment, the first time ratio (1 / a) may be a predetermined fixed value or a variable value that can be changed by external control. For example, in the time ratio detection unit 112, the time voltage generation unit VG1 may change the voltage ratio (for example, resistance division ratio) of the comparison time TXon with respect to the ON duration time TCon in response to external control. Alternatively, in the ON duration setting unit 412, the current source CS21 (or current source CS22) may change the current value in response to external control. Similarly, the second time ratio may be a predetermined fixed value or a variable value that can be changed by external control.

Here, the setting range of the first time ratio (1 / a) will be described with reference to FIG. FIG. 41 shows a correspondence relationship between the input voltage Vin and the fluctuation amount (Δi) of the average current value of the inductor current for each set value of the first time ratio (1 / a). Here, the fluctuation amount (Δi) of the average current value of the inductor current is expressed by the ratio of the assumed value (the average current value of the inductor current obtained by simulation) to the desired value of the average current value of the inductor current. In FIG. 41, the uppermost straight line corresponds to the case of “1 / a = 1 / 2.22”, and the central straight line corresponds to the case of “1 / a = 1 / 2.00”. The lower straight line corresponds to the case of “1 / a = 1 / 1.82”. Here, the ratio of the target current value iTG to the desired value of the average current value of the inductor current is set to “0.976” when “1 / a = 1 / 2.22”, and “1 / a = 1 / 2.00 ”is set to“ 1.000 ”, and“ 1 / a = 1 / 1.82 ”is set to“ 1.026 ”. . For example, when the first time ratio (1 / a) is “1 / 2.22”, the target current value iTG is set to 0.976 times the desired value of the average current value of the inductor current. Further, when the input voltage Vin is “120 V”, the ratio (iP / iS) of the minimum current value iS to the maximum current value iP of the inductor current is set to be “0.6”. . When the voltage value of the input voltage Vin is changed from “120V” to “360V”, as shown in FIG. 41, the fluctuation amount (Δi) of the average current value of the inductor current is “1 / a = 1 / 2.22”. Is "about 1.05", "1 / a = 1 / 2.00" is "1.00", and "1 / a = 1 / 1.82" Is "about 0.95". Thus, when the first time ratio (1 / a) is 1 / 2.22 or more and 1 / 1.82 or less, the fluctuation amount of the average current value of the inductor current with respect to the fluctuation of the input voltage Vin is predetermined. Can be within the allowable range (about 5%). Similarly, the second time ratio (1 / b) is preferably 1 / 2.22 or more and preferably 1 / 1.82 or less.

[Modification of step-down chopper device]
In the above embodiment, the inductor L1 and the load element RD may be interchanged with each other. Further, instead of the free wheel diode D1, a switching element that is turned off during a period in which the switching element SW is in an on state and turned on in a period in which the switching element SW is in an off state may be provided. Furthermore, as shown in FIG. 42, the step-down

chopper devices

1, 2, 3, 3a, 4, 5, and 6 may be low-side step-down chopper devices. In FIG. 42, the switching element SW is provided in a current path (first current path) between the input node Nin2 and the intermediate node N2. Inductor L1 is provided in series with load element RD in the current path (second current path) between intermediate node N2 and input node Nin1. The free-wheeling diode D1 is provided in a current path (third current path) between the intermediate node N2 and the input node Nin1.

(Image display device)
As shown in FIG. 43, the step-down

chopper devices

1, 2, 3, 3a, 4, 5, and 6 may be mounted on the image display device as light source driving devices. The image display device illustrated in FIG. 43 includes a light source device 7, a display unit 8, and a display control unit 9. The light source device 7 includes light

source driving devices

71R, 71G, 71B and

light emitting elements

72R, 72G, 72B. The light

source driving devices

71R, 71G, 71B correspond to any of the step-down

chopper devices

1, 2, 3, 3a, 4, 5, 6, and the

light emitting elements

72R, 72G, 72B correspond to the load element RD. The light

source driving devices

71R, 71G, and 71B control the load current iRD that flows through the

light emitting elements

72R, 72G, and 72B in response to the control by the display control unit 9, respectively. The

light emitting elements

72R, 72G, 72B emit light according to the load current iRD.

The display unit 8 includes a condenser tube 81, a lens 82, a light valve 83, a lens 84, and a screen 85. Light emitted from the

light emitting elements

72R, 72G, and 72B is transmitted to the condenser tube 81 through the optical fiber and is collected in the condenser tube 81. The light condensed in the condenser tube 81 is applied to the light valve 83 through the lens 82. The light valve 83 spatially modulates the light emitted from the condenser 81 through the lens 82 in response to control by the display control unit 9. The light spatially modulated by the light valve 83 is projected onto the screen 85 via the lens 84.

The display control unit 9 controls the light source device 7 and the display unit 8 based on the video signal and the synchronization signal so that the video shown in the video signal is projected on the screen 85. For example, the display control unit 9 controls the drive timing of the light

source driving devices

71R, 71G, 71B (light emission timing of the

light emitting elements

72R, 72G, 72B), the spatial modulation processing in the light valve 83, and the like.

As described above, the above-described step-down chopper device can suppress the fluctuation of the average current value of the inductor current due to the variation of the time variation gradient of the inductor current and can operate not only in the critical mode but also in the continuous mode. It is useful as a constant current power source such as a driving device.

1, 2, 3, 3a, 4, 5, 6 Step-down chopper device RD Load element SW Switching element L1 Inductor D1 Reflux diode (reflux element)
11, 21, 31, 31a, 41, 51, 61 Control circuit 101 Switching

current detection unit

102, 202, 302, 302a Turn-on

cycle adjustment unit

103, 203, 303, 303a Switching control unit 301 Discontinuous state detection unit 401 On-continuation

Time adjustment unit

402, 502, 603 Switching control unit 501 Discontinuous state detection unit 601 Inductor current detection unit 602 Off duration adjustment unit 7 Light source device 8 Display unit 9 Display control unit

Claims

A step-down chopper device for controlling a load current flowing through a load element,
A switching element provided in a first current path between the first input node and the intermediate node among first and second input nodes to which an input voltage is applied between each other;
An inductor provided in series with the load element in a second current path between the intermediate node and the second input node;
A reflux element provided in a third current path between the intermediate node and the second input node and configured to return current to the second and third current paths during a period in which the switching element is in an off state; ,
The instantaneous current value of the switching current flowing through the switching element when the elapsed time from the turn-on of the switching element becomes a first time ratio with respect to the duration from the turn-on to turn-off of the switching element is determined in advance A step-down chopper device comprising: a control circuit that controls ON / OFF of the switching element so as to approach a current value.
In claim 1,
The control circuit detects an instantaneous current value of the switching current when the elapsed time from the turn-on of the switching element becomes the first time ratio with respect to the duration from the turn-on to turn-off of the switching element, A step-down chopper device that controls a turn-on cycle of the switching element according to a difference between an instantaneous current value of the switching current and the target current value.
In claim 2,
The control circuit includes:
A switching current detector for detecting a current value of the switching current;
A turn-on elapsed time corresponding to an elapsed time from turn-on of the switching element is detected, and the turn-on elapsed time is first with respect to a predetermined on-duration that defines a duration from turn-on to turn-off of the switching element. The current value of the switching current detected by the switching current detector when the time ratio is reached is detected as the instantaneous current value of the switching current, and the difference between the instantaneous current value of the switching current and the target current value A turn-on period adjusting unit that adjusts a turn-on period of the switching element according to
Switching that turns on the switching element based on the turn-on period adjusted by the turn-on period adjusting unit, and turns off the switching element when the turn-on elapsed time detected by the turn-on period adjusting unit reaches the on duration A step-down chopper device comprising a control unit.
In claim 2,
The control circuit includes:
A switching current detector for detecting a current value of the switching current;
A turn-on elapsed time corresponding to an elapsed time from the turn-on of the switching element is detected, an on-duration time corresponding to a duration from the turn-on to the turn-off of the switching element is detected, and the turn-on elapsed time is set to the on-duration time In contrast, the current value of the switching current detected by the switching current detector when the first time ratio is reached is detected as an instantaneous current value of the switching current, and the instantaneous current value of the switching current and the target A turn-on period adjusting unit that adjusts a turn-on period of the switching element according to a difference with a current value;
The switching element is turned on based on the turn-on cycle adjusted by the turn-on cycle adjusting unit, and the current value of the switching current detected by the switching current detection unit reaches a predetermined maximum current value. A step-down chopper device comprising: a switching control unit that turns off the switching element.
In claim 3 or 4,
The control circuit detects a discontinuous state in which a current value of a return current flowing through the second and third current paths is lower than a predetermined current value during a period from a turn-off to a turn-on of the switching element. A state detector;
The turn-on period adjusting unit is
If the discontinuous state is not detected by the discontinuous state detection unit, the instantaneous current value of the switching current when the turn-on elapsed time becomes the first time ratio with respect to the on-continuation time And adjusting the turn-on period of the switching element according to the difference between the target current value and
When the discontinuous state is detected by the discontinuous state detecting unit, the current continuous time corresponding to the elapsed time from the turn-on of the switching element to the detection by the discontinuous state detecting unit when the switching element is turned on Is obtained by dividing the instantaneous current value of the switching current when the turn-on elapsed time becomes the first time ratio with respect to the ON duration time by the target current value. A step-down chopper device that adjusts a turn-on cycle of the switching element so as to approach the obtained current ratio.
In claim 1,
The control circuit includes a first arrival time from when the switching element is turned on to when the current value of the switching current reaches the target current value with respect to a duration from the turn-on to turn-off of the switching element. A step-down chopper device that controls a duration from a turn-on to a turn-off of the switching element so as to be a time ratio.
In claim 6,
The control circuit includes:
A switching current detector for detecting a current value of the switching current;
The arrival time from when the switching element is turned on until the current value of the switching current detected by the switching current detector reaches the target current value is defined as the duration from the turn-on of the switching element to the turn-off. An on-duration adjusting unit that adjusts the on-duration so as to be the first time ratio with respect to the on-duration;
A switching control unit that turns on the switching element based on a predetermined turn-on period, and turns off the switching element when the ON duration adjusted by the ON duration adjustment unit elapses after the switching element is turned on; A step-down chopper device comprising:
In claim 7,
The control circuit detects a discontinuous state in which a current value of a return current flowing through the second and third current paths is lower than a predetermined current value during a period from a turn-off to a turn-on of the switching element. A state detector;
The step-down chopper device, wherein the switching control unit turns on the switching element when the discontinuous state is detected by the discontinuous state detection unit.
In claim 6,
The control circuit includes:
A switching current detector for detecting a current value of the switching current;
An inductor current detector for detecting a current value of an inductor current flowing through the inductor;
The arrival time from when the switching element is turned on until the current value of the switching current detected by the switching current detector reaches the target current value is defined as the duration from the turn-on of the switching element to the turn-off. An on-duration adjusting unit that adjusts the on-duration so as to be the first time ratio with respect to the on-duration;
An arrival time from when the switching element is turned off until the current value of the inductor current detected by the inductor current detection unit reaches the target current value is defined as a duration from turn-off to turn-on of the switching element. An off duration adjusting unit that adjusts the off duration so as to be a second time ratio with respect to the off duration;
After the switching element is turned on, the switching element is turned off when the on-duration time adjusted by the on-duration adjusting unit elapses. After the switching element is turned off, the switching element is adjusted by the off-duration adjusting unit A step-down chopper device comprising: a switching control unit that turns on the switching element when the off duration time has elapsed.
In any one of claims 1 to 9,
The step-down chopper device wherein the first time ratio is 1 / 2.22 or more and 1 / 1.82 or less.
In claim 9,
The first time ratio is 1 / 2.22 or more and 1 / 1.82 or less,
The step-down chopper device wherein the second time ratio is 1 / 2.22 or more and 1 / 1.82 or less.
A step-down chopper device according to any one of claims 1 to 11,
Comprising the load element,
The light source device, wherein the load element is a light emitting element driven by the load current.
A light source device according to claim 12,
An image display device comprising: a display unit that displays an image using light emitted from the light emitting element.