JP5993786B2 - DC / DC converter circuit module and DC / DC converter - Google Patents

Description

  The present invention relates to a DC / DC converter for converting a DC voltage, and a circuit module for a DC / DC converter used in the DC / DC converter.

  As a step-down DC / DC converter for stepping down an input voltage, there is known a method of converting a pulse voltage generated by switching the input voltage at a predetermined switching frequency into an output voltage by smoothing it with a smoothing circuit. ing. There is also known a circuit module for a DC / DC converter configured by integrating an input voltage switching circuit in an integrated circuit or as a hybrid IC. Such a DC / DC converter circuit module functions as a DC / DC converter as a whole by connecting a smoothing circuit to the outside.

  As described above, a DC / DC converter that converts an input voltage into a pulse voltage and converts the pulse voltage into an output voltage by smoothing the pulse voltage with a smoothing circuit reduces the capacitance due to deterioration of the capacitor used in the smoothing circuit. The pulse voltage cannot be sufficiently smoothed. Therefore, the ripple voltage increases. Therefore, a technology is known that detects the ripple voltage included in the smoothed output voltage and reduces the ripple voltage of the output voltage output from the smoothing circuit by increasing the switching frequency when the ripple voltage exceeds the reference value. (For example, refer to Patent Document 1).

JP 2000-350448 A

  However, increasing the switching frequency of the DC / DC converter increases the frequency of switching. Since the switching element generates a loss at the timing of switching the current, the switching loss increases as the frequency of switching increases, and the voltage conversion efficiency of the DC / DC converter decreases.

  On the other hand, the ripple voltage of a DC / DC converter is not always a problem. There is no problem even if a ripple voltage is included in the output voltage of the DC / DC converter as long as it is within the allowable range of the load circuit that receives the supply of the output voltage from the DC / DC converter. Therefore, there is a need for a user such as a device designer who incorporates a DC / DC converter into a device to adjust the ripple voltage included in the output voltage of the DC / DC converter according to the allowable range of the load circuit. .

  An object of the present invention is to provide a DC / DC converter circuit module and a DC / DC converter that can easily adjust a ripple voltage included in an output voltage of a DC / DC converter according to an allowable range of a load circuit. That is.

The circuit module for a DC / DC converter according to the present invention switches an input voltage input from the outside and supplies the smoothed circuit to the smoothing circuit by smoothing the switched input voltage by the smoothing circuit. A circuit module for a DC / DC converter for generating an output voltage, wherein the input voltage is supplied to the smoothing circuit by being turned on, and the supply of the input voltage to the smoothing circuit is cut off by being turned off; A switching unit that performs the switching, a voltage detection unit that detects the output voltage, and a switching process that causes the switching unit to perform the switching by periodically turning on and off the switching unit at a fixed duty ratio. The output voltage is set to a predetermined upper side during the switching process. When it exceeds the reference voltage, a first switching mode and a stop processing for stopping the switching process by turning off the switching unit, the switching unit, in accordance with the output voltage detected by the voltage detecting section A switching control unit capable of executing a second switching mode that is periodically turned on and off at a duty ratio; a setting receiving unit that receives the setting of the upper reference voltage; and a current that flows from the switching unit to the smoothing circuit is detected. A current detection unit that performs the second switching mode when the current detected by the current detection unit during execution of the second switching mode falls below a preset threshold current. Is stopped and execution of the first switching mode is started .

According to this configuration, the input voltage input from the outside is switched by the switching unit and supplied to the smoothing circuit. The switched input voltage is smoothed by a smoothing circuit. Thereby, an output voltage is generated. The generated output voltage is detected by the voltage detector. The switching control unit executes a first switching mode including a switching process and a stop process. In the switching process, the switching unit is periodically turned on and off, and the switched input voltage is smoothed by a smoothing circuit to generate an output voltage. In addition, the setting reception unit receives the setting of the upper reference voltage. When the output voltage exceeds the upper reference voltage during the execution of the switching process, the switching unit is turned off, the switching process is stopped, and the output voltage decreases. As a result, the ripple voltage included in the output voltage is limited based on the upper reference voltage. In this case, the user sets the upper reference voltage corresponding to the allowable range of the load circuit in the setting reception unit, so that the ripple voltage included in the output voltage is adjusted to a voltage corresponding to the allowable range of the load circuit. Therefore, it becomes easy for the user to adjust the ripple voltage included in the output voltage according to the allowable range of the load circuit.
According to this configuration, the switching control unit can change the duty ratio of switching by the switching unit in the second switching mode. Therefore, for example, even when a change occurs in the current consumption of the load circuit and the output voltage fluctuates, the output voltage is adjusted by changing the duty ratio for turning on and off the switching unit according to the output voltage. Becomes easy.
Further, when the current consumption of the load circuit decreases, the current flowing from the switching unit to the smoothing circuit decreases. In such a case, power loss may occur due to unnecessary switching unless the frequency of switching is changed only by changing the duty ratio for turning on and off the switching unit in the second switching mode. Therefore, according to this configuration, when the current flowing from the switching unit to the smoothing circuit falls below the threshold current during execution of the second switching mode, execution of the second switching mode is stopped and execution of the first switching mode is started. The In the first switching mode, when the current flowing from the switching unit to the smoothing circuit decreases, the time taken for the output voltage to exceed the upper reference voltage until it falls below the on-reference voltage increases, and the time during which the switching process is stopped is increased. become longer. As a result, when the current flowing from the switching unit to the smoothing circuit decreases, the frequency of switching decreases, so that the power loss reduction effect increases.

  Further, the first switching mode further includes a start process for starting the switching process when the output voltage falls below a preset ON reference voltage during the stop period of the switching process by the stop process. Is preferred.

  According to this configuration, in the first switching mode, when the output voltage falls below the on-reference voltage during the stop period of the switching process, the switching process is started and the output voltage increases. As a result, the output voltage is maintained within a certain voltage range defined based on the upper reference voltage and the on-reference voltage. Further, since the switching process is stopped from when the output voltage exceeds the upper reference voltage until it falls below the on-reference voltage, power loss caused by the switching process is reduced. At this time, the higher the upper reference voltage, the longer it takes for the output voltage to exceed the upper reference voltage before it falls below the on-reference voltage. Therefore, the higher the upper reference voltage, the lower the switching frequency and the greater the power loss reduction effect. And since the setting reception part which receives the setting of an upper side reference voltage is provided, the user can set an upper reference voltage as large as possible within the range in which a ripple voltage is settled in the tolerance | permissible_range of a load circuit. As a result, it becomes easy to reduce the switching frequency while limiting the ripple voltage included in the output voltage within the allowable range of the load circuit.

  The switching control unit stops the execution of the first switching mode when the output voltage falls below a lower reference voltage lower than the on-reference voltage during the execution of the first switching mode, and the second switching mode is stopped. It is preferable to start execution of the mode.

  When the output voltage falls below the on-reference voltage during execution of the first switching mode, the switching process is started. However, when the current consumption of the load circuit increases, the output voltage may not be increased even when the switching process is started, and may further decrease. Therefore, according to this configuration, when the output voltage falls below the lower reference voltage lower than the on-reference voltage during execution of the first switching mode, execution of the first switching mode is stopped and execution of the second switching mode is started. Is done. In the second switching mode, even when the current consumption of the load circuit increases and the output voltage decreases, the output voltage is increased by changing the duty ratio for turning on / off the switching unit according to the output voltage. It becomes easy to make.

  The setting reception unit preferably includes a connection terminal to which a resistor can be connected, and receives the setting of the upper reference voltage in accordance with a resistance value of the resistor connected to the connection terminal.

  According to this configuration, the user can set the upper reference voltage by connecting a resistor having a resistance value corresponding to the upper reference voltage to be set to the connection terminal, so that the upper reference voltage can be easily set. It becomes.

  A DC / DC converter according to the present invention includes the above-described DC / DC converter circuit module and the smoothing circuit.

  According to this configuration, it becomes easy for the user to adjust the ripple voltage included in the output voltage of the DC / DC converter according to the allowable range of the load circuit.

  According to the DC / DC converter circuit module and the DC / DC converter having such a configuration, the user sets the upper reference voltage in accordance with the allowable range of the load circuit in the setting reception unit, so that it is included in the output voltage. The ripple voltage is adjusted to a voltage according to the allowable range of the load circuit. Therefore, it becomes easy for the user to adjust the ripple voltage included in the output voltage according to the allowable range of the load circuit.

It is a block diagram which shows an example of a structure of the DC / DC converter using the circuit module for DC / DC converters concerning one Embodiment of this invention. 2 is a timing chart for explaining the operation of the DC / DC converter circuit module and the DC / DC converter shown in FIG. 1. 6 is a timing chart for explaining that the switching interval is widened by increasing the upper reference voltage.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

  FIG. 1 is a block diagram showing an example of the configuration of a DC / DC converter using a DC / DC converter circuit module according to an embodiment of the present invention. A DC / DC converter 1 shown in FIG. 1 includes a DC / DC converter circuit module 2, a smoothing circuit 3, a voltage setting resistor RLIM (resistance), and voltage dividing resistors RA and RB.

  The smoothing circuit 3 smoothes the pulse voltage Vp output from the DC / DC converter circuit module 2. A voltage obtained by smoothing the pulse voltage Vp by the smoothing circuit 3 is output to the load circuit 4 connected to the outside of the DC / DC converter 1 as the output voltage Vout of the DC / DC converter 1.

  The smoothing circuit 3 includes an inductor L and a capacitor C, for example. One end of the inductor L is connected to the DC / DC converter circuit module 2, and the other end of the inductor L is connected to the load circuit 4. The other end of the inductor L is connected to the circuit ground via the capacitor C.

  The voltage dividing resistors RA and RB convert the output voltage Vout into a feedback voltage Vfb by dividing the output voltage Vout. Thereby, the voltage dividing resistors RA and RB convert the output voltage Vout into a voltage range in which voltage detection is possible in the DC / DC converter circuit module 2. When the resistance value of the voltage dividing resistor RA is Ra and the resistance value of the voltage dividing resistor RB is Rb, the feedback voltage Vfb is expressed by the following equation (1).

Feedback voltage Vfb = Vout × {Rb / (Ra + Rb)} (1)
The DC / DC converter circuit module 2 is composed of, for example, an integrated circuit, a hybrid IC, a printed wiring board, and the like. The DC / DC converter circuit module 2 includes a voltage detection unit 21, a switching control unit 22, a current detection unit 23, a switching unit SW, an oscillator OSC, and connection terminals 201, 202, 203, and 204. The switching control unit 22 includes an FET drive control unit 221 and a switching mode control unit 222.

  The connection terminal 204 is a power receiving terminal that receives an input of a DC input voltage Vin. The connection terminals 201 and 202 can be connected to a voltage setting resistor RLIM. The connection terminals 201 and 202 correspond to an example of a setting reception unit. The connection terminal 203 is an output terminal that outputs the pulse voltage Vp output from the DC / DC converter circuit module 2 to the smoothing circuit 3.

  The connection terminals 201, 202, 203, and 204 may be any terminals that can electrically connect the DC / DC converter circuit module 2 to an external circuit. As the connection terminals 201, 202, 203, and 204, various connection means such as connection pins of integrated circuits and hybrid ICs, through holes and wiring patterns of printed wiring boards, connectors, and terminal blocks can be used.

  The switching unit SW switches the input voltage Vin received by the connection terminal 204, and outputs the switched voltage to the smoothing circuit 3 via the current detection unit 23 and the connection terminal 203.

  Switching unit SW includes switching elements Q1 and Q2. The switching elements Q1, Q2 are, for example, FETs (Field Effect Transistors). Switching elements Q1 and Q2 are not limited to FETs, and may be, for example, bipolar transistors or other switching elements.

  The drain of the switching element Q1 is connected to the connection terminal 204, the source of the switching element Q1 is connected to the drain of the switching element Q2, and the source of the switching element Q2 is connected to the circuit ground. A connection point P1 between the source of the switching element Q1 and the drain of the switching element Q2 is connected to the smoothing circuit 3 via the current detection unit 23 and the connection terminal 203.

  The switching unit SW supplies the input voltage Vin to the smoothing circuit 3 when the switching element Q1 is on and the switching element Q2 is off, and when the switching element Q1 is off and the switching element Q2 is on The supply of the input voltage Vin to the smoothing circuit 3 is cut off. That is, the on state of the switching unit SW is a state in which the switching element Q1 is on and the switching element Q2 is off, and the off state of the switching unit SW is a state in which the switching element Q1 is off and the switching element Q2 is on.

  Hereinafter, turning on the switching element Q1 and turning off the switching element Q2 is simply referred to as turning on the switching unit SW, and turning off the switching element Q1 and turning on the switching element Q2 simply turns off the switching unit SW. .

  The oscillator OSC is an oscillation circuit such as a crystal oscillator or a ceramic oscillator. The oscillator OSC outputs a clock signal serving as a reference for switching the input voltage Vin by the switching unit SW to the switching control unit 22.

  The voltage detector 21 detects the output voltage Vout indirectly by detecting the feedback voltage Vfb. Further, the voltage detector 21 compares the feedback voltage Vfb with a preset reference voltage and outputs a signal indicating the comparison result to the switching mode controller 222.

  The voltage detection unit 21 includes comparators CMP1, CMP2, CMP3, reference voltage sources E1, E2, E3, voltage dividing resistors RC, RD, and a resistor RE. The comparators CMP1, CMP2, and CMP3 may be error amplifiers.

  The reference voltage sources E1, E2, E3 are constant voltage circuits that output a preset reference voltage. The reference voltage source E1 outputs a reference voltage Vref1. The reference voltage source E2 outputs a reference voltage Vref2. The reference voltage source E3 outputs a reference voltage Vref3.

  The voltage dividing resistors RC and RD are voltage dividing resistors for dividing the feedback voltage Vfb. The voltage dividing resistors RC and RD are connected in series between a connection point P2 between the voltage dividing resistor RA and the voltage dividing resistor RB and the circuit ground. A connection point P 3 between the voltage dividing resistors RC and RD is connected to the connection terminal 202.

  One end of a voltage setting resistor RLIM is connected to the connection terminal 202. The other end of the voltage setting resistor RLIM is connected to the connection terminal 201. The connection terminal 201 is connected to the + side input terminal of the comparator CMP1. The reference voltage Vref1 output from the reference voltage source E1 is input to the negative side input terminal of the comparator CMP1. A resistor RE for providing hysteresis in the operation of the comparator CMP1 is connected between the output terminal and the + side input terminal of the comparator CMP1. The output terminal of the comparator CMP1 is connected to the switching mode control unit 222. The voltage setting resistor RLIM is a resistance element having a resistance value Rlim.

  As a result, the comparator CMP1 causes the output signal Vout to be at a high level when the output voltage Vout exceeds the upper reference voltage Vupper set according to the voltage setting resistor RLIM, so that the output voltage Vout becomes the upper reference voltage Vupper. Is output to the switching mode control unit 222.

  Note that a configuration without the resistor RE may be employed, but the provision of the resistor RE can prevent malfunction due to noise. A method for setting the upper reference voltage Vupper based on the voltage setting resistor RLIM will be described later.

  The negative input terminal of the comparator CMP2 is connected to the connection point P2 of the voltage dividing resistors RA and RB, and the feedback voltage Vfb is input to the negative input terminal of the comparator CMP2. The reference voltage Vref2 output from the reference voltage source E2 is input to the + side input terminal of the comparator CMP2. The reference voltage Vref2 is a voltage that satisfies the following expression (2) based on the preset ON reference voltage Von and the resistance values Ra and Rb.

Vref2 = Von × {Rb / (Ra + Rb)} (2)
The comparator CMP2 sets the output signal to a high level when the feedback voltage Vfb is lower than the reference voltage Vref2. The feedback voltage Vfb has a relationship represented by the above equation (1) with the output voltage Vout, and the reference voltage Vref2 has a relationship represented by the above equation (2). Accordingly, the feedback voltage Vfb being lower than the reference voltage Vref2 means that the output voltage Vout is lower than the ON reference voltage Von.

  That is, when the output voltage Vout falls below the on-reference voltage Von, the comparator CMP2 sets the output signal to a high level, thereby generating a signal indicating that the output voltage Vout has fallen below the on-reference voltage Von. Output to.

  The negative input terminal of the comparator CMP3 is connected to the connection point P2 of the voltage dividing resistors RA and RB, and the feedback voltage Vfb is input to the negative input terminal of the comparator CMP3. The reference voltage Vref3 output from the reference voltage source E3 is input to the + side input terminal of the comparator CMP3. The reference voltage Vref3 is set to a voltage that satisfies the following expression (3) based on the preset lower reference voltage Vlower and the resistance values Ra and Rb.

Vref3 = Vlower × {Rb / (Ra + Rb)} (3)
The comparator CMP3 sets the output signal to a high level when the feedback voltage Vfb is lower than the reference voltage Vref3. The feedback voltage Vfb has a relationship represented by the above equation (1) with the output voltage Vout, and the reference voltage Vref3 has a relationship represented by the above equation (3). That the voltage Vfb is lower than the reference voltage Vref3 means that the output voltage Vout is lower than the lower reference voltage Vlower.

  That is, when the output voltage Vout falls below the lower reference voltage Vlower, the comparator CMP3 sets the output signal to a high level, thereby switching a signal indicating that the output voltage Vout has fallen below the lower reference voltage Vlower. Output to the unit 222.

  Note that the logic levels of the output signals of the comparators CMP1, CMP2, and CMP3 are examples, and the output signal may be set to a low level instead of the high level as described above.

  The current detection unit 23 is a current detection circuit that detects a current that flows from the switching unit SW to the smoothing circuit 3, that is, an output current Iout that flows from the connection point P1 to the load circuit 4 via the smoothing circuit 3. The current detection unit 23 is configured by a current detection circuit such as a shunt resistor or a Hall element.

  The FET drive control unit 221 is configured by a logic circuit, for example. The FET drive control unit 221 controls on / off of the switching unit SW by controlling on / off of the switching elements Q1, Q2, respectively. The FET drive control unit 221 controls the frequency and duty ratio for turning on and off the switching unit SW based on the clock signal output from the oscillator OSC and the control signal from the switching mode control unit 222.

  The switching mode control unit 222 is a control circuit configured using, for example, a state machine or a logic circuit. The switching mode control unit 222 is not limited to an example configured using a state machine or a logic circuit, and may be configured using, for example, a microcomputer.

  The switching mode control unit 222 can execute a PWM (Pulse Width Modulation) mode (second switching mode) and a PFM (Pulse Frequency Modulation) mode (first switching mode).

  In the PWM mode, the switching mode control unit 222 outputs a control signal to the FET drive control unit 221 to turn on the switching unit SW at a preset PWM switching period and with a duty ratio corresponding to the output voltage Vout. Turn off.

  In the PWM mode, the switching mode control unit 222 is configured so that the output voltage Vout becomes a preset target voltage based on the output voltage Vout (or feedback voltage Vfb) detected by a voltage detection circuit (not shown). The drive control unit 221 controls the duty ratio for turning on / off the switching unit SW.

  Specifically, in the PWM mode, when the output voltage Vout is less than the target voltage, the switching mode control unit 222 performs switching with respect to the duty ratio of the switching unit SW, that is, the switching cycle of the switching unit SW, by the FET drive control unit 221. The ratio of the period during which the part SW is on is increased. In the PWM mode, the switching mode control unit 222 causes the FET drive control unit 221 to decrease the duty ratio of the switching unit SW when the output voltage Vout exceeds the target voltage.

  According to the PWM mode, the switching control unit can change the duty ratio of switching by the switching unit SW. Therefore, for example, even when the consumption current of the load circuit 4 changes and the output voltage Vout changes, the output voltage Vout can be changed by changing the duty ratio for turning on and off the switching unit SW according to the output voltage Vout. It becomes easy to adjust Vout.

  Then, when the output current Iout detected by the current detector 23 falls below the preset threshold current Ith during the execution of the PWM mode, the switching mode control unit 222 stops the execution of the PWM mode and the PFM mode. Start execution. The threshold current Ith is set to a current value of about 10 mA, for example.

  In the PFM mode, the switching mode control unit 222 is a switching process in which the FET drive control unit 221 periodically turns on / off the switching unit SW at a preset PFM switching cycle and at a preset duty ratio Dpfm. And when the output signal of the comparator CMP1 becomes high level during the switching process, that is, when the output voltage Vout exceeds the upper reference voltage Vupper, the switching unit SW is turned off to stop the switching process. Run.

  Further, in the PFM mode, the switching mode control unit 222 further outputs when the output signal of the comparator CMP2 becomes high level during the stop period of the switching process by the stop process, that is, when the output voltage Vout falls below the on-reference voltage Von. Then, a start process for starting the switching process is executed.

  Then, when the output signal of the comparator CMP3 becomes high level during the execution of the PFM mode, that is, when the output voltage Vout falls below the lower reference voltage Vlower lower than the on-reference voltage Von, the switching mode control unit 222 performs the PFM mode. Is stopped and PWM mode is started.

  Next, a method for setting the upper reference voltage Vupper based on the voltage setting resistor RLIM will be described.

  The resistance values of the voltage dividing resistors RA, RB, RC, RD are Ra, Rb, Rc, Rd, the resistance value of the resistor RE is Re, the resistance value of the voltage setting resistor RLIM is Rlim, and the voltage at the connection point P3 is Assuming Uin, the high level output voltage of the comparator CMP1 is Vdd, and the low level output voltage of the comparator CMP1 is −Vdd, the condition that the output voltage Vout is equal to or higher than the upper reference voltage Vupper is as follows: Indicated by

Vref1 ≦ (−Vdd−Uin) × {Re / (Rlim + Re)} + Uin (4)
Here, if Re / (Rlim + Re) is D,
Vref1 ≦ (−Vdd−Uin) × D + Uin
Uin ≧ (Vref1 + Vdd × D) / (1-D).

Since Uin = Vfb × {Rd / (Rc + Rd)} and Vfb = Vout × {Rb / (Ra + Rb)} from the above equation (1),
Vout × {Rb / (Ra + Rb)} × {Rd / (Rc + Rd)} ≧ (Vref1 + Vdd × D) / (1-D).

Therefore,
Vupper = [{(Ra + Rb) × (Rc + Rd)} / (Rb × Rd × Rlim)] × {(Rlim + Re) × Vref1 + Re × Vdd} (5)
It becomes.

  That is, the upper reference voltage Vupper can be set to an arbitrary voltage value by setting the resistance value Rlim of the voltage setting resistor RLIM based on the above equation (5). Thereby, the user who uses the DC / DC converter circuit module 2 connects the voltage setting resistor RLIM having the resistance value Rlim satisfying the above formula (5) to the connection terminals 201 and 202 which are examples of the setting receiving unit. Thus, the upper reference voltage Vupper can be set to an arbitrary voltage value.

  In addition, the user can set the upper reference voltage Vupper by connecting the voltage setting resistor RLIM having a resistance value corresponding to the upper reference voltage Vupper to be set to the connection terminal. Easy to set up.

  The upper reference voltage Vupper is not limited to an example in which the upper reference voltage Vupper is set according to the resistance value Rlim of the voltage setting resistor RLIM. For example, a setting switch such as a dip switch or a rotary switch may be connected to the connection terminals 201 and 202. Then, the DC / DC converter circuit module 2 may accept the setting of the upper reference voltage Vupper according to the setting value of such a setting switch.

  Next, operations of the DC / DC converter circuit module 2 and the DC / DC converter 1 configured as described above will be described.

  FIG. 2 is a timing chart for explaining operations of the DC / DC converter circuit module 2 and the DC / DC converter 1 shown in FIG. FIG. 2 shows a waveform indicating the ON / OFF state of the switching unit SW, a waveform indicating the current value of the output current Iout, and a waveform indicating the voltage value of the output voltage Vout.

  First, at timing T1, the switching mode control unit 222 executes the PWM mode.

  In the PWM mode, the switching mode control unit 222 outputs a control signal to the FET drive control unit 221 to turn on the switching unit SW at a preset PWM switching period and with a duty ratio corresponding to the output voltage Vout. Turn off. The pulse voltage Vp output from the connection terminal 203 is smoothed by the smoothing circuit 3. Then, the output voltage Vout obtained by being smoothed by the smoothing circuit 3 is maintained substantially at the target voltage.

  When the current consumption of the load circuit 4 decreases and the output current Iout falls below the threshold current Ith (timing T2), the switching mode control unit 222 stops the PWM mode operation and starts executing the PFM mode.

  In the PFM mode, the switching mode control unit 222 performs a switching process in which the FET drive control unit 221 periodically turns on / off the switching unit SW at the PFM switching period and with the duty ratio Dpfm. The switching period for PFM is set to be longer than the switching period for PWM.

  When the output voltage Vout exceeds the upper reference voltage Vupper, the output signal of the comparator CMP1 becomes high level. When the output signal of the comparator CMP1 becomes high level, the switching mode control unit 222 executes a stop process for turning off the switching unit SW and stopping the switching process (timing T3).

  Timing T3 indicates the timing when the switching period for PFM has elapsed from the timing T4 when the switching unit SW is turned on immediately before the timing T3, that is, the timing when the switching unit SW was supposed to be turned on in the switching process.

  At timing T3, the switching process is stopped and the switching unit SW is turned off. As a result, since the output voltage Vout gradually decreases, the output voltage Vout is prevented from rising beyond the upper reference voltage Vupper, and the possibility that a ripple voltage exceeding the upper reference voltage Vupper is generated in the output voltage Vout is reduced. Is done.

  As a result, the ripple voltage included in the output voltage Vout is limited based on the upper reference voltage Vupper. In this case, the user sets the upper reference voltage Vupper according to the allowable range of the ripple voltage in the load circuit 4, so that the ripple voltage included in the output voltage Vout is adjusted to a voltage according to the allowable range of the load circuit 4. The Therefore, it becomes easy for the user to adjust the ripple voltage included in the output voltage Vout according to the allowable range of the load circuit 4.

  Further, in the PFM mode, when the output voltage Vout exceeds the upper reference voltage Vupper, the switching of the switching unit SW is stopped. Therefore, the switching unit SW is generated more than the case where the switching of the switching unit SW is always performed as in the PWM mode. Power loss can be reduced.

  As shown in the timing T2, when the consumption current of the load circuit 4 decreases and the output current Iout falls below the threshold current Ith, the switching mode control unit 222 stops the PWM mode operation and starts executing the PFM mode. As a result, when the current consumption of the load circuit 4 decreases, the power loss generated in the switching unit SW can be reduced as compared with the case where the PWM mode operation is continued.

  When the output voltage Vout falls below the ON reference voltage Von (timing T5), the output signal of the comparator CMP2 becomes high level. When the output signal of the comparator CMP2 becomes high level, the switching mode control unit 222 starts switching processing, and the FET drive control unit 221 periodically turns on and off the switching unit SW. As a result, the output voltage Vout gradually increases.

  As described above, the switching mode control unit 222 starts the switching process when the output voltage Vout falls below the on-reference voltage Von during the stop period of the switching process by the stop process, so the output voltage Vout is set to the on-reference voltage Von. And a voltage range between the upper reference voltage Vupper and the upper reference voltage Vupper.

  When the output voltage Vout exceeds the upper reference voltage Vupper (timing T6), the output signal of the comparator CMP1 becomes high level. When the output signal of the comparator CMP1 becomes a high level, the switching mode control unit 222 turns off the switching unit SW and stops the switching process.

  When the switching process is stopped and the switching unit SW is turned off, the output voltage Vout gradually decreases. When the output voltage Vout falls below the ON reference voltage Von (timing T7), the output signal of the comparator CMP2 becomes high level. When the output signal of the comparator CMP2 becomes high level, the switching mode control unit 222 starts switching processing, and the FET drive control unit 221 periodically turns on and off the switching unit SW.

  Here, FIG. 2 shows a state in which the consumption current of the load circuit 4 increases in the period after the timing T7. In the PFM mode in which the PFM switching period and the duty ratio are fixed to Dpfm, the output current Iout that can be supplied to the load circuit 4 is limited to a certain current or less. Therefore, in the period from the timing T7 to the timing T8, since the output current Iout is insufficient with respect to the consumption current of the load circuit 4, the output voltage Vout is gradually increased even though the switching unit SW is switched. It has dropped to.

  When the output voltage Vout falls below the lower reference voltage Vlower (timing T8), the output signal of the comparator CMP3 becomes high level. When the output signal of the comparator CMP3 becomes high level, the switching mode control unit 222 stops executing the PFM mode and starts executing the PWM mode.

  In the PWM mode, the switching mode control unit 222 turns on and off the switching unit SW at a duty ratio corresponding to the output voltage Vout. Therefore, even when the consumption current of the load circuit 4 increases and the output voltage Vout decreases, the switching mode control unit 222 increases the duty ratio for turning on and off the switching unit SW, thereby increasing the output current Iout. Can be increased more than when the PFM mode is executed, and the output voltage Vout can be increased.

  As described above, when the output voltage Vout falls below the lower reference voltage Vlower lower than the on-reference voltage Von during the execution of the PFM mode, the switching mode control unit 222 stops the execution of the PFM mode and executes the PWM mode. By starting, the output voltage Vout can be increased even when the current consumption of the load circuit 4 increases.

  Here, in the PFM mode, unlike the PWM mode in which the switching cycle is always constant, the switching interval may become large, such as the interval Tw1 between timings T4 and T5 and the interval Tw2 between timings T6 and T7. As the switching interval increases, the ripple voltage of the output voltage Vout increases. On the other hand, when the switching interval is reduced, the switching frequency of the switching unit SW is increased, so that power loss generated in the switching unit SW is increased.

  If the load circuit 4 can tolerate the ripple voltage of the output voltage Vout, there is no problem even if it increases. Therefore, from the viewpoint of reducing the power loss generated in the switching unit SW, it is desirable to increase the switching interval in the PFM mode until the ripple voltage of the output voltage Vout becomes a voltage close to the upper limit of the allowable range of the load circuit 4.

  The ripple voltage of the output voltage Vout increases as the upper reference voltage Vupper increases, and decreases as the upper reference voltage Vupper decreases. Therefore, if the upper reference voltage Vupper is set to a high voltage value, it is possible to reduce the power loss generated in the switching unit SW instead of increasing the ripple voltage. On the other hand, if the upper reference voltage Vupper is set to a low voltage value, the ripple voltage can be reduced instead of increasing the power loss generated in the switching unit SW.

  Therefore, by setting the upper reference voltage Vupper to a voltage value corresponding to the upper limit of the ripple voltage that the load circuit 4 can tolerate, the power loss that occurs in the switching unit SW while suppressing the adverse effect of the ripple voltage on the load circuit 4 is suppressed. Can be reduced.

  However, the range of the ripple voltage that can be tolerated by the load circuit 4 varies depending on the type and specification of the load circuit 4 connected to the DC / DC converter 1. Therefore, when the upper reference voltage Vupper is a fixed value, the ripple voltage may exceed the allowable range of the load circuit 4 and the load circuit 4 may malfunction. Further, the ripple voltage is made smaller than necessary with respect to the allowable range of the load circuit 4, and there is a possibility that the power loss generated in the switching unit SW increases.

  Therefore, in the DC / DC converter 1 shown in FIG. 1, the user appropriately sets the resistance value Rlim of the voltage setting resistor RLIM so that the upper reference voltage Vupper corresponds to the upper limit of the ripple voltage that the load circuit 4 can tolerate. The voltage value can be easily set. As a result, it is easy to reduce the power loss generated in the switching unit SW while suppressing the adverse effect of the ripple voltage on the load circuit 4.

  FIG. 3 is a timing chart for explaining that the switching interval is widened by increasing the upper reference voltage Vupper. The timing chart shown in FIG. 3 shows the operation of the DC / DC converter 1 when the upper reference voltage Vupper is set to a voltage higher than the upper reference voltage Vupper in the timing chart shown in FIG.

  The operation of the DC / DC converter 1 at the timings T1 to T5 shown in FIG. 3 is the same as the operation of the DC / DC converter 1 at the timings T1 to T5 shown in FIG.

  According to the timing chart shown in FIG. 3, by setting the upper reference voltage Vupper to a voltage higher than that in the timing chart shown in FIG. 2, the timing chart shown in FIG. 3 is more than the switching interval Tw1 in the timing chart shown in FIG. It can be seen that the switching interval Tw3 at becomes larger.

  The voltage detection unit 21 does not necessarily include the comparator CMP2 and the reference voltage source E2, and the PFM mode does not necessarily include the start process. The voltage detector 21 does not necessarily include the comparator CMP3 and the reference voltage source E3, and the switching controller 22 does not necessarily change from the PFM mode to the PWM mode when the output voltage Vout falls below the lower reference voltage Vlower. There is no need to switch to. In addition, the current detection unit 23 is not provided, and the switching control unit 22 does not necessarily have to switch from the PWM mode to the PFM mode when the current detected by the current detection unit 23 falls below the threshold current Ith. Further, the switching control unit 22 may not execute the PWM mode.

DESCRIPTION OF SYMBOLS 1 DC / DC converter 2 DC / DC converter circuit module 3 Smoothing circuit 4 Load circuit 21 Voltage detection part 22 Switching control part 23 Current detection part 201,202 connection terminal (setting reception part)
203, 204 Connection terminal 221 FET drive control unit 222 Switching mode control unit C Capacitor CMP1, CMP2, CMP3 Comparator Dpfm Duty ratio E1, E2, E3 Reference voltage source Iout Output current Ith Threshold current L Inductor OSC Oscillator Q1, Q2 Switching element RA, RB, RC Voltage dividing resistor RE resistor RLIM voltage setting resistor SW switching unit Vfb feedback voltage Vin input voltage Vlower lower reference voltage Von on reference voltage Vout output voltage Vp pulse voltage Vref1, Vref2, Vref3 reference voltage Vupper upper reference voltage

Claims (5)

A circuit module for a DC / DC converter that switches an input voltage inputted from the outside and supplies the smoothed circuit to the smoothing circuit, and smoothes the switched input voltage by the smoothing circuit, thereby causing the smoothing circuit to generate an output voltage. There,
A switching unit that performs the switching by supplying the input voltage to the smoothing circuit by turning on and shutting off the supply of the input voltage to the smoothing circuit by turning off;
A voltage detector for detecting the output voltage;
A switching process in which the switching unit is periodically turned on and off at a fixed duty ratio to cause the switching unit to perform the switching, and the output voltage exceeds a predetermined upper reference voltage during the switching process. A first switching mode including a stop process for turning off the switching unit and stopping the switching process, and the switching unit is cycled at a duty ratio corresponding to the output voltage detected by the voltage detection unit. A switching control unit capable of executing a second switching mode to be turned on and off automatically,
A setting receiving unit for receiving the setting of the upper reference voltage;
A current detection unit for detecting a current flowing from the switching unit to the smoothing circuit;
Equipped with a,
The switching control unit stops execution of the second switching mode when the current detected by the current detection unit falls below a preset threshold current during execution of the second switching mode. A circuit module for a DC / DC converter that starts executing a switching mode . The first switching mode further includes:
2. The circuit module for a DC / DC converter according to claim 1, further comprising a start process that starts the switching process when the output voltage falls below a preset ON reference voltage during the stop period of the switching process by the stop process. . The switching controller is
The execution of the first switching mode is stopped and the execution of the second switching mode is started when the output voltage falls below a lower reference voltage lower than the ON reference voltage during the execution of the first switching mode. 2. The circuit module for a DC / DC converter according to 2 . The setting reception unit
The resistor comprises a connection terminal connectable, in accordance with the resistance value of the resistor connected to the connection terminals, DC / DC converter according to any one of claims 1 to 3, accept the setting of the upper reference voltage Circuit module. A circuit module for a DC / DC converter according to any one of claims 1 to 4 ,
A DC / DC converter comprising the smoothing circuit.

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