JP2017143599A - Switching power source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve response to a load change in a switching power source device that exerts CRM control.SOLUTION: A switching power source device comprises: an inductor L1; a switching element Q, Qconnected to the inductor; an error voltage generation part 7 that generates an error voltage SE from a feedback voltage based on an output voltage Vout and from a reference voltage Vref; a slope voltage generation part 4 that generates a slope voltage SLP; a comparison part 8 that generates a comparison signal SC by comparing an error voltage and a slope voltage; drive parts 5, 6 that generate a drive signal for switching the switching element from an on-state to an off-state on the basis of a comparison signal; and a CRM (critical mode) control part 2 that variably controls a switching period for the switching element such that current flowing in the inductor when the switching element switches from an off-state to an on-state becomes equal to zero. The CRM control part changes the switching period in a direction opposite to the direction in which a switching period in the CRM control is changed by detection of a load change.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply device.

  Conventionally, various switching power supply devices have been developed. In particular, some boost converters perform control called CRM (CRitical Current Mode) control.

  For example, when the boost converter has a configuration in which an upper switching element and a lower switching element are connected and the other end of a coil to which an input voltage is applied to one end is connected to the connection point, the lower switching element is turned on. As a result, the coil current flowing through the coil increases, and the excitation energy is accumulated. When the lower switching element is turned off and the upper switching element is turned on, the excitation energy is released and the coil current is reduced.

  In the CRM control, the coil current is controlled to be zero at the timing when the coil current decreases and the upper switching element is switched on to the lower switching element. When the load is a heavy load, compared with the normal current mode control, the switching period is longer in the CRM control and the number of times of switching is reduced, so that the switching loss can be reduced.

  As an example of the related art related to the above, Patent Document 1 can be cited.

JP 2014-239620 A

  The boost converter that performs CRM control performs feedback control that feeds back the output voltage in order to keep the output voltage constant. More specifically, the error amplifier generates an error voltage based on the feedback voltage based on the output voltage and the reference voltage, and detects that the slope voltage has increased and reached the miscalculation voltage by comparing the slope voltage with the error voltage. Then, the lower switching element that was turned on is switched off. Thereby, the ON period of the lower switching element is adjusted.

  Here, in the case of load fluctuation (increase in load current) in which the load suddenly becomes heavy, the switching cycle is adjusted to be long by CRM control. At this time, the error voltage increases in order to maintain the duty (ratio of the ON period of the lower switching element to the switching period) by feedback control. Further, the miscalculation voltage increases corresponding to the decrease of the output voltage due to the load fluctuation. Therefore, both factors cause the error voltage to increase, so that the response for achieving the desired duty is delayed, and the output voltage undershoot increases.

  In view of the above situation, an object of the present invention is to provide a switching power supply capable of improving the response to load fluctuations in a switching power supply that performs CRM control.

In order to achieve the above object, a switching power supply according to an aspect of the present invention is provided.
An inductor;
A switching element connected to the inductor;
An error voltage generator that generates an error voltage from a feedback voltage based on the output voltage and a reference voltage;
A slope voltage generator for generating a slope voltage;
A comparison unit that compares the error voltage with the slope voltage to generate a comparison signal;
A drive unit that generates a drive signal for switching the switching element from on to off based on the comparison signal;
A CRM (critical mode) control unit that variably controls the switching period of the switching element so that a current flowing through the inductor becomes zero when the switching element is switched from OFF to ON,
The CRM control unit includes a detection unit that detects a load variation, and is configured to change the switching cycle in a direction opposite to a direction in which the switching cycle is changed in CRM control by detection of the detection unit (first Constitution).

  In the first configuration, when the load is detected by the detection unit, the CRM control unit may shorten the switching cycle (second configuration).

  In the first or second configuration, the detection unit may detect the load variation by detecting that the output voltage exceeds a threshold voltage (third configuration).

  In the first or second configuration, the detection unit may detect the load variation by receiving an external signal indicating the load variation (fourth configuration).

  In the first or second configuration, the detection unit may detect the load fluctuation by detecting that the rate of change of the load current exceeds a threshold value (fifth configuration).

  In any one of the first to fifth configurations, the CRM control unit may restart CRM control after detecting the load fluctuation (sixth configuration).

Further, in the sixth configuration, the detection unit detects the load variation by detecting that the output voltage exceeds a first threshold voltage,
The CRM control unit may resume CRM control by detecting that the output voltage exceeds a second threshold voltage (seventh configuration).

  In the seventh configuration, the second threshold voltage may be set to a value different from the first threshold voltage (eighth configuration).

  A display device according to another aspect of the present invention includes the switching power supply device having any one of the first to eighth configurations, and a display unit to which power is supplied from the switching power supply device ( Ninth configuration).

  In the ninth configuration, the detection unit included in the switching power supply device may receive an external signal indicating switching between a blanking period and a display period.

  According to the present invention, it is possible to improve responsiveness to load fluctuations in a switching power supply device that performs CRM control.

It is a figure which shows the structure of the switching power supply device which concerns on one Embodiment of this invention. It is a figure which shows the example of 1 structure of a CRM control part. It is a timing chart which shows the example of a waveform of various signals at the time of CRM control. It is a timing chart which shows the example of a waveform of various signals at the time of normal current mode control. It is a timing chart which shows the example of control at the time of the load change which becomes heavy. It is a timing chart which shows the example of control at the time of the load change which becomes heavy. It is the schematic which shows the example of a waveform change of the coil electric current when CRM control is performed at the time of the load fluctuation which becomes heavy. It is a timing chart which shows the example of control at the time of the load fluctuation which lightens a load. It is a block diagram which shows the structure of the television which concerns on one Embodiment of this invention. It is a front view of the television which concerns on one Embodiment of this invention.

  An embodiment of the present invention will be described below with reference to the drawings.

<Configuration of switching power supply device>
FIG. 1 is a diagram showing a configuration of a switching power supply device according to an embodiment of the present invention. A switching power supply device 1 shown in FIG. 1 is a boost converter that boosts an input voltage Vin to generate an output voltage Vout and supplies the output voltage Vout to a load (not shown).

  The switching power supply device 1 includes a switching driver 10, a coil L1 (inductor), which is a discrete element provided outside the switching driver 10, an upper switching element Q1, a lower switching element Q2, a bootstrap capacitor Cb, capacitors C1, C2, and resistors. R1 and R2.

  An input voltage Vin is applied to one end of the coil L1. The other end of the coil L1 is connected to a connection point P where the source of the upper switching element Q1 composed of an N channel MOSFET (MOS field effect transistor) and the drain of the lower switching element Q2 composed of an N channel MOSFET are connected. Is connected. The source of the lower switching element Q2 is connected to the ground terminal via the resistor R1. The drain of the switching element Q1 is connected to the output terminal To together with one end of the capacitor C1. The other end of the capacitor C1 is connected to the ground terminal.

  The switching driver 10 includes a CRM control unit 2, a drive logic unit 3, a slope voltage generation unit 4, an upper driver 5, a lower driver 6, an error amplifier 7, a comparator 8, a resistor R3, and a resistor R4. A semiconductor device (IC) in which components are integrated. The switching driver 10 also has external terminals T1 to T7 for establishing a connection with the outside.

  The resistor R3 and the resistor R4 are connected in series between the output terminal To where the output voltage Vout is generated and the ground terminal. A feedback voltage Vfb generated by dividing the output voltage Vout by the resistors R 3 and R 4 is applied to the inverting input terminal (−) of the error amplifier 7. A reference voltage Vref is applied to the non-inverting input terminal (+) of the error amplifier 7.

  The error amplifier 7 (error voltage generator) generates an error voltage SE by amplifying the difference between the feedback voltage Vfb and the reference voltage Vref. The output terminal of the error amplifier 7 is connected to the inverting input terminal of the comparator 8 and is connected to a series connection configuration of the resistor R2 and the capacitor C2 via the external terminal T6. That is, the error voltage SE is applied to the inverting input terminal of the comparator 8.

  A connection point between the lower switching element Q2 and the resistor R1 is connected to the slope voltage generation unit 4 via the external terminal T5. The slope voltage generation unit 4 adds the detection voltage Vd of the current flowing through the lower switching element Q2 generated at the connection point and a predetermined slope voltage (sawtooth wave or triangular wave) to generate and output the slope voltage SLP. To do. Thereby, the function of current mode control is achieved. The slope voltage SLP is applied to the non-inverting input terminal of the comparator 8.

  The comparator 8 (comparison unit) compares the error voltage SE with the slope voltage SLP and outputs a comparison signal SC as a comparison result to the drive logic unit 3. The drive logic unit 3 (drive unit) generates a pulsed drive signal SD based on the comparison signal SC output from the comparator 8 and the control signal S1 output from the CRM control unit 2. The upper driver 5 generates a gate signal G1 based on the drive signal SD, and applies the gate signal G1 to the gate of the upper switching element Q1. In order to drive the upper switching element Q1, which is an N-channel MOSFET, a bootstrap capacitor Cb is inserted between the external terminal T1 connected to the upper driver 5 and the source of the upper switching element Q1.

  The lower driver 6 generates a gate signal G2 based on the drive signal SD, and applies the gate signal G2 to the gate of the lower switching element Q2.

<Configuration of CRM control unit>
Next, the configuration of the CRM control unit 2 will be described with reference to FIG. The CRM control unit 2 includes a logic control unit 21, a zero cross detection unit 22, a hysteresis comparator 23, a resistor 24, a resistor 25, input terminals T21 to T23, and an output terminal T24.

  The zero cross detector 22 is connected to an input terminal T21 connected to a connection point P (FIG. 1) where the switching voltage SW is generated. Thereby, the zero cross detection part 22 can detect the zero cross where the coil current Icoil which flows into the coil L1 crosses zero when the upper side switching element Q1 is ON. The zero cross detection unit 22 outputs the detection signal DT to the logic control unit 21.

  The resistor 24 and the resistor 25 are connected in series between the input terminal T22 and the ground terminal. Since the input terminal T22 is connected to the output terminal To (FIG. 1), the output voltage Vout is divided by the resistors 24 and 25 to generate a divided voltage Vdv. The hysteresis comparator 23 compares the divided voltage Vdv with the threshold voltages VT1 and VT2, and outputs a comparison signal CP to the logic control unit 21 as a comparison result. The hysteresis comparator 23, the resistor 24, and the resistor 25 constitute a detection unit that detects a load variation.

  In addition, a clock signal CLK having a predetermined frequency (for example, 24 MHz that is 32 times that when the switching frequency is 750 kHz) is input to the logic control unit 21 via an input terminal T23. The logic control unit 21 generates the control signal S1 by counting the clock signal CLK and outputs it to the drive logic unit 3 (FIG. 1) via the output terminal T24.

<About CRM control>
Next, the operation of CRM control will be described using the timing chart shown in FIG. In FIG. 3, waveform examples of the clock signal CLK, the control signal S1, the switching voltage SW, the coil current Icoil, the error voltage SE, and the slope voltage SLP are shown in order from the top.

  At timing t1, when the logic control unit 21 raises the control signal S1 to a high level in response to the falling of the pulse of the clock signal CLK, the lower switching element Q2 is turned on based on the drive signal SD from the drive logic unit 3. The upper switching elements Q1 are each switched off. Thereby, the switching voltage SW becomes the ground level, the coil current Icoil flowing through the coil L1 and the lower switching element Q2 starts increasing, and the slope voltage SLP also starts increasing. At this time, the logic control unit 21 starts counting the clock signal CLK.

  Thereafter, when the slope voltage SLP reaches the error voltage SE at timing t2, the lower switching element Q2 is switched off and the upper switching element Q1 is switched on based on the comparison signal SC and the drive signal SD. That is, the on period Ton of the lower switching element Q2 from timing t1 to t2 is adjusted according to the error voltage SE.

  When the lower switching element Q2 is turned off, the switching voltage SW becomes High level, and the coil current Icoil flowing through the coil L1 and the upper switching element Q1 starts to decrease. Then, in response to the fall of the clock signal CLK when the logic control unit 21 counts the clock signal CLK to a predetermined target count, the logic control unit 21 raises the control signal S1 (timing t3). Accordingly, the upper switching element Q1 is switched off and the lower switching element Q2 is switched on.

  At this time, the logic control unit 21 adjusts the target count number according to the detection signal DT output from the zero cross detection unit 22. More specifically, when the detection signal DT indicates that the coil current Icoil is on the plus side, the target count is increased, and when the detection signal DT indicates that it is on the minus side, the target count is decreased. Thus, the coil current Icoil when the lower switching element Q2 is switched from OFF to ON is controlled to be maintained at zero. By adjusting the target count number, the switching cycle Tsw (= the on period Ton of the lower switching element Q2 + the off period Toff) is variably adjusted.

  Here, as a comparative example with the timing chart of the CRM control shown in FIG. 3, FIG. 4 shows a timing chart when the normal current mode control is performed without performing the CRM control. In this case, the switching period Tsw is fixed. When the load is a heavy load, as can be seen from comparison with FIG. 4, in FIG. 3 in which CRM control is performed, the switching cycle Tsw becomes longer and the number of times of switching decreases, so that it becomes possible to reduce the switching loss.

<Operation when load fluctuation occurs>
Next, an operation when a load change occurs will be described. FIG. 5 is a timing chart showing an example of the behavior of each signal when the load suddenly increases. However, FIG. 5 shows the operation when the CRM control is always performed. The output voltage Vout, the load current ILOAD, and the switching cycle Tsw are shown in order from the top of FIG.

  As shown in FIG. 5, when the load suddenly increases, the load current ILOAD suddenly increases from I1 to I2. At this time, as schematically shown in FIG. 7, the coil current Icoil once rises to the plus side, but the lower switching element Q2 is finally turned from OFF to ON by gradually adjusting the switching cycle Tsw to be longer. The coil current Icoil at the switching timing becomes zero and the switching cycle Tsw is stabilized. As shown in FIG. 5, the switching period Tsw is stabilized after the load current ILOAD reaches I2.

  However, when the switching cycle Tsw is adjusted to increase in this way, the error voltage SE rises so as to maintain the duty (ratio of the ON period Ton to the switching cycle Tsw) by feedback control. Further, the error voltage SE rises by feedback control in response to a decrease in the output voltage Vout due to an increase in load. That is, the error voltage SE increases in both directions due to both factors, so that the response with a desired duty is delayed, and the undershoot of the output voltage Vout increases as shown in FIG.

  Therefore, in the present embodiment, the following control is performed. As shown in FIG. 6, when the load current ILOAD increases, the output voltage Vout decreases, and the hysteresis comparator 23 detects that the output voltage Vout crosses the threshold voltage Vth1 from the plus side to the minus side. CP is output to the logic control unit 21 (timing t11). Then, the logic control unit 21 cancels the CRM control mode, and shortens the switching cycle Tsw by decreasing the target count number for counting the clock signal CLK. More specifically, a constant value is maintained after the switching period Tsw is linearly decreased. In addition, you may reduce nonlinearly, without reducing linearly.

  By shortening the switching cycle Tsw in this way, the error voltage SE decreases so as to maintain the duty by feedback control. On the other hand, the error voltage SE rises by feedback control corresponding to the decrease in the output voltage Vout due to the increase in load. Therefore, since the change direction of the error voltage SE is reversed for each factor, the response with a desired duty is fast, and the undershoot of the output voltage Vout is suppressed. For comparison, it can be seen that the undershoot of the output voltage Vout can be reduced with the control method of the present embodiment, as the output voltage Vout of FIG.

  In this embodiment, the hysteresis comparator 23 detects that the output voltage Vout has crossed the threshold voltage Vth2 from the minus side to the plus side, and the comparison signal CP is output to the logic control unit 21 (timing t12). Then, the logic control unit 21 resumes CRM control. As a result, the switching cycle Tsw is adjusted to gradually increase and then stabilized to a constant value. The threshold voltage Vth2 is set to be higher than the threshold voltage Vth1 to prevent chattering.

  In the above embodiment, the control function corresponds to a case where the load suddenly changes so that the load becomes heavy. However, a function corresponding to a case where the load changes suddenly so that the load becomes light as described below may be provided. In that case, the configuration of the CRM control unit 2 (FIG. 2) may be further provided with a configuration similar to the configuration related to the hysteresis comparator 23.

  Assume that the load current ILOAD suddenly drops as shown in the timing chart of FIG. At this time, when the added hysteresis comparator detects that the output voltage Vout has risen and crossed the threshold voltage Vth3 from the minus side to the plus side, the logic control unit 21 cancels the CRM control mode and sets the target count. The switching period Tsw is lengthened by increasing the number.

  As a result, the error voltage SE rises so as to maintain the duty by feedback control. On the other hand, the error voltage SE decreases by feedback control in response to the increase of the output voltage Vout due to the decrease of the load. Therefore, since the change direction of the error voltage SE is reversed for each factor, the response with a desired duty is quickened, and the overshoot of the output voltage Vout is suppressed. The effect can be seen by comparing with the behavior of the output voltage Vout in the case where the CRM control is always performed as indicated by the broken line in FIG.

  When the added hysteresis comparator detects that the output voltage Vout has crossed the threshold voltage Vth4 (<Vth3) from the plus side to the minus side, the logic control unit 21 resumes the CRM control. As a result, the switching cycle Tsw is adjusted to be gradually shorter and then stabilized to a constant value.

<Application to TV>
FIG. 9 is a block diagram illustrating a configuration example of a television (display device) on which the switching power supply device of the present embodiment is mounted. FIG. 10 is a front view of a television equipped with a switching power supply device. The television X of this configuration example includes a tuner unit X1, a decoder unit X2, a display unit X3, a speaker unit X4, an operation unit X5, an interface unit X6, a control unit X7, and a power supply unit X8. Have.

  The tuner unit X1 selects a broadcast signal of a desired channel from a reception signal received by an antenna X0 externally connected to the television X.

  The decoder unit X2 generates a video signal and an audio signal from the broadcast signal selected by the tuner X1. The decoder unit X2 also has a function of generating a video signal and an audio signal based on an external input signal from the interface unit X6.

  The display unit X3 outputs the video signal generated by the decoder unit X2 as a video. As the display unit X3, a liquid crystal display unit, a plasma display unit, or the like can be used. When the display unit X3 is a liquid crystal display unit, the display unit X3 includes a liquid crystal panel, a source driver, a gate driver, and the like.

  The speaker unit X4 outputs the audio signal generated by the decoder unit X2 as audio.

  The operation unit X5 is one of human interfaces that accept user operations. As the operation unit X5, a button, a switch, a remote controller, or the like can be used.

  The interface unit X6 is a front end that receives an external input signal from an external device (such as an optical disk player or a hard disk drive).

  The control unit X7 comprehensively controls the operations of the respective units X1 to X6. As the control unit X7, a CPU (central processing unit) or the like can be used.

  The power supply unit X8 supplies power to the units X1 to X7. The switching power supply device of this embodiment can be included in the power supply unit X8. At this time, the switching power supply device preferably supplies power to the display unit 3. In the display unit X3 as a load, the current consumption fluctuates abruptly (substantially in a pulse shape) when switching between the blanking period, which is a non-display period, and the display period. Therefore, the switching power supply according to this embodiment is effective. It becomes.

<Other variations>
The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment. That is, the above-described embodiment is an example in all respects and should not be considered as limiting, and the technical scope of the present invention is not the description of the above-described embodiment, but the claims. It should be understood that all modifications that come within the meaning and range of equivalents of the claims are included.

  For example, in the above-described embodiment, it is detected that the output voltage Vout has exceeded the threshold voltage as the timing for releasing the CRM control mode. However, the CRM control unit 2 causes the load to fluctuate from the outside of the switching power supply device 1. The CRM control mode may be canceled in response to an external signal indicating In the example applied to the television X, the CRM control unit 2 may receive an external signal indicating switching between the blanking period and the display period from the control unit X7.

  Further, for example, the CRM control unit 2 may detect that the rate of change of the load current ILOAD exceeds a threshold value and cancel the CRM control mode.

  For example, the upper switching element Q1 may be replaced with a diode.

  The present invention can be used for a switching power supply device applied to a display device, for example.

DESCRIPTION OF SYMBOLS 1 Switching power supply device 2 CRM control part 3 Drive logic part 4 Slope voltage generation part 5 Upper side driver 6 Lower side driver 7 Error amplifier 8 Comparator 10 Switching driver L1 Coil Cb Bootstrap capacitor Q1 Upper side switching element Q2 Lower side switching element C1, C2 Capacitors R1 to R4 Resistors T1 to T7 External terminal To Output terminal 21 Logic controller 22 Zero cross detector 23 Hysteresis comparator 24, 25 Resistors T21 to T23 Input terminal T24 Output terminal X TV X0 Antenna X1 Tuner X2 Decoder X3 Display X4 Speaker unit X5 Operation unit X6 Interface unit X7 Control unit X8 Power supply unit

Claims (10)

An inductor;
A switching element connected to the inductor;
An error voltage generator that generates an error voltage from a feedback voltage based on the output voltage and a reference voltage;
A slope voltage generator for generating a slope voltage;
A comparison unit that compares the error voltage with the slope voltage to generate a comparison signal;
A drive unit that generates a drive signal for switching the switching element from on to off based on the comparison signal;
A CRM (critical mode) control unit that variably controls the switching period of the switching element so that a current flowing through the inductor becomes zero when the switching element is switched from OFF to ON,
The CRM control unit includes a detection unit that detects a load variation, and the switching cycle is changed in a direction opposite to a direction in which the switching cycle is changed in CRM control by detection of the detection unit. Power supply.   2. The switching power supply device according to claim 1, wherein when the load is detected by the detecting unit, the CRM control unit shortens the switching cycle.   The switching power supply according to claim 1, wherein the detection unit detects the load variation by detecting that the output voltage exceeds a threshold voltage.   The switching power supply according to claim 1, wherein the detection unit detects the load fluctuation by receiving an external signal indicating the load fluctuation.   3. The switching power supply device according to claim 1, wherein the detection unit detects the load fluctuation by detecting that a change rate of a load current exceeds a threshold value. 4.   The switching power supply according to any one of claims 1 to 5, wherein the CRM control unit restarts CRM control after detecting the load fluctuation. The detection unit detects the load variation by detecting that the output voltage exceeds a first threshold voltage,
The switching power supply according to claim 6, wherein the CRM control unit restarts CRM control by detecting that the output voltage exceeds a second threshold voltage.   The switching power supply device according to claim 7, wherein the second threshold voltage is set to a value different from the first threshold voltage. The switching power supply device according to any one of claims 1 to 8,
And a display unit to which power is supplied from the switching power supply device.   The switching power supply device according to claim 9, wherein the detection unit included in the switching power supply device receives an external signal indicating switching between a blanking period and a display period.

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