Switching power supply device

Abstract

To provide a switching power supply device which can facilitate control of a drive frequency.SOLUTION: A switching power supply device (100) comprises: a power supply circuit (1) which is configured to have a switching element (M1) and to generate output voltage (Vout) by switching of the switching element; a triangular wave generation unit (3) which is configured to generate a triangular wave signal (V-) formed by superimposing feedback voltage (Vfb) based on the output voltage; and a comparator (2) which is configured to compare the triangular wave signal with reference voltage (V+) having a hysteresis width, wherein the switching element is switched on the basis of a comparison result of the comparator, and the triangular wave generation unit makes an inclination of the triangular wave signal variable.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a switching power supply device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a hysteresis control method is known as a control method for switching power supply devices (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-125107 A Summary of the Invention [Problem to be solved by the invention]

[0004] Here, in a switching power supply device using a hysteresis control method, there is room for improvement in the control of the drive frequency.

[0005] An object of the present disclosure is to provide a switching power supply device that can facilitate control of the drive frequency. [Means for solving the problem]

[0006] For example, a switching power supply device according to one aspect of the present disclosure may include: A power supply circuit having a switching element and configured to generate an output voltage by switching the switching element; a triangular wave generating unit configured to generate a triangular wave signal having a feedback voltage superimposed thereon based on the output voltage; a comparator configured to compare the triangular wave signal with a reference voltage having a hysteresis width; Equipped with The switching element is switched on and off based on a comparison result of the comparator, The triangular wave generating section is configured to vary the slope of the triangular wave signal. Effect of the Invention

[0007] According to the exemplary switching power supply device of the present disclosure, it is possible to easily control the drive frequency. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a configuration of a switching power supply device according to a comparative example. [Diagram 2] FIG. 2 is a diagram showing an example of the waveforms of the triangular wave signal V− and the reference voltage V+. [Diagram 3] FIG. 3 is a diagram showing a specific example of a switching power supply device according to a comparative example. [Figure 4] FIG. 4 is a diagram showing an example of waveforms when the drive frequency is changed by changing the hysteresis width of the reference voltage V+. [Diagram 5] FIG. 5 is a diagram showing a configuration of a switching power supply device according to an exemplary embodiment of the present disclosure. [Figure 6] FIG. 6 is a diagram showing an example of waveforms when the drive frequency is changed by the switching power supply device according to the embodiment of the present disclosure. [Figure 7] FIG. 7 is a diagram illustrating an example of a control voltage generating section that generates the control voltage Vc. [Figure 8] FIG. 8 is a diagram showing a modified example of the triangular wave generating unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.

[0010] <1. Comparative Example> 1 is a diagram showing a configuration of a switching power supply device 10 according to a comparative example. The switching power supply device 10 uses a hysteresis control method. The switching power supply device 10 includes a DC / DC converter 1 and a comparator 2.

[0011] The DC / DC converter 1 has a switching element (not shown) and converts an input voltage, which is a DC voltage, into an output voltage, which is a DC voltage, by switching the switching element. A triangular wave signal V- on which a feedback voltage based on the output voltage is superimposed is output from the DC / DC converter 1. The triangular wave signal V- is input to an inverting input terminal (-) of a comparator 2. A reference voltage V+ is input to a non-inverting input terminal (+) of the comparator 2. The comparator 2 compares the triangular wave signal V- with the reference voltage V+, and outputs an output signal Sout as a comparison result. In the DC / DC converter 1, the switching element is switched based on the output signal Sout.

[0012] FIG. 2 is a diagram showing an example of the waveforms of the triangular wave signal V- and the reference voltage V+. The reference voltage V+ has a hysteresis width H. When the triangular wave signal V- rises, the reference voltage V+ is at a first level V1, and the output signal Sout is at a high level. When the triangular wave signal V- exceeds the first level V1 (timing t1), the output signal Sout becomes a low level. Then, the on / off state of the switching element is switched based on the output signal Sout, and the reference voltage V+ is switched from the first level V1 to a second level V2. V2 is lower than V1.

[0013] Then, when the triangular wave signal V- drops below the second level V2 (timing t2), the output signal Sout goes high. Then, the on / off state of the switching element is switched based on the output signal Sout, and the reference voltage V+ is switched from the second level V2 to the first level V1. Then, the triangular wave signal V- rises again.

[0014] In this way, the output signal Sout becomes a pulse signal. One period of the output signal Sout, that is, the switching drive frequency, is determined by the slope (speed of change) of the triangular wave signal V- and the hysteresis width H.

[0015] Fig. 3 is a diagram showing a specific example of a switching power supply device 10 according to a comparative example. In the configuration shown in Fig. 3, a DC / DC converter 1 is configured as an asynchronous step-down converter. The DC / DC converter 1 shown in Fig. 3 includes a switching element M1, a diode D1, an inductor L1, an output capacitor Co, voltage dividing resistors Rd1 and Rd2, and a gate driver Dr.

[0016] The switching element M1 is composed of an N-channel MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). The drain of the switching element M1 is connected to an application terminal of an input voltage Vin. A node NA, at which the source of the switching element M1 and the cathode of the diode D1 are connected, is connected to one end of an inductor L1. The other end of the inductor L1 is connected to one end of an output capacitor Co. The anode of the diode D1 and the other end of the output capacitor Co are connected to an application terminal of a ground potential.

[0017] The gate of the switching element M1 is driven by the gate driver Dr, and the switching element M1 is switched. The switching of the switching element M1 steps down the input voltage Vin to generate an output voltage Vout. The output voltage Vout is generated at a node NB to which one end of the output capacitor Co and the other end of the inductor L1 are connected. The output voltage Vout is applied to a load LD. The voltage-dividing resistors Rd1 and Rd2 are connected in series between the node NB and the application terminal of the ground potential. As a result, the output voltage Vout is divided by the voltage-dividing resistors Rd1 and Rd2.

[0018] An RC circuit consisting of a resistor R1 and a capacitor C1 is connected in parallel with the inductor L1. Specifically, one end of the resistor R1 is connected to a node NA. The other end of the resistor R1 is connected to one end of the capacitor C1 at a node NC. The other end of the capacitor C1 is connected to a node NB.

[0019] The voltage of the node NA changes depending on whether the switching element M1 is on or off. On the other hand, the voltage of the node NB hardly changes due to smoothing by the output capacitor Co. Therefore, by connecting the above RC circuit between the nodes NA and NB, a ripple can be generated at the node NC. The output voltage Vout is divided by the voltage dividing resistors Rd1 and Rd2 to generate a feedback voltage, which is superimposed on the above ripple to generate a triangular wave signal V-. The gate driver Dr switches the switching element M1 based on the output signal Sout output from the comparator 2. Specifically, when the output signal Sout is at a high level, the switching element M1 is turned on, and when the output signal Sout is at a low level, the switching element M1 is turned off.

[0020] Here, in order to change the drive frequency, it is possible to consider a method of changing the slope of the triangular wave signal V-. However, in the configuration shown in Fig. 3, since the nodes NA and NB are arranged on the circuit of the DC / DC converter 1, they cannot be operated from the outside, and the slope of the triangular wave signal V- cannot be changed during driving. As a result, for example, it is not possible to change the drive frequency depending on the drive conditions.

[0021] On the other hand, in order to change the drive frequency, a method of changing the hysteresis width of the reference voltage V+ is also considered. Figure 4 is a diagram showing an example of waveforms when the drive frequency is changed by changing the hysteresis width of the reference voltage V+. Figure 4 shows an example of the drive frequency being 1 MHz and 1.5 MHz, and also shows an example of the waveforms of the reference voltage V+ and the triangular wave signal V-, as well as an example of the waveform of the output signal Sout.

[0022] As shown in Figure 4, the hysteresis width is set to 0.1 V to set the drive frequency to 1 MHz, and 0.07 V to set the drive frequency to 1.5 MHz. In this way, when the drive frequency is in the MHz range, the hysteresis width needs to be small, and in the example of Figure 4, in order to change the drive frequency, it is necessary to change the hysteresis width by 30 mV, which is the difference between 0.1 V and 0.07 V, making control difficult.

[0023] In addition, an output signal Sout_B obtained by logically inverting the output signal Sout is also shown in Fig. 4. In the case of a synchronous rectification type DC / DC converter 1 in which the diode D1 in the configuration of Fig. 3 is replaced with a lower-side switching element, the lower-side switching element may be switched based on the output signal Sout_B.

[0024] 2. Switching power supply device of the present disclosure 5 is a diagram showing a configuration of a switching power supply device 100 according to an exemplary embodiment of the present disclosure. The switching power supply device 100 includes a DC / DC converter 1, a comparator 2, and a triangular wave generating unit 3.

[0025] The configuration of the DC / DC converter 1 in FIG. 5 is the same as that in FIG. 3 described above, except for the RC circuit formed by the resistor R1 and the capacitor C1, and therefore will not be described in detail.

[0026] The triangular wave generating unit 3 is a circuit provided outside the DC / DC converter 1 and generates a triangular wave signal V-. The comparator 2 compares the reference voltage V+ with the triangular wave signal V- to generate an output signal Sout1. The output signal Sout1 is a pulse signal. The gate driver Dr drives the switching element M1 based on the output signal Sout1. Specifically, when the output signal Sout1 is at a high level, the switching element M1 is in an on state, and when the output signal Sout1 is at a low level, the switching element M1 is in an off state. The comparator 2 also outputs an output signal Sout2 that is a logical inversion of the output signal Sout1. The output signal Sout2 is used for control in the triangular wave generating unit 3.

[0027] The triangular wave generating unit 3 includes an upper switching element Q1, a lower switching element Q2, a resistor R2, and a capacitor C2. Both the upper switching element Q1 and the lower switching element Q2 are configured by N-channel MOSFETs. The drain of the upper switching element Q1 is connected to an application terminal of a control voltage Vc. The source of the upper switching element Q1 is connected to a drain of the lower switching element Q2 at a node N1. The source of the lower switching element Q2 is connected to an application terminal of a ground potential.

[0028] The gate of the high-side switching element Q1 is driven by an output signal Sout1. The gate of the low-side switching element Q2 is driven by an output signal Sout2. This causes the high-side switching element Q1 and the low-side switching element Q2 to be switched in a complementary manner.

[0029] An RC circuit 31 including a resistor R2 and a capacitor C2 is connected to the node N1. Specifically, one end of the resistor R2 is connected to the node N1. The other end of the resistor R2 is connected to one end of the capacitor C2 at the node N2. The other end of the capacitor C2 is connected to a terminal to which a ground potential is applied.

[0030] A pulsed switch voltage SW generated at a node N1 by switching between the upper switching element Q1 and the lower switching element Q2 is converted into a triangular wave signal V- by an RC circuit 31. The RC circuit 31 is an example of a low-pass filter. A feedback voltage Vfb obtained by dividing the output voltage Vout by voltage dividing resistors Rd1 and Rd2 is superimposed on the triangular wave signal V-.

[0031] When the output signal Sout1 is at a high level, the output signal Sout2 is at a low level, the upper switching element Q1 is in the ON state, and the lower switching element Q2 is in the OFF state. At this time, the switch voltage SW is at a high level, and the triangular wave signal V- rises. On the other hand, when the output signal Sout1 is at a low level, the output signal Sout2 is at a high level, the upper switching element Q1 is in the OFF state, and the lower switching element Q2 is in the ON state. At this time, the switch voltage SW is at a low level, and the triangular wave signal V- falls.

[0032] In addition, in the complementary switching of the upper switching element Q1 and the lower switching element Q2, a simultaneous off period (so-called dead time) may be provided to suppress the through current.

[0033] Here, when the control voltage Vc is changed, the slope of the triangular wave signal V- changes, and therefore the drive frequency can be changed. The control voltage Vc may be changed automatically during operation, or may be set by a resistor or the like externally attached to a semiconductor device having at least a part of the configuration of the switching power supply device 100.

[0034] Fig. 6 is a diagram showing an example of waveforms when the drive frequency is changed by the switching power supply device 100 according to the embodiment of the present disclosure. Fig. 6 shows an example in which the drive frequency is set to 1 MHz and 1.5 MHz as an example, and shows example waveforms of the reference voltage V+ and the triangular wave signal V-, and example waveforms of the output signals Sout1 and Sout2.

[0035] In the example of FIG. 6, the drive frequency is 1 MHz by setting the control voltage Vc=5V, and 1.5 MHz by setting the control voltage Vc=7.5V. As shown in FIG. 6, by changing the control voltage Vc, the slope of the triangular wave signal V- changes, and the drive frequency changes. Specifically, the higher the control voltage Vc, the larger the slope of the triangular wave signal V- becomes, and the higher the drive frequency becomes. Thus, in order to change the drive frequency in the MHz range, in the example of FIG. 6, it is sufficient to change the control voltage Vc by 2.5V, which is the difference between 7.5V and 5V, and control is easier than in the case of FIG. 4 described above.

[0036] <3. Control voltage generation section> Fig. 7 is a diagram showing an example of a control voltage generating unit that generates a control voltage Vc. The control voltage generating unit 4 shown in Fig. 7 has a current sensor 41, a resistor 42, an NPN transistor 43, a resistor 44, an NPN transistor 45, and a capacitor 46.

[0037] The current sensor 41 detects a load current flowing through the load LD. The current sensor 41 outputs the detected load current as a voltage signal. The voltage signal is applied to one end of a resistor 42. The other end of the resistor 42 is connected to the base of an NPN transistor 43. The emitter of the NPN transistor 43 is connected to an application end of the ground potential. The collector of the NPN transistor 43 is connected to one end of a resistor 44 and to the base of an NPN transistor 45. The other end of the resistor 44 and the collector of the NPN transistor 45 are connected to an application end of the power supply voltage Vdd. A capacitor 46 is connected between the emitter of the NPN transistor 45 and the application end of the ground potential. A control voltage Vc is generated at the emitter of the NPN transistor 45.

[0038] The smaller the load current is, the lower the voltage signal output from the current sensor 41 becomes, and therefore the on-resistance of the NPN transistor 43 becomes higher. As a result, the base voltage of the NPN transistor 45 obtained by dividing the power supply voltage Vdd by the resistor 44 and the on-resistance of the NPN transistor 43 becomes higher. Therefore, the control voltage Vc becomes higher. The NPN transistor 45 functions as a regulator. According to such a control voltage generating unit 4, when the load is light, the control voltage Vc can be increased and the drive frequency can be raised. In other words, the drive frequency can be automatically changed according to the load during driving.

[0039] An operational amplifier may be inserted between the current sensor 41 and the resistor 42 .

[0040] <4. Modifications> Fig. 8 is a diagram showing a modified example of the triangular wave generating unit 3. The triangular wave generating unit 3 shown in Fig. 8 differs from Fig. 5 in that the upper switching element Q1 is configured by a P-channel MOSFET. As a result, as shown in Fig. 8, it is sufficient to drive the gates of both the upper switching element Q1 and the lower switching element Q2 by the output signal Sout2.

[0041] <5.Other> In addition to the above-mentioned embodiment, various technical features disclosed in this specification can be modified in various ways without departing from the spirit of the technical creation. In other words, the above-mentioned embodiment should be considered to be illustrative and not restrictive in all respects, and the technical scope of the present invention should not be limited to the above-mentioned embodiment, but should be understood to include all modifications that fall within the meaning and scope equivalent to the scope of the claims.

[0042] For example, in the switching power supply device of the present disclosure, the DC / DC converter may be, for example, a step-up DC / DC converter.

[0043] <6. Notes> As described above, the switching power supply device (100) according to one embodiment of the present disclosure has: A power supply circuit (1) having a switching element (M1) and configured to generate an output voltage (Vout) by switching the switching element; a triangular wave generating unit (3) configured to generate a triangular wave signal (V-) superimposed with a feedback voltage (Vfb) based on the output voltage; a comparator (2) configured to compare the triangular wave signal with a reference voltage (V+) having a hysteresis width; Equipped with The switching element is switched on and off based on a comparison result of the comparator, The triangular wave generating section is configured to vary the slope of the triangular wave signal (first configuration).

[0044] In the above first configuration, the triangular wave generating section (3) may be configured to vary the slope of the triangular wave signal based on a variable control voltage (Vc) (second configuration).

[0045] In the second configuration, the triangular wave generating unit (3) an upper switching element (Q1) connected to the application terminal of the control voltage (Vc); a lower switching element (Q2) connected to the upper switching element at a first node (N1); a low-pass filter (31) configured to convert a switch voltage (SW) occurring at the first node into the triangular wave signal; having The upper switching element and the lower switching element may be driven complementarily based on the output signals (Sout1, Sout2) of the comparator (third configuration).

[0046] In the third configuration, the low-pass filter may be an RC circuit (31) (fourth configuration).

[0047] In the third or fourth configuration, both the upper switching element (Q1) and the lower switching element (Q2) are formed of N-channel MOSFETs, The gate of the upper switching element is driven by a first output signal (Sout1) of the comparator, The gate of the low-side switching element may be driven by a second output signal (Sout2) that is the logical inversion of the first output signal (fifth configuration).

[0048] In the third or fourth configuration, the upper switching element (Q1) is a P-channel MOSFET, The lower switching element (Q2) is composed of an N-channel MOSFET, The gates of both the upper switching element and the lower switching element may be driven by the common output signal (Sout2) output from the comparator (sixth configuration).

[0049] In any of the third to sixth configurations, a simultaneous off period may be provided when the upper switching element and the lower switching element are complementarily driven (seventh configuration).

[0050] In addition, in any one of the second to seventh configurations, a configuration may be made (eighth configuration) further comprising a control voltage generating section (4) configured to generate the control voltage (Vc) in accordance with a load.

[0051] In the eighth configuration, the control voltage generating unit (4) a current sensor (41) configured to detect an overcurrent; a first resistor (42) having a first end to which a voltage based on a voltage signal output from the current sensor is applied; a first NPN transistor (43) having a base connected to the second end of the first resistor; a second resistor (44) having a first terminal connected to the collector of the first NPN transistor and a second terminal connected to an application terminal of a power supply voltage (Vdd); a second NPN transistor (45) having a base connected to the collector of the first NPN transistor and a collector connected to the second end of the second resistor; a capacitor (46) connected to the emitter of the second NPN transistor; (ninth configuration).

[0052] In any of the first to ninth configurations, the power supply circuit may be a step-down DC / DC converter (1) (tenth configuration). [Industrial Applicability]

[0053] The present disclosure can be used in switching power supply devices for various applications. [Explanation of symbols]

[0054] 1 DC / DC Converter 2. Comparator 3 Triangular wave generator 4. Control voltage generator 10. Switching power supply 31 RC circuit 41 Current Sensor 42 Resistance 43 NPN Transistor 44 Resistance 45 NPN transistor 46 Capacitor 100 Switching power supply C1, C2 capacitors Co Output capacitor D1 Diode Dr Gate driver L1 Inductor LD load M1 Switching element Q1 Upper switching element Q2 Lower switching element R1,R2 resistance Rd1, Rd2 voltage dividing resistor

Claims

1. A power supply circuit having a switching element and configured to generate an output voltage by switching the switching element; a triangular wave generating unit configured to generate a triangular wave signal having a feedback voltage superimposed thereon based on the output voltage; a comparator configured to compare the triangular wave signal with a reference voltage having a hysteresis width; Equipped with The switching element is switched on and off based on a comparison result of the comparator. The triangular wave generating unit varies a slope of the triangular wave signal.

2. 2. The switching power supply device according to claim 1, wherein the triangular wave generating section varies a slope of the triangular wave signal based on a variable control voltage.

3. The triangular wave generating unit includes: an upper switching element connected to an application terminal of the control voltage; a lower switching element connected to the upper switching element at a first node; a low pass filter configured to convert a switch voltage appearing at the first node into the triangular wave signal; having 3. The switching power supply according to claim 2, wherein the upper switching element and the lower switching element are complementarily driven based on an output signal of the comparator.

4. 4. The switching power supply device according to claim 3, wherein the low-pass filter is an RC circuit.

5. Both the upper switching element and the lower switching element are formed of N-channel MOSFETs, the gate of the upper switching element is driven by a first output signal of the comparator; 4. The switching power supply device according to claim 3, wherein a gate of the lower switching element is driven by a second output signal that is a logical inversion of the first output signal.

6. The upper switching element is composed of a P-channel MOSFET, The lower switching element is composed of an N-channel MOSFET, 4. The switching power supply according to claim 3, wherein the gates of both the upper switching element and the lower switching element are driven by a common output signal output from the comparator.

7. 4. The switching power supply according to claim 3, wherein a simultaneous off period is provided when the upper switching element and the lower switching element are complementarily driven.

8. The switching power supply device according to claim 2 , further comprising a control voltage generating unit configured to generate the control voltage in response to a load.

9. The control voltage generating unit is a current sensor configured to detect a load current; a first resistor having a first end to which a voltage based on a voltage signal output from the current sensor is applied; a first NPN transistor having a base connected to the second end of the first resistor; a second resistor having a first terminal connected to the collector of the first NPN transistor and a second terminal connected to an application terminal of a power supply voltage; a second NPN transistor having a base connected to the collector of the first NPN transistor and a collector connected to the second end of the second resistor; a capacitor connected to the emitter of the second NPN transistor; 9. The switching power supply device according to claim 8, further comprising:

10. 10. The switching power supply device according to claim 1, wherein the power supply circuit is a step-down DC / DC converter.

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