Control method of switching power supply circuit, control circuit and switching power supply circuit

Abstract

The present invention discloses a control method, a control circuit, and a switching power supply circuit. The switching power supply circuit includes a main switch tube, a synchronous rectifier tube, and an inductive element. When a switching signal indicates that the synchronous rectifier tube switches from on to off, and the main switch tube switches from off to on, the gate voltage of the synchronous rectifier tube is pulled down to a value below the synchronous rectifier tube threshold voltage and above zero voltage by utilizing the resistor-capacitor delay effect, and a timing is started. When it is detected that the gate voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the gate voltage of the synchronous rectifier tube is pulled down to zero voltage. The present invention can reduce the conduction of the synchronous rectifier tube body diode from the time when the synchronous rectifier tube is turned off to the time when the main switch tube is turned on, thereby reducing switching losses and improving conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a control method, a control circuit and a switching power supply circuit. Background Art

[0002] In switching power supplies, synchronous rectifiers replace freewheeling diodes to improve system efficiency. However, when the synchronous rectifiers are turned off and the main switch is turned on, a dead time is required to prevent shoot-through. During this dead time, the main switch has not yet turned on, but the synchronous rectifiers have already turned off, and current flows through the body diode of the synchronous rectifiers. When the main switch turns on, reverse recovery current flows due to the conduction of the synchronous rectifier's body diode. This reverse recovery current causes significant switching losses. Therefore, improving and optimizing the switching process between turning off the synchronous rectifiers and turning on the main switch is a pressing issue in switching power supplies. Summary of the Invention

[0003] In view of this, an object of the present invention is to provide a control method, a control circuit and a switching power supply circuit for a switching power supply circuit, so as to solve the problem in the prior art that the synchronous rectifier tube body diode is turned on when the synchronous rectifier tube is turned off and the main switch tube is turned on, thereby reducing the system efficiency.

[0004] The technical solution of the present invention is to provide a control method for a switching power supply circuit, wherein the switching power supply circuit includes a main switch tube, a synchronous rectifier tube and an inductive element. When the switching signal indicates that the synchronous rectifier tube switches from on to off and the main switch tube switches from off to on, the gate voltage of the synchronous rectifier tube is pulled down to a value lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage by utilizing the resistor-capacitor delay effect, and timing is started. When it is detected that the gate voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the gate voltage of the synchronous rectifier tube is pulled down to zero voltage.

[0005] Optionally, when the switching signal indicates that the synchronous rectifier tube switches from on to off and the main switch tube switches from off to on, the gate voltage of the synchronous rectifier tube is pulled down to a value close to but lower than the synchronous rectifier tube threshold voltage.

[0006] Optionally, the gate of the synchronous rectifier is connected to the reference ground through a circuit formed by a first switch tube and a second switch tube in series, and the gate of the synchronous rectifier is connected to the control end of the first switch tube through a first resistor.

[0007] Optionally, the first capacitor and the first resistor are connected in parallel, or the anode of the first diode is connected to the control terminal of the first switch tube, and the cathode is connected to the gate of the synchronous rectifier tube.

[0008] Another technical solution of the present invention is to provide a control circuit for a switching power supply circuit, wherein the switching power supply circuit includes a main switch tube, a synchronous rectifier tube and an inductive element. When the switching signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the gate voltage of the synchronous rectifier tube is pulled down to a level lower than the synchronous rectifier tube threshold voltage and higher than zero voltage by utilizing the resistor-capacitor delay effect, and timing is started. When it is detected that the gate voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the gate voltage of the synchronous rectifier tube is pulled down to zero voltage.

[0009] Optionally, a synchronous rectifier driving circuit is included, which includes a first switching tube, a second switching tube, a first resistor and a driving amplifier circuit. The gate of the synchronous rectifier is connected to the reference ground through a circuit formed by the first switching tube and the second switching tube in series, and the gate of the synchronous rectifier is connected to the control end of the first switching tube through the first resistor.

[0010] Optionally, the synchronous rectifier driving circuit also includes a first capacitor or a first diode, the first capacitor and the first resistor are connected in parallel, or the anode of the first diode is connected to the control end of the first switching tube, and the cathode is connected to the gate of the synchronous rectifier.

[0011] Optionally, the synchronous rectification drive circuit also includes a delay circuit and a pull-down circuit, the delay circuit receives a switching signal, the pull-down circuit receives the output voltage of the delay circuit, and pulls down the gate of the synchronous rectifier tube according to the output voltage of the pull-down circuit; when the switching signal indicates that the synchronous rectifier tube is from on to off and the main switch tube is from off to on, the delay circuit delays the first time and the pull-down circuit pulls down the gate of the synchronous rectifier tube.

[0012] Optionally, the synchronous rectification drive circuit also includes a comparison circuit and a pull-down circuit, the comparison circuit receives a main switch tube drive signal, the pull-down circuit receives the output voltage of the comparison circuit, and pulls down the gate of the synchronous rectifier tube according to the output voltage of the comparison circuit; when the comparison circuit detects that the main switch tube drive voltage is higher than the first drive voltage, the pull-down circuit pulls down the gate of the synchronous rectifier tube.

[0013] Another technical solution of the present invention is to provide a switching power supply circuit.

[0014] Compared with the prior art, the circuit structure and method of the present invention have the following advantages: reducing the conduction of the synchronous rectifier tube body diode when the synchronous rectifier tube is turned off to when the main switch tube is turned on, reducing switching losses, and improving conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the circuit schematic diagram of the BUCK step-down circuit with synchronous rectifier tube;

[0016] Figure 2 Schematic diagram of waveforms of the switching signal PWM, the main switch tube gate voltage TG, and the synchronous rectifier tube gate voltage BG of the present invention;

[0017] Figure 3 This is the circuit schematic diagram of the BOOST boost circuit with NMOS as the synchronous rectifier;

[0018] Figure 4 This is the circuit schematic diagram of the BOOST boost circuit with the synchronous rectifier being PMOS;

[0019] Figure 5 1 is a circuit diagram of a synchronous rectifier driving circuit with a diode and a resistor in one embodiment of the present invention;

[0020] Figure 6 1 is a circuit diagram of a synchronous rectifier driving circuit according to an embodiment of the present invention;

[0021] Figure 7 1 is a circuit diagram of a synchronous rectifier driving circuit with a diode and a resistor in another embodiment of the present invention;

[0022] Figure 8 1 is a circuit diagram of a synchronous rectifier driving circuit with capacitors and resistors in one embodiment of the present invention;

[0023] Figure 9 1 is a circuit diagram of a synchronous rectifier driving circuit in which the synchronous rectifier is a PMOS in a BOOST circuit according to an embodiment of the present invention;

[0024] Figure 10 This is a circuit diagram of a synchronous rectifier driving circuit in which the synchronous rectifier is a PMOS in a BOOST circuit in another embodiment of the present invention. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments and covers any substitution, modification, equivalent method and solution made within the spirit and scope of the present invention.

[0026] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can also fully understand the present invention without description of these details.

[0027] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the drawings are simplified and not to exact proportions, and are only used for the purpose of conveniently and clearly illustrating the embodiments of the present invention.

[0028] The present invention provides a control circuit for a switching power supply circuit, which includes a main switch tube, a synchronous rectifier tube, and an inductive element. When the switching signal indicates that the synchronous rectifier tube switches from on to off, and the main switch tube switches from off to on, the gate voltage of the synchronous rectifier tube is pulled down to a voltage lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage by utilizing the delay effect of resistors and capacitors, and timing is started. When it is detected that the gate voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the gate voltage of the synchronous rectifier tube is pulled down to zero voltage. Taking the BUCK step-down circuit as an example, please refer to Figure 1 The figure shows a BUCK circuit with synchronous rectification. The drive circuit receives the PWM signal generated by the control circuit and generates the main switch tube drive pole voltage TG and the synchronous rectifier tube drive pole voltage BG. Please refer to Figure 2 Figure 2 shows the waveforms of the switching signal PWM, the main switch driver voltage TG, and the synchronous rectifier driver voltage BG in a buck circuit. At time t01, the synchronous rectifier driver voltage BG is pulled down to V01, which is lower than the synchronous rectifier threshold voltage and higher than zero voltage. When the main switch driver voltage TG is detected to have risen to a first voltage, the synchronous rectifier driver voltage is pulled down to zero voltage at time t02. Another embodiment is to pull the synchronous rectifier driver voltage down to V01 at time t01 and start timing. At time t02, when the timing reaches the first time, the synchronous rectifier driver voltage is pulled down to zero voltage.

[0029] The present invention is not limited to the BUCK step-down circuit, and can be used in any switching power supply circuit with synchronous rectification, for example, it can also be used in the BOOST circuit. Figure 3 The figure shows the BOOST circuit with NMOS synchronous rectifier tube M03; please refer to Figure 4 As shown in FIG. 1 , a BOOST circuit in which the synchronous rectifier tube M03 is a PMOS is shown.

[0030] Please refer to Figure 5 As shown, taking the BUCK step-down circuit as an example, in one embodiment, the control circuit includes a synchronous rectifier tube drive circuit, which includes a first switch tube, a second switch tube, a first resistor and a drive amplifier circuit. The gate of the synchronous rectifier tube is connected to the reference ground through a circuit formed by the first switch tube and the second switch tube being connected in series, and the gate of the synchronous rectifier tube is connected to the control end of the first switch tube through the first resistor.

[0031] Taking the BUCK step-down circuit as an example, when the switching signal indicates that the synchronous rectifier tube is switched from on to off, and the main switch tube is switched from off to on, the synchronous rectifier tube driving electrode voltage BG is high, and the M120 gate is also high through the resistor R110, and the M130 gate changes from low to high. At this time, since the M120 gate is high, M120 and M130 will pull down the synchronous rectifier tube driving electrode voltage BG. When the M120 gate voltage drops below the threshold voltage, the synchronous rectifier tube driving electrode voltage BG is no longer pulled down. Due to the R110 and M120 gate capacitance (that is, Figure 6 Due to the RC delay effect of C130 in the circuit, the synchronous rectifier driver voltage BG decreases faster than the M120 gate voltage. When the M120 gate voltage drops to the threshold voltage, the synchronous rectifier driver voltage BG will be lower than the threshold voltage. Therefore, the synchronous rectifier driver voltage BG will eventually stay at a level slightly lower than the M120 threshold voltage. By adjusting the sizes of M120 and R110, the decreasing speed of the synchronous rectifier driver voltage BG and the final platform voltage can be controlled.

[0032] In one embodiment, please refer to Figure 6 As shown, the circuit includes a capacitor C130, which can be the parasitic capacitance of the gate of the first switch transistor M120 or an external capacitor. Therefore, the delay effect is the resistance-capacitance delay effect of the resistor R110 and the capacitor C130. Other embodiments also include a capacitor C130. To simplify the circuit, a parasitic capacitor is used to represent the equivalent capacitor C130. Therefore, the capacitor C130 is omitted in the drawings and descriptions that follow.

[0033] In one embodiment, please refer to Figure 5 As shown, the synchronous rectification driving circuit further includes a non-overlapping logic circuit 140 and a pull-up circuit. Figure 5 In the example, the pull-up circuit is implemented using a PMOS transistor M110. The switching signal PWM generates non-overlapping drive signals for M110 and M130 through a non-overlap logic circuit 140, preventing both M110 and M130 from being on simultaneously, thus preventing shoot-through. Pull-up circuit M110 turns on the synchronous rectifier by pulling up BG. When the synchronous rectifier is off, M110 turns off.

[0034] In one embodiment, please refer to Figure 5As shown, the synchronous rectifier drive circuit also includes a first diode D110, the anode of the first diode being connected to the control terminal of the first switching transistor, and the cathode being connected to the gate of the synchronous rectifier. As the synchronous rectifier drive voltage BG decreases, the first diode D110 pulls down the gate of M120. When the M120 gate voltage drops close to the threshold voltage, the pull-down of the synchronous rectifier drive voltage BG weakens, and the synchronous rectifier drive voltage BG decreases gradually. At this point, the first diode D110 no longer conducts. The function of the first diode D110 is to accelerate the initial drop of the M120 gate. Otherwise, if only R110 pulls down, the M120 gate will drop too slowly, causing the synchronous rectifier drive voltage BG to discharge too quickly and the final platform voltage to be too low.

[0035] The gate of the synchronous rectifier is connected to the reference ground through a circuit formed by the first switch tube and the second switch tube in series. The positions of the first switch tube and the second switch tube can be interchanged. The first switch tube can be connected to the reference ground, such as Figure 7 As shown, the second switch tube can also be connected to the reference ground, such as Figure 5 shown.

[0036] In one embodiment, please refer to Figure 8 As shown, the synchronous rectifier driving circuit further includes a first capacitor, and the first capacitor and the first resistor are connected in parallel. In other words, Figure 6 and Figure 7 The first diode D110 in FIG. 1 can be replaced by a first capacitor C110 .

[0037] In one embodiment, please refer to Figure 5 As shown, the synchronous rectification drive circuit also includes a delay circuit 120 and a pull-down circuit 130. The delay circuit 120 receives a switching signal, and the pull-down circuit 130 receives the output voltage of the delay circuit 120, and pulls down the gate of the synchronous rectifier tube according to the output voltage of the pull-down circuit 120; when the switching signal indicates that the synchronous rectifier tube is from on to off and the main switch tube is from off to on, the delay circuit 120 delays the first time, the pull-down circuit 130 pulls down the gate of the synchronous rectifier tube, and the synchronous rectifier tube is turned off.

[0038] In another embodiment, please refer to Figure 7As shown, the synchronous rectification driving circuit further includes a comparison circuit 160 and a pull-down circuit 130. The comparison circuit 160 receives the main switch tube driving signal TG, and the pull-down circuit 130 receives the output voltage of the comparison circuit 160 and pulls down the gate of the synchronous rectifier tube according to the output voltage of the comparison circuit 160. When the comparison circuit 160 detects that the main switch tube driving voltage is higher than the first driving voltage, the pull-down circuit pulls down the gate of the synchronous rectifier tube, and the synchronous rectifier tube is turned off.

[0039] Used for Figure 3 The synchronous rectifier drive circuit of the BOOST boost circuit and Figure 5-Figure 8 The difference is that the synchronous rectifier driver circuit's power supply is between the BST voltage and the SW voltage, rather than between the power supply terminal VD and the reference ground. A capacitor maintains a relatively stable voltage between BST and SW. This voltage is then replenished through VD when the lower transistor is turned on, resulting in a relatively stable supply voltage between BST and SW.

[0040] Please refer to Figure 9 As shown, Figure 4 An embodiment of a synchronous rectifier driving circuit 200 for a BOOST boost circuit in which the synchronous rectifier is a PMOS. The driving circuit includes a synchronous rectifier driving circuit 200, which includes a switch tube M220, a switch tube M210, and a driving amplifier circuit 210. The gate BG of the synchronous rectifier is connected to the power supply terminal VD through a circuit formed by the switch tubes M210 and M220 connected in series. The gate BG of the synchronous rectifier is connected to the control terminal of the switch tube M210 through a resistor R210. The switching signal PWM is connected to the driving electrode of M220 through the driving amplifier circuit 210. When the switching signal indicates that the synchronous rectifier is switching from on to off and the main switch tube is switching from off to on, the driving electrode voltage of the synchronous rectifier is pulled up to a level higher than the threshold voltage of the synchronous rectifier through the resistor R210 and the resistance-capacitance delay effect from the gate of M210 to the power supply capacitor. Since M210 is a PMOS, the threshold voltage is pulled up to a value higher than the threshold voltage of the synchronous rectifier, so that the synchronous rectifier is not turned on. The switch tube M220 and the switch tube M210 can be interchanged. Figure 9 In the circuit, M220 is connected to the power supply terminal VD, and the drain of M210 is connected to the gate BG of the synchronous rectifier. Figure 10 In the circuit, M210 is connected to the power supply terminal VD, and the drain of M220 is connected to the gate BG of the synchronous rectifier.

[0041] In one embodiment, please refer to Figure 9 As shown, the synchronous rectification driving circuit further includes a non-overlapping logic circuit 240 and a pull-down circuit. Figure 9In the example, the pull-down circuit is implemented using an NMOS M230. The switching signal PWM generates non-overlapping drive signals for M220 and M230 through a non-overlap logic circuit 240, preventing both M220 and M230 from being on simultaneously, thus preventing shoot-through. Pull-down circuit M230 turns on the synchronous rectifier by pulling down BG. When the synchronous rectifier is off, M230 turns off.

[0042] The technical solution of the present invention is to provide a control method for a switching power supply circuit, wherein the switching power supply circuit includes a main switch tube, a synchronous rectifier tube and an inductive element. When the switching signal indicates that the synchronous rectifier tube switches from on to off and the main switch tube switches from off to on, the gate voltage of the synchronous rectifier tube is pulled down to a value lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage by utilizing the resistor-capacitor delay effect, and timing is started. When it is detected that the gate voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the gate voltage of the synchronous rectifier tube is pulled down to zero voltage.

[0043] Optionally, when the switching signal indicates that the synchronous rectifier tube switches from on to off and the main switch tube switches from off to on, the gate voltage of the synchronous rectifier tube is pulled down to a value close to but lower than the synchronous rectifier tube threshold voltage.

[0044] Optionally, the gate of the synchronous rectifier is connected to the reference ground through a circuit formed by a first switch tube and a second switch tube in series, and the gate of the synchronous rectifier is connected to the control end of the first switch tube through a first resistor.

[0045] Optionally, the first capacitor and the first resistor are connected in parallel, or the anode of the first diode is connected to the control terminal of the first switch tube, and the cathode is connected to the gate of the synchronous rectifier tube.

[0046] Although the embodiments are described and explained separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that they can be replaced and integrated between the embodiments. If there is anything not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0047] The above-described embodiments do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the above-described embodiments shall be included in the scope of protection of this technical solution.

Claims

1. A method for controlling a switching power supply circuit, the method comprising: when a switching signal indicates that the synchronous rectifier is switching from on to off, and the main switch is switching from off to on, the method utilizes a resistor-capacitor delay effect to pull down the gate voltage of the synchronous rectifier to a value below the synchronous rectifier threshold voltage and above zero voltage, and starts timing; and when it is detected that the gate voltage of the main switch rises to a first voltage or the timing reaches a first time, the gate voltage of the synchronous rectifier is pulled down to zero voltage; in, The gate of the synchronous rectifier is connected to one end of a circuit formed by a first switching tube and a second switching tube connected in series. The gate of the synchronous rectifier is connected to the control end of the first switching tube through a first resistor. The resistor in the resistor-capacitor delay effect is the first resistor, and the capacitor in the resistor-capacitor delay effect is connected to the control end of the first switching tube.

2. The control method of the switching power supply circuit according to claim 1, wherein: When the switching signal indicates that the synchronous rectifier tube switches from on to off and the main switch tube switches from off to on, the gate voltage of the synchronous rectifier tube is pulled down to a value close to but lower than the synchronous rectifier tube threshold voltage.

3. The control method of the switching power supply circuit according to claim 2, wherein: The gate of the synchronous rectifier is connected to the reference ground through a circuit formed by the first switch tube and the second switch tube being connected in series.

4. The control method of the switching power supply circuit according to claim 3, wherein: The first capacitor and the first resistor are connected in parallel, or the anode of the first diode is connected to the control end of the first switch tube, and the cathode is connected to the gate of the synchronous rectifier tube.

5. A control circuit for a switching power supply circuit, the switching power supply circuit comprising a main switch, a synchronous rectifier, and an inductive element. When a switching signal indicates that the synchronous rectifier switches from on to off and the main switch switches from off to on, the control circuit utilizes a resistor-capacitor delay effect to pull down the gate voltage of the synchronous rectifier to a value below the synchronous rectifier threshold voltage and above zero voltage, and starts timing. When it is detected that the gate voltage of the main switch rises to a first voltage or the timing reaches a first time, the gate voltage of the synchronous rectifier is pulled down to zero voltage. in, The control circuit includes a synchronous rectifier tube drive circuit, which includes a first switching tube, a second switching tube and a first resistor. The gate of the synchronous rectifier tube is connected to one end of a circuit formed by the first switching tube and the second switching tube in series. The gate of the synchronous rectifier tube is connected to the control end of the first switching tube through the first resistor. The resistor in the resistance-capacitance delay effect is the first resistor, and the capacitor in the resistance-capacitance delay effect is connected to the control end of the first switching tube.

6. The control circuit of the switching power supply circuit according to claim 5, wherein: The synchronous rectifier driving circuit also includes a driving amplifier circuit. The gate of the synchronous rectifier is connected to the reference ground through a circuit formed by the first switch tube and the second switch tube connected in series. The driving amplifier circuit is connected to the driving pole of the second switch tube.

7. The control circuit of the switching power supply circuit according to claim 6, wherein: The synchronous rectifier driving circuit also includes a first capacitor or a first diode, the first capacitor and the first resistor are connected in parallel, or the anode of the first diode is connected to the control end of the first switch tube, and the cathode is connected to the gate of the synchronous rectifier tube.

8. The control circuit of the switching power supply circuit according to claim 6, wherein: The synchronous rectifier driving circuit also includes a delay circuit and a pull-down circuit. The delay circuit receives a switching signal, and the pull-down circuit receives the output voltage of the delay circuit and pulls down the gate of the synchronous rectifier according to the output voltage of the pull-down circuit. When the switching signal indicates that the synchronous rectifier is switched from on to off and the main switch is switched from off to on, the delay circuit delays the first time and the pull-down circuit pulls down the gate of the synchronous rectifier.

9. The control circuit of the switching power supply circuit according to claim 6, wherein: The synchronous rectifier driving circuit also includes a comparison circuit and a pull-down circuit. The comparison circuit receives a main switch tube driving signal, and the pull-down circuit receives an output voltage of the comparison circuit and pulls down the gate of the synchronous rectifier according to the output voltage of the comparison circuit. When the comparison circuit detects that the main switch tube driving voltage is higher than the first driving voltage, the pull-down circuit pulls down the gate of the synchronous rectifier.

10. A switching power supply circuit, characterized in that: Comprising the control circuit according to any one of claims 5 to 9.

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