Control circuit for realizing rapid turn-off of MOSFET

Abstract

The invention relates to the technical field of circuit design, in particular to a control circuit for realizing quick turn-off of an MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). The control circuit for realizing quick turn-off of the MOSFET comprises a pulse width modulation (PWM) controller, a charge and discharge control loop, the MOSFET Q6 and a capacitor C1, a capacitor Cgs is connected between the grid electrode and the source electrode of the MOSFET Q6, when the voltage of the capacitor Cgs reaches a conduction threshold value, the MOSFET Q6 is switched on, and otherwise, the MOSFET Q6 is switched off; when the pulse width modulation PWM controller outputs a low level, the capacitor C1 is charged; when high level is output, the capacitor C1 is discharged, the capacitor C1 provides negative voltage between the grid electrode and the source electrode of the MOSFET Q6, current in the capacitor Cgs is rapidly pumped away, the voltage of the capacitor Cgs is rapidly reduced, rapid discharging is achieved, and therefore the MOSFET Q6 is turned off more rapidly. According to the control circuit for realizing the rapid turn-off of the MOSFET, by applying a negative voltage between the grid electrode and the source electrode of the MOSFET and increasing the discharge current, the turn-off of the MOSFET is further accelerated, and the problem that the turn-off time of a conventional MOSFET control circuit is relatively long is solved.

Description

Technical Field

[0001] The invention relates to the technical field of circuit design, and in particular to a control circuit for realizing fast shutdown of MOSFET. Background Art

[0002] In the entire system of the switching power supply, the switching loss of MOSFET (MOS tube) accounts for a large proportion, and the switching loss includes turn-on loss and turn-off loss. Unlike the conduction loss, the switching loss can be reduced as much as possible through artificial means to improve the efficiency of the power supply system.

[0003] Because voltage and current are both analog quantities, when MOSFET is turned off, the current cannot change suddenly, that is, it cannot drop from a certain value to zero instantly. The MOSFET is turned off in a process where the current gradually returns to zero. To achieve fast MOSFET shutdown, the conventional method is to use a small discharge resistor to make the capacitance between the MOSFET gate and source almost short-circuit, but this method still takes a long time to turn off the MOSFET, and there will be a large turn-off loss.

[0004] In order to solve the above problem and speed up the shutdown of MOSFET, the present invention proposes a control circuit for realizing fast shutdown of MOSFET. Summary of the invention

[0005] In order to make up for the defects of the prior art, the present invention provides a simple and efficient control circuit for realizing fast shutdown of MOSFET.

[0006] The present invention is achieved through the following technical solutions:

[0007] A control circuit for realizing fast shutdown of MOSFET, characterized by comprising a pulse width modulation PWM controller, a charge and discharge control loop, a MOSFET Q6 and a capacitor C1;

[0008] The capacitor C1 is used for charging and energy storage;

[0009] When the pulse width modulation PWM controller outputs a low level, the capacitor C1 is charged through the charge and discharge control loop; when the pulse width modulation PWM controller outputs a high level, the capacitor C1 is discharged through the charge and discharge control loop;

[0010] A capacitor Cgs is connected between the gate and source of the MOSFET Q6. When the voltage of the capacitor Cgs reaches the conduction threshold, the MOSFET Q6 is turned on, otherwise it is turned off.

[0011] When the pulse width modulation PWM controller outputs a high level, the capacitor C1 provides a negative voltage between the gate and source of MOSFETQ6, which quickly draws the current in the capacitor Cgs, causing its voltage to drop rapidly, thereby achieving rapid discharge and turning off MOSFETQ6 faster.

[0012] When the pulse width modulation PWM controller outputs a low level, transistors Q3 and Q5 are turned off, the base of transistor Q2 is pulled high by resistor R3, transistor Q2 is turned off, the emitter of transistor Q1 is pulled low by resistors R8 and R9, transistor Q1 is turned on, and the 15V voltage reaches the base of transistor Q4 through transistor Q1 and resistor R4, that is, the base of transistor Q4 is at a high level, and transistor Q4 is turned on;

[0013] At this time, the charge and discharge control loop includes two current loops: the capacitor C1 charging loop and the capacitor Cgs charging loop:

[0014] Capacitor C1 charging circuit: 15V voltage flows through resistor R7, diode D3, capacitor C1, diode D2, transistor Q4 and ground in sequence to charge capacitor C1. At this time, the voltage across capacitor C1 is low at the diode D2 end and high at the diode D3 end.

[0015] Capacitor Cgs charging circuit: 15V voltage flows through transistor Q1 and resistor R8 in sequence, reaches the gate of MOSFET Q6, charges the capacitor Cgs between the gate and source of MOSFET Q6, and MOSFET Q6 is turned on.

[0016] When the pulse width modulation PWM controller outputs a high level, in the charge and discharge control loop, the base of transistor Q5 is at a high level, and Q5 is turned on; the emitter of transistor Q3 is pulled down by diode D1 and transistor Q5, the base is at a high level, transistor Q3 is turned on, transistor Q1 is turned off, and transistor Q2 is turned on; the capacitor Cgs between the gate and the source of MOSFET Q6 is discharged through the loop resistor R8, transistor Q2, diode D1 and transistor Q5, and finally to the ground;

[0017] Furthermore, when the pulse width modulation PWM controller outputs a high level, in the charge and discharge control loop, the anode of the diode D2 has been pulled down by the diode D1, and the transistor Q4 is cut off. At this time, the capacitor C1 stops charging, and the voltage difference across the capacitor C1 forms a negative voltage between the gate and source of the MOSFET Q6, which can quickly draw away the current in the capacitor Cgs, achieve rapid discharge, and thus make the MOSFET Q6 turn off faster.

[0018] In the charge and discharge control circuit, the on-state voltage drop of the diode is 0.7V, the on-state voltage drop of the resistor is negligible, and the on-state voltage drop of the transistor is 0.3V;

[0019] When the pulse width modulation PWM controller outputs a low level, the voltage across the charged capacitor C1 is: 15-0.7-0.7-0.3=13.3V;

[0020] Furthermore, the voltage at the end of the capacitor C1 connected to the diode D2 is 0.3+0.7=1V, and the voltage at the end of the capacitor C1 connected to the diode D3 is 15-0.7=14.3V, and the voltage difference is 14.3-1=13.3V;

[0021] When the pulse width modulation PWM controller outputs a high level, the transistor Q5 pulls down the voltage at one end of the capacitor C1 to 0.3V, and the voltage at the end of the capacitor C1 connected to the diode D2 that stops charging is 0.3-13.3=-13V, and the negative voltage applied between the gate and source of the MOSFET Q6 is -13V; the -13V voltage difference quickly draws away the current in the capacitor Cgs, achieving rapid discharge, thereby causing the MOSFET Q6 to shut down faster.

[0022] The charge and discharge control circuit includes five transistors, respectively labeled as Q1, Q2, Q3, Q4 and Q5, three diodes, respectively labeled as D1, D2 and D3, and nine resistors, respectively labeled as R1, R2, R3, R4, R5, R6, R7, R8 and R9;

[0023] The pulse width modulation PWM controller is connected to the base of the transistor Q3 through the resistor R1, and is connected to the base of the transistor Q5 through the resistor R2;

[0024] The collector of the transistor Q3 is simultaneously connected to the 15V voltage, the bases of the transistors Q1 and Q2, and a resistor R3 is connected between the transistor Q3 and the 15V voltage; the emitter of the transistor Q3 is simultaneously connected to the collectors of the transistors Q2, Q4 and Q5;

[0025] A diode D2 is also connected between the collectors of the transistor Q3 and the transistor Q4, and a diode D1 is also connected between the transistor Q3 and the transistor Q5; the anodes of the diodes D1 and D2 are connected to the emitter of the transistor Q3;

[0026] The capacitor C1 is connected in parallel with both ends of the diode D1;

[0027] The transistors Q1, Q3, Q4 and Q5 are all NPN transistors, and the transistor Q2 is a PNP transistor;

[0028] The 15V voltage is also connected to the collectors of transistors Q1 and Q5 at the same time, and a resistor R7 and a diode D3 are also provided between the 15V voltage and the transistor Q5, wherein the anode of the diode D3 is connected to the 15V voltage;

[0029] The emitter of the transistor Q1 is simultaneously connected to the emitter of the transistor Q2, the base of the transistor Q4 and the gate of the MOSFETQ6, a resistor R4 is further provided between the transistor Q1 and the transistor Q4, and a resistor R8 is further provided between the transistor Q1 and the MOSFETQ6;

[0030] A resistor R5 is connected between the base and emitter of the transistor Q4, and a resistor R6 is connected between the base and emitter of the transistor Q5; meanwhile, the emitters of the transistors Q4 and Q5 are both grounded;

[0031] The MOSFETQ6 is connected to the voltage VCC via the drain, a capacitor Cgs is connected between the gate and the source, a resistor R9 is connected in parallel at both ends of the capacitor Cgs, and the MOSFETQ6 is grounded via the source.

[0032] The resistance values ​​of the resistors R1 and R2 are both 1K, the resistance values ​​of the resistors R3 to R7 are all 10K, the resistance value of the resistor R8 is all 10Ω, and the resistance value of the resistor R9 is all 4.7K.

[0033] The beneficial effect of the present invention is that the control circuit for realizing fast shutdown of MOSFET applies a negative voltage between the gate and source of MOSFET to increase the discharge current, thereby further accelerating the shutdown of MOSFET and solving the problem of long shutdown time of conventional MOSFET control circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Attached Figure 1 The schematic diagram of the control circuit for realizing fast shutdown of MOSFET in the present invention. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0037] As attached Figure 1As shown, the control circuit for realizing fast shutdown of MOSFET includes a pulse width modulation PWM controller, a charge and discharge control loop, MOSFET Q6 and a capacitor C1;

[0038] The capacitor C1 is used for charging and energy storage;

[0039] When the pulse width modulation PWM controller outputs a low level, the capacitor C1 is charged through the charge and discharge control loop; when the pulse width modulation PWM controller outputs a high level, the capacitor C1 is discharged through the charge and discharge control loop;

[0040] A capacitor Cgs is connected between the gate and source of the MOSFET Q6. When the voltage of the capacitor Cgs reaches the conduction threshold, the MOSFET Q6 is turned on, otherwise it is turned off.

[0041] When the pulse width modulation PWM controller outputs a high level, the capacitor C1 provides a negative voltage between the gate and source of MOSFETQ6, which quickly draws the current in the capacitor Cgs, causing its voltage to drop rapidly, thereby achieving rapid discharge and turning off MOSFETQ6 faster.

[0042] When the pulse width modulation PWM controller outputs a low level, transistors Q3 and Q5 are turned off, the base of transistor Q2 is pulled high by resistor R3, transistor Q2 is turned off, the emitter of transistor Q1 is pulled low by resistors R8 and R9, transistor Q1 is turned on, and the 15V voltage reaches the base of transistor Q4 through transistor Q1 and resistor R4, that is, the base of transistor Q4 is at a high level, and transistor Q4 is turned on;

[0043] At this time, the charge and discharge control loop includes two current loops: the capacitor C1 charging loop and the capacitor Cgs charging loop:

[0044] Capacitor C1 charging circuit: 15V voltage flows through resistor R7, diode D3, capacitor C1, diode D2, transistor Q4 and ground in sequence to charge capacitor C1. At this time, the voltage across capacitor C1 is low at the diode D2 end and high at the diode D3 end.

[0045] Capacitor Cgs charging circuit: 15V voltage flows through transistor Q1 and resistor R8 in sequence, reaches the gate of MOSFET Q6, charges the capacitor Cgs between the gate and source of MOSFET Q6, and MOSFET Q6 is turned on.

[0046] When the pulse width modulation PWM controller outputs a high level, in the charge and discharge control loop, the base of transistor Q5 is at a high level, and Q5 is turned on; the emitter of transistor Q3 is pulled down by diode D1 and transistor Q5, the base is at a high level, transistor Q3 is turned on, transistor Q1 is turned off, and transistor Q2 is turned on; the capacitor Cgs between the gate and the source of MOSFET Q6 is discharged through the loop resistor R8, transistor Q2, diode D1 and transistor Q5, and finally to the ground;

[0047] Furthermore, when the pulse width modulation PWM controller outputs a high level, in the charge and discharge control loop, the anode of the diode D2 has been pulled down by the diode D1, and the transistor Q4 is cut off. At this time, the capacitor C1 stops charging, and the voltage difference across the capacitor C1 forms a negative voltage between the gate and source of the MOSFET Q6, which can quickly draw away the current in the capacitor Cgs, achieve rapid discharge, and thus make the MOSFET Q6 turn off faster.

[0048] In the charge and discharge control circuit, the on-state voltage drop of the diode is 0.7V, the on-state voltage drop of the resistor is negligible, and the on-state voltage drop of the transistor is 0.3V;

[0049] When the pulse width modulation PWM controller outputs a low level, the voltage across the charged capacitor C1 is: 15-0.7-0.7-0.3=13.3V;

[0050] Furthermore, the voltage at the end of the capacitor C1 connected to the diode D2 is 0.3+0.7=1V, and the voltage at the end of the capacitor C1 connected to the diode D3 is 15-0.7=14.3V, and the voltage difference is 14.3-1=13.3V;

[0051] When the pulse width modulation PWM controller outputs a high level, the transistor Q5 pulls down the voltage at one end of the capacitor C1 to 0.3V, and the voltage at the end of the capacitor C1 connected to the diode D2 that stops charging is 0.3-13.3=-13V, and the negative voltage applied between the gate and source of the MOSFET Q6 is -13V; the -13V voltage difference quickly draws away the current in the capacitor Cgs, achieving rapid discharge, thereby causing the MOSFET Q6 to shut down faster.

[0052] The charge and discharge control circuit includes five transistors, respectively labeled as Q1, Q2, Q3, Q4 and Q5, three diodes, respectively labeled as D1, D2 and D3, and nine resistors, respectively labeled as R1, R2, R3, R4, R5, R6, R7, R8 and R9;

[0053] The pulse width modulation PWM controller is connected to the base of the transistor Q3 through the resistor R1, and is connected to the base of the transistor Q5 through the resistor R2;

[0054] The collector of the transistor Q3 is simultaneously connected to the 15V voltage, the bases of the transistors Q1 and Q2, and a resistor R3 is connected between the transistor Q3 and the 15V voltage; the emitter of the transistor Q3 is simultaneously connected to the collectors of the transistors Q2, Q4 and Q5;

[0055] A diode D2 is also connected between the collectors of the transistor Q3 and the transistor Q4, and a diode D1 is also connected between the transistor Q3 and the transistor Q5; the anodes of the diodes D1 and D2 are connected to the emitter of the transistor Q3;

[0056] The capacitor C1 is connected in parallel with both ends of the diode D1;

[0057] The transistors Q1, Q3, Q4 and Q5 are all NPN transistors, and the transistor Q2 is a PNP transistor;

[0058] The 15V voltage is also connected to the collectors of transistors Q1 and Q5 at the same time, and a resistor R7 and a diode D3 are also provided between the 15V voltage and the transistor Q5, wherein the anode of the diode D3 is connected to the 15V voltage;

[0059] The emitter of the transistor Q1 is simultaneously connected to the emitter of the transistor Q2, the base of the transistor Q4 and the gate of the MOSFETQ6, a resistor R4 is further provided between the transistor Q1 and the transistor Q4, and a resistor R8 is further provided between the transistor Q1 and the MOSFETQ6;

[0060] A resistor R5 is connected between the base and emitter of the transistor Q4, and a resistor R6 is connected between the base and emitter of the transistor Q5; meanwhile, the emitters of the transistors Q4 and Q5 are both grounded;

[0061] The MOSFETQ6 is connected to the voltage VCC via the drain, a capacitor Cgs is connected between the gate and the source, a resistor R9 is connected in parallel at both ends of the capacitor Cgs, and the MOSFETQ6 is grounded via the source.

[0062] The resistance values ​​of the resistors R1 and R2 are both 1K, the resistance values ​​of the resistors R3 to R7 are all 10K, the resistance value of the resistor R8 is all 10Ω, and the resistance value of the resistor R9 is all 4.7K.

[0063] The embodiment described above is only one specific implementation of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A control circuit for realizing fast shutdown of MOSFET, characterized in that: It includes a pulse width modulation PWM controller, a charge and discharge control loop, a MOSFET Q6 and a capacitor C1; The capacitor C1 is used for charging and energy storage; When the pulse width modulation PWM controller outputs a low level, the capacitor C1 is charged through the charge and discharge control loop; when the pulse width modulation PWM controller outputs a high level, the capacitor C1 is discharged through the charge and discharge control loop; A capacitor Cgs is connected between the gate and source of the MOSFET Q6. When the voltage of the capacitor Cgs reaches the conduction threshold, the MOSFET Q6 is turned on, otherwise it is turned off. When the pulse width modulation PWM controller outputs a high level, the capacitor C1 provides a negative voltage between the gate and source of MOSFETQ6, which quickly draws the current in the capacitor Cgs, causing its voltage to drop rapidly, thereby achieving rapid discharge and turning off MOSFETQ6 faster.

2. The control circuit for realizing fast shutdown of MOSFET according to claim 1, characterized in that: When the pulse width modulation PWM controller outputs a low level, transistors Q3 and Q5 are turned off, the base of transistor Q2 is pulled high by resistor R3, transistor Q2 is turned off, the emitter of transistor Q1 is pulled low by resistors R8 and R9, transistor Q1 is turned on, and the 15V voltage reaches the base of transistor Q4 through transistor Q1 and resistor R4, that is, the base of transistor Q4 is at a high level, and transistor Q4 is turned on; At this time, the charge and discharge control loop includes two current loops, namely, a capacitor C1 charging loop and a capacitor Cgs charging loop.

3. The control circuit for realizing fast shutdown of MOSFET according to claim 2, characterized in that: In the capacitor C1 charging circuit, the 15V voltage flows through the resistor R7, the diode D3, the capacitor C1, the diode D2, the transistor Q4 and the ground in sequence to charge the capacitor C1. At this time, the voltage across the capacitor C1 is low at the diode D2 end and high at the diode D3 end.

4. The control circuit for realizing fast shutdown of MOSFET according to claim 2, characterized in that: In the capacitor Cgs charging loop, the 15V voltage flows through the transistor Q1 and the resistor R8 in sequence, reaches the gate of the MOSFET Q6, charges the capacitor Cgs between the gate and the source of the MOSFET Q6, and the MOSFET Q6 is turned on.

5. The control circuit for realizing fast shutdown of MOSFET according to claim 1 or 3, characterized in that: When the pulse width modulation PWM controller outputs a high level, in the charge and discharge control loop, the base of transistor Q5 is at a high level, and Q5 is turned on; the emitter of transistor Q3 is pulled down by diode D1 and transistor Q5, the base is at a high level, transistor Q3 is turned on, transistor Q1 is turned off, and transistor Q2 is turned on; the capacitor Cgs between the gate and the source of MOSFET Q6 is discharged through the loop resistor R8, transistor Q2, diode D1 and transistor Q5, and finally to the ground; Furthermore, when the pulse width modulation PWM controller outputs a high level, in the charge and discharge control loop, the anode of the diode D2 has been pulled down by the diode D1, and the transistor Q4 is cut off. At this time, the capacitor C1 stops charging, and the voltage difference across the capacitor C1 forms a negative voltage between the gate and source of the MOSFET Q6, which can quickly draw away the current in the capacitor Cgs, achieve rapid discharge, and thus make the MOSFET Q6 turn off faster.

6. The control circuit for realizing fast shutdown of MOSFET according to claim 1, characterized in that: The charge and discharge control circuit includes five transistors, respectively labeled as Q1, Q2, Q3, Q4 and Q5, three diodes, respectively labeled as D1, D2 and D3, and nine resistors, respectively labeled as R1, R2, R3, R4, R5, R6, R7, R8 and R9; The pulse width modulation PWM controller is connected to the base of the transistor Q3 through the resistor R1, and is connected to the base of the transistor Q5 through the resistor R2; The collector of the transistor Q3 is simultaneously connected to the 15V voltage, the bases of the transistors Q1 and Q2, and a resistor R3 is connected between the transistor Q3 and the 15V voltage; the emitter of the transistor Q3 is simultaneously connected to the collectors of the transistors Q2, Q4 and Q5; A diode D2 is also connected between the collectors of the transistor Q3 and the transistor Q4, and a diode D1 is also connected between the transistor Q3 and the transistor Q5; the anodes of the diodes D1 and D2 are connected to the emitter of the transistor Q3; The capacitor C1 is connected in parallel with both ends of the diode D1; The transistors Q1, Q3, Q4 and Q5 are all NPN transistors, and the transistor Q2 is a PNP transistor; The 15V voltage is also connected to the collectors of transistors Q1 and Q5 at the same time, and a resistor R7 and a diode D3 are also provided between the 15V voltage and the transistor Q5, wherein the anode of the diode D3 is connected to the 15V voltage; The emitter of the transistor Q1 is simultaneously connected to the emitter of the transistor Q2, the base of the transistor Q4 and the gate of the MOSFETQ6, a resistor R4 is further provided between the transistor Q1 and the transistor Q4, and a resistor R8 is further provided between the transistor Q1 and the MOSFETQ6; A resistor R5 is connected between the base and emitter of the transistor Q4, and a resistor R6 is connected between the base and emitter of the transistor Q5; meanwhile, the emitters of the transistors Q4 and Q5 are both grounded; The MOSFETQ6 is connected to the voltage VCC via the drain, a capacitor Cgs is connected between the gate and the source, a resistor R9 is connected in parallel at both ends of the capacitor Cgs, and the MOSFETQ6 is grounded via the source.

7. The control circuit for realizing fast shutdown of MOSFET according to claim 4, characterized in that: The resistance values ​​of the resistors R1 and R2 are both 1K, the resistance values ​​of the resistors R3 to R7 are all 10K, the resistance value of the resistor R8 is all 10Ω, and the resistance value of the resistor R9 is all 4.7K.

8. The control circuit for realizing fast shutdown of MOSFET according to claim 6, characterized in that: In the charge and discharge control circuit, the conduction voltage drop of the diode is 0.7V, the conduction voltage drop of the resistor is negligible, and the conduction voltage drop of the transistor is 0.3V; When the pulse width modulation PWM controller outputs a low level, the voltage across the charged capacitor C1 is: 15-0.7-0.7-0.3=13.3V; Furthermore, the voltage at the end where the capacitor C1 is connected to the diode D2 is 0.3+0.7=1V, the voltage at the end where the capacitor C1 is connected to the diode D3 is 15-0.7=14.3V, and the voltage difference is 14.3-1=13.3V.

9. The control circuit for realizing fast shutdown of MOSFET according to claim 8, characterized in that: When the pulse width modulation PWM controller outputs a high level, the transistor Q5 pulls down the voltage at one end of the capacitor C1 to 0.3V, and the voltage at the end of the capacitor C1 connected to the diode D2 that stops charging is 0.3-13.3=-13V, and the negative voltage applied between the gate and source of the MOSFET Q6 is -13V; the -13V voltage difference quickly draws away the current in the capacitor Cgs, achieving rapid discharge, thereby causing the MOSFET Q6 to shut down faster.

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