CN203313043U

CN203313043U - Negative-voltage drive circuit of high-frequency MOSFET

Info

Publication number: CN203313043U
Application number: CN2013203635708U
Authority: CN
Inventors: 杨毅
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-06-24
Filing date: 2013-06-24
Publication date: 2013-11-27
Anticipated expiration: 2023-06-24

Abstract

The utility model discloses a negative-voltage drive circuit of a high-frequency MOSFET, comprising a charge circuit, a discharge circuit, a transformer T, a MOSFET Q and a buffer capacitor C2. The charge circuit is composed of a blocking capacitor C1 and current limiting resistors R1 and R2; the discharge circuit is composed of a voltage stabilizing diode D and a discharge resistor R3; a dotted terminal at a primary side of the transformer T is connected with the positive pole V+ of a power supply and an unlike terminal at the primary side of the transformer T is connected with the drain of the MOSFET; the source of the MOSFET Q is grounded; and the positive pole of the buffer capacitor C2 is connected with the drain D of the Q and the negative pole of the buffer capacitor C2 is connected with the source S of the Q. An output point of a PWM signal of a microprocessor is connected with the gate G of the MOSFET through the current limiting resistor R1 and the blocking capacitor C1. The negative-voltage drive circuit is simple in structure and low in cost, and the MOSFET can be automatically turned off when the microprocessor malfunctions so as to prevent a primary winding of the transformer from being switched on for a long time and prevent the current of the primary winding from being too large to cause damage to devices.

Description

A kind of negative pressure drive circuit of High-frequency MOSFET

Technical field

The utility model belongs to power electronics and drives applied technical field, relates in particular to a kind of negative pressure drive circuit of High-frequency MOSFET.

Background technology

Switching Power Supply, because volume is little, lightweight, the efficiency advantages of higher, is applied more and more universal.MOSFET because switching speed is fast, easily parallel connection, required driving power be little etc., and advantage has become one of the most frequently used device for power switching of Switching Power Supply.Power MOSFET belongs to voltage-controlled device, and when the voltage between its grid and source electrode surpassed threshold voltage, MOSFET will conducting.Because there is junction capacitance in MOSFET, during shutoff, the unexpected rising of its drain electrode and source electrode both end voltage will produce interference voltage at grid and source electrode two ends by junction capacitance, and the interference voltage ripple will cause the false triggering of MOSFET.The turn-off circuit impedance of the complementary drive circuit that tradition is commonly used is little, and turn-off speed is very fast, but it can not provide negative pressure, therefore its anti-interference is poor.Simultaneously, traditional high-frequency low-power MOSFET drive circuit, lack the MOSFET protective circuit, and when circuit breaks down, when the PWM of output was continuously high level, MOSFET, by long-time conducting, caused circuital current excessive, causes the serious problems such as circuit element infringement.

Summary of the invention

Defect and deficiency for above-mentioned prior art existence, the purpose of this utility model is, a kind of negative pressure drive circuit of High-frequency MOSFET is provided, the utility model not only can meet the demand of pulse transformer high-frequency work, can also provide simultaneously negative pressure to drive, and prevent from hindering for some reason the excessive situation of primary winding current caused.

In order to realize above-mentioned task, the utility model adopts following technical solution:

A kind of negative pressure drive circuit of High-frequency MOSFET, comprise charging circuit, discharge circuit, transformer T, MOSFET pipe Q and buffering capacitor C 2, and described charging circuit is comprised of capacitance C1, current-limiting resistance R1 and R2; Described discharge circuit is comprised of voltage stabilizing didoe D and discharge resistance R3; The former limit Same Name of Ends of described transformer T connects positive source V+, and former limit non-same polarity connects the drain electrode of MOSFET; The source ground of described MOSFET pipe Q; The positive pole of described buffer capacitor C2 connects the drain D of Q, and the negative pole of C2 connects the source S of Q.The output point of microprocessor pwm signal is connected with the grid of MOSFET with capacitance C1 through current-limiting resistance R1.

The beneficial effects of the utility model are: when the PWM of microprocessor output becomes 5V by 0V, the capacitance both end voltage is not undergone mutation, the cathode voltage of capacitor C 1 sports high voltage, the voltage difference of capacitor C 1 positive and negative polarities is not undergone mutation, therefore the positive pole of capacitor C 1 also sports high voltage, make the voltage between MOSFET tube grid G and source S surpass threshold voltage, at this moment MOSFET pipe Q is open-minded.When microprocessor breaks down, when PWM was continuously 5V, higher than the MOSFET source voltage, electric capacity discharged by resistance due to the voltage of capacitance positive pole, until Vgs is during lower than gate threshold voltage, MOSFET turn-offs.Discharge process is the intrinsic response of RC circuit, by choosing suitable capacitance and resistance, can realize the different armature winding turn-off times.When the PWM of microprocessor output became 0V by 5V, the capacitance both end voltage was not undergone mutation, and now the positive pole of capacitance reduces 5V, makes Vgs be less than gate threshold voltage, and the MOSFET of armature winding turn-offs.

This circuit structure is simple, with low cost, and, when microprocessor breaks down, can automatically shut down MOSFET, prevents that the primary winding is open-minded for a long time, avoids that primary winding current is excessive causes device infringement.

The accompanying drawing explanation

Below in conjunction with the drawings and specific embodiments the utility model is further explained explanation.

Fig. 1 is circuit theory diagrams.

Fig. 2 is groundwork waveform in circuit.

In Fig. 1, T is the small-power pulse transformer, and Q is the MOSFET pipe, and C1 is that capacitance, D are voltage stabilizing didoe, and R1 and R2 are current-limiting resistance, and R3 is discharge resistance.

In Fig. 2, D is duty ratio, and T is switch periods, and DT is ON time, and (1-D) T is the turn-off time, and Vg is input pwm pulse waveform, and Vgs is the grid of power MOSFET and the voltage between source electrode.

Embodiment

In Fig. 1, discharge resistance R3 and capacitance C1 form discharge circuit, when pwm signal is low-voltage by high-voltage variable, capacitance are discharged, and stop armature winding to continue conducting, avoid primary winding current excessive.Capacitance C1, voltage stabilizing didoe D and current-limiting resistance R1 and R2 form charging circuit, when pwm signal becomes high voltage by low-voltage, capacitance are charged.The former limit Same Name of Ends of small-power pulse transformer T connects positive source V+, and former limit non-same polarity connects the drain D of MOSFET, the source S ground connection of MOSFET.The output point of microprocessor pwm signal is connected with the grid of MOSFET with capacitance C1 through current-limiting resistance R1.

Fig. 2 is the several main waveform in drive circuit, and the duty ratio of establishing pwm signal is D, and switch periods is T.In the DT ON time, pwm signal is by being continuously 5V, and the voltage Vgs between MOSFET grid and source electrode constantly descends after reaching maximum, and the MOSFET of armature winding is open-minded.At (1-D) T blocking interval, the PWM output signal becomes low level, and the voltage Vgs between MOSFET grid and source electrode is dropped rapidly to negative pressure, and the gate charge repid discharge has realized that the negative pressure of MOSFET drives shutoff.

The opening process of MOSFET is the charging process of RC circuit, and the numerical value by rational selection capacitance and discharge resistance is the service time of control transformer armature winding accurately, avoids that primary winding current is excessive causes the device infringement.Microprocessor breaks down, and when the pwm signal of output was continuously high level, the voltage Vgs between MOSFET grid and source electrode reduced automatically, and namely MOSFET can automatically shut down.

Claims

1. the negative pressure drive circuit of a High-frequency MOSFET, it is characterized in that, comprise charging circuit, discharge circuit, transformer T, MOSFET pipe Q and buffering capacitor C 2, the former limit termination positive source of the same name V+ of described transformer T, former limit non-same polarity connect the drain D of MOSFET pipe Q; The source S ground connection of described MOSFET pipe Q; The positive pole of described buffer capacitor C2 connects the drain D of Q, and the negative pole of C2 connects the source S of Q.

2. as the negative pressure drive circuit of High-frequency MOSFET as described in claim 1, it is characterized in that, described charging circuit is comprised of capacitance C1, current-limiting resistance R1 and R2, and the positive pole of described capacitance C1 is connected with the grid G of MOSFET; Described current-limiting resistance R1 is connected on negative pole and the pwm signal input point two ends of capacitance C1; Described current-limiting resistance R2 is connected on the grid G two ends of positive pole and the MOSFET of C1.

3. as the negative pressure drive circuit of High-frequency MOSFET as described in claim 1, it is characterized in that, described discharge circuit comprises voltage stabilizing didoe D and discharge resistance R3, and the negative pole of described voltage stabilizing didoe D is connected with the positive pole of capacitance C1; Described discharge resistance R3 is connected on the source S two ends of positive pole and the MOSFET of voltage stabilizing didoe D.