Interference elimination circuit and method applied to conduction moment of field effect transistor

Abstract

The invention discloses an interference elimination circuit and method applied to the conduction moment of a field effect transistor. The connection of each electronic component of the interference elimination circuit is as follows: a drain electrode of a first field effect transistor is connected with a main circuit, a grid electrode is connected with one end of a first resistor, and a source electrode is connected with one end of a second resistor and an input positive electrode of a low-pass filter circuit; the other end of the first resistor is connected with a first triode collector, one end of a capacitor and a field-effect tube driving circuit anode; the other end of the second resistor is connected with the input cathode of the low-pass filter circuit; the drain electrode of the second field-effect tube is connected with the output anode of the low-pass filter circuit and the anode of the current sampling circuit, the grid electrode is connected with the emitters of the first and second triodes, and the source electrode is connected with the collector electrode of the second triode, the other end of the third resistor, the anode of the diode, the cathode of the field-effect tube driving circuit and the cathode of the current sampling circuit; the first triode base electrode is connected with the second triode base electrode, the other end of the capacitor, one end of the third resistor and the diode cathode. Interference of current pulse on the current sampling circuit when the field effect transistor is conducted is eliminated.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to an interference elimination circuit and method applied to the moment when a field effect tube is turned on. Background Art

[0002] Field effect tubes are widely used as power switches in various types of small and medium power switching power supplies. However, in actual circuits, when the field effect tube is turned on, the instantaneous discharge current pulse amplitude of the equivalent capacitance between its drain and the negative electrode of the DC power supply is very large, which affects the normal operation of the current sampling circuit and easily causes the current sampling circuit to misjudge the actual current peak value, thereby erroneously triggering the power supply short-circuit current protection and peak current control mechanism. To this end, the present invention proposes a circuit to eliminate the interference of the current pulse when the field effect tube is turned on on the current sampling circuit. Summary of the invention

[0003] The first purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide an interference elimination circuit applied to the moment when a field effect tube is turned on, which can effectively eliminate the interference of the current pulse generated when the field effect tube as a power switch in the switching power supply is turned on to the current sampling circuit.

[0004] The second object of the present invention is to provide a method for eliminating interference applied to the moment when a field effect tube is turned on.

[0005] The first object of the present invention is achieved by the following technical scheme: an interference elimination circuit applied to the moment of field effect tube conduction, used to eliminate the interference of the current pulse generated when the field effect tube as a power switch in the switching power supply is turned on to the current sampling circuit, comprising a first field effect tube, a second field effect tube, a first resistor, a second resistor, a third resistor, a capacitor, a first triode, a second triode, a diode, a field effect tube driving circuit and a low-pass filter circuit; the field effect tube driving circuit outputs a positive voltage for turning on the first field effect tube, and outputs a zero voltage or a negative voltage for turning off the first field effect tube; the drain of the first field effect tube is connected to the main circuit of the switching power supply; the gate of the first field effect tube is connected to one end of the first resistor; the other end of the first resistor is respectively connected to the collector of the first triode, one end of the capacitor and the field effect tube driving circuit; The first field effect tube is connected to the positive electrode of the driving circuit; the source of the first field effect tube is connected to one end of the second resistor and the input positive electrode of the low-pass filter circuit; the other end of the second resistor is connected to the input negative electrode of the low-pass filter circuit, and the second resistor and the low-pass filter circuit are both connected to the reference ground GND; the drain of the second field effect tube is respectively connected to the output positive electrode of the low-pass filter circuit and the positive electrode of the current sampling circuit; the gate of the second field effect tube is respectively connected to the emitter of the first triode and the emitter of the second triode; the base of the first triode is respectively connected to the base of the second triode, the other end of the capacitor, one end of the third resistor and the negative electrode of the diode; the source of the second field effect tube is respectively connected to the collector of the second triode, the other end of the third resistor, the positive electrode of the diode, the negative electrode of the field effect tube driving circuit and the negative electrode of the current sampling circuit.

[0006] Preferably, the field effect transistor driving circuit outputs a positive voltage so that when the equivalent capacitor discharge current pulse when the first field effect transistor is turned on exists, the second field effect transistor is saturated and turned on, and after the current pulse disappears, the second field effect transistor is turned off.

[0007] Preferably, the field effect transistor driving circuit outputs a driving voltage via the positive and negative terminals, i.e., the positive and negative electrodes. When the driving voltage is a positive voltage, i.e., the positive electrode potential is higher than the negative electrode potential, the first field effect transistor can be turned on. When the driving voltage is a zero voltage or a negative voltage, i.e., the positive electrode potential is lower than the negative electrode potential, the first field effect transistor can be turned off.

[0008] Preferably, the positive voltage output by the field effect transistor driving circuit is 15 volts, and the negative voltage is between -15 and 0 volts.

[0009] Preferably, the second resistor plays a role in current sampling, that is, the source current of the first field effect tube generates a voltage proportional to the current through the second resistor. This voltage is sent to the current sampling circuit after the high-frequency component is filtered out by the low-pass filter circuit for current control and protection of the switching power supply.

[0010] Preferably, the first field effect transistor is an N-channel enhancement type power switch tube; the second field effect transistor is an N-channel enhancement type low-power tube.

[0011] Preferably, the first transistor is an NPN type low-power transistor, and the second transistor is a PNP type low-power transistor.

[0012] The second object of the present invention is achieved by the following technical solution: a method for eliminating interference applied to the moment when a field effect tube is turned on. The method is based on the above-mentioned interference elimination circuit to eliminate the interference of the current pulse generated when the field effect tube as a power switch in the switching power supply is turned on to the current sampling circuit. The specific implementation process is as follows:

[0013] When the field effect tube driving circuit outputs a positive voltage to turn on the first field effect tube via the first resistor, the positive voltage is also applied to the gate of the second field effect tube via the capacitor, so that the second field effect tube is saturated and turned on, thereby short-circuiting the input of the current sampling circuit, and preventing the current pulse at the moment of turning on the first field effect tube from entering the current sampling circuit via the low-pass filter circuit to interfere with the current sampling circuit; at the same time, the field effect tube driving circuit charges the capacitor via the third resistor, and the voltage across the capacitor gradually increases, that is, the voltage between the gate and the source of the second field effect tube gradually decreases. When this voltage drops to a value lower than the turn-on voltage of the second field effect tube, the second field effect tube will be turned off, so that the input of the current sampling circuit will no longer be short-circuited, so that the current sampling circuit can detect the source current of the first field effect tube for current control and protection of the switching power supply; when the field effect tube driving circuit outputs zero voltage or negative voltage to turn off the first field effect tube, the capacitor is discharged to zero voltage or negative voltage through the diode, so that the second field effect tube can be turned on again when the field effect tube driving circuit outputs a positive voltage next time.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0015] At the moment when the field effect tube of the present invention is turned on, its source current pulse will not enter the current sampling circuit, thereby not interfering with the normal operation of the current sampling circuit. This effectively eliminates the interference of the current pulse generated when the field effect tube as a power switch in the switching power supply is turned on to the current sampling circuit, and is worthy of promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the schematic diagram of the interference elimination circuit. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0018] Example 1

[0019] This embodiment discloses an interference elimination circuit applied to the moment of field effect tube conduction, which is used to eliminate the interference of the current pulse generated when the field effect tube as a power switch in the switching power supply is turned on to the current sampling circuit. Figure 1 As shown, it includes a first field effect transistor Q1, a second field effect transistor Q2, a first resistor R1, a second resistor R2, a third resistor R3, a capacitor C1, a first triode T1, a second triode T2, a diode D1, a field effect transistor drive circuit and a low-pass filter circuit; the field effect transistor drive circuit outputs a positive voltage for turning on the first field effect transistor Q1, and outputs a zero voltage or a negative voltage for turning off the first field effect transistor Q1; the drain of the first field effect transistor Q1 is connected to the main circuit of the switching power supply; the gate of the first field effect transistor Q1 is connected to one end of the first resistor R1; the other end of the first resistor R1 is respectively connected to the collector of the first triode T1, one end of the capacitor C1 and the positive electrode of the field effect transistor drive circuit; the source of the first field effect transistor Q1 is connected to one end of the second resistor R2 and the low-pass filter circuit The other end of the second resistor R2 is connected to the input negative electrode of the low-pass filter circuit, and the second resistor R2 and the low-pass filter circuit are both connected to the reference ground GND; the drain of the second field effect transistor Q2 is respectively connected to the output positive electrode of the low-pass filter circuit and the positive electrode of the current sampling circuit; the gate of the second field effect transistor Q2 is respectively connected to the emitter of the first triode T1 and the emitter of the second triode T2; the base of the first triode T1 is respectively connected to the base of the second triode T2, the other end of the capacitor C1, one end of the third resistor R3 and the negative electrode of the diode D1; the source of the second field effect transistor Q2 is respectively connected to the collector of the second triode T2, the other end of the third resistor R3, the positive electrode of the diode D1, the negative electrode of the field effect transistor driving circuit and the negative electrode of the current sampling circuit.

[0020] Specifically, the field effect transistor driving circuit outputs a positive voltage to turn on the first field effect transistor Q1. During the equivalent capacitor discharge current pulse, the second field effect transistor Q2 is saturated and turned on. After the current pulse disappears, the second field effect transistor Q2 is turned off.

[0021] Specifically, the field effect transistor driving circuit outputs a driving voltage via the positive and negative terminals, i.e., the positive and negative electrodes. When the driving voltage is a positive voltage, i.e., the positive electrode potential is higher than the negative electrode potential, the first field effect transistor Q1 can be turned on. When the driving voltage is a zero voltage or a negative voltage, i.e., the positive electrode potential is lower than the negative electrode potential, the first field effect transistor Q1 can be turned off.

[0022] Specifically, the positive voltage output by the field effect transistor driving circuit is generally 15 volts, and the negative voltage is generally between -15 and 0 volts.

[0023] Specifically, the second resistor R2 plays a role in current sampling, that is, the source current of the first field effect transistor Q1 generates a voltage proportional to the current through the second resistor R2, and this voltage is sent to the current sampling circuit after the high-frequency component is filtered out by the low-pass filter circuit for current control and protection of the switching power supply.

[0024] Specifically, the first field effect transistor Q1 is an N-channel enhancement type power switch tube; the second field effect transistor Q2 is an N-channel enhancement type low-power tube; the first transistor T1 is an NPN type low-power transistor; and the second transistor T2 is a PNP type low-power transistor.

[0025] Example 2

[0026] This embodiment discloses a method for eliminating interference applied to the moment when a field effect tube is turned on. The method is based on the interference elimination circuit described in Example 1 to eliminate the interference of the current pulse generated when the field effect tube as a power switch in the switching power supply is turned on to the current sampling circuit. The specific implementation process is as follows:

[0027] When the field effect tube driving circuit outputs a positive voltage and turns on the first field effect tube Q1 through the first resistor R1, the positive voltage is also applied to the gate of the second field effect tube Q2 through the capacitor C1, so that the second field effect tube Q2 is saturated and turned on, thereby short-circuiting the input of the current sampling circuit, and preventing the current pulse at the moment of turning on the first field effect tube Q1 from entering the current sampling circuit through the low-pass filter circuit to interfere with the current sampling circuit; at the same time, the field effect tube driving circuit charges the capacitor C1 through the third resistor R3, and the voltage across the capacitor C1 gradually increases, that is, the gate of the second field effect tube Q2 is charged. The voltage between the electrode and the source gradually decreases. When this voltage drops to a value lower than the turn-on voltage of the second field effect tube Q2, the second field effect tube Q2 will be turned off, thereby no longer short-circuiting the input of the current sampling circuit, so that the current sampling circuit can detect the source current of the first field effect tube Q1, which is used for current control and protection of the switching power supply; when the field effect tube driving circuit outputs zero voltage or negative voltage to turn off the first field effect tube Q1, the capacitor C1 is discharged to zero voltage or negative voltage through the diode D1, so that the second field effect tube Q2 can be turned on again when the field effect tube driving circuit outputs a positive voltage next time.

[0028] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. An interference elimination circuit applied to the moment of field effect tube conduction, used to eliminate the interference of the current pulse generated when the field effect tube as a power switch in the switching power supply is turned on to the current sampling circuit, characterized in that: The invention comprises a first field effect tube (Q1), a second field effect tube (Q2), a first resistor (R1), a second resistor (R2), a third resistor (R3), a capacitor (C1), a first triode (T1), a second triode (T2), a diode (D1), a field effect tube driving circuit and a low-pass filter circuit; the field effect tube driving circuit outputs a positive voltage for turning on the first field effect tube (Q1), and outputs a zero voltage or a negative voltage for turning off the first field effect tube (Q1); the drain of the first field effect tube (Q1) is connected to the main circuit of the switching power supply; the gate of the first field effect tube (Q1) is connected to one end of the first resistor (R1); the other end of the first resistor (R1) is respectively connected to the collector of the first triode (T1), one end of the capacitor (C1) and the positive electrode of the field effect tube driving circuit; the source of the first field effect tube (Q1) is connected to one end of the second resistor (R2) and the low-pass filter circuit; The second field effect tube (Q2) is connected to the positive input electrode of the low-pass filter circuit; the other end of the second resistor (R2) is connected to the negative input electrode of the low-pass filter circuit, and the second resistor (R2) and the low-pass filter circuit are both connected to the reference ground GND; the drain of the second field effect tube (Q2) is respectively connected to the positive output electrode of the low-pass filter circuit and the positive electrode of the current sampling circuit; the gate of the second field effect tube (Q2) is respectively connected to the emitter of the first triode (T1) and the emitter of the second triode (T2); the base of the first triode (T1) is respectively connected to the base of the second triode (T2), the other end of the capacitor (C1), one end of the third resistor (R3) and the negative electrode of the diode (D1); the source of the second field effect tube (Q2) is respectively connected to the collector of the second triode (T2), the other end of the third resistor (R3), the positive electrode of the diode (D1), the negative electrode of the field effect tube driving circuit and the negative electrode of the current sampling circuit.

2. The interference elimination circuit applied to the moment of field effect tube conduction according to claim 1, characterized in that: The field effect tube driving circuit outputs a positive voltage to turn on the first field effect tube (Q1) while an equivalent capacitor discharge current pulse exists, and the second field effect tube (Q2) is saturated and turned on. After the current pulse disappears, the second field effect tube (Q2) is turned off.

3. The interference elimination circuit applied to the moment of field effect tube conduction according to claim 1, characterized in that: The field effect tube driving circuit outputs a driving voltage via positive and negative electrode terminals, i.e., positive and negative electrodes. When the driving voltage is a positive voltage, i.e., the positive electrode potential is higher than the negative electrode potential, the first field effect tube (Q1) can be turned on. When the driving voltage is a zero voltage or a negative voltage, i.e., the positive electrode potential is lower than the negative electrode potential, the first field effect tube (Q1) can be turned off.

4. The interference elimination circuit applied to the moment of field effect tube conduction according to claim 1, characterized in that: The positive voltage output by the field effect tube driving circuit is 15 volts, and the negative voltage is between -15 and 0 volts.

5. The interference elimination circuit applied to the moment of field effect tube conduction according to claim 1, characterized in that: The second resistor (R2) plays a role in current sampling, that is, the source current of the first field effect tube (Q1) generates a voltage proportional to the current through the second resistor (R2), and the voltage is sent to the current sampling circuit after the high-frequency component is filtered out by the low-pass filter circuit for current control and protection of the switching power supply.

6. The interference elimination circuit applied to the moment of field effect tube conduction according to claim 1, characterized in that: The first field effect tube (Q1) is an N-channel enhancement type power switch tube; the second field effect tube (Q2) is an N-channel enhancement type low power tube.

7. The interference elimination circuit applied to the moment of field effect tube conduction according to claim 1, characterized in that: The first transistor (T1) is an NPN type low-power transistor, and the second transistor (T2) is a PNP type low-power transistor.

8. A method for eliminating interference applied to the moment when a field effect tube is turned on, characterized in that: The method is based on the interference elimination circuit described in any one of claims 1 to 7 to eliminate the interference of the current pulse generated when the field effect tube as a power switch in the switching power supply is turned on to the current sampling circuit, and the specific implementation process is as follows: When the field effect tube driving circuit outputs a positive voltage to turn on the first field effect tube (Q1) via the first resistor (R1), the positive voltage is also applied to the gate of the second field effect tube (Q2) via the capacitor (C1), so that the second field effect tube (Q2) is saturated and turned on, thereby short-circuiting the input of the current sampling circuit, thereby preventing the current pulse at the moment of turning on the first field effect tube (Q1) from entering the current sampling circuit via the low-pass filter circuit to interfere with the current sampling circuit; At the same time, the field effect tube driving circuit charges the capacitor (C1) via the third resistor (R3), and the voltage across the capacitor (C1) gradually increases, that is, the voltage between the gate and the source of the second field effect tube (Q2) gradually decreases. When the voltage drops to a value lower than the turn-on voltage of the second field effect tube (Q2), the second field effect tube (Q2) is turned off, so that the input of the current sampling circuit is no longer short-circuited, so that the current sampling circuit can detect the source current of the first field effect tube (Q1) for current control and protection of the switching power supply. When the field effect tube driving circuit outputs a zero voltage or a negative voltage to turn off the first field effect tube (Q1), the capacitor (C1) is discharged to a zero voltage or a negative voltage via the diode (D1), so that the second field effect tube (Q2) can be turned on again when the field effect tube driving circuit outputs a positive voltage next time.

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