Circuit for turning off switching power transistor and driving chip

Abstract

This application provides a switching power transistor cutoff control circuit and driver chip, relating to the field of power electronics technology. The circuit includes: a first controllable switch, a voltage drop detection circuit, and a switch controller. The first controllable switch is coupled to the switching power transistor and controls the switching power transistor to cut off when the first controllable switch is turned on. The switch controller is configured to receive a forced turn-on signal output by the voltage drop detection circuit and an input turn-on signal, and controls the duration of the first controllable switch being on based on the signal with the longest duration. In this application, the voltage drop detection circuit is configured to detect an output current used to drive the switching power transistor when the first controllable switch is turned on, ensuring that the output current is sufficiently small when the first controllable switch is turned off to switch the on / off state of the switching power transistor, thereby reducing an oscillating voltage generated on a parasitic inductor and sufficiently discharging a capacitive load, thereby improving the safety and lifespan of the driver chip for the switching power transistor.

Claims

1. A switching power transistor cutoff control circuit, characterized in that it comprises: The system comprises a first controllable switch, a voltage drop detection circuit, and a switch controller; wherein the first controllable switch is coupled to a power transistor, and the power transistor is controlled to turn off when the first controllable switch is turned on; the input terminal of the voltage drop detection circuit is controllably connected to the first controllable switch during the on-phase of the first controllable switch, and detects the on-state voltage drop of the first controllable switch during connection; and outputs a forced on-state signal when the on-state voltage drop of the first controllable switch is greater than or equal to a first reference voltage, until the on-state voltage drop of the first controllable switch is less than a second reference voltage; the first input terminal of the switch controller is connected to the output terminal of the voltage drop detection circuit, and the output terminal of the switch controller is connected to the control terminal of the first controllable switch; the switch controller is used to receive the forced on-state signal and the input on-state signal, and controls the on-state time of the first controllable switch based on the signal with the longest duration.

2. As in request item 1, the switching power transistor cutoff control circuit, wherein, It further includes: a conduction time controller; wherein, the input terminal of the voltage drop detection circuit is connected to the first controllable switch via the conduction time controller, and the conduction time controller controls the first controllable switch to be connected to the voltage drop detection circuit for all or part of the time in the conduction state.

3. As in request item 2, the switching power transistor cutoff control circuit, wherein, This time period is from when the first controllable switch is turned on until the on-state voltage drop of the first controllable switch reaches its peak value.

4. As in request item 2, the switching power transistor cutoff control circuit, wherein, This portion of the time is within a set time after the first controllable switch is turned on.

5. As in request item 2, the switching power transistor cutoff control circuit, wherein, The voltage drop detection circuit includes a comparator circuit and a reference voltage output circuit. The first input terminal of the comparator circuit is connected to the voltage drop detection terminal via a turn-on controller. The voltage drop detection terminal is one of the terminals of the first controllable switch used to connect to the control terminal of the switching power transistor. The turn-on time controller is used to connect the first input terminal of the comparator circuit to the voltage drop detection terminal when the first controllable switch is turned on. The output terminal of the comparator circuit is connected to the control terminal of the reference voltage output circuit. The first reference voltage output terminal and the second reference voltage output terminal of the reference voltage output circuit are both connected to the second input terminal of the comparator circuit. The reference voltage output circuit is used to output a first reference voltage to the second input terminal of the comparator circuit when the comparator circuit outputs a first reference signal, and to output a second reference voltage to the second input terminal of the comparator circuit when the comparator circuit outputs a second reference signal. The comparator circuit outputs a first level signal when the voltage at the voltage drop detection terminal input to the first input terminal is greater than the first reference voltage or the second reference voltage input to the second input terminal; and outputs a second level signal when the voltage at the voltage drop detection terminal input to the non-inverting input terminal is less than the first reference voltage or the second reference voltage input to the inverting input terminal. The common terminal of the comparator circuit output terminal and the control terminal of the reference voltage output circuit is connected as the output terminal of the voltage drop detection circuit and the first input terminal of the switch controller.

6. As in request item 5, the switching power transistor cutoff control circuit, wherein, The comparator circuit includes: an operational amplifier; wherein the forced conduction signal is a high-level signal; the non-inverting input of the operational amplifier is connected to the voltage drop detection terminal via the conduction controller; the inverting input of the operational amplifier is connected to the first reference voltage output terminal and the second reference voltage output terminal of the reference voltage output circuit; and the output terminal of the operational amplifier is connected to the control terminal of the reference voltage output circuit. The reference voltage output circuit is used to output a first reference voltage to the inverting input terminal of the operational amplifier when the operational amplifier outputs a high-level signal, and to output a second reference voltage to the inverting input terminal of the operational amplifier when the operational amplifier outputs a low-level signal.

7. As in request item 6, the switching power transistor cutoff control circuit, wherein, The reference voltage output circuit includes: a first reference voltage circuit, a second reference voltage circuit, an inverter, a first reference voltage switch, and a second reference voltage switch; wherein, the control terminal of the second reference voltage switch serves as the control terminal of the reference voltage output circuit and is connected to the output terminal of the operational amplifier, and its common terminal is connected to the control terminal of the first reference voltage switch via the inverter; the inverting input terminal of the operational amplifier is connected to the first terminal of the first reference voltage circuit and the first terminal of the second reference voltage circuit; the second terminals of the first reference voltage circuit and the second reference voltage circuit are grounded; the first reference voltage switch and the second reference voltage switch are turned on when a high-level signal is input to the control terminal and turned off when a low-level signal is input to the control terminal; Specifically, this operational amplifier is used to output a low-level signal when the voltage at the voltage drop detection terminal input to the non-inverting input is less than the first reference voltage input to the inverting input, thereby turning off the second reference voltage switch and turning on the first reference voltage switch, so that the first reference voltage provided by the first reference voltage circuit is input to the inverting input; when the voltage at the voltage drop detection terminal input to the non-inverting input is greater than the first reference voltage input to the inverting input, it outputs a high-level signal to turn on the second reference voltage switch and turn off the first reference voltage switch, so that the second reference voltage provided by the second reference voltage circuit is input to the inverting input; and when the voltage at the voltage drop detection terminal input to the non-inverting input is less than the second reference voltage input to the inverting input, it outputs a low-level signal to turn on the first reference voltage switch and turn off the second reference voltage switch, so that the first reference voltage provided by the first reference voltage circuit is input to the inverting input.

8. As in request item 1, the switching power transistor cutoff control circuit, wherein, It further includes: a second controllable switch; wherein, the first end of the first controllable switch is connected to the power supply end through the second controllable switch, the common end of the first end of the first controllable switch and the second controllable switch is connected to the control end of the switching power transistor, and the second end of the first controllable switch is connected to one end of the switching power transistor and grounded.

9. A switching power transistor cutoff control circuit as described in any of requests 1 to 8, wherein, The switch controller is specifically used to receive the forced conduction signal, the input conduction signal, and the minimum conduction time control signal, and to control the conduction time of the first controllable switch based on the signal with the longest time.

10. A switching power transistor driver chip, characterized in that it comprises: Such as the switching power transistor cutoff control circuit of any of the requests 1 to 9.

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