A circuit avoiding leading edge overshoot

Abstract

The invention discloses a circuit for avoiding leading edge overshoot, which includes a power load or a power transmission load; a power switch tube Q2; an RC constant circuit; a constant control and performance optimization resistor R2, which cooperates with the RC constant circuit to control the overshoot signal shielding switch tube The control signal of Q1; the overshoot signal shielding switch tube Q1, which is used to shield the leading edge overshoot of the current sampling signal generated by the power switch tube Q2; and the system protection circuit. The beneficial effects of the present invention are: avoiding the leading edge overshoot of the detected signal produced by the switch tube Q2, realizing the protection circuit to monitor and protect the power switch tube in each working cycle, and protecting all The signal with leading edge overshoot generated by controlling the switching of the switch tube with high and low levels is practical, has the characteristics of strong practicability, simple circuit structure, convenient debugging and low production cost.

Description

technical field [0001] The invention relates to a circuit for avoiding leading edge overshoot, and relates to the technical field of electronic circuit control. Background technique [0002] Electronic circuits with power switches are more and more widely used in real life, such as switching power supplies, motor drives, high-frequency heating, etc. In these fields, the power switch tube is used as the core component to achieve power output and adjust the power level. However, it is a vulnerable part. If the system circuit is not protected or the response of the protection circuit is slow, the power switch tube will be easily damaged, which will affect System stability. [0003] In order to protect the power switch tube, engineers have designed various protection circuits, some of which use current transformers to sample current signals, but current transformers are mainly used in occasions where the current signal is an AC signal, such as a full bridge circuit And in the ...

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Problems solved by technology

In these fields, the power switch tube is used as the core component to achieve power output and adjust the power level. However, it is a vulnerable part. If the system circuit is not protected or the response of the protection circuit is slow, the power switch tube will be easily damaged, which will affect system stability

[0003] In order to protect the power switch tube, engineers have designed various protection circuits, some of which use current transformers to sample current signals, but current transformers are mainly used in occasions where the current signal is an AC signal, such as a full bridge circuit And in the half-bridge circuit, if it is a unipolar circuit, the current transformer is usually used before the rectifier bridge, and the fastest sampled signal frequency is the power frequency, so for the unipolar DC signal, use the current transformer The protection circuit made is difficult to realize that the power switch tube whose working frequency exceeds the power frequency can be detected and protected in each cycle of its actual work. In addition, the cost of sampling the current transformer is usually higher than the sampling cost of the sampling resistor.

In fact, when the switch tube is turned on, the power current passing through the inductive load is theoretically a triangular wave. If a sampling resistor is used to sample the current, according to Ohm's law, the voltage on the sampling resistor will be a triangular wave that is strictly proportional to the current. The peak value appears at the moment when the switch tube is turned off. This feature makes it easy for designers to control the peak value of the current flowing through the switch tube. The current signal passing through the switch tube is not an ideal triangular wave, but an overshoot will appear at the leading edge of the ideal triangular wave, and because the power load requires that the power loop impedance should not be large, and considering the heating problem of the sampling resistor, the sampling resistor is generally taken as The value is very small, according to Ohm's law, the voltage signal after sampling by the resistor is also very small, and the semiconductor element has a conduction voltage, which makes it difficult to process the sampling signal with leading edge overshoot current, if let The protection circuit directly judges the current sampling signal, so the protection circuit often misjudges the short overshoot signal of the current sampling waveform as the effective peak current generated by the power load flowing through the power switch tube. In this way, the protection The circuit will make a wrong turn-off protection for the power switch tube. Therefore, many circuits that use sampling resistors to sample current waveforms for protection usually smooth and filter the entire signal and take the average value for protection judgment. In this way, the protection of the circuit The response speed cannot keep up with every cycle of the power switch tube, and the performance of such a protection circuit is far behind the protection circuit that can monitor and protect every cycle of the power switch tube, and the performance of the protection circuit directly affect the performance of the entire system

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