Hysteresis comparison control circuit

Abstract

The invention relates to a hysteresis comparison control circuit. According to one scheme, the hysteresis comparison control circuit comprises two same self-locking circuits, a positive feedback branch, a power supply voltage input end, a power supply voltage output end, a control signal input end and a grounding end; the self-locking circuit comprises two switching tubes, a diode and three resistors; the anode of the diode is connected with a control signal input end, the cathode of the diode is connected with the control end of the first switch tube through the first resistor, one end of the second resistor is connected with the control end of the first switch tube, the other end of the second resistor and one end of the first switch tube are jointly connected with a grounding end, one end of the second switch tube is a self-locking circuit input end, and the other end of the second switch tube is a self-locking circuit output end; the input end of the first self-locking circuit is a power supply voltage input end, and the output end is connected with the input end of the second self-locking circuit; the output end of the second self-locking circuit is a power supply voltage output end; and the positive feedback branch can maintain the state of the power supply voltage output end after the control signal is cancelled. According to the invention, self-locking and self-unlocking can be realized.

Description

technical field [0001] The invention relates to the technical field of electronic circuits, in particular to a control circuit with a hysteresis function. Background technique [0002] A complete switching converter usually has various protections, such as input under-voltage protection, output over-voltage protection, output short-circuit protection, output over-current protection, over-temperature protection, etc. In order to obtain reliable protection, these protection circuits often use automatic The lock circuit is controlled. [0003] Such as Picture 1-1 As shown, it is the existing self-locking circuit. Its working principle is that when the voltage of the control signal Vc is higher than a certain value to make the NPN transistor Q1 conduct, the PNP transistor Q3 is also conducted, and the output voltage Vout is high. Level, Vout is powered by the input voltage Vin, specifically, Vout=Vin-VEC3 (VEC3 is the voltage drop from the emitter to the collector of the triod...

AI Technical Summary

Problems solved by technology

but Figure 1-2 The problem with the circuit shown is that when the temperature of the converter decreases so that the resistance of the NTC thermistor RT1 increases and the control signal Vc decreases, the output voltage of the converter is still zero because the circuit is self-locking and cannot be unlocked by itself. Self-recovery cannot be realized. If you want to restore the output of the converter at this time, you need to power off the input voltage of the converter and re-supply the converter. Obviously, this artificial power-off and restart operation is more cumbersome

However, if the ambient temperature where the customer uses the converter product is lowered or the load of the converter is reduced so that the temperature of the converter is lowered, in order to save energy, the fan is no longer required to run to cool the converter, and the temperature of the NTC thermistor RT1 will drop. As the resistance increases, the control signal Vc decreases, but because the circuit is self-locked and cannot be unlocked by itself, the output voltage Vout will continue to supply power to the fan, which will cause unnecessary energy loss because the fan cannot be powered off, and the life of the fan will also decrease. sharply shortened

[0006] Obviously, Picture 1-1 The reason why the self-locking circuit in the circuit is self-locking is due to the addition of a positive feedback branch composed of diode D3 and resistor R5. When the divided voltage generated by diode D1, resistor R1A, and resistor R1B is approximately equal to the conduction voltage drop of transistor Q1, transistors Q1 and Q3 will be in a continuous oscillation state of conduction-off-conduction, resulting in the output voltage Vout also It will oscillate back and forth between high and low levels. Obviously, the working state of such a circuit is not stable

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