Circuit and method for switch power supply feedback voltage detection and sampling and holding

Abstract

The invention provides a circuit and a method for switch power supply feedback voltage detection and sampling and holding. The circuit provided by the invention comprises a clock control circuit, a control sampling clock, a sampling and holding circuit, a waiting state control circuit, a learning state control circuit, an increment control circuit, a system control circuit and a delay circuit, wherein the sampling and holding circuit samples an input voltage at different time in two paths and selects a larger value to be output; the waiting state control circuit controls sampling and waits till a waveform is stable; the learning state control circuit controls the time sequence of a learning state; the increment control circuit controls an increment circuit which realizes two adjacent times of sampling; the system control circuit controls a finite state machine together with other circuits; and the delay circuit realizes required delay. In the method of the invention, an entire switching period of a switch power supply is divided into five states in turn: a PWM open state, a waiting state, a learning state, a detection state and a demagnetization ending state; the five states form the finite state machine; and the detection and sampling and holding of a feedback voltage can be realized by controlling the state switching and output of the finite state machine.

Description

technical field [0001] The present invention relates to integrated circuits. More specifically, the present invention relates to a control circuit of a switching power supply chip. Background technique [0002] Switching power supplies have been widely used in various electronic devices. For safety, switching power supplies use transformer isolation, which provides isolation between the primary and secondary. In order to stabilize the system output, the system should work in a negative feedback closed-loop state. The classic approach is to use optocoupler devices and TL431 to achieve isolated feedback. But the cost of the system will increase a lot. In order to reduce costs, the auxiliary winding of the transformer has been used to realize the feedback of the power output. Of course, this method is also isolated and safe. However, many technologies cannot accurately measure the feedback voltage of the transformer, such as Randolph D.W. Shelly's US patent (US4302803) "Re...

AI Technical Summary

Problems solved by technology

However, the accuracy of these existing technologies is not high, the error of the sampled feedback voltage is large, and the output voltage of the system cannot be precisely controlled

And the consistency of the transformer parameters is high, which increases the product cost

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