Flyback Converter Control Circuit Using Input Output Voltage Sampling
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Solution Overview
Problem
The control accuracy of output current in flyback converters is compromised due to errors in current sampling, particularly caused by parasitic capacitance and sampling delays, which limits the range of dimming and accuracy in both isolated and non-isolated converters.
Innovation Solution
A control circuit and method that utilize first and second sampling modules to output voltage signals reflecting input and output voltages, allowing the control module to calculate and adjust the turn-on time of the switch based on these signals, thereby directly controlling the output current without relying on peak current sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If peak current sampling is used to control output current, then the control method is simple, but the control accuracy deteriorates due to parasitic capacitance and sampling delays
Solution Approach 1:
The patent replaces the mechanical/electrical sampling method (current sampling) with a voltage-based control method. Instead of sampling the peak current Ipk which is affected by parasitic capacitance and timing delays, the invention uses voltage signals from the auxiliary winding to control the switch turn-on time, thereby eliminating the harmful effects of current sampling errors.
2Reliability
If zero-crossing point detection of secondary side current is used to obtain turn-on time, then the timing can be obtained, but the measurement precision deteriorates due to ringing and sampling delay
Solution Approach 1:
The patent introduces an intermediary approach by using the auxiliary winding voltage signal as a mediator to determine the turn-on time. Instead of directly detecting the zero-crossing point of the secondary side current which suffers from ringing and delay, the invention uses the auxiliary winding voltage which provides a cleaner, more accurate timing reference for controlling the switch turn-on moment.
Data Source
AI summary
Embodiments of the present application provide a control circuit and a control method of a flyback converter, the control circuit comprises: a first sampling module, a second sampling module, and a control module; the first sampling module is coupled to the control module and the flyback converter, and outputs a first voltage signal to the control module; the second sampling module is coupled to the control module and the flyback converter, and outputs a second voltage signal to the control module; where the first voltage signal reflects an input voltage of the flyback converter, the second voltage signal reflects an output voltage of the flyback converter; the control module outputs a control signal according to the first voltage signal and the second voltage signal, and the control signal reflects a turn-on time of the switch in the flyback converter.