The flyback conversion circuit converts electric energy into magnetic field energy and stores it in the transformer when the switch tube is turned on, and then converts magnetic energy into electrical energy and transmits it to the load when the switch tube is turned off.
The single-ended flyback conversion circuit is derived from the Buck-Boost conversion circuit. The circuit diagram is shown in the figure
For the principle design of the flyback conversion circuit, please refer to the article "DC/DC: Single-ended flyback DC conversion circuit design and matlab/Simulink simulation (including source code)".
Closed-loop control circuit: use PI control as the controller to build a voltage single-loop feedback control isolated flyback converter. The control circuit is shown in the figure:
First, set the expected output voltage value U_ref according to the requirements of the technical indicators, and make a difference between the expected output voltage value U_ref and the actual voltage value U_o to obtain the current control error U_eer. The amount Uc1 is limited by the upper and lower limits to obtain the current control amount Uc, and Uc is compared with the sawtooth wave Sw to obtain the current PWM pulse. When the input or load of the Buck converter changes, the current output voltage U_o will change, and the feedback control circuit will automatically generate a new control value U_c. After comparing with the sawtooth wave Sw, a PWM pulse with a new duty cycle is obtained. Thereby adjusting the main circuit to quickly recover to the desired output voltage value.
Experimental simulation:
Technical indicators: Design a closed-loop isolated conversion DC voltage power supply with an input of 12V-24V and an output of 30V , and use a PI controller to build a voltage feedback circuit .
Simulation circuit model building
See the simulation program at the bottom of the article
Experimental results
Input 12V, output 30V
Input 18V, output 30V
Input 24V, output 30V
How to obtain the simulation program: V♥ Gonghao " Positive Energy Electronics Technology "