As shown, the circuit adds an optical coupler (CNY75A) and adjustable precision shunt regulator (TL431). Current limiting resistor R3, R4 and R5 for the sampling resistor. When
Uo changes, the voltage on the sampling and TL431 internal 2.5V reference voltage, K side potential changes, changes CNY75A the launch tube (LED) operating current and luminous intensity, and then through the optocoupler to adjust the control WSl57 side current, duty cycle can be finely adjusted to achieve precise purpose of regulation. CNY75A electrical isolation also play a role. Found this switch Sv 0.1% power, SI 0.78%.