In a typical implementation, the EN/UV pin is driven by anoptocoupler. The collector of the optocoupler transistor isconnected to the EN/UV pin and the emitter is connected tothe SOURCE pin. The optocoupler LED is connected in serieswith a Zener diode across the DC output voltage to be regulated.When the output voltage exceeds the target regulation voltagelevel (optocoupler LED voltage drop plus Zener voltage), theoptocoupler LED will start to conduct, pulling the EN/UV pinlow. The Zener diode can be replaced by a TL431 referencecircuit for improved accuracy.