The circuit shown on this slide has voltage control loop implementation, sensing the voltage across the voltage divider on the output of the power supply and driving the optocoupler to provide feedback to the primary side controller. The optocoupler provides an isolation barrier of up to 2,500 volts of isolation. This allows for providing feedback to the primary side without ever having the possibility of the high voltage on the primary side ending up on the secondary side, presenting a shock hazard to the user or damaging the electronics on the secondary side. Therefore, an optocoupler, which ST does not provide, is used as part of the feedback loop with the CV/CC controller. What the device provides is the constant voltage and constant current control signal that is fed back through the optocoupler which provides an isolation barrier similar to what a transformer does.