.The Isocom TLP521-1XGB optocoupler is a 4-pin DIP device with a phototransistor output and is ROHS compliant. It can provide 0.1 volts at 1 mA and 20 mA of current. This optocoupler is used to prevent high voltage spikes from damaging sensitive electronic components by providing an isolated barrier between them. It can also be used to provide a level of protection from electromagnetic interference (EMI).