The Optoisolator IC (Error Amp) In Power Supply
In this new article, we will now be talking about the use of the Optoisolator IC which is commonly used in the feedback circuit on a variety of power supplies that are autovolt on my opinion. Most power supplies like DVD players and Chargers that I have repair using an Optoisolator IC with a value of PIC817, this power supply is autovolt, which means it can be plugged either on a 220 volts or 110 volts supply source.
According to Sirkevin, an ELAB forum member:
If you are repairing a power supply that do not use Optoisolator IC as a feedback that means if all the secondary output voltages read zero volt then we can say that the primary section have problem. It could be a dry joints, a broken circuit track , bad FET and power IC, leaky or shorted diode and transistor, cap that have high ESR or even an open circuit in resistor (start up resistor). However if the power supply use Optoisolator IC then there is chances the secondary side components that corresponding to the Optoisolator IC may have problem. If you concentrate only on the primary section, i can say you may not find out the culprit. A shorted optoisolator IC and TL431 IC could cause no power symptom (zero output voltage) and you may thought that it was the primary section fault.
Understanding the design of the power supply is one of the key to be successful in repairing power supply. Practicing repairing different type of power supply (don’t just do repairs-you have also to understand how it works) will make you better in repairing any type of power supply problems.
In Optoisolator IC also called as an optocoupler, photocoupler, or optical isolator, a shorted pin 3 and 4 pin ,which is the side of the photo transistor, could result to no secondary B+ voltage output while a shorted pin 1 and pin 2, which is the side of the LED, could result to over voltage in the secondary B+ output.