PLEASE I NEED HELP.
I came across two inverter circuit , one has optocoupler as its feed back path, while the other does not but they both serve the same purpose of ensuring output voltage of the inverter does not drop. My question is , what is the reason for the 4N35 optocoupler ? which function does it perform ?

19 views yet no comment, nawa oo.

Very simple - voltage isolation, the optocoupler maintains the isolation
between the output and input.

nisol:
Very simple - voltage isolation, the optocoupler maintains the isolation
between the output and input.

Not only voltage isolation, but voltage regulation.
Here's what the optocoupler does; The inverter chip usualy has two pin for sensing feedback voltage. One of the pin is used for setting the reference voltage using a resistor voltage divider network, the other pin is used for sensing the feedback voltage coming from the output of the inverter.
When the feedback voltage exceeds the reference voltage, the chip shuts off the two output pins driving the MOSFETs. When the reference voltage exceeds the feedback voltage the chip switches on the two output pins.
Without the feedback,the circuit would still run but without a voltage regulation and the device would operate at full power despite no load being connected to its output.
So here's how the voltage regulation is achieved; let's take for example, we set our reference voltage to be 4.5v. Then we generated 5v dc from the output (220v ac) using a voltage divider network and diodes. We then feed this 5v to the feedback pin.
Whenever we switch on the circuit, due to the reluctance of transformers, the output voltage wouldn't swing to 220v instantly. It will ramp from 1v-2v-3v until it gets to 220v, so does the 5v extracted from the output. This transition takes some few nanoseconds. Now let's concentrate on the 5v fed to the feedback pin. Once this voltage reaches 5v the feedback voltage has now exceeded the reference voltage. The chip will then shut down the two output pin. When this happens the 5v being generated from the output will go down to 4.9v-4.8v-4.7v-4.6v-4.5v-4.4v and so on. This transition takes less nanoseconds than the ramping up. The chip having sensed the feedback voltage to be 4.4v which is lower than the reference voltage, will now switch on the two output pins and the power production continues. This cycle is repeated endlessly. The implication is that inverter will never allow the feedback voltage to exceed 4.6v. And because this feedback voltage was gotten directly from the output, the output voltage also will never exceed a certain voltage, even when a load is connected to the output. It is a kind of pulse width modulation technique