Hi folks,

As diving into solar inverter circuit diagrams, I have just noticed a circuit that I didn't get its purpose use, which is the supply circuit for UC3845 in the main SPS in VMII inverters.

I have attached a screenshot for reference (The part where exists the 2SC5353).

I just wondered why we don't eliminate all the transistors and zener diodes and keep only the series 50K resistor.

If anyone can explain the circuit would be highly appreciated.

Best Regards

That is a very basic linear regulator, which will regulate to the zener voltage - ~1.2V.

I would assume it is there because the supply voltage is a lot higher than they want into U8?

Yeah correct, the supply voltage is about 180V.