# VM129 and V Out

When I power my VM129 board by a transformer (230Vac 50Hz to 2x12Vac 500mA) and measure then AC voltage at the ‘AC 12V INPUT’ it shows 12.65V AC which I guess is OK. If I now measure the DC voltage at the ‘V Out’ without anything else connected to the board I get 16.02V DC rather than something close to expected 12V DC. Why is that? The resistor at position R20 is a 4K7.

This is perfectly normal.
Please check theory on bridge rectifiers and smoothing caps.
12.65V x 1.41 -1.2 = 16.6V

OK and thank You.
So, on the board VM129 the V out should be considered as an unregulated 16Vdc / 200mA power output or isn’t 200 mA it’s max amp either.

By the way, can you explain for me the number 1.2 in Your formula?

Vout is current limited unregulated DC out.

1.41 = sqrt (2)

sqrt (2) = 1.41
I was asking about the last number in Your formula and is 200mA correct?

Sorry, I meant 1.41
1.2 = 2 diode drops from diode bridge.

200mA is the max. current, as indicated in the manual, due to the series resistor.

Thank You for Your replies and good bye from now.