Negative to Positive DC Voltage Convertor

[basit701]

Hello Guys!

After sorting out the transformer configuration problem for my dual voltage supply, another problem exists now. The digital voltmeter i am using has three wires:
1) +12Volt (to turn on the voltmeter)
2) Ground
3) Voltage Measuring

The voltage is measured with respect to ground wire.

However if i connect the voltmeter supply terminal to +12 V and ground and then measure - voltage it does not measure the voltage. The output voltage shown is zero. I was thinking to use op amp 741 inverting configuration with gain of -1 to convert the -ve voltage to +ve voltage but the op amp VCC and VEE limit is 20 volt and my output voltage is 20+.

Any suggestions to resolve this issue?

[Waff0l]

I say, take a different opamp which can operate at higher supply voltages like a LM2904


-edit - which is still too small  , also, does your DVM measure above +12V (its supply voltage)?

[Zero999]

The LM2904 has a maximum total supply voltage of 36V which is no better than the uA741. In fact the uA741 (not the C version) has a maximum total supply voltage of 44V.