# Half wave rectifier question

Discussion in 'General Electronics Chat' started by coinmaster, Mar 16, 2016.

1. ### coinmaster Thread Starter Member

Dec 24, 2015
342
6
So I have a transformer winding that is 15vac and I'm trying to get 20vdc out of it using a half wave rectifier but it is acting weird.

V1 signifies the transformer winding.
I'm getting 0v at the junction between D1 and C1 and I'm getting -20v at the junction between V1 and D1. If I reverse the diode then I get +20v at the junction between V1 and D1. Why am I getting DC at the input and not at the output?

2. ### mcasale Member

Jul 18, 2011
210
12
First thing is to add a load resistor across C1, because you are charging C1 to the peak value of V1 (15*1.414 = 21.2v). The simulator likes at least a small load.

If you are measuring at the + side of V1, you should see V1 - only AC - no DC. Are you using an oscilloscope or a multimeter?

3. ### coinmaster Thread Starter Member

Dec 24, 2015
342
6
Well the simulator works fine. It's real life that is acting weird. V1 is just representing my transformer.
Multimeter.

4. ### crutschow Expert

Mar 14, 2008
12,498
3,059
Sounds like something in your circuit is wired incorrectly.
What type of transformer is it?
The real circuit should basically act the same as the simulator shows.

5. ### coinmaster Thread Starter Member

Dec 24, 2015
342
6
It's a toroidal transformer I pulled from a tube amp.
I'm using a 15v output wire and connecting the diode and capacitor to it as shown in the simulator, actually the wire is 30vAC because it is connected in series but the winding itself is being rectified.
It's reading 21v AC and -20v DC on the winding and 0v at the diode-capacitor junction.

EDIT: Actually I just noticed the 15v wire is connected in series to the other toroidal so it is 30vAC by default, not 15v.

Last edited: Mar 16, 2016
6. ### crutschow Expert

Mar 14, 2008
12,498
3,059
I don't understand what you mean by "the winding itself is being rectified"?
If that a separate rectifier from the external rectifier, then that would explain your results.

7. ### coinmaster Thread Starter Member

Dec 24, 2015
342
6
As in the transformer coil itself is being rectified to DC. But I just solved it, there was some outputs on the transformer that needed to be connected to ground. Thanks for the help