[dude_500]

I'm working on building a 150V supply for an amp and have an isolation transformer. I also have 1N5062 diodes to use in the rectifier design.

Right now I have build a full wave rectifier with 2 diodes, positives connected to the AC terminals with the center-tap ground. I get nothing out of this for some reason. No DC voltage is read at all. I read the AC voltage before the two diodes, but no DC voltage after it with respect to the center tap ground. Is there perhaps some characteristic of this diode I don't understand?

I was thinking of trying a 4-diode full wave bridge rectifier design, but then wasn't sure about grounding. From what I've found online, I would get negative aspects of the AC wave into the negative output of the bridge so wouldn't it short out/be unsafe to place that negative onto chassis ground? Would that design require isolated ground? I'd really rather not need isolated ground.

 

[ivant]

Is this how you connected?

Just realised... 1n5062 is an avalanche diode. Similar to zeners, they conduct in reverse. Not suited for this application
http://en.wikipedia.org/wiki/Avalanche_diode

 

[dude_500]

Yes that is exactly how I have it wired, and have made other supplies this way before but it doesn't give any voltage. I'm wondering if somehow these diodes are non-standard or something? I was suggested to use these diodes in particular so I'm not sure what's going on.

 

[dsavitsk]

Quote:

Originally Posted by ivant /img/forum/go_quote.gif Just realised... 1n5062 is an avalanche diode. Similar to zeners, they conduct in reverse. Not suited for this application

Not so. They work great, and in fact have the advantage of effectively a built-in snubber which reduces switching noise -- by one account to 25dB below that of the 1N4007.

Tyler, take a step back and be sure everything is connect correctly, that you have the right diodes in the right way, etc. Remember, these are dangerous voltages so care and patience is required. Be sure the fuse is not blown -- you are using a fuse, right?

If need be, try something like a 1N4007 to see if you can get the circuit working with a different part. But, the 5062's will sound better.

 

[ivant]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif Not so. They work great, and in fact have the advantage of effectively a built-in snubber which reduces switching noise -- by one account to 25dB below that of the 1N4007. Tyler, take a step back and be sure everything is connect correctly, that you have the right diodes in the right way, etc. Remember, these are dangerous voltages so care and patience is required. Be sure the fuse is not blown -- you are using a fuse, right? If need be, try something like a 1N4007 to see if you can get the circuit working with a different part. But, the 5062's will sound better.

I'm not a pro in circuit design so i might be wrong. Whats the advantage in using an avalanche diode in this application that calls for a normal diode anyway?

 

[dude_500]

It is fused but it isn't blown. If I AC test directly on the transformer side of the diodes I get 130 AC, however just past the diodes I get nothing on a DC test with negative on the chassis. The center tap is connected to my grounding lines and chassis.

The diodes point correctly unless these are marked backwards or something. The lines point away from the transformer.

 

[dsavitsk]

check to make sure your diodes still conduct.

 

[dude_500]

Interesting, I get 12M ohm probing "backwards" and 6M ohm in the proper meter orientation on the diode.

I also get this on completely new and unused backup diodes. Is it possible I actually got a "bad batch"? They are from mouser.

 

[dsavitsk]

You need to use the diode setting on your meter -- the resistance setting won't overcome the forward drop.

 

[dude_500]

My meter shows 0.5V passing through in diode mode in the correct direction and 0V backwards, so I guess the diodes are fine.

I'll re-check the wires tomorrow, but I don't understand how this is possible. Literally 1 millimeter before the diodes there is 130AC and 1 millimeter after the diodes directly join there is no DC power. I've checked that the center-tap ground is connected to the chassis numerous times.

 

[dude_500]

I looked at the data sheet and it looks like the center tap is actually a non-connected "static shield". This would definitely cause the problems I'm having.

I'll need to use 4-diodes in a bridge configuration, but what I don't understand about bridges is it seems to me that the negative side of the bridge output will be as far negative voltage as the positive side is positive. Do I need to keep my post-rectifier ground isolated from the chassis (which is earth grounded), or is the negative terminal of the bridge actually neutral somehow?

EDIT: Disregard the question, I did some testing and found that there was no relative voltage between the chasis and either the positive or negative terminals of the bridge, since it is isolated by the transformer. It hooks up fine and gives me a nice 175V at the end of the capacitor grid.