Suitable diodes.

[kickerfox]

I'm building a 12vdc to 350vdc power supply for a mobile tube application and I'm having some troubles. I can light a pair of 120v 40w lamps in series right off the secondary. With the rectifier diodes installed and no load I get 350vdc regulated output but as soon as I place a load on the output the diodes get hot and it can not light the lamps.

I have 4 1n5399 diodes in there now. Rated at 1000v 1.5a 2us. Are they not fast enough?

The attached schematic is roughly what I'm dealing with. I may have modified some values here and there. I'm using an un-gapped core from a PC PSU which I rewound with 10 turn CT primary and 160 turn CT turn secondary.

 

[MicrosiM]

I'm building a 12vdc to 350vdc power supply for a mobile tube application and I'm having some troubles. I can light a pair of 120v 40w lamps in series right off the secondary. With the rectifier diodes installed and no load I get 350vdc regulated output but as soon as I place a load on the output the diodes get hot and it can not light the lamps.

I have 4 1n5399 diodes in there now. Rated at 1000v 1.5a 2us. Are they not fast enough?

The attached schematic is roughly what I'm dealing with. I may have modified some values here and there. I'm using an un-gapped core from a PC PSU which I rewound with 10 turn CT primary and 160 turn CT turn secondary.

Try any thing like MUR series, or any thing fast, that diode you are using will heat because its slow and its not for SMPS Use.

 

[kickerfox]

Try any thing like MUR series, or any thing fast, that diode you are using will heat because its slow and its not for SMPS Use.

Anything axial lead about the size of the 1n400x or 1n53xx?

How does this waveform look? It's off the drain of one of the mosfets.

 

[kickerfox]

Found some 1000v 1a 200us diodes that worked. That's the fastest thing the electronics shop had that would fit in my board. I now have over 100w worth of 350vdc.

165w in gets me ~120w out. Not the most efficient supply but it's working. Would dialing in the frequency help the efficiency? I'm at around 50khz currently.

 

[wally7856]

I do not even understand why it is working at all. You have the diodes configured for a +- supply but have the - diodes D4 and D5 shorted to your main circuit ground.

 

[kickerfox]

I do not even understand why it is working at all. You have the diodes configured for a +- supply but have the - diodes D4 and D5 shorted to your main circuit ground.

They are connected to ground, not shorted. There is no connection to 0 of the 175-0-175 output. This is a single rail supply. 250v caps are cheap.