Simplistic MosFET HV Shunt Regs

[albertli]

seperated ps box

Hi Salas,

I'm in designing the 2 boxes for my 26 and I know I should run the B+ cable as short as possible, but I have to leave the power box far away from the signal chassis. What is the maximum length I could run my cable from the reg to the signal chassis. Or I could place the reg in the signal chassis by the opt???

BR

Albert

 

[dvb projekt]

Feed the reg´s from your planned PSU chassis and place them into the amp chassis,
as near as possible to the socket of the #26

 

[albertli]

Big thanks

 

[manamanam]

R1 =33R, you can get 60ma!

Thanks Quanghao!

 

[kacernator]

Sudden problem

Hi,

I have sudden problem with Salas regulator. The R5 5.6k resistor burns. I already changed MJE350 for new one, without any success. Has IRF840 failed?

Thanks.

 

[Salas]

That resistor has current (near 1mA normally) determined by IRF840's Vgs. Has to be around 4V. If not, you have a failed Mosfet.

 

[kacernator]

I replaced IRF8400 and still 5.6k burns out. So I changed the whole board regulator and both mosfets for new one. After firing it up the R10 47 Ohm burns out and IRF9610 is dead. Something weird is going on, do you have a clue?

Thanks

 

[Salas]

You have to give the story again so we can think. Where you used it, how set, how sinked, for how long it worked alright, is it P2P, a board, possible changes pre or post reg by then.

 

[kacernator]

I have hybrid amplifier. I was changing power amp regulator from LM317 also to shunt regulator. In preamp I have two Salas shunt regs, one for each channel. Before making the changes to poweramp the amp was running on daily bassis for few months with Salas shunt regs in preamp without any flaw. After firing the modified amp up, one of the preamp reg blew and keeps blowing. Other channel reg works ok. I changed the whole faulty reg board, put new mica insulators, new mosfets in etc. - I did this twice already. At second the reg seems to be running ok, so I tried to measure the output voltage and just when I touched with my DMM on output, the 220 Ohm gate stopper at 9610 blew, diodes seems to be dead and mosfet will be probably dead too (didnt checked that now).
Without regulator preamp is working fine on this channel.

 

[Salas]

So you made extras for the power stage. What technology is the power stage? Tube with output trafo? All the regs are having common power source with the ones that feed the power stage? What is the difference between the good working channel and the blowing one? Something intervenes, like an RC filter, or they are identical the two channels between their regs?

 

[kacernator]

Yes they are identical. It is really strange. The 9610 just keeps blowing.

 

[Salas]

Something interferes in one channel that does not in the other. Is it one or two power regs? Also inform us about the previous questions.

 

[AndrewT]

could the 9610 be failing (or being damaged and failing later) at start up and taking out other components?

 

[Salas]

Easily. Too many parameters. But one fully regulated channel working and other not, is weird. Could be not taking them regs for OPT and oscillating, coupling to others through common power source, but I would expect the same problem in both channels.

 

[kacernator]

Something interferes in one channel that does not in the other. Is it one or two power regs? Also inform us about the previous questions.

There are four power regs, positive and negative for each channel. Everything is star grounded. Power stage is mosfet source follower +12V at 600mA. Seperate trafos for preamp and power amp. Each channel and preamp/power amp has its power supply.

 

[Salas]

In that case, since one channel is OK, its a matter of what is differently made or grounded or... in some detail, or what part failed and is not detected.

 

[kacernator]

Zener diodes

Hi,

how important are the small zener diodes across GS of mosfets? Will they protect regulator from output short circuit?

Thanks.

 

[Salas]

They will protect the gates from transients. Take out all Zeners if in doubt.

 

[kacernator]

I dont have them installed in, never had, so was thinking if zeners could save the mosfet in case when output is shorted?

 

[Salas]

In brief shorted output the most, they can help against fast failures.