Simplistic Mosfet HV Shunt Regs - Page 409 - diyAudio
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Old 30th August 2013, 07:09 AM   #4081
Cassiel is offline Cassiel  Libya
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To make myself completely clear, I read you say that too much series resistance is bad, so if 355 volts is too much for the circuit I'm thinking of increasing the regulator current to drop as much voltage as possible in my CRC filter, maybe a 800 ohm resistor would be OK.

*Now I'm thinking that at startup before the regulator starts sinking current maybe there would be too many volts for the transistor regardless of my resistor. Damn I hate to be in the dark. I shouldn't have started this nightmare.
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Last edited by Cassiel; 30th August 2013 at 07:33 AM.
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Old 30th August 2013, 09:38 AM   #4082
Salas is offline Salas  Greece
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At 30mA CCS we are talking only 3W dissipation on the input Mosfet at 100V dif.
Which is fine for 10mA load. Maybe with 68 Ohm R1 (verify in practice). I guess you may try it at 250V out.
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Old 30th August 2013, 06:35 PM   #4083
Cassiel is offline Cassiel  Libya
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OK thanks, that resistor sets the current but I'm worried about the MPSA92. In your 400 volts schematic you replaced it with the 2n6520. My question was: can the MPSA92 take 350 volts input voltage? I also have mj350's but, as I know next to nothing about transistors, I'm afraid a copy and paste wouldn't work. My ideal B+ out is 300 volts.
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Old 30th August 2013, 08:19 PM   #4084
Salas is offline Salas  Greece
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It won't see the input voltage, only the output voltage. At 250V and 4K7 load it should be comfortable for own dissipation. Maybe in 300V also. Say 280-290V to be safer. MJE350 will work too but the MPSA92 is faster if it will endure. 20MHz VS 5MHz.
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Old 30th August 2013, 08:27 PM   #4085
Cassiel is offline Cassiel  Libya
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Thanks I was waiting for your reply. All systems green. There I go, may the force be with me.
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Old 8th September 2013, 01:49 AM   #4086
Cassiel is offline Cassiel  Libya
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Default The first casualty

Hi again, the 470 ohm resistor at the 9240's gate is toast. Also the cap that bypasses the LED's gets too hot. Well everything gets too hot but I reckon that cap shouldn't. Any ideas? Regulator works. Here's a picture.
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Old 8th September 2013, 02:25 AM   #4087
Cassiel is offline Cassiel  Libya
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I must add that I was measuring things when, for a fraction of a second, the lights went out (LEDs) but everything went back to normal. After a while I smelled the stink and sure enough, that resistor was toast. The regulator still works.



*OK, I read 840 Ohms between Gate and Source. Is this normal?
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Old 8th September 2013, 06:47 AM   #4088
Salas is offline Salas  Greece
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Some oscillation must have happened while you were probing. The resistor probably survived though charred. Else, without gate drive it would not work.
Replace the gate resistor and use a low ESR LEDs cap when able. That one cap you got now just remove it.
It should read 3-4V between gate and source when the 9240 is working. Congratulations for having a hardwired reg working on first time despite a small incident.
Don't probe around the MOSFETs if not necessary. It should be hot on both MOSFETs when everything works of course.
Measure the voltage drop on R1 and divide by its value to know at what CCS current your reg runs.
If you did not use a load on the output then the parallel part (840) was at its hottest because it did not share a portion of the available current.
You should keep a proportion of 20-30mA extra current on top of your target load max demand. That you can arrange by judging R1 value.
*For anybody else reading this is the SSHV0 we talk now with BJTs in the Vref, big Mosfet etc. As in post #2. A retro design that many still like for its "warm" tone.
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Old 8th September 2013, 02:40 PM   #4089
Cassiel is offline Cassiel  Libya
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OK thanks, that I will do. I have to congratulate you as well because it took me ten seconds to realize my preamp sounded so much better with your regulator on.

The circuit regulates - playing with the trimmer the minimum difference between voltage in and voltage out is 36 volts. This is my second circuit in this kind of board, first one was just a single transistor (a Dallas Rangemaster) guess I was lucky until I pushed my luck too far, that is.
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Old 1st October 2013, 08:45 PM   #4090
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Salas:
I'm using your SSHV2 feeding four triode halves (balanced amp) and each one of the triodes is CCS'ed on the anode with cascoded DN2540's. Normally when running this circuit i have a small 0,1 - 1,0uf coupling cap before the ccs's. And today i do have two small 0,1uF caps there, and it sounds really great to my ears. But would you recommend to remove them? or should i have one of them left or what would you think?
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