Simplistic MosFET HV Shunt Regs

[mbrennwa]

I am thinking about my next tube project. This will need some 440 VDC for B+ at 60 mA or so. I found an SSHV2 kit in my parts box (2 boards + parts), sooo... but wait! The SSHV2 is rated to 380 VDC max. output, which is too low for my project. Can I modify the SSHV2 to suit my needs? How?

 

[Salas]

First you would need a higher voltage rated Q1 like the IXTP01N100D then you should use higher value R9 R10 like 82k. Watch the isolation to main sink be good and better use a sturdy Schottky diode instead of the D3 Zener for faster low threshold clamping.

 

[Vernonia1]

Salas I was thinking of using the SSHV2 as the bias supplies for my 6550/KT88PP driver (-200V, 10mA)and output stage (-100V, 4mA) grid bias. Do you see any issues with this implementation?

 

[Salas]

But this is a positive polarity supply unit and you need negative bias voltages

 

[Vernonia1]

OMG.......... I knew that

 

[mbrennwa]

First you would need a higher voltage rated Q1 like the IXTP01N100D then you should use higher value R9 R10 like 82k. Watch the isolation to main sink be good and better use a sturdy Schottky diode instead of the D3 Zener for faster low threshold clamping.

Thanks! I don't quite understand "use a sturdy Schottky diode instead of the D3 Zener for faster low threshold clamping". I actually don't understand what this diode does, or how the error amp works, so... could you recommend a specific part?

 

[Salas]

Its a protection measure for Q5 and Q6 while C2 charges and there is voltage difference or for when there is bad handling or some transient. Say an MBR1100. Same orientation as the silkscreen shows for the D3 Zener.

 

[merlin el mago]

Salas will be very complicated to mod the schematic to have no NFB?

 

[Salas]

NFB is inherent in this, doesn't have an external control loop to break. No NFB would mean no regulator basically but a passively stabilized PSU like the DCSTB for the DCG3 but in HV form.

 

[merlin el mago]

Thanks for your explanation.

Salas do you know where to buy in Europe the IXTP08N50D2 or IXTP01N100D?

TIA
Felipe

 

[euro21]

where to buy in Europe the IXTP08N50D2 or IXTP01N100D?

IXTP01N100D mouser.com

IXTP08N100D2 too.

 

[merlin el mago]

Mouser is very expensive 20€00 shipping

 

[euro21]

Over 50 Eur the shipping is free.

 

[merlin el mago]

Thanks Bela.

 

[joztom]

This is the best supplier:
Transfer Multisort Elektronik – Spletni katalog | 220.000 izdelkov v ponudbi

Delivery is about 9€ per DHL

 

[euro21]

Only these Ixys made MOSFETs are depletion types.

Technology

 

[euro21]

using IXYS MOSFETs in HV application

As you can see in my previous post, IXYS made several depletion mode FETs, but only some practically usable in tube DIY.

High (500...1000V) voltage, low -few hundred mA- current (smaller surface=smaller capacitances), moderate Ciss, extra low Crss and Qg (charging storage).

RDS(on), dissipation (PD) and thermal coefficient (RthJ) are not so important.

 

[acamilicko]

First you would need a higher voltage rated Q1 like the IXTP01N100D then you should use higher value R9 R10 like 82k. Watch the isolation to main sink be good and better use a sturdy Schottky diode instead of the D3 Zener for faster low threshold clamping.

Hi Salas,

I have a similar request for more than 400V, and don't have IXTP's locally, but what I can find are for example: STP3NB60, BUZ77B (600V) and IRFBG30 (1000V). Can I use some of those?

Thanks

 

[Salas]

It must be depletion mode NMOS (normally on). All those you mentioned are enhancement mode (normally off) usual parts.

 

[acamilicko]

Jesus, I must read a bit electric parts theory before I ask... Thanks for explanation! Cheers!