Simplistic MosFET HV Shunt Regs

Avoid a peak. For various reasons, not only possible harm. Glitches can activate the choke to radiate an interference field. 220uF standard value for C2 should be enough for your moderate mA.

This is a detail of the simulation 20 seconds after the start of the AC. The initial ripple has been eliminated. So the shunt should filter out the residual ripple? Would I have a good power section like this?
 

Attachments

  • 2019-10-16 (3).png
    2019-10-16 (3).png
    150.7 KB · Views: 293
  • 2019-10-16 (4).png
    2019-10-16 (4).png
    139.4 KB · Views: 294
diyAudio Chief Moderator
Joined 2002
Paid Member
Dissipation of it is Vout*Ibias where Ibias is the extra current you allow in the CCS setting beyond the load's own consumption. If it is 20mA extra as usually recommended then 80V*20mA is 1.6W. That's roughly because a little of it goes to the other transistors.

So you don't need a really big sink for the shunt MOSFET in your case. You had used a big sink in your picture link so its cool for that but you could also be using less than 20mA extra right now. If so, adjust the CCS setting accordingly.

Don't test the shunt reg unloaded for long when with smaller sink because it will be burning the whole CCS setting of mA at 80V on the shunt MOSFET in such an occasion. 1.6W becomes 6.4W then.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
The total load is 70mA, 2x15mA for the two preamplifier channels and 2x20mA for the two shunts. Then I will proceed to the construction of the filtering as well as to simulation.

If not satisfied in the end, two RC branches after the CLC (one going to each reg's input), could be easily added to improve ripple filtering while contributing some isolation between them.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
Hi Salas

I am building a SSHV2 for my phono amp which has estimated power consumption of 200mA at 250V. With 270V input and a 2K resistor as load, I adjusted R4 with voltage at TP at maximum 1.07V but the output only has 206V.

Which part should I check to diagnose the problem ?

Your T.P. shows that you got 107mA max to provide but your 2K test load wants 125mA to sustain 250V so the output current limits and drops the max voltage. Absolute CC max depends on individual DN2540 IDSS characteristic. Spec printed next to T.P. R5 on the SSHV2 diagram in the guide says good for 20-100mA setting. All those things point to your build works as expected.

200mA at 250V is 50W by the way. Are you sure such a spec is right for a phono? 20mA maybe?
 
Your T.P. shows that you got 107mA max to provide but your 2K test load wants 125mA to sustain 250V so the output current limits and drops the max voltage. Absolute CC max depends on individual DN2540 IDSS characteristic. Spec printed next to T.P. R5 on the SSHV2 diagram in the guide says good for 20-100mA setting. All those things point to your build works as expected.

200mA at 250V is 50W by the way. Are you sure such a spec is right for a phono? 20mA maybe?

Hi Salas

Thanks for your prompt reply. Attached my phono amp schematic, could you advise the power consumption of the amp?
 

Attachments

  • Toccoto MK II Pre-amp.jpg
    Toccoto MK II Pre-amp.jpg
    92.1 KB · Views: 356
diyAudio Chief Moderator
Joined 2002
Paid Member
Can't say anything sure off hand. Guessing about 15mA for the output stage, about 3mA for the second stage and about 1-6mA for the input stage depending on k147 idss. So 19-25mA per channel maybe. But I could be guessing way off.

Configure your DMM in series mA mode and measure pulled current between your previous PSU +Vout and the preamp's +V input point. That's the only proper way to know.
 
Can't say anything sure off hand. Guessing about 15mA for the output stage, about 3mA for the second stage and about 1-6mA for the input stage depending on k147 idss. So 19-25mA per channel maybe. But I could be guessing way off.

Configure your DMM in series mA mode and measure pulled current between your previous PSU +Vout and the preamp's +V input point. That's the only proper way to know.

Thanks Salas

Your guessing is very close, actual consumption is 59mA.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
That's for two channels consumption I assume. One PSU for both. In that case set SSHV2 for T.P. 0.8V i.e. 80mA CC*.
To simulate around 60mA actual load at 250V the equivalent dummy load would be 4K.
Say 3x12K 10W resistors in parallel or 4x1K 5W-10W resistors in series.
They will burn 15W like two channels of the real preamp would. So be careful where you sit them and how you handle them.
The shunt MOSFET will be burning near 4W on either dummy loading or when powering the preamp so sink it accordingly.

Good luck and let us know.



*If with dual mono PSU (one per channel) T.P. should be 0.5V and dummy loads ~8K each. Shunt MOSFETS burning 4W each.
 
Hi Salas

The SSHV2 was working fine with my phono amp with T.P. set at 80 but was suddenly failed a couple days ago. All semiconductors burnt. After I replace all semiconductors and connected the SSHV2 to a 5K resistor, the output voltage raise gradually to about 200V and then drop to below 20V. The portion for setting the working current is working fine as I can set the voltage at T.P., could you advise what should I do to diagnose the problem.