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Simplistic Mosfet HV Shunt Regs
Simplistic Mosfet HV Shunt Regs
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Old 23rd October 2019, 11:55 AM   #6011
Salas is offline Salas  Greece
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Simplistic Mosfet HV Shunt Regs
Quote:
Originally Posted by bigpandahk View Post
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?
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Old 23rd October 2019, 12:11 PM   #6012
Embehu is offline Embehu  Viet Nam
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Originally Posted by Salas View Post
By the way, forgot to ask you before, what is the application circuit you want this 80V-90V PSU for? Is it for a low anode voltage tube preamp?
Hi, itís for 6dj8 buffer and I just lower down to 75VDC for more safety
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Old 23rd October 2019, 03:33 PM   #6013
bigpandahk is offline bigpandahk  Hong Kong
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Quote:
Originally Posted by Salas View Post
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?
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File Type: jpg Toccoto MK II Pre-amp.jpg (92.1 KB, 129 views)
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Old 23rd October 2019, 04:34 PM   #6014
Salas is offline Salas  Greece
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Simplistic Mosfet HV Shunt Regs
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.
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Old 24th October 2019, 12:09 AM   #6015
bigpandahk is offline bigpandahk  Hong Kong
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Quote:
Originally Posted by Salas View Post
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.
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Old 24th October 2019, 10:30 AM   #6016
Salas is offline Salas  Greece
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Simplistic Mosfet HV Shunt Regs
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.
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Old 24th October 2019, 12:07 PM   #6017
euro21 is offline euro21  Hungary
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Simplistic Mosfet HV Shunt Regs
"Current draw is around 60 - 70mA for both channels"

http://community.fortunecity.ws/rive...a/Toccata.html
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Old 24th October 2019, 02:03 PM   #6018
Salas is offline Salas  Greece
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Simplistic Mosfet HV Shunt Regs
So bigpanda's 59mA is very near to the original build's range and that's reassuring. Tubes and JFETs have high enough bias tolerances.
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Old 24th October 2019, 03:19 PM   #6019
bigpandahk is offline bigpandahk  Hong Kong
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Thanks Salas and Euro21, hope can finish the amp on Sunday.
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