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OLD THREAD Simplistic Mosfet HV Shunt (The Simpler Simplistic Design by Salas)

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Nikon1975

Member
Joined 2009
Dissipation is not too difficult:

Q1[mW] =Iccs * (Vccs-Vload) in any condition

Note (Vccs-Vload)< 200 V otherwise you fry Q1

Q3[mW] = Iccs * Vload when the regulator is unloaded (worst case scenario)
Q3[mW] = (Iccs - Iload) * Vload when the load is draining current

NOTE: Current are expressed in mA, voltages in V and power in mW

Here I have no idea about Q2 and Q4.

Best Regards,

Davide
 
R

regal

Member
Joined 2004
Nikon1975 said:
Dissipation is not too difficult:

Q1[mW] =Iccs * (Vccs-Vload) in any condition

Note (Vccs-Vload)< 200 V otherwise you fry Q1

Q3[mW] = Iccs * Vload when the regulator is unloaded (worst case scenario)
Q3[mW] = (Iccs - Iload) * Vload when the load is draining current

NOTE: Current are expressed in mA, voltages in V and power in mW

Here I have no idea about Q2 and Q4.

Best Regards,

Davide
Click to expand...

Thanks for doing this, Salas PM'd me that the Q3 load is actually 1.2* Iccs*Vload if I remember correctly.

There is also a voltage limitation on Q2 depending on the transistor used, can't remember which but there are details around this that should be added.

Also Iccs should be = X*Iload, not sure a definative answer as to what X should equal I've seen 120% up to 200% recommended.

Also there is a minimum for Vccs - Vload, I think it is 20V's, but it is important for proper regulation.

Last VA of transformer recommended at 2x Iccs ( so 4x Iccs if using one transformer to supply 2 boards for stereo)

All this goes to the most difficult task of finding an appopriate heatsink for your chassis. I posted a link to a guy on ebay that will cut to size various different heatsinks that can be on the back of your chassis and pretty much hidden out of view. I could find nothing at Digikey or Mouser that could be integrated into a classic tube amp chassis.

Just can't wait to get the boards and my damn 3 month back ordered edcor PS transformer.
 
Last edited:
N

Nikon1975

Member
Joined 2009
Step by step instruction DRAFT

Regal, I included your comments.

THIS IS A DRAFT, NOT SURE INFORMATIONS ARE CORRECT !!

Component choice are my guess, please comment on that.

INSTRUCTIONS

1) Determine operating voltage (Vload) and MAX load current (Iload). This come from your project, what do you want to power with the regulator?


2) If Vload>300 V
Q2=MPSA94
R3= 82K/5W
R4=220K/2W
If Vload< 300 V
Q2=MJE350
R3=56K/5W
R4=120K/2W
3) Iload+25mA < Iccs < 2 * Iload or 1.2 * Iload < Iccs < 2 * Iload

Vload + 25 V < Vccs < Vload + 50V

(NOTE: higher values of Iccs and vccs improve performances, but increase the heat production, I would start with a minimum needed difference between Iload and Iccs and vccs)

4) Make a first estimate of R1 using the following table
Iccs=40mA >>R1=56R/1W
Iccs=50mA >>R1=47R/1W
Iccs=60mA >>R1=33R/1W
Iccs=80mA >>R1=22R/1W
Iccs=100mA >>R1=20R/1W

5) Use PSU2 to determine the AC voltage needed considering the chosen topology of the filter. The transformer should be rated for 2 *Iccs.
If a center tapped transformer is used, populate only D10 and D12
If a normal transformer is used, install all the diodes and use the two contacts marked AC to connect the transformer. CT do not need to be connected

6) Set the trimmer R8 to 500 ohm

7) connect as dummy load a 15K/20W resistor (NOTE: I think this has to be increased in extreme applications)

8) connect two voltmeters, set on DC, one on the dummy load and one on R1, they will measure Vload and Vr1.

9) power the circuit

10) with extreme care, and the left hand behind your back, adjust the output voltage to Vload.

11) Note the voltage Vr1 measured on R1 (should be in the range of few volts). The real Iccs can be calculated Iccs=Vr1/R1

12) Compare Iccs calculated with the project Iccs and reduce or increase the value (reducing R increase the current) so that they match. To do that iterate the process.

13) power off the circuit and wait for all the capacitor to discharge.

14) When Icss and Vload measured are OK, power off the circuit and wait for all the capacitor to discharge, disconnect the dummy load, disconnect the volt meters, and connect the real load.


HEAT DISSIPATION

Q1[mW] =Iccs * (Vccs-Vload) in any condition

Note (Vccs-Vload)< 200 V otherwise you fry Q1

Q3[mW] = 1.2 * Iccs * Vload when the regulator is unloaded (conservative in the worst case scenario. Avoid to operate the circuit without load, but the heat sink should be capable of the maximum dissipation, that can occur in case the load has a failure, e.g. burned filament )
Q3[mW] = (Iccs - Iload) * Vload when the load is draining current

NOTE: Current are expressed in mA, voltages in V and power in mW

Here I have no idea about Q2 and Q4.

COMPONENT CHOICE

D9-D12 FRED diodes 1000 V 1A
R2 and R6 Carbon Composite (gate stopper)
Other resistors metal film, rated for 400 V
C2 and C3 WIMA MKP
C4 and C5 High ripple current, low ESR
R8 Multi turn trimmer

TIPS

The pads are not tinned. To avoid oxidation put a thin layer of tin on them.

PLEASE NOTE THIS IS A DRAFT, DON'T TAKE IT AS INSTRUCTIONS UNTIL IS NOT CORRECTED !!

Davide
 
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