Simplistic MosFET HV Shunt Regs

[merlin el mago]

Still triying to fix (CCS can go max. 10mA) first I checked trimmer and was OK also I checked the CCS following your instructions : I tied F+ & F0 together (the output connector's far left and right points). I looked for 1.5-2V VGS across each healthy DN2540 (outer pins) when the CCS is LV powered. VGS Q1 1.2VDC & Q2 0,0XVDC. Checked the related CCS diodes and are fine, removed the DN2540 & checked with Atlas Peak DCA75 & what surprie both DN2540 are OK?

 

[Salas]

Q2 VGS 0 in LV test is no good. Are you sure Q2 is good? Is there a dead Zener across Q2? Maybe there is oscillation in the CCS and sticks? See with the scope.

 

[merlin el mago]

Yes Q2 VGS 0 in LV test is no good, I desoldered to change for a new one but before checked with Atlas DCA75 before to trash and measued as OK. Also I suspected like you about a dead Zener Diode: removed the two ans measured OK, I will look with the scope. Also desoldered & measured Q1 to calm my mind and measured OK.

 

[merlin el mago]

Really Q2 measures 0.123V & Q1 1.270 with measuring at TP 0.110V

 

[merlin el mago]

I don't know what happened to R1: measures only 1R, now the CCS is OK, time to check the rest.

 

[Salas]

Hmm weird to have a wacky resistor. But anything can happen as it proved.

 

[merlin el mago]

Only can reach with 123Vin = 118Vout, mine target 100V set SSHV2 CCS 50mA (30mA for the load & the rest for SSHV2)?

 

[merlin el mago]

Have I to change something due to the fact the reg. is working in the low minimum output voltage?

 

[Salas]

Make the two same value ref resistors smaller (R9 R10)

 

[merlin el mago]

I have on hand: 56K, 33K & 12K?

 

[merlin el mago]

Wich one?

 

[Salas]

56K I would have tried first when looking for 100V

 

[merlin el mago]

Thank you Salas.

 

[merlin el mago]

Salas what are the proper voltages for VBE ksa1381 & VGS sk117gr?

 

[Salas]

Vbe about 0.6-0.75V Vgs about 0.4V-0.75V

 

[merlin el mago]

Thanks. What's the hFE value of KSA1381, I ask because there are several grades: C,D,E & F? Or no matter?

 

[merlin el mago]

Works like a charm, thank you Salas.

N.B. Mine KSA1381 hFE 107-109 so range D high or E low.

 

[Salas]

D class is about there, not too high HFE. Can be down to 75 sometimes even. I have some that low. HV transistors are not high HFE in general.

Congrats for fixing it and also getting it to work at 100V range.

 

[merlin el mago]

Thanks to you. If someone have the same problem now can fix it.

 

[swich401]

Sorry if this was asked previously in this thread; Wondering if it is possible to use the SSHV2 to produce 600V regulated power. Start with approx 700V raw. Potentially with the use of IXTP08N100D2 within the cascode and a different MOSFET than the IRF840?