Simplistic mosFET HV Shunt Regs

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#2,765
Ah! Oh!
Right, I wants to power up a vintage 8" field coil speaker, voltage should be around 95volts, and current 50mA. more or less.
Exact values only when tuned on the fly, because of the driver responsiveness depends on the acoustical application, open baffle in this case.
The main question here is to know if an electrodynamics coil acts as an fixed load.
The VCCS is a servo-controlled supply and designed for one specific fixed
load.
Or contrary the coil acts as an power amplifier and present a changing load to this supply, the VCCS will try to compensate....so, in effect they will be
working against eachother.
 
#2,766
Better not bet on a shunt regulator. Shunt regulators are better than series regulators in absorbing EMF but can be finicky to a largely varying inductive load regarding their stability.
If you want to make one and see in practice its all to you, especially if you can spare it for some alternative application, but no sure predictions.
 
#2,768
Hi Salas,
Today I have turned on phono stage and the rich ,natural sound from yesterday turned to lifeless and unpleasent.I measured the Uin ,Uout everything fine.Calculated the set current on R1.It is set to 50mA.When I measured the current it was 55mA.The IRF840 is unussualy cool.Do you think that IRF840 is burned somehow during start up.Before start up I have changed EZ80 to EZ81 and everything measured fine until listening.I thought that tube was reason but EZ80 in place again work the same.I am using 8microF-3.5H-80microF 3.5H-80microF prefilter.The both rectifier anodes have 200ohm resistance in series like in EZ80 datasheet and the sound was beautiful until today.Please help me if you have idea what might be the problem.
 
#2,773
bigpandahk said:
I tried to built the SSHV 1 but upto now, having burnt more than twenty semicon (FET, LED, MOSFET, ZENER), still can't get it work. Can anyone suggest a step by step safe way to test the circuit? Thanks
Click to expand...

I think Salas and other knowledgeable folks have posted some pretty good steps in safe testing. Personally, I never test any high voltage circuit without using a voltage variac, I put a couple of DMM's on the key circuit points and bring the voltage up slowly and observe the meters. Sometimes that doesn't even work if there's a serious issue and something can burn before switching off the AC!
I've built the first revision of the Salas SSHV and made a PCB for it, it works just fine. Are you using a PCB already made? Or are you using point-to-point wiring? If FETs are blowing, sounds like the gate voltage is being exceeded; or a FET backwards? Do you have a zener across the drain to source? I had this issue when I first built it, and found that the Vds was exceeded during the charge up of the capacitor. Another thing is to make sure the load is adequate for the desired output current.
Perhaps you know someone that could go through the board with you before powering up?
Hope that helps...it can be frustrating to figure these things out!

Gary
 
#2,774
Thanks Salas and Roger57 's prompt reply. My target setting is 300V 75mA and the raw DC is 400V CLC. I changed the 56ohm to 22ohm for higher current. Last night I tested my latest built, connected a 5.6k 20W resistor as load, the output voltage go up to about only 25V, after a few second, the 22ohm on fire and the 9610 gone.

Will built a simple CRC connect to variac for testing again.
 
#2,775
Your raw DC is high for the 9610 at such CCS before it settles especially if there is a charging peak in an underdamped CLC pre-filter. Also much heat will be developed with 75mA and 100V drop over the reg. Burn some before. As you are, delete R10, C1, damp the input with 100 Ohm series, stick a 47uf/450V input to ground, a 12V Zener from top of the 1uf Vref capacitor C2 to Vo rail with cathode up and have a go. I suppose you already use clamping zeners on gates before the 220R stoppers to sources on both Mosfets. If not, look at the link from post#1 for SSHV1 again. Your R3 should be 82K/5W with such Vin. If all fails maybe a SSHV2 on a PCB would be better for you, but we can't be sure of any possible other difficulties in your case.
 
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