I'm embarrassed, I just discovered that I don't need to make changes to SSHV2. I have had a breakdown just completing the plate, which half-strangled the power of the SSHV2. I couldn't say the cause or when it was fixed. But since then I thought it was necessary to modify and now I'm sorry, I tangled up here without needing to.
Hi, I still suffering SSHV2 breakdowns. It handles 165mA. but after a while explodes Q1. Please see IXTP02N. I think it occurs when I power on the Variac transformer 3000mA. I see a great spike on my volt dial meter at power on.
So I ordered a cheap inrush current limiter (for motors) just to try if can fix it.
So I ordered a cheap inrush current limiter (for motors) just to try if can fix it.
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You are driving a field coil, no? That's a big inductor. A di/dt through the coil will generate a voltage. Maybe a zener protection diode is called for to prevent an overvoltage condition on the FET?
Hi Marcus, thanks, yes the load is a field coil. Zener protection is present, as established by circuit design.
For now, it works by going up and down the variac control before turning it on and off. And the annoying blow to the speaker also disappears.
I measured the variac drives 95VAC / 650mA. to the diode bridge. The other day I got punished to blown up this bridge after a choke input try. And a cold power on of course. Now again CLC.
I find here in diyaudio "soft as a Feather Pillow (SFP) SSR Soft Start Circuit".
For now, it works by going up and down the variac control before turning it on and off. And the annoying blow to the speaker also disappears.
I measured the variac drives 95VAC / 650mA. to the diode bridge. The other day I got punished to blown up this bridge after a choke input try. And a cold power on of course. Now again CLC.
I find here in diyaudio "soft as a Feather Pillow (SFP) SSR Soft Start Circuit".
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I was thinking that you may be getting an inductive kickback from the field coil resulting from high di/dt in the coil during turn on and/or turn off. If that is the case you might want to consider adding protection across the field coil, between F0 and F+ on the schematic. Suitable protection diodes back-to-back would clamp the voltage spike on turn-on and turn-off and prevent it getting back to the SSHV2.
Keep in mind this is just a guess on my part. Inductive kickback is something that can occur when the the current in a coil changes rapidly. It may or may not be the cause of your failures. In any event, I don't think that adding some zener protecxtion would hurt anything. @Salas may wish to chime in here.
I would make them hefty, maybe 2 watts or so? That's just WAG, I'm not sure how much energy they will need to absorb from, the coil. The zener voltage should be greater than the SSHV2 output voltage, but significantly less than the max vds of your FETs. Your Vout is around 80VDC, is it not? And vds max for the IXYS Fets is 500V. 2 Watt 160 or 200 Volt zeners should work.
I would make them hefty, maybe 2 watts or so? That's just WAG, I'm not sure how much energy they will need to absorb from, the coil. The zener voltage should be greater than the SSHV2 output voltage, but significantly less than the max vds of your FETs. Your Vout is around 80VDC, is it not? And vds max for the IXYS Fets is 500V. 2 Watt 160 or 200 Volt zeners should work.
It makes sense place an extra protection to the input cascode CCS stage vs. the variac heavy in-rush current. And then to the output vs. the kickback of the coil. Thats's for sure, my load is somewhat different as intended. For example, I can't exceed much from 6V difference Vin- Vout without suffering heavy increase of heat and noticed also a worsening of sound quality. Less open soundfield and somewhat clogged sound if I put heat over Q1.
Hi, I wants to replace the Variac ( load is 95VAC / 650mA.) and order a custom OCore transformer. How much current must be for a quiet and cool operation? Capacity available (VA) is: 80, 100, 120, 200...
Consumption is near 60VA, but I barely remember.. Salas recommend almost twice as a rule, isn't? Even more in my such a kind load?
Thanks in advanced,
Jordi
Consumption is near 60VA, but I barely remember.. Salas recommend almost twice as a rule, isn't? Even more in my such a kind load?
Thanks in advanced,
Jordi
