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Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Justin wrote ...
nzoomed wrote ...
loneoceans wrote ...
nzoomed wrote ...
Im still having trouble finding suitable TVS diodes for 24V gate operation. The closest ive got are P6KE22CA, these have a breakdown voltage start at 24.4v and the maximum clamping voltage is 35V. I really need them to clamp at around 26 or 27V ideally, but all the TVS i see have a far lower breakdown voltage, that means it will breakdown well under 24V.
Those are fine. Just lower your 24V input to the UD2 to 22V.
I cant easily do that as im using a transformer, i could rectify it and use a voltage regulator i guess to feed 22VDC into the DC input.
You might try these.
I see those on RS also, but their clamping voltage is rather high at 53V. If 53V is OK, then I should be OK with mine rated at 35V
Registered Member #9879
Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37
nzoomed wrote ...
Justin wrote ...
nzoomed wrote ...
loneoceans wrote ...
nzoomed wrote ...
Im still having trouble finding suitable TVS diodes for 24V gate operation. The closest ive got are P6KE22CA, these have a breakdown voltage start at 24.4v and the maximum clamping voltage is 35V. I really need them to clamp at around 26 or 27V ideally, but all the TVS i see have a far lower breakdown voltage, that means it will breakdown well under 24V.
Those are fine. Just lower your 24V input to the UD2 to 22V.
I cant easily do that as im using a transformer, i could rectify it and use a voltage regulator i guess to feed 22VDC into the DC input.
You might try these.
I see those on RS also, but their clamping voltage is rather high at 53V. If 53V is OK, then I should be OK with mine rated at 35V
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Justin wrote ...
Working Voltage: 25.6 V Breakdown Voltage: 28.5 V Clamping Voltage: 41.4 V
I don't see 53V anywhere. It breaks down at 28.5 Volts.
RS tells me the clamping voltage is 53.5V I take it that clamping voltage is important, since its fully conducting even though it breaks down much lower? If i run my gates at 24V, and the breakdown voltage on my diodes starts at 24.4V, is this OK? You obviously dont want them clamping the whole signal.
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
from my PM on this topic:
The 35V figure is when they are passing their rated current. They'll do the job, though you should really be using ones rated at 24V rather than 22V (see link: ,4294866063 ) BTW the gates won't instantly pop with excess voltage so i wouldn't worry too much.
(yes i should have qualified "excess" - I believe others have had gates up at the 35V level without instant failure. Obviously crazy voltages will kill them instantly)
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hydron wrote ...
from my PM on this topic:
The 35V figure is when they are passing their rated current. They'll do the job, though you should really be using ones rated at 24V rather than 22V (see link: ,4294866063 ) BTW the gates won't instantly pop with excess voltage so i wouldn't worry too much.
(yes i should have qualified "excess" - I believe others have had gates up at the 35V level without instant failure. Obviously crazy voltages will kill them instantly)
Thanks for that info. I just got your message also :)
I have not had much to do with TVS diodes before, so ive been learning alot!
Anyway, ive been testing my driver board again, and ive found that i am indeed getting a signal on all fout GDT pins, but the second pin on each output is weaker, and both are not a square wave.
I think its not helping that i dont have a 10x probe on my scope when probing the IC pins, but ive traced it back to IC5 and the scope is showing a strong signal on pin6, but very faint on the scope on pin3 with little or no signal showing (when i get hold of a digital scope this weekend i should have better readings hopefully).
The signal on these pins is similar pattern to what i posted on the screenshot earlier. So my main concern is im not getting a square wave. All the MOSFETS are working fine.
I thought i would test it under load with the GDT connected to see what i got on the scope, I assume this noise from the GDT and UD is completley normal from what ive read? Its quite loud, and it changes pitch when i adjust the beats on the MIDI controller.
Its also very vague what the jumper does (SV1) next to the tunable inductor. From what i understand and going by the schematic, its designed to bypass the inductor? I dont get any signal output from the UD if this jumper is set to pins 1-2, pins 2-3 give me a signal output.
My signal generator is injecting a 50KHz signal into the CT input. These are the scope shots i took from the GDT connected to the UD, its far from the square wave im supposed to be getting, but hopefully this will point me into the right direction on whats wrong.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Just one more question. Does it matter what mode the MIDI interrupter is set to when testing? Ive got it set to spark gap mode so its putting out a constant signal to the UD.
My other concern is if my signal generator is not working properly.
I was also told to ground pin 6 of the optical receiver, as this should allow the driver to put out a square wave without the MIDI interrupter connected, I tried this, and I got no signal.
All the IC voltages appear to be correct on the rails etc. but one thing i see a fault with is D12, im getting +5 on the anode, which is normal, but im getting nearly 5v on the cathode side (about 4.8v) does this mean the diode is breaking down and letting current pass through?
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Im still getting nowhere with my U.D board and am running out of ideas.
Ive got hold of a decent signal generator and scope now and I get a clean square wave on all four MOSFET outputs if i connect pin 6 to ground on the optical receiver. With the GDT connected, i get the same clean square wave, albeit at a higher voltage for whatever reason. The GDT used to make alot of noise, but it now no longer does also, which is some concern to me, as i expect that its not getting enough current, yet the voltage is 24VAC at the MOSFET outputs.
If i disconnect this pin from ground and hook up the MIDI interrupter, i no longer get any square wave on the second pair of pins and the GDT output is similar to the scope shots ive posted earlier. When changing the BPS etc on the interrupter, the gaps between these spikes change accordingly, but thats it. Im suspecting that its harmonics that is giving me a reading of about 60-80v, but ive tested the transformer and its putting out a perfect 1:1 ratio when i test it on the scope with a signal generator to the input.
TIA for any suggestions, this is driving me crazy right now, im so close to getting this darn coil working!
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
nzoomed wrote ...
All the IC voltages appear to be correct on the rails etc. but one thing i see a fault with is D12, im getting +5 on the anode, which is normal, but im getting nearly 5v on the cathode side (about 4.8v) does this mean the diode is breaking down and letting current pass through?
I had some problems with a recent UD2.7C build. The design and board is fine, but had some faulty components. A diode and IC had to be replaced. These things happen. Are you using an ST fiber receiver? If so did you remember to remove D13? Does the signal LED come on when you fire up the interrupter? It should. If it's not, follow the signal until you lose it and then check the components on that part of the board. This requires some debugging skills but no better way to learn how the UD driver works.
If you are getting an input signal but no U1-U4 square wave output, track backwards until you find the input signal and again find suspect components. A good sig gen and scope will be essential. 2 things that really helped me 1) Learn and understand the UD circuit, 2) Follow LoneOceans testing and debugging notes !
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Graham Armitage wrote ...
nzoomed wrote ...
All the IC voltages appear to be correct on the rails etc. but one thing i see a fault with is D12, im getting +5 on the anode, which is normal, but im getting nearly 5v on the cathode side (about 4.8v) does this mean the diode is breaking down and letting current pass through?
I had some problems with a recent UD2.7C build. The design and board is fine, but had some faulty components. A diode and IC had to be replaced. These things happen. Are you using an ST fiber receiver? If so did you remember to remove D13? Does the signal LED come on when you fire up the interrupter? It should. If it's not, follow the signal until you lose it and then check the components on that part of the board. This requires some debugging skills but no better way to learn how the UD driver works.
If you are getting an input signal but no U1-U4 square wave output, track backwards until you find the input signal and again find suspect components. A good sig gen and scope will be essential. 2 things that really helped me 1) Learn and understand the UD circuit, 2) Follow LoneOceans testing and debugging notes !
OK thanks for that info. Yes the signal LED does come on and flash at the same time as the LED on my interrupter. Ive had a friend who is an electrical engineer help me over the phone and he has explained to me in good detail how it works. He told me what pins to check for signals on the IC's etc, and said that if you ground pin 6 of the optical receiver (yes im using the ST connector, D13 is removed) you should get a perfect square wave, which i am, but perhaps there is a problem with one of the IC's ad=s you say.
Who was your supplier? I got everything from mouser. What Parts were at fault with you?
I might check those, as i do wonder if an IC is at fault.
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Building my first DRSSTC - Updated thread...
