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DRSSTC: Feeback problem (Steve's driver)

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LAN_403

hv-friekie

Sat Jan 22 2011, 08:24AM

Registered Member #2273 Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37

Hey guys,

I have a major problem with my drsstc. I am using steve's newest driver with my on pcb layout. The bridge is made form 2 semikron skm300gb12v IGBTs.
However, when i turn on the interrupter the drsstc works for like half a second before loosing the feedback signal. The bridge is supplied by a ringcore transfore which gives me 72V on the capacitor.
And after loosing the feedbacksignal it don't helps to turn the interrupter on and of, i have to restart the whole driver. But then the process repeats, i get signal for a short time and then it stops again.
I have no idea how to fix this.
I added some pictures.

Best regards,

Philipp, Germany

Mads Barnkob

Sat Jan 22 2011, 09:18AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Hey Philipp

If you loose the feedback signal, then it must be because the primary circuit does not oscillate...

Have you tested you driver with a signal generator as the feedback input? (Just scoping! Power to the bridge would likely kill your IGBTs) It could just be a simple 555 timer.

Since you made your own PCB, there could still be some mistakes in that, do you mind posting the PCB layout? I made my PCB too for the same driver and I messed up a couple of things too :)

hv-friekie

Sat Jan 22 2011, 12:06PM

Registered Member #2273 Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37

Thank you foryour answer.

Have you tested you driver with a signal generator as the feedback input? (Just scoping! Power to the bridge would likely kill your IGBTs) It could just be a simple 555 timer.

Yes, i did this before hooking it up to the IGBT's and everything. I used a 555 with a seriell resonant circuit to produce a sine wave, it oscillated at abut 20khz.
I got a nice, interrupted 20khz square wave, so the driver generally works.

Here is the schematic and the pcb layout:

hv-friekie

Sat Jan 22 2011, 02:21PM

Registered Member #2273 Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37

I just realized that i get a feedback signal up to a specific on time.
When i start turning up the on time the tc starts working, i can pull about 4cm sparks.
But when i want to increase the on time to get longer sparks, i am loosing feedback again.
Can somebody explain this to me?

Linas

Sat Jan 22 2011, 03:16PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

I don't like idea use quite slow IGBT is small DRSSTC which has high Fo.
Second, if you run your coil with low voltage on bridge use single core 100T CT, it can help keep signal right shape and test diodes, maybe they can block signal
Also try change polarity of CT, it heps sometimes

hv-friekie

Sat Jan 22 2011, 04:48PM

Registered Member #2273 Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37

First, these are no slow IGBTs and this is not a small teslacoil. Secondary is 80cmX15cm and toroid is 45cmX15cm, so the frequency is about 80khz.

And i already replaced the 1:1000 CT with a 1:140 oen again, the results got better but i am still LOOSING feedback at a higher on time.

What to you mean by the diodes? Do you suppose that the diodes between the 1st schmitttrigger and the ct broken? I could test them.

With the polarity of the ct, i have already changed it. Bt then i get no output, so i guess the polarity i am using i right

Gregory

Sat Jan 22 2011, 06:47PM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226

the problem can be the OCD that disable the tesla coil, it can happen if you dont configured the reference potenciometer of the OCD

hv-friekie

Sun Jan 23 2011, 10:47AM

Registered Member #2273 Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37

Yes, i also was supposing that. But the OCD LED doesn't shine, and the reference is set to more than 1V.
Furthermore, at the moment the OCD is dissabled, i short circuit the connector for the ct.
What i could try is making a bridge between pin 7 and 8, then it would be 100% sure that the ocd doesn't stop the signal.

Let me try that now.

Bennem

Sun Jan 23 2011, 11:06AM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi there,

Does your Torx173 optical receiver give an inverted signal output?
as Steves circuit is designed for an inverted one, as he uses the ***2412T
if not, you need to add another schmit trigger.

Just a thought.
Mel

hv-friekie

Sun Jan 23 2011, 11:28AM

Registered Member #2273 Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37

Man, i am impressed you you guys try to understand the problem and see that tiny details.
I would be very pleased if you were right, unfortunately i already fixed this in my schematic by using pin 6 instead of pin 5 at the IC6A in my schematic.
This should invert the signal again, shouldn't it?

By the way, i bridged pin 7 and 8 at the lm311 to completly disable the oc protection, but there is no improvment.

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