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DRSSTC no oscillation

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steven968

Sat Dec 17 2011, 01:01PM

Registered Member #3516 Joined: Wed Dec 15 2010, 10:40AM
Location: Australia
Posts: 32

Hi all,

I built a 1kw DRSSTC. However when I test it,there was no sign of spark, and no voltage on topload. It seems the coil is not oscillating. The coil is based on Steve's DRSSTC 1 with Steve's ultimate driver. I scoped the gate of IGBT and the waveform looks perfect(with 100kHz sinwave feedback), but I got pretty weird waveform when the feedback is disconnected. The coil is running at 220v AC.
some infos are shown below:
primary inductance(with secondary put in): 22uH
primary inductance(without secondary): 16.66uH
MMC: 0.05uF at 3.68kV AC
secondary inductance: 61950.35uH
topload: 18.127pF
resonance freq: 150kHz
IGBT: IRG4PC50UD

How to solve the problem?

Here is what I get without feedback:

Here is the IGBT gate waveform, no sign of ringing:-D

dude_500

Sat Dec 17 2011, 06:06PM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

Well, it looks like it's oscillating in your second picture... maybe the primary and secondary are just vastly out of tune? Try changing the primary tap around a lot.

Goodchild

Sat Dec 17 2011, 07:54PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Your first waveform looks normal, basically that is the start up pules saturating the GDT core.

When you have the feedback connected is the switching fast like say double the resonant freq of the primary? This could be an indication that the system is phased incorrectly. The solution is to reverse the leads on ether the GDT primary or feedback CT. (not both just one ;P)

steven968

Sun Dec 18 2011, 07:43AM

Registered Member #3516 Joined: Wed Dec 15 2010, 10:40AM
Location: Australia
Posts: 32

dude_500 wrote ...

Well, it looks like it's oscillating in your second picture... maybe the primary and secondary are just vastly out of tune? Try changing the primary tap around a lot.

Well this waveform was generated when I use a signal generator for feedback. Signal generator was set at 100kHz
just see if the GDT is working properly

zzz_julian_zzz

Mon Dec 19 2011, 06:30AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

I second demotion to Good child, The problem could be in phasing.

But what i recommend you to do first is to try it with fixed oscillator running @ 150khz(same as your fres) attach it to the feed back circuit, that is (remove c1 and r1 from U.D. and directly feed the timer oscilator)

IF this does not work either, check if you have voltage in your bridge, If you are introduce 220v in your bridge, you should measure atleast 330v on the filter capacitor (power/electrolytics)

You have computation specs for your coil so i pressume that it is in tune atleast.

IF the oscillator thing did work, you can try then the feed CT. (please answer these: what is the ratio you are using in your feedback transformer?, type of ferrite core? how about your GDT? does this materials are what is needed?

if all correct and still not working, try reversing the phasing of feedback transformer feed lines and also the GDT and the PRiMARY leads. REVERSE it ONE BY ONE only. Obrserve each possible combination if it is oscillating.

you should be also hearing a ticking sound as in the interrupter BPS rate from your GDT, if not, problem is in interrupter or in the GDT itself.

steven968

Mon Dec 19 2011, 10:32AM

Registered Member #3516 Joined: Wed Dec 15 2010, 10:40AM
Location: Australia
Posts: 32

zzz_julian_zzz wrote ...

I second demotion to Good child, The problem could be in phasing.

But what i recommend you to do first is to try it with fixed oscillator running @ 150khz(same as your fres) attach it to the feed back circuit, that is (remove c1 and r1 from U.D. and directly feed the timer oscilator)

IF this does not work either, check if you have voltage in your bridge, If you are introduce 220v in your bridge, you should measure atleast 330v on the filter capacitor (power/electrolytics)

You have computation specs for your coil so i pressume that it is in tune atleast.

IF the oscillator thing did work, you can try then the feed CT. (please answer these: what is the ratio you are using in your feedback transformer?, type of ferrite core? how about your GDT? does this materials are what is needed?

if all correct and still not working, try reversing the phasing of feedback transformer feed lines and also the GDT and the PRiMARY leads. REVERSE it ONE BY ONE only. Obrserve each possible combination if it is oscillating.

you should be also hearing a ticking sound as in the interrupter BPS rate from your GDT, if not, problem is in interrupter or in the GDT itself.

Thanks for your analysis, I reckon the problem is that it's not tuned. The primary inductance and MMC was measured using LCR meter, and the secondary specs was calculated. I didn' t adjust the tap on primary when testing

Feedback trans info: 1:1089
ferrite core type: unknown. The GDT and the feedback trans use the same type of core. GDT works great, so I reckon the feedback would have the same performance as the GDT

zzz_julian_zzz

Mon Dec 19 2011, 11:24AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

If you tuned theoretically using javatc. It will probably work (but not in optimum performance) BUT.. it should work even if you are far away in perfect tuning.. I mean here is that you should get an actual sparks (wimpy from untuned system but you will at least get some).

there should be atleast 1mm spark.

steven968

Mon Dec 19 2011, 01:34PM

Registered Member #3516 Joined: Wed Dec 15 2010, 10:40AM
Location: Australia
Posts: 32

I didn't use javatc but deepfriedneon for all my calculations.
And no spark at all, not even electricity on topload.

Gregory

Mon Dec 19 2011, 06:42PM

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

Meybe a 1:1089 is a very high ratio and it can be not sensible for your system starts. Try a 1:500 and phasing

zzz_julian_zzz

Tue Dec 20 2011, 08:29AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

btw, how did you know that your GDT is working? because of the scoped waves?

how about the half bridge? how do you know that there are no wrong connection in there? this includes power filter capacitor, bypass cap, TVS, zener diodes accross E and C of the IGBT, IGBT pin connection, and the GDT WIRE OUTPUT (polarity).

how about the resistor in the gate? check if it is open or not. Zener diodes are not shorted and schotkey diodes too.

CHECK EVERY ELEMENT IN YOUR HALF-BRIDGE. i believe the problem lies in there. I assume that your logic circuit is in good design because of the waveform you posted., ARE THE primary leads connected properly in to the bridge? how about the secondary?

Tuning using DEEP FRIED will bring you into atleast 80% into actual tuning frequency AND not too far so that it will not spark at all.

With your phasing problem, remove your 1:1000 ct and wind another 1:70 ct in a black ferrite. post the pic here so that we can see what really cause you these problems.

put an oscillator as i previously suggested to you, then if this not work, some thing is not right. but if this worked for you, try using CT (1:70).

post the result. but please do as i suggest to you. Thank you

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