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Micro SSTC - problems

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Dr. H.

Sun Sept 16 2007, 06:34PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi to all. I am new to this site so don't be tu harsh on me

. I have built a VTTC a while ago and i decidet it was time to go to something little . So few days ago i decided to build a sstc based on Steve Ward's Mirkro SSTC (everyone has to start from somewhere

)

So i built the circuit and it looks like this

I've tried it a few times and for about 10min without any problems so i decidet to box it

But now when i turn it on it doesn't wont to start oscilate every time. Because my gate drive chip is inverting (icl7667) when it doesn't oscilate it shorts out my power suply. What might be the cause of these problem? Short antena ?!?!
Hire are some pic while it is running, it;s casing and what's inside the box . And one wast question - how do you insert picture like a link ???
Any help will be useful

Excuse my english i am from bulgaria

Marko

Sun Sept 16 2007, 08:01PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi Huben, and welcome

Oscillation start and massive turn-off losses are among standard problems with that kind of circuit.. Can be changed to class E, but I don't think it's worth for you.

What do the other IC's in your circuit do? Are you using start-up oscillator?

You actually put too much effort into that coil and board. I think it would be great to transform it into a small H-bridge coil.

Sulaiman

Sun Sept 16 2007, 09:09PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Temporarily for testing try moving the coil and primary away from the box
the metal box may be causing problems ?

Dr. H.

Mon Sept 17 2007, 11:49AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi to all. The other ic is a cd4000. I use the inverter for the signal from the interuptor (wich i now remove bacause there is no need for it in this smal coil). The two other IC's are the gate drive chip on the right and the 555 for the start-up oscilator.
Alsou i've tried the cass E operation, but wit the same input voltage i get smaller streamers. The only benefit is that the mosfet isn't warming at all.
Hi Sulaiman. When it was out from the box it was running OK. But when i put it into the box i took the antena out of the box (it can be seen on the pics - a orange wire). The antena is going out from the box from very smal hole and the box is groundet (the socndary base is attached to the box also so they are groundet at one point, i don'd know if this is a problem, you will answer this

). I was thinkin is there any possibility that the capacitance where the antena is going through the matel casing to be causing problems ?

And one more question - how do you determine the coupling ?

Dr. H.

Thu Sept 20 2007, 11:25AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Is there any suggestions guys

Marko

Thu Sept 20 2007, 12:24PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I would definitely go for a small half or full bridge. Designs like this are favourite and work great:

The coil looks big enough, what's it's resoant frequency?

Dr. H.

Thu Sept 20 2007, 04:32PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

I was also thinking the same Marko. I was looking around and i found the ctc-labs circuit http://www.ctc-labs.de/html/micro_sstc_2.html
But i have some questions. In the description of the ciruit he says that he uses a irf740 but in the circuit is shown as irf640. I was thinking is it possible if i use a irf740 to power it directly from one way rectified mains (220v). The transistors are 400v (740s) so they must survive, but would i need to change the number of the turns of the primari? Also i will make a new secondary that will be with lower resonant frequency (about his size so i won't need changing values). Also i can't de drive chips he use. Is it possible to change them with ICL7667 (2x 1.5A in IC ) ?

Sync

Fri Sept 21 2007, 05:09AM

Registered Member #510 Joined: Sat Feb 10 2007, 09:28AM
Location: Hannover
Posts: 12

You can use the ICL7667, they're fine... But take care of the different pinout. (Mmm. It actually could be the same o.0)
IRF740s and IRF640s are the same but the breakdown voltage.
I don't think that you have to change the primary... Just try it and tell us how it works (;

Sulaiman

Fri Sept 21 2007, 06:20AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Irrespective of the type of SSTC that you choose
I still think that putting a steel box directly beneath the TC is a bad idea
the steel will kill the performance.

I wouldn't have steel within a couple of coil diameters proximity
e.g. 6" primary requires 12" clearance.
The distance is debatable - but the principle isn't.

Dr. Drone

Fri Sept 21 2007, 07:10AM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

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