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Dr. H.

Wed Oct 03 2007, 07:09AM

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

So hire is the last scope traces. I won't be trying to make them faster (they are now in the range of 80nS ). So whay do you yhink guys

Bauerb2

Wed Oct 03 2007, 11:02AM

Registered Member #973 Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66

very nice. are these with the paralleled drivers or just the single? even so, these pulses look fine to me. now if only i could get that sort of result from my gdt i would be happy. i keep getting a voltage droop of 3-4 volts and the waves look terrible. i've tried both increasing and decreasing the gdt windings, and increasing/ decreasing the coupling cap. i have yet to find a certain direction to aim for that will make it better.

what was your final choice value for the decoupling caps? and what ic's did you use: the tc4420 or the ICL7667?

--pz-- andrew

Dr. H.

Wed Oct 03 2007, 11:34AM

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

Hi Bauerb2

. On the scope trace above i use paralleled drivers (when i use single the waveform is not much different - just a little bit slower rise and fall times). I use tc4422 (in the schetatic is tc4420 ). Decoupling is 470nF. I first tried with ICL7667 but they are very slow (compared to the TCs) and have only 3A pic. Why don't you post some pics of your signal ?

Also what kind of feritte core are you using ?

ragnar

Wed Oct 03 2007, 01:17PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Bauerb2 wrote ...

...i keep getting a voltage droop of 3-4 volts and the waves look terrible. i've tried both increasing and decreasing the gdt windings, and increasing/ decreasing the coupling cap...

A 'droop' from the start to the end of the pulse generally indicates saturation -- try doubling the number of windings or running at a higher frequency to see if the droops start to straighten out.

Bauerb2

Wed Oct 03 2007, 07:51PM

Registered Member #973 Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66

the frequency its running at is 50khz slower than the actual fres of the sstc secondary (fres = 330kHz. The test quare wave freq i am using = 280kHz) so i can try that now i suppose (for some reason the freq changed on me since i built the test circuit.) anyway.. i have tried sooo many different numbers of turns. so check it out.

turns
10-14 = drooped madness
15-20 = less droop, slower rise/fall (not sure of exact time, scope isnt tuned properly)
20-24 = almost perfect, but the rise/fall times are relatively slow.
30+ = starting to resemble a sine wave.

since i am lazy and dont feel like ordering a new core, i used one from a computer psu. dimensions are 2.7cm outer diamter, with a 1.2cm height. inner diamter is 1.4cm.

here are some pics:
first one is the gate waveform with 22 turns drivign a full bridge; each gate having a 10ohm res. (5v/div 1uS/div again, dont trust these) with temporary coupling caps total charge of 1.68uF (works a little better than the series electrolytic caps i mentioned b4) the waveform has gotten better i suppose..

second is the setup which includes the 555 running very close to 50% at around 280khz, there's the logic nand chip (only to invert signal) and then the 4 tc4420's running 2 high 2 low parallel.

if i am testing this wrong or wiring something weird, please tell me, it will help.

thanks

-Andrew

Experimentonomen

Wed Oct 03 2007, 08:21PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

Do us a favor and replace that iron powder dc filter with a proper ferrite toroid.

You wonÂ´t regret it, youÂ´ll get so much better performance and cooler uccÂ´s.

Bauerb2

Wed Oct 03 2007, 09:36PM

Registered Member #973 Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66

haha yup i knew someone would immediately destroy my hopes and dreams and make me feel bad. i knew before i even wound it that it wouldn't work as good as it should. have mercy, for this is my first sstc and i am a little new.

i have used these toroids b4 in other projects like a battery desulfator and others, and i assumed they were all the same. i knew there were different types of cores, but i didnt know which kind this one was.

w/e

thanks hfsstc i will replace it as soon as possible.

pz - Andrew

Dr. H.

Thu Oct 04 2007, 05:33AM

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

When i was starting to built my very first SSTC (whcih didn't work at all

) i was also trying to use this type of cores (at that time i didn't know that they are not suited for that kind of purpose). My waveforms looked exactly like yours, my core was warming up a lot, and my drive tranzistors were also heating a lot). I've changed the core and everything worked perfekt. Just order some, or pull ot from something. I have used cores from microwave filters (i dont know how good is the core but up to 300khz they were perfect

)

Dr. H.

Thu Oct 04 2007, 08:19AM

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

Last night i started testing the bridg.W With no load there is a little ringing on 17v - first picture (i think normal). With a smal lamp (12v) for load it worked perfekt - second picture. So i decidet to tested it with a 300 DC and a 75W lamp for load. I connected the variav through a 500W bulb for protection and tryed. I increased the voltage gradualy and everything worked great until i hit 280v DC - then one of the transistors shorted. When i touched them they were exptremely hot. Today i replaced the bwoln transistor, and i saw something interesting - the transistor had become so hot that it had melted the nylon busher (i don't now how it is called) that separates the screw from the metal plate of the transistor. I've changed the thermal pad with silica and now works better but it will neew bigger radiators

.
After replacing the transistor i connected the primary, put the secondary and have a go. With input of 36V and 2.4A it gave about 2sm (0.8 inch) of streamers and about 4sm to grounded object. The transistors were getting a little warm.
So i hooked the scope to the primary and saw something interesting on the scope - the third picture. Excuse for the bad picture, the flash have ruind it

. Could someone tell me why it is looking like that

After that i hooked it to the variak and have a go. At about 80v AC, half wave rectified it gave about 7sm of streamers, but the transistors started getting very hot so i stoped the test.
So the question now is why the waveforms look like that ???
On the picture the streamers look little but actualy the are longer

Marko

Thu Oct 04 2007, 10:58AM

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

Have you got the feedback to work? Are you sure PLL isn't locking to a wrong mode there?
The way your gate waveform rings just doesn't look good to me.

You need to make sure your coil's frequency falls into locking range of the PLL. That's why you need to adjust those pin 11/12 resistors after all.

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