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Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Shrad wrote ...
still not
I'll need to mount my variac and slowly ramp voltage to see what's going on
the pity is I think I have an issue with my PLL, I can't get the small streamers back with a single switch...
Gah, PLLs are always a pain in the ass . If you have a scope with 2 channels/probes, you should probably try to tune the phase (the pot on the VCO if you use the same kind of schematic i am used to). If you are running your secondary out of phase... Well, i think i need not explain.
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
Do you have insulating pads between your transistors and heatsinks? I can't quite tell from the pictures. If not, then that would definitely prevent the bridge from functioning. Try switching to two separate heatsinks without insulating pads to get better thermal performance without shorting the MOSFETs' drains.
What type of diodes are you using in your bridge? Are you sure that they are ultra fast recovery diodes rated to withstand the voltage and current that you will be putting through them? I use MUR860 in my SSTC.
If it still doesn't work, then the best course of action would probably be to rig up a super simple 74HC14 antenna feedback driver just to test the bridge. That way, you could narrow down the problem to either the bridge or the PLL.
Registered Member #1642
Joined: Sun Aug 17 2008, 11:36PM
Location: Black Canyon City
Posts: 96
Here's some reading up you may want to do on the 4046 in this article. At least this is how I approached my project and tuning the PLL: Good luck, Hank
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
Thanks Dr
I had forgotten that website and it sure is a nice ressource... I think I'll redesign my PLL driver and bridge based on more resources and readings
The understanding of the 4046 is indeed the key to success I think, and I need more tweaking points in order to tune it to the best
as for heatsinks and mosfets/igbts, I use a single heatsink but it has top quality insulator pads with arctic silver between each interface
diodes are ultra fast schottky rectifiers (20 or 40ns, I dont recall well) rated 400V 16A in a TO220 body (have a tray of them bought 5€ at a flea market)
Now the thing to do is read about that 4046 more deeply, and design something more flexible (I was thinking the simpler the better, but it's not always the case)
I will also have some read about coupling and primary positioning, as I believe the more coupled the better with these kind of coils
I have hope, because at 200VDC, just before the single switch popped, the streamers were 1 inch or something of very nice purple swords
EDIT: it seems, by that failure, that the PLL was in fact locked on an harmonic, why I had moderate breakout and instant destruction of the bridge
I'll make another driver with plenty of test points, and SMD layout to get better repartition of the components
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Inducktion wrote ...
I thought Schottky's had no reverse recovery time...
I think he me have mistaken it for a schottky or something, because schottky diodes are rarely 400v. The highest i have seen is 200, unless they are silicon carbide.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
sorry, you are right
I either misread a datasheet or read a bugged one as they are 100V ones
data:
I'll have to find some better diodes
I won't have much time this next month to work on my coil as I'll be very busy at work (at least two week of work 3 hours away from home, lodging there etc..)
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classic 4046 PLL tesla coil tips
. If you have a scope with 2 channels/probes, you should probably try to tune the phase (the pot on the VCO if you use the same kind of schematic i am used to). If you are running your secondary out of phase... Well, i think i need not explain.
