gdt problems and suggestions for drsstc driver? / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

gdt problems and suggestions for drsstc driver?

1 2 3 next

Move Thread

LAN_403

the_anomaly

Mon Apr 10 2006, 03:25PM

Registered Member #19 Joined: Thu Feb 02 2006, 03:19PM
Location: Jacksonville, FL
Posts: 168

Iâ€™m planning on building a small drsstc in the near future so I started playing with driving igbts. I am using a timer to feed a square wave to an npn to increase the pulse power, and sending that pulse to the gdt. At the moment I only have 555 timers and no ucc chips so I am stuck using npns to increase the pulse into the gdt.

Here is my schematic. Basically I took jimGs' drsstc schematic and replaced his driver with a 555 timer and left the fullbridge. I have only built my driver for seeing if its feasable.

This is the wave coming from the gdt. I had reversed my scope connections so the wave is read inverted to what I will fed to an igbt. If I increase the sweep on the scope, the wave looks like a sharp rise and fall and then goes slightly negative.

Then I tried to apply this wave to an igbt. I put the probe across the collector to emitter is this correct?

This is what I got. It looks like the igbt is turning on and off correctly but is it correct.

here is the board and gdt all connected. So does everything look good or should I make changes?

vasil

Mon Apr 10 2006, 03:49PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Its look like more an OLTC than a DRSSTC.Practically you pulse the rail voltage through the primary tank. I dont think it is enough to see sparks flying.

HV Enthusiast

Mon Apr 10 2006, 04:20PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

By looking at the photo, you appear to be using the wrong material for your GDT. Your core appears to be a powdered iron core, not ferrite.

Steve Conner

Mon Apr 10 2006, 04:46PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Your gate driver circuit is no good. You should use a NPN and PNP transistor together at least, so it can drive the GDT in both directions. The spike you're seeing is a kickback when the NPN transistor turns off.

Avalanche

Mon Apr 10 2006, 06:18PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Have a look at Richie Burnetts schematic, here :

I've used something similar with sucess. The only thing is you need an inverted and non inverted drive signal... although I suppose it would work by reversing the NPN and PNP transistors on 1 row.

Adam Horden

Mon Apr 10 2006, 07:29PM

Registered Member #176 Joined: Tue Feb 14 2006, 09:35PM
Location:
Posts: 44

You are using a powered iron toroid. I have used these in line chokes but theeyhave two low a permability to be used as a gate drive transformer. Looks for cores that are usally blue or red. Avoid yellow.

As for gate driver you could use a push pull with two transistors or a inverting and non inverting mosfet driver IC. You need to swing the gate +Ve and -Ve.

Adam

the_anomaly

Mon Apr 10 2006, 07:33PM

Registered Member #19 Joined: Thu Feb 02 2006, 03:19PM
Location: Jacksonville, FL
Posts: 168

Thanks for the suggestions. I should have checked the board earlier cause after dinner I went straight back to work and hooked it all together. I will use a pnp with the npn when my digikey order comes in on Thursday.

The full bridge I built.

The whole circuit at the moment.

Here is the bridge wave while its all running. I used 2 nine volt batteries one for the driver and one for the bridge to see how it performed under really low power.

Marko

Mon Apr 10 2006, 07:37PM

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

Flyback type converter is a bad idea to drive GDt's. It can maybe pass when you drive only one transistor and just then.
I use to get dreadful looking waveform this way (on my flyback driver) but it still seems to work quite good on my flyback driver.

You should power the GDT with half or full bridge of transistors (or maybe use 2 primaries) and use one preamplifier stage or darlingtons.

the_anomaly

Wed Apr 12 2006, 10:41AM

Registered Member #19 Joined: Thu Feb 02 2006, 03:19PM
Location: Jacksonville, FL
Posts: 168

ok. I've changed the gdt core to ferrite and used speaker wire to wrap the secondaryâ€™s. I've also ordered some ucc37322 chips to drive the gdt as Iâ€™ve seen many drsstcs use them. From what Iâ€™ve learned a ucc chip is used to boost a 555 signal and then adjusts the signal with feedback from the tc using an antenna. I want to use Steve W's class e sstc ucc chip configuration because I only want to use one ucc. To drive the gdt in both directions can I use a 555 that gives a positive then negative(and back again) square wave into the ucc? Or will I have to use another ucc?

Dr. Shark

Wed Apr 12 2006, 11:31AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

You can do both, a single UCC contains two switches so it already does the full job, but by using two you can double the voltage you get out. Until you get the UCCs just try any pair of NPN and PNP in a totem-pole configuration, it usually works reasonably well.

Another point: You should twist all fife wires together before winding them on the core, this gives lower leakage inductance.

1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob