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Gate drive signal

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LAN_403

furnace

Thu Nov 07 2013, 08:34AM

Registered Member #4992 Joined: Wed May 23 2012, 03:57PM
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Posts: 108

This is the signal coming from my two tc chips without the load of the gdt ,so this is where the problem is because the signal coming from my pll is clean and thats why i think the 2 tc chips are faulty but than again i dont know if it is also normal to look like this with my experience.

Dr. Dark Current

Thu Nov 07 2013, 01:31PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

That ringing is probably fake, a small loop of wire to the scope's ground clip can result in this. Or you have a bad quality bypass cap on the IC, or the bypass cap isn't close enough. But what really matters is the waveform with the GDT loaded.

furnace

Thu Nov 07 2013, 06:23PM

Registered Member #4992 Joined: Wed May 23 2012, 03:57PM
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I actully managed to get the signal clean on the secondary of the gdt with back to back diodes which is the first pic but than the signal still looks like this when i start the inverter on the second pic.

IamSmooth

Fri Nov 08 2013, 12:41AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Show a picture of the actual circuit. Show the wire connections from the GDT to the resistor to the gate.

Are you sure the capacitors on your rail supply are good?

If you look at this page I have various waveforms

Your ringing looks like high inductance. Once I see the picture of your setup it should be apparent, but I bet your leads are too long. You need to increase R to 10-12R and significantly shorten your leads. Are the resistors wire-wound? I did not see a response to someone else's question about this. If so, you must get rid of them. If you look at some of the pictures I went to great efforts to do this and shield the leads. I also had ground planes on the boards to help shield from noise.

furnace

Fri Nov 08 2013, 11:48AM

Registered Member #4992 Joined: Wed May 23 2012, 03:57PM
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This is the hole circuit iamsmooth.The variac with the rectifier and bus caps,15volt supply on bread board , pll driver with 2 tc chips, inverter with snubber caps, ultra fast and shotky bypass diodes and gdt. The bypass caps for the half bridge with the coupling toroid and then the tank. I replaced the wire wound resistors on the gdt with18ohm alluminium resistors.

IamSmooth

Fri Nov 08 2013, 01:55PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Wires too long
No shielding

I'm surprised you don't get tv reception with those antennas

Look at my project
Everything is tight
You need to burn a circuit board with extremely close connections
You need grounding lanes around the gate connection
15r is too much. This slows the rise time and can also cause overheating

7.5 to 10 was good for me at 12kw
Use the resistor types u used. I can look up the model number if you need me to do so

You must clean yo the wiring mess you have before you do anything else

Proud Mary

Fri Nov 08 2013, 04:52PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

There are times when we all have to go back to basics, and I suggest you make a study of electrical and electronic wiring techniques if you ever want your circuits to work properly and safely.

I suggested earlier in this thread that poor layout and long straggling wires were an open invitation to instability and parasitic oscillation, and I'm afraid no one will be able to help you diagnose your circuit until you re-wire it in a workmanlike manner. As it is, there are simply too many possible sources of malfunction - indeed, I would be surprised if something thrown together like yesterday's spaghetti worked at all.

This Navy teaching material is a good start:

As for those prototyping boards, I call them a matrix of dry joints just waiting to happen.

Don't be discouraged! We've all been there!

HV Enthusiast

Fri Nov 08 2013, 06:54PM

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

I agree with the response by both IamSmooth and Proud Mary.

Clean up those wires. For the gate drive circuit, at the minimum, get a piece of copper clad board and build your circuit on that using the bottom as a ground (return plane). Keep all connections short and any physical electrical loops as SMALL as possible.

For any wires connecting the output of the gate driver (switching) to the transformers, twist tightly together. This will reduce inductance and keep that electrical loop as small as possible.

If you just think in term of physical electrical loops, thats a start. Route your wire (both board traces and point-to-point wiring) to MINIMIZE the physical area made by the loops your wires are making.

A electrical circuit with a loop shaped like a CIRCLE will be the maximum loop area.

An electrical circuit with the wires twisted tightly together will be the smallest your loop can be.

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