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4hv.org :: Forums :: Tesla Coils
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Resistor in Steve's universal driver.
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BSVi
Tue Jul 03 2012, 01:41PM Print
BSVi Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83
 		Hi. I can't understand - what is the puprose of R11 resistor?
Link2

I beleived that it's there to dampen GDT oscillations, but the picture stays the same for all the resistor values.

Here are scope shots with no resistor attached, 100 ohms and 10 ohms: The picture stays the same.
1341322899 1637 FT0 Gdt Inf

1341322900 1637 FT0 Gdt 100

1341322900 1637 FT0 Gdt 10
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Steve Conner
Tue Jul 03 2012, 02:39PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
 		I use the same arrangement in my driver. It is to dampen a low frequency resonance (a few kHz) between the GDT magnetizing inductance and the DC block capacitor.

The oscillations you show there are high frequency ones, so they are probably caused by something else.
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BSVi
Tue Jul 03 2012, 03:42PM
BSVi Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83
 		Where should I look to see those low-frequency oscillations?

This resistor is bad thing if you are planing to run CW coil, that's why I'm asking :)
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Kizmo
Tue Jul 03 2012, 04:43PM
Kizmo Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
 		Why bad?

Im using this driver with few logic side mods in my induction heater. Gate drive section is identical to original.
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BSVi
Tue Jul 03 2012, 05:43PM
BSVi Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83
 		Kizmo, doesnt it heats up? 10 ohm resistor should dissapate 50W of power in CW mode.

Ok, can see this effect in the simulator, but can't see it in real life. I should investigate a bit why :)
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BSVi
Tue Jul 03 2012, 08:23PM
BSVi Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83
 		Here are shots of the begingng of the burst with 10ohm resistor and without one. I can see, no difference at all. The drivers are IXDN630.


1341347017 1637 FT141072 1

1341347017 1637 FT141072 2
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Steve Conner
Tue Jul 03 2012, 09:54PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
 		You need to zoom out much further to see the entire burst. You should see a slow "bounce" in the DC level.

The resistor doesn't dissipate any power because the capacitor shorts the AC voltage across it, and the DC voltage should be zero.
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BSVi
Wed Jul 04 2012, 04:00AM
BSVi Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83
 		The simulator predicts that the beginning of the busrts should have DC offset, but it doesnt.

Here my full burst and simulation. The burst is measured on GDT's secondary side just before RD networks.


1341374913 1637 FT0 1



1341374409 1637 FT141072 2


You are right. The resistor doesnt dissapate substantial power. It's my mistake. But, never the less, I want to see this effect with my scope, but can't reproduce it. Thank you.
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Steve Ward
Thu Jul 05 2012, 12:36AM
Steve Ward Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
 		The low frequency ringing usually shows up at the end of the burst, due to imperfect volt-seconds balance storing some energy in the L and C of this circuit. You have some high frequency ringing (which looks pretty bad) but i dont see the LF ringing that often showed up with my drivers, so i dont know what to tell you.

To damp the HF ringing in your gates you would likely need to either reduce the leakage inductance, or add some resistance in series with the GDT.

As mentioned, this resistor does not pose a problem for CW operation. My latest driver puts a 1uF cap in series with this damping resistor to limit DC current through the resistor if your gate driver happens to output DC for some reason.
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