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Hi all. I am currently working on medium sized drsstc with steve's OCD driver, closely this one A driver seems runs great, even everithing worked on first time . But I have a bad feeling about this Gate waveform as u can see there are a ringing spikes on max and min voltage. I dont know what this ringing may cause, any ides? I notices the ringing rise with rising voltage on bridge as u can see there is no ringing on 9V on bridge and awful looking one on 36V. I dont know if this is a commnon problem, but can it be some misunderstanding in my old tesla oscilloscope if it is displays somkinda wrong? I dont have a explanation for this. I have done some reading here but nothing helped. Anyway i thing its a wery usefull stuff!
Here are some my specifications:
GDT winding: 8:16:16:16:16 10ohm and paralel schottky diode on every Gate 15V zeners on GS GDT cap 1uF MKT transistors HGTG30N60B3D (oscillosope Tesla BM550)
Any more informations u need just write here and I will responde.
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
put larger Rgate and also, you can calculate diference between Tdon and Tdoff, and use another resisitor in series to gate diode. so if you have 10Ron, and 20ns tdon and 200ns tdoff use 1R+1N5819.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
If the ringing isn't present when the DC bus voltage to the H-bridge is zero, and it gets worse as you increase the DC bus voltage.... Then, i'd hazard a guess that it is one of the following:
1. Forced reverse recovery of the free-wheel diodes when each MOSFET turns on. What devices are you using for the switches and what devices for the free-wheel diodes?
2. Shoot-through (cross conduction) between the MOSFETs if the turn-on is set faster than turn-off.
...or maybe even...
3. Ringing of the stray inductance in the supply wiring (diode's clamping loop) if the bridge layout is sloppy.
What was the load you had connected to the bridge during the test?
Have you included some dead-time on the drive waveforms?
What decoupling capacitance do you have across the DC bus supply right at the H-bridge?
The schottky diodes should be pointing away from the MOSFET gates with a resistor in parallel with them. You could try increasing this resistor to slow down device turn-on and see if it improves the ringing situation.
Hi Richie, I am using a HGTG30N60B3D IGBT's in full bridge and free-wheel diodes are just those internal. I am running whole coil during test as this is a feedback driver system. My oscilloscope has a 27pF input, is this a dead-time parameter?, if not what is? I have a 5uF decoupling capacitance on bridge. I have right way connected diode on resistor, just need to increase the resistance.
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Ugly gate waveform, what to do?
