Originally Posted by chrugel  This will be my next move:
Replace the 1n4007 diodes in the gate network with HER105.This beacase the HER105 is a super fast diode compared to the slow 1n4007, trr of 50nS compared to 2000nS Replace the IRFP260 transistors with IRF640.The gate capacitance of the 260 is 5200pF while that of the 640 is1300pF. The original UHU was designed for IRF540 which has a capacitance of 1700pF Create a RLC snubber network on the output with these values:
R 25 Ohm
L 5uH
C 6nF
Since it seems to be nearly impossible to obtain this inductor at the time beeing this will be omitted and there will only be a RC snubber there for preliminary tests.
I dont think this should be any problem since the C is so small, of cause this will yeld higher dv/dt rates at the motor.
(frantically searching the web for diy inductor design formulas . . .  )
Just to be clear, my goal is not a HP UHU controller just a high voltage version without the snubber heating problem and cross-conduction.
Ultimate goal: 150V 3 A
regards
chris |
I don't know about the PCB you are using, changing the output Mosfets by IRF640 is a wise decision, also replacing the bootstrap diodes by HER105. You might get a big improvement just by doing that. Add a couple of 100K 1/2 W carbon composition resistors from the high side mosfets' sources to power ground.
I recommend using the same output snubber used with the HP_UHU it was calculated for that voltage range. Current won't be a problem. Reduce the gate resistance to 51 ohms and get rid of the diode resistor combination at once. You can leave the 15 V zeners on the gates. Do another test. Resetting and UHU chip losing eeprom contents depends a lot on the ground noise and that is dependent on the PCB design.
If you were able to completely suppress cross-conduction, ground noise is not going to become a big deal, but all depends on the logic ground and power ground being connected only at one point near the power ground terminal.
Good Luck!
Snubbers act as "dissipative" high dv/dt energy suppressors, in a certain way they act as low pass (dissipative) filters. The calculations are completely different to "normal" low pass filters.
Kreutz.