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Registered Member #1571
Joined: Wed Jul 02 2008, 03:26AM
Location: Bendigo Victoria Australia
Posts: 44
Hi there,
I have added a file to this post and its an LT spice sim of a Cockcroft Walton Multiplier. Its of a single ended flyback design to drive the CW in resonance with a snubber added.
My problem is with the snubber.. while it does stop the voltage rising too high on the collector of the IGBT (and thus avoiding blowing the device up) the average power on the snubber resistor and series resistor in no way reflects the power in the IGBT. The average power in the IGBT is ~33Watts yet the average power in the 10 ohm resistor is 360Watts. That's really high and I understand that snubbers should not dissipate even a tenth of this power. Is there something wrong with my design or is this what I should expect with an air coil of this size? That my snubber should dissipate that amount of power... if so why?
..do I really need components of this size (>300W 10ohm resistor) in this instance....
(If you run this in LT once running you can use the ALT button pressed and click on the component - that will display the trace for power used... once the sim has finished you can click on the particular trace name with the control button depressed and this will show you the average power or voltage or current depending on what the trace was showing..)
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
This kind of snubber really wastes energy. Can't you use a simple capacitor? And look at the power in the series resistance of the primary coil. Why are you rising the power supply so slowly? The simulation takes forever in this way. Better to use an ideal switch instead of the complicated IGBT while debugging the basic operation.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Antonio wrote ...
This kind of snubber really wastes energy. Can't you use a simple capacitor? And look at the power in the series resistance of the primary coil. Why are you rising the power supply so slowly? The simulation takes forever in this way. Better to use an ideal switch instead of the complicated IGBT while debugging the basic operation.
I haven't looked at the schematic yet, but if this is the standard flyback with RCD snubber, yes, you do want a R there. The energy stored in the leakage inductance of the flyback has to go somewhere, so it will either cause the IGBT to avalanche (sad sad transistor) or you want it dissipated in a resistor.
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Problems interpreting the results of a spice model for a CW stack - Snubber power values seem high.
