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Registered Member #1596
Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65
So I guess ZCS keeps the width of ON pulse fixed while ZVS keeps the OFF time constant? And power is adjusted by changing frequency. In the full bridge ZVT approach phase varies.
What control method should I go with? I dont have any preference either IGBTs or MOSFETs will work. My concerns are stability and regulation range. As well as the best method for constant current source.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Would you mind giving some details of what your load will be? The SLR converter is particularly suited to charging capacitors, and driving low impedance loads such as an arc. The issue with them is that they lose their constant current nature at the peak of their output voltage, so you must either design the transformer to allow for higher voltage than you expect your load to run at, or look at other types of converters.
The SLR is relatively stable, and will deliver fairly constant current output with no special feedback control over it. So if you need constant current within say 10-20% regulation, this could be the way to go. I also found it to be the most reliable way of driving my large ferrite-based HV transformers. Much better than any hard-switched methods ive tried.
Registered Member #1596
Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65
The load is an arc discharge. But its quasistable, eventually it breaks and needs reignition. The high voltage is only needed to brake the gap, after that relatively constant current should be fine, I dont care what the voltage is during discharge but expect it it to be significantly lower than needed for the breakdown.
But once the arc propagates and grows voltage needs to adjust to try to keep the current and if there is no current it should go to the maximum to break the gap again. So at the maximum voltage high current is not really needed, just to brake the gap and start the arc.
What about ballast resistors? Should I use one as well?
Registered Member #1596
Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65
Steve, I still dont quite understand yr driver. If I connect the wiper of R3 to any of its legs, it will be just another potentiometer in series with R4. This looks redundant and cannot be right. My Spice modelling fails to reflect any adjustments.
Alright, so the flip flop logic is clear to me, but still cannot model the Schmidt trigger part of the circuit. Basically it should generate a one shot, one of the pots should adjust the width of the pulse (on time) and another dictates the repetition frequency.
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ZVT etc... Please, help to decide on control logic!
