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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Hey all. I need some help...
I've been told to make a 30 kV supply that can dish out 1 mA. Not hard, since it's only 30 watts of juice.
Problem is the supply is limited to 14 volts (at around 2 - 3 amps)
30 kV is preferably regulated, though I guess I could just modify the duty cycle manually to achieve it (I have a HV meter I can use to measure it)
Would a standard 555 timer flyback driver be able to achieve this? Or should I try something a little different, or maybe make it resonant, with a cap across the primary?
Or screw flyback topology drivers and go with a push pull halfbridge?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
a flyback circuit and a 3-6 stage dublier that is powered buy a SG3525 might work. it has all of the stuff in it to make it work so it would regulate. you would have to sample the output with a HV divider for feedback. maby some one has already done it. I know Patric has a thread about his.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Since flyback transformers (LOPT here in UK) with > 30 kV rating are available (I have 10x HR6549 35.5 kV rated ones ;) and 1 mA is well within specifications, no multiplier would be required. Some form of output or load capacitance would be required.
A 555 + mosfet with fixed duty cycle would provide a constant output POWER so if the output current changes so will the output voltage. Simple burst-fire = enable/disable feedback can be used for voltage regulation.
I would use UC2825 (high drive current) and PSMN8R7-80PS (low Rdson) (both cheap/available) because they are what I have , this combination allows output voltage regulation and current limit. (the first digit for UCxxx ics is temperature rating so UC1825 or UC3825 are similar) The external component count for 555 and 2825 are similar. Good quality/low-esr capacitors are required for the dc supply. A new primary winding for the LOPT will be required.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
I don't think you can use the flyback topology for this. The efficiency probably won't be high enough without some careful engineering (like Steve Ward's active snubber circuit).
If your supply sags to 12V under load, you'll need 2.5A for the 30W.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
Just curious ... what's the plan? Diode split (DC) flyback with PWM drive and current limiter on the primary like Sulaiman suggested? With a repetitive avalanche rated MOSFET, TVS, (regenerative-)snubber or a hope and a prayer?
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Stepping 12 volts up to 30 kV....at 1 mA?
