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Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
Checked the archives already... I have a switch question.
Just for fun, I built a circuit that, when placed very close to an ion source such as a cathode tube style television set or an Ionic Breeze air cleaner, etc, scavenges enough airborne ions to power small loads such as an LED or small motor. A pointed wire is placed near the ion source to receive the energy (like a small lightning rod) and charges a HV capacitor which discharges through a 1kV gas-filled spark arrestor into a Buck-Converter (spark arrestor in the place of Q1...HV cap not shown). The Buck-Converter steps down the 1kV pulses down to a relatively smooth 5-10 volts which powers the light loads. L1 is 12mH, C1 can be anywhere between 3300-22,000 uf to work okay.
I want to replace the 1kV gas-filled spark arrestor with a semi-conductor switch so I can drive the switch with my Function Generator.
Already tied a CLARE CPC1788J 1kV Opto-Isolated Mosfet but can't seem to get it to work in this application. Can anybody recommend other devices for me to try? Preferably Isolated devices. Thanks in advance. (Btw, tried to attached the schematic from the EDIT mode using the INSERT IMAGE feature... but wouldn't work)
Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
Patrick:
Yes. I want to replace the 2 terminal gas-filled arrestor with a silicon-switch that I can control with my function gen.
Essentially, I am asking for advice on what device to use for Q1 (that can handle 1kV (+/-) and is preferably isolated so I don't fry my function gen).
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
A high voltage MOSFET or IGBT with a gate drive transformer using well insulated windings seems like it should do the trick. 1.5kV IGBT's can be bought in the $5 price range.
I'm guessing that the voltage on the input cap will keep rising if not enough current is drawn from it, so you can either assure that enough load current is drawn, or you could put a bleeder resistor or a safety spark arrestor (which could be implemented with solid-state devices like zener diodes, MOV's, or BJT's using avalanche breakdown) if you want to make sure that the main switching transistor does not accidentally break down.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I think the key would be the extremely low leakage current of the gas tube switch. A MOSFET or IGBT could well leak more than the current you're trying to collect.
Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
My Function Gen is basic function $150 version.
Steve, I'm beginning to think the reason the CLARE CPC1788J OptoIsolated Mosfet isn't working in this application is indeed because it leaks too much, thus never allowing the HV cap to develop much voltage.
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Switch Question
