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Registered Member #2121
Joined: Fri May 15 2009, 01:05AM
Location:
Posts: 10
Based off what I have seen from uzzors design, can I replace the power fet with a power darlington. I might need to use a predriver (such as a bd139) to produce enough current to drive the base of the MJ10012 I have access too
Alternativly, can I use a TV flyback transistor. Its a 2SD1878.
I intend to use my boost converter to charge a MOC (microwave oven capacitor) bank to around 350v then dump the energy into a car coil for the ignition system of a home made gas turbine. The switching will be handled by a 555 timer, dischgarging the cap at 1hz rate, at the same time deenergising the boost converter so its not shorted out when the firing SCR triggers. The boost converter will be switched on and off via a solid state relay.
The 1hz rate I have selected should be more than sufficient to allow the 3uf set of mocs to charge up.
Registered Member #1694
Joined: Sat Sept 13 2008, 09:13AM
Location: Australia
Posts: 108
If the drain source breakdown voltage is fairly high, its resistance is fairly low and the 555 is capable of delivering enough current to turn it fully on I don't see why it wouldn't work.
Registered Member #2121
Joined: Fri May 15 2009, 01:05AM
Location:
Posts: 10
ok - sorry I took ages to reply.
The transistor (MJ10012) is rated at 600 volts, base current of 2 amps (I cannot see a 555 sourcing this), and a resistance of 27ohms.
It looks like I will have to use a predriver (mabye a BD139 or something along those lines) to properly drive this transistor. Will this work or should I use one of the TV flyback HOT's I have - ones a 2SD1878, which has a base current of 100ma, 1500volts and has an internal snubber diode. Its resistance isnt in its data sheet.
I have got the oscillator (555) running at anywhere from 3khz to 39khz. I can adjust it via a trimpot.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
A quick check; IF the 3uF is fully discharged each cycle (it may not be) then at 350 V & 1 kHz that's 187 Watts At 100 % efficiency a 12 V system would need 15 Adc. The peak transistor current will be around 40 Amps !
Registered Member #2121
Joined: Fri May 15 2009, 01:05AM
Location:
Posts: 10
This is a lot of power!! I'm thinking mabye finish the boost converter and use it for something else (got some old hard discs here - mabye make a disc launcher), and use a 12 volt to 240v inverter rectified to charge up my cap.
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Boost Converter Mosfet
