Junkbox boost converter update

Sep 18, 2016 9 Replies
M

So I replaced the feedback divider with a scaled up resistor network, with the top resistor in the megohm series. I also added a high-current PNP pulldown at the gate, driven from three sections of 4093 output; collector to ground, ~150 ohms across base and emitter, also 10k pulldown on the gate.



Efficiency is up to 85% at 150V and 20mA output, which is a lot better. I could probably improve things a little further by actually grinding the math to select the "correct" values for the gate pulldown and base-emitter resistor. But it's good enough for now for the one-off project.



What's really killing me is the 4 ohm on state resistance of the 600 volt MOSFET...I think a 300V part would work OK here and probably drop the on state resistance below an ohm. I just don't have one in stock... ; )


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J

You can't parallel the ones you have at hand?

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W

Well, it's been 9 days since I suggested the PNP and a better MOSFET. This shows one thing that's wrong with junkbox designing: If your approach was more along the lines of engineering, pick the right part and order it, you'd have had it many days ago, and be reporting stellar performance.

Thanks, - Win
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T

Aren't junkbox projects great? It's the perfect excuse to not order parts, or complain that winding a custom transformer is too hard!

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

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P

You just need a good enough junkbox. ;)

Cheers

Phil Hobbs

(Building high technology out of my drawer cabinets for 30 years now.)

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
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M

My local electronics parts store (yep, there are actually a few left that still have decent selections of real stuff) has some more appropriate N channel MOSFETS in stock.

$7.50 for an NTE2385? Screw you, NTE! You go to heck!

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M

Mine is 30' by 40', and it's still not big enough. :(

Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
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A

It ain't how big it is, it's what's in it.

Mark L. Fergerson

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M

You're welcome to explore it, but at your own risk. No search & rescue team will come looking for you! ;-)

Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
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