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Junkbox boost converter update

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... ; )

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

Reply to
John S 

--
 Thanks, 
    - Win
Reply to
Winfield Hill

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
Reply to
Winfield Hill

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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Reply to
Tim Williams

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
Reply to
Phil Hobbs

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!

Reply to
matt

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! ;-)
Reply to
Michael A. Terrell

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

Mark L. Fergerson

Reply to
Alien8752

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! ;-)
Reply to
Michael A. Terrell

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