Comments on: AVR boost converter

By: andre

andre — Sun, 12 Jul 2009 13:41:48 +0000

yeah, was chatting to Mr Sprite on IRC just now.

BTW if you need small FETs, take apart old electret mikes as they have one. Its an N channel JFET but for low power applications this doesen’t matter.

Another source for MOSFETs is the buck circuits from dead PC motheboards- a minute with a heatgun will remove them with no damage if they are surface mount, otherwise use chipquik.

By: biojae

biojae — Thu, 09 Jul 2009 23:50:01 +0000

I got my arduino to output 20v with this circuit :-)

By: piet

piet — Thu, 09 Jul 2009 16:54:07 +0000

other interesting 2-transistor step-up/down circuits:
http://www.romanblack.com/smps/smps.htm

By: DarkFader

DarkFader — Thu, 09 Jul 2009 08:00:06 +0000

does an ATTiny have an analog input to monitor the voltage for example?

By: carlton

carlton — Thu, 09 Jul 2009 03:14:45 +0000

A schottky diode would be a quick way to increase effiency. Yes, a pmos could be used (synchronous rectifier), but you need to add some logic / use extra pins to assure there isn’t cross conduction (both fets on at same time, shorting vout to ground).

also, you’d do better with a more capable gate driving scheme for the fet than the (probably weak) pwm signal from the ic.

probably overkill, but that’d likely get the highest efficiency / longest battery life.

By: Tyler

Tyler — Wed, 08 Jul 2009 21:38:51 +0000

He should replace the diode with a p-type MOSFET and he’ll get much better efficiency. There’s a good bit of power being burned up on the diode. Would probably send him to the mid to high 80′s efficiency wise.

By: johnnywaffles

johnnywaffles — Wed, 08 Jul 2009 17:44:20 +0000

Gosh darnit i’ve done this before with a zilog 8 pin proc outputting 5 khz on a mosfet…I didn’t deem it publish worthy i was able to power a blue led off of a AAA battery

By: yu

yu — Wed, 08 Jul 2009 16:35:30 +0000

opps i guess i didnt read the whole question… sorry…

By: yu

yu — Wed, 08 Jul 2009 16:27:22 +0000

@Lupin, I dont think adding a cap in series will work. The point of pulling the inductor to ground is to allow current to flow through the inductor. Then, when it switches off, the inductor will continue to drive that current to the cap. With a cap in series, the current in the inductor will go to zero once the cap is full. after that, you will need a way to discharge that cap inorder to have current flow through it.

By: lupin

lupin — Wed, 08 Jul 2009 09:20:47 +0000

I have known this hack before – now i know where from :)

By: geekabit

geekabit — Wed, 08 Jul 2009 08:37:56 +0000

haven't you covered this before?

By: Lupin

Lupin — Wed, 08 Jul 2009 07:44:22 +0000

There should be a capacitor in series to the switch (with discharge resistor in parallel) so that you can hold the switch for a longer time without running too much current through the coil. Or wouldn’t that work? I am not so sure…

By: guyfrom7up

guyfrom7up — Wed, 08 Jul 2009 03:30:29 +0000

This is great, I’ve thought about this, but I could never figure out how to easily get it jump started. He did is so simply and elegantly, great job! My original idea was have like a super cap, but this is wayyyy better.

By: Jeff Epler

Jeff Epler — Tue, 07 Jul 2009 23:51:25 +0000

I recall this being discussed on an avr-related mailing list (maybe avr-chat?) in the mid 2000s, including nicely-formatted ASCII circuit art. Unfortunately, I am not able to find the message online or in my personal archives. My recollection is that this concept was proposed (including the bootstrap switch) but never tested.

By: arthur

arthur — Tue, 07 Jul 2009 23:08:46 +0000

AWESOME.

I love the crude “bootstrap”. Brilliant.