Discrete boost converter circuit?

[mark_in_manc]

Hi folks
For OT reasons which we shan't discuss, I need 12v at about 2A from a noisy, dirty supply which is perhaps 5-7v, and which might have spikes on it now and again. I've fried one Chinese surface-mount boost converter already (I'm not sure why) and I have another on order - but I fancy making one on veroboard, learning how it works, and being able to fix it. My eyesight and soldering skills are not up to working with surface mount.

Can anyone point me in the direction of a design, article, what have you? I've done a bit of googling, but even the small degree of hand-holding involved in someone here saying 'this one's alright' would be confidence boosting.

thanks
Mark

[Radio Wrangler]

Try the National/Ti apps notes and data sheet for LM5022. It's a controller for a discrete power transistor boost or SEPIC converter.

David

[MrBungle]

I like the Mc34063 Ics. They're cheap and cheerful (20 for £1 from china) but they're unconditionally stable and whack a logic level MOSFET on the switch driver and you're good for silly amounts of current.

You can build your own with a 555 as the oscillator and an LM311 as a voltage comparator to a zener reference if you want as well. Use a BD139 or a MOSFET as a switch and you're in business.

[Oldcodger]

Similar idea- I wanted a stable / clean supply for an in car item from car voltage. I only needed about 200mA, but the idea is similar- drop the 12v to something like 5v , using something like a 7805 and then buck boost ( I used a 5-12v convertor chip, but other stuff is available ) to get 5 v clean up to 12v at rated current.

[kellys_eye]

Elektor February 1992 did a good article on SMPS supplies using the ubiquitous MC34064 (a 3-pin device, still readily available for 50p/60p at Farnell) that could deliver 4V to 20V at 4.5A from an 8-35V input.

The article is very detailed and I'd be happy to forward it if interested (1.4Mb pdf).

The circuit diagram is shown below.

[mark_in_manc]

That sounds interesting - I'll PM you, thanks.

By the way, I'm always impressed when people (like you) say in ***** magazine, issue ** (month) (year) there's an article xyz... (a bit like 'it says in John chap 89 vs 4-67... ). Is my memory really failing more than everyone else, or is there some kind of searchable database going on which I don't know about?!!

[Boater Sam]

I've got lots of BS170 if you want to play.

[Ed_Dinning]

Hi Mark, if you do not need in/out isolation then all you will need is a toroid for energy storage and design is much simplified

[MrBungle]

Good point. Look up a Royer Oscillator.

I've built a couple. One of them caught fire which was "interesting".