Efficiently Regulate 12VDC Down to 3VDC

Which do you want? I'd go with simple, there's no need for efficiency in this case.

then something is wrong. It should run cold.

NT

Define "efficiency" - design time, assembly time, component count, cost per unit, life expectancy ?

It won't. It draws a few mA itself, but at best it would get warm.

Any linear regulator will have to dissipate as much heat- more if you get rid of the diodes, so if that is an issue a switching regulator is the only way to go. Or slap a heatsink on ye olde LM317 and call it a day as Phil suggess.

--sp

We have been happy with the TPS62177DQCT in our products. The data sheet provides everything you need to know to use it.

Cheers

Which makes me think that that either Kevin's circuit is drawing much more current than he thinks, or he's somehow mis-configured the regulator (which for a three terminal device would take some doing).

Sylvia.

ISTR, from ~35 years ago, that 78xx devices from some manufacturers had a "surprising" pinout. I presume evolution has intervened in the meantime.

Get a cheap mobile charger for the cigarette lighter. Most of the older devices internally use a mc34063. Output voltage can simply set by replacing one resistor in the voltage divider.

or the reg is taking off.

Thanks Fred, and to all others who responded. I am now confident about proceeding with my project.

Kevin Foster

Something else to consider is that a white LED makes a pretty good 3V shunt regulator. It also provides good visible indication of operation. You can get higher current by making an emitter follower with the LED from base to GND, but the output will be about 0.6V higher than the LED. If it's too much, a green or yellow LED is about 2-2.5V.

If you use a 3 terminal regulator, make sure it is properly bypassed on input and output. Some of them can oscillate and dissipate a lot of power on light loads.

Good luck on your project.

Paul

Unless it is oscillating wildly at ~10MHz due to inadequate decoupling.

Regards, Martin Brown

Yep, that was my thinking too (see earlier post)