Electronics Question (Voltage Regs)

[SteveC]

Hi Guys,

I need your help here - I need to get a 12Volt supply from my car. Might sound easy, you think. But no - I need a regulated 12V output from the car. The '12V' in a car can be anywhere from 12V up to ~15V, and that's too much for what I want.

I also need this voltage at 2-3Amps.

I've tried a standard 2A 12V voltage Regulator (3 pin, TO22 style), but it really needs 14.5V absolute minumum to give me a nice 12V. (I also have a 5V version which works fine).

Is there such a thing which will do what I want? (something like a low-drop-out 12V, 2A regulator).

------------------
Cheers,
Steve

"Life is what we make of it, yet most of us just fake"

[SteveC]

aha.... would http://us.st.com/stonline/books/pdf/docs/6738.pdf (page 7) do it? Looks like to me that it works on 13.8Volts and upward - should be fine when the engine is running?

------------------
Cheers,
Steve

"Life is what we make of it, yet most of us just fake"

[rugger]

There are voltage multiplier curcits that can help if you need to keep Voltage significantly beyond 12V to keep the regulator happy.

They are made using diodes, I just can't remember the curcit plans.

Also, you should use some large capacitors before the regulator (4700microfrad or more) across the positive and negative lines. This will smooth out the fluctuations in input current. Be sure to use a diode to prevent the current from flowing backwards back into the cars curcits unless the voltage multiplier already does it.

One thing to remember when using diodes though, silicon diode require 0.6 volts before passing current. If you need this 0.6 volts, use germinanium diode, that consume much less.
<PRE>
eg (not including multiplier curcit)

+ ---|>|---+----[regulator]-----
diode | |
= capacitor | Computer
| | here
- ------------------------------
</PRE>


[This message has been edited by rugger (edited 24 May 2001).]

[arbymo]

rugger
I don't think that voltage multipliers circuites (diodes/capacitors combo) would work with DC source.

coz they use the polarity cycling of the voltage source to multipy the voltage.

Unless he has an AC generator in his.

[LvR]

SteveC

If you can live with quite a bit of heat generated by the regulator circuitry, then you can mail me and I can forward you a "crowbar" design - this design is based on the excess voltage being dropped over a high power series resistor, with a transistor drawing the unwanted current.


------------------
Lawrence

[Sasq]

arybmo, from memory the voltage doublers work, just don't ask me how, if it was ac you would use a step-up transformer.

a couple (3) of 7912(from memory) 1 amp voltage regulators in parallel would probably keep you out of trouble, but I'd throw in a smoothing cap to keep some noise out of the circuit

Dan

Sorry if the numbers are wrong, but its been a long time and my reference books are about 8056kms away

[SteveC]

Thanks for the replies guys!

Just waiting on looking some things up later.

------------------
Cheers,
Steve

"Life is what we make of it, yet most of us just fake"

[This message has been edited by SteveC (edited 25 May 2001).]

[Wombat]

What about this guy? http://www.arisecomputer.com/ps/html/ace916.htm

[SteveC]

F*CK!! argh!! I think I've blown my mainboard! Sh*t it cost me quite a bit too - it's not a normal board, it's quite compaxt, and has no PCI/ISA slots, it has onboard everything (intel 810).

It could be the RAM or CPU dead, I'll check that tomorrow. The PC powers up, but I get nothing on screen, and no beeps.

I have a feeling I may have put 14 and a bit volts into the 12 volt line from a so called 12 volt PSU I've been using - this mainboard derives a lot of its voltages from the 12V line.

I've spent quite a bit of time and money on this project, I hope to god it's not the board... I doubt I'll be able to find another. I've even built a custom clear perspex (plex-glass) box for it and everything.

I'll come back to it in the morning - it's gone 3AM here and it's probably my tiredness that's killed it...

------------------
Cheers,
Steve

"Life is what we make of it, yet most of us just fake"

[SteveC]

Right, I tested the RAM, and it was fine, however the CPU doesn't work (although it could be the Slotket I used is dead).

I've got to hunt down another socket 370 celery chip now, and I think give up on my home made PSU idea. I'll stick to the inverter and the proper PSU for the mainboard (assuming it still works, of course).

------------------
Cheers,
Steve

"Life is what we make of it, yet most of us just fake"