[time-nuts] Low Drop Out Voltage Regulator
Hal Murray
hmurray at megapathdsl.net
Fri Mar 9 01:19:46 EST 2007
> Can anybody recommend a low drop out voltage regulator that will work
> with a 2 volt input differential, and a output of 22 volts at 2 amps ?
2 V is not low dropout.
> What I have in mind is a 28 volt DC power supply, and 24 volt
> batteries, and a rubidium oscillator that will run at 22 volts.
Do you want a regulator to charge the batteries or one to run the rubidium
osc? If the latter, what's the battery voltage under load near end of
charge? You may need a LDO to get 22 out when the 24 has sagged a bit.
Beware that LDOs like to oscillate. You need some damping in the filter
caps. In general, electoylytics work fine but (good, low ESR) tantalums are
asking for troubles and ceramics guarantee it unless you add a series
resistor to provide ESR.
The LM317 is the standard adjustable old, low-tech, non-LDO regulator. It's
only guaranteed for 1.5A, but the data sheets say 2.2 typ.
Amazing. I can't find any input-output or dropout specs in TI's data sheet.
ST's has a graph of dropout voltage vs temperature. 2.5V at 1.5A Same for
National.
If I was designing something like this, I'd probably make a pass through the
usual suspects and see what their selector-guide said. TI, National, ST,
Linear-Technology...
Plan B is to go to DigiKey and type LDO (or regulator) into their search box
and narrow things down from there.
Another approach would be to use a switching regulator rather than LDO.
That's probably easier if you have 48V of batteries so you are always buck
rather than boost/buck if your 24V batteries sag below 22V.
--
These are my opinions, not necessarily my employer's. I hate spam.
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