[time-nuts] Low Drop Out Voltage Regulator

[David Forbes]

At 10:23 PM -0600 3/8/07, Brian Kirby wrote:
>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 ?
>
>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.
>
>Brian N4FMN

Brian,

I've been slowly putting together the same thing. I decided on the following:

A 28V supply used as a float charger to keep the SLA battery at full 
charge at all times. The power supply is rated at less than the 
startup current of the Rb source - the SLA battery will warm up the 
Rb unit, with the automatic overcurrent limit of the supply keeping 
things safe. Charge the SLA before use!

The float voltage to keep a 24V SLA happy is about 27.0V. The power 
supply I found is a standard Power-One open frame linear with 1A 
current limit. It has a voltage adjust pot to set it to 27.0V. A 
series diode is placed between the power supply and the battery to 
keep current from flowing into the supply when AC fails. The float 
voltage measurement is done at the battery end of the diode.

The end result is that the Rb runs at 27V when the AC power is good, 
otherwise at 24V. For a non-super-critical application, this should 
be sufficient. The frequency error as a result of the voltage change 
is documented in the Rb source datasheet, I would hope.

-- 

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/