AVR-Chat

I havent been following this back-up power supply circuit very closely so I
may be way off track here but...

If I had a LOAD that was feed from 110 VAC POWER SUPPLY and wanted to supply
emergency power to it in the time of a power outage here is how I would do
it.

I would start off with the POWER SUPPLY voltage a little bet larger than the
BATTERY.
Read that sentence again, its a must. Four alkaline batteries (4.8 = 4 x
1.2) and the output of a 5 volt regulator should work fine.

On a piece of paper write horizonallly the words BATTERY, POWER SUPPLY and
LOAD
Individually circle each one
Put a lead out of the top and bottom of each
Mark the top leads + (positive) and bottom leads - (negative)
Connect all the negative leads
Connect the POWER SUPPLY through a diode to the LOAD
Connect the BATTERY through a diode to the LOAD

Because the voltage on the positive terminal of the LOAD from the POWER
SUPPLY is greater than the voltage from the BATTERY current WILL NOT flow
through the diode connected to the BATTERY.

As soon as you unplug the POWER SUPPLY the BATTERY will take over supplying
power to the load. This will continue until the BATTERY runs down or power
is restored to the POWER SUPPLY. The LOAD will never know if is is on POWER
SUPPLY or BATTERY. It will on so never know when the POWER SUPPLY drops out
or comes back on.

All you need, besides the BATTERY, POWER SUPPLY and LOAD is 2 diodes.

Mike

PS Like I said at the start. I have missed a lot of this thread so I don't
know everything that has been, and is being, talked about. Designing many
custom circuits over the past 40 years, power supply circuits are duck soup.

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