I'm building a radio receiver with an audio output which I'd like to have
backed up by an on board 'UPS' using 7.2 volts worth of Ni-Cads - so it
can run on either mains or batteries with a seamless changeover, and
charge the batteries when mains is available. The peak current requirement
of the receiver is about 250mA - it has a small power amp and LS built in
for monitoring.

What would be a suitable management IC to do all of this? The range seems
rather bewildering and I'd like to short circuit the selection process. ;-)

--
*Save the whale - I'll have it for my supper*

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
I'm building a radio receiver with an audio output which I'd like to have
backed up by an on board 'UPS' using 7.2 volts worth of Ni-Cads - so it
can run on either mains or batteries with a seamless changeover, and
charge the batteries when mains is available. The peak current requirement
of the receiver is about 250mA - it has a small power amp and LS built in
for monitoring.

What would be a suitable management IC to do all of this? The range seems
rather bewildering and I'd like to short circuit the selection process.
;-)


You don't need an IC to do that unless you want intelligent battery
charging. Simply use a diode in series with the battery supply and make sure
the voltage of the supply from the mains PSU is greater than the battery
voltage so the diode is reverse biased when mains is present. This will
allow the mains derived supply to power the radio and disconnects the
batteries. When the mains supply goes down, the diode is forward biased and
the batteries take over. It's completely seamless. A humble 1N400x series
diode should be more than ample.

Obviously you'd need to bypass the diode with another diode wired the other
way round in series with a resistor to trickle charge the batteries, or you
could make a more elaborate constant current design switchable between
proper charge (C/10 or whatever) and trickle charge.

Dave

In article ,
Dave D wrote:
You don't need an IC to do that unless you want intelligent battery
charging. Simply use a diode in series with the battery supply and make
sure the voltage of the supply from the mains PSU is greater than the
battery voltage so the diode is reverse biased when mains is present.
This will allow the mains derived supply to power the radio and
disconnects the batteries. When the mains supply goes down, the diode
is forward biased and the batteries take over. It's completely
seamless. A humble 1N400x series diode should be more than ample.

Obviously you'd need to bypass the diode with another diode wired the
other way round in series with a resistor to trickle charge the
batteries, or you could make a more elaborate constant current design
switchable between proper charge (C/10 or whatever) and trickle charge.

I was hoping for an IC to do all this - UPS - charging and maintence
charge and changeover all in one go. I'm sure they must exist. ;-)

--
*I finally got my head together, now my body is falling apart.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman:
Why, oh why make it difficult??..... less to go wrong with the series
diodes and resistor trickle charge.... just about bullet proof.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


snipped:
"Dave Plowman (News)" wrote in message
...

I was hoping for an IC to do all this - UPS - charging and maintence
charge and changeover all in one go. I'm sure they must exist. ;-)

In article ,
sofie wrote:
Why, oh why make it difficult??..... less to go wrong with the series
diodes and resistor trickle charge.... just about bullet proof.

Because it doesn't do what I want.

--
*There are 3 kinds of people: those who can count & those who can't.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
sofie wrote:
Why, oh why make it difficult??..... less to go wrong with the series
diodes and resistor trickle charge.... just about bullet proof.

Because it doesn't do what I want.


I beg to differ, unless you have a requirement that you haven't stated in
your OP. We're not mind readers. :-)

Dave

In article ,
Dave D wrote:
Why, oh why make it difficult??..... less to go wrong with the
series diodes and resistor trickle charge.... just about bullet
proof.

Because it doesn't do what I want.


I beg to differ, unless you have a requirement that you haven't stated
in your OP. We're not mind readers. :-)

I need a rather more sophisticated charger - a reasonably fast recharge
then maintenance charge.

--
*A 'jiffy' is an actual unit of time for 1/100th of a second.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Dave D wrote:
Why, oh why make it difficult??..... less to go wrong with the
series diodes and resistor trickle charge.... just about bullet
proof.
Because it doesn't do what I want.


I beg to differ, unless you have a requirement that you haven't stated
in your OP. We're not mind readers. :-)

I need a rather more sophisticated charger - a reasonably fast recharge
then maintenance charge.


Then you use a diode for the "UPS" functionality and look for a
sophisticated charger?

"Jussi Peltola" wrote in message
...
Dave Plowman (News) wrote:
In article ,
Dave D wrote:
Why, oh why make it difficult??..... less to go wrong with the
series diodes and resistor trickle charge.... just about bullet
proof.
Because it doesn't do what I want.


I beg to differ, unless you have a requirement that you haven't stated
in your OP. We're not mind readers. :-)

I need a rather more sophisticated charger - a reasonably fast recharge
then maintenance charge.


Then you use a diode for the "UPS" functionality and look for a
sophisticated charger?

My thoughts exactly.

Dave