AVR-Chat

> -----Original Message-----
> From: Adam Read [mailto:asread@bigpond.com] 
> Sent: Thursday, 18 March 2004 5:10 PM
> To: AVR-Chat@yahoogroups.com
> Subject: [AVR-Chat] Re: back-up power supply circuit
> 
> 
> Jay and anyone else interested:
> 
> Personally I'd use a relay to switch between supplies, thusly.
> 
> 1 o----  /------o 4
>        ) |
>        ) |   /---o 5
>        ) o | o
> 2 o----    |
>            o
>            3 
> 
>    Hook pin 1 to your input dc supply.  Pin 2 goes to ground.  Pin 3 
> is your input to your DC regulator.  
>    Pin 4 is the pin that will be short to pin 3 WHEN THE COIL IS 
> ENERGISED.  This means, naturally, that pin 5 is short to pin 3 WHEN 
> THE COIL IS NOT ENERGISED.  (Please excuse the "shouting", I'm just 
> trying to emphasise the point).  Pin 4 is therefore the pin which 
> you connect to your DC supply, and pin 5 is connected to your backup 
> supply.
>    If you use large enough caps on the input to your DC regulator, 
> the time taken to switch between supplies should be dampened, with 
> no or little loss of power to the circuit, depending on load, of 
> course. 

Ummmmmmm I would use an AC relay and put it before your bridge, or the
extra caps to keep the supply up for switchover will also keep the relay
energised, you could also use a diode after the bridge but before the
filter caps and take the +supply for the relay from between the diode
and bridge.

Regards,

Kat.

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