For one of the projects we have on the go at present, I'm using a 78L05 
regulator to drop the 24V incoming supply down to 5V for the PIC and 
MAX1485. The board's relay is a low power 24V type, so only draws about 
8.5mA when energised.

With the 78L05, the idle current draw from the 24V supply was about 
4.7mA. Swapping it out for an LM2931-5 regulator dropped that to about 
1.4mA, quite an improvement as the relay is off most of the time.

That's good enough for this application, but it got me thinking about 
the few wasted mA * 19V (24V - 5V) in the linear regulator. This design 
is through hole, but had to be compact so I didn't even try to fit a 
switching regulator in.

I chose 24V for low cable losses, as there are up to 70 devices on a 
common power and data buss. Relays are easy and cheap to buy in 24V too.

Are there any small, low-current, hi-efficiency switching regulators out 
there that are still reasonably priced? I realise that a 78L05 is hard 
to beat price wise, but are there good alternatives out there?
David...

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David Duffy        Audio Visual Devices P/L
Unit 8, 10 Hook St, Capalaba 4157 Australia
Ph: +61 7 38235717      Fax: +61 7 38234717
Our Web Site: www.audiovisualdevices.com.au
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