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Need advice on 40vdc to 5vdc @ 80ma

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blueroomelectronics

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I'm looking for suggestions on bringing 40vdc down to 5vdc
The trick is making it run as cool as possible. I could use a switch mode regulator like a National Semi simple switcher but the normal current requirement is less than 1ma and I thought it might be possible and cheaper to use a 78l05, lm317 or similar. The 80ma requirement is to run a latching relay (approx 8 time per hour) I figure a decent filter cap could take on the load.
Suggestion , advice welcome.
 
I would use an LM317, 2.8W isn't that much power so you won't need a huge heat sink.

If you want to go down the switching route then I always suggest this site, although the efficiency won't be as good as 93% with 40V in and 5V out.
 
You might consider using a 5W zener diode in series, such as 1N5364BG or maybe the next higher voltage one (36V) 1N5365BG.
 
Problem is the heat, it's a thermostat afterall.
The black regulator is neat but I need it to handle a fairly wide range of power sources.
 
Those switchmode 7805 replacements are cool, but $10 each. I'll play with the black regulator or an LM2575 simple switcher. I should be able to use a low current inductor.
 
if the load is too less perhaps you may consider simple zenor with series resistor at 5mA overall current and the zenor can geive the requisite load of try using a old MC34063 in switching mode and sure it will serve your needs.

Datasheet may be referred at www.alldatasheet.com

Sarma
 
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