Need advice on 40vdc to 5vdc @ 80ma - Electronic Circuits Projects Diagrams Free

blueroomelectronics · 25th August 2007, 07:19 PM

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.

Hero999 · 25th August 2007, 07:48 PM

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.

k7elp60 · 26th August 2007, 12:55 AM

You might consider using a 5W zener diode in series, such as 1N5364BG or maybe the next higher voltage one (36V) 1N5365BG.

blueroomelectronics · 26th August 2007, 02:55 AM

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.

technogeek · 26th August 2007, 03:09 AM

I have not been able to find these to gauge pricing but they're pretty neat:

http://www.recom-international.com/s...or_R-78xx.html

blueroomelectronics · 26th August 2007, 04:15 AM

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.

mvs sarma · 26th August 2007, 07:57 AM

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

pc88 · 26th August 2007, 09:01 AM

Another possibility is this approach:

http://www.edn.com/contents/images/61302di.pdf

See the article "Linear regulator = low-cost dc/dc converter". Probably not as efficient, but an interesting idea nonetheless.

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25th August 2007, 07:19 PM	(permalink)
blueroomelectronics	Need advice on 40vdc to 5vdc @ 80ma 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. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

25th August 2007, 07:48 PM	(permalink)
Hero999	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. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

26th August 2007, 12:55 AM	(permalink)
k7elp60	You might consider using a 5W zener diode in series, such as 1N5364BG or maybe the next higher voltage one (36V) 1N5365BG. __________________ The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best. Show me a different way. I have an open mind.

26th August 2007, 02:55 AM	(permalink)
blueroomelectronics	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. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

26th August 2007, 03:09 AM	(permalink)
technogeek	I have not been able to find these to gauge pricing but they're pretty neat: http://www.recom-international.com/s...or_R-78xx.html

26th August 2007, 04:15 AM	(permalink)
blueroomelectronics	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. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

26th August 2007, 07:57 AM	(permalink)
mvs sarma	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 Last edited by mvs sarma; 26th August 2007 at 08:01 AM.

26th August 2007, 09:01 AM	(permalink)
pc88	Another possibility is this approach: http://www.edn.com/contents/images/61302di.pdf See the article "Linear regulator = low-cost dc/dc converter". Probably not as efficient, but an interesting idea nonetheless.