Cascade Regulators or not? - Electronic Circuits Projects Diagrams Free

jnnewton · 24th October 2007, 10:53 PM

I normally regulate 24vdc down to 5 for projects involving a microcontroller. Now i have one where i have a need for 12vdc also. is there any advantage (heat, effeciency, etc.) to regulating the 12vdc down to 5 instead of going straight from 24 to 5. I use the d2pak type regulators (7805, 7812). Are there any disadvantages (noise, tolerance)? Thanks

dknguyen · 25th October 2007, 01:06 AM

Just that the heat generated from burning off the extra voltage is spread over two regulators instead of one. YOu could do 24->12->5, just make sure the 12V regulator isn't overloaded and has the extra capacity to also handle the current drawn by the 5V loads. You could also just use a 24-12 and 24-5. DOesn't realy matter since you need two regulators anyways.

aussiepoof · 25th October 2007, 01:16 AM

Quote:

Originally Posted by jnnewton

I normally regulate 24vdc down to 5 for projects involving a microcontroller. Now i have one where i have a need for 12vdc also. is there any advantage (heat, effeciency, etc.) to regulating the 12vdc down to 5 instead of going straight from 24 to 5. I use the d2pak type regulators (7805, 7812). Are there any disadvantages (noise, tolerance)? Thanks

You *really* need to consider using a switchmode device such as the Simple Switcher line from National Semiconductor. I was regulating 5v from 21v which got very warm... with an LM2595T-5.0 I get 5v using the regulator, a schottky diode, an inductor and a cap which stays cool to the touch without a heatsink.

By far the better way to go as cool electronics lasts longer than hot electronics :-)

P.

Sceadwian · 25th October 2007, 01:24 AM

24-5 is what, 20% efficiency with a linear regulator? Horrible.

Krumlink · 25th October 2007, 02:41 AM

Doesn't one of the regulators hog all the current until it pops, then it moves onto popping the next one? I had a problem like this with too much heat generation. at 7.2V and 500ma, I was generating 1.8Watts of heat, which is quite a lot for what I generally use. I would definitely use a switching Regulator to prevent all that waste. At 12V and for example 100ma, that is 6 Watts, which is really hot. Use a Active Heat sink to pull the heat off or you should use a switching regulator.

jnnewton · 25th October 2007, 02:45 AM

Thanks guys, i will use the switching regulator. thanks guys.

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24th October 2007, 10:53 PM	#1
jnnewton	Cascade Regulators or not? I normally regulate 24vdc down to 5 for projects involving a microcontroller. Now i have one where i have a need for 12vdc also. is there any advantage (heat, effeciency, etc.) to regulating the 12vdc down to 5 instead of going straight from 24 to 5. I use the d2pak type regulators (7805, 7812). Are there any disadvantages (noise, tolerance)? Thanks

25th October 2007, 01:06 AM	#2
dknguyen	Just that the heat generated from burning off the extra voltage is spread over two regulators instead of one. YOu could do 24->12->5, just make sure the 12V regulator isn't overloaded and has the extra capacity to also handle the current drawn by the 5V loads. You could also just use a 24-12 and 24-5. DOesn't realy matter since you need two regulators anyways.

25th October 2007, 01:24 AM	#4
Sceadwian	24-5 is what, 20% efficiency with a linear regulator? Horrible. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

25th October 2007, 02:41 AM	#5
Krumlink	Doesn't one of the regulators hog all the current until it pops, then it moves onto popping the next one? I had a problem like this with too much heat generation. at 7.2V and 500ma, I was generating 1.8Watts of heat, which is quite a lot for what I generally use. I would definitely use a switching Regulator to prevent all that waste. At 12V and for example 100ma, that is 6 Watts, which is really hot. Use a Active Heat sink to pull the heat off or you should use a switching regulator. __________________ IF YOU WANT TO HELP FINE IF NOT PLEASE DON"T PEE IN MY CHEERO'S

25th October 2007, 02:45 AM	#6
jnnewton	Thanks guys, i will use the switching regulator. thanks guys.