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

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.

jnnewton said:

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

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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.

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

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.

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