[sdiy] Best way to get a +3.3V rail from +15V?
neil.johnson97 at ntlworld.com
Thu Mar 7 17:49:37 CET 2013
Scott Gravenhorst wrote:
> I'm wondering about using another regulator between +15 and +3.3. Maybe a +8v. I would think
> that the heat dissapation should be less for the +3.3 regulator. Some heat might also be expected
> on the +8v reg. It's either that or a power resistor as previously mentioned.
How would that help?
Vdrop x Iload = (15 - 3.3) * 0.2 = 11.7 * 0.2 = 2.34W
Vdrop1 x Iload = (15 - 8) * 0.2 = 7 * 0.2 = 1.4W
Vdrop2 x Iload = (8 - 3.3) * 0.2 = 4.7 * 0.2 = 0.94W
Ptot = 1.4 + 0.94 = 2.34W
The same power is dissipated, this time shared between two heatsinks.
You'd get the same effect using a single regulator and a larger
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