[sdiy] Best way to get a +3.3V rail from +15V?

Neil Johnson 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?

Single regulator:
  Vdrop x Iload = (15 - 3.3) * 0.2 = 11.7 * 0.2 = 2.34W

Dual regulator:
  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
heatsink.

Neil
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