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Resistor Wattage — Parallax Forums

Resistor Wattage

LightfootLightfoot Posts: 228
edited 2006-11-06 03:36 in General Discussion
regulatorzd7.jpg

What should the wattage of that three ohm resistor be, 12 watts I assume?

Power supply will be 12 volts, LM7812 draws 1 amp, BD536 collecor current is 8 amps.

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Comments

  • terahertzterahertz Posts: 55
    edited 2006-11-06 03:36
    I would guesstimate 5W would be good.

    Because: Q1 I(ec) = 8A, LM7812 I = 1A, therefore·I(total)= 9A. So: (Q1 I(eb) + R1(I)) = 1A. At most R1(I)=1A, 3(R1(I))=3 Watts.
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