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Power Calc
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Dan Green
Jul 25, 2023, 7:54:00 PM7/25/23
to
Okay, here's anohter dumb quesiton.
Say I have a resistor across the mains power supply. Say its 10k for
argeuments sake. Mains here is about 115VAC. So the resistor will
disspate 1.3 watts give or take by my rekoning. Now say I put a diode
in series with the resistor. Does the power dispataion now halve?
just curious.
Say I have a resistor across the mains power supply. Say its 10k for
argeuments sake. Mains here is about 115VAC. So the resistor will
disspate 1.3 watts give or take by my rekoning. Now say I put a diode
in series with the resistor. Does the power dispataion now halve?
just curious.
Phil Hobbs
Jul 25, 2023, 8:44:52 PM7/25/23
to
so blocking the current in one direction halves the average dissipation.
The diode drops some voltage when conducting, so the dissipation is
slightly less than half in real life.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics,
Electro-optics, Photonics, Analog Electronics
Phil Allison
Aug 16, 2023, 12:14:44 AM8/16/23
to
Dan Green wrote:
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** Conducting for half the time, or any other fraction, reduces the heat in a resistor by that same fraction.
The *average value* of the current through or voltage across the resistor is also halved but this is not so for the *RMS* value. RMS values follow the heating effect on a resistance so will be reduced by 0.7071 ( 1/sq rt 2) or in your example from 115 down to 80.6 volts.
.... Phil
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The *average value* of the current through or voltage across the resistor is also halved but this is not so for the *RMS* value. RMS values follow the heating effect on a resistance so will be reduced by 0.7071 ( 1/sq rt 2) or in your example from 115 down to 80.6 volts.
.... Phil
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