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Rectified 24VAC to DC value?

tjk84

Feb 14, 2021
5
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Feb 14, 2021
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1. If I rectify a 24VAC signal using an MB6S, do I multiply it by sqrt(2) to get my DC value?

I am rectifying a 24VAC signal using a MB6S which leads to a voltage regulator in a constant current configuration which powers an LED that uses about 9.75VDC. I am trying to calculate how much power is dissipated at the voltage regulator but I need to know the regulator's input voltage and the regulator's output voltage to calculate the voltage dropping across the regulator. Then I'll use this voltage drop to calculate the power dissipated.

2. Do AC power supplies usually output in RMS or Pk? I'm using a Precision 9801 AC Power source and my actual thermal temperature measurements are different when I power the regulator with 24VAC from the AC source and when I power the regulator with 34VDC from a DC power source (24V * sqrt(2) = 34VDC).
 

AnalogKid

Jun 10, 2015
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Jun 10, 2015
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2,884
1. The peak voltage output of a full wave diode bridge rectifier is sqrt2 x Vin(RMS), minus the forward voltage (Vf) drops of two diodes.The Vf for power rectifiers is larger than that of small signal diodes and transistors. For a 24 Vac input, the peak output voltage will be around 32 V. Note that at that point it has 100% ripple. The size of the filter capacitor has a direct bearing on everything downstream. A larger filter cap means less ripple, which means higher power dissipation in a downstream regulator.

2. Wall warts with an AC output list the RMS output voltage.

ak
 

tjk84

Feb 14, 2021
5
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Feb 14, 2021
Messages
5
I just realized that RMS is the equivalent to DC in terms of power. My question is answered. Thank you
 

crutschow

May 7, 2021
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May 7, 2021
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Note that in a real rectifier circuit, you have to subtract the forward drop of the rectifier (one for half-wave and full-wave, two for a bridge) from the calculated AC peak.
 
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