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Old 7th May 2003, 06:15 PM   #11
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It works out as half through the maths although the correct way to calculate is to multiply the swing by 0.707 (the reciprocal of the square root of 2).

If the supplies are +/-20v, your peak output swing will be 16.4v whereas the RMS will be 16.4 * 0.707 = 12.6v. This will result in an RMS current of 1.45A into 8R, giving 16.82W RMS output power.

Nice one,
David.
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Old 20th September 2013, 08:34 PM   #12
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sooo for a +-35 power supply i would get

8 ohms
35-3.6=31.4
(31.4*31.4)/8 = 123watts
123*0.707=87 watts rms correct???

for 4 ohms = 246 watts
174watts rms correct???


Can two OPA541 in parrallel handle this power without plowing up?
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Old 21st September 2013, 05:43 PM   #13
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Old 22nd September 2013, 09:52 PM   #14
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so then how do I calculate the power output?
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Old 23rd September 2013, 01:27 AM   #15
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Quote:
Originally Posted by lawbadman View Post
so then how do I calculate the power output?
You take the Peak Voltage and multiply time .707 ( square root of 2 divided by 2). Square the result and divide by the load resistance. So your 31 Volt peak output is 21.9 Vrms. Squared is 480.35 and divided by 8 is 60.04. BTW it's hard to get accurate to 3 digits.

If you're measuring the Peak to Peak Voltage you will need to divide by 2 to get to the peak Voltage or else you'll get an answer 4 times larger than it should be.

It gets a little more interesting as the power supply varies with the power output which is why power is specified with continuous sine wave drive. ALSO, the power varies when the line Voltage changes as well. If you measure power with 117 Volt line an the line goes up to 125, a ratio of 1.068 %, the power can go up 1.068 SQUARED or 1.14.

This must be done with a scope to stay out of clipping.

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