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Formula to get Milliwat Power by Load

post #1 of 2
Thread Starter 

Dear All:

 

I need to calculate the max power in mw for a Cmoy design using an opa2134 opamp.

 

The opa2134 datasheet states that the max current by channel is 35mA.

 

I'm using this formula:

P = I^2 * R = ((0.035)^2) * 16  =  0.0196 W = 19.6 mw @ 16 Ohm

P = I^2 * R = ((0.035)^2) * 32  =  0.0392 W = 39.2 mw @ 32 Ohm

 

I have seen on datasheets that the Power Output raises when the load decreases, but with this calculation the power from a Load

of 16 to a load of 32 ohm is increasing.

 

Is there any error on the calculation?

 

Regards.

Alfredo Mendiola Loyola

Lima, Peru-

post #2 of 2

Your calculations are correct.

 

Assuming a constant voltage, a smaller load will use more power because it draws more current. You are assuming a constant current.

 

The op amp is a voltage amplifier, so it may be more useful for you to consider the max voltage instead of max current. On this data sheet ( http://www.ti.com/lit/ds/symlink/opa134.pdf ) it says the typical current is 35mA, but does not list a max. It lists some max voltages for higher load impedance, however I think the op amp is not designed for low impedance loads, so you may not find the information you need on the data sheet.

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