How do I calculate the current consumption and power dissipation?

Current consumption is the current that flows from BATTERY into the power supply terminal of the audio power IC and is measured using an ammeter as shown in Fig. 1. The input power can be calculated to multiply the current consumption by BATTERY voltage.

Fig. 1 Current Consumption Measurement Circuit
Fig. 1 Current Consumption Measurement Circuit

Fig. 2 shows how to measure the output power dissipation.
In case of BTL*1 amplifiers, connect a load resistor acting as an equivalent to a loudspeaker between the output terminals, and measure the AC voltage (rms) across the load resistor with an AC voltmeter.
The output power is calculated using the obtained AC voltage and load resistance value. (Output power = AC voltage ^2/Load resistance)

*: In order to calculate the total output power for a product with multiple internal amplifiers, calculate each output power channel by channel and add them up as the total output power.
*1: BTL:Bridge Tied Load

Fig. 2 Power Dissipation Measurement Circuit
Fig. 2 Power Dissipation Measurement Circuit
Fig. 3 Pd vs Output power
Fig. 3 Pd vs Output power

Finally, the power dissipation is calculated by the following formula.
Power dissipation Pd = Input power: Pin - Total output power : Pout(Total) = BATTERY voltage: Vbat * current consumption: Iin – output power/1ch * Number of channels N (for multiple amplifier product when each output power is same)

Note that accurate results cannot be obtained if a voltage drop occurs due to wiring resistance, etc. during measurement. To avoid it, our recommendation is to measure the voltage near the terminals of the audio power IC.

As a reference, an example of 4-channel audio power IC is shown as below.
When BATTERY is 14.4V and the output power is 1W for each channel, power dissipation is calculated as follows.
BATTERY voltage: Vbat = 14.4V
Current consumption: Iin = 0.8A (measured)
Output Power: Pout = 1W (per channel)
Number of channels: N = 4 channels

Power dissipation : Pd = (Vbat * Iin)- (Pout * N)
             = (14.4 * 0.8) – (1 * 4)
               = 11.52 - 4
               = 7.52 [W]

This calculation shows the intersection of the dashed lines in Pd vs output power chart in Fig. 3.

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