What is the apparent power of ATX power supply?

Last Update Time: 2019-04-04 11:53:03

Considering that the ATX power supply uses AC 220V as the input source, we will only discuss the apparent power of the AC 220V with the ATX power supply as the load.

Power is defined as the product of voltage and current. But for AC 220V, its voltage is the variation of star sine waveform. If according to the definition of power, the AC 220V power at different times must also be a variable value. In short, this power is not a constant value, it should vary over time.

At the same time, we can use a clamp AC ammeter (UT202) and a multimeter to measure the AC current and AC voltage of the real ATX power supply when it is working, as shown in figure 1 (the ATX power supply in the figure is no-load).

The clamp AC current meter measured the AC current of this ATX power supply at no load of 0.079A. In addition, the voltage of 220V AC power is measured by a multimeter to be 233V.

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Figure 1. AC current and AC voltage.


Here there is a contradiction between the constant voltage / current values measured by the clamp AC ammeter and the multimeter and the current / voltage of 220V AC, which is in fact an unsteady value varying with time.


It can be seen that when we really measure the power of alternating current (measured by instruments), people actually carry out a reasonable equalization transformation of the voltage / current that changes with time. That is, the measured AC electricity 220V is 233V, AC current is 0.079A is an average value (actual "effective value").


This article is from Allicdata Electronics Limited.