How Is the Power of a DC Power Supply Calculated?
1. The power of a conventional DC power supply is equal to the product of voltage and current, and the formula is: P=UI.
2. For pure resistance circuits such as resistance wires and lamps, the formulas "current square resistance" and "voltage square resistance" derived from Ohm's law can be used for calculation.
3. However, for non pure resistance circuits such as motors, only the formula of "voltage multiplied by current" can be used. Ohm's law does not apply to non pure resistance, that is, voltage and current are not proportional.
This is because the motor generates a "back electromotive force" during operation. For example, if the external voltage is 8 volts, the resistance is 2 ohms, and the back potential is 6 volts, the current at this time is (8-6)/2=1 (ampere), not 4 ampere. Therefore, the power is 8 x 1=8 watts.
Another Joule's law is the resistance heating formula, which states that the heating power is "the square of the current multiplied by the resistance", and this is always correct.
Also, in the above example, the motor's heating power is 1 x 1 x 2=2 (watts), which means the total output power of the motor is 8 watts, the heating power is 2 watts, and the remaining 6 watts are used for machine operation.
P=IU, Commonly known as the universal formula, it can be used at any time.
P = I ² * R, Used to calculate whether the currents in a circuit are equal or for electrical heating purposes.
P = U ²/R, Used when the voltage is equal in the circuit.
Reasons for electric power generation
1. The input terminal of a switching power supply usually adopts a rectification and filtering circuit composed of rectifier diodes and filtering capacitors. After rectifying the 220V AC input current, direct contact container filtering is performed to obtain a DC voltage with a relatively small and smooth waveform.
However, the rectification and filtering circuit composed of rectifying diodes and filtering capacitors is a combination of nonlinear elements and energy storage elements. The voltage waveform Vi of the AC input path is a sine wave, but the angle at which the rectifying elements conduct is less than 180 °, usually around 60 °, which can cause severe distortion of the AC waveform, resulting in a pulse like pattern.
