What is the accuracy of the power adapter?

The accuracy of the power adapter generally refers to the voltage regulation accuracy, including the output DC voltage accuracy range, the output DC current adjustment rate, and the output DC ripple noise. The ripple noise includes the maximum ripple voltage and the maximum ripple noise voltage.

Voltage regulation accuracy refers to the output DC voltage accuracy range of the output voltage of the power adapter. Generally, this range is ±5%, which is also an international industry standard. The output voltage range of the power adapter is ±5% of the nominal output voltage, such as a 5V power supply. The output voltage range of the adapter is: 4.75-5.25V, the output voltage range of the 12V power adapter is: 11.4-12.6V, the output voltage range of the 19V power adapter is: 18.05-19.95V, and the output voltage range of the 24V power adapter For: 22.8-25.2V.

​ The voltage stability coefficient of the power adapter, under the conditions of constant load current and ambient temperature, the relative change of the input voltage causes the relative change of the output voltage. The voltage adjustment rate of the power adapter, when the relative change of the input voltage +10%, the output The relative change of voltage, voltage stability coefficient and voltage adjustment rate indicate the influence of input voltage change on output voltage, so only one of them needs to be tested.

​ Power adapter output resistance and current regulation rate, the output resistance of the power adapter is the same as the output resistance of the amplifier, and its value is the absolute value of the ratio of output voltage to output current when the input voltage is constant. Current regulation rate, the output current changes from 0 to The relative change in output voltage at maximum. The output resistance and current regulation indicate the effect of changes in load current on the output voltage.

​ Since the switching tube of the switching power supply works in a high-frequency switching state, during each switching process, electric energy is “pumped” from the input end to the output end, forming a charging and discharging process on the output capacitor, resulting in a change in the output voltage Fluctuation, and the frequency of this fluctuation is the same as the switching frequency of the switching tube. This fluctuation is the output ripple, which is the AC component superimposed on the output DC.

The amplitude of the ripple is the peak-to-peak value between the peak and the trough of the AC component. .

The noise is a high-frequency pulse train generated by the switching power supply itself, which is caused by the sharp pulses that occur at the moment when the switch is turned on and off. The frequency of the noise is much higher than the switching frequency, and the magnitude of the noise voltage is largely related to The topology of the switching power supply, the winding of the transformer, the parasitic parameters in the circuit, the external electromagnetic environment during the test, and the layout design of the PCB are related. The ripple and noise waveforms can be seen with an oscilloscope, and the frequency of the ripple is the same as the frequency of the switching tube. , and the noise frequency is twice that of the switching tube.

The sum of the peak-to-peak value of the ripple voltage and the peak-to-peak value of the noise voltage is the ripple and noise voltage, and its unit is mVp-p.