General solution for power module application testing

1. DC output module power supply ripple and noise test

The output ripple of the DC output module power supply includes common mode and differential mode. The differential mode ripple includes the ripple of the switching frequency and the high-frequency noise far higher than the switching frequency, as shown in Figure 1. The former is mainly composed of the switching frequency and harmonics, and the latter is mainly generated by the rapid voltage and current changes of the power switching device. Both are signals that need to be detected. Common mode noise is the output ripple caused by the existence of the potential difference of the grounding point. This signal flows in the same direction along the output line and is eventually converted into a differential mode signal on the load to affect the operation of the system. The same principle applies. During the test, if the impedance of the two signal lines of the probe is different, the common mode signal will also be converted into a differential mode signal, affecting the real ripple. The common mode signal is closely related to the grounding method and can be suppressed by filtering measures. It does not belong to the ripple test range of the module power supply. Here we only introduce the test method of differential mode ripple.




The output pins of the low-power module (=50W) are connected to parallel copper foil strips, followed by capacitors. A 20MHz bandwidth oscilloscope is used to test and record the peak-to-peak noise voltage at the output end. The length of the two parallel copper foil strips is between 51mm and 76mm (2inch and 3inch), and the distance between the two parallel copper foil strips is 2.54mm (0.1inch).

The distance between the C welding point and the module output terminal is 25.4mm (1inch). The oscilloscope probe contact point is shown in Figure (a). The test point is about 51mm from the module output terminal. The thickness and width of the copper foil tape (the sum of the two parallel copper foil tapes) ensure that the voltage drop is less than 2%.

The output pin of the high-power module (>50W) is connected to the parallel copper foil tape, followed by the capacitor. Use a 20MHz bandwidth oscilloscope to test and record the peak-to-peak noise voltage at the output end; the length of the two parallel copper foil tapes is between 51mm and 76mm (2inch and 3inch), and the distance between the two parallel copper foil tapes is 2.54mm (0.1inch); the distance between the C1 welding point and the module module output terminal is 25.4mm (1inch), and the distance between the C2 welding point and the oscilloscope probe is 12.7mm. C1 is a 1?F polyester capacitor or ceramic capacitor (X7R or X5R type) and C2 is a 10?F tantalum capacitor. The oscilloscope probe point is shown in Figure (b). The test point is
about 51mm away from the module output terminal. The thickness and width of the copper foil tape (the sum of two parallel copper foil tapes) ensure that the voltage drop is less than 2%.

⑵ Slowly adjust the output load from 0 to the rated load, and record it when the peak-to-peak noise voltage at the output end reaches the maximum value;

⑶ Adjust the input voltage to the maximum and minimum values, and test and record the maximum value of the peak-to-peak noise voltage when the load changes within the empty and full load range;

⑷ Take the maximum value of all test values ​​as the peak-to-peak noise voltage.

This test method is accepted by most module power supply manufacturers and is preferred when conditions permit.