dcdc module power supply ripple test method!

The index of the dcdc module is a very important parameter. In order to determine the quality of the power supply,dcdc module power supplyThe output ripple is measured. However, the ripple value measured by many people is often hundreds of mV, or even hundreds of mV, which is far larger than the larger ripple value provided in the device manual. This is mainly caused by incorrect measurement methods.

Oscilloscope parameter requirements: support bandwidth limit function: general oscilloscopes support 20MHz bandwidth limit, such as: SDS1102CM.

Probe requirements: In order to make the ground wire as short as possible, try to use the original test short needle of the probe. The copper wire in the class wire is of moderate strength (still a little soft, please recommend if there is a better one). Other candidates are solder wire and cutters. Choose the 1X non-attenuation gear. Generally, when the passive probe is in the 1X gear, its bandwidth is limited to 6MHz/10MHz bandwidth, so that the front end can effectively filter out the interference of high-frequency noise and reduce the impact of ripple measurement.

dcdc module power supply ripple measurement method:

1. Limit the bandwidth of the oscilloscope to 20MHz (most of the low-end oscilloscope gears are limited to 20MHz, and high-end products have a 200MHz bandwidth limit option), the purpose is to avoid the high frequency noise of the digital circuit from affecting the ripple measurement, and try to ensure the accuracy of the measurement ；

2. Set the coupling mode to AC coupling, which is convenient for measurement (use a smaller gear to carefully observe the ripple, and do not care about the DC level);

3. Ensure that the probe grounding is as short as possible (the main reason for the measurement ripple of hundreds of mV is that the grounding wire is too long), try to use the original short test needle that comes with the probe. If there is no short test needle, you can remove the ground wire and shell of the probe to expose the probe crust, and wind the self-made ground wire around the probe crust to ensure that the length of the ground wire is less than 1cm;

4. The oscilloscope ground is suspended, and only the probe ground is shared with the reference point of the test signal. Do not share the ground with the test equipment by other means. This will introduce a lot of ground noise to the ripple measurement. For example: when the oscilloscope and other instruments share the power strip, the switches of other instruments may cause noise interference to the test through the ground wire.