Study Notes | How to reduce the ripple noise voltage

Recently, I need to design a filter to deal with the problem of a ripple voltage caused by a SMPS(Switch Mode Power Supply). But it need so much tricky to solve this problem. So here is a guideline to make it more easily to slove this problem.

1. How to measure the ripple voltage ?

The methods to measure the ripple voltage are diverse, but there is a standard which is developed by a Japan Power Module Manufacturer (TDK Power). It provide a standard procedure called JEITA-RC9131A to measure a power supply’s output ripple voltage. Here is the detailed method.

It suggest that DUT need to be connect with a special filter circuit like below:

And Prober should not be connected as close as possible to the load and not to the power output pin/terminal. Here is some wrong way to put the prober listed below:

2. What cause the ripple noise ?

Errr… This problem is somebit of difficult. The Main source is from the DC-DC Switch MOSFET‘s transisent current change which called SWITCH CURRENT. Because power supply is working under switch mode, so the distribution parameter of PCB will make a oscillation during the switching on/off period which cause a overshoot or undershoot phenomenon.

So sum it up,  the ripple noise caused by switch current in a switch mode power supply.

3. How to minimize the ripple noise ?

Err..  This is a very  challenging problem to give a proper anwer.  After Googlized the internet, I got some solution to make it works.

Method 1: Use a Passive Filter at the power output pin

(To be continued… Busy working)

About Chenxiang Hsu

A Geek, An engineer, a programmer, and a Model Maker.