Among the common problems in the application of power modules, reducing the ripple noise at the load end is the concern of most users. So how to reduce the ripple noise of the module? From the perspective of ripple noise waveform, test method, module design and application, Puke Technology elaborates several methods to effectively reduce output ripple noise.
A common measurement tool for ripple noise is the oscilloscope + probe method
Ripple and noise are: the fluctuation of the same frequency as the switching frequency of the power supply superimposed on the output of the DC power supply is ripple, and the high-frequency noise is noise.
The generation of ripple is caused by the intermittent energy transmitted by the switch. Starting from the internal design of the switching power supply, the frequency of the switching tube can be increased to reduce the energy transmitted each time, thereby reducing the ripple and increasing the transmission. The inductance value L of the energy reduces the sudden peak value of the current, thereby reducing the fluctuation amplitude of the ripple.
From outside the module, especially on the client side, the output filter capacitor can be added to reduce the ripple, but the capacitor cannot be increased indefinitely, because most switching power supply modules have a maximum capacitive load limit.
Ripple noise test method
For the ripple and noise test of small and medium-sized power module power supply, the industry mainly adopts the parallel line test method and the contact method. Among them, the parallel line test method is used for products with relatively large pin spacing, and the relying test method is used for products with small module pin spacing.
But no matter whether you use the parallel line test method or the relying test method, you need to limit the bandwidth of the oscilloscope to 20MHz.
Parallel line test
Note 1: C1 is a high frequency capacitor with a capacity of 1μF; C2 is a tantalum capacitor with a capacity of 10μF.
Note 2: The distance between two parallel copper foil strips is 2.5mm, and the sum of the voltage drop of the two parallel copper foil strips should be less than 2% of the output voltage
Reliable test method: the difference between removing the ground clip test
To test the ripple noise, the ground clip needs to be removed, mainly because the ground clip of the oscilloscope will absorb various high-frequency noises, which cannot truly reflect the output ripple noise of the power supply and affect the measurement results.
Influence of output filter capacitor: The capacitance and ESR of the output filter capacitor also have a direct impact on the ripple noise output by the module.
Influence of Inductance on Ripple Noise: The inductance of inductance and parasitic capacitance also have significant influence on ripple noise. Generally, when the inductance is large, the ripple suppression effect is obvious, and the inductance with a small parasitic capacitance has a good effect on noise suppression.
