Switching power supply: introduction to solutions for reducing ripple and noise voltages
Reduce EMI interference
Using a metal shell for shielding to reduce external electromagnetic field radiation interference. To reduce electromagnetic interference input from the power cord, an EMI filter is added at the power input end.
Use capacitors with good high-frequency performance and low ESR at the output end
Aluminum or tantalum electrolytic capacitors using polymer solid electrolytes are the best output capacitors, characterized by small size and large capacity, low ESR impedance at high frequencies, and allowing for large ripple currents. It is most suitable as an output capacitor for high-efficiency, low-voltage, high current buck DC/DC converters and DC/DC module power supplies.
Adopting frequency synchronization with the product system
To reduce output noise, the switching frequency of the power supply should be synchronized with the frequency in the system, that is, the switching power supply adopts an external synchronous input system frequency, so that the switching frequency is the same as the system frequency.
Avoid mutual interference between multiple module power supplies
There may be multiple module power supplies working together on the same PCB. If the module power supply is unshielded and located very close, it may interfere with each other and increase the output noise voltage. To avoid such mutual interference, shielding measures can be taken or they can be appropriately moved away to reduce the interference caused by their mutual influence.
Add LC filter
To reduce the ripple and noise of the module power supply, LC filters can be added to the input and output terminals of the DC/DC module.
Increase LDO
Adding a low dropout linear regulator (LDO) after the output of a switching power supply or module power supply can significantly reduce output noise to meet the special requirements of circuits with noise, and the output noise can reach the level of μ V.
Due to the voltage difference (difference between input and output voltage) of LDO being only a few hundred mV, the standard voltage can be output at a slightly higher output of the switching power supply than LDO by a few hundred mV, and its loss is not significant.
Add active EMI filters and active output ripple attenuators
Active EMI filters can attenuate common mode and differential mode noise between 150kHz and 30MHz, and are particularly effective in attenuating low-frequency noise. At 250kHz, it can attenuate 60dB common mode noise and 80dB differential mode noise, and the efficiency can reach 99% at full load.
The output ripple attenuator can reduce power output ripple and noise by more than 30dB in the range of 1-500kHz, and can improve dynamic response and reduce output capacitance.
