Switching Power Supplies: The Solution to Minimizing Ripple and Noise Voltage
A capacitor with good high-frequency performance and low ESR is used at the output end
It is best to use aluminum or tantalum electrolytic capacitors with polymer solid electrolytes as output capacitors, which are characterized by small size and large capacitance, low ESR impedance at high frequencies, and large allowable ripple current. It is most suitable for high-efficiency, low-voltage, high-current step-down DC/DC converters and DC/DC module power supplies as output capacitors.
Adopt frequency synchronization with production system
In order to reduce the 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 the frequency of the external synchronous input system, so that the switching frequency is the same as the frequency of the system.
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 supplies are not shielded and they are close together, they may interfere with each other and increase the output noise voltage. In order to avoid this kind of mutual interference, shielding measures can be adopted or they can be properly kept away to reduce the interference of their mutual influence.
Add LC filter
In order to reduce the ripple and noise of the module power supply, an LC filter can be added to the input and output ends of the DC/DC module.
increase LDO
Adding a low-dropout linear regulator (LDO) after the switching power supply or module power output can greatly reduce the output noise to meet the needs of circuits with special noise requirements, and the output noise can reach μV level.
Since the voltage difference of the LDO (the difference between the input and output voltages) is only a few hundred mV, the standard voltage can be output when the output of the switching power supply is a few hundred mV higher than that of the LDO, and the loss is not large.
Add active EMI filter and active output ripple attenuator
Active EMI filters can attenuate common-mode and differential-mode noise between 150kHz and 30MHz, and are particularly effective at attenuating low-frequency noise. At 250kHz, it can attenuate 60dB of common-mode noise and 80dB of differential-mode noise, and the efficiency can reach 99% at full load.
The output ripple attenuator can reduce the power supply output ripple and noise by more than 30dB in the range of 1~500kHz, and can improve the dynamic response and reduce the output capacitance.
