Switching Power Supplies: Solutions to Reduce Ripple and Noise Voltage
Adopting capacitors with good high-frequency performance and low ESR at the output side
The use of polymer solid-state electrolyte aluminium or tantalum electrolytic capacitors for the output capacitor is the best, which is characterized by small size and large capacity, low ESR impedance at high frequencies, allowing large ripple current. It is most suitable for high-efficiency, low-voltage, high-current step-down DC/DC converter and DC/DC module power supply as output capacitor.
Adopting frequency synchronisation with the product system
In order to reduce the output noise, the switching frequency of the power supply should be synchronised with the frequency in the system, i.e., the switching power supply adopts external synchronisation to input the frequency of the system, so that the frequency of the switch is the same as that 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 supply is not shielded, and close to each other, it may interfere with each other to increase the output noise voltage. To avoid such mutual interference, shielding measures can be used or they can be appropriately moved away from each other to reduce their mutual interference.
Increase LC filter
In order to reduce the ripple and noise of the module power supply, you can add LC filters to the input and output of the DC/DC module.
Add LDO
In the switching power supply or module power supply output and then add a low dropout linear regulator (LDO) can significantly reduce the output noise to meet the needs of the special requirements of the noise circuit, the output noise can be up to μV level.
As the LDO voltage difference (difference between the input and output voltage) is only a few hundred mV, the output of the switching power supply is slightly higher than the LDO a few hundred mV can be output standard voltage, and its loss is not large.
Increase 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 in attenuating low frequency noise. At 250kHz, it can attenuate 60dB of common mode noise and 80dB of differential mode noise with 99% efficiency at full load.
Output ripple attenuator can reduce power supply output ripple and noise in the range of 1 to 500kHz more than 30dB, and can improve dynamic response and reduce output capacitance.
