Causes of Low-Frequency Ripple in DC Power Supplies
The low-frequency ripple of DC power supply is mainly manifested in five aspects: input low-frequency ripple, high-frequency ripple, common mode ripple noise caused by parasitic parameters, ultra-high frequency resonance noise generated during power device switching, and ripple noise caused by closed-loop regulation control.
The low-frequency ripple is related to the filter capacitance of the output circuit. The capacity of capacitors cannot increase indefinitely, resulting in residual low-frequency ripple in the output. After attenuation by the DC/DC converter, low-frequency noise appears in the output of the DC stabilized power supply, which largely depends on the ratio of the DC/DC converter and the gain of the control system. The ripple suppression effect of current controlled DC/DC converters is slightly better than that of voltage controlled DC/DC converters. But its output low-frequency AC ripple is relatively large. To achieve low ripple output of DC stabilized power supply, filtering measures must be taken for the ripple of low-frequency power supply. The use of pre voltage in the front stage can improve the closed-loop gain of DC/DC converters.
Several common low-frequency ripple suppression methods:
A. Increase the inductance and capacitance parameters of the output low-frequency filter to reduce low-frequency ripple to the required specifications.
B. Adopting feedforward control method to reduce low-frequency ripple components.
A high-frequency power switch conversion circuit with high-frequency ripple noise, which converts the input DC voltage of the high-frequency switch power supply equipment to achieve a stable output rectifier filter. Its output is the same switching operating frequency. The high-frequency ripple frequency is mainly affected by the size conversion frequency of the external circuit and the DC stabilized power supply. The structure and parameters of the output filter should be designed to increase the operating frequency of the power converter as much as possible to reduce the requirements of the high-frequency switch ripple filter.
