Detailed description of ripple in high-voltage power supply

The ripple of a high-voltage power supply refers to the periodic variation in the output voltage of the power supply, which is composed of two main parts: the ripple generated by the control inverter and the ripple generated by the voltage doubling circuit.

I、 Control the ripple generated by the inverter

1. Low frequency ripple:

The magnitude of low-frequency ripple is related to the capacitance of the filtering capacitor in the output circuit. Due to the limited size of high-voltage power supplies, the capacity of electrolytic capacitors cannot be infinitely increased, resulting in low-frequency ripple output mainly caused by current fluctuations during rectification. Moreover, the output ripple frequency will vary depending on the rectification circuit, and the main method to suppress ripple is to filter out low-frequency ripple. The low-frequency ripple has a longer period and a larger amplitude.

2. High frequency ripple:

High frequency ripple noise is mainly generated by the switching frequency and its harmonics in switching power supplies. The input DC voltage undergoes high-frequency conversion through power conversion devices, and then undergoes rectification and filtering to achieve stable voltage output. There will be high-frequency ripple at its output that is the same as or a multiple of the operating frequency. The frequency of high-frequency ripple is much higher than the input AC frequency, usually including the switching frequency and its harmonics. The conversion frequency of high-voltage power supply, the structure and parameters of output filtering circuit affect high-frequency ripple. In order to minimize the output of high-frequency ripple as much as possible, the operating frequency of power conversion circuit can be increased.

3. Cross ripple

Generated by the interaction between the rectifier and the filter. This kind of ripple is usually a complex waveform formed by the combined action of multiple rectifiers and filters in the power supply. The frequency of cross ripple may be related to both input frequency and switching frequency, resulting in complex waveforms.

4. Power supply noise and interference

The wires of the power devices inside the high-voltage power supply have parasitic inductance, and there are parasitic capacitances between the power devices and the heat sink as well as the primary and secondary sides of the transformer. When the square wave voltage passes through the power devices, common mode ripple noise is generated at the output end of the high-voltage power supply. The high-frequency noise generated by switching devices during operation, as well as magnetic field interference from the surrounding environment or internal power supply, can all produce different types of ripples. To effectively reduce ripple noise output, parasitic capacitance between power devices, heat sinks, transformers, and chassis ground can be minimized.

II、 Ripple generated by voltage doubling circuit

Voltage doubling circuits are typically used to increase the input voltage to a higher voltage level. Due to the asymmetry of the voltage doubler circuit and the asymmetry and nonlinearity of the voltage doubler and rectifier components, ripple voltage is inevitably present in the voltage doubler. The generation methods of DC high voltage include full wave high-frequency voltage doubling rectification and half wave high-frequency voltage doubling rectification. The ripple generated by high-frequency voltage doubling rectification is a complex harmonic signal. The output voltage of multiple voltage rectification is formed by repeatedly charging and discharging multiple capacitors, and the frequency of these ripples is usually related to the power supply frequency and its multiples. The more multiple voltage series connections, the greater the ripple.