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Source and control of quad output switching power supply

Source and control of quad output switching power supply

The output ripple of the quad output switching power supply mainly comes from five aspects: input low-frequency ripple, high-frequency ripple, common mode ripple noise caused by parasitic parameters, ultra-high-frequency resonance noise generated in the switching process of power devices, and ripple noise caused by closed-loop regulation control.

1. several common methods for low-frequency ripple suppression:
A. Increase the inductance and capacitance parameters of the output low-frequency filter to reduce the low-frequency ripple to the required index.
B. The feedforward control method is adopted to reduce the low-frequency ripple component.

2. Several common methods for high-frequency ripple suppression:
A. Increase the working frequency of the switching power supply to increase the frequency of high-frequency ripple, which is beneficial to suppress the output high-frequency ripple.
B. Increase the output high-frequency filter to suppress the output high-frequency ripple.
C. Multi-stage filtering is adopted.

3. Common methods for reducing output common mode ripple noise:
A. Specially designed EMI filter is adapted for output.
B. Reduce the switch burr range.

4. Quad output switching power supply needs to have a  closed-loop control for the output voltage. Inappropriate regulator parameter design can also cause a ripple. When the output wave enters the regulator loop through the feedback network, it may lead to the self-excited oscillation of the regulator and cause an additional ripple. This ripple voltage generally has no fixed frequency.

This part of ripple can be suppressed by the following methods:
A. Increase the compensation network to the ground during the regulator output, the regulator compensation can inhibit the regulator self-excitation ripple increase.

B. The rational selection of open loop magnification and parameters of the closed-loop controller. Excessive open loop magnification can sometimes cause self-excited oscillation of regulator, making the output lines for a content increase. Too small open-loop magnification deteriorates the output voltage stability and ripple content increases. So the open-loop magnification of the regulator and parameters of the closed-loop controller need to have a rational selection. Debugging should be adjusted according to the load condition.

C. In the feedback channel, no pure hysteresis filter is added to minimize the delay and hysteresis, so as to increase the rapidity and timeliness of closed-loop regulation, which is beneficial to suppress the output voltage ripple.




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