Switchmode Power and High Ripple Current

Embedded engineers know that the load current in some applications (like DC motor loads, DC-AC inverters and DC-DC converters) has a large ripple component. Usually, switch mode power supplies power such applications. But unexpected problems may occur if you use such power supplies.

The reason is, the storage capacitors (output) receive power in the form of ‘packets’, which is supplied at a regular rate. The converter maintains a steady load by supplying power in predictable ‘packets’, ensuring that the capacitor is topped up, thus producing a steady output.

But if the ripple current is more than 5% of the DC power supply, the power supply may begin to show over current phenomena. In addition, the control loops may begin to show instability when the pulse rate of the load harmonizes with the switching frequency of the power supply.

This is bad news because high ripple current puts too much load on the output capacitors, leading to early failure. But there is a practical solution to this problem.

An external capacitance with low ESR can ensure a steady load power supply. Embedded engineers should ensure the external capacitance is capable of keeping the ripple current below 5% of the output voltage. If you want a long-term solution to these problems, try custom power supplies.