Key Points of This Article:

1. Definition and analysis of ripple noise in switching power supplies

2. Causes of ripple noise in switching power supplies

3. Why ripple noise in switching power supplies is so high

4. How to mitigate ripple noise in switching power supplies

I. Definition

Ripple noise in switching power supplies:

During the process of outputting DC voltage in switching power supplies, the switching action of the switch transistor generates high-frequency pulse currents. These currents pass through output capacitors and inductors, causing voltage fluctuations and thereby generating AC voltage at the output, which is known as ripple noise.

II. Causes

From the definition, it can be seen that ripple noise in switching power supplies is mostly caused by the switching action of the switch transistor, which can be summarized as follows:

When the switch transistor is switched, there are instantaneous changes in current and voltage, resulting in high-frequency noise, i.e., ripple noise.

The causes of ripple noise in switching include those generated by the switching power supply itself and those from external electromagnetic interference (EMI), which enters the switching power supply through radiation or the power line.

III. Why Is Ripple Noise in Switching Power Supplies So High?

Ripple is the fluctuation in output DC voltage, which is related to the switching action of the switching power supply.

Scenario: When the switch transistor is turned off, the inductor stores energy and the capacitor discharges, causing the current to decrease.

At this point, the magnetic field energy in the inductor is converted into electrical energy in the capacitor, and then the voltage across the capacitor rises. At this point, the electrical energy in the capacitor is converted back into magnetic field energy in the inductor, causing the inductor current to rise, thus repeating this process.

This forms an oscillating loop, resulting in ripple noise.

IV. How to Mitigate Ripple Noise

Methods to reduce ripple noise include:

1. Device selection: Use high-quality capacitors and inductors (large capacitance) to reduce the amplitude of ripple voltage. Low-ESR capacitors can be used to reduce the ESR of capacitors, minimizing the impact of capacitor internal resistance on filtering efficiency.

2. Filtering circuit: Implement multiple-stage filtering circuits, such as LC filters, RC filters, etc., to improve filtering efficiency.

3. Stable switching: Use linear regulators to further stabilize the output DC voltage of the switching power supply and reduce the amplitude of ripple noise.

4. Adopt suitable layout and grounding methods: Suitable layout and grounding methods can effectively reduce electromagnetic interference and common-mode interference at the output of the switching power supply.