How to reduce the ripple of power adapters

The service life of electronic products directly affects the cost-effectiveness of electronic products, so how to reduce the ripple of power adapters? Today, let's follow the manufacturer to learn more!

1. PCB wiring and layout

Feedback lines should avoid magnetic components, switching tubes, and power diodes. The placement and routing of output filtering capacitors are crucial for ripple noise, and the length of each circuit is equivalent, meaning that high-frequency current will be evenly distributed to each capacitor. If the PCB is a multi-layer board, the closest layer to the main current circuit layer can be selected for grounding, which can effectively solve the noise problem

2. Add RCD between the D-stage of the field-effect transistor and the input positive

Generally, the reverse recovery time of field-effect transistors is 2-3 times slower than that of diode D1 to avoid the formation of direct current, which generates a strong magnetic field and can increase output noise interference. Therefore, the gate resistor R4 can be artificially used to slow down the switching speed of the transistor.

3. Parallel RC at the DS end of a field-effect transistor

A RC circuit can be connected in parallel at both ends of the field-effect transistor DS to effectively reduce noise interference, as shown in Figure 2. The capacitance C2 is generally around 100P, and excessive capacitance can lead to increased switching losses of the field-effect transistor. The resistance R2 is generally selected to be less than 10 Ω.

4. Reduce transformer leakage inductance

The use of sandwich winding method can make the coupling of the primary winding tighter, reduce leakage inductance, and thus achieve the goal of reducing noise.

5. Output diode connected in parallel at both ends RC

During the reverse recovery period of a diode during high-speed conduction and shutdown, the parasitic inductance and capacitance of the diode will generate high-frequency oscillations. To suppress high-frequency oscillations, an RC buffer circuit can be added at both ends of the diode as shown in Figure 2. The resistance R3 is generally between 1 Ω and 100 Ω, and the capacitance C3 is generally between 100pF and 1nF. If the power supply operates at a low frequency and meets the efficiency requirements, diode D3 can choose a diode with a slower reverse recovery time.

6. Output plus secondary LC filtering

LC has a significant effect on noise and ripple suppression. The appropriate inductance and capacitance value should be selected based on the ripple frequency. However, due to the low price and small size of cylindrical inductors, cylindrical inductors are generally chosen in LC. However, cylindrical inductors are open magnetic structures that can cause serious magnetic interference to the surrounding area. We can use two inductors placed side by side with opposite current flow directions, which helps guide magnetic flux from one magnetic column to another, thereby reducing electromagnetic interference