Reduce the ripple of the power adapter, you can start from the following points.
1. PCB alignment and layout
Feedback lines should avoid magnetic components, switching tubes and power diodes. Output filter capacitor placement and alignment is critical to ripple noise, each circuit length is equivalent that the high-frequency current will be evenly distributed to each capacitor. If the PCB is a multilayer board, you can choose and the main current loop layer of the nearest layer over ground, over ground can effectively solve the noise problem.
2. The field-effect tube D level and the input between the positive plus RCD
Generally choose the reverse recovery time of the field effect tube to be 2 to 3 times slower than the diode D1, in order to avoid the formation of straight-through current, this current will generate a strong magnetic field, can increase the output noise interference, so you can artificially slow down the switching speed of the switching tube through the gate resistor R4.
3. The field effect tube DS end parallel RC
Can be connected in parallel with an RC circuit at both ends of the field-effect tube DS can also effectively reduce noise interference as shown in Figure 2, capacitor C2 is generally around 100P, the capacitance value will lead to increased switching losses in the field-effect tube, the resistance R2 is generally selected less than 10Ω resistance.
4. Reduce transformer leakage inductance
The use of sandwich winding method can make the primary and secondary winding coupling more closely, so that leakage inductance can be reduced, so as to reduce the purpose of noise.
5. The output diode ends in parallel with the RC
Diode in high-speed on and off, reverse recovery period, the diode's parasitic inductance and capacitance will generate high-frequency oscillations, in order to suppress high-frequency oscillations can be added to both ends of the diode RC buffer circuit shown in Figure 2, the resistance R3 generally in 1Ω ~ 100Ω, capacitance C3 generally in 100pF ~ 1nF, if the power supply operating frequency is low, the efficiency to meet the requirements, diode D3 can be selected Reverse recovery time is slower diode.
6. The output plus two LC filtering
LC noise and ripple suppression effect is relatively obvious, according to the ripple frequency to select the appropriate inductor capacitance value, but due to the advantages of low price column inductors small size, so the general LC inductor will mostly choose column inductors, however, column inductors are open magnetic structure, the surrounding will produce more serious magnetic interference, we can use two inductors placed side-by-side, and the opposite direction of current inflow, that helps guide the magnetic flux from We can use two inductors placed side by side, and the current inflow direction is opposite, that is, it helps to guide the magnetic flux from one magnetic column to another, thus can reduce electromagnetic interference. For more information about power adapter, please visit Shenzhen BON Electronics Co.，LTD.
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