To 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 of ripple noise is critical, each loop length is equivalent that is, 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 of ground cover, ground cover can effectively solve the noise problem!
2, field effect tube D level and the input between the positive plus RCD
General selection of field effect tube reverse recovery time than the diode D1 2 to 3 times slower to avoid the formation of straight-through current, this current will produce 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 at both ends of the field effect tube DS an RC circuit can also be effective in reducing noise interference as shown in Figure 2, capacitance C2 is generally in the 100P or so, the capacitance value is too large will lead to an increase in the switching loss of the field effect tube, resistor R2 is generally selected less than 10Ω resistance.
4, reduce transformer leakage
Sandwich winding method can make the primary and secondary winding coupling more closely, so that the leakage inductance can be reduced, so as to achieve the purpose of reducing noise.
5, output diode ends parallel RC
Diode in high-speed conduction and shutdown, reverse recovery period, the diode's parasitic inductance and capacitance will produce high-frequency oscillation, in order to inhibit high-frequency oscillation in the diode terminals plus RC buffer circuit as shown in Figure 2, resistor R3 is generally in the range of 1Ω ~ 100Ω, capacitance C3 is generally in the range of 100pF ~ 1nF, if the power supply operating frequency is lower, the efficiency of meeting the requirements of the diode, then the diode can be selected D3! Reverse recovery time slower diode.
6, the output plus two LC filter
LC noise and ripple suppression effect is more obvious, according to the ripple frequency to select the appropriate inductor capacitance value, but because of the advantages of low price and small size of the column inductor, so the general LC inductor will choose the majority of column inductors, however, column inductors are open magnetic structure, the surrounding will produce a more serious magnetic interference, we can use the two inductors are placed side by side, and the current inflow in the opposite direction, that is, to help guide the magnetic flux from the We can use two inductors placed side by side with the current flowing in the opposite direction, which helps to guide the magnetic flux from one magnetic column to another, thus reducing the electromagnetic interference.
