The topology of a flyback switching power supply, when the FET is turned on, the input current flows through the transformer and FET. Then the FET is turned off, the input current flows through the electromagnetic induction to the output of the transformer to achieve energy transfer. As the transformer’s leakage inductance and the parasitic capacitance of the FET produce oscillation, the vibration generated by the decompression peak, in the energy transfer process, also passed to the output, forms the noise.
A good design layout to suppress noise In the design process, adding the FET absorption circuit at both ends will reduce spikes and thus can effectively reduce the power supply module output noise.
In the practical application, adding the module input and output capacitance, good PCB layout can further reduce module output ripple and noise. PCB layout, according to the current on the release of the capacitor, the power module ripple noise is no longer a problem