The paper introduces the principle of switch power which is composed by current control type PMW UC3842 and analyzes the shortage of protective circuit and proposes an improving idea.

Moreover, its operation process principles and critical parameters are analyzed, its simulation results proved that the novel single stage high power switch source's power factor can achieve 0.995.

The working principle of colour TV supply source circuit and fault analysis were described. Some maintenance examples are helpful for repairing other switch supply source circuits.