Patent ID: 6987677

Claim:
A power-supply switching method comprising: producing a driving output from a rectifying smoothing circuit for driving a switching control circuit having an input voltage and hysteresis low-voltage mistaken operation circuit; accumulating in a capacitor energy corresponding to a range of voltage of said hysteresis low-voltage mistaken operation circuit from a protective voltage to a release voltage; supplying a startup current from a primary side startup circuit to said switching control circuit, wherein said hysteresis low-voltage mistaken operation circuit prohibits said primary side startup circuit from starting up said switching control circuit based on energy accumulated in said capacitor; producing a primary rectified output from a primary side rectifying circuit; producing a secondary rectified output from a secondary side rectifying circuit; receiving said primary rectified output by a primary winding of a converter transformer; producing a tertiary output from a tertiary winding of said converter transformer, which is wound in a direction opposite to that of the primary winding; switching said primary rectified output; and providing an error feed back signal by an output detection circuit to said switching control circuit via a photocoupler to control the switching element by said switching control circuit; wherein after said primary side startup circuit supplies said startup current to said switching control circuit, a tertiary output of said tertiary winding is rectified and smoothed by said rectifying smoothing circuit to produce said driving output; wherein said tertiary output is lower than said protective voltage when a current supplied to a secondary winding of said converter transformer, which is wound in a direction opposite to that of the primary winding, is less than a predetermined setting load current, and said tertiary output is higher than said protective voltage when a current into said secondary winding is greater than said predetermined setting load current; and wherein the switching control circuit enters into a standby state when said input voltage is less than or equal to said release voltage.