Patent ID: 7719860

Claim:
A power supply comprising: a transformer (T) having a primary winding, a secondary winding and a third winding; a DC voltage input section ( 2 ) which receives an AC voltage and applies a DC voltage that is said input AC voltage rectified and smoothed to said primary winding of said transformer (T); a switching section (Q 1 ) which generates a voltage on said primary winding of said transformer (T) by switching a current flowing in said primary winding of said transformer (T); a rectifying and smoothing section ( 4 ) which rectifies and smoothes a voltage generated on said secondary winding of said transformer (T), and supplies the rectified, smoothed voltage to said load, a drive control section ( 6 ) which supplies a pulse signal for said switching section (Q 1 ) to switch said current to said switching section (Q 1 ) as the drive signal, thereby driving and controlling said switching section (Q 1 ); a capacitor (C 3 ) which applies a charged voltage to a power line of said drive control section ( 6 ) as the drive control voltage; a charge circuit section ( 13 , 14 , R 21 ) which supplies a current to said capacitor (C 3 ) from said DC voltage input section ( 2 ) to charge said capacitor (C 3 ) when said DC voltage input section ( 2 ) starts inputting a DC voltage to said primary winding of said transformer (T); an auxiliary power supply section ( 7 ) which rectifies a voltage generated on said third winding (n 3 ) of said transformer (T) and applies that voltage to said capacitor (C 3 ) to charge said capacitor (C 3 ); a charge control section ( 17 ) which stops charging of said capacitor (C 3 ) from said charge circuit section ( 13 , 14 , R 21 ) when the drive control voltage to be supplied to said power line of said drive control section ( 6 ) becomes equal to or greater than a preset voltage value; an operation stop section ( 15 ) which detects an output current to be supplied to said load, compares a current value of said detected output current with a preset current value for determining whether said load is light or not, and stops an operation of said drive control section ( 6 ) when the current value of said detected output current becomes less than the preset current value for determining whether said load is light or not; and a time measuring section ( 16 ) which measures a time after said operation stop section ( 15 ) stops the operation of said drive control section ( 6 ), and outputs a switch-on signal to said charge control section ( 17 ) when a preset time elapses since measuring, wherein said charge control section ( 17 ) resumes charging said capacitor from said charging circuit when said switch-on signal is output from said time measuring unit ( 16 ).