Patent ID: 8437152
Filing Date: 2013-05-07
Classification: H02M,Y02B

Abstract:
1. A switching power source device comprising a primary winding of a transformer and a main switching element both connected in series to a DC power source, a voltage-resonant capacitor connected in parallel to said main switching element, a synchronized rectification control circuit for producing synchronized control signals to turn said rectification switching element from off to on after turning-off of said main switching element and to turn said rectification switching element from on to off before turning-on of said main switching element, a pulse width elongation circuit for extending on-pulse width of said rectification switching element, and a main control circuit for producing main drive signals to turn said main switching element off and on with an operation frequency responsive to on-pulse width of said rectification switching element extended by said pulse width elongation circuit, wherein said pulse width elongation circuit comprises: an oscillation circuit for generating oscillation signals of its frequency sufficiently lower than operation frequency of said main switching element, a timer capacitor electrically charged by the synchronized control signal from said synchronized rectification control circuit, said timer capacitor starting electrical discharge with a given time constant upon cease of outputting the synchronized control signal, and a comparator for comparing voltage of the oscillating signal from said oscillation circuit with voltage of said timer capacitor, when charged voltage of said timer capacitor exceeds voltage of oscillating signal from said oscillation circuit, said comparator switches said rectification switching element from off to on, and when discharged voltage of said timer capacitor is equal to or less than voltage of oscillating signal from the oscillation circuit, said comparator switches said rectification switching element from on to off.