Patent ID: 8537574
Filing Date: 2013-09-17
Classification: H02M

Abstract:
1. A power source controlling semiconductor integrated circuit to control a current flowing through a primary side winding of a voltage converting transformer of an insulated direct-current power source device having the transformer, the circuit comprising: a first external terminal to which a detected voltage from a secondary side of the transformer is fed back through a photocoupler; a control circuit to generate and output a control signal of a switching element to control the current flowing through the primary side winding according to the voltage of the first external terminal and an input voltage applied to a terminal of the primary side winding of the transformer; a voltage generating circuit to generate an internal reference voltage based on the input voltage applied to the terminal of the primary side winding of the transformer; a pull-up section to be connected to the first external terminal to pull up a potential of the first external terminal to the internal reference voltage to enable giving a bias voltage to a light receiving element of the photocoupler, externally connected to the first external terminal; a first voltage comparing circuit having one input terminal connected to the first external terminal and another input terminal to which a first reference voltage is applied, wherein the control circuit is adapted to stop outputting the control signal based on an output of the first voltage comparing circuit when the voltage of the first external terminal is lower or higher than the first reference voltage; a second voltage comparing circuit having one input terminal connected to the first external terminal and another input terminal to which a second reference voltage of a potential higher than that of the first reference voltage is applied, wherein the control circuit is adapted to stop outputting the control signal based on the output of the first voltage comparing circuit and an output of the second voltage comparing circuit when the voltage of the first external terminal is lower than the first reference voltage or higher than the second reference voltage; and a delay circuit to delay the output of the second voltage comparing circuit, wherein the control circuit is adapted to delay stop control of the outputting in response to a signal from the delay circuit when the voltage of the first external terminal is judged to be higher than the second reference voltage by the second voltage comparing circuit.