Abstract: A voltage conversion circuit and a switching power supply device achieving both a good response and a low loss of a power supply voltage, wherein a main voltage conversion portion (circuit block) for conversion an AC voltage to a DC voltage, an auxiliary voltage conversion portion for the same conversion but in transit period up to shifting to a stationary state, a voltage limiting portion (Zener diode) for limiting the DC voltage output from the auxiliary voltage conversion portion to a constant limit-voltage, and an output control switch (transistor) connected in the output pass and for switching the pass to conductive or nonconductive possible to apply a higher voltage in between a voltage at the output node and the limit-voltage based on their magnitude relation.

Abstract: A synchronized rectification circuit and a switching power supply device having little power loss with respect to a wide range of input voltages and having a high efficiency, comprising first and second switch elements, first and second capacitors connected with each other capable to equalize held voltages thereof in response to sift of an input AC voltage to intermediate voltage (for example 0V), a first driving circuit for turning on a switch element according to the held voltage changed in response to shift the input AC voltage to 0V from a negative polarity voltage and turning off the switch element earlier than a time where the input voltage shifts to the negative polarity voltage from 0V, and a second driving circuit to drive a switch element in the same way but in reverse phase.

Abstract: A synchronous rectification circuit of a switching power supply device where circuit elements such as rectification switch elements are protected when an abnormality occurs in an output of a transformer, wherein a (fault) detecting circuit detects an abnormality of a trigger signal transmitted from a transformer, a shutoff circuit quickly cuts off a discharge route of an inductor (coil) forming a gate drive signal source of a first transistor (NMOS transistor) when the (fault) detecting circuit detects an abnormality, and a (linear) driver holds (clamps) a drain-source voltage of the NMOS transistor at a constant voltage and turns on the NMOS transistor by that constant voltage so as to prevent it from turning off immediately when the detecting circuit detects an abnormality.

Abstract: A synchronous rectification circuit of a switching power supply device where circuit elements such as rectification switch elements are protected when an abnormality occurs in an output of a transformer, wherein a (fault) detecting circuit detects an abnormality of a trigger signal transmitted from a transformer, a shutoff circuit quickly cuts off a discharge route of an inductor (coil) forming a gate drive signal source of a first transistor (NMOS transistor ) when the (fault) detecting circuit detects an abnormality, and a (linear) driver holds (clamps) a drain-source voltage of the NMOS transistor at a constant voltage and turns on the NMOS transistor by that constant voltage so as to prevent it from turning off immediately when the detecting circuit detects an abnormality.

Abstract: A voltage conversion circuit and a switching power supply device achieving both a good response and a low loss of a power supply voltage, wherein a main voltage conversion portion (circuit block) for conversion an AC voltage to a DC voltage, an auxiliary voltage conversion portion for the same conversion but in transit period up to shifting to a stationary state, a voltage limiting portion (Zener diode) for limiting the DC voltage output from the auxiliary voltage conversion portion to a constant limit-voltage, and an output control switch (transistor) connected in the output pass and for switching the pass to conductive or nonconductive possible to apply a higher voltage in between a voltage at the output node and the limit-voltage based on their magnitude relation.

Abstract: A synchronized rectification circuit and a switching power supply device having little power loss with respect to a wide range of input voltages and having a high efficiency, comprising first and second switch elements, first and second capacitors connected with each other capable to equalize held voltages thereof in response to sift of an input AC voltage to intermediate voltage (for example 0V), a first driving circuit for turning on a switch element according to the held voltage changed in response to shift the input AC voltage to 0V from a negative polarity voltage and turning off the switch element earlier than a time where the input voltage shifts to the negative polarity voltage from 0V, and a second driving circuit to drive a switch element in the same way but in reverse phase.

Abstract: In charging a gate of a NMOS transistor Q1, the charging speed is adjustable by varying a resistor R1. When an inputted pulse signal VIN reverses to a negative voltage, a diode D2 turns off. Then, current flows along a discharging loop formed by the gate capacitor, the resistor R1, the emitter of the transistor Q2, the base of the transistor Q2, the resistor R2 and the capacitor C1, the transformer T1 and the source of the NMOS transistor Q1. A reverse bias voltage is applied to the gate of the NMOS transistor Q1, thereby keeping the NMOS transistor Q1off-state stably.

Abstract: In charging a gate of a NMOS transistor Q1, the charging speed is adjustable by varying a resistor R1. When an inputted pulse signal VIN reverses to a negative voltage, a diode D2 turns off. Then, current flows along a discharging loop formed by the gate capacitor, the resistor R1, the emitter of the transistor Q2, the base of the transistor Q2, the resistor R2 and the capacitor C1, the transformer T1 and the source of the NMOS transistor Q1. A reverse bias voltage is applied to the gate of the NMOS transistor Q1, thereby keeping the NMOS transistor Q1 off-state stably.

Abstract: A switching power supply apparatus has a plurality of switching power supply circuits. A control IC (IC1) in a switching power supply circuit generates a PWM drive signal and a synchronizing signal, and also generates DC voltage according to a duty ratio of the PWM drive signal. A control IC (IC2) in the other switching power supply circuit is provided with the synchronizing signal from the IC1 via a transformer, and controls based on a PWM drive signal synchronized with the synchronizing signal. Therefore, switching timing completely matches among the plurality of switching power supply circuits.