Abstract: A multi-output switching power supply of the present invention includes: a series resonant circuit which is connected in parallel with a first switching element or a second switching element, and includes a current resonance capacitor, a resonant reactor and a primary winding of a transformer, which are connected in series; a first rectifying and smoothing circuit which rectifies and smoothes a voltage generated in a first secondary winding of the transformer, and outputs a first output; a second rectifying and smoothing circuit which has a first diode for rectifying a voltage generated in a second secondary winding of the transformer, a reactor having energy stored therein by the voltage rectified by the first diode and a second diode for regenerating the energy into an output, and which rectifies a current flowing through the reactor and outputs a second output; and a control circuit which alternately turns on and off the first and second switching elements based on the first output.

Abstract: In an overheat protection circuit for power supply devices in the present invention, overheat protection is provided by using a Schottky barrier diode (SBD) in place of a dedicated thermosensor. The overheat protection circuit is designed to flow reverse leakage current Ir resulting from temperatures of the SBD thermally coupled with a rectifier diode to a photocoupler inside an output-voltage detecting circuit in a direct-current power supply device. Thereby, where the reverse leakage current of the SBD is increased (where temperatures of the rectifier diode are elevated due to overload), a feedback signal of the output-voltage detecting circuit is increased to decrease the output voltage, thereby the direct-current power supply device is protected from overheat.

Abstract: A switching-mode power supply capable of causing conduction through a synchronous rectifier switch exactly when required. Included is a transformer having a primary winding connected to a pair of DC input terminals via an active switch, and a secondary winding connected to a pair of DC output terminals via a synchronous rectifier and a smoothing capacitor. The synchronous rectifier is a parallel connection of a synchronous rectifier switch and a diode. In order to cause conduction through the synchronous rectifier switch while the diode is conducting, there is provided a synchronous rectifier control circuit comprising two current sources, a conduction period determination circuit, and a synchronous rectifier switch control pulse forming circuit.

Abstract: A current flowing through a reactor flows through a resistor, which generates a voltage in accordance with the value of the current. As the voltage generated by the resistor is greater than or equal to the threshold of a transistor, the transistor is in an on state. As the current flowing through the reactor decreases and the voltage generated by the resistor becomes lower than the threshold of the transistor, the transistor turns off and an NMOS turns on. Accordingly, the gate voltage of an NMOS is decreased by a diode, ensuring that the NMOS is turned off before the current flowing through the secondary winding of a transformer becomes zero.

Abstract: A switching power source device is provided which comprises a secondary MOS-FET 9 connected between a secondary winding 6 of a transformer 2, a reactor 11 connected in parallel to secondary winding 6 of transformer 2 for accumulating energy during the on-period of primary MOS-FET 4, and a secondary control circuit 12 connected to reactor 11 and a control terminal of secondary MOS-FET 9. Secondary control circuit 12 serves to turn secondary MOS-FET 9 off to accumulate energy in reactor 11, turn secondary MOS-FET 9 on to discharge energy accumulated in reactor 11, and turn secondary MOS-FET 9 off upon completion of energy release from reactor 11.

Abstract: The present invention is provided with a series circuit in which a first switching element and a second switching element are connected in series at both ends of an output of an input rectifier circuit for rectifying an alternating current of an alternating current power supply, a resonant circuit in which a primary winding of a transformer and a current resonant capacitor are connected in series at both ends of the first switching element or the second switching element, a rectifying and smoothing circuit for rectifying and smoothing a voltage generated across a secondary winding of the transformer during an on-period of the first switching element or the second switching element, a control circuit for alternately turning on/off the first switching element and the second switching based on a voltage from the rectifying and smoothing circuit, and a voltage detecting circuit for outputting a voltage detecting signal when a voltage at both ends of one switching element of the first switching element and the sec

Abstract: A DC-to-DC converter incorporates a transformer having a primary winding connected to a pair of DC input terminals via an active switch, which turns on and off under the control of a feedback circuit, and a secondary winding connected to a pair of DC output terminals via a synchronous rectifier and a smoothing capacitor. The synchronous rectifier is a parallel connection of a synchronous rectifier switch and a diode. A synchronous rectifier control circuit is connected to the synchronous rectifier switch for causing conduction therethrough while the active switch is off. The synchronous rectifier control circuit comprises a capacitor for determination of the conducting periods of the synchronous rectifier switch, and a logic network for on/off control of the synchronous rectifier switch according to whether the active switch is on or off and whether the capacitor voltage is higher than a predefined threshold or not.

Abstract: A DC-to-DC converter incorporates a transformer having a primary winding connected to a pair of DC input terminals via an active switch, which turns on and off under the control of a feedback circuit, and a secondary winding connected to a pair of DC output terminals via a synchronous rectifier and a smoothing capacitor. The synchronous rectifier is a parallel connection of a synchronous rectifier switch and a diode. A synchronous rectifier control circuit is connected to the synchronous rectifier switch for causing conduction therethrough while the active switch is off. The synchronous rectifier control circuit comprises a capacitor for determination of the conducting periods of the synchronous rectifier switch, and a logic network for on/off control of the synchronous rectifier switch according to whether the active switch is on or off and whether the capacitor voltage is higher than a predefined threshold or not.

Abstract: A current flowing through a reactor flows through a resistor, which generates a voltage in accordance with the value of the current. As the voltage generated by the resistor is greater than or equal to the threshold of a transistor, the transistor is in an on state. As the current flowing through the reactor decreases and the voltage generated by the resistor becomes lower than the threshold of the transistor, the transistor turns off and an NMOS turns on. Accordingly, the gate voltage of an NMOS is decreased by a diode, ensuring that the NMOS is turned off before the current flowing through the secondary winding of a transformer becomes zero.

Abstract: A switching power supply includes a first series circuit formed by connecting first and second switching elements in series at both ends of a direct-current power source, a second series circuit formed by connecting a resonant capacitor, a resonant reactor, and a primary winding of a transformer in series at both ends of the switching element, a rectifying-smoothing circuit configured to rectify and smooth a voltage generated on a secondary winding of the transformer, and a control circuit configured to turn the first and second switching elements and on and off alternately based on an output voltage from the rectifying-smoothing circuit. Here, the control circuit sets an on-period of the second switching element to a predetermined time period longer than a half value of a cycle of a resonant current attributable to the resonant reactor and the resonant capacitor, and controls an on-period of the first switching element based on the output voltage from the rectifying-smoothing circuit.

Abstract: An object of this power supply device is to enable an overheat protection level and an overvoltage protection level to be set accurately.