Startup circuit, switching power source ic, and switching power source apparatus

Abstract

A startup circuit includes a MOSFET that is connected between a startup power source and an auxiliary power source made of a smoothing capacitor and passes a startup current from the startup power source to the smoothing capacitor, a JFET that has a drain terminal connected to a drain terminal of the MOSFET and a source terminal connected through a resistor to a gate terminal of the MOSFET, and a pinch-off voltage controller that controls a pinch-off voltage of the JFET to a first reference voltage at startup and to a second reference voltage, which is lower than the first reference voltage, after startup.

Description

technical field [0001] The present invention relates to a starting circuit for starting a switching power supply device, an IC for switching power supply using the starting circuit, and a switching power supply device. Background technique [0002] Conventionally, a junction field effect transistor, a switching power supply IC, and a switching power supply are disclosed which sufficiently provide a start-up capability and can expand a stable operating range. A JFET having a plurality of source regions for one drain region has its source electrodes divided into a plurality of groups, so that a plurality of JFETs can be formed equivalently to one JFET. In the starting circuit of the switching power supply using this JFET, the JFET that supplies the gate signal of the Nch-MOSFET for starting and the JFET that supplies the current to the capacitive element (smoothing capacitor) through the Nch-MOSFET for starting share the role, thereby realizing The increase of the starting cu...

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Problems solved by technology

[0016] And, after starting, in order to turn off the MOSFET 127, the nMOSFET 134 of the power supply unit 131 is turned on, and the gate voltage of the MOSFET 127 is approximately at the GND level. Therefore, the pinch-off voltage Vp is applied to the resistor 126, and the current I flowing at this time (=Vp / R1, R1 is the resistance value of the resistor 126) becomes useless consumption current

In order to suppress power consumption, when the pinch-off voltage Vp is set low, the MOSFET 127 is not turned on when VCC is applied, and the starting circuit 133 cannot be started.

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