Startup circuit
AssigneeAzbil Corporation
InventorTetsuya Kajita
Life of this patent
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Abstract
Disclosed is a startup circuit comprises a current path comprising a circuit including a P-channel MOS transistor, a P-channel MOS transistor, and an N-channel MOS transistor connected in series. After a constant current circuit is started, the N-channel MOS transistor is turned on, an operating current is fed through the current path, and an N-channel MOS transistor is turned off to cut off a startup current. After the startup current is cut off, the gate voltage of the P-channel MOS transistor is controlled by the voltage (bias voltage during operation of the constant current circuit) of a node, a drain-source voltage of the P-channel MOS transistor is reduced, and the operating current flowing through the current path is limited.
Claims4
A startup circuit performing supply of a startup current to a constant current circuit generating a constant current by receiving supply of a power supply voltage when starting the supply of the power supply voltage to the constant current circuit, the startup circuit comprising:
- a switching element that is turned on when the supply of the power supply voltage is started and performs the supply of the startup current to the constant current circuit;
- and
- a startup current cut-off circuit cutting off the supply of the startup current to the constant current circuit by turning off the switching element after the constant current circuit is started,
- wherein the startup current cut-off circuit comprises:
- a current path through which a current turning off the switching element flows as an operating current;
- and
- an operating current limiting element limiting the operating current flowing through the current path after the switching element is turned off since the operating current flows through the current path.
Dependencies are inferred from the claim text.