US 6,208,123 B1 · Voltage regulator with clamp circuit

Abstract

Current drawn from a power supply at the start-up of a voltage regulator is reduced by providing a clamp circuit to clamp the input voltage of an output transistor in the voltage regulator for a predetermined period of time after start-up. The voltage regulator preferably comprises an error amplifier for producing an error signal depending upon the difference between a divided portion of the regulated output voltage and a reference voltage, the error signal for controlling the output transistor to regulate the output voltage thereof, and the clamp circuit includes a charge storage device connected to a current source, and a switch circuit having a first terminal connected to a first voltage sufficient to place the output transistor in a high-resistance state, a second terminal connected to the error signal and the input of the output transistor, and a third terminal connected to the charge storage device for controlling an ON/OFF state of the switch circuit. When the voltage regulator is started, the voltage at the input of the output transistor is clamped to a voltage sufficient to maintain the output transistor in a high-resistance state for a predetermined period of time until the voltage across the charge storage device is brought by the current source to a voltage sufficient to activate the switch circuit so that the voltage at the input terminal of the output transistor is no longer clamped and is controlled by the error signal.

Claims31

Dependent claims

In a voltage regulator having at least an error amplifier and an output transistor for producing an output voltage, the improvement comprising:

a clamp circuit for placing the output transistor in one of a high resistance state for a given period of time and a varying resistance state in which the on-resistance is reduced gradually as time elapses when the voltage regulator is placed in operation to thereby prevent the output transistor from turning on fully for the given period of time after the voltage regulator is placed in operation.

A voltage regulator circuit comprising:

an output circuit for outputting a regulated output voltage;
a comparison circuit for comparing a fed back portion of the regulated output voltage with a predetermined voltage and outputting a comparison signal dependent upon the comparison result;
and a circuit for preventing current in the output circuit from reaching a maximum level for a predetermined period of time after the voltage regulator is placed in operation, the circuit comprising a clamp circuit for clamping the voltage supplied to a transistor in the output circuit to a predetermined value for a predetermined period of time after the voltage regulator is placed in operation so as to limit current flow in the transistor.

A voltage regulator comprising:

an error amplifier for producing an error signal based on a difference between a reference voltage and a fed back portion of a regulated output voltage of the voltage regulator;
an output transistor for receiving the error signal for producing the regulated output voltage;
and a clamp circuit for clamping the output voltage of the error amplifier to a given value to prevent the output transistor from being turned on for a given period of time exceeding a duration of a transient condition of the error amplifier after the voltage regulator is placed in operation.

In a voltage regulator having at least an error amplifier having a transient condition when placed in operation and an output transistor for producing an output voltage, the improvement comprising:

a circuit for preventing the output transistor from turning on for a given period of time exceeding the duration of the transient condition after the voltage regulator is placed in operation, the circuit comprising a clamp circuit for placing the output transistor in one of a high resistance state for a given period of time exceeding the duration of the transient period and a varying resistance state in which the on-resistance is reduced gradually as time elapses after the duration of the transient period when the voltage regulator is placed in operation.

Dependencies are inferred from the claim text.

Voltage regulator with clamp circuit

Life of this patent

Voltage regulator with clamp circuit

Life of this patent

Abstract

Claims31