US 2006/0133000 A1Published application

Overcurrent protection circuit and DC power supply

AssigneeFreescale Semiconductor, Inc.

InventorHiroyuki Kimura

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Abstract

An overcurrent protection circuit and DC power supply that are subtly affected by process and device differences, have small input and output voltage drops, and set maximum and short-circuit current values. In a normal operation mode, a first operational amplifier and an output transistor keep the output voltage constant. In a current limiting mode, when a large current is input to an input terminal due to transient response, a second detection transistor and a third operational amplifier control a second control transistor to keep the maximum current of the output transistor constant. When voltage decreases during a foldback mode, a first detection transistor and a second operational amplifier control a first control transistor to control short-circuit current of the output transistor. A second operational amplifier decreases output current in accordance with the output voltage with a current source that maintains constant mutual conductance.

Claims6

Dependent claims

An overcurrent protection circuit, comprising:

an output control device including a control terminal for controlling power between an input terminal and an output terminal of the overcurrent protection circuit;
a first comparator, connected to the control terminal of the output control device, for comparing a reference voltage with a voltage of the output terminal of the overcurrent protection circuit and outputting a comparison result;
first and second detection devices, each of which includes a control terminal that receives the comparison result, for detecting a proportional current value that is proportional to current flowing through the output control device;
a second comparator, connected to an output terminal of the first detection device, for comparing the proportional current value with a first reference current value provided by a first current source;
a first control device, connected to an output terminal of the second comparator, for controlling a voltage of the control terminal of the output control device;
a second current source, connected to an output terminal of the second detection device, for providing a second reference current value;
a third comparator for comparing a voltage of the output terminal of the second detection device with a voltage of an output terminal of the output control device;
and
a second control device, connected to an output terminal of the third comparator, for controlling a voltage of the control terminal of the output control device.

6 more elements

Dependencies are inferred from the claim text.