Cherry Semiconductor Corporation

Claudio Tuozzolo

George E Schuellein

A foldback circuit which responds to a voltage differential between the input and output terminals of a voltage regulator in excess of a foldback threshold by lowering the current limit threshold of a current limit circuit. The foldback circuit includes a transistor with a base coupled to the input voltage and an emitter coupled to the output voltage. The collector when conducting provides a current that decreases the current limit threshold. Diodes in the path between the input and output voltages through the transistor may be used in establishing the foldback threshold.

Temperature insensitive foldback network

A voltage regulator with a current limit circuit for limiting pass current in a pass transistor below a current limit threshold and a foldback circuit for lowering the current limit threshold when the voltage differential between the input and output terminals of the voltage regulator exceeds a foldback threshold, where the current limit threshold has a negative temperature coefficient, the current limit circuit comprising two transistors coupled to a sense resistor such that the difference in emitter-to-base voltages of the transistors is equal to the voltage drop of the sense resistor, where the collectors of the two transistors provides first and second currents to first and second resistors, respectively, where the first current is responsive to a pass current flowing through the sense resistor and decreases when the pass current increases, where the second current is independent of the pass current, and the foldback circuit provides a third current to the second resistor when the voltage differential between the input and output terminals of the voltage regulator exceeds the foldback threshold. A comparator circuit compares a first voltage drop developed across the first resistor with a second voltage drop developed across the second resistor, and limits base current to the pass transistor based upon the ratio of first and second voltage drops to thereby prevent the pass current from exceeding the current limit threshold.

Low voltage current limit circuit with temperature insensitive foldback

A thermal shut down circuit with built-in temperature hysteresis, comprising first and second transistors configured as a bistable trigger circuit. The two transistors switch either a first or second emitter current through a bias resistor, thereby establishing a voltage hysteresis. By applying a reference voltage to the base of the first transistor, temperature dependent state transitions occur. A buffer transistor coupled to the collector of the second transistor allows the thermal shut down circuit to turn ON or OFF an auxiliary circuit. Thermal communication between the auxiliary circuit and the base-emitter junction of the first transistor allows the thermal shut down circuit to shut down the auxiliary circuit when the temperature exceeds a shutdown temperature, and thermal hysteresis built into the thermal shut down circuit prevents undesirable ON-OFF oscillation of the auxiliary circuit.

Thermal limit circuit with built-in hysteresis

A circuit providing start-up capability and foldback protection to a voltage regulator. A start-up circuit provides a start-up signal to initiate current flow to a load and also provides a foldback signal to set a current limit threshold under an over-load or short-circuit condition. A signal generator circuit operating on the regulated output voltage of the voltage regulator provides a current limit signal and a start-up control signal. The start-up circuit provides the start-up signal in response to the start-up control signal. The current limit signal sets the current limit threshold under normal operating conditions after start-up.

Growing community of inventors

Cranston, RI, United States of America

Claudio Tuozzolo