Microchip Technology Inc.

Christian Albrecht

Philippe Deval

Scott Dearborn

Daniel Leonescu

Matthew Williams

The regulated output voltage of a voltage regulator is maintained up to a current limit, I, then as the load impedance continues to decrease the output current does not increase past the current limit, I, but rather the output voltage decreases forcing the output current to also decrease to satisfy Ohm's Law: I=V/Z. When the output voltage drops below the regulated voltage value because of current limiting the voltage regulator shifts from a current limit mode to a current foldback mode wherein the output current decreases with the decrease in output voltage until the output current reaches a current foldback minimum, I, at an output voltage of substantially zero volts. As the load impedance increases so will the output voltage and current until the output voltage is back at substantially the regulation voltage value, and the output current is less than or equal to the current limit, I.

Voltage regulator having current and voltage foldback based upon load impedance

A differential input operational amplifier has a voltage clamp differential transistor pair coupled to an input differential transistor pair of the operational amplifier. The voltage clamp differential transistor pair limits the output voltage of the operational amplifier by taking over control of the operational amplifier circuits from the input differential transistor pair as the output voltage approaches a clamp voltage value. A reference voltage may be used to set the output voltage at which the input differential transistor pair will be clamped by the voltage clamp differential transistor pair. Below the clamp voltage, operation of the input differential transistor pair will not be affected. At the clamp voltage the input differential transistor pair will no longer control the output of the differential amplifier, rather the voltage clamp differential transistor pair will control the maximum voltage output of the differential amplifier. Both positive and negative limiting of the operational amplifier output voltage may be accomplished.

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Echandens, Switzerland

Christian Albrecht