Low voltage dropout regulator
AssigneeTexas Instruments Incorporated
InventorJames E. Schroeder
Life of this patent
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Abstract
A high efficiency dropout regulator (60) drives an output transistor (22) with a PNP transistor (52) if the overhead voltage from input (14) to output (26) is below a predetermined voltage. If the overhead voltage exceeds the predetermined voltage, then a second PNP transistor (64) and an NPN transistor (72) are used to drive the output transistor (22), resulting in a large reduction of power loss. The current drawn from the output transistor (22) by the NPN transistor (72) is returned to the output.
Claims14
A low dropout regulator for generating a desired output voltage comprising:
- an input for receiving an input voltage in excess of the desired output voltage;
- an output for generating the desired output voltage;
- a first current control element operable to conduct a current between said input and said output;
- first control circuitry for controlling the current through said first current control element when said input voltage exceeds the desired output voltage by less than a predetermined voltage;
- and
- second control circuitry including a NPN transistor for controlling the current through said first current control element when said input voltage exceeds said desired output voltage by at least said predetermined voltage.
A low dropout regulator for generating a desired voltage comprising:
- an input for receiving an input voltage;
- an output operable to supply the desired voltage;
- an output transistor operable to conduct current between said input and said output;
- a first driving transistor for driving said output transistor by drawing current from the base of said output transistor and supplying said drawn current to the output;
- differential circuitry for generating a voltage corresponding to the voltage present at said output;
- a second driving NPN transistor operable to drive said first driving transistor in response to said differential voltage when said input voltage exceeds said output voltage by more than a predetermined voltage;
- and
- a third driving transistor operable to drive said output transistor in response to said differential voltage when the voltage difference from said input to output does not exceed said predetermined voltage.
A method of generating a desired output voltage in a voltage regulator comprising the steps of:
- receiving an input voltage from an input;
- conducting current from said input to an output;
- controlling the amount of current conducted from input to output with a first control circuit if said input voltage exceeds the desired output voltage by less than a predetermined voltage;
- and
- controlling the amount of current conducted from said input to said output with a second control circuit including an NPN transistor if said input voltage exceeds the desired output voltage by at least said predetermined voltage.
Dependencies are inferred from the claim text.