Voltage-activated, constant current sink circuit
AssigneeMicrel, Inc.
InventorSean Montgomery
Life of this patent
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Abstract
Voltage-activated and accurate current sink, and method of providing same. In one aspect, a circuit for accurately sinking current includes a zener diode coupled to a power source at the cathode of the zener diode, and first and second transistors, where the first transistor has its collector coupled to the power source and its base coupled to the cathode of the zener diode, and the second transistor has its base coupled to the anode of the zener diode and its emitter coupled to ground. A resistor is coupled between the emitter of the first transistor and the collector of the second transistor.
Claims24
A circuit for accurately sinking current, the circuit comprising:
- a zener diode coupled to a power source at the cathode of the zener diode;
- first and second transistors, wherein the first transistor has its collector coupled to the power source and its base coupled to the cathode of the zener diode, and wherein the second transistor has its base coupled to the anode of the zener diode and its emitter coupled to ground;
- and
- a resistor coupled between the emitter of the first transistor and the collector of the second transistor.
A method for accurately sinking current, the method comprising:
- preventing current received from a power source from flowing through a resistor when an input voltage is below a predetermined voltage level, the predetermined voltage level determined by the voltage rating of a zener diode;
- and
- allowing a constant current flow through the resistor above the predetermined voltage level by switching on a transistor at a voltage above the voltage rating of the zener diode.
Dependencies are inferred from the claim text.