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.
Claims27
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, wherein the power source supplies power to a powered device coupled to the circuit, wherein the resistance value of the resistor designates a power class for the powered device.
A method for accurately sinking current using a current sink circuit, 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 in the current sink circuit;
- and
- allowing a constant current flow though the resistor when the input voltage is above the predetermined voltage level, wherein the constant current flow is allowed by at least one and not more than two transistors in the current sink circuit, and wherein the constant current flow is allowed by switching on one of the transistors in response to a voltage that is above the voltage rating of the zener diode and is provided at the cathode of the zener diode.
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;
- a resistor coupled between the emitter of the first transistor and the collector of the second transistor;
- and
- a limit circuit for isolating a load from the power source when the output voltage of the power source is within a predefined voltage range.
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 when the input voltage is above the predetermined voltage level by switching on a transistor in response to a voltage that is above the voltage rating of the zener diode and is provided at the cathode of the zener diode, wherein the power source supplies power to a powered device coupled to the transistor, wherein the level of current flowing through the resistor is used by the power source to classify the power requirements of the powered device.
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;
- allowing a constant current flow through the resistor when the input voltage is above the predetermined voltage level by switching on a transistor in response to a voltage that is above the voltage rating of the zener diode and is provided at the cathode of the zener diode;
- and
- isolating a load from the power source when the output voltage of the power source rises above a second predetermined voltage, using a limit circuit coupled to the transistor.
Dependencies are inferred from the claim text.