Current sensing circuit
AssigneeMotorola, Inc.
InventorRobert S. Wrathall
Life of this patent
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Abstract
A current sensing circuit is disclosed wherein a small portion of a load current is sampled through a sensing resistor and a substantially larger portion of the load current is allowed to bypass the sensing resistor. A first high current vertical MOS transistor is coupled between the load and the ground terminal. A second vertical MOS transistor is coupled in series between the load and ground terminal. The transistors are constructed in a vertical MOS cellular construction whereby the first transistor comprises on the order of three-thousand cells and the second transistor comprises a single cell. A signal is taken across the sensing resistor and may be provided as feedback to a control means driving the first and second transistors for performing a current limiting or constant current function.
Claims8
A current sensing circuit coupled between a load having a load current passing therethrough and a supply voltage terminal, comprising:
- a first current means coupled between said load and said supply voltage terminal for carrying a first portion of said load current;
- resistive means coupled to said supply voltage terminal for providing a voltage drop;
- second current means coupled between said load and said resistive means for carrying a second portion of said load current, said first portion being substantially larger than said second portion;
- control means coupled to said first current means and said second current means for biasing said first current means and said second current means;
- output means coupled to a first node between said second current means and said resistive means for providing an output.
A current sensing circuit having an input terminal for receiving a load current, a supply voltage terminal and an output terminal, comprising:
- a first transistor having current carrying electrodes coupled between said input terminal and said supply voltage terminal;
- a second transistor having a first current carrying electrode coupled to said input terminal;
- resistive means coupled between a second current carrying electrode of said second transistor and said supply voltage terminal for providing a voltage drop, wherein said second current carrying electrode is also coupled to said output terminal;
- and
- a drive circuit coupled to a control electrode of each of said first and second transistors.
A circuit for providing a constant current to a load comprising:
- first current means coupled between said load and a supply voltage terminal for carrying a first portion of said current;
- resistive means coupled to said supply voltage terminal for providing a voltage drop;
- second current means coupled between said load and said resistive means for carrying a second portion of said current, said first portion being substantially larger than said second portion;
- control means coupled to said first and second current means for controlling the value of said first portion and said second portion;
- and
- drive means coupled from a node between said resistive means and said second current means to said control means and for driving said control means.
Dependencies are inferred from the claim text.