Current mode current sense circuits and methods
AssigneeMaxim Integrated Products, Inc.
InventorGabriel Eugen Tanase
Life of this patent
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Abstract
Current mode current sense circuits and methods that may provide a current output proportional to the sensed current, and that provide current sensing at a fixed voltage drop. Sensing is by way of a transistor coupled in series with the load, with circuitry clamping the voltage drop across the transistor to a predetermined level, and providing a current output proportional to the current in that transistor. Various embodiments are disclosed, including circuits for high side and low side sensing, and which are capable of operation in the presence of short circuits.
Claims14
A current sense circuit comprising:
- first and second transistors, each having first and second terminals and a control terminal;
- the conduction through each transistor between the first and second terminals being controlled by the voltage between the control terminal and the first terminal of the respective transistor;
- the first transistor having its first and second terminals configured to connect in series with a first power supply terminal and a load;
- the first terminal of the second transistor being connected to the first terminal of the first transistor, and the control terminal of the second transistor being connected to the control terminal of the first transistor;
- a first control loop responsive to a reference voltage to clamp the first to second terminal voltages of the first and second transistors to a predetermined voltage;
- and,
- a second control loop providing a sense circuit output current linearly varying with the current through the second transistor.
A method of sensing current using transistors, each having first and second terminals and a control terminal, the current flow between the first and second terminals being controlled by the voltage between the control terminal and the first terminal, comprising:
- coupling the first and second terminals of the first transistor in series with a source of power and a load;
- using a first control loop responsive to a set voltage, mirroring a current proportional to the current through the first transistor to a second transistor while maintaining the voltages between the control terminal and the first terminal of the first and second transistors equal;
- and
- also maintaining the voltages between the first and second terminals of the first and second transistors equal;
- and,
- providing a current sense output responsive the current between the first and second terminals of the second transistor.
A method of current sensing comprising:
- providing first and second transistors, the first transistor being N times the size of the second transistor;
- passing the current to be sensed through the first transistor;
- controlling the first and second transistors so that the voltages across the first and second transistors are equal to a reference voltage and independent of the input current to replicate the current in the first transistor in the second transistor in a ratio of 1/N;
- and,
- providing an output that varies linearly proportional to the current in the second transistor.
Dependencies are inferred from the claim text.