Saturation-controlled loop current regulator
First Claim
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1. A process transmitter comprising:
- device circuitry that generates values that are to be conveyed on a current loop;
a series control transistor in series between the current loop and the device circuitry; and
a saturation prevention circuit that prevents the series control transistor from entering saturation by preventing a voltage across the series control transistor measured between an emitter and a collector of the series control transistor from dropping below a forward bias voltage of a diode in the saturation prevention circuit.
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Abstract
A process transmitter includes device circuitry that generates values that are to be conveyed on a current loop. A series control transistor is in series between the current loop and the device circuitry and a saturation prevention circuit prevents the series control transistor from entering saturation.
39 Citations
15 Claims
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1. A process transmitter comprising:
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device circuitry that generates values that are to be conveyed on a current loop; a series control transistor in series between the current loop and the device circuitry; and a saturation prevention circuit that prevents the series control transistor from entering saturation by preventing a voltage across the series control transistor measured between an emitter and a collector of the series control transistor from dropping below a forward bias voltage of a diode in the saturation prevention circuit. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A process field device comprising:
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control loop connectors for connection to a process control loop; device circuitry; and an interface in series between a control loop connector and the device circuitry wherein the interface controls a current level on the control loop and provides a power output that has a maximum power that scales with a voltage provided on the process control loop wherein the interface comprises a series transistor and a bias circuit wherein the bias circuit of the series transistor prevents the series transistor from saturating by limiting an emitter-collector voltage across the series transistor from dropping below a forward bias voltage drop across a diode. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A process field device comprising:
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two loop connectors for connection to a current loop; device circuitry; and an interface in series between one of the two loop connectors and the device circuitry such that current in the current loop passes through the interface to the device circuitry wherein the interface is capable of controlling a current level in the current loop while providing a fixed voltage drop between the current loop and the device circuitry for a plurality of current levels passing through the interface from the current loop to the device circuitry wherein the interface comprises a series transistor, a shunt transistor, and at least one diode such that the voltage drop between the current loop and the processing circuit is across the series transistor and the at least one diode and the shunt transistor prevent the voltage drop across the series transistor from being less than a forward bias voltage across the at least one diode. - View Dependent Claims (14)
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15. A process field device comprising:
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two loop connectors for connection to a current loop; device circuitry; and an interface in series between one of the two loop connectors and the device circuitry such that current in the current loop passes through the interface to the device circuitry wherein the interface is capable of controlling a current level in the current loop while providing a fixed voltage drop between the current loop and the device circuitry for a plurality of current levels passing through the interface from the current loop to the device circuitry wherein the interface comprises; a series transistor, a shunt transistor, an amplifier, wherein the amplifier is connected to the base of the shunt transistor and drives the shunt transistor to maintain a voltage drop across the series transistor; a first voltage divider connected to the device circuitry; and a second voltage divider connected to the current loop through a diode, wherein a non-inverting input of the amplifier is connected to the first voltage divider and an inverting input of the amplifier is connected to the second voltage divider.
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Specification