Low Heat Dissipation I/O Module Using Direct Drive Buck Converter

• US 20100320990A1
• Filed: 08/27/2010
• Published: 12/23/2010
• Est. Priority Date: 02/28/2007
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: TERDAN, Dale R., CHEN, Xiaofan
• Granted Patent: US 8,093,882 B2
• Time in Patent Office: Days
• US Class Current: 323/286
• CPC Class Codes: H03K 19/0008 Arrangements for reducing power consumption

Abstract

A current-loop output circuit for an industrial controller provides for low power dissipation and reduced part count by driving current loads of different resistances directly from a switched voltage source. Proper filtering and design of a feedback loop allows the necessary transient response times to be obtained.

Claims

1. A current loop circuit for an industrial controller comprising:

a first input configured to receive a compliance voltage;

a second input configured to receive a command signal from the industrial controller;

an output connection configured to be connected to a load device;

a switched power converter having at least one switch responsive to a switching signal to selectively establish a conductive path between the first input and the output connection;

a first current sense device configured to generate a first current signal representative of a current output from the switched power converter;

a second current sense device configured to generate a second current signal representative of a current conducted through the load device;

a feedback circuit generating an error signal dependent on the command signal, the first current signal, and the second current signal; and

a gating circuit generating the switching signal dependent on the error signal.

2. The current loop circuit of claim 1 further comprising a low pass filter connected in series between the switched power converter and the output connection.

3. The current loop circuit of claim 2 wherein the low pass filter has multiple stages and wherein the first current sense device measures the current before at least one of the multiple stages to generate the first current signal.

4. The current loop circuit of claim 3 wherein at least one of the multiple stages of the low pass filter includes an inductor and the first current signal is generated after the stage including the inductor.

5. The current loop circuit of claim 1 wherein the command signal is selected to provide a 4-20 mA current to the load device.

6. The current loop circuit of claim 1 wherein the switched power converter is a buck converter.

7. The current loop circuit of claim 1 wherein the command signal corresponds to one of at least two predetermined current levels.

8. The current loop circuit of claim 7 wherein the industrial controller is configured to execute a stored program to control an industrial process and the command signal is calculated by the stored program.

9. In an industrial controller configured to provide a control signal corresponding to one of at least two predetermined current levels to a plurality of current loop circuits, each current loop circuit comprising:

a logic circuit receiving the control signal from the industrial controller and generating a command signal;

a load terminal configured to connect the current loop circuit to a load device;

a switched power converter having at least one switch responsive to a switching signal to selectively establish a conductive path between a compliance voltage and the load terminal;

a first current sense device configured to generate a first current signal representative of a current output from the switched power converter;

a second current sense device configured to generate a second current signal representative of a current conducted through the load device;

a feedback circuit generating an error signal dependent on the command signal, the first current signal, and the second current signal; and

a gating circuit generating the switching signal dependent on the error signal.

10. The industrial controller of claim 9 further comprising a low pass filter having multiple stages connected in series between the switched power converter and the load terminal

11. The current loop circuit of claim 10 wherein at least one of the stages of the low pass filter includes an inductor and the first current sense device measures the current after the stage including the inductor.

12. The current loop circuit of claim 9 wherein the industrial controller is configured to execute a stored program which determines the control signal for controlling at least a portion of a controlled process.

13. A method of regulating current supplied by a two-wire current loop circuit in response to a command signal generated by an industrial controller to control an industrial device, comprising the steps of:

providing a switched power converter having a first input receiving a switching signal, a second input electrically connected to a compliance voltage, and an output electrically connected to the load device, wherein the switched power converter selectively establishes a conductive path between the compliance voltage and the industrial device responsive to the switching signal;

measuring a first current at the output of the switched power converter;

measuring a second current flowing through the load device;

calculating an error signal based on the command signal, the first current, and the second current; and

generating the switching signal responsive to the error signal.

14. The method of claim 13 further comprising the step of filtering the current in the conductive path with a low pass filter having multiple stages wherein the low pass filter is connected in series between the output of the switched power converter and the load device.

15. The method of claim 14 wherein at least one stage of the low pass filter includes an inductor and the first current is measured after the stage of the filter having the inductor.

16. The method of claim 13 wherein the command signal corresponds to one of at least two predetermined current levels.

17. The method of claim 13 wherein generating the command signal further comprises the steps of:

executing a program stored on the industrial controller to determine a desired control value for the load device; and

converting the control value to the command signal with a logic circuit.