Current Control for Power Stealing

• US 20140299670A1
• Filed: 04/05/2013
• Published: 10/09/2014
• Est. Priority Date: 04/05/2013
• Status: Active Grant

• Current Assignee: Emerson Electric Company
• Original Assignee: Emerson Electric Company
• Inventors: Ramachandran, Anil, Zikes, Bradley C.
• Granted Patent: US 9,684,316 B2
• Time in Patent Office: Days
• US Class Current: 236/1.C
• CPC Class Codes: G05D 23/19 characterised by the use of electric means G05D23/1393 takes precedence

Abstract

A thermostat for use in a climate control system has a power stealing circuit that provides power from a voltage supply through a load of the climate control system when the load is in an “off” mode. The power stealing circuit has a current limiting circuit that provides a maximum level of instantaneous current predetermined to be a threshold beyond which the load is switched to an “on” mode.

Claims

1. A thermostat for use in a climate control system, the thermostat comprising:

a power stealing circuit configured to provide power from a voltage supply through a load of the climate control system when the load is in an “

off”

mode, the power stealing circuit having a current limiting circuit configured to provide a maximum level of instantaneous current predetermined to be a threshold beyond which the load is switched to an “

on”

mode.

2. The thermostat of claim 1, wherein the maximum level of instantaneous current corresponds to a maximum voltage threshold at which the load is not switched to the “

on”

mode.

3. The thermostat of claim 1, wherein the power stealing circuit is configured to provide power to one or more circuits ancillary to the thermostat.

4. The thermostat of claim 3, wherein the one or more ancillary circuits comprise one or more of the following:

a radio transceiver, a backlight, and a sensor.

5. The thermostat of claim 1, wherein the current limiting circuit comprises a Zener diode connected with a pair of transistors having connected collectors.

6. The thermostat of claim 1, wherein the current limiting circuit comprises a constant current diode or a constant current regulator.

7. The thermostat of claim 1, wherein the maximum level of instantaneous current is predetermined without regard to resistance of the load.

8. A power stealing circuit for obtaining power from a voltage source through a control system load that is in an “

off”

mode, the power stealing circuit comprising a current limiting circuit configured to provide a maximum level of instantaneous current predetermined not to cause the load to be switched to an “

on”

mode, the maximum level of instantaneous current corresponding to a maximum voltage threshold at which the load is not switched to the “

on”

mode.

9. The power stealing circuit of claim 8, wherein the maximum level of instantaneous current is predetermined without regard to resistance of the load.

10. A thermostat comprising the power stealing circuit of claim 8.

11. The power stealing circuit of claim 8, wherein the power stealing circuit is configured to provide power to a thermostat.

12. The power stealing circuit of claim 11, wherein the power stealing circuit is configured to provide power to one or more circuits ancillary to the thermostat.

13. The power stealing circuit of claim 12, wherein the one or more ancillary circuits comprise one or more of the following:

a radio transceiver, a backlight, and a sensor.

14. The power stealing circuit of claim 8, wherein the current limiting circuit comprises a Zener diode connected with a pair of transistors having connected collectors.

15. The power stealing circuit of claim 8, wherein the current limiting circuit comprises a constant current diode or a constant current regulator.

16. A method of providing power stealing in a climate control system to provide power through a load that is in an “

off”

mode to one or more ancillary circuits of the system, the method comprising;

determining a maximum value of instantaneous current for providing the power that would not cause the load to be switched to an “

on”

mode; and

using the maximum value to limit current through the load in the “

off”

mode.

17. The method of claim 16, further comprising inputting the current to one or more capacitors of the climate control system.

18. The method of claim 16, wherein the maximum value of instantaneous current is determined relative to a maximum voltage turn-on threshold.

19. The method of claim 16, wherein the one or more ancillary circuits include a thermostat.

20. The method of claim 16, further comprising determining the maximum level of instantaneous current without regard to resistance of the load.