Actuator power control circuit having fail-safe bypass switching

• US 8,760,103 B2
• Filed: 09/30/2011
• Issued: 06/24/2014
• Est. Priority Date: 09/30/2011
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Bokusky, Mark David, Sibilski, Robert, Jasiczek, Liliana
• Primary Examiner(s): Masih, Karen
• Application Number:
  US13/250,889
• Publication Number:
  US 20130082634A1
• Time in Patent Office: 998 Days
• Field of Search: 318/563, 318/810, 318/400.09, 318/494, 361/49, 363/21.15
• US Class Current: 318/563
• CPC Class Codes: G05B 9/02 electric

Abstract

A system for controlling power to actuators. For example, a controller may output a signal having a variable duty cycle waveform for controlling current to an actuator via an interface circuit between the controller and the actuator. Changing the duty cycle may change the amount of current to the actuator. The controller may provide a control signal that optimizes power consumption by the actuator for efficiency purposes. However, if the controller fails, then no control signal may be available to allow current to the actuator, particularly in situations where the actuator may need to be operationally tested. To avoid such situations, fail-safe bypass switching may be incorporated into the interface circuit. Upon absence of a control signal from the controller, the circuit may provide a default signal in lieu of the control signal to maintain current to the actuator.

Claims

1. A power control system comprising:

a switching circuit; and

a digital controller connected to the switching circuit; and

wherein;

the switching circuit controls an amount of current from a power supply to an actuator according to a control signal from the controller;

if the controller fails to provide the control signal to the switching circuit then the switching circuit controls the amount of current from the power supply to the actuator according to a default control signal; and

the actuator is a component of a heating, ventilating and air conditioning system.

2. The power control system of claim 1, wherein:

the control signal comprises a digital waveform having an adjustable duty cycle;

increasing the duty cycle increases the amount of current from the power supply to the actuator; and

decreasing the duty cycle decreases the amount of current from the power supply to the actuator.

3. The power control system of claim 1, wherein:

the switching circuit comprises;

a first terminal connected to an output terminal of the controller;

a second terminal connected to a first connector for the power supply; and

a third terminal connected to a first connection of the actuator; and

a fourth terminal connected to a second connector for the power supply; and

the actuator comprises a second connection connected to the second connector for the power supply.

4. The power control system of claim 3, wherein the switching circuit further comprises:

a transistor having a first terminal connected to the first terminal of the switching circuit, a second terminal connected to the third terminal of the switching circuit, and a third terminal connected to the second terminal of the switching circuit; and

an impedance element having a first end connected to the second connector for the power supply and a second end connected to the first terminal of the transistor.

5. The power control system of claim 4, wherein:

the transistor is an NPN transistor;

the first terminal of the transistor is a base;

the second terminal of the transistor is a collector; and

the third terminal of the transistor is an emitter.

6. The power control system of claim 4, wherein:

the transistor is an N-channel FET;

the first terminal of the transistor is a gate;

the second terminal of the transistor is a drain; and

the third terminal of the transistor is a source.

7. The power control system of claim 2, wherein:

the digital waveform comprises a first level and a second level and switches from one level to the other level; and

the duty cycle of the digital waveform is a period of time at the first level divided by a period of time of one cycle of the waveform.

8. The power control system of claim 7, wherein the default signal is provided by an impedance element connected to a polarity of the power supply or an output of a signal generator.

9. The power control system of claim 8, wherein the default signal is sufficient to at least momentary in a continuous fashion turn on the transistor if the controller fails to provide the control signal to the switching circuit.

10. The power control system of claim 9, wherein the control signal overrides the default signal.

11. The power control system of claim 1, wherein:

the switching circuit comprises;

a first terminal connected to an output terminal of the controller;

a second terminal connected to a first connector for the power supply; and

a third terminal connected to a first connection of the actuator;

a fourth terminal connected to a second connector for the power supply;

a first FET having a gate connected to the first terminal, a source connected to the second terminal and having a drain;

a second FET having a gate, having a source connected to the second terminal and a drain connected to the first connection of the actuator;

a first impedance element having a first end connected to the gate of the first FET and a second end connected to the second terminal;

a second impedance element having a first end connected to the drain of the first FET and having a second end connected to the gate of the second FET;

a third impedance element having a first end connected to the gate of the second FET and a second end connected to the fourth terminal; and

the first and second FETs are P-channel FETs; and

the actuator comprises a second connection connected to the second connector for the power supply.

12. A method for control of power to an actuator, comprising:

varying an amount of electrical power to an actuator; and

switching the electrical power on and off from an electrical power source to the actuator to provide the varying an amount of power to the actuator; and

wherein;

the switching the electrical power is according to a control signal;

a controller outputs the control signal; and

if the controller outputs no control signal, then a default signal is provided in lieu of the control signal.

13. The method of claim 12, wherein:

the control signal has a first state and a second state;

the first state switches on the electrical power to the actuator and the second state turns off the electrical power to the actuator;

durations of the first state and the second state comprise a cycle of the control signal;

the control signal has a plurality of cycles over a duration of time;

the control signal has a duty cycle which is a duration of a first state divided by a duration of the cycle; and

the duty cycle of the control signal is varied by the controller to vary the amount of electrical power to an actuator to satisfy certain power requirements for the actuator.

14. The method of claim 13, wherein if the control signal fails to appear from the controller as a source resulting in a control signal failure, then the control signal failure causes the default signal to appear from another source in lieu of the control signal.

15. The method of claim 14, wherein the default signal comes from a voltage source and has a first state.

16. The method of claim 14, wherein the default signal comes from a signal generator that provides the default signal having a first state, a second state and a duty cycle.

17. The method of claim 12, wherein the actuator is a component of a heating, ventilating and air conditioning system.

18. A power control circuit for an actuator comprising:

an actuator;

a fail-safe bypass switching circuit connected to the actuator;

a power supply connected to the fail safe bypass switching circuit; and

a controller connected to the fail-safe bypass switching circuit; and

wherein;

the actuator comprises a motor winding;

the power supply provides a power signal to the a fail-safe bypass switching circuit;

the controller provides a control signal to the fail-safe bypass switching circuit;

the fail-safe bypass switching circuit outputs the power signal having a waveform resembling a waveform of the control signal; and

if the controller fails to provide a control signal, then the fail-safe bypass switching circuit provides a second control signal in lieu of the control signal from the controller.

19. The circuit of claim 18, wherein:

the control signal comprises a multi-level waveform having a variable duty cycle to control power to the actuator;

the second control signal is selected from a group of connections consisting of a connection to a polarity of the power supply and a connection to a signal generator; and

the actuator is a component of a heating, ventilating and air conditioning system.