CURRENT ZERO CROSSING DETECTOR IN A DIMMER CIRCUIT

• US 20090167265A1
• Filed: 12/12/2006
• Published: 07/02/2009
• Est. Priority Date: 12/12/2005
• Status: Active Grant

• Current Assignee: Clipsal Australia Pty., Ltd. (Schneider Electric SE)
• Original Assignee: Clipsal Australia Pty., Ltd. (Schneider Electric SE)
• Inventors: Vanderzon, James Robert
• Granted Patent: US 8,729,875 B2
• Time in Patent Office: Days
• US Class Current: 323/271
• CPC Class Codes: H03K 17/133 in field-effect transistor switches
• CPC Class Codes: H03K 17/6874 in a symmetrical configuration
• CPC Class Codes: H03K 17/6877 the control circuit comprising active elements different from those used in the output circuit
• CPC Class Codes: H05B 39/02 Switching on, e.g. with predetermined rate of increase of lighting current

Abstract

A method and circuit for controlling the delivery of power having a current component to a load having an inductive component, the method comprising selectively switching power to the load with a switch, wherein the switch is caused to operate at the threshold of saturation during a conduction state such that the switch self commutates to its off state when the magnitude of the current through the load is substantially zero. The method and circuit may be used in a number of applications for detecting a current zero crossing and may be applied to circuits such as dimmer circuits.

Claims

1. A method of controlling the delivery of power having a current component to a load having an inductive component, the method including selectively switching power to the load with a switch, wherein the switch is caused to operate at the threshold of saturation during a conduction state such that the switch self commutates to its off state when the magnitude of the current through the load is substantially zero.

2. A method as claimed in claim 1 wherein the switch is a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor).

3. A method as claimed in claim 2 wherein the MOSFET is caused to operate at the threshold of saturation by controlling a biasing voltage applied to the switch.

4. A method as claimed in claim 3 wherein the biasing voltage is controlled by comparing a voltage across the MOSFET with a reference voltage and adjusting the biasing voltage to a level to cause the MOSFET to operate at the threshold of saturation when the voltage across the MOSFET falls below the reference voltage.

5. A method as claimed in claim 3 wherein the biasing voltage is adjusted to zero upon the MOSFET self-commutating to the non-conducting state.

6. A method as claimed in claim 4 wherein the value of the reference voltage is increased up to a maximum reference voltage exponentially.

7. A circuit for controlling the delivery of power having a current component to a load having an inductive component, the circuit comprising a switch and a switch control means for causing the switch to operate at the threshold of saturation during a conduction state such that the switch commutates to its off state when the magnitude of the load current is substantially zero.

8. A circuit as claimed in claim 7 wherein the switch is a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor).

9. A circuit as claimed in claim 8 wherein the switch control means is a comparator for comparing a voltage across the MOSFET with a reference voltage, to control a biasing voltage of the MOSFET.

10. A circuit as claimed in claim 9 wherein the comparator is a transistor having the voltage across the MOSFET applied to a first terminal of the transistor, and the reference voltage applied to a base terminal of the transistor.

11. A circuit as claimed in claim 10 wherein the transistor is an npn bipolar transistor and the voltage is applied to an emitter terminal of the npn bipolar transistor.

12. A circuit as claimed in claim 9 wherein the reference voltage is produced by a capacitor charging to a maximum value to provide an inverse exponential rise in the reference voltage up to the maximum value.

13. A dimmer circuit for controlling the delivery of power having a current component to a load having an inductive component, wherein the dimmer circuit comprises the circuit arrangement of the second aspect of the present invention.

14. A method of detecting a load current zero crossing, the method comprising causing a switch to operate at the threshold of saturation during a conduction state such that the switch will self-commutate to the off state when the load current reaches zero crossing.

15. A circuit for detecting a load current zero crossing, the circuit arrangement comprising:

a switch having an on state, an off state and a saturation state; and

a switch control means for causing the switch to operate at a threshold of its saturation state during the on state so as to self-commutate into the off-state when the load current reaches zero crossing.