INRUSH CURRENT LIMITER FOR AN LED DRIVER

• US 20110025217A1
• Filed: 06/24/2010
• Published: 02/03/2011
• Est. Priority Date: 08/03/2009
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Yu, Xiangxu, Zhan, Xiaodong, Greenfeld, Fred F.
• Granted Patent: US 8,339,055 B2
• Time in Patent Office: Days
• US Class Current: 315/219
• CPC Class Codes: H02H 9/001 limiting speed of change of electric quantities, e.g. soft switching on or off progressive control of electronic switches for eliminating interferences H03K17/16
• CPC Class Codes: H02M 3/335 using semiconductor devices only
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/50 responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits

Abstract

An inrush current limiter for use with an LED driver including a current limiting device, a bypass switch device, and a switch drive. The current limiting device is placed in the input current path of the LED driver to limit input current to a predetermined maximum level in response to an AC conductive angle modulated voltage. The bypass switch device is coupled in parallel with the current limit device. The switch drive turns on the bypass switch device to at least partially bypass the current limiting device as a voltage level of an input of a switching converter rises. The input current remains sufficiently high without exceeding the maximum level. The switch drive is implemented with a delay network driven either by a separate transformer winding or by a snubber network. The delay network may have a delay based on the delay caused by the current limiting device.

Claims

1. An inrush current limiter for use with an LED driver, wherein the LED driver includes an input current path comprising a full wave rectifier, a low pass filter, and a switching converter in which the LED driver converts an AC conductive angle modulated voltage to a DC output voltage, said inrush current limiter comprising:

a current limiting device for coupling in the input current path of the LED driver, wherein said current limiting device limits input current to a predetermined maximum current level in response to the AC conductive angle modulated voltage;

a switch device having a current path coupled in parallel with said current limiting device and having a control terminal; and

a switch drive coupled to said control terminal of said switch device and for coupling to the switching converter, wherein said switch drive turns on said switch device to at least partially bypass said current limiting device as a voltage level of an input of the switching converter rises in response to the AC conductive angle modulated voltage.

2. The inrush current limiter of claim 1, wherein the AC conductive angle modulated voltage has a peak voltage level, and wherein said current limiting device comprises a resistor having a resistance which is determined by said peak voltage level and said predetermined maximum current level.

3. The inrush current limiter of claim 1, wherein the low pass filter includes a capacitance, wherein said current limiting device comprises a resistance which forms a time constant with said capacitance of said filter, and wherein said switch drive includes a delay based on said time constant.

4. The inrush current limiter of claim 1, wherein the switching converter comprises a transformer having a first primary winding coupled to the input current path, and wherein said switch drive comprises:

a second primary winding provided on the transformer; and

a delay network coupled to said second primary winding and to said control terminal of said switch device.

5. The inrush current limiter of claim 4, wherein said current limit device delays voltage increase across the first primary winding of the transformer based on a time constant, and wherein said delay network delays activation of said switch device by a time period based on said time constant.

6. The inrush current limiter of claim 4, wherein said delay network comprises a resistor-capacitor circuit.

7. The inrush current limiter of claim 1, wherein the switching converter comprises a transformer with a primary winding, and wherein said switch drive comprises:

a snubber network for coupling across the primary winding of the transformer; and

a delay network having an input coupled to said snubber network and having an output coupled to said control terminal of said switch device.

8. The inrush current limiter of claim 7, wherein said snubber network comprises a resistor-capacitor circuit, and wherein said delay network comprises a resistive voltage divider.

9. The inrush current limiter of claim 7, wherein the snubber network comprises a resistor-capacitor and rectifier circuit, and wherein said delay network comprises a resistor-capacitor circuit.

10. A light emitting diode driver, comprising:

an input network which converts an AC conductive angle modulated voltage to a rectified voltage, said input network including an input current path;

a switching converter, comprising;

a transformer having a first primary winding coupled to said input network and having a secondary winding;

a switching device coupled to said first primary winding of said transformer for switching current through said first primary winding; and

an output network coupled to said secondary winding for developing a DC output voltage;

a current limiting device coupled in said input current path of said input network for limiting input current to a predetermined maximum current level in response to said AC conductive angle modulated voltage;

a bypass device having a current path coupled in parallel with said current limiting device, and having a control terminal; and

a bypass control network having an input coupled to said switching converter and an output coupled to said control terminal of said bypass device, wherein said bypass control network turns on said bypass device to at least partially bypass said current limiting device as a voltage level of said primary winding of said transformer increases in response to the AC conductive angle modulated voltage.

11. The light emitting diode driver of claim 10, wherein said bypass control network comprises:

a second primary winding provided on said transformer; and

a delay network having an input coupled to said second primary winding and having an output coupled to said control terminal of said bypass device.

12. The light emitting diode driver of claim 11, wherein said current limiting device delays voltage increase of said first primary winding based on a time constant, and wherein said delay network delays activation of said bypass device by a time period based on said time constant.

13. The light emitting diode driver of claim 10, wherein:

said bypass device comprises a transistor having a control terminal, having a first current terminal and having a second current terminal;

wherein said bypass control network comprises;

a second primary winding provided on said transformer having a first end coupled to said first current terminal of said transistor and having a second end;

a diode having an anode coupled to said second end of said second primary winding and having a cathode;

a first resistor having a first end coupled to said cathode of said diode and having a second end coupled to said control terminal of said transistor;

a second resistor coupled between said control terminal of said transistor and said second current terminal of said transistor; and

a capacitor coupled between said control terminal of said transistor and said second current terminal of said transistor.

14. The light emitting diode driver of claim 10, wherein:

said input network comprises an electromagnetic interference filter including a capacitance;

wherein said current limiting device comprises a resistance which forms a time constant with said capacitance of said electromagnetic interference filter to delay voltage increase across said first primary winding of said transformer; and

wherein said bypass control network comprises a delay network which activates said bypass device after a delay based on said time constant.

15. The light emitting diode driver of claim 10, wherein said bypass control network comprises:

a snubber network coupled across said first primary winding of said transformer; and

a delay network having an input coupled to said snubber network and an output coupled to said control terminal of said bypass device.

16. The light emitting diode driver of claim 15, wherein:

said snubber network comprises;

a diode having an anode coupled to a first end of said first primary winding of said transformer and having a cathode;

a capacitor having a first end coupled to said cathode of said diode and having a second end coupled to a second end of said first primary winding of said transformer; and

a first resistor having a first end coupled to said cathode of said diode and having a second end; and

wherein said delay network comprises;

a second resistor having a first end coupled to said second end of said first resistor and having a second end coupled to said second end of said first primary winding of said transformer; and

a third resistor having a first end coupled to said first end of said second resistor and having a second end coupled to said control terminal of said bypass device.

17. The light emitting diode driver of claim 15, wherein:

said snubber network comprises;

a diode having an anode coupled to a first end of said first primary winding of said transformer and having a cathode;

a first capacitor having a first end coupled to said cathode of said diode and having a second end coupled to a second end of said first primary winding of said transformer; and

a first resistor having one end coupled to said cathode of said diode and having a second end coupled to said second end of said first primary winding of said transformer; and

wherein said delay network comprises;

a second resistor having a first end coupled to said first end of said first capacitor and having a second end coupled to said control terminal of said bypass device;

a third resistor having a first end coupled to said second end of said second resistor and having a second end coupled to a current terminal of said bypass device;

a second capacitor having a first end coupled to said second end of said second resistor and having a second end coupled to said current terminal of said bypass device; and

a fourth resistor having a first end coupled to said control terminal of said bypass device and having a second end coupled to said current terminal of said bypass device.

18. The light emitting diode driver of claim 10, wherein:

said input network comprises;

a full wave rectifier having an input receiving said AC conductive angle modulated voltage and an output providing a rectified voltage on a rectified node relative to a reference node;

an electromagnetic interference filter, comprising;

a first capacitor coupled between said rectified node and said reference node;

a first resistor having a first end coupled to said rectified node and having a second end;

a second resistor having a first end coupled to said reference node and having a second end;

a second capacitor coupled between said second end of said first resistor and said second end of said second resistor;

a common mode inductor having a first winding with a first end coupled to said second end of said first resistor and a second end, and having a second winding with a first end coupled to said second end of said second resistor and a second end coupled to ground; and

a third capacitor having a first end coupled to ground and having a second end coupled to a first end of said primary winding of said transformer; and

wherein said bypass device comprises a resistor coupled between said second end of said first winding of said common mode inductor and said second end of said third capacitor.

19. A light emitting diode control system, comprising:

a dimmer having an input receiving an AC line voltage and an output providing an AC conductive angle modulated voltage; and

a light emitting diode driver, comprising;

an input network which converts said AC conductive angle modulated voltage to a rectified voltage, said input network including an input current path;

a switching converter, comprising;

a transformer having a primary winding coupled to said input network and having a secondary winding;

a switching device coupled to said first primary winding of said transformer for switching current through said first primary winding; and

an output network coupled to said secondary winding for developing a DC output voltage;

a current limiting device coupled in said input current path of said input network for limiting input current to a predetermined maximum current level in response to said AC conductive angle modulated voltage;

a bypass device having a current path coupled in parallel with said current limiting device, and having a control terminal; and

a bypass control network having an input coupled to said switching converter and an output coupled to said control terminal of said bypass device, wherein said bypass control network turns on said bypass device to at least partially bypass said current limiting device as a voltage level of said primary winding of said transformer increases in response to said AC conductive angle modulated voltage.

20. The light emitting diode control system of claim 19, wherein said input current path and said current limiting device delays voltage increase across said primary winding of said transformer in response to said AC conductive angle modulated voltage by a time period, and wherein said bypass control network delays activation of said bypass device based on said time period to limit input current to said predetermined maximum current level.

21. A method for limiting inrush current of an LED driver, wherein the LED driver includes an input current path comprising a full wave rectifier, a low pass filter, and a switching converter in which the LED driver converts an AC conductive angle modulated voltage to a DC output voltage, said method comprising:

limiting the inrush current to a predetermined maximum current level using a current limiting device placed in the input current path of the LED driver; and

bypassing the current limiting device for each half cycle of the AC conductive angle modulated voltage so that input current does not exceed the predetermined maximum current level.