LED DRIVER CIRCUIT WITH OPEN LOAD DETECTION

• US 20160095174A1
• Filed: 09/29/2014
• Published: 03/31/2016
• Est. Priority Date: 09/29/2014
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: VAUGHAN, Peter, PREGITZER, Ricardo L. J.
• Granted Patent: US 9,332,614 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3575 by means of dummy loads or bleeder circuits, e.g. for dimmers
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/50 responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
• CPC Class Codes: H05B 47/10 Controlling the light source

Abstract

Various examples directed to LED driver circuits capable of detecting the removal of an LED load are disclosed. In one example, the LED driver circuit may include a bleeder and load disconnect detection circuit having a bleeder circuit and a bleeder controller coupled to control the bleeder circuit. The bleeder controller may cause the bleeder circuit to draw a bleeder current that functions to supplement a load current drawn by an LED load to cause an input current of the LED driver circuit to be greater than a minimum holding current of a dimmer circuit. The bleeder controller may be further configured to detect a disconnect of the LED load based on the input current of the LED driver circuit, the bleeder control signal, and/or the bleeder current. In response to detecting a disconnect of the LED load, the bleeder controller may disable operation of the bleeder circuit.

Claims

1. A bleeder and load disconnect detection circuit for a light-emitting diode (LED) driver circuit, the bleeder and load disconnect detection circuit comprising:

a bleeder circuit;

an input current sense circuit coupled to receive an input current of the LED driver circuit and to output a low-pass filtered input current sense signal representative of the input current, wherein the input current sense circuit includes a signal conditioning circuit coupled to receive the input current, and output the low-pass filtered input current sense signal, and wherein the input current comprises a bleeder current conducted through the bleeder circuit and a load current conducted through a load of the LED driver circuit; and

a controller coupled to receive the low-pass filtered input current sense signal from the input current sense circuit and coupled to output a control signal to the bleeder circuit to control the bleeder current, wherein the controller is configured to;

cause, using the control signal, the bleeder circuit to conduct a variable amount of the bleeder current to cause a value of the input current to be greater than a minimum current, wherein the variable amount of the bleeder current is determined based on the low-pass filtered input current sense signal;

determine that the load has been disconnected from the LED driver circuit; and

in response to determining that the load has been disconnected from the LED driver circuit, causing, using the control signal, the bleeder circuit to prevent conduction of the bleeder current.

2. The bleeder and load disconnect detection circuit of claim 1, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether the control signal is an ON signal that causes the bleeder circuit to conduct a non-zero amount of bleeder current during a predetermined segment of time during each of one or more consecutive half line cycles of the input current; and

in response to determining that the control signal is the ON signal during the predetermined segment of time during each of the one or more consecutive half line cycles, determining that the load has been disconnected from the LED driver circuit.

3. The bleeder and load disconnect detection circuit of claim 1, further comprising a bleeder current sense circuit coupled to receive the bleeder current and coupled to output a bleeder current sense signal to the controller.

4. The bleeder and load disconnect detection circuit of claim 3, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether a value of the bleeder current decreases below a threshold value during each of one or more consecutive half line cycles of the input current based on the bleeder current sense signal; and

in response to determining that the bleeder current does not decrease below the threshold value during each of the one or more consecutive half line cycles of the input current, determining that the load has been disconnected from the LED driver circuit.

5. The bleeder and load disconnect detection circuit of claim 3, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether a value of the bleeder current is within a threshold deviation amount for each of one or more consecutive half line cycles of the input current based on the bleeder current sense signal; and

in response to determining that the value of the bleeder current is within the threshold deviation amount for each of the one or more consecutive half line cycles of the input current, determining that the load has been disconnected from the LED driver circuit.

6. The bleeder and load disconnect detection circuit of claim 1, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether a value of the control signal is within a threshold deviation amount for each of one or more consecutive half line cycles of the input current; and

in response to determining that the value of the control signal is within the threshold deviation amount for each of the one or more consecutive half line cycles of the input current, determining that the load has been disconnected from the LED driver circuit.

7. The bleeder and load disconnect detection circuit of claim 1, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether the value of the input current is within a threshold deviation amount for each of one or more consecutive half line cycles of the input current based on the low-pass filtered input current sense signal; and

in response to determining that the value of the input current is within the threshold deviation amount for each of the one or more consecutive half line cycles of the input current, determining that the load has been disconnected from the LED driver circuit.

8. The bleeder and load disconnect detection circuit of claim 1, wherein the bleeder and load disconnect detection circuit is coupled to receive a phase-controlled rectified input voltage from a dimmer circuit and a rectifier.

9. The bleeder and load disconnect detection circuit of claim 8, wherein the dimmer circuit comprises a phase-controlled trailing-edge dimmer circuit.

10. The bleeder and load disconnect detection circuit of claim 1, wherein the minimum current is a holding current of a phase-controlled leading-edge dimmer circuit.

11. A light-emitting diode (LED) driver circuit comprising:

an input to be coupled to receive an alternating current (ac) input voltage;

a dimmer circuit coupled to the input to receive the ac input voltage and output a phase-controlled ac input voltage;

a rectifier coupled to receive the phase-controlled ac input voltage and output a phase-controlled rectified input voltage;

a power converter coupled to receive the phase-controlled rectified input voltage and output a regulated output signal to a load; and

a bleeder and load disconnect detection circuit coupled between the rectifier and the power converter, the bleeder and load disconnect detection circuit comprising;

a bleeder circuit;

an input current sense circuit coupled to receive an input current of the LED driver circuit and to output a low-pass filtered input current sense signal representative of the input current, wherein the input current sense circuit includes a signal conditioning circuit, coupled to receive the input current, and output the low-pass filtered input current sense signal, and wherein the input current comprises a bleeder current conducted through the bleeder circuit and a load current conducted through the load of the LED driver circuit; and

a controller coupled to receive the low-pass filtered input current sense signal from the input current sense circuit and coupled to output a control signal to the bleeder circuit to control the bleeder current, wherein the controller is configured to;

cause, using the control signal, the bleeder circuit to conduct a variable amount of the bleeder current to cause a value of the input current to be greater than a minimum current, wherein the variable amount of the bleeder current is determined based on the low-pass filtered input current sense signal;

determine that the load has been disconnected from the LED driver circuit; and

in response to determining that the load has been disconnected from the LED driver circuit, causing, using the control signal, the bleeder circuit to prevent conduction of the bleeder current.

12. The LED driver circuit of claim 11, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether the control signal is an ON signal that causes the bleeder circuit to conduct a non-zero amount of bleeder current during a predetermined segment of time during each of one or more consecutive half line cycles of the input current; and

in response to determining that the control signal is the ON signal during the predetermined segment of time during each of the one or more consecutive half line cycles, determining that the load has been disconnected from the LED driver circuit.

13. The LED driver circuit of claim 11, further comprising a bleeder current sense circuit coupled to receive the bleeder current and coupled to output a bleeder current sense signal to the controller.

14. The LED driver circuit of claim 13, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether a value of the bleeder current decreases below a threshold value during each of one or more consecutive half line cycles of the input current based on the bleeder current sense signal; and

in response to determining that the bleeder current does not decrease below the threshold value during each of the one or more consecutive half line cycles of the input current, determining that the load has been disconnected from the LED driver circuit.

15. The LED driver circuit of claim 13, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether a value of the bleeder current is within a threshold deviation amount for each of one or more consecutive half line cycles of the input current based on the bleeder current sense signal; and

in response to determining that the value of the bleeder current is within the threshold deviation amount for each of the one or more consecutive half line cycles of the input current, determining that the load has been disconnected from the LED driver circuit.

16. The LED driver circuit of claim 11, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether a value of the control signal is within a threshold deviation amount for each of one or more consecutive half line cycles of the input current; and

in response to determining that the value of the control signal is within the threshold deviation amount for each of the one or more consecutive half line cycles of the input current, determining that the load has been disconnected from the LED driver circuit.

17. The LED driver circuit of claim 11, wherein determining that the load has been disconnected from the LED driver circuit comprises:

determining whether the value of the input current is within a threshold deviation amount for each of one or more consecutive half line cycles of the input current based on the low-pass filtered input current sense signal; and

in response to determining that the value of the input current is within the threshold deviation amount for each of the one or more consecutive half line cycles of the input current, determining that the load has been disconnected from the LED driver circuit.

18. The LED driver circuit of claim 11, wherein the dimmer circuit comprises a phase-controlled leading-edge dimmer circuit.

19. The LED driver circuit of claim 11, wherein the dimmer circuit comprises a phase-controlled trailing-edge dimmer circuit.

20. The LED driver circuit of claim 11, wherein the minimum current is the amount necessary to guarantee the correct operation of the dimmer circuit.

21. The LED driver circuit of claim 11, wherein the input current sense circuit comprises:

a sense resistor coupled to receive the input current; and

a signal conditioning circuit, wherein the signal conditioning circuit is coupled to receive a voltage across the sense resistor.