LED DRIVER CIRCUIT AND LED DRIVING METHOD

• US 20180014369A1
• Filed: 06/19/2017
• Published: 01/11/2018
• Est. Priority Date: 07/07/2016
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Korea Semiconductor Limited (ON Semiconductor Corporation)
• Inventors: KIM, Young-Jong, EUM, Hyun-Chul
• Granted Patent: US 10,362,643 B2
• Time in Patent Office: Days
• 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 45/395 Linear regulators
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: H05B 45/50 responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
• CPC Class Codes: H05B 45/59 for reducing or suppressing flicker or glow effects
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A light emitting diode (LED) driver circuit includes an LED string and a conducting state detection circuit. The conducting state detection circuit detects a conducting state of the LED string, and generates a discharge control signal upon sensing that the LED string is in a non-conducting state. A current source generates a discharge current according to the discharge control signal when the LED string is in the non-conducting state. A passive bleeder provides current compensation by internal regulator operation. An LED spike current suppression circuit suppresses spike current that can occur when the input voltage increases above a threshold. A bias supply circuit has an input capacitor that provides a bias voltage.

Claims

1. A light emitting diode (LED) driver circuit, comprising:

a dimmer connected to an AC input;

a rectifier circuit that is configured to receive the AC input from the dimmer, and to rectify the AC input to generate an input voltage;

an LED string having a first end that is connected to the input voltage, the LED string comprising at least one LED element;

an LED conducting state detection circuit configured to detect a conducting state of the LED string, and to generate a discharge control signal in response to sensing the LED string in a non-conducting state wherein an LED current does not flow to the LED string; and

a current source that is connected to the first end of the LED string, the current source being configured to generate a discharge current according to the discharge control signal when the LED string is in the non-conducting state.

2. The LED driver circuit of claim 1, wherein the current source generates the discharge current having a level according to the discharge control signal after a delay period from a time point of sensing the non-conducting state of the LED string.

3. The LED driver circuit of claim 1, wherein the LED conducting state detection circuit is configured to detect the conducting state of the LED string from a first end of the at least one LED element.

4. The LED driver circuit of claim 3, wherein the first end of the at least one LED element is a cathode of the at least one LED element.

5. The LED driver circuit of claim 3, wherein the first end of the at least one LED element is an anode of the at least one LED element.

6. The LED driver circuit of claim 1, wherein the LED conducting state detection circuit is configured to detect the conducting state of the LED string from a sense voltage developed on a sense resistor by the LED current.

7. The LED driver circuit of claim 1, wherein the LED conducting state detection circuit is configured to detect the conducting state of the LED string from an output of an amplifier that is configured to regulate the LED current.

8. The LED driver circuit of claim 1, wherein the LED conducting state detection circuit comprises:

a first transistor connected between a first node and a ground and operates according to a voltage at a first end of the at least one LED element; and

a charging circuit connected to the first node,

wherein the discharge control signal follows a voltage of the first node.

9. A light emitting diode (LED) driver circuit, comprising:

an LED string having a first end that is connected to an input voltage, the LED string comprising at least one LED element;

at least one channel connected to the at least one LED element;

a sense resistor having a first end that is connected to the at least one channel and a second end that is connected to ground;

at least one regulator connected between the at least one channel and the first end of the sense resistor and configured to control current flowing through the at least one channel based on a control voltage; and

a passive bleeder connected between the input voltage and the first end of the sense resistor.

10. The LED driver circuit of claim 9, wherein the at least one regulator comprises:

a transistor connected between the at least one channel and the first end of the sense resistor; and

an amplifier comprising a first input connected to the control voltage, a second input connected to the first end of the sense resistor, and an output connected to a gate of the transistor.

11. The LED driver circuit of claim 9, wherein the passive bleeder comprises a resistor and a capacitor connected in series between the input voltage and the first end of the sense resistor.

12. A light emitting diode (LED) driver circuit, comprising:

an LED string having a first end that is connected to an input voltage, the LED string comprising at least one LED element;

at least one channel connected to the at least one LED element;

a sense resistor having a first end that is connected to the at least one channel;

at least one regulator connected between the at least one channel and the first end of the sense resistor and configured to control current flowing through the at least one channel based on a control voltage; and

a spike current suppression circuit that is configured to pull down an output of an amplifier of the at least one regulator when the input voltage is below a threshold voltage.

13. The LED driver circuit of claim 12, wherein the at least one regulator comprises:

a transistor connected between the at least one channel and the first end of the sense resistor; and

the amplifier comprising a first input connected to the control voltage, a second input connected to the first end of the sense resistor, and the output connected to a gate of the transistor.

14. The LED driver circuit of claim 13, wherein the spike current suppression circuit comprises:

another transistor having a drain connected to the output of the amplifier, a source that is connected to ground, and a gate that is connected to receive an input threshold voltage that is indicative of a level of the input voltage.

15. A light emitting diode (LED) driver circuit, comprising:

an LED string having a first end that is connected to an input voltage, the LED string comprising at least one LED element;

at least one channel connected to the at least one LED element;

an LED current controller that is configured to regulate current through the at least one channel; and

a bias supply circuit that is configured to provide a bias voltage to the LED current controller, the bias supply circuit comprising a capacitor, a first diode, and a second diode,

wherein a first end of the capacitor is connected to the input voltage, a second end of the capacitor is connected to an anode of the first diode, a cathode of the second diode is connected to the second end of the capacitor, and a cathode of the first diode provides the bias voltage.

16. The LED driver circuit of claim 15, wherein the anode of the second diode is connected to ground.

17. The LED driver circuit of claim 15, wherein the second diode is a Zener diode.

18. The LED driver circuit of claim 15, further comprising a resistor that is in series with the capacitor.

19. The LED driver circuit of claim 15, further comprising a dimmer that is configured to modulate the input voltage.

20. The LED driver circuit of claim 15, wherein the LED current controller comprises at least one regulator, the at least one regulator comprising:

a transistor connected between the at least one channel and a sense resistor; and

an amplifier comprising a first input connected to a control voltage, a second input connected to the sense resistor, and an output connected to a gate of the transistor.