LED driver circuit and method

• US 9,420,653 B2
• Filed: 11/19/2010
• Issued: 08/16/2016
• Est. Priority Date: 11/19/2010
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Van de Maele, Wim Piet, Rankovic, Zoran, Voorde, Luc Vander, Hall, Jefferson W.
• Primary Examiner(s): Taningco, Alexander H
• Assistant Examiner(s): Kim, Seokjin
• Application Number:
  US12/950,935
• Publication Number:
  US 20120126719A1
• Time in Patent Office: 2,097 Days
• Field of Search: 362/555, 315/291
• US Class Current: 1/1
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

An LED driver circuit and a method for driving the LED driver circuit. In accordance with an embodiment the LED driver circuit includes a voltage follower circuit and a calibration circuit coupled to the voltage follower circuit. First and second currents may be injected into the node and a current is sunk from the node. In accordance with another embodiment, the LED driver circuit asserts a non-zero voltage across the light emitting diode in a first phase of a drive cycle and asserts a fixed non-zero current in the light emitting diode in a second phase of the drive cycle.

Claims

1. A method for driving a light emitting diode with a driver circuit, comprising:

operating the driver circuit in a calibration phase in response to the light emitting diode emitting light at a first level, wherein operating the driver circuit in the calibration phase includes;

providing a comparator having first and second inputs and an output, the second input coupled to a first node and the output coupled to the first node;

providing a voltage follower circuit having first, second, and third terminals, the first terminal coupled for receiving an input signal from a first digital-to-analog converter circuit, the second terminal coupled to the first node, and the third terminal coupled to a second node;

providing a reference voltage at the first input of the comparator;

generating a first voltage at the second input of the comparator in response to a first current that flows from the first node and a second current that flows towards the first node, the second current having first and second components; and

changing a level of the second current in response to the first voltage being more than or less than the reference voltage at the first input of the comparator; and

operating the driver circuit in an active phase in response to the light emitting diode emitting light at a second level, the second level greater than the first level, wherein operating the driver circuit in the active phase includes;

generating a third current that flows through the light emitting diode towards the first node.

2. The method of claim 1, further including generating a control signal to change a level of the first component of the second current in response to comparing the voltage at the first node with the reference voltage, wherein the second current is greater than the first current in response to the voltage at the first node being greater than the reference voltage and the second current is less than the first current in response to the voltage at the first node being less than the reference voltage.

3. The method of claim 2, wherein changing the level of the second current in response to the first voltage being more than or less than the reference voltage includes changing the voltage at the first node to be closer to the reference voltage.

4. The method of claim 1, further including:

providing a second digital-to-analog converter, wherein the second digital-to-analog converter is an n-bit digital-to-analog converter; and

providing a controlled current source, the controlled current source having a control terminal and first and second current carrying terminals, the control terminal coupled to the n-bit digital-to-analog converter, the first current carrying terminal coupled for receiving a source of operating potential, and the second current carrying terminal coupled to the first node, wherein changing the level of the second current includes increasing the first component of the second current by an amount corresponding to a least significant bit of the n-bit digital-to-analog converter in response to the first voltage being less than the reference voltage or decreasing the first component of the second current by an amount corresponding to a least significant bit of the n-bit digital-to-analog converter in response to the first voltage being greater than the first reference voltage.

5. The method of claim 1, further including generating a fourth current in response to the driver circuit operating in the calibration phase, wherein the fourth current flows through the light emitting diode and has a level equal to a difference between the first current and the second current in response to the second current being less than the first current.

6. A method for driving a light emitting diode, comprising:

providing a voltage follower circuit having first, second, and third terminals;

coupling a first source of current to the second terminal;

coupling a light emitting diode to the second terminal;

providing a driver circuit comprising;

a comparator having first and second inputs and an output, the first input coupled to the first node and a reference voltage coupled to the second input;

a control circuit having an input and an n-bit output, the input coupled to the output of the comparator;

an n-bit digital-to-analog converter having an n-bit input and output, the n-bit input coupled to the n-bit output of the control circuit; and

wherein

the first source of current has a control terminal, a first current carrying terminal and a second current carrying terminal, the output of the n-bit digital-to-analog converter coupled to the control terminal of the first source of current, the first current carrying terminal coupled for receiving the first source of operating potential, and the second current carrying terminal coupled to the first node;

providing a first voltage at the first input of the comparator;

operating in a calibration phase in response to receiving a first signal at the first terminal, wherein operating in the calibration phase includes;

injecting a first current from the first source of current into a first node;

adjusting the first current from the first source of current in response to the first voltage being greater than or less than the reference voltage;

injecting a second current into the first node, wherein the second current flows through and causes the light emitting diode to emit light at a first emission level, and wherein the second current is at a first level that is a nonzero level and an intensity of the light is at a first emission level; and

sinking a third current from the first node, the third current flowing through the third terminal of the voltage follower circuit;

operating in an active phase in response to receiving a second signal at the first terminal, wherein operating in the active phase includes;

increasing the second current to a second nonzero current level that is higher than the first nonzero level, wherein the light emitting diode emits light at a second emission level that is higher than the first emission level.

7. The method of claim 6, wherein providing the driver circuit further includes:

providing an operational amplifier having first and second inputs and an output, wherein the first input of the operational amplifier is coupled to the first node and to the first input of the comparator and the second input of the operational amplifier is coupled to the second input of the comparator;

providing a second source of current, the second source of current having a control electrode and first and second current carrying electrodes, the control electrode of the second source of current coupled to the output of the operational amplifier and the second current carrying electrode coupled to the first node; and

adjusting a fourth current from the second source of current in response to the first voltage being greater than or less than the reference voltage.

8. A light emitting diode driver circuit, comprising:

a first amplifier having first and second inputs and an output;

a transistor having a control electrode and first and second current carrying electrodes, the control electrode directly coupled to the output of the first amplifier and the second current carrying electrode coupled to the first input of the first amplifier and to a third node, wherein the transistor provides a first current that flows at a first current level or a second current level through the first current carrying electrode in response to a signal at the second input of the first amplifier;

a first current source having first and second terminals, the first terminal coupled to the first current carrying electrode of the transistor and to a first node and the second terminal coupled to a second node, wherein the light emitting diode drive circuit is configured to always transmit a nonzero current through one or more diodes coupled between the first and second nodes;

a comparator having first and second inputs and an output, the first input coupled to the first node and a voltage source coupled between the second input of the comparator and the second node;

a control circuit having and input and an n-bit output, the input coupled to the output of the comparator;

an n-bit digital-to-analog converter having an n-bit input and an output, the n-bit input coupled to the n-bit output of the control circuit;

a second amplifier having first and second inputs and an output, the first input coupled to the first input of the comparator, the second input coupled to the second input of the comparator and to the voltage source, and the output coupled to the first node.

9. A light emitting diode driver circuit, comprising:

a voltage follower circuit having first and second current carrying terminals;

a first resistor having first and second terminals, the first terminal coupled to the first current carrying terminal of the voltage follower circuit to form a third node, the voltage follower and the first resistor configured to provide a first current capable of flowing at a first current level or a second current level through the voltage follower circuit; and

a calibration circuit having first and second terminals, the first terminal serving as a second node and the second terminal coupled to the second current carrying terminal of the voltage follower circuit to form a first node, the calibration circuit comprising a first current source, the first current source having a control terminal and first and second terminals that serve as the first and second terminals of the calibration circuit, the second terminal of the current source coupled to the first node, wherein the calibration circuit further includes comparator having first and second inputs and an output, the first input coupled to the first node and a voltage source coupled between the second input and the second node;

a control circuit having and input and an n-bit output, the input coupled to the output of the comparator;

an n-bit digital-to-analog converter having an n-bit input and output, the n-bit input coupled to the n-bit output of the control circuit, the output of the n-bit digital-to-analog converter coupled to the control terminal of the first current source;

a first amplifier having first and second inputs and an output, the first input coupled to the first input of the comparator, the second input coupled to the second input of the comparator, and the output coupled to the first node.

10. A light emitting diode driver circuit, comprising:

a voltage follower circuit having first and second current carrying terminals;

a first resistor having first and second terminals, the first terminal coupled to the first current carrying terminal of the voltage follower circuit to form a third node, the voltage follower and the first resistor configured to provide a first current capable of flowing at a first current level or a second current level through the voltage follower circuit; and

a calibration circuit having first and second terminals, the first terminal serving as a second node and the second terminal coupled to the second current carrying terminal of the voltage follower circuit to form a first node, the calibration circuit comprising a first current source, the first current source having a control terminal and first and second terminals that serve as the first and second terminals of the calibration circuit, the second terminal of the current source coupled to the first node, wherein the calibration circuit further comprises;

a second current source having a control terminal and first and second terminals, wherein the second current source is a controlled current source and wherein the control terminal of the second current source is coupled to the output of the first amplifier, the first terminal is coupled to the second node, and the second terminal is coupled to the first node;

a first operational amplifier having an inverting input, a noninverting input and an output, the output of the first operational amplifier coupled to the control terminal of the second current source;

a voltage source having first and second terminals, the first terminal coupled to the second node and the second terminal coupled to the noninverting input of the first operational amplifier;

a comparator having an inverting input, a noninverting input and an output, the noninverting input of the comparator coupled to the noninverting input of the first operational amplifier and to the second terminal of the voltage source; and

a control circuit having an input and output, the input of the control circuit coupled to the output of the comparator and the output of the control circuit coupled to the control terminal of the second current source.

11. The light emitting diode driver circuit of claim 10, further including a current digital-to-analog converter coupled between the control circuit and the control terminal of the second current source.

12. A light emitting diode driver circuit, comprising:

a voltage follower circuit having first and second current carrying terminals;

a first resistor having first and second terminals, the first terminal coupled to the first current carrying terminal of the voltage follower circuit to form a third node, the voltage follower and the first resistor configured to provide a first current capable of flowing at a first current level or a second current level through the voltage follower circuit; and

a calibration circuit having first and second terminals, the first terminal serving as a second node and the second terminal coupled to the second current carrying terminal of the voltage follower circuit to form a first node, the calibration circuit comprising a first current source, the first current source having a control terminal and first and second terminals that serve as the first and second terminals of the calibration circuit, the second terminal of the current source coupled to the first node, wherein the calibration circuit comprises;

a voltage source having first and second terminals, the first terminal coupled to the second node;

an operational transconductance amplifier having an inverting input, a noninverting input and an output, the output of the operational transconductance amplifier coupled to the first node;

a comparator having an inverting input, a noninverting input and an output, the noninverting input of the comparator coupled to the noninverting input of the operational transconductance amplifier and to the voltage source and the inverting input of the comparator coupled to the inverting input of the operational transconductance amplifier and to the first node; and

a control circuit having an input and output, the input coupled to the output of the comparator and the input coupled to the control terminal of the first current source.

13. The light emitting diode driver circuit of claim 12, further including a current digital-to-analog converter coupled between the control circuit and the control terminal of the first current source and a second current source having a control terminal coupled to the output of the operational transconductance amplifier, a first terminal coupled to the second node, and a second terminal coupled to the first node.