Electronic Circuits for Driving Series Connected Light Emitting Diode Strings

• US 20090128045A1
• Filed: 11/10/2008
• Published: 05/21/2009
• Est. Priority Date: 11/16/2007
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: AlNahas, Bassem, Szczeszynski, Gregory, Mangtani, Vijay
• Granted Patent: US 8,169,161 B2
• Time in Patent Office: Days
• US Class Current: 315/185.R
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: H05B 45/347 Dynamic headroom control [DHC]
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

Electronic circuits provide an error signal to control a regulated output voltage signal generated by a controllable DC-DC converter for driving one or more series connected strings of light emitting diodes.

Claims

1. An electronic circuit for driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the electronic circuit comprising:

a plurality of current regulators, each having a respective input node and a respective output node, the input node or the output node coupled to an end of a respective one of the plurality of series connected light emitting diode strings, wherein each current regulator is configured to pass a respective predetermined current through the respective one of the plurality of series connected light emitting diode strings to which it is coupled; and

a multi-input error amplifier having a plurality of input nodes and an output node, wherein each one of the plurality of input nodes is coupled to the input node or the output node of a respective one of the plurality of current regulators, and wherein the multi-input error amplifier is configured to generate an error signal at the output node of the error amplifier.

2. The electronic circuit of claim 1, wherein the error signal is indicative of an arithmetic mean of signals appearing at the input nodes or the output nodes of the plurality of current regulators.

3. The electronic circuit of claim 1, wherein the controllable DC-DC converter is coupled to receive the error signal, wherein the controllable DC-DC converter comprises an input node configured to receive a voltage and an output node at which regulated output voltage is generated by the controllable DC-DC converter, wherein the error signal is configured to control the regulated output voltage.

4. The electronic circuit of claim 3, wherein the controllable DC-DC converter comprises a switching regulator.

5. The electronic circuit of claim 4, wherein the error signal is indicative of an arithmetic mean of signals appearing at the input nodes or the output nodes of the plurality of current regulators.

6. An electronic circuit for driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the electronic circuit comprising:

a plurality of current regulators, each having a respective input node and a respective output node, the input node or the output node coupled to an end of a respective one of the plurality of series connected light emitting diode strings, wherein each current regulator is configured to pass a respective predetermined current through the respective one of the plurality of series connected light emitting diode strings to which it is coupled; and

a plurality of error amplifiers, each having a respective input node and a respective output node, wherein each one of the plurality of input nodes of the plurality of error amplifiers is coupled to the input node or the output node of a respective one of the plurality of current regulators, wherein the output nodes of the plurality of error amplifiers are coupled to a junction node, wherein the plurality of error amplifiers is configured to generate an error signal at the junction node.

7. The electronic circuit of claim 6, wherein each one of the plurality of error amplifiers is configured to be able to sink a different amount of current than it is able to source.

8. The electronic circuit of claim 6, wherein the controllable DC-DC converter is coupled to receive the error signal, wherein the controllable DC-DC converter comprises an input node configured to receive a voltage and an output node at which regulated output voltage is generated by the controllable DC-DC converter, wherein the error signal is configured to control the regulated output voltage.

9. The electronic circuit of claim 8, wherein the controllable DC-DC converter comprises a switching regulator.

10. The electronic circuit of claim 9, wherein each one of the plurality of error amplifiers is configured to be able to sink a different amount of current than it is able to source.

11. An electronic circuit for driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the electronic circuit comprising:

a plurality of current regulators, each having a respective input node and a respective output node, the input node or the output node coupled to an end of a respective one of the plurality of series connected light emitting diode strings, wherein each current regulator is configured to pass a respective predetermined current through the respective one of the plurality of series connected light emitting diode strings to which it is coupled;

a plurality of switches, each having a respective input node, a respective output node, and a respective control node, wherein each one of the input nodes of the plurality of switches is coupled to the input node or the output node of a respective one of the plurality of current regulators, wherein the output nodes of the plurality of switches are coupled together resulting in a composite signal;

a digital channel select circuit coupled to the control nodes of the plurality of switches and configured to close each one of the plurality of switches sequentially and periodically; and

an error amplifier having an input node and an output node, wherein the input node of the error amplifier is coupled to receive the composite signal, wherein the error amplifier is configured to generate an error signal at the output node of the error amplifier.

12. The electronic circuit of claim 11, wherein the error amplifier is configured to be able to sink a different amount of current than it is able to source.

13. The electronic circuit of claim 11, wherein the controllable DC-DC converter is coupled to receive the error signal, wherein the controllable DC-DC converter comprises an input node configured to receive a voltage and an output node at which regulated output voltage is generated by the controllable DC-DC converter, wherein the error signal is configured to control the regulated output voltage.

14. The electronic circuit of claim 13, wherein the controllable DC-DC converter comprises a switching regulator.

15. The electronic circuit of claim 14, wherein the error amplifier is configured to be able to sink a different amount of current than it is able to source.

16. An electronic circuit for driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the electronic circuit comprising:

a plurality of field effect transistors (FETs), each FET having a respective drain, source, and gate, wherein each FET is configured to pass a predetermined current from the respective drain to the respective source;

a plurality of resistors, each having respective first and second ends, each resistor coupled at the first end to a respective source of one of the plurality of FETs forming a respective current sense node, wherein the drain of each FET or the second end of each resistor is coupled to an end of a respective one of the plurality of series connected light emitting diode strings;

a plurality of amplifiers, each amplifier having a respective input node coupled to a respective current sense node, and each amplifier having a respective output node coupled to a respective gate of a respective FET, wherein each one of the plurality of amplifiers is configured to generate a respective control voltage signal at the respective output node indicative of a control of the respective FET for the respective FET to pass the predetermined current from the respective drain to the respective source;

a maximum select circuit having a plurality of input nodes coupled to receive the control voltage signals from the plurality of amplifiers and having an output node, wherein the maximum select circuit is configured to select a largest one of the control voltage signals and to generate a signal representative of the largest one of the control voltage signals at the output node; and

an error amplifier having an input node and an output node, wherein the input node of the error amplifier is coupled to the output node of the maximum select circuit, wherein the error amplifier is configured to generate an error signal at the output node of the error amplifier.

17. The electronic circuit of claim 16, wherein the controllable DC-DC converter is coupled to receive the error signal, wherein the controllable DC-DC converter comprises an input node configured to receive a voltage and an output node at which regulated output voltage is generated by the controllable DC-DC converter, wherein the error signal is configured to control the regulated output voltage.

18. The electronic circuit of claim 17, wherein the controllable DC-DC converter comprises a switching regulator.

19. An electronic circuit for driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the electronic circuit comprising:

a plurality of current regulators, each having a respective input node and a respective output node, the input node or the output node coupled to an end of a respective one of the plurality of series connected light emitting diode strings, wherein each current regulator is configured to pass a respective predetermined current through the respective one of the plurality of series connected light emitting diode strings to which it is coupled;

a plurality of switches, each having a respective input node, a respective output node, and a respective control node, wherein each one of the input nodes of the plurality of switches is coupled to the input node or the output node of a respective one of the plurality of current regulators, wherein the output nodes of the plurality of switches are coupled together resulting in a composite signal;

a comparator coupled to receive the composite signal and configured to generate a comparison signal;

a digital channel select circuit coupled to receive the comparison signal and coupled to the control nodes of the plurality of switches and configured to close each one of the plurality of switches sequentially for a time period responsive to the comparison signal; and

an error amplifier having an input node and an output node, wherein the input node of the error amplifier is coupled to receive the composite signal, wherein the error amplifier is configured to generate an error signal at the output node of the error amplifier.

20. The electronic circuit of claim 19, wherein the error amplifier is configured to be able to sink a different amount of current than it is able to source.

21. The electronic circuit of claim 19, wherein the controllable DC-DC converter is coupled to receive the error signal, wherein the controllable DC-DC converter comprises an input node configured to receive a voltage and an output node at which regulated output voltage is generated by the controllable DC-DC converter, wherein the error signal is configured to control the regulated output voltage.

22. The electronic circuit of claim 21, wherein the controllable DC-DC converter comprises a switching regulator.

23. The electronic circuit of claim 22, wherein the error amplifier is configured to be able to sink a different amount of current than it is able to source.

24. A method of driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the method comprising:

attempting to pass a respective predetermined current through each one of the plurality of series connected light emitting diode strings, resulting in a respective voltage appearing at an end of each one of the plurality of series connected light emitting diode strings; and

summing each one of the voltages to generate an error signal to control the DC-DC converter.

25. A method of driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the method comprising:

attempting to pass a respective predetermined current through each one of the plurality of series connected light emitting diode strings, resulting in a respective voltage appearing at an end of each one of the plurality of series connected light emitting diode strings;

generating respective intermediate signals representative each one of the voltages; and

summing the intermediate signals to generate an error signal to control the DC-DC converter.

26. A method of driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the method comprising:

attempting to pass a respective predetermined current through each one of the plurality of series connected light emitting diode strings, resulting in a respective voltage appearing at an end of each one of the plurality of series connected light emitting diode strings;

sampling each one of the voltages sequentially and periodically to generate voltage samples; and

summing the voltage samples to generate an error signal to control the DC-DC converter.

27. A method of driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the method comprising:

attempting to pass a respective predetermined current through each one of the plurality of series connected light emitting diode strings with a respective feedback current control circuit, resulting in a respective voltage appearing at an end of each one of the plurality of series connected light emitting diode strings, wherein a control node of the feedback circuit generates a control voltage that changes in a direction opposite to a change of the respective voltage;

detecting a largest one of the control voltages; and

generating an error signal representative of the largest one of the control voltages to control the DC-DC converter.

28. A method of driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the method comprising:

attempting to pass a respective predetermined current through each one of the plurality of series connected light emitting diode strings, resulting in a respective voltage appearing at an end of each one of the plurality of series connected light emitting diode strings;

sampling each one of the voltages sequentially to generate voltage samples;

comparing each one of the voltage samples to a threshold signal to generate a comparison signal, wherein each one of the voltage samples has a time period responsive to the comparison signal; and

summing the voltage samples to generate an error signal to control the DC-DC converter.