LED (LIGHT-EMITTING DIODE) STRING DERIVED CONTROLLER POWER SUPPLY
An LED lighting device includes an auxiliary power supply that supplies power to a control circuit of the LED lighting device that receives an input from a terminal of a light-emitting diode (LED) string of the lighting device that has a substantially lower voltage than the line voltage to which the lighting device is connected. The terminal may be within the LED string, or may be an end of the string. A linear regulator may be operated from the voltage drop across a number of the LEDs in the string so that the energy wasted by the auxiliary power supply is minimized. In other designs, the auxiliary power supply may be intermittently connected in series with the LED string only when needed. The intermittent connection can be used to forward bias a portion of the LED string when the voltage supplied to the LED string is low, increasing overall brightness.
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1. Field of the Invention
The present invention relates generally to lighting device power sources such as those included within light-emitting diode (LED) lamps, and in particular to a control circuit for an LED lighting device power source that is powered from a LED string controlled by the control circuit.
2. Background of the Invention
Lighting control and power supply integrated circuits (ICs) are in common use in both electronic systems and in replaceable consumer lighting devices, e.g., light-emitting-diode (LED) and compact fluorescent lamp (CFL) replacements for traditional incandescent light bulbs.
In order to power LED lighting device from a typical AC power line voltage, the AC power line voltage must somehow be reduced to the relatively low voltage required by the LEDs in the lighting device. One manner in which the reduction is accomplished is to connect the LEDs in series to form a string, which is then supplied from a greater supply voltage. The greater supply voltage is generally provided from a switching power converter that controls the current provided to the LED string and also generally performs some voltage conversion to an intermediate voltage supplied to the LED string. The control circuits that operate the switching power supply typically also require a power supply voltage much less than the voltage of the AC line voltage. The power supply voltage is typically generated from a linear power supply. Generating the controller power supply voltage from the typical linear power supply wastes energy and adds some complexity to the circuit.
Therefore, it would be desirable to provide a LED lighting device that has improved energy efficiency and/or reduced complexity.
SUMMARY OF THE INVENTIONA control circuit for controlling power supplied to one or more lighting devices, an integrated circuit (“IC”) for controlling such a circuit and a method of operation of the circuit provide improved efficiency, reduced complexity and/or other benefits in LED lighting devices.
The circuit includes a switching power converter with a magnetic storage element and a switching element for controlling the current supplied to one or more strings of light-emitting diodes (LEDs) from a line voltage input source. The circuit supplies power to a control circuit that controls the switching element of the switching power converter from a terminal of the LED string, which may be a terminal within the LED string, or a terminal at the end of the LED string. The terminal has a voltage substantially less than a voltage of the input voltage source, so that the LED string provides at least a portion of the voltage drop from the voltage of the AC line source to the power supply input of the control circuit.
The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings.
The present disclosure reveals circuits and methods for powering and controlling strings of series-connected light-emitting diodes (LEDs), in which auxiliary power for control circuits that control a switching power supply within a lighting device including the LEDs is provided from an LED string itself. In particular embodiments, strings of light-emitting diodes (LEDs) are packaged to replace incandescent lamps. A power supply voltage is supplied or generated from a terminal of an LED string within the lighting device, which may be a terminal within the LED string, or an end of the LED string. Since the voltage provided from the terminal is substantially greater than a voltage provided from the rectified AC line voltage at the input of the switching power supply, energy that would otherwise be wasted in producing the auxiliary power supply voltage is conserved.
Referring now to
An integrated circuit (IC) 10 includes controller circuit 14 to operate switching transistor N1, which is illustrated as external to IC 10, but that alternatively may be included within IC 10. Controller circuit 14 may be a pulse-width modulator, or other suitable controller capable of controlling the amount of energy transferred by inductor L1, by the activation of switching transistor N1. The value may be controlled according to dimming values DIM, which may be provided by a source internal or external to integrated circuit 10 and may, alternatively or in combination, be optionally determined by a dimming detection circuit 12 that detects a dimming level of a dimmer controlling the line voltage from which power supply voltage +VS is derived. A voltage sense circuit 16 can be provided to further inform controller circuit 14 of the magnitude of power supply voltage +VS. An auxiliary power supply 20 provides auxiliary power supply voltage VDD to internal circuits of integrated circuit 10, in particular to controller circuit 14 which only needs to generate sufficient output voltage swing to fully turn on switching transistor N1. In the examples given herein, various circuits that produce auxiliary power supply voltage VDD from a terminal of the LED string formed by LEDs D1A-D1Z within lighting device LD1 are shown. The terminal may be a terminal within the LED strings, or an end of the LED string, as shown. The voltage at the terminal has a substantially lower voltage, e.g., 12V-15V than the voltage across capacitor C1, e.g., 40V, so that energy is saved by not dissipating power that would otherwise be wasted by regulating auxiliary power supply voltage VDD to the lower voltage.
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While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form, and details may be made therein without departing from the spirit and scope of the invention.
Claims
1. A lighting circuit, comprising:
- a plurality of series-connected light-emitting diodes, wherein the series-connected light-emitting diodes are coupled between an input voltage source and an input voltage return associated with the input voltage source;
- a switching power converter having a magnetic storage element and a switching element for controlling a current supplied through the plurality of series-connected light-emitting diodes;
- a control circuit for controlling the switching element of the switching power converter, wherein a power supply input of the control circuit is provided by a power supply voltage generated from a terminal of the plurality of series-connected light-emitting diodes having a voltage substantially less than a voltage of the input voltage source;
- a switching circuit coupled in series with the plurality of series-connected light-emitting diodes and the input voltage source, wherein the switching circuit alternatively couples the terminal of the plurality of series-connected light-emitting diodes to the input voltage return in a first switching state and to the power supply input of the control circuit in a second switching state; and
- a second plurality of series-connected light-emitting diodes coupled between the switching circuit and the input voltage return, wherein the switching circuit alternatively supplies current to the second plurality of series-connected light-emitting diodes and to the power supply input.
2-4. (canceled)
5. The lighting circuit of claim 1, wherein the switching circuit comprises:
- a switch for intermittently coupling the plurality of series-connected light-emitting diodes to the input voltage return in the first switching state; and
- a diode coupled between the plurality of series-connected light-emitting diodes and the power supply input of the control circuit.
6. The lighting circuit of claim 1, further comprising a comparison circuit for controlling the switching circuit by comparing the power supply voltage to a threshold voltage, wherein the comparison circuit sets the second switching state in response to a magnitude of the power supply voltage being less than a magnitude of the threshold voltage.
7-11. (canceled)
12. A method of generating an auxiliary power supply for a circuit controlling the transfer of power from an input voltage source to a lighting device comprising plurality of series-connected light-emitting diodes, the method comprising:
- controlling charging of a magnetic storage element from the input voltage source and discharging of the magnetic storage element to apply energy stored in the magnetic storage element to provide a voltage across the plurality of series-connected light-emitting diodes, wherein the controlling is performed by a control circuit that controls a switching circuit coupled to the magnetic storage element; and
- generating a power supply voltage supplied to a power supply input of the control circuit from a terminal of the plurality of series-connected light-emitting diodes having a voltage substantially less than a voltage supplied across the plurality of series-connected light-emitting diodes, wherein the generating comprises alternatively coupling the terminal of the plurality of series-connected light-emitting diodes to the input voltage return in a first switching state, to the power supply input of the control circuit in a second switching state and to a second plurality of series-connected light-emitting diodes in a third switching state.
13. (canceled)
14. The method of claim 12, wherein the generating further comprises:
- comparing the power supply voltage to a threshold voltage; and
- setting the second switching state in response to a magnitude of the power supply voltage being less than a magnitude of the threshold voltage.
15-19. (canceled)
20. An integrated circuit for operating a lighting circuit comprising a plurality of series-connected light-emitting diodes coupled between an input voltage source and an input voltage return associated with the input voltage source by a switching power converter, the integrated circuit comprising:
- a control circuit for controlling a switching element of the switching power converter; and
- an auxiliary power supply input terminal for receiving a connection from another terminal of the plurality of series-connected light-emitting diodes having a voltage substantially less than a voltage of the input voltage source;
- an auxiliary power supply circuit for generating a voltage from the auxiliary power supply input terminal to provide a power supply voltage at a power supply input of the control circuit, wherein the auxiliary power supply circuit comprises a switching circuit coupled in series with the plurality of series-connected light-emitting diodes and the input voltage source, wherein the switching circuit alternatively couples the auxiliary power supply input terminal to the input voltage return in a first switching state and to the power supply input of the control circuit in a second switching state; and
- a lighting current output terminal for connection to a second plurality of series-connected light-emitting diodes, and wherein the switching circuit alternatively supplies current to the lighting current output terminal and to the power supply input.
21-22. (canceled)
23. The integrated circuit of claim 20, wherein the switching circuit comprises:
- a switch for intermittently coupling the auxiliary power supply input terminal to the input voltage return in the first switching state; and
- a diode coupled between the auxiliary power supply input terminal and the power supply input of the control circuit.
24. The integrated circuit of claim 20, further comprising a comparison circuit for controlling the switching circuit by comparing the power supply voltage to a threshold voltage, wherein the comparison circuit sets the second switching state in response to a magnitude of the power supply voltage being less than a magnitude of the threshold voltage.
25-26. (canceled)
Type: Application
Filed: Mar 20, 2014
Publication Date: Sep 24, 2015
Applicant: CIRRUS LOGIC, INC. (Austin, TX)
Inventors: John L. Melanson (Austin, TX), Eric King (Dripping Springs, TX), Rahul Singh (Austin, TX)
Application Number: 14/220,472