This application relates generally to driving LEDs using a high-voltage driver, and more specifically this application relates to an apparatus and method for using a current controlled boost circuit connected to an AC mains to provide a higher voltage DC power to the LED array.
Using LEDs for lighting applications is becoming more and more popular as the cost of LEDs drops due to manufacturing improvements. LED lighting often utilizes an array of individual LEDs, such as a plurality of LEDs connected in series, to increase the amount of light outputted to a desired amount. Because LEDs typically operate from a DC voltage source, the AC voltage that is typically found as a power source needs to be converted to DC power in order to drive the LED array, and thus an LED driver is provided to convert the AC source to a DC power supply for driving the array.
However, current systems provide DC voltage outputs that are typically less than the voltage of the AC source, which is often at 120V for household applications. It has been determined that it would be desirable to increase the voltage at which an LED array operates to an amount that is greater than the line voltage, but it is always desirable to reduce the size, cost, and number of components that are utilized in such lighting application. Accordingly, desirable would be a way to provide a high-voltage DC power source higher than the AC source voltage for driving an LED array while also reducing the cost, complexity, and size of the components utilized.
Provided are a plurality of embodiments the invention, including, but not limited to, an apparatus comprising: an LED array including a plurality of LEDs connected in a series for providing illumination; and an LED driver for providing an operating voltage to the LED array. The LED driver includes a rectifier circuit for rectifying an AC power source into a DC power source providing a DC source voltage; a filter for filtering the DC source voltage; a voltage boost circuit for boosting the DC source voltage for providing an LED drive voltage; and an oscillating circuit for driving the voltage boost circuit at an oscillation frequency, wherein the oscillating boost circuit is self-oscillating.
Also provided is an apparatus comprising: an LED array including a plurality of LEDs connected in a series for providing illumination; and an LED driver for providing an operating voltage to the LED array. The LED driver includes: a rectifier circuit for rectifying an AC power source into a DC power source providing a DC source voltage having an RMS voltage value about equal to the RMS voltage value of the AC power source; a filter for filtering the DC source voltage; a voltage boost circuit for boosting the DC source voltage for providing an LED drive voltage; and an oscillating circuit for driving the voltage boost circuit at an oscillation frequency, wherein the oscillating boost circuit is self-oscillating.
For the above apparatus, the LED drive voltage can be utilized for driving the LED array such that the voltage drop across the LED array has an RMS voltage value that is greater than the RMS voltage value of the AC power source.
Still further provided is an apparatus comprising: an LED array including a plurality of LEDs connected in a series for providing illumination; and an LED driver for providing an operating voltage to the LED array. The LED driver includes: a rectifier circuit for rectifying an AC power source into a DC power source providing a DC source voltage having an RMS voltage value about equal to the RMS voltage value of the AC power source; a filter for filtering the DC source voltage; a voltage boost circuit for boosting the DC source voltage for providing an LED drive voltage; an oscillating circuit for driving the voltage boost circuit at an oscillation frequency, wherein the oscillating boost circuit is self-oscillating; a bootstrap oscillator power supply for providing power to the oscillating circuit during a power-up phase; an oscillator power supply for supplying power to the oscillator after the power-up phase; a current detecting circuit for controlling a duty cycle of the boost circuit; and a current averaging circuit for filtering out voltage peaks otherwise provided in the oscillating circuit,
For the above apparatus, the LED drive voltage is utilized for driving the LED array such that the voltage drop across the LED array has an RMS voltage value that is greater than the RMS voltage value of the AC power source.
Also provided is an LED Driver for driving an LED array, the LED driver comprising: a rectifier circuit for rectifying an AC power source into a DC power source providing a DC source voltage having an RMS voltage value about equal to the RMS voltage value of the AC power source; a filter for filtering the DC source voltage; a voltage boost circuit for boosting the DC source voltage for providing an LED drive voltage; an oscillating circuit for driving the voltage boost circuit at an oscillation frequency, wherein the oscillating boost circuit is self-oscillating; a bootstrap oscillator power supply for providing power to the oscillating circuit during a power-up phase; an oscillator power supply for supplying power to the oscillator after the power-up phase; a current detecting circuit for controlling a duty cycle of the boost circuit; and a current averaging circuit for filtering out voltage peaks otherwise provided in the oscillating circuit.
For the above driver, the LED drive voltage is utilized such that the voltage drop across an output has an RMS voltage value that is greater than the RMS voltage value of the AC power source. Furthermore, a power efficiency of the LED driver is greater than 90%.
Also provided are any of the above devices further comprising a dimmer compatibility circuit that is inactive when dimming is not being performed and active when dimming is being performed.
Further provided are any above devices having a power efficiency of greater than 90%, or a power efficiency equal to or greater than 95%.
Also provided are additional embodiments of the invention, some, but not all of which, are described hereinbelow in more detail.
The features and advantages of the examples of the present invention described herein will become apparent to those skilled in the art to which the present invention relates upon reading the following description, with reference to the accompanying drawings, in which:
Generally, a boost circuit is utilized to boost the line voltage to operate an LED array at a higher voltage, in order to improve efficiencies of operation. The boost circuit is designed for high efficiency.
The Oscillator 44 is powered by an Oscillator power supply 43 that receives power from the boost circuit 41, but because on startup the boost circuit 41 needs time to come up to a steady operating state, the oscillator bootstrap power circuit 42 is provided to initially provide startup power to the oscillator 44. The oscillator 44 sets the operating frequency of the voltage boost circuit, as described in more detail hereinbelow.
An output protection and control circuit 46 is provided to perform a number of protection functions for the boost device 40. For example, the output protection and control circuit 46 prevents large peak currents from feeding the oscillator circuit, it controls the duty cycle of the boost circuit, and it performs overvoltage control of the boost circuit output.
An output filter 47 is provided to filter out ripple currents output by the boost circuit 41, and to provide further dimmer compatibility. A dimming compatibility circuit 48 can also be provided to further improve compatibility with dimming circuits.
Of course, various numbers of LEDs could be provided in each series string depending on the output voltage of the LED array driver and also depending on the voltage drop across the LEDs. For example, where the voltage drop across each LED is about 3V, and the output of the driver 100 is about 200V, a series string would have 66 LEDs. Furthermore, any number of LED strings could be connected in parallel depending on the total light output that was desired, from 1 string to 2 or more strings. Of course, each additional string connected in parallel increases the current that must be provided by the driver 100 by an integer multiple amount, thereby increasing the required size (power capacity) of its components.
The boost circuit is provided by transformer winding T1A, Q4, and D16. Basically, the oscillating circuit drives Q4 to switch on and off at the oscillating frequency (about 100 kHz), leading T1A to charge when Q4 is on, and forcing T1a to discharge into the LED load(s) while boosting the load voltage when Q4 is turned off. The push-pull amplifier prevents Q4 from drawing too much current from the oscillating circuit during this switching operation, as drawing too much current could otherwise shut down the oscillation.
The oscillation circuit is powered by an oscillator power supply (supplying Vcc) comprising a secondary winding of the transformer T1B, in combination with blocking dual diode D5 and C8 acting as a filter to average out the voltage output by T1B. However, upon startup, because the boost circuit is not yet charged and the oscillating circuit not yet oscillating, a bootstrap startup power supply comprised of D2, R1, R16, and Q3, with zener diode D4 acting as a voltage regulator (set at 15V in the example), are arranged as shown for providing an initial Vcc to start the oscillating and boost circuits. The bootstrap circuit detects when the oscillator power supply is sufficiently charged and operating, at which time Q1 is turned off to basically shut off the current provided by the bootstrap power supply.
Three components/circuits are provided in the example embodiment of
The circuit of
The dimmer compatibility circuit is added in applications where the LED array is desired to have broad compatibility with dimmer circuits and provides a more desirable incandescent lamp equivalent type of dimming curve. It also provides a lower programmed light output at the minimum dimmer setting inputs and assists with slowly starting the light output on the way up when increasing the dimming input.
Thus, the dimmer compatibility circuit can be utilized with the example LED driver circuit(s) to provide a more adaptable solution for replacing incandescent lighting. Accordingly, an LED driver as disclosed herein, along with the dimmer compatibility circuit, if such compatibility is desired, can be utilized in an LED lighting system for use as replacements to existing solutions designed for incandescent lighting (such as for replacing a 100 watt A-19 incandescent lamp, for example), or for new lighting situations where incandescent lighting may have been preferable in the past. Furthermore, the LED driver can be used in new customized lighting solutions where high-efficiency LED lighting is desirable, such as for public lighting, office lighting, etc.
Many other example embodiments of the invention can be provided through various combinations of the above described features. Although the invention has been described hereinabove using specific examples and embodiments, it will be understood by those skilled in the art that various alternatives may be used and equivalents may be substituted for elements and/or steps described herein, without necessarily deviating from the intended scope of the invention. Modifications may be necessary to adapt the invention to a particular situation or to particular needs without departing from the intended scope of the invention. It is intended that the invention not be limited to the particular implementations and embodiments described herein, but that the claims be given their broadest reasonable interpretation to cover all novel and non-obvious embodiments, literal or equivalent, disclosed or not, covered thereby.
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