Patent Application
20130033176
Presently, much lighting used for applications such as rail lighting, for example, still uses incandescent light bulbs. However, incandescent light bulbs are inefficient and need to be replaced regularly. Some applications may use a very large number of incandescent light bulbs. As a result, if the light bulbs regularly fail, having a large number of incandescent light bulbs creates a high cost due to both the cost of the new bulb and labor associated with its replacement.
In addition, some lighting systems require the incandescent light bulbs to be electrically connected in series. Traditional incandescent light bulbs can be connected in series across an AC or DC power supply. This allows lights to be used where the only supply available may be much higher than the voltage rating of the lights. Since the impedance of the incandescent light bulbs is constant, each receives an equal share of the total voltage and so operate predictably. Furthermore, since a filament bulb is a resistive load when connected in a serial string across an AC supply, power factor is unity.
However, other types of light sources may not behave as a traditional incandescent light bulb behaves when connected in series. As a result, simply replacing an incandescent light bulb with another type of light source is not trivial. For example, other types of light sources may have features of their behavior that prevent proper operation if electrically connected in series.
The present disclosure relates generally to a light emitting diode (LED) luminaire. In one embodiment, the LED luminaire comprises a base, a heat sink coupled to the base, a power supply coupled to an interior volume of the heat sink, one or more LEDs coupled to the power supply, wherein the one or more LEDs are coupled to a circuit configured to provide a constant input impedance and a lens coupled to the heat sink and enclosing the one or more LEDs.
The present disclosure also provides a lighting system. In one embodiment, lighting system comprises a plurality of light emitting diode (LED) luminaires, wherein the plurality of light emitting diode luminaires is electrically connected in series, wherein each one of the plurality of LED luminaires comprise a circuit configured to provide a constant input impedance.
The present disclosure also provides a circuit for an light emitting diode (LED) luminaire. In one embodiment, the circuit for the LED luminaire comprises a power factor correction control integrated circuit (IC), wherein the power factor correction control IC has a plurality of pins and wherein a first one of the plurality of pins is connected to one or more resistors that set a current based upon a varying supply voltage.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.
Embodiments of the present disclosure are directed towards a light emitting diode (LED) luminaire for connection in series. As noted above, some light sources have behavior that prevents proper operation if electrically connected in series. LED luminaires with power factor corrected drivers are one example of such a light source.
Traditional LED circuits include a current control loop, also referred to as a current regulator. The current control loop adjusts the current delivered to the LED as it detects changes in voltages within the circuit. When the luminaires having LEDs are simply connected in series, across an alternating current (AC) supply, the load will have poor power factor due to the non-linear nature of the LEDs. Furthermore, simple resistance current limiting for LEDs is very inefficient.
More sophisticated LED luminaires generally utilize switch mode topologies for maximum efficiency along with power factor correction circuits and circuitry to control the LED current. But such circuitry has the effect of changing the input impedance to the LED luminaire as the supply voltage changes. As the supply voltage reduces, the LED luminaire draws more current to maintain a constant output power, so reducing the input impedance. If the supply voltage increases the input current is reduced, so raising the input impedance.
As a result, if two or more such LED luminaires were to be connected in series across either an AC or DC supply, a situation will arise whereby one or more luminaires reduce their input impedance to a minimum to try and maintain output power, while another luminaire goes to its maximum. This results in a severe voltage imbalance. This imbalance will not only result in improper operation, but likely in failure of one or more of the luminaires if connected across a supply greater than the rating of an individual luminaire.
In one embodiment, the circuit 200 is without the current control loop illustrated in the circuit 100. In other words, the current control loop is absent from the circuit 200. Said another way, the circuit 200 does not have a current control loop or any type of current regulator monitoring the LED circuit current.
The circuit 200 comprises a power factor correction control integrated circuit (IC) 202 having a plurality of pins labeled 1-8. Notably, the circuit 200 directly connects a feedback pin (pin 1) to the return through a resistor R3, thus, disabling the current control loop. Unlike the circuit 100, the circuit 200 does not include the over voltage protection, LED current feedback or the over temperature control.
In one embodiment, the LED current (at a given supply voltage) is set by resistors R1, R2 and VR1, which drive the input-current wave-shape programming pin, pin 3. Rather than a fixed reference supply voltage, as is usual when constant LED current is desired, the supply voltage (which can vary) is the reference determining the LED current in the present circuit 200. The LED current may now be set by the input voltage, thus, achieving the desired constant input impedance.
The peak current in the switching FET Q1 is limited by means of current sense resistor R9 and the peak current sense pin, pin 4. This determines how much power is transferred through the transformer to the LEDs, so limiting their current.
In the embodiment illustrated in
As a result, when LED luminaires having the circuit 200 are electrically connected in series, the LEDs will operate properly due to the design of the circuit 200 in achieving constant input impedance. In other words, the LEDs will no longer malfunction due to one of the luminaires attempting to compensate for changes in voltage, thereby, removing voltage from one luminaire and putting a large voltage across another.
Referring back to
The circuit 200 maintains power factor correction. Power factor correction may be defined as forcing the input current to follow the same shape as the input voltage. In other words, the input current is corrected to form a sine wave when driven from an AC supply. Power factor correction is important for some applications where a company can be penalized by the power generating companies for bad power factor that can generate harmonics that can cause problems for the power generation system.
The circuit 200 illustrated in
In one embodiment, the LED luminaire 300 comprises a housing 302, a power supply 306, a heat sink 310 and an outer lens 318. In one embodiment, the power supply 306 may be designed with the circuit 200 illustrated in
In one embodiment, the housing 302 may be a Edison base. In one embodiment, the heat sink 310 may include one or more fins 324 to help dissipate heat away from the LED luminaire 300.
In one embodiment, the LED luminaire 300 may be assembled by inserting the power supply 306 into the housing 302. In one embodiment, the housing 302 may include potting. A gasket 304 may be placed in between the housing 302 and the heat sink 310. An insulator 308 may be placed on top of the power supply 306. The insulator 308 may be fabricated from a material such as Mylar®, for example.
In one embodiment, the power supply 306 may be aligned and inserted into the heat sink via slots 322 illustrated in
In one embodiment, a semiconductor package 320, e.g., a D2 PAK, of the power supply 306 is in contact with a protruding portion 330 of the heat sink 310. In one embodiment, the semiconductor package 320 may be bonded to the heat sink 310 via an adhesive or epoxy. Notably, the power supply 306 is in direct contact with multiple points of an interior volume of the heat sink 310. This helps to quickly dissipate heat out of the LED luminaire 300 and require less potting.
Referring back to
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
