LED driver for providing power to parallel LEDs

An LED driver is provided. The LED driver has a constant current power source. In some embodiments, the constant current power source is an electrical input configured for connection to a source of power at a constant current. In some embodiments, the source of power is a constant current regulator. The LED driver also includes a switch electrically connected to the constant current power source. The switch has at least two outputs wherein the switch is configured to selectively connect the constant current power source to each of the at least two outputs. The switch is configured to connect each of the at least two outputs for a pre-determined period of time.

FIELD OF THE DISCLOSURE

The present disclosure relates to LED lighting, and in particular, to constant current power supplies.

BACKGROUND OF THE DISCLOSURE

In the United States, airfield lighting is the subject of regulation by the Federal Aviation Administration (“FAA”). For example, runway and taxiway signs must conform to the “Specification for Runway and Taxiway Signs,” published by the FAA in Advisory Circular 150/5345-44K. Power for such lighting is outlined in the FAA Specification, and is available in the form of constant RMS current of 2.8 A to 6.6 A via constant current regulators (“CCR”). Conventional LED lighting drivers take power from a CCR loop and convert it to feed LEDs at a constant current. In order for this topology to work, LEDs electrically connected to and driven by a lighting driver must connected in series (the LEDs are series connected with each other to form a string). Where multiple parallel strings of series LEDs are used, previous systems powered each string of LEDs using a separate lighting driver.

BRIEF SUMMARY OF THE DISCLOSURE

An LED driver is provided. The LED driver has a constant current power source. In some embodiments, the constant current power source is an electrical input configured for connection to a source of power at a constant current. In some embodiments, the source of power is a constant current regulator. The LED driver also includes a switch electrically connected to the constant current power source. In some embodiments, the switch may be or may include, for example, a MOSFET. The switch has at least two outputs wherein the switch is configured to selectively connect the constant current power source to each of the at least two outputs. In an exemplary embodiment, an LED driver has four outputs. The switch is configured to connect each of the at least two outputs for a pre-determined period of time. In some embodiments, the LED driver includes a processor operably connected to the switch. The processor may be programmed to cause the switch to sequentially connect to each of the at least two outputs for a pre-determined period of time.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides the ability of using a single LED driver with parallel LEDs (or parallel strings of LEDs). In this way, large LED strings requiring high voltages can be split into a number of smaller strings allowing for the use of lower (i.e., safer) voltages.

The present disclosure can be embodied as an LED driver10for providing power to one or more parallel LEDs90or strings of LEDs. The LED driver10includes a constant current power source12. Such a constant current power source12may be a circuit included within the LED driver10. For example, the constant current power source12may be a circuit having a current regulator within the LED driver10. In another embodiment, the constant current power source is an input (e.g., a set of input pins) of the LED Driver10, wherein the input is configured to be connected to a source of power at a constant current. For example, the LED driver may have a constant current power source which is an input terminal configured to be electrically connected to a CCR loop of an airfield.

The LED driver10has a switch14connected to the constant current power source12. The switch14has at least two outputs15, and the switch14is configured to selectively connect the constant current power source12to each of the at least two outputs15. For example, the switch14may connect source12to a first of the outputs15, and then it may be switched to connect source12to a second of the outputs12. By using a fast switch14, the power from the constant current power source12can be time-sliced across each of the outputs15to provide an effective constant current which is the average of the instantaneous current. As such, the switch14must be fast enough to provide an instantaneous current to each output15that is effectively a constant current for the application at hand. For example, where a string of LED drivers is connected to each output of the LED driver, the current is switched to each string of LEDs at a rate which is imperceptible to a human observer. In the case of LEDs, an exemplary time period, which has been found to be suitable, is 1/120 second, though the time may be longer or shorter. A more particular example, is discussed below. An example of a suitable switch is a MOSFET. Other suitable switches will be apparent to one having skill in the art in light of the present disclosure.

To provide an average current of value X Amps to each of N outputs, the LED driver is configured to provide a constant driver current of X*N Amps. This driver current is sliced over a time period T such that each output is connected to the driver current for a time T÷N. In this way, a power of X*N is provided to each output (e.g., a string of LEDs connected to each output) for a period of T÷N resulting in an average power of X during time T.

The LED driver10may include a processor20which is operably connected to the switch14. The processor20is configured to cause the switch14to sequentially connect each of the at least two outputs15to the constant current power source12. In this way, each output15can be connected to the power source12for a pre-determined period of time (i.e., at a pre-determined rate).

In a particular example depicted inFIG. 2, an LED driver110is connected to four strings190of LEDs195. Each string190comprises a plurality of LEDs195connected in series. Each string190of LEDs is configured to be driven by a 100 mA current. As such, the LED driver110is configured to provide a constant current of 400 mA to a selected output115of a four-output switch114. A processor120of the exemplary LED driver is programmed to operate the switch at a rate of 1000 Hz such that each output of the switch is cycled with power for 1 ms and then disconnected for 3 ms. Each output115of the switch114is provided with power in sequence such that only one of the four outputs has power at any time (see, e.g.,FIG. 3). The connection between the power source112and the switch outputs115may be made in a make-before-break fashion. In this way, the instantaneous current through each string alternates between 0 mA (for 3 ms) and 400 mA (for 1 ms), and the average current through each string of LEDs is 100 mA (an effective constant current of 100 mA).

Although the present disclosure has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the spirit and scope of the present disclosure.