Patent Grant
9336704
The present disclosure relates generally to devices, circuits, and methods for driving light emitting diode (LED) display panels. More particularly, the present disclosure relates to devices, circuits, and methods for driving the LED display panels, so as to enhance power supply efficiency, to increase LED driver circuitry integration and to reduce heat dissipation.
In recent years, devices and applications involving LEDs (i.e., light emitting diodes) are gaining popularity. Such devices and applications range from light sources for general illumination, signs and signals, to display panels, televisions, etc. Regardless of the applications, LED driver circuits are used in supplying power to the LEDs.
An LED panel refers to a device that includes an array of LEDs that are connected together, or a device that includes plurality of sub-modules, each sub-module having such an LED array. LED panels usually employ arrays of LEDs of a single color or different colors. When individual LEDs are used in certain display applications, each LED usually represents a display pixel. An RGB LED unit refers to a cluster of three LEDs, namely, a red LED, a green LED, and a blue LED. When RGB LED units are used in certain display applications, each RGB LED unit may represent a display pixel. Surface mounted RGB LED units usually have four pins, one pin for each of the red, green, and blue LEDs and the fourth pin for either a common anode or a common cathode.
LED arrays are traditionally arranged in a common anode scan configurations, in which the anode of the LEDs are electronically connected to a power source via a switch element, while the cathodes of the LEDs are electronically connected to the output of current sink. In such a configuration, an N-MOS driver is often used as the current sink. An N-MOS is preferable over a P-MOS because N-MOS has a larger current capacity and a lower RDS (on) for a given design configuration.
In a common anode configuration, all RGB LEDs are connected to the same power supply and are supplied the same voltage. As is well-known in the art, the red LED forward voltage is significantly lower than that of green and blue LEDs. If the same supply voltage is used for the red, green, and blue LEDs, adjustments are required to match the forward voltages of individual LEDs, for example, by installing a bias resistor between the power supply and the LED. In that case, a significant amount of energy is dissipated as heat on the bias resistor. For example, if the supply voltage is 5 volts, since the forward voltage drop of a red LED is about 2.0 volts, approximately 60% of the energy is lost as heat on the bias resistor. Excessive heat dissipation wastes energy and complicates the design of driver circuitry because extra consideration needs to be given to increased demand of heat removal.
In addition, the display resolution increases when the size of the pixel pitch becomes smaller. The size of the pixel pitch is partially determined by the printed circuit board that holds a variety of components. Such components are, for example, a constant current driver, a decoder, power MOSFETs to control scan line switching, and bias resistors for some LEDs (such as red LEDs) to reduce LED driver operating voltage. In a design that these components are mounted on a PCB (printed circuit board) as discrete parts, the number of layers on a PCB needs to be increased. Such a design increases manufacturing cost as well as the difficulties in both noise reduction and pixel patch size reduction. In such a design with discrete parts, other problems may arise, such as timing control, parasitic capacitance, and ghost images, etc.
There is a need to design a highly integrated LED driving circuit with reduced cost, reduced heat dissipation, and reduced noise, which is capable of driving high resolution LED displays.
In one embodiment, there is provided a driver circuit for an LED display panel. The circuit comprises an array of R/G/B LEDs arranged in a common cathode configuration; an analog driver which comprises a first constant current driver to drive green LEDs, a second constant current driver to drive blue LEDs, and a third constant current driver to drive red LEDs; an analog power module electrically coupled to the first, the second, and the third constant current drivers, the analog power module further comprises a first power source and a second power source; and a digital controller for transmitting digital control signals to the analog driver. The digital controller is powered by a digital power module.
In another embodiment, there is provided a method for powering LED display panels. The method comprises powering an analog driver using an analog power module, the analog power module comprises a first power source and a second power source; and powering a digital controller using a digital power module, the digital controller transmits digital control signals to the analog driver.
In another embodiment, there is provided an LED display system. The display system comprises an LED array arranged in a common cathode configuration; an analog driver that provides a constant current to drive the LED array; a digital controller for transmitting digital signal to the analog driver. The digital controller is powered by an internal low-dropout regulator residing on the chip, and the analog driver is powered by a first power source and a second power source.
The teachings of the present disclosure can be readily understood by considering the following detailed description in conjunction with the accompanying drawings.
The Figures (FIG.) and the following description relate to the embodiments of the present disclosure by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and/or methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of the claimed inventions.
Reference will now be made in detail to several embodiments of the present disclosure(s), examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the present disclosure for the purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
The driver controller chip 120 includes an analog driver 101 and a digital controller 102. A digital control signal source 103 is transmitted to the digital controller 102, from which a control signal 104 is transmitted to the analog driver 101. Digital voltage VDDD is coupled to the digital controller while analog voltage VDDA is coupled to the analog driver. The analog driver includes a plurality of constant current drivers, Ib[i] is constant current driver for the ith column blue LED, i is 0 through n−1, Ig[i] is constant current driver for the ith column green LED, i is 0 through n−1, Ir[i] is constant current driver for the ith column red LED, i is 0 through n−1. The analog driver also includes a plurality of switches, sw[j] is the switch for the jth row R/G/B LEDs. In the traditional scheme, VDDD and VDDA are both supplied by same power module 106. The power module 106 has a single power source 105.
In the common cathode configuration as depicted in
In the embodiment of
In this embodiment, the LED array module 250 includes an array of R/G/B LEDs arranged in the common cathode configuration. The driver controller chip 220 comprises an analog driver 201 and a digital controller 202. A digital control signal 203 source is transmitted to digital controller 202, which generates control signals for the analog driver 201.
VDDB, VDDG, and VDDR are voltages for blue LEDs, green LEDs, and red LEDs, respectively. VDDB and VDDG are connected to power source 207 and have a higher voltage, e.g., approximately 3.8V, while VDDR is connected to power source 206 and has a lower voltage, e.g., approximately 2.8V. Alternatively, VDDB and VDDG can be supplied by two different power sources.
The VDDR is coupled to the LDO 205 and through which supplies the digital controller 202 with a voltage, for example, 1.8V or lower. A lower VDDD provides better power consumption efficiency because power consumption of the digital parts is significant. The dynamic power consumed by the digital parts is proportional to C·V2·f:P=C·V2·f, where C is a constant.
The analog driver includes a plurality of constant current drivers, Ib[i] is constant current driver for the ith column blue LED, i is 0 through n−1, Ig[i] is constant current driver for the ith column green LED, i is 0 through n−1, Ir[i] is constant current driver for the ith column red LED, i is 0 through n−1. The analog driver also includes a plurality of switches, sw[j] is the switch for the jth row R/G/B LEDs.
The analog driver 301 includes a plurality of constant current drivers, Ib[i] is constant current driver for the ith column blue LED, i is 0 through n−1, Ig[i] is constant current driver for the ith column green LED, i is 0 through n−1, Ir[i] is constant current driver for the ith column red LED, i is 0 through n−1. The analog driver 301 also includes a plurality of switches, sw[j] is the switch for the jth row R/G/B LEDs.
Embodiments of the present disclosure have been described in detail. Other embodiments will become apparent to those skilled in the art from consideration and practice of the present disclosure. Accordingly, it is intended that the specification and the drawings be considered as exemplary and explanatory only, with true scope of the present disclosure being set forth in the following claims.
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| Number | Date | Country | |
|---|---|---|---|
| 20150109190 A1 | Apr 2015 | US |
