purpose this application note provide some information integrated circ

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Drivers Light Emitting Displays Appnote
purpose this application note provide some information integrated circuits presently available drive Light Emitting Diodes (LED) displays interface them various displays. Background displays come various sizes (0.1" 0.8"), colors (red, high-efficiency red, green, yellow blue), fonts (7/9/14/16 segment, dot-matrix, bargraph), types (common anode, common cathode, multi-digit). brightness essentially proportional current through each element within display should have same current brightness variation apparent. display subsystem made from several elements. Figure Display system
circuits using logic transistors, Figure Figure Circuits transistor darlington transistor
Latch Main Data System Memory
Decoder
Driver
Display
Transistor
Darlington Transistor
partitioning these elements dependent drivers used; therefore display driver chosen dependent specifications display application. Also some types displays require using multiplexing technique because internal interconnections. This only applicable multi-digit displays. Typical Circuits Figure shows very basic circuit driving LED. series resistance easily calculated from following formula. Figure Basic circuit drive
seen that (saturation voltage) driver going factor determining series limiting resistor. Therefore darlington versus single output transistor will have different current limiting resistor values maintain constant current through LED. Figure Common cathode display
Figure Common anode display
2000 Infineon Technologies Corp. Optoelectronics Division Jose, www.infineon.com/opto 1-888-Infineon (1-888-463-4636) OSRAM Opto Semiconductors GmbH Regensburg, Germany www.osram-os.com +49-941-202-7178
2000-13
Figure Common cathode display with driver
Data Input
Figure Open collector type driver with common anode display
7448 Equivalent
7447 equivalent
Figure Common anode display with driver
Figure Open collector type driver with common cathode display
7447 Equivalent
7449 equivalent
Data Input
Selection factor choosing display and/or driver will whether display common cathode common anode type display. Another factor that different drivers high wired into different configurations. From Figures 6/7/8/9, appear obvious combine seven series resistors (Rs) into common resistor common line. However this should done because possible variation from segment segment. Variation cause variation current, resulting segment brightness differences. Table list some most common drivers available. Besides having different current drive capabilities, product have feature which make them easier particular application: Serial versus parallel input data Data latching type drivers Blanking Drive ripple blanking input (rbo) with pulse width modulation vary brightness Multi-digit drivers Constant current drivers Advantage constant current driver affect brightness, important with different color LEDs.
Multiplexing multiplex system, corresponding segment each digit bussed together driven from segment drive usual current limiting resistors. display data presented serially digit decoder driver together with appropriate digit signal (Figure 10). more information multiplexing, Appnote (Multiplexing Displays). simplify design procedure alphanumeric displays would consider OSRAM Intelligent Displays. This device family incorporates necessary interface control with drivers memory built-in with display. This means designer need concerned about memory, multiplex circuitry, character generator, drivers these provided inside modular unit. More information these products available OSRAM Optoelectronics Data Book. Circuits shown this Appnote reference only responsibility OSRAM Optoelectronics. Products continually being improved vendors and/or obsoleted; therefore consult factory.
2000 Infineon Technologies Corp. Optoelectronics Division Jose, www.infineon.com/opto 1-888-Infineon (1-888-463-4636) OSRAM Opto Semiconductors GmbH Regensburg, Germany www.osram-os.com +49-941-202-7178
Appnote
2000-13
Figure Block diagram-4 digit multiplexed display
Data Storage
Segment Decoder
Segment Driver
Data Selector Digit Selector
Digit Digit Digit Digit Driver Driver Driver Driver
2000 Infineon Technologies Corp. Optoelectronics Division Jose, www.infineon.com/opto 1-888-Infineon (1-888-463-4636) OSRAM Opto Semiconductors GmbH Regensburg, Germany www.osram-os.com +49-941-202-7178
Appnote
2000-13

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