Driving 7-Segment Discharge Display Tubes with National Semiconductor

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Driving 7-Segment Discharge Display Tubes with National Semiconductor

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Driving 7-Segment Discharge Display Tubes with National Semiconductor Drivers
Driving 7-Segment Discharge Display Tubes with National Semiconductor Drivers
INTRODUCTION Circuitry driving high voltage cold cathode discharge 7-segment displays such Sperry Information Displays Burroughs Panaplex greatly simplified monolithic integrated circuits from National Semiconductor They DS8880 high voltage cathode decoder driver DS8884A high voltage cathode decoder driver addition satisfying displays' parameter requirements including high output breakdown voltage these circuits have capability programming segment current providing constant current sinking display segments This feature alleviates problem achieving uniformity brightness with unregulated display anode voltage National cirucits drive displays directly Sperry Information Display Burroughs Panaplex used principally calculators digital instruments These 7-segment multi-digit displays form characters passing controlled currents through appropriate anode segment combinations cathode digit will glow when voltage greater than ionization voltage applied between (the cathode) anode that digit multiplexed mode operation digit position selected driving anode that digit with positive voltage pulse same time selected cathode segments driven with negative current pulse This causes potential between anode selected cathodes exceed ionization level causing visible glow discharge Generally these displays exhibit following characteristics ``on'' current segment from mode) multiplex mode) high tube anode supply voltage 180V 200V moderate ionization voltage 170V Once element fires operating voltage drops approximately 150V light output becomes direct function current which controlled current limiting current regulating cathode circuits Current regulation therefore most desirable since brightness will then constant large anode voltage changes Tube anode cathode ``off'' voltage approximately 100V maximum ``off'' cathode leakage Correspondingly specifications cathode driver must complimentary approximately follows high ``off'' output breakdown voltage minimum typical ``on'' output voltage maximum ``on'' output current segment maximum ``off'' leakage current
called Beckman Displays
National Semiconductor Application Note April 1986
allow operation without anode voltage regulation cathode driver must able sink constant current each output with output ``on'' voltage ranging from (see Figure following brief description circuits offered National
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Cathode Driver Output Characteristic
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Currents Temperature FIGURE DS8880 HIGH VOLTAGE CATHODE DECODER DRIVER DS8880 offers 7-segment outputs with high output breakdown voltage minimum constant current-sink outputs programmable output current from
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C1995 National Semiconductor Corporation
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RRD-B30M115 Printed
APPLICATION circuit built-in decoder interface directly Sperry Panaplex displays minimizing exter-
components (Figure inputs driven outputs directly optimized systems with supplies
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FIGURE Operation From DS8880 decoder driver provides unconditional well leading trailing zero blanking utilizes negative input voltage clamp diodes Typically output current varies only output voltage changes Operating power supply voltage device used multiplexed operation Available 16-pin cavity packages DS7880 guaranteed over full military operating temperature range DS8880 molded over industrial range
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FIGURE Interfacing Directly With Output
DS8884A HIGH VOLTAGE CATHODE DECODER DRIVER DS8884A offers 9-segment outputs with high output breakdown voltage minimum constant current-sink outputs programmable from also offers input negative positive voltage clamp diodes restoring input load current maximum APPLICATION DS8884A decodes four lines input drives 7-segment digits gas-filled displays There separate inputs additional outputs direct control decimal point comma cathodes inputs cou-
pled (Figure outputs (Figure AC-coupled outputs (Figure using only capacitor This means device useful applications where level shifting required used multiplexed operation available 18-pin molded package Other advantages DS8884A typical output current variation output voltage changes operating power supply voltage Inputs have pull-up resistors increase noise immunity coupled applications DS8884A guaranteed over operating temperature range
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FIGURE Data Interfacing Directly With Output
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Note Capacitive coupling between logic segment drivers used only when segment drivers turned ``OFF'' during digit-to-digit transistions
FIGURE Cathode Data Coupled From MOS-Output
Driving 7-Segment Discharge Display Tubes with National Semiconductor Drivers
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT NATIONAL SEMICONDUCTOR CORPORATION used herein Life support devices systems devices systems which intended surgical implant into body support sustain life whose failure perform when properly used accordance with instructions provided labeling reasonably expected result significant injury user
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critical component component life support device system whose failure perform reasonably expected cause failure life support device system affect safety effectiveness
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National does assume responsibility circuitry described circuit patent licenses implied National reserves right time without notice change said circuitry specifications

Driving 7-Segment Discharge Display Tubes with National Semiconductor

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