Dwg. EP-059 Tungsten-filament incandescent lamps exhibit very-hig

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Dwg. EP-059 Tungsten-filament incandescent lamps exhibit very-hig

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PRIMER DRIVING INCANDESCENT LAMPS
Dwg. EP-059
Tungsten-filament incandescent lamps exhibit very-high positive temperature coefficient resistance with cold filament resistance being approximately filament resistance. When incandescent lamp initially turned cold filament minimum resistance will normally allow peak current. Within current falls approximately current. This high lamp turn-ON current (commonly called "in-rush" current), contribute poor lamp reliability destroy semiconductor lamp drivers. Even active part device output survive short-duration peak current, internal bonding wires "fuse" open. High-current drivers paralleled drivers, rated handle peak inrush current, prove cost prohibitive. simple methods shown here controlling lamp in-rush current standard power driver applications. Warming resistors (Figure protect both driver lamp preheating lamp between cold values. general recommendation provide warming current rated operating current. This will reduce in-rush current approximately Depending amount warming current, lamp "glow" might visible under low-light conditions. This method also provides reduced filament breakage vibration adds significant power consumption when lamp OFF. Alternatively, inexpensive current-limiting resistor (Figure used protect lamp driver, which will dissipate only small amount power when lamp minimum resistor value easily calculated VCE(sat) where rated lamp current rated peak driver current supply voltage VCE(sat) driver saturation voltage rated peak current rated lamp voltage
Figure Lamp "Warming" Resistor
Dwg. EP-059-1
Figure Current-Limiting Resistor
LIMITING
WARMING
PRIMER DRIVING INCANDESCENT LAMPS
NORMAL LAMP IN-RUSH CURRENT
SCALE
LAMP CURRENT
required resistor power rating determined filament current usually RS). slightly reduced lamp voltage, caused series resistor voltage drop RS), should have minimum effect lamp brightness will prolong lamp life. brightness important concern, supply voltage increased* compensate driver saturation voltage series resistor voltage drop alternatively, negative-temperature coefficient resistor used where cold resistance. Lamps also efficiently driven current-limited power drivers without need warming current-limiting resistors. These current-limited drivers listed below. With these drivers, during turn-ON, high in-rush current sensed internal low-value resistor and/or thermal-gradient sensing circuit. During this transition period, output stage driven linear fashion, limiting current while filament resistance increases value (Figure lamp current falls, output stage goes into saturation applies full supply voltage lamp.
CURRENT LIMIT
TIME
Dwg. WH-001-1
Allegro Channels Lamp Driver(s) Driver UDN/UDQ2543B UDN2547B
Maximum Current Limit Continuous Current Value
Figure Lamp Current Time
UDN2549B/EB UGQ5140K Hall
Some Allegro drivers, with over-current protection form fault latch UDN2987A), cannot used lamp driver applications except with stringent design efforts. applications controlling multiple lamp filaments, internal clamp diodes connected together through appropriate current-limiting resistor simple "lamp test" switch. side-effect with current-limiting method that lamp turn-on time will increase, generally this unimportant noticeable.
Multiplexed lamps must typically operated voltage times nominal operating voltage (where number digits), obtain sufficient brightness.
Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 Copyright 1994, Allegro MicroSystems, Inc.
PRIMER DRIVING INCANDESCENT LAMPS
reference, approximations, light output incandescent lamp (other than long life (>5000 hrs) halogen-cycle lamps) varies power applied voltage-to-design voltage ratio, lamp current varies 0.55 power voltage ratio, lamp life varies inversely 12th power voltage ratio (Figure
LIFE (VAPPLIED/VDESIGN)
NOMALIZED CHARACTERISTIC
CURRENT 0.55 (VAPPLIED/VDESIGN)
0.75
CANDLEPOWER
(VAPPLIED/VDESIGN)
0.90 0.92 0.94 0.96 0.98
APPLIED VOLTAGE/DESIGN VOLTAGE RATIO
Dwg. GP-048A
Figure Lamp Characteristics Reduced Voltage
PRIMER DRIVING INCANDESCENT LAMPS
Allegro MicroSystems, Inc. reserves right make, from time time, such departures from detail specifications required permit improvements design products. information included herein believed accurate reliable. However, Allegro MicroSystems, Inc. assumes responsibility use; infringements patents other rights third parties which result from use.
Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

Dwg. EP-059 Tungsten-filament incandescent lamps exhibit very-hig

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