Zero-Temperature Coefficient Reference Diodes MicroNotes 203, zen

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Zero-Temperature Coefficient Reference Diodes MicroNotes 203, zen

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Zero-Temperature Coefficient Reference Diodes
MicroNotes 203, zeners were described with their characteristic positive temperature coefficient herein) nominal voltages exceeding five volts. sensitive applications requiring precision voltage reference varying temperature environments, near zero significant value tightly controlling voltage beyond what zener provide itself. Special zener diodes that further designed have extremely have been identified zero-TC reference diodes simply reference diodes. Reference diodes made possible combining described positive zener series with more forward biased junctions that display negative Each forward biased junction typically contributes negative mV/° seen MicroNote 203, zener progressively increases positive magnitude zener diode voltage nominals increase above five volts. Since negative positive characteristics forward zener biased diodes approximately linear with increasing temperature, they judiciously combined into several series combinations near zero performance. voltage this reference diode configuration also becomes total zener voltage added forward voltages with junctions. Reference diodes very mature product packages such
DO-7 DO-35 JEDEC registered outlines. More recently they have also become available surface mount configurations such DO-213AA outlines often called MELFs. These packages typically rated range since their application significant power dissipation. This adequate applied power to100 when operated rated test currents with voltage nominals 11.7 volts. These conservative operating power levels then allow required power derating from elevated operating temperature range high 150° while providing near zero reference voltage performance IZT. Zero-TC reference diodes usually rated effective performance percent change nominal degree (%/° change over defined temperature range. Within reference diode product family, this often starts ±0.01 ±0.0002 some examples. these values significantly less than zener voltage regulator element itself which high +0.1 most often stated terms what historically been called method" This simply defines ratio maximum specified voltage change expressed percentage nominal divided overall operating temperature range been further defined many JEDEC military specs include specific temperature points standardized testing such 100° 150° These also dependent
overall temperature range specified reference diode. When testing these specific temperatures, greatest voltage change occur between temperatures rather than just temperature extremes (thus method). This suggests also nonlinear despite being expressed terms Nonlinear characteristics only recognized easily tight tolerance zero-TC reference diodes 0.001%/° less. such examples, voltage change sufficiently small over wide temperature range observe this possible characteristic. Since reference diodes with forward compensating elements affected operating current, important operate them very near their specified test current compared conventional zener diodes (see MicroNote 201). This important added operating condition achieve rated performance reference diodes. operating current exceeds IZT, will shift positive direction compared that observed IZT. operated below IZT, will shift negative example response curve popular 1N821 1N829 series versus operating current when
Figure Typical change temperature coefficient with change operating current 1N821 thru 1N829
Series
deviating from their nominal rating shown Figure Also additional voltage changes from dynamic impedance effects must also considered such applications where operating current held relatively constant shown Figure should apparent applications requiring very small voltage changes that well controlled constant current source desired optimum reference voltage performance. example method improving constant current regulation reference diode shown Figure initial zener higher voltage compared reference diode offers improved current control latter. Note that reference diode then determined (VZ1 VZ2)/RS2 where comparatively small operating current changes occur despite notable changes source voltage current first stage zener determined MicroNote VZ1)/ circuit shown Figure particularly useful when voltage changes line source (VS) would
Figure Example circuit improved current regulation reference diode zener voltage regulator
diode (VZ1 VZ2)/RS2. should also much lower than final regulated load resistance (RL) parallel with reference diode. Also proper operation. desirable reduce zener voltage regulator further constant current control over broad operating temperatures reference diode, zener also changed higher voltage reference diode than VZ2. some special applications where variation current must tolerated, reference diodes additionally specified behavior more than operating current. However this effectively requires comparatively small value often specified median operating current compliance greater values above below median. This also anticipated from example curve shown Figure With this predictable behavior, also suggests multiple operating currents seldom specified additional testing sufficient tight tolerance reference diodes selected used their rated centered within moderate variation. popular 1N821 1N829 reference diodes nominal volts designed with zener forward junction facing opposite directions. This with individual where both junctions integrated into individual p-n-p n-p-n) chip. These designs also available lower operating currents 0.5, 1.0,
1N4565 1N4584 series with slightly higher voltage nominal volts ±5%. Radiation hard options also available (see MicroNote 050). Additional voltage designs available with three forward biased junctions series compensate progressively higher zener voltages. These configurations have historically provided zero-TC reference diodes volt nominals with forward junctions, 11.7 volt with three forwards addition zener. JEDEC registrations 1N3154 1N3157A volts 1N935 1N940B volts 1N941 1N946B 11.7 volts There also current variants with nominal voltages volts volts. these basic designs also available chips single series stacks) hybrid applications. Special modularized multiple assemblies involving additional series combinations basic designs described herein also available achieve much higher voltage reference diodes. This provided 1N4057 1N4085 series with voltages progressively volts. These additive higher voltage designs placed into larger bodied axial leaded configurations convenient application with relatively minimal size penalties.
cause excessieu dode tons VZ2. zener voltage regulator
must greater than when selecting that desired operating current reference
Figure Typical change Zener voltage with change operating current 1N821 thru 1N829

Zero-Temperature Coefficient Reference Diodes MicroNotes 203, zen

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