Zener_Diode - Zener Diode A zener diode is a p-n junction...

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Zener Diode A zener diode is a p-n junction diode designed for stabilizing ( or regulating) i.e. keeping steady the output voltage of a d.c. power supply. Power supplies are needed to provide a d.c. output voltage for electronic circuits such as computers, telephone systems and radios. The symbol for a zener diode and its characteristic curve is shown. The characteristic curve shows that when forward biased, the zener conducts like an ordinary diode. However, it is normally used in reverse bias where the reverse current is negligible until the reverse voltage V R reaches a certain value, V z called the zener or reference voltage. Once V z is reached, the current suddenly increases and the voltage V z is maintained across the zener. For operation, the reverse current must fall between minimum and maximum values I zMIN and I ZMAX . A zener current below I zMIN will not turn the zener on, while a current above I ZMAX will destroy the zener. A minimum value of reverse current I ZK must be maintained in order to keep the diode in breakdown for voltage regulation. A nominal zener voltage V ZT is usually specified on a data sheet at a value of reverse current called the zener test current I ZT . All zeners come with ratings from the manufacturer such as the reference voltage V z and maximum power rating, P Zmax (where P Zmax = V z x I Zmax ).
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I F /mA I R /mA V F /V V R /V V Z @ I ZT I Zmin I Zmax Reverse Bias Forward Bias Electrical circuit symbol zener diode I ZK (zener knee current) I ZT (zener test current) I ZK (zener maximum current) (V z is usually specified at the zener test current I ZT , and is designated V ZT .) Zener Equivalent Circuit The figures show the ideal and practical models of a zener diode in reverse breakdown. V z (a) Ideal (b) Practical It has a constant voltage drop equal to the nominal zener voltage. This constant voltage drop is represented by a dc voltage even though the zener diode does not actually produce an emf voltage.
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The dc source simply indicates the effect of reverse breakdown is a constant voltage across the zener terminals. The zener impedance Z Z is included in the practical model of a zener diode. Since the actual voltage curve is not ideally vertical, a change in zener current ( I Z ) produces a small change in zener voltage ( V Z ) V R I R V Z  Z Z Z = V Z / I Z I ZK I ZM 0 By Ohm’s law the ratio of Z V to Z I is the impedance as expressed in the following equation Z Z z I V Z Normally Z Z is specified at I ZT and is designated Z ZT . In most cases the assumption is made that Z Z is constant over the full linear range of zener current values and is purely resistive. Example
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Zener_Diode - Zener Diode A zener diode is a p-n junction...

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