 | Author | Message | < Analog Electronic ~ Temperature-compensated zener diode | | eric | | Posted: Thu Oct 05, 2006 2:41 am Post subject: Temperature-compensated zener diode | | | | Site Admin Joined: 01 Jan 1970 Posts: 311 | G. Kleine
Only zener diodes rated at 6 V
have a negligible temperature
coefficient (TC). At lower ratings,
the coefficient becomes
negative, and at higher ratings,
positive. At a rating of 30 V,
the coefficient is 0.01% K–1,
and remains constant at higher
ratings.
The present transistor circuit
enables a positive TC to be
compensated by making use of
the negative TC (–2.2 mV K–1)
of the base-emitter junction
For instance, an 18 V
zener diode has a TC of
16 mV K–1, which is ×7.3 as
large as the TC of the baseemitter
junction in T1. This
gives a guide to the ratio of the
resistors in potential divider
R1-R2: R1 must be ×6.3 as
large as R2. If, therefore, R2 is
chosen as 1 kΩ, R1 needs to be
6.3 kΩ. Therefore, to obtain an
overall zener voltage of 18 V, a
zener diode rated at 15 V is
needed in the D1 position.
If the zener voltage itself is
not too critical, but it must be
unaffected by temperature
changes, variable compensation
may be obtained as shown in Figure
2 The potentiometer should
preferably be a 10-turn type.
The transistor in both cases
may be general purpose n-p-n
type such as the
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