Semiconductor Fundamentals Unit 4 – Diode Wave Shaping and Zener Regulation
Exercise 2 – The Zener Diode
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to demonstrate the operation of a zener
diode by using a dc characteristic curve. You will verify your results with a multimeter.
DISCUSSION
- Reverse biased resistance of a diode is very large, so there is little current flow until
breakdown voltage is reached (where reverse current increases rapidly). Breakdown voltage
is also called avalanche or zener voltage and ranges from 3V to 200V. - Zener diodes are PN junction diodes designed to operate at the avalanche voltage.
- The schematic symbol for a zener diode has a Z-shaped line at its cathode.
- A zener diode has a forward voltage the same as a conventional diode.
- Dc characteristic curve for a zener diode, in forward bias, is the same as a rectifier diode. In
reverse bias direction, current flow is very small until zener voltage is reached. The knee of
the curve is the zener region (breakdown point). - Zener test current, specified by the manufacturer, is the current at which the zener voltage is
within the tolerance range. - The part of the curve where the current increases slowly with increases in the zener voltage is
the soft region. - At the stiff region of the curve, the current increases rapidly with very small increases in the
zener voltage.