Facebook
Google
GitHub
LinkedinDiscrete Semiconductor Devices and Circuits
Zener Diodes
23 questions By Tony R. Kuphaldt
-
Question 19 of 23
Prior to the advent of zener diodes, gas-discharge tubes and bulbs were commonly used as voltage regulating devices.
Explain how such a device regulates voltage, and comment on whether or not this type of device is still practical in modern circuit design.
Reveal answerGas discharge devices, like zener diodes, exploit the sharply vertical portions of their current/voltage transfer functions to regulate voltage over a wide range of current:
Notes:The gas discharge lamp’s transfer function may be confusing to analyze at first, but it makes sense once students recall the principle of gas ionization with increasing voltage. Ask them to explain what the significance of each graph’s vertical portions is, in the context of voltage regulation.
-
Question 20 of 23
Precision voltage reference regulators are often constructed of two zener diodes connected in series like this:
Explain why two zener diodes provide greater stability than a single zener diode would, and also draw a circuit showing a voltage source, so this component functions as a complete voltage reference.
Reveal answerTwo zener diodes provide better stability than a single zener diode because the thermal coefficients of the diodes in their respective modes are complementary. This assumes, of course, that the reverse-biased diode uses the avalanche effect to regulate voltage.
A functioning voltage regulator circuit might look like this:
Notes:Some students may become confused by the word “complementary” as it is used in the answer. Ask all your students to explain what this word means, in the context of two temperature coefficients and increased stability.
-
Question 21 of 23
It is possible to purchase oven-stabilized zener ICs (integrated circuits). Explain what these are, and what they are useful for.
Reveal answerOven-stabilized zeners are used for precision voltage references. I’ll let you research how they are constructed and how they function.
Notes:Challenge your students to show you a datasheet for one of these devices!
