B9 - Section B9: Zener Diodes When we first talked about...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Section B9: Zener Diodes When we first talked about practical diodes, it was mentioned that a parameter associated with the diode in the reverse bias region was the breakdown voltage, V BR , also known as the peak-inverse voltage (PIV). This was a bad thing before – the whole avalanche breakdown, large current, overheating device and total destruction thing. .. Well, guess what? Under specific fabrication conditions, a diode may be created that will not be destroyed if the breakdown voltage is exceeded, as long as the current does not exceed a defined maximum (to prevent overheating). These devices are known as zener diodes and they are designed to have an avalanche characteristic that is very steep. The IV characteristic curve and diode symbols for the regular and zener diodes are given to the right (Figure 3.38 of your text). In the forward bias region, the zener behaves like a regular diode within specified current and/or power limits. The magic of these devices comes in when we get into the reverse bias region. As previously mentioned, the zener is designed to have an almost vertical avalanche characteristic at the breakdown voltage – hereinafter also called the zener voltage, and it is ideal for use in voltage regulation. The limiting (maximum) power for a zener diode is given by P z =V z I zmax and is a function of the design and construction of the diode. The knee of the curve (the current for which |v D |=V Z ) is generally approximated as 10% of I zmax , or I zmin =0.1I zmax . There are two distinctly different mechanisms that may cause breakdown in a zener diode: 1. Above approximately eight (8) volts, the predominant mechanism is avalanche breakdown , also referred to as impact ionization or avalanche multiplication . This process begins with thermally generated minority carriers that acquire enough kinetic energy to break covalent bonds and create an EHP through collisions with crystal atoms. The free carriers created through this collision contribute to the reverse current and may also possess enough energy to participate in collisions, creating further EHPs and the avalanche effect.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2. The high field emission or zener breakdown mechanism is the second method of disrupting the covalent bonds of the crystal and increasing the
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 02/14/2012.

Page1 / 5

B9 - Section B9: Zener Diodes When we first talked about...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online