Subjects to cover
Basic Diodes
Signal Diodes
Switching Diodes
Rectifiers
Schottky Diodes
Germanium Diodes
Constant Current Diodes
Stabistors
Varactors
Diacs
TVS
High Efficiency Rectifiers
LEDs
Photodiodes
Voltage Reference Diodes
Germanium Diodes
Constant Current Diodes
Stabistors
Varactors
Diacs
TVS
High Efficiency Rectifiers
LEDs
Photodiodes
Voltage Reference Diodes
Zeners
Families of Zener Diodes
ICs
LM385
LM336
LM431
LM432
LM399
LM103
LM113
LM336
LM611
LED
IR
Red
Orange
Yellow
Green
Blue (6 Volt or higher power source)
UV (6 Volt or higher power source)
White (6 Volt or higher power source)
Packages
Leaded
Surface Mount
Fast, Super Fast, Ultra Fast...
Speed is relative. This is very much so with the technologic world of electronics. We must put
little value in part descriptions that define parts as Fast, Low Noise, Low Power and so on. What is Fast this
year will likely be mediocre five years from now. What is fast for a rectifier is not fast for a signal diode. A
few years ago National Semiconductor came out with a line of Op Amps that were fast. Since Super Fast
and Ultra Fast had already been used to describe previous generations NSC described this new line as being
“Damn Fast”. Gee, how can you get faster than that?
When you read data sheets that use such descriptions realize that unless the statement is followed
by numbers that quantify and qualify they are almost without meaning. Faster than what? Less noise than
what?
Light Emitting Diodes
All diodes emit some energy when forward biased. As holes combine with electrons in the
junction region energy is released. In most silicon diodes this is IR radiation. The frequency (color) of the
radiation depends on the chemistry of the material we use to make the diode.
Basics
Passing on all the rudimentary lessons we move straight to the schematic symbols and circuits
stage. Schematic symbols are fairly standardized. They may be found with circles around them in older
schematics. None the less you should be able to recognize the symbols. Mostly the symbol is made up of an
arrow pointing towards a bar. Current will flow in only one direction through the diode and not in the other
direction. Conventional current (positive charges) flow with the direction of the diode. This is true with all
semiconductor symbols.
(diode schematic symbols)
The signal diode or rectifier is the basic symbol. We have a modification of this basic symbol for
Zener Diodes, Schottky Diodes, Tunnel Diodes, TVS (Transient Voltage Suppressers) and so on.
Phraseology and symbols may vary somewhat between different manufacturers and cultures (Western,
Eastern and European).
Forward bias and reverse bias
Uses of basic diodes
AM detection
We can use them to remove an amplitude modulated signal from an RF signal.
(Example)
AC power rectification
We can use them to convert an AC power source into DC.
(Example)
Power Steering
(Line power vs Battery power)
(signal limiting diodes)
Logic
(Diode logic gates)
Diode characteristics
Forward Voltage Drop
When forward biased the diode will drop a fairly set voltage depending on the material the diode
is made of. Below an operational current the diode will drop very little voltage yet have a high resistance.
As current increases the diode starts dropping a higher voltage and current decreases. At full conduction the
voltage across the diode starts leveling out and increases little with an increase in current.
Our first diode exercise is intended to give a first hand demonstration of this.
(First diode exercise)
Reverse Breakdown Voltage
When reverse biased the diode has a high resistance up to the Breakdown voltage limit. Below this
breakdown voltage the only current the diode passes is Leakage current. This is due to minority current
carriers and impurities in the diode. Typically this is above 75 Volts for even small signal diodes. With
exceptions of course.
Turn on and turn off speed
Another primary characteristic is a question of how fast a diode can turn on and off. Turning on
usually isn’t a problem. We are applying force in turning a diode on. It is the turning off of a diode that
usually determines the speed limitations in semiconductors. Turning on puts current carriers in the junction
region. To turn off this junction region must be voided of current carriers. This is a slow drift of charges.
Turn on time is swift. Turn off time is slow.
Material
Silicon has been the most popular material to work in. A junction made of Silicon requires a
voltage of around 600 mV before the full point of conduction is reached. Germanium only requires a
voltage of around 400 mV. We can identify the material by measuring this voltage. If you did Diode
Exercise #1 you noted how much voltage we would typically find across a junction at any given current.
The voltages are consistent enough.
Exercises to do:
Basic Diode
1N4148
1N4448
1N914
1N4450
1N270 (Germanium Diode, = 1N34)
1N3600
1N400x (1N4001 through 1N4007)