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Electronics 101.4: Diodes

SCHOOL OF MAKING

Electronics 101.4:

Diodes

Electricity’s one-way street

o far we’ve looked at resistors,

capacitors, and inductors. These all

work in a pretty straightforward way.

With this part of the series, we’re

going to venture into something quite

different: semiconductors. We’ll start

with the simplest: the diode.

Diodes are physically simple, yet electrically very

interesting. Resistors, capacitors, and inductors are

what we call linear components. A resistor is the

classic example: double the voltage across it and

the current through it doubles.

A diode is a non-linear component; the first

we’ve had a close look at (the LED is, in fact,

a diode, and we used one in issue 9). It’s also the

first semiconductor we’ve had a close look at.

A diode is polarised. If you recall, resistors are not

polarised; it doesn’t matter which way you connect

them. We found that some capacitors are polarised,

and some aren’t; it depends on how they are

constructed. Diodes are always polarised. You may

have noticed that LEDs only work one way around.

That’s because they’re diodes.

First, how is it non-linear? Have a look at Figure 1.

It shows the current vs. voltage for a resistor. You

can see that when the voltage is doubled in either

direction, the corresponding current doubles. Now

look at Figure 2. It’s the same current vs. voltage

curve for a diode. It should be clear that it’s not

linear. In fact it’s a very different behaviour.

Between the two knees of the curve (at Vbd and

Vd) practically no current flows through the diode.

S

YOU’LL NEED

Solderless

breadboard

Two different

voltage power

supplies

(e.g. 5 V and 3.3 V or

battery holders with

a different number

of AAs)

A few 1N4001 and

1N4148 diodes

Some LEDs

Various resistors,

from 100 Ω to 1 kΩ

Jumper wires, etc.

Dave Astels

daveastels.com

Dave’s career started

in the 8-bit days, with

the Z80 and 6502, and

he’s been working with

computers ever since.

Check him out at

daveastels.com and

learn.adafruit.com

Figure 1

Resistor’s linear current vs.

voltage curve

I

V