Diodes, LEDs, Transistors

What is a Diode

A fabricated P -M Junction Device

Diode Current Flow

Current flows in one direction

Diode Rectification

Converts AC into DC

Diode Connections

Anode - Connection P Type (Positive)

Cathode- Connection N Type (Negative)

Diode Symbol

An Arrow with a line drawn in front of it

• Back of the Arrow is the Anode

• Front of the Arrow is the Cathode

The line at the front of a diode represents the (Front or Back)

Front

Forward Baise is connect

Positive to the Anode

Negative to the Cathode

Reserve Bias

Positive to the Cathode

Negative to the Anode

Diode Materials and Voltage Drop

• Germanium Devices - 0.3-0.4 Volts

• Silicone Devices - .7 Volts

A Diode will not conduct Current until

A Greater the Barrier Volage is applied

Diode curve is

non-linear

Forward Bias behaves as a

• closed switch

Reverse Bias Behaves as an

• Open Switch

Diodes should always have a

• Series Resistor or Load to limit the amount of current

Damage maybe caused by the following

• Excessive heat, if current is not limited

What is used to prevent damage

Heat Sink

The bigger the Diode usually means

it can handle more power

Best way to check the direction of a Diode

Voltage Tester

What does LED Stand For

• Light Emitting Diode

LED must be connected

• long lead (Anode) to Positive

• Short Lead (Cathode) to Negative

Is LED Voltage Drop bigger or smaller then a Rectifier Diode?

• Bigger about 1.6v - 3v depending on the colour

Typical LED operating Current is

20mA

Calculating LED Voltage Drop

24v - 1.6v (LED) = 22.4 Volts

LED Anode and Cathode

• Long Lead= Anode (Positive)

• Short Lead= Cathode (Negative)

Types of Transistors

• TO 18 Case

• TO 220 Case

• Type 3 Case

How to identify a Transistor

When transistor is held with the leads facing you and down,

• Left lead is the emitter

• Right lead the base

The case of the Emitter is the

Collector

What are the 2 types of Transistor?

• PNP

• NPN

PNP Transistor connection must have

• Positive Voltage connected to the Emitter

• Negative Voltage connected to the Collector

• Base must be connected in the same polarity as the collector to forward Bias transistor

NPN Transistor connection must have

• Collector connect Positive Voltage

• Emitter connected to the Negative

Forward Bias Transistor