ACTIVE DEVICES
OBJECTIVES
To become familiar with basic Tubes
and Semiconductors
To be able to name their parts
To understand their basic function
To be able to answer exam questions
ACTIVE DEVICES
To be an active device, the component
must in some way control electron flow.
To be an electronic circuit (rather than
an electrical circuit) the circuit must
contain at least one active device.
ACTIVE DEVICES
Controlling electron flow means
controlling current and/or voltage.
Static Current = current-controlled
Static Voltage = voltage-controlled
Active Devices allow small signals to
control large signals.
Most common benefit of a control
circuit is AMPLIFICATION.
Classification of
Materials
INSULATORS - GLASS
- WOOD
- PLASTICS
CONDUCTORS - GOLD
- SILVER
- COPPER
- ALUMINUM
SEMICONDUCTORS - SILICON
- GERMANIUM
INSULATOR
No free Electrons to
move in orbit
Atoms require a
large amount of
energy input to allow
the electrons to
jump (conduct)
CONDUCTOR
Free electrons are flying about atom
Small amounts energy required to move
electron from one atom to the next
(conduction)
Electron Current Flow
SEMICONDUCTOR
Conductive impurities added to
insulators
SEMICONDUCTORS
Some Types:
Silicon
Germanium
Gallium Arsenide
ALMOST THE SAME AS AN INSULATOR
CONDUCTION (current flow) IS
CONTROLLED BY DOPING (IMPURITIES)
AND BY ELECTRIC FIELDS (BIASING)
Semiconductors
Impurities are added to the germanium,
silicon etc to create ‘flavours’ of each
variety (called doping). This makes
germanium or silicon with:
P type material (more positive, missing
a valence electron)
N type material (more negative,
additional valence electron)
Semiconductors
-JUNCTION-The point where the P and
N material meets
-BIAS- The polarity of the electricity
required to make current flow
-REVERSE BIAS- The polarity of the
electricity required to make current stop
flowing
DIODE
Anode- positive
Cathode - negative
Diode
Diode-
Equilibrium some holes move to
N region some electrons move to
P region and no current flows.
Creates depletion zone.
Diode- Zero Bias
no current flows in
circuit
Diode
Zero Bias
Diode- forward bias
current flows –ve to +ve
Diode – reverse bias
blocks current (or
unwanted signals)
Diode Voltage Drops
Cause by depletion zone. Once a diode
conducts you always measure the
same voltage across it
Silicon diode = 0.7v
Schottky diode =
0.3v
Germanium diode =
0.2v
DIODES
Simple P N junction semiconductor
Electrons build up in the depletion zone
until current flows (si .7v, ge .2 v)
Conducts in one direction (forward
bias)
Blocks current in reverse direction
(reverse bias)
Electrical equivalent to a valve (on/off)
DIODES
DIODES
Used as detectors of weak radio signals
(crystal radio) by taking high frequency
and converting to the envelope
Used to convert A.C. to D.C. (rectify)
Used as a voltage regulator (constant
voltage)
Used to block or isolate circuitry (in a
battery operated device it prevents
damage by reverse battery installation)
WhaT IS a transistor 1:20
Diode Rectifiers
½ wave rectified- pulsing D.C. (negative cycle
blocked)
Full Wave Rectifiers
Power supply. Centre tap transformer,
each diode conducts on half cycle.
Provides a D.C. output with ripple.
Full Wave Rectifiers
Bridge Rectifier- four Diodes each
Diode Bridge Rectifier
Each half cycle is rectified using two
diodes
Diode Rectifiers
Input A.C
½ wave rectifier
Full wave rectifier or
DC. This output is
filtered with
capacitors to make
as smooth as
required
Zener Diodes
Zener is designed to
be mounted
backwards (positive of
battery to cathode). In
forward bias it acts
like a normal diode.
Voltage Regulator Voltage remains
constant at output for
its designed value. (R
limits current), even
when input voltage
varies.
LED
light emitting diode
Emit light when current
flows through them.
Colour is dependent
on LED. Tri- colour,
two diodes
TRANSISTORS
All have three legs or
conductor leads
Collector
Emitter
Base (usually control)
Made from
semiconductor
sandwich
NPN or PNP
TRANSISTOR
TRANSISTOR MODEL
Base- small amount of
water goes in and lifts up
flapper
Collector has huge
reservoir of water
Flapper opens, water
rushes from collector to
the emitter
Base also adds water.
An increase in base
water forward biases the
circuit and amplifies with
the extra water
Transistor Types
Transistor Types and
Parts
Transistor
Configurations
Typically three types of configurations:
Common Emitter -both the signal
source and the load share the emitter
Common Collector - both the signal
source and the load share the collector
Common Base - both the signal source
and the load share the base
Transistor
Configurations
Common Emitter
Input base, output
collector. Amplifies
weak radio signals
Common Collector
Input base, output is
emitter. ( emitter
follower). Unity
output voltage but
follows input very
closely, good
current gain.
Transistor
Configurations
Common Base:
Emitter is input,
collector is output,
base is common
Used for audio preamps and VHF and
UHF due to its
impedance
matching
Transistor clip
How a transistor
works
First transisitor
FETfield effect transistor
A type of transistor
but leads called:
Drain
Source
Gate (controls)
FETS are normally
on and gate bias
(controls) flow.
(voltage at gate stops
the FET output)
Acts most like a
vacuum tube
MOSFET
metal oxide field effect
transistor
n-Channel JFET
p-Channel JFET
Field effect transistors
3:50
Advantages of
Transistors/FETS
Small
Inexpensive
Easily Manufactured
Good Amplification
Fast Switching
Low Power Consumption
Easily matches stages in circuits
IC’s (Integrated Circuits)
Entire circuits on a single substrate
(blanket)
Smaller chassis required
Reliable and reproducible results
Low cost
Require less power to perform the
control function
IC- complex circuits
build on a substrate
Semiconductors Worst
Enemies
HEAT- protected by heat sinks, fans, air
openings in cases. High power devices
require special coolants.
Static Discharge – protected by good
grounding in A.C. line, ground plates,
shields, straps (away from carpets)
EMF/EMI electromagnetic
frequency/interference. Protected by
grounding and shielding, circuit design.
PERFECT MACHINE
efficiency
TRUE MACHINE
Energy cannot be created or destroyed
AMPLIFICATION
Energy cannot be
created or destroyed
The amplified signal is
achieved by adding
another power source.
The transistor
(amplifier) takes this
power and uses it to
duplicate the input
signal and make it
larger
AMPLIFIER GAIN
A=GAIN
AMPLIFICATION
AMPLIFIED
Current
Voltage
Power
NOT AMPLIFIED
Resistance
Capacitance
Inductance
Commonly Amplified
Signals in Amateur Radio
AUDIO – 20 Hz – 20 kHz (high fidelity)
SPEECH – 300 –3400 Hz (radio audio)
RF (radio frequency) – 3 kHz –300 GHz
(allotted band within this range)
Microwave – 300 MHz – 300 GHz
(EHF)
Vacuum Tubes
Glass or metal tube with
air pumped out
(vacuum)
DIODE
Filament (heater)
Cathode (inner tube)
Anode (plate- outer
cylinder)
Grid ( grid acts as a
control - becomes a
triode)
Vacuum Tube Operation
Diode
Filament (Cathode) heats
Cathode emits electrodes
into the ‘space charge’
Anode surrounding
cathode is charged more
positively
Current flows from cathode
to anode
Creates a Rectifier – A.C.
becomes pulsating D.C.
Triode Amplifier
Addition of Grid between
plate and cathode
Grid made negative to
plate, and plate made
positive with respect to
cathode
Some electrons are repelled
back (feedback,heat give
amplification)
Grid very negative no
current (cut-off)
Grid less negative more
current flows
Rectifier Tube
Tube Advantages/
Disadvantages
Tubes provide amplification of infinite
harmonics for audio amps- warm rich sound
High power
Bulky
Dissipates large amounts of Heat
Costly
Fragile
Unreliable
Transistor vs Tube
(NPN Transistor and N-Channel
FET)
Transistor
FET
Triode
Input
Emitter
Source
Cathode/
filament
Output
Collector
Drain
Plate/
Anode
Control
Base
Gate
Control
Grid
Troubleshooting
Plugged in? Each individual assembly,
sub assembly, board or chip on board.
Turned on? Each individual assembly.
Inputs at each stage ok (connectors)?
Outputs at each stage ok (connectors)?
Power Supply (wall warts) , cord. Swap
it if you can’t measure it.
Batteries present, ok.
Troubleshooting
Look for burnt chips, swollen
components, bad/loose solder
connections, burnt cooper traces,
broken wires, burnt wires, bent pins.
Microprocessor equipment. POST
power on self test.
Resets, software or hardware switches,
power cycle/reboot.