Solid State University
Understand the following components:
Potentiometers
Thermistors
Capacitors
Diodes
Zener Diodes
Transistors
Potentiometers
Differentiate between potentiometers
and rheostats
A rheostat changes current flow in a series circuit
A potentiometer is a voltage sensor in parallel
Less resistance
Rheostat
More resistance
Rheostat
Potentiometer
Potentiometer
Very low current
4 volt
Potentiometer
Used as a sensor
2 volt
poor ground
Potentiometer
2.5 volt
(should be 2 volt)
open ground
Potentiometer
5 volt
(should be 2 volt)
Rheostats are wired in series with the load
their purpose is to change amp flow
Potentiometers sense motion
check for: reference voltage
good ground
un-interrupted signal
0.01
5.03
4.51
5.02
4.51 V
V
0.52
4.52 V
V
0.52
0.0 VV
MIL lamp lit. TPS code
What is wrong?
Thermistors
Thermistors change resistance with temperature
Negative Temperature Coefficient thermistors
decrease in resistance when they heat
Commonly used to sense changing temperatures
High Resistance
when Cold!
Low Resistance
when Hot!
Hot
or
Cold?
COLD!
4.52 V
Hot
or
Cold?
HOT!
1.53 V
1.15
1.45 V
Gauge reads colder than actual temperature
0.49 V
0.02
Gauge reads colder than actual temperature
0.47 V
Gauge reads colder than actual temperature
Thermistors
Thermistors are checked with an Ohmmeter
or a Voltmeter
A temperature probe or thermometer should
be used when checking
Capacitors
Capacitors store an electrical charge
Capacitors provide an alternate path for
electrons and act as a current “shock absorber”
Capacitors are commonly used to suppress noise
alternators
coils
motors
Capacitors
Capacitors are rated in microfarads
Capacitors are connected in parallel
with a load
they can be checked with an ohmmeter for
short or open circuits
Find the
Capacitor
EMI & RFI
When coils turn off they self induce and create a
voltage surge
this surge can create electromagnetic interference
and radio frequency interference
capacitors absorb this surge to dampen interference
Semiconductors
Conductors have 3 or fewer electrons in the
valence ring of the atom
copper has one
aluminum has three
Insulators have 5 or more electrons in the
valence ring of the atom
Semiconductors
Elements with four valence electrons are
not good as insulators or conductors
Silicon, when is a crystal form, shares
valence electrons to make a good insulator
Silicon can be “doped” to add electrons to
the valence ring or remove electrons from
the valence ring
Semiconductors
Silicon doped with phosphorous (which has five
electrons in the valence ring) will create an “N”
type semiconductor
Silicon doped with boron (which has three
electrons in the valence ring) will create a “P” type
semiconductor
Diodes
Placing an “N” type semiconductor with a
“P” type will create a diode.
In a forward biased diode current will flow
with a small amount of resistance
Too much current will overheat and destroy
the diode
Diodes
Reverse biasing a diode will create very high
resistance at the center of the diode and current
will not flow
Too much voltage will overcome the internal
resistance and the diode will short out
0.0 V
12.6
Arrow shows conventional theory (hole flow)
Diodes wired like this will block current
12.0
12.6
0.1 V
Arrow shows conventional theory (hole flow)
Diodes wired like this will allow current to
flow with a slight voltage drop
Testing Diodes
Diodes require .2 - .6 volts to forward bias
Digital ohmmeters may not supply this
voltage with ohm check
use diode check feature when using DVOM
Testing Diodes
Shorted diodes on alternators will allow A/C
voltage that may confuse a control module
Routine checks with oscilloscope are easy
Anti- Spike Diodes
Clamping or Anti-Spike diodes protect
sensitive control modules
Anti- Spike Diodes
Functioning anti spiking diodes will exhibit
un-equal resistance when reversing polarity
(using an analogue meter)
Failure in Anti- Spike Diodes
An open, or shorted diode will damage
computer control modules
Open diodes allow spike voltages to harm
electronic components
Shorted diodes (and relay coil windings) will
cause too much current to flow and burn out
switching transistors in computers
Testing Anti- Spike Diodes
Open diodes will show equal resistance
with reversed polarity (using an analogue
meter)
Shorted diodes will show equal, and low
resistance
Open Diode
Shorted Diode
Good Diode
Good Diode
Types of Diodes
Positive diode
Negative diode
Zener Diode
Light Emitting Diode (LED)
Transistors
Transistors can act as a relay
they use a small signal current to control
a larger working current
Transistors can act as a signal amplifier
PNP transistor
Points In Permanently
Will conduct current when the base sees a
Negative polarity
NPN transistor
Never Points In
Base must be Positive to allow transistor to
conduct current
Transistors
Transistors are damaged by too much current
Transistors are damaged by high voltage