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

Rheostat

Less resistance

Rheostat

More resistance

Potentiometer

4 volt

PotentiometerVery low current

2 volt

PotentiometerUsed as a sensor

2.5 volt(should be 2 volt)

Potentiometerpoor ground

5 volt(should be 2 volt)

Potentiometeropen ground

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

5.03 V5.02 V4.51 V4.51 V0.01 V0.01 V

4.52 V0.52 V

0.52 V0.0 V 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!

4.52 VHot or Cold?COLD!

1.53 VHot or Cold?HOT!

1.45 V1.15 V

Gauge reads colder than actual temperature

0.49 V0.02 V

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

12.6 V 0.0 V

Arrow shows conventional theory (hole flow)

Diodes wired like this will block current

Arrow shows conventional theory (hole flow)

Diodes wired like this will allow current to flow with a slight voltage drop

12.6 V12.0 V 0.1 V

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