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 Potentiometer Very low current

2 volt Potentiometer Used as a sensor

2.5 volt (should be 2 volt) Potentiometer poor ground

5 volt (should be 2 volt) Potentiometer open 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 V 5.02 V 4.51 V 0.01 V

4.52 V 0.52 V

0.0 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 V Hot or Cold? COLD!

1.53 V Hot 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 V 12.0 V 0.1 V

Testing Diodes Diodes require 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

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