Basic Electronics CHAPTER 1 LECTURE 1 & 2 ENGR. KASHIF SHAHZAD

Course Details  Text Book: Electronic Principles 7 th Edition by Albert Malvino & David J Bates  Course Instructor: Engr. Kashif Shahzad   Cell:  Course homepage: 

Course Breakdown Assignments:10% Quizzes:10% Others:05% Mid Term:25% (2/3) Terminal:50%(8/12)

Course Outline Chapter #Chapter NameExam Question Number 1Introduction1 2Semiconductors2 3Diode Theory3 4Diode Circuits4 5Special Purpose Diodes5 6Bipolar Junction Transistors6 7Transistor Fundamentals7 8Transistor Biasing8 9AC Models8

Course Outline Chapter #Chapter NameExam Question Number 10Voltage Amplifiers9 12Power Amplifiers9 13JFETs10 14MOSFETs10 15Thyristors11 16Frequency Effects11 17Differential Amplifiers12 18Operational Amplifiers12

Introduction CHAPTER # 1

Three kinds of formulas The definition: The law: The derivation: Invented for a new concept Summarizes a relationship that exists in nature Obtained by manipulating other formulas using mathematics C = Q V {defines what capacitance is} Q = CV f = K Q1Q2Q1Q2 d2d2 {does not require verification} {verified by experiment}

RLRL 10 V An ideal voltage source maintains a constant output voltage, regardless of the value of R L. The ideal model can be called the first approximation. V R L = 10 Volts

RLRL 10 V A real voltage source has a series resistance. This model is called the the second approximation. RSRS V R L < 10 Volts When R L is equal to or greater than 100 times R S, a real voltage source is stiff and the first approximation can be used.

RLRL 1 A An ideal current source maintains a constant output current, regardless of the value of R L. The ideal model can be called the first approximation. I R L = 1 Ampere

RLRL 1 A I R L < 1 Ampere A real current source has a shunt resistance. RSRS This model is called the the second approximation. When R S is equal to or greater than 100 times R L, a real current source is stiff and the first approximation can be used.

Thevenin’s theorem can be used to replace any linear circuit with an equivalent voltage source called V TH and an equivalent resistance called R TH. 6 k  4 k  3 k  RLRL 72 V Remove the load. Calculate or measure V TH across the open terminals. V TH Remove the source.Calculate or measure R TH. R TH

The input impedance of a voltmeter should be at least 100 times greater than the Thevenin resistance to avoid loading error. When working with actual circuits, please remember this guideline: DMMs are usually not a problem since they typically have an impedance of 10 M 

6 k  4 k  3 k  RLRL 72 V 6 k  (R TH ) RLRL 24 V (V TH ) The original circuit The Thevenin equivalent circuit

Norton’s theorem can be used to replace any linear circuit with an equivalent current source called I N and an equivalent resistance called R N. 6 k  4 k  3 k  RLRL 72 V Short the load to find I N. ININ R N is the same as R TH. RNRN

6 k  4 k  3 k  RLRL 72 V The original circuit The Norton equivalent circuit 6 k  (R N ) RLRL 4 mA (I N )

THEVENIN & NORTON THEVENIN’S THEOREM: Consider the following: Network 1 Network 2 A B Figure 10.1: Coupled networks. For purposes of discussion, at this point, we consider that both networks are composed of resistors and independent voltage and current sources 1

THEVENIN & NORTON THEVENIN’S THEOREM: Suppose Network 2 is detached from Network 1 and we focus temporarily only on Network 1. Network 1 A B Figure 10.2: Network 1, open-circuited. Network 1 can be as complicated in structure as one can imagine. Maybe 45 meshes, 387 resistors, 91 voltage sources and 39 current sources. 2

Network 1 A B THEVENIN & NORTON THEVENIN’S THEOREM: Now place a voltmeter across terminals A-B and read the voltage. We call this the open-circuit voltage. No matter how complicated Network 1 is, we read one voltage. It is either positive at A, (with respect to B) or negative at A. We call this voltage V os and we also call it V THEVENIN = V TH 3

THEVENIN & NORTON THEVENIN’S THEOREM: We now deactivate all sources of Network 1. To deactivate a voltage source, we remove the source and replace it with a short circuit. To deactivate a current source, we remove the source. 4

THEVENIN & NORTON THEVENIN’S THEOREM: Consider the following circuit. Figure 10.3: A typical circuit with independent sources How do we deactivate the sources of this circuit? 5

THEVENIN & NORTON THEVENIN’S THEOREM: When the sources are deactivated the circuit appears as in Figure Figure 10.4: Circuit of Figure 10.3 with sources deactivated Now place an ohmmeter across A-B and read the resistance. If R 1 = R 2 = R 4 = 20  and R 3 =10  then the meter reads 10 . 6

THEVENIN & NORTON THEVENIN’S THEOREM: We call the ohmmeter reading, under these conditions, R THEVENIN and shorten this to R TH. Therefore, the important results are that we can replace Network 1 with the following network. Figure 10.5: The Thevenin equivalent structure. 7

THEVENIN & NORTON THEVENIN’S THEOREM: We can now tie (reconnect) Network 2 back to terminals A-B. Figure 10.6: System of Figure 10.1 with Network 1 replaced by the Thevenin equivalent circuit. We can now make any calculations we desire within Network 2 and they will give the same results as if we still had Network 1 connected. 8

THEVENIN & NORTON THEVENIN’S THEOREM: It follows that we could also replace Network 2 with a Thevenin voltage and Thevenin resistance. The results would be as shown in Figure Figure 10.7: The network system of Figure 10.1 replaced by Thevenin voltages and resistances. 9

THEVENIN & NORTON THEVENIN’S THEOREM: Example Find V X by first finding V TH and R TH to the left of A-B. Figure 10.8: Circuit for Example First remove everything to the right of A-B.

THEVENIN & NORTON THEVENIN’S THEOREM: Example continued Figure 10.9: Circuit for finding V TH for Example Notice that there is no current flowing in the 4  resistor (A-B) is open. Thus there can be no voltage across the resistor. 11

THEVENIN & NORTON THEVENIN’S THEOREM: Example continued We now deactivate the sources to the left of A-B and find the resistance seen looking in these terminals. R TH Figure 10.10: Circuit for find R TH for Example We see, R TH = 12||6 + 4 = 8  12

THEVENIN & NORTON THEVENIN’S THEOREM: Example continued After having found the Thevenin circuit, we connect this to the load in order to find V X. Figure 10.11: Circuit of Ex 10.1 after connecting Thevenin circuit. 13

The Norton dual 6 k  (R N ) RLRL 4 mA (I N ) 6 k  (R TH ) RLRL 24 V (V TH ) A Thevenin equivalent circuit R N = R TH I N = V TH R TH

Troubleshooting A solder bridge between two lines effectively shorts them together. A cold solder joint is effectively an open circuit. An intermittent trouble is one that appears and disappears (could be a cold solder joint or a loose connection).

An open device The current through it is zero. The voltage across it is unknown. V = zero x infinity {indeterminate}

A shorted device The voltage across it is zero. The current through it is unknown. I = 0/0 {indeterminate}

Semiconductors CHAPTER # 2

One valence electron The nucleus plus the inner electron orbits Core diagrams for copper and silicon: Four valence electrons Copper Silicon

Silicon atoms in a crystal share electrons. Valence saturation: n = 8 Because the valence electrons are bound, a silicon crystal at room temperature is almost a perfect insulator.

Inside a silicon crystal Some free electrons and holes are created by thermal energy. Other free electrons and holes are recombining. Recombination varies from a few nanoseconds to several microseconds. Some free electrons and holes exist temporarily, awaiting recombination.

Silicon crystals are doped to provide permanent carriers. Hole Free electron Pentavalent dopant Trivalent dopant (n type) (p type)

The free electrons in n type silicon support the flow of current. This crystal has been doped with a pentavalent impurity.

This crystal has been doped with a trivalent impurity. The holes in p type silicon support the flow of current. Note that hole current is opposite in direction to electron current.

Semiconductors The most popular material is silicon. Pure crystals are intrinsic semiconductors. Doped crystals are extrinsic semiconductors. Crystals are doped to be n type or p type. An n type semiconductor will have a few minority carriers (holes). A p type semiconductor will have a few minority carriers (electrons).

PN Junction Doping a crystal with both types of impurities forms a pn junction diode. Some electrons will cross the junction and fill holes. A pair of ions is created each time this happens. Negative ion Positive ion As this ion charge builds up, it prevents further charge migration across the junction.

The pn barrier potential Electron diffusion creates ion pairs called dipoles. Each dipole has an associated electric field. The junction goes into equilibrium when the barrier potential prevents further diffusion. At 25 degrees C, the barrier potential for a silicon pn junction is about 0.7 volts.

PN Each electron that migrates across the junction and fills a hole effectively eliminates both as current carriers. This results in a region at the junction that is depleted of carriers and acts as an insulator. Depletion layer

Forward bias The carriers move toward the junction and collapse the depletion layer. If the applied voltage is greater than the barrier potential, the diode conducts.

Reverse bias The carriers move away from the junction. The depletion layer is reestablished and the diode is off.

Diode bias Silicon diodes turn on with a forward bias of approximately 0.7 volts. With reverse bias, the depletion layer grows wider and the diode is off. A small minority carrier current exists with reverse bias. The reverse flow due to thermal carriers is called the saturation current.

Diode breakdown Diodes cannot withstand extreme values of reverse bias. At high reverse bias, a carrier avalanche will result due to rapid motion of the minority carriers. Typical breakdown ratings range from 50 volts to 1 kV.

Energy levels Extra energy is needed to lift an electron into a higher orbit. Electrons farther from the nucleus have higher potential energy. When an electron falls to a lower orbit, it loses energy in the form of heat, light, and other radiation. LED’s are an example where some of the potential energy is converted to light.

The p side of a pn junction has trivalent atoms with a core charge of +3. This core attracts electrons less than a +5 core. Energy Abrupt junction P-side Valence band Conduction band N-side In an abrupt junction, the p side bands are at a slightly higher energy level. Real diodes have a gradual change from one material to the other. The abrupt junction is conceptual.

Energy P-side Valence band N-side Conduction band Energy bands after the depletion layer has formed To an electron trying to diffuse across the junction, the path it must travel looks like an energy hill. It must receive the extra energy from an outside source. Energy hill

Junction temperature The junction temperature is the temperature inside the diode, right at the pn junction. When a diode is conducting, its junction temperature is higher than the ambient. There is less barrier potential at elevated junction temperatures. The barrier potential decreases by 2 mV for each degree Celsius rise.

Reverse diode currents I S, the saturation current, doubles for each 10 degree Celsius rise in temperature. It is not proportional to reverse voltage. The surface of a crystal does not have complete covalent bonds. The holes that result produce a surface-leakage current that is directly proportional to reverse voltage.