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ELEC1

Introductory Electronics

System Synthesis

• Systems and Subsystems
       input
       input transducers
       process
       process subsystems
       output
       output transducers
       feedback ( sometimes )
• System Diagrams
       process boxes
       lines represent information flow
       analysis of whole systems into major subsystems
       analysis of subsystems into simpler subsystems

Signals

• Signals
       analogue
       digital

Basics

• Basic Electronics
       voltage (V)
       current (I)
       resistance (R)
       power (P)
       zero volt point in a circuit ( Potential and Potential Difference )
• Ohm's Law              R = V / I        V = I R        I = V / R
• Series Resistors       RT = R1 + R2 + R3 + ...
• Parallel Resistors     RT = 1 / ( 1 / R1 + 1 / R2 + 1 / R3 ... )
• Resistor E24 Values
• Resistor colour codes
• BS 1852 codes
• Power     P = I V      P = V² / R     P = I² R
• Power dissipated in resistors

Diodes

• Silicon diodes
       graph shape
• LEDs
       resistor calculations
       power calculations
       graph shape
• Zener diodes
       resistor calculations
       power calculations
       graph shape
• Interpret data sheets

Resistive Transducers

• Switch        ON: R = 0        OFF: R = ∞
       Digital output
       COM = Common
       NO = Normally open
       NC = Normally closed
• LDR
       Log graph scales
       Current limiting resistor
       Voltage divider
       Analogue Output
• Thermistors
       Log graph scales
       Current limiting resistor
       Voltage divider
       Analogue Output
       Negative temperature coefficient
• Potentiometer
• Voltage divider
       Analogue Output
       output is proportional to angle or position

Transistors and MOSFETs

• NPN switch circuits
• N Channel switch circuits
• Compare devices
       speed
       current gain
       input resistance
       Vbe = 0.7 Volts        V_ce= 0.2 Volts        V_ds = 0.02 Volts
• Back EMF diode in inductive circuits

Output Devices

• electromagnetic relays
• solenoids
• motors
•      back EMF diode in the inductive circuits above
• buzzers
• seven-segment displays

Operational amplifiers ( op amps )

• Summary
• Ideal Op Amp
       Inverting
       Non-inverting input
       Power supply requirements
       Output voltage swing limitations ( ideal and real )
       Saturation
• Comparator
       Analogue Input
       One Bit Digital Output
       Analogue to Digital Converter

Logic Gates

• NOT, AND, OR, NAND, NOR and EX-OR
       symbols
       circuits
       truth tables
• Combinational logic
• Boolean algebra
• Field Programmable Gate Arrays
       Make any gate from NAND gates
       Make any gate from NOR gates
• Simplify logic circuits or expressions
• Karnaugh maps

ELEC2

Further Electronics

Capacitors

• Capacitors
       store energy in the form of charge
       block a direct current
       allow the passage of an alternating current
       unit of capacitance is the Farad
       usually measured in pF, nF and µF
       working voltage
       polarisation ( electrolytic and tantalum capacitors )
       leakage current
• In Series       CT = 1 / ( 1 / C1 + 1 / C2 + 1 / C3 + ... )
• In Parallel    CT = C1 + C2 + C3 ...

Resistor Capacitor Timing Circuits

• The Time Constant and RC Timing Circuits
       T = R C
       V = 0.63Vs ( charging )    Vs is the supply voltage
       V = 0.37Vs ( discharging )    Vs is the supply voltage
       50% Charge or Discharge
            T = 0.69 R C
       100% Charge or Discharge
            Tt = 5 R C
       sketch voltage / time graphs for charging and discharging

555 Timer

• Inside the 555
• Monostable
       circuit diagram
       One stable state
       T = 1.1 R C
       How it works
• Astable
       circuit diagram
       No stable states
       How it works
       Low Time:     t_L = 0.7 R_B C
   
       High Time:     t_H = 0.7 (R_A + R_B) C
   
       Frequency:     f = 1.44 / (R_A + 2 R_B ) C

Sequential Logic

• bistable latch based on NAND gates
       operation
        function
• D-type flip-flop
       symbol
       operation
       function
• Shift Register
       circuit diagram
       operation
      applications
• Counters - Up to 4 bits
       Feedback to make a D-type flip-flop divide by 2
       Up counter
       Down counter
       Modulo-N counters
       Timing diagrams    

Number Systems

• Binary, Decimal and Hexadecimal
       convert a 4-bit binary number to decimal
       convert a 4-bit binary number to hexadecimal
       Binary Coded Decimal ( BCD )
       BCD decoder for a seven segment display

Operational Amplifiers

• ideal op-amp properties
       Input resistance = ∞
       Output resistance = zero
       Gain Bandwidth Product
       The product of voltage gain and bandwidth is a constant
• Gain = V_out / V_in
• Voltage bandwidth is the frequency range where Vout is at least 70% of the maximum
• Power bandwidth is the frequency range where Vout is at least 50% of the maximum
• inverting amplifier
       circuit
       Vout = - Vin Rf / Rin
       Gain = - Rf / Rin
       input resistance = Rin ( usually a low value )
       the inverting input is a Virtual Earth
• summing amplifier
       circuit
       Vout = - Rf ( V1 / R1 + V2 / R2 + V3 / R3 )
       input resistance = Rin ( for each input )
       the inverting input is a Virtual Earth
• difference amplifier
       circuit
       Vout = ( V₊ - V_- ) R_f / R₁
       input resistance = 2 R₁ ( usually a low value )
• non-inverting op-amp amplifier
       circuit
       V_out / V_in = 1 + R_f / R_in
       input resistance is equal to that of the op-amp
• voltage follower
       circuit
       applications
       voltage gain = 1
       current and power gain can be very large
       input resistance is equal to the resistance of the op-amp
• SUMMARY / Key Facts

Power Amplifiers

• Power bandwidth the frequency range where Power_out is at least 50% of the maximum
• Power gain = P_out / P_in
• MOSFET source followers ( N and P Channel )
       estimate the power dissipated in a source follower
       methods for removing the excess heat
• Heat Sinks
       Conduction - use a metal like aluminium
       Convection - have a large surface area to let the heated air rise
       Radiation - use a matte black surface to maximise heat radiation
• Push Pull Amplifier - MOSFET - BJT
       Estimate the maximum power output
       Advantages and Disadvantages
       Compare with a Class A single ended circuit
       Cross over distortion is reduced by
            biasing the MOSFETs with diodes and resistors
            including the MOSFETS in the negative feedback path
       Clipping, Limiting, Saturation
            The output is limited by the power supply voltage
            Increase the voltage but don't exceed the MOSFET ratings.