1.1 Types of Resistors

• Fixed Resistors (Carbon Film, Metal Film, Wire-wound, etc.)
  
  

• Variable Resistors (Potentiometers, Rheostats, Trimmers)
  
  

• Special Resistors (Thermistors, Photoresistors, Shunt Resistors)
  
  

1.2 Resistor Selection Criteria

To select a resistor, you need any two of these four quantities:

1. Resistance (R)
   
   

2. Voltage (V)
   
   

3. Current (I)
   
   

4. Power (P)
   
   

Ohm’s Law:

V = I × R

Power Formula:

P = V × I = I² × R = V² / R

1.3 Example Calculation

For an LED circuit with:

• Voltage drop (V) = 3V
  
  

• Current (I) = 20mA (0.02A)
  
  

• Supply Voltage = 9V
  
  

Required Resistor:
R = (V_remaining) / I = (9V - 3V) / 0.02A = 300Ω

If a 300Ω resistor is unavailable, alternatives:

• Three 100Ω resistors in series: R_total = R₁ + R₂ + R₃ = 100Ω + 100Ω + 100Ω = 300Ω
  
  

• Using the next standard value: R = 330Ω
  
  

• Using an SMD Resistor with code ‘301’, which represents 300Ω.
  
  

2.1 Types of Capacitors

• Fixed Capacitors (Ceramic, Electrolytic, Film, Tantalum, etc.)
  
  

• Variable Capacitors (Trimmers, Tuning Capacitors)
  
  

• Supercapacitors (High Capacitance up to 12000 Farads)
  
  

2.2 Capacitor Selection Criteria

To select a capacitor, you need:

1. Capacitance (C)
   
   

2. Voltage Rating (V)
   
   

Capacitance in Series and Parallel

C_total, series = 1 / ( (1 / C₁) + (1 / C₂) + (1 / C₃) + ... )

C_total, parallel = C₁ + C₂ + C₃ + ...

2.3 Frequency Dependence

• Capacitive Reactance (X_C):
  X_C = 1 / (2π f C)
  
  

• Self-Resonant Frequency (f_res): The frequency at which inductive and capacitive reactance cancel out.
  
  

3.1 Types of Inductors

• Air Core Inductors
  
  

• Iron Core Inductors
  
  

• Ferrite Core Inductors
  
  

• Variable Inductors
  
  

3.2 Inductor Selection Criteria

To select an inductor, consider:

1. Inductance (L)
   
   

2. Maximum Current (I_max)
   
   

3. Saturation Current (I_sat)
   
   

Inductance in Series and Parallel

L_total, series = L₁ + L₂ + L₃ + ...

L_total, parallel = 1 / ( (1 / L₁) + (1 / L₂) + (1 / L₃) + ... )

3.3 Frequency Dependence

• Inductive Reactance (X_L):
  X_L = 2π f L
  
  

• Inductive reactance increases with frequency.
  
  

4.1 Voltage Divider Rule

Used to obtain a specific voltage from a larger voltage source.

V_out = V_in × (R₂ / (R₁ + R₂))

Example:
For a 9V input, if R₁ = 2kΩ and R₂ = 1kΩ,

V_out = 9V × (1kΩ / (2kΩ + 1kΩ)) = 3V

4.2 Current Limiting with a Resistor

• Resistors in series limit current.
  
  

• Resistors in parallel adjust resistance to control current.
  
  

I = V / R

5.1 Fuses (Overcurrent Protection)

• Fuses break the circuit when current exceeds a safe limit.
  
  

• Made of materials that melt without flames.
  
  

5.2 Varistors (Overvoltage Protection)

• Resistance decreases when voltage increases.
  
  

• Protects circuits from voltage spikes.