A multivibrator is an electronic circuit that generates continuous square wave or rectangular wave oscillations. It is a type of waveform generator. It is commonly used in electronic circuits for various purposes. (Signal generation, timing, and pulse generation).
There are two main types of multivibrators: astable and monostable.
Astable Multivibrator:
An astable multivibrator is a free-running oscillator circuit that continuously switches between two states without any external input.
It has two distinct voltage levels, typically high and low.
The circuit consists of two cross-coupled amplifying devices (such as transistors or op-amps) and a feedback network.
The output waveform is a square wave. It’s an equal amount of time spent with each state.
Monostable Multivibrator:
A monostable multivibrator, also known as a one-shot multivibrator.
It has only one stable state.
Once triggered, it remains in the unstable state for a predetermined period before returning to the stable state.
Common applications include pulse generators, time delay circuits, and pulse-width modulation.
A capacitor consists of two conducting plates separated by an insulating medium. It can store electric charges, in the form of voltage in electric field. That blocks direct current. This opposes any sudden change of voltage applied to it. That only allows the Alternating current. That makes the time delay
C=Ԑ o Ԑr A / d farad A=area of each plate in m2,
d=distance between the plates in meter, Ԑr =relative dielectric constant(permittivity).
The resistor is a passive two-terminal electronic components. It function is to limit or reduce(resist) the flow of current or divide the voltage in a circuit. The unit of the resister is ohm(Ω). The resistance r of any material is proportional to its length and inversely proportional to its area of cross-section A.
R=ρl/A Ω
ρ=specific resistance or resistivity of the material.
Symbol
Type
Fixed Type
Wire wound resistor
Carbon film resistor
Metal film resistor
Carbon composition resistor
Carbon resistor
Film type resistor
Chip resistor
Variable Type
Rheostat
Potentiometer
Trimmer
Preset
Color Code
Color
Digit value
Multiplier
Multiplied Out
Tolerance
Black
0
100
1
Brown
1
101
10
Red
2
102
100
Orange
3
103
1,000
Yellow
4
104
10000
Green
5
105
100,000
Blue
6
106
1,000,000
Violet
7
107
10,000,000
Gray
8
108
100,000,000
White
9
109
1,000,000,000
Gold
±5%
Silver
±10%
Power
Measuring power across a resistor (Ohm’s Power Law)
Ohms Law
Ohm’s law describes the fundamental behavior of resistors.
LED Current Limiting
For example, assume you have a 9V battery to power an LED. If your LED is red, it might have a forward voltage around 1.8V. If you want to limit the current to 10mA, use a series resistor of about 720Ω.
Kirchhoff’s Law
Kirchhoff’s law can be used to analyses networks of resistors.
Resistor networks
Voltage Dividers
Resistivity properties of materials
Material
ρ (Ωm) at 20°C
σ (S/m) at 20°C
Temperature coefficient (1/°C) x10^-3
Silver
1.59×10−8
6.30×107
3.8
Copper
1.68×10−8
5.96×107
3.9
Gold
2.44×10−8
4.10×107
3.4
Aluminum
2.82×10−8
3.5×107
3.9
Tungsten
5.60×10−8
1.79×107
4.5
Zinc
5.90×10−8
1.69×107
3.7
Nickel
6.99×10−8
1.43×107
6
Lithium
9.28×10−8
1.08×107
6
Iron
1.0×10−7
1.00×107
5
Platinum
1.06×10−7
9.43×106
3.9
Tin
1.09×10−7
9.17×106
4.5
Lead
2.2×10−7
4.55×106
3.9
Manganin
4.82×10−7
2.07×106
0.002
Constantan
4.9×10−7
2.04×106
0.008
Mercury
9.8×10−7
1.02×106
0.9
Nichrome
1.10×10−6
9.09×105
0.4
Carbon (amorphous)
5×10−4 to 8×10−4
1.25 to 2×103
-0.5
Application of Resistors
variable resister is used in volume control in the TV application,
LED Current Limiting
Examples
Example 1
find the resistance of a copper wire of 0.75km long and having a cross sectional area of 0.01cm2. (take ρ=1.72×10-8ohm-m).
ANS=12.9ohm
Example 2
find the cross sectional area of an aluminium wire of 700m long and having a resistance of 0.24ohm (take ρ=2.83×10-8ohm-m)
ANS=8.254×10-5m2.
Example 3
if a R = 300 ohm is attached across the terminals of a V = 12 volt battery, then a current of (V/R)12 / 300 = 0.04 amperes flows through that.
Example 4 (Ohm’s law equations)
Consider a 1-ohm resistor in a circuit with a voltage drop from 100V till 10V across its terminals. What is the current through the resistor? The triangle reminds us that:
Example 5 (Ohm’s law equations)
Consider a 10-ohm resistor in a circuit subject to a current of 2 Ampere and a voltage of 120V. What is the voltage drop across the resistor? Using the triangle shows us that:
Answerer Thus the voltage at the end terminal is 120-20 = 100 V.
Example 6 (Ohm’s Power Law)
What must be the minimal power rating of this resistor?
Answer: According to the wheel, P=I^2*R= 0.100^2*50=0.5 W. So the minimal power rating should be at least 0.5W, but recommended is to go high above this value for extra reliability and lifetime.
Example 7 (Ohm’s Power Law)
What is the current in the circuit?
This is a basic example of Ohm’s law. Voltage and resistance are known, so we can calculate current with the equation: I=V/R=6/1.2=5 A.
Example 8 (Ohm’s Power Law)
An electric heater (resistor) with a consumption of 1kW is connected in a circuit with 8A current. What is the voltage drop over the heater?
Voltage can be expressed in current and power with the formula: V=P/I= 1000/8=125 V
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