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Electronics Circuits – Multivibrator

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.
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Electronic Devices – Capacitor

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).
  • Ԑ o=dielectric constant(permittivity)of free space,
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Electronic Devices – Resistor

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

ColorDigit valueMultiplierMultiplied OutTolerance
Black01001 
Brown110110 
Red2102100 
Orange31031,000 
Yellow410410000 
Green5105100,000 
Blue61061,000,000 
Violet710710,000,000 
Gray8108100,000,000 
White91091,000,000,000 
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

Materialρ (Ωm) at 20°Cσ (S/m) at 20°CTemperature coefficient (1/°C) x10^-3
Silver1.59×10−86.30×1073.8
Copper1.68×10−85.96×1073.9
Gold2.44×10−84.10×1073.4
Aluminum2.82×10−83.5×1073.9
Tungsten5.60×10−81.79×1074.5
Zinc5.90×10−81.69×1073.7
Nickel6.99×10−81.43×1076
Lithium9.28×10−81.08×1076
Iron1.0×10−71.00×1075
Platinum1.06×10−79.43×1063.9
Tin1.09×10−79.17×1064.5
Lead2.2×10−74.55×1063.9
Manganin4.82×10−72.07×1060.002
Constantan4.9×10−72.04×1060.008
Mercury9.8×10−71.02×1060.9
Nichrome1.10×10−69.09×1050.4
Carbon (amorphous)5×10−4 to 8×10−41.25 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


Reference Website


Video tutorial

Basic Electricity – Resistance and Ohm’s law