What are active elements?
An active element is a component or a device in a circuit that is capable of generating or producing energy. In reality, energy is stored in the active elements in a non-electrical form that is then converted into an electrical form. Active elements can be categorized into current and voltage sources as both provide a drive to the circuit and manage the flow in it. Voltage sources are those sources due to which the voltage at the terminal is equal to the voltage present internally. On the other hand, current sources keep the terminal current same as that of the internal current. Thus voltage sources have series impedances that are relatively the same, while current sources would have shunt admittances almost equal to zero.
In an ideal voltage source, the current from the source varies depending on the load connected. Likewise in an ideal current source, the voltage across the source varies depending on the circuit parameters. However, it is not possible practically to construct an ideal source.
Sources can be classified into two types: mainly independent sources and dependent sources. In independent sources, the generated voltage or current does not rely on any other circuit voltage or current and the value is constantly unaffected. Whereas, dependent sources have a voltage that depends on any other circuit current or voltage.
Independent sources are those that generate electrical energy. The output voltage of an independent voltage or current source does not depend on any circuit element i.e. whatever load or passive element is attached, its value of energy dissipation will not alter. an ideal voltage source has zero internal resistance and can never be short-circuited.
The internal ideal current source has infinite internal resistance due to which maximum voltage drop is there and all of the current flows out into the circuit. It can never be open-circuited.
THE ABOVE TWO MENTIONED GRAPHS SHOW HOW A PRACTICAL INDEPENDENT CURRENT AND VOLTAGE SOURCE DIFFERS FROM THE IDEAL ONE.
Dependent sources, also referred to as controlled sources, do supply energy to the circuit but they rely on any other factor, either current or voltage, of the source for their functionality.
There are four further categories of how these dependent sources rely on other independent sources of the circuit or even any varying quantity such as current or voltage across a branch. These are usually represented by a diamond-shaped source that shows that it is dependent.
These descriptions are described as:
- VOLTAGE-CONTROLLED VOLTAGE SOURCE
- VOLTAGE-CONTROLLED CURRENT SOURCE
- CURRENT CONTROLLED CURRENT SOURCE
- CURRENT CONTROLLED VOLTAGE SOURCE
VOLTAGE-CONTROLLED VOLTAGE SOURCE (VCVS)
A voltage-controlled voltage source has its output a factor of times the voltage at any other point on the circuit.
Where α is a constant and Vx is the voltage across any given element.
VOLTAGE CONTROLLED CURRENT SOURCE (VCCS)
A voltage-controlled current source has its output a factor times to the voltage at any other point on the circuit. The output is current
Where β is a constant and Vx is the voltage across any given element.
CURRENT CONTROLLED CURRENT SOURCE (CCCS)
A current-controlled current source gives an output that depends upon the current flowing through any part of the circuit. The output current is
Where γ is a constant and Ix is the current across any given element.
CURRENT CONTROLLED VOLTAGE SOURCE:
A current-controlled voltage source gives an output that depends upon the current across any part of the circuit. The output voltage is
Where μ is a constant and Ix is the current flowing in the circuit taken into consideration.
There are a number of active elements that are both independent and dependent and so they contribute to the circuit by providing a flow into it.
Some of them are mentioned below:
- Ø Power supply
- o A.c
- o D.c
- o Batteries
- Ø Generators
- Ø Transformers
- Ø Transistors
- Ø Operational amplifier
And many more.
This report gives a brief description of how these elements function thus completing the circuit.
A power supply is a device that supplies electric power to an electric load. It controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or voltage supplied by the power supply’s energy source.
Common examples of this include
- Power supplies that convert ac line voltage to dc voltage.
- Energy storage devices such as batteries and fuel cells.
- Electromechanical systems such as generators and alternators.
- Solar power.
AC POWER SUPPLY
An ac power supply typically takes the voltage from the main supply and makes it to the desired voltage. It is actually the sinusoidal waveform that comes as an input to the circuit.
DC POWER SUPPLY:
It is a straight-line wave form that is constant and is rectified form of the A.c supply. Batteries give DC supply. Mobile phones operate on dc supply.
A battery is a device that converts stored chemical energy to electrical energy. USES:
Energy sources in many households.
There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times.
Batteries come in many sizes, from miniature cells used in hearing aids and wristwatches to room-size battery banks that serve as backup power supplies in telephone exchanges and computer data centers.
The electric generator works over the principle of converting mechanical energy, provided by the external system, into electrical energy by the principle of magnetic induction. They provide power that runs machines in factories, provides lighting, and operates home appliances.
The size of large generators is usually measured in kilowatts. One kilowatt equals 1,000 watts.
There are two main types of generators.
Direct-current (DC) generators produce an electric current that always flows in the same direction.
Alternating-current (AC) generators, or alternators, produce an electric current that reverses direction many times every second.
Both kinds of generators work on the same scientific principles. But they differ in the ways they are built and used.
Transformers work over the principle of magnetic induction. there are two types of winding namely primary and secondary. When a current is supplied to the primary winding a magnetic flux is generated in the coil and by the law of magnetic induction and continuous change in magnetic flux, a voltage is induced at the secondary coil which is used as the output.
The number of turns of the coil usually contributes by increasing or decreasing the output voltage. This is known as:
· Step up transformer: where voltage is increased at the output terminal.
· Step down transformer: that reduces the voltage at the output terminal.
According to a website following description of the transistor and its working is shown.
Transistors are semiconductors found everywhere in electronic circuits. They are used as amplifiers and switching devices. As amplifiers, they are used in high and low-frequency stages, oscillators, modulators, detectors, and in any circuit needing to perform a function. In digital circuits, they are used as switches.
Being forward or reverse-biased, a transistor allows current to pass through or even oppose it depending upon its placement. Moreover, it depends upon the base current flowing.
Some types of transistors are:
- Bipolar junction transistor
- Field- effect transistor
- Diffusion transistor
- Unijunction transistor, etc
OPERATIONAL AMPLIFIER (op-amp):
An operational amplifier is a device used to compare between two voltages being input into it and amplify it.
It is used as
It compares the two voltages that can be monitored in terms of temperature change or light dependency as well. It involves the usage of negative feedback where one output is used as an input next time.
It uses negative feedback but not all of the output voltage is fed back into the inverting input (-)
Here the input voltage is applied to the non-inverting input; part of the output voltage is fed back to the inverting input.
Thus, by op-amp usage, the gain is increased to a higher value but it is made sure that the overall gain is almost the same due to which distortion is less and the signal remains constant for large. frequencies as well.
Gơ=output voltage/input voltage
An ideal op-amp has the following characteristics:
1. Infinite open loop gain voltage(no feedback used)
2. Infinite input resistance(no current drawn from supply)
3. Zero output resistance(no internal resistance no voltage drop)
4. Infinite bandwidth(same over large frequencies)
5. Infinite slew rate( time delay between input and output)
6. Zero noise contribution