active versus passive devices

7/30/2019 Active Versus Passive Devices

1/6

Active Versus Passive Devices

Active devices : the devices in which the electron flow( current) can be controlled

electrically.

Passive devices : the devices where electron flow ( current ) cannot be controlled

electrically.

Linear and Nonlinear generally applies to Active devices, even if there is no Passive

device perfect linear.

Following the above definition, diode is an Active device.

Electronic components are classed into either being Passive devices orActive devices. Active devices are different from passive devices. Thesedevices are capable of changing their operational performance, maydeliver power to the circuit, and can perform interesting mathematical

functions. While a device that does not require a source of energy for itsoperation.

What are Active Devices?

An active device is any type of circuit component with the ability to electrically

control electron flow (electricity controlling electricity). In order for a circuit to be

properly called electronic, it must contain at least one active device. Active

devices include, but are not limited to, vacuum tubes, transistors, silicon-

controlled rectifiers (SCRs), and TRIACs.


2/6

All active devices control the flow of electrons through them. Some active

devices allow a voltage to control this current while other active devices allow

another current to do the job. Devices utilizing a static voltage as the controlling

signal are, not surprisingly, called voltage-controlled devices. Devices working on

the principle of one current controlling another current are known as current-controlled devices. For the record, vacuum tubes are voltage-controlled devices

while transistors are made as either voltage-controlled or current controlled

types. The first type of transistor successfully demonstrated was a current-

controlled device.

What are Passive Devices?

Components incapable of controlling current by means of another electrical

signal are called passive devices. Resistors, capacitors, inductors, transformers,

and even diodes are all considered passive devices.

Passive devices are the resistors, capacitors, and inductors required to build

electronic hardware. They always have a gain less than one, thus they can not

oscillate or amplify a signal. A combination of passive components can multiply a

signal by values less than one, they can shift the phase of a signal, they can

reject a signal because it is not made up of the correct frequencies, they can

control complex circuits, but they can not multiply by more than one because

they lack gain.

Diodes

Diodes are basically a one-way valve for electrical current. They let it flow in one

direction (from positive to negative) and not in the other direction. Most diodes

are similar in appearance to a resistor and will have a painted line on one end

showing the direction or flow (white side is negative). If the negative side is on


3/6

the negative end of the circuit, current will flow. If the negative is on the positive

side of the circuit no current will flow. More on diodes in later sections.

Integrated CircuitsIntegrated Circuits, or ICs, are complex circuits inside one simple package.

Silicon and metals are used to simulate resistors, capacitors, transistors, etc. It is

a space saving miracle. These components come in a wide variety of packages

and sizes. You can tell them by their "monolithic shape" that has a ton of "pins"

coming out of them. Their applications are as varied as their packages. It can be

a simple timer, to a complex logic circuit, or even a microcontroller

(microprocessor with a few added functions) with erasable memory built inside.


4/6

First Transistor

TransistorsA transistor is a semiconductor device, commonly used as an amplifier or an

electrically controlled switch. The transistor is the fundamental building block of

the circuitry in computers, cellular phones, and all other modern electronic

devices.

Because of its fast response and accuracy, the transistor is used in a wide

variety of digital and analog functions, including amplification, switching, voltage

regulation, signal modulation, and oscillators. Transistors may be packaged

individually or as part of an integrated circuit, some with over a billion transistorsin a very small area - part of a trend of increasing transistor density known as

Moore's Law.

Transistor stands for transit resistor, the temporary name, now permanent, that

the inventors gave it. These semidconductors control the electrical current

flowing between two terminals by applying voltage to a third terminal. You now

have a minature switch, presenting either a freeway to electrons or a brick wall to

them, depending on whether a signal voltage exists. Bulky mechanical relays that

used to switch calls, like the crossbar shown above, could now be replaced with

transistors. There's more.

Transistors amplify when built into a proper circuit. A weak signal can be boosted

tremendously. Let's say you have ten watts flowing into one side of the transistor.

Your current stops because silicon normally isn't a good conductor. You now

introduce a signal into the middle of the transistor, say, at one watt. That changes

the transistor's internal crystalline structure, causing the silicon to go from an


5/6

insulator to a conductor. It now allows the larger current to go through, picking up

your weak signal along the way, impressing it on the larger voltage. Your one

watt signal is now a ten watt signal.

Transistors use the properties of semi-conductors, seemingly innocuous

materials like geranium and now mostly silicon. Materials like silver and copper

conduct electricity well. Rubber and porcelain conduct electricity poorly. The

difference between electrical conductors and insulators is their molecular

structure, the stuff that makes them up. Weight, size, or shape doesn't matter, it's

how tightly the material holds on to its electrons, preventing them from freely

flowing through its atoms.

Resistors

Capacitors

A capacitor is a passive electrical component that can store energy in theelectric field between a pair of conductors (called "plates"). The process of

storing energy in the capacitor is known as "charging", and involves electric

charges of equal magnitude, but opposite polarity, building up on each plate. A

capacitor's ability to store charge is measured by its capacitance, in units of

farads.


6/6

Capacitors are often used byengineersin electric and electronic circuits as

energy-storage devices. They can also be used to differentiate between high-

frequency and low-frequency signals. This property makes them useful in

electronic filters. Practical capacitors have series resistance, internal leakage of

charge, series inductance and other non-ideal properties not found in atheoretical, ideal, capacitor.

A wide variety of capacitors have been invented, including small electrolytic

capacitors used in electronic circuits, basic parallel-plate capacitors, mechanical

variable capacitors, and the early Leyden jars, among numerous other types of

capacitors.
http://rozgarsamachar.net/tag/engineer-jobs/http://rozgarsamachar.net/tag/engineer-jobs/http://rozgarsamachar.net/tag/engineer-jobs/http://rozgarsamachar.net/tag/engineer-jobs/

active versus passive devices

Documents