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Active Versus Passive Devices

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Electronic components are classed into either being Passive devices or Active devices. Active devices are different from passive devices. These devices are capable of changing their operational performance, may deliver power to the circuit, and can perform interesting mathematical functions. While a device that does not require a source of energy for its operation.

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.

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.

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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 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.

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Integrated Circuits

Integrated 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.

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First Transistor

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Transistors

A 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 transistors in 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 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

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Capacitors

A capacitor is a passive electrical component that can store energy in the electric 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.

Capacitors are often used by engineers in 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 a theoretical, 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.

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need more explanation on applications of all active and passive devices in ckt

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TANIMU SULEIMAN on February 27, 2012:

THANKS YOU FOR PROVIDED US WITH GOOD INFORMATIONS

Tanimowo on February 27, 2012:

Transit resistor still remain its name.

Diode is explain as clear as itself.

many others helps research work.

GOOD INFORMATION.

rp srivas on February 26, 2012:

good decribed satisfied

arpit on February 18, 2012:

short and sweet. good described..

but diode active or passive new confusion arises.....

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prasanjeet sarkar on January 26, 2012:

nice explanation with example

anjili on January 23, 2012:

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virs6 on January 23, 2012:

I'm confused about diode as a passive device as what you've stated above, while i've also read some information stating that diode is an active device.

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Goldi on November 28, 2011:

Thanks for giving information regarding active and passive component. Its very useful for me. Thanks again.

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Nagabhushan on October 09, 2011:

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swathi on September 19, 2011:

it is better to post the basic differenc between the element and device

ash on September 14, 2011:

i thought this whole electrical components were combined and put together in IC and would probably work independently bt i ws wrong it worked together forming chip

SARWAN KUMAR on September 12, 2011:

i mean to say more that u can have more than active devices in single circuit.

SARWAN KUMAR on September 12, 2011:

u can have two active devices in single circuit.

SARWAN KUMAR on September 12, 2011:

diode is an active diode not the passive one because these can change the waveform of the signal and it the one of the definitions of active devices.

SARWAN KUMAR on September 12, 2011:

Resistors also control the electron flow as they resist the electrons to limit the current to certain specific value though they are not called the active components. Explain why?

surbhi on August 24, 2011:

defination of active device &passive device must be in form of distingushed.

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good information , thank

nazim shah on January 15, 2011:

scr is the activwe componenet

vinod on January 04, 2011:

nice theory

Ahmed hamisu on November 20, 2010:

Thanks for ur concise information on active and passive devices

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ARUN KUMAR on November 10, 2010:

ITS VERY VERY INFORMATIVE.. THANKS....

matheen on October 07, 2010:

diode is a passive device and it also a non linear device....diode have only forward direction so it is a nonlinear and diode have only a two terminals not there other external terminal(pin) by sending a vcc so is a passive ....resistor,capacitors and inductor are only a liner other devices allare non liner because of there are effecting a input signals..........before elements are not effecting it just changing voltage ans current value not signals ..........yes i got it

nikoy on October 07, 2010:

nice Info

Rabbia on October 03, 2010:

please give a detail explanation of active and passive circuit with video

warubna on September 29, 2010:

good

..... on September 14, 2010:

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rahul malode on September 12, 2010:

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Amilcar Peres on April 28, 2010:

What is main reasonI cannot have two active devices in the same circuit?

regards,

Amílcar Peres

Captain on April 24, 2010:

It was use full. However many websites states that DIODE is an Active device.

Confused.....!

mandeep on April 22, 2010:

lc circuit can act as ossilator right???

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Keerthana on February 27, 2010:

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krishnaveni on January 22, 2010:

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Niteen on October 28, 2009:

short but sweet....thanks

AJISH on October 16, 2009:

VERY SIMPLE WORDS AND UNDERSTAND EASILY.THANKS FOR CREATION

Sam on August 18, 2009:

Not clear

Mandeep on August 11, 2009:

Hi,

Thanks for refreshing my knowledge about active and passive devices.

The information is very helpful.

Regards,

Mandeep

snehal on July 13, 2009:

good information

snehal on July 13, 2009:

good information

snehal on July 13, 2009:

good information

nivram on June 02, 2009:

diodes should be active devices right?

ezekiel on April 15, 2009:

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kevinbernard31 from Oregon, USA on November 29, 2008:

Lot of information on basic electronics. Got refreshed my knowledge of electronics.

guidebaba from India on November 15, 2008:

Nice Explanation aanaedwards.

quicksand on November 02, 2008:

I thought diodes were incorporated into integrated circuits, and were never used seperately in circuits as individual components.

Bill Souza on October 08, 2008:

I really like your website. It is very informative. I will come back and check out your upgrade.

Bill