How it a Transistor an active device? Because it it not producing energy. We just feed it with energy and it amplifies it and that too not on his own but using a bias battery. So how it is considered to be an active device? Please can anyone provide full explanation?
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9\$\begingroup\$ You simply misunderstand the meaning of the word "actiove". No reputable electronics source would take "active" to mean "must provide energy". \$\endgroup\$– Russell McMahon ♦Commented Jan 30, 2014 at 5:50
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1\$\begingroup\$ This is a really good question. It's a shame that none of the answers are satisfactorily convincing. The usual rhetoric I hear is that "transistors are active because they're in ICs and ICs need a power supply", but this doesn't apply to discrete transistors at all. Supercat's answer below is as close to satisfactory as I've ever heard, but it still sounds like a bit of a tautology: "they're active because they're not passive". \$\endgroup\$– PolynomialCommented Dec 3, 2016 at 13:08
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\$\begingroup\$ @Polynomial, I agree to you, however - what is your answer? To me, "signal amplification" capability is a good criterion for defining an active device. \$\endgroup\$– LvWCommented Mar 24, 2019 at 13:23
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7 Answers
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There are three(*) common ideal passive devices: resistors, inductors, and capacitors; the behavior of each establishes a precise ratio between voltage and either instantaneous current, the derivative of current with respect to time, and the integral of current over time. The behavior of a typical real-world resistor, inductor, or capacitor may be very accurately modeled as a combination of resistors, inductors, and capacitors wired together in some fashion.
(*) Some people argue for the existence of a fourth type of passive component, a "memrister", whose behavior would establish a ratio between the integral of voltage over time and the integral of current over time, but unlike the other ideal passive components which are well-approximated by real-world counterparts that don't require an outside power source, no memrister has been constructed that can come close to achieving that.
As for why transistors are considered active, it's because they're not resistors, inductors, or capacitors, and they do not establish a ratio among voltage and current, its derivative, or its integral
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3\$\begingroup\$ In other words: "active component" is used as synonyme for "component with nonlinear V-I relationship". Also a diode is considered an active component (which is even more counterintuitive because it is just either conducting or blocking; a behaviour which sounds quite passive). \$\endgroup\$– CurdCommented Jun 30, 2017 at 9:27
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\$\begingroup\$ Are you sure that a diode "is considered" an active element? Who says this? I am not convinced about this - is it a commonly agreed definition? I don`t think so. \$\endgroup\$– LvWCommented Mar 24, 2019 at 13:13
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\$\begingroup\$ To me, the term "active" involves "amplification properties". More correct: Conversion from DC power into ac signal output power. \$\endgroup\$– LvWCommented Mar 24, 2019 at 13:20
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\$\begingroup\$ @LvW: Diodes can be used in combination with AC voltage sources and passive components to amplify signals. \$\endgroup\$– supercatCommented Mar 24, 2019 at 16:25
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\$\begingroup\$ @supercat, can you provide an example, please? \$\endgroup\$– LvWCommented Mar 25, 2019 at 9:18
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Active component doesn't mean it can produce energy. It means the device needs energy to work and it can manipulate the given energy to the output.
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\$\begingroup\$ That doesn't explain much because it is not clear what you mean by "manipulate". E.g. a diode is an active component. How does it "manipulate the given energy to the output"? (It does; but it is not clear and you have to explain more). \$\endgroup\$– CurdCommented Jun 30, 2017 at 9:32
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1\$\begingroup\$ BTW: also resistors need energy to work. \$\endgroup\$– CurdCommented Jun 30, 2017 at 9:37
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That does not matter if it uses biasing to amplify input or not, the main thing here is that i can amplify the input.
see you cannot carry such operation with resister or inductors
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Basically, An active device is any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity). Thus, transistor is an active device.
Note that active device doesn't mean it just produces energy.
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 called voltage-controlled devices.
Devices working on the principle of one current controlling another current are known as current-controlled devices.
BJT is current controlled, while FET is voltage controlled active device.
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\$\begingroup\$ No - BJT`s are also voltage-controlled. (I know that several books are stating the opposite; they are wrong!). \$\endgroup\$– LvWCommented Mar 24, 2019 at 13:18
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In my understanding, MOSFETs or other active devices are called active because there are "sources" in their calculation models, a VCCS in small signal analysis for instance.Passive devices, however,do not incorporate any source.
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Basically, all, passive devices are ohmic devices or made of ohmic conductors. They follow ohm's law. Their resistance become constant and linear, once steady state of current flow is achieved. Then the I amps increases, when voltage is increased. If you plot I current in y axis, and V voltage in x axis, the plot is linear straight line with constant slope 1/R. Because ordinary circuits have ohmic conducting materials. But electronic circuits have semiconductors. Semiconductors, don't follow ohm's law. Initally semiconductors offer very high resistance for current flow, but beyond break open voltage of 0. 7 volts, they give way suddenly, losing their resistance completely, allowing large current to flow. So the plot graph will not be linear, and slope will not be constant. The circuit will not obey ohm's law. This peculiar property of the semiconductors, is being used to use them as amplifiers. After the break voltage, semiconductors, become super conductors, producing large current gain. But energy can't be produced by semiconductors. Energy is only provided by EMF voltage source, and it remains constant and obeys kirchoff II law. Accidental discovery of electrical property of a pure silicon crystal in bell's lab in New jersey, gave to the world semiconductors, transistors and ICs.
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1\$\begingroup\$ There is much confused thinking in this post. \$\endgroup\$ Commented Mar 24, 2019 at 13:41
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Active components absorb energy and convert to heat and passive components give their energy back to the circuit.
You can use op amps to integrate or differentiate signals.
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5\$\begingroup\$ By your definition a resistor is an Active component (it absorbs energy and converts it to heat) \$\endgroup\$– user16222Commented Jan 31, 2014 at 11:23