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Is Diode active device??

Discussion in 'Homework Help' started by chinusneha, Jan 8, 2010.

  1. chinusneha

    chinusneha New Member

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    Diode is active or passive and why???
     
  2. chinusneha

    chinusneha New Member

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    please explain whether diode is active or passive
     
    Last edited: Jan 8, 2010
  3. Miles Prower

    Miles Prower Member

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    A diode is definitely a passive device. It takes no power from a DC rail to convert the DC into another type of signal. Consider a crystal set: it requires no battery or other external source of power other than the RF it's demodulating.
     
  4. dave

    Dave New Member

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  5. Sceadwian

    Sceadwian Banned

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    Diodes are capable of acting as switches, in other words they are capable of controlling the electricity which is flowing through them, they even have linear regions which can be used for amplification though not nearly as good as a transistor, this makes them active devices. Using supplied power is not a pre-requisite of being an active device, however if you want to require that as a technicality of something being considered and active device the non-linear voltage/current graph and voltage drop of a diode exhibit that behavior.

    Everywhere I've looked there is only one definition for something to be called an active device, and that is.
    A diode meets that requirement. It is the simplest form of active device unless you want to consider air as an active device in a spark gap circuit =)
     
    Last edited: Jan 9, 2010
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello there,


    I assume we are talking about a regular diode, and not a special diode type like a tunnel diode.

    I was taught that in order to qualify as an active device, the device has to be capable of delivering an infinite amount of energy.
    That means voltage and current sources pretty much, and probably anything that can be made from voltage and current
    sources.
    A diode on the other hand, is a consumer of energy and therefore can not be an active device. Many people share this view also.

    Another interesting thing about active devices is that they can have a large range of DIFFERENT current levels for the EXACT
    same terminal voltage. For example, 5.000v and 100 amps, or 5.000v and 1 amp, with the very same device (by whatever
    means it takes). Passive elements can only approximate this behavior.

    My personal view is that anything (or it's model) that can supply energy is active, and anything that consumes energy is passive.
    This isnt 100 percent accurate but it seems more like what most people i've talked to over the years think.
    In other words, a power supply is active because it can deliver energy.

    Another thing to think about is: Is a light dependent resistor (LDR) an active element? See if you can answer this one too.
     
    Last edited: Jan 11, 2010
  7. Vizier87

    Vizier87 Active Member

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    I'll give it a shot..... yes? Since it covers photoelectric effect? (Waiting with eyes wide open)
     
    Last edited: Jan 11, 2010
  8. Sceadwian

    Sceadwian Banned

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    MrAl, I'm sorry but that has no basis in any information I've ever found, I have found no definition anywhere that requires an active device to use power, the ONLY requirement I am aware of to be called an active device is that the device must be capable of controlling the electron flow through it, which the diode qualifies for because it's two gate voltages determine weather or not it can conduct current, hence active. Passive devices aren't capable of controlling current through themselves. All semiconductors are active devices.


    LDR's are active devices, more obviously than a diode is.
    The main reason some sites reference a diode as being a passive device is because there's no way to separately control it's switching function, IE it has no gate. This does not however preclude it from being an active device as it controls electron flow, based on applied voltage.

    Power usage has absolutely nothing whatsoever to do with being called an active device. Please site any references you can find that say otherwise.
     
  9. Sceadwian

    Sceadwian Banned

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    Here's a link I found on wikianswers, which I'm assuming was garnered from an electrical engineering book, I wish I could find a refrence to it, but I believe active device has a much broader usage than the limited one you've given it.

    WikiAnswers - Why diode is active device when all other active devices require external power supply
    A diode can meet two of those requirements.
     
  10. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,


    Vizier:
    Let's talk about this a bit more.

    Sceadwian:
    You quoted from WikiAnswers, and who says that that site has the last word on
    what is an what is not anything? You are guessing that they got it from an
    electrical engineering handbook, but i know for a fact that i really did get
    my answer from an electrical engineering circuit analysis handbook (maybe
    there is one in digital form on the web somewhere that anyone might find?).

    I like their switch definition though, but then how about a regular switch...
    is that an active device too just because it can switch on or off?

    So what about an LED then? Is that an active device too?

    Perhaps it is better to think of a device as active or passive in a given
    circuit rather than try to define exactly if something is one thing or the
    other without reference to some actual circuit where it is used.
    For example, a transistor sitting unconnected on the bench top is not active,
    or how about a transistor that is in a circuit that controls it in such a
    way that between it's collector and emitter it behaves exactly like a resistor?

    Still, it's very hard to call an LED an active device.

    How about a light bulb?
     
    Last edited: Jan 12, 2010
  11. Sceadwian

    Sceadwian Banned

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    As far as an active device being a switch I wasn't quiet clear enough. The definitions I've found say to be called an active device under the switch definition you need to be able to electrically control an electric current. I would think that linearity of the switching point would come into question so a lightbulb doesn't count obviously, and in the usage of an LED it's not an active device in it's general usage, however in the Joule thieves that I've made they can cause the whole circuit to start blinking near the diodes conduction voltage limits and the batteries voltage recovery time causing the diode to become an active part in the rest of the circuit.

    So I guess what I'm really trying to say is that a diode can be an active device, however it's often used as a passive part of a circuit. Doesn't mean it always a passive device. Depends on the circuit and it's part in it. In the case of something like an AC fed voltage doubler it is very much an active device.
     
    Last edited: Jan 12, 2010
  12. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again Scead,


    Well i dont know, i tend to agree with you pretty much when we look at it as a switch. Maybe my book was being a bit less general that's all.
    I also agree that i think we should not try to classify every single device as being active or passive, one or the other, but should take into
    consideration other things like how it is being used or what context it is being used in. That makes the question, "Is it active or passive",
    a bit incomplete in itself. That's life i guess. Wikipedia takes this view too in a discussion about passive devices, and it's an interesting
    read. They talk about different forms of passivity.

    http://en.wikipedia.org/wiki/Passivity_(engineering)
     

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