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is a diode an active device or passive device

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Full Member level 3
Jul 11, 2005
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Hi all,
I have a simple question. Is the diode an active device or an passive device and why???

thanx in advance

Diode is an active device, since it can be used as an waveform generator (half wave rectifier, for ex).

Hence it is catagorized as active device.


Yes it is an active device since it requires an external power source, to operate it in forward or reverse bias.

It depends what is the meaning of "active".

If you mean unlinearity of the characteristics due to applied voltage - that is one case

But if meaning is ability to amplification that is different . Anyway, tunnel diode does amplification as well .

P.S. Sorry, i forget what does term "active" mean.))

it is an active device.since its impedence is positive,or v-i chara lies in 1&2 quadrants.

is it ok
with regards sabu

sabu said:
it is an active device.since its impedence is positive,or v-i chara lies in 1&2 quadrants.

is it ok
with regards sabu

if VxI on first and third quadrant ,power will dissipated for 2 and 4 quadrant power will be consumption
first and third quadrant ----->P=VxI or -Vx-I(nothing but VI)..leads to positive power will be released...doide belongs to this category
SECOND and foruth quadrant ----->P=-VxI or Vx-I...power will be consumed

It depends on what type of a diode you mean.
In most cases (rectifier, Zener, etc.) a diode is, no doubt, a PASSIVE device. Only in some special cases like with a tunnel diode, when its negative resistance region is used, it can be considered as an ACTIVE device.

Best Regards

"an activity" vs. "a passivity" of a device is exactly defined although the exact math evidence for a concrete device is not so easy. E.g. the activity of a linear N-port is determined by some particular properties of its immitance matrix (immitance = either impedance or admitance; so immitance matrices are Y, Z, H or G)
see also: Guillemin, E.A., Synthesis of Passive Networks, John Wiley & Sons, 1957

Very simplified:
passive devices only dissipate a power from an external source,
active devices have an ability of amplifying a signal at one port of the device and deliver it to another port of it, where a load is connected, ie. they have some power gain > 1 (power itself is taken from a power supply, of course)

Any non-linear device can be considered to be an active device, in that it is capable of providing incremental power gain. Of course, the power gain can only occur in the incremental (small signal) sense.

think simplely,
active device need power to bias them.then they can work as we want.

the most general reperesentation of a diod is aresiistor with aswitch or .7 volts battery , this combination is midway between passive and active .


If the i-v characterisitics of the diode are in region I and III, then it is a passive device (always dissipating power). I think most diodes fall into this category. Even in rectifiers, they are definitely not being used to amplify because they either are dissipating power (forward bias) or little power (reverse bias).

When I think of active devices, I usually, think of transistors that we can control by external stimulus (like a base current in a BJT or gate-source voltage in a FET).

Best regards,

I try to do the following categorisation:

All known devices are global passive because they dissipate power. If you bias a device at some operating point and consider only the signal derivation from this point you can amplify signal. So ouput signal power is greater than input power as in the case of bipolar transistor or MOS. Or the device could generate signal power. That is the case for a tunnel diode around the operating point. So active seems to apply for devices which could generate or amplify signal power but must spend DC power for that.

This is a problem puzzled me a long time . 3ks vertan replys .

A Device is said to be active if...

(i) It is a source of Power in the circuit...

(ii) It amplifies any voltage or current in a circuit...

(iii) It acts as a switch ie., has modes equivalent to ON and OFF...

e.g., transistor amplifies and can also act as a switch...

SO, diode is also said to be an active device.

Active device: Needs power to work
Passive device: Does not power to work.

Take Transistor. You have to amplify a signal. Consider an input signal with a very small power (negligible). So if you want to amplify that signal to a very high magnitude you need power. You get that power from the supply voltage from the battery (usually denoted as Vcc).
So that

Output power of the signal/ Input power of the signal can be >1 ( You should note that you get that additional power from the battery source).

Passive devices on the other hand won't amplify anything. They may give you impedence. They will never give you power. So they don't need power to operate.

So that

Output power of the signal/ Input power of the signal can never be greater than 1. ( As energy is dissipated in the form of heat in passive devices, Power gain will never be equal to 1)

Coming to diode. I am a bit confused though. I would say that a normal diode is a passive device. I am not sure. I think if you consider two or more diodes together it is indeed possible to make it an active device. For eg: Consider transistors which are made of diodes. So it can also come under active device.

I would suggest not to spent to much time to this question - it's a matter of definition only.

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