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define: transistor - Google SearchWat is a transistor?
Actually a transistor [can be modeled as] a current controlled current source. The voltage stuff comes out because xxxxxxxxxx.A transistor is an electronic component used in a circuit to control a large amount of current or voltage with a small amount of voltage or current given to it.
Actually willbe, you have it backwards =) On an atomic scale the transistor is a voltage controlled device, the current is only because the junctions aren't isolated. This is however merely a technicality, you'll never see it taught that way in school. Unless perhaps you're going into advanced semi-conductor theory.
I'm sure you know the well-known relationsip between Vbe and emitter current (the diode equation). This relationship (voltage control mode) can be very useful, e.g. in making a logarithmic amplifier.No you have it wrong. On an atomic scale a bjt is a charge controlled device as is a FET. The bjt is a minority carrier device, whereas FETs are majority carrier. On the macro scale, bjt is current controlled, and FET is voltage controlled.
Every semiconductor maker and university in the world knows and acknowledges this.
SCIENCE HOBBYIST: how transistor works, an alternate viewpoint
Claude, you're mistaking 'charge controlled' to mean current controlled. Current is not required to flow for the semi conductor effect to exist. The fact that current has to flow in a BJT for it to function is only because of it's design, the voltage field itself is what is actually doing the work to switch the semi conductor's conduction state. It's easiest to visualize if you only look at a simple PN junction, it's the voltage causing the change in the depletion layer that causes current to flow in the diode. ALL semi conductor devices (SCR's BJT's FET's) work the same way, due to their internal construction though you get all the varried effects you see from different devices.
Again, this is completely academic and not required information to understand or use transistors in the real world because the model of the transistor as a current controlled device is more logical to the way it actually functions, do not mistake this for the REASON for it to function though.
I'm sure you know the well-known relationsip between Vbe and emitter current (the diode equation). This relationship (voltage control mode) can be very useful, e.g. in making a logarithmic amplifier.
Also see https://www.electro-tech-online.com/custompdfs/2009/04/log104-1.pdf
Charge = difference in the number of electrons/holes between two areas, this is voltage not current. It's is the STATIC charge that determines the state of a semi conductor junction. Charge is NOT current.Every semi maker classifies both FETs and bjts as charge controlled at the mIcro level
You used electric field to to describe what sets up the drift currents, again showing that it's the charge that's causing the current to flow.Now when an external bias is provided, the electric field results in drift current. But this electric field is a result of the external source, battery, or generator. The chemical energy conversion (battery) or mechanical energy conversion (generator) sets up the E field.
I didn't say otherwise, those currents are inherent in the structural design of a BJT heterojunction, the currents themselves however are NOT what cause the semi conductor to change conduction states it is in fact that Vbe that determines how a transistor functions, the currents that results from teh Vbe being forward biased are incidental to the reason for it's functioning even if they are what make it useful.Seting up a circuit in the lab with a reasonably good scope and signal generator will affirm the above. A change in base current precedes a change in collector/emitter current. At low frequencies it may be hard to see, but at high frequencies it's visible.
I see not one mention of a PN junction being controlled by a current anywhere.The p-n junction possesses some interesting properties which have useful applications in modern electronics. A p-doped semiconductor is relatively conductive. The same is true of an n-doped semiconductor, but the junction between them is a nonconductor. This nonconducting layer, called the depletion zone, occurs because the electrical charge carriers in doped n-type and p-type silicon (electrons and holes, respectively) attract and eliminate each other in a process called recombination. By manipulating this nonconductive layer, p-n junctions are commonly used as diodes: circuit elements that allow a flow of electricity in one direction but not in the other (opposite) direction. This property is explained in terms of the forward-bias and reverse-bias effects, where the term bias refers to an application of electric voltage to the p-n junction.
I'm just slightly confused why on multiple occasions in Claude's post he says that they're charged control devices and then proceeds to say that they're current controlled devices.
Charge = difference in the number of electrons/holes between two areas, this is voltage not current. It's is the STATIC charge that determines the state of a semi conductor junction. Charge is NOT current.
You used electric field to to describe what sets up the drift currents, again showing that it's the charge that's causing the current to flow.
I didn't say otherwise, those currents are inherent in the structural design of a BJT heterojunction, the currents themselves however are NOT what cause the semi conductor to change conduction states it is in fact that Vbe that determines how a transistor functions, the currents that results from teh Vbe being forward biased are incidental to the reason for it's functioning even if they are what make it useful.
The depletion region in a semi conductor PN junction IS the cause of the voltage imballance within the junction.
I see not one mention of a PN junction being controlled by a current anywhere.