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transistor basics

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So...

Wat is a transistor???? :eek:

Hehe. Just kidding. :D

Here is a definition that seems to receive universal praise. Seriously, if you repeat this you will never be questioned.


A transistor is a 3-terminal semiconductor device useful for amplification and/or switching.
 
No claude, you haven't. Because electric fields do not require the transfer of energy to exist, they require the transfer of energy to be created not to maintain their existence, once the field is established energy is not required to be added to maintain the charge, this is the basics of how a FET functions however it is also the basis of how a BJT functions it's just hidden under the fact that those voltages cause currents to flow which have mathematical equivalents that are more useful than the voltage models.

The presence of the voltage field itself not the transfer of the charge carriers is what causes semi conductors to change conduction states. This is most readily apparent in FET's, but the same applies to BJT's, due to the non-isolated nature of BJT's though current will flow. Even in FETs some current will flow but this is because the real world is much more complicated than theory, it does not however change the fact that it is the ELECTRIC FIELD not charge transfer which causes the conduction state of a semi conductor to change. Charge difference is required to establish the voltage but this does NOT mean that the charge transfer is the cause of the semi conductor effect.

I would recommend again reading through this page. It explains it all pretty clearly.
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html
 
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No claude, you haven't. Because electric fields do not require the transfer of energy to exist, they require the transfer of energy to be created not to maintain their existence, once the field is established energy is not required to be added to maintain the charge, this is the basics of how a FET functions however it is also the basis of how a BJT functions it's just hidden under the fact that those voltages cause currents to flow which have mathematical equivalents that are more useful than the voltage models.

The presence of the voltage field itself not the transfer of the charge carriers is what causes semi conductors to change conduction states. This is most readily apparent in FET's, but the same applies to BJT's, due to the non-isolated nature of BJT's though current will flow. Even in FETs some current will flow but this is because the real world is much more complicated than theory, it does not however change the fact that it is the ELECTRIC FIELD not charge transfer which causes the conduction state of a semi conductor to change. Charge difference is required to establish the voltage but this does NOT mean that the charge transfer is the cause of the semi conductor effect.

I would recommend again reading through this page. It explains it all pretty clearly.
Transistor Operating Details

I've read this link before, and nowhere does it say that currents are caused by voltages. It covers the collector current in terms of Ib, Vbe, & Ie, which is what I've stated.

The electric field is provided by the external source. That is what I'm saying. Ib and Vbe do not provide the electric field. You keep reiterating that charges move in an E field. I already know that. But creating an E field requires work and that requires I and V both. Without both I and V, there would be no E field. The presence of the voltage means that work was already done creating the field. You're going in circles.

Take a bjt used as an amp. The dc bias point is established. Say this is a PA system application. When the singer sings, the acoustic power is transduced into electric power by the mic. Then the bjt stage provides both voltage and current gain. The power required to constantly change the E field is done by the singer. The changing E field represents changing energy, which is power. I and V must both be nonzero as power is I*V. Hence modulating an E field requires I and V both. Both I and V are produced by the work performed by the singer. I does not cause V, as V does not cause I.

It's too easy. You keep saying that V causes I, but have nothing to back it up with. Every aspect of this issue has been thoroughly examined for decades. You are not bringing new info.

All semiconductor makers can't be wrong.
 
Not to jump into the fray of your discussion, but was curious about your patent.

Regarding log amps, please refer to U.S. patent no. 5,670,775, which I received in 1997, for a unique log amo used w/ photodiodes. I am well aware of the logarithmic I-V relation in diodes. Cheers.

Did you obtain this through your company or was this a self funded venture? If the latter did the investment payoff.

Now back to your discussion :)
 
Electrical curriculum: What is Voltage?
Getting any closer Claude?
It's is the electric field that causes the semi conductor effect. That is all I'm saying.

I've read this link before, and nowhere does it say that currents are caused by voltages. It covers the collector current in terms of Ib, Vbe, & Ie, which is what I've stated.
The base-emitter voltage **broken link removed** can be considered to be the controlling variable in determining transistor action. The collector current is related to this voltage by the Ebers-Moll relationship (sometimes labeled the Shockley equation)
The currents CAN NOT exist without the bias voltages to produce the semi conductor effect to alter the conductivity of the material that allow the currents to exist.

Again let me state that in words that may clearly illustrate my point. NO CURRENT can flow until those electric field potentials are met. The charge transfer (current flow) required to establish those voltages again have no relation to the fact that the voltage field itself is what causes the transistor to change conduction states.
 
Not to jump into the fray of your discussion, but was curious about your patent.



Did you obtain this through your company or was this a self funded venture? If the latter did the investment payoff.

Now back to your discussion :)
Through the company. Yes, it paid off very well. For optical recognition of patterns, a log amp is very useful. This amp topology solved a long standing problem and made photodetection much easier. It uses a diode as a logging element.
 
Electrical curriculum: What is Voltage?
Getting any closer Claude?
It's is the electric field that causes the semi conductor effect. That is all I'm saying.

The currents CAN NOT exist without the bias voltages to produce the semi conductor effect to alter the conductivity of the material that allow the currents to exist.

Again let me state that in words that may clearly illustrate my point. NO CURRENT can flow until those electric field potentials are met. The charge transfer (current flow) required to establish those voltages again have no relation to the fact that the voltage field itself is what causes the transistor to change conduction states.

The currents cannot exist w/o bias voltage? I've stated that same thing repeatedly. Every electrical device known requires I & V. I can never exist w/o V. We both know that. But, hear me out, V cannot exist w/o I. Neither can exist independently of the other under dynamic conditions.

How does one establish Vbe? Since charges must be displaced in order to get a depletion layer, motion of charges occurs before the voltage builds. Ib chronologically precedes Vbe. But Ib is not the cause of Vbe, nor vice-versa.

Let's look at a simple p-n 2 terminal device, an LED. Is an LED a current-controlled light source, or voltage-controlled? Both I & V are indispensable, as the LED will not emit light w/o both of them. Conservation of energy requires that for every mW of optical output, at least 1 mW of electrical power input is needed, plus that to cover losses. The I*V product has to be non-zero so that power is non-zero. Fair enough?

But how shall we drive the LED? Let's say we wish to operate at 10 mA, and the forward drop at 10 mA w/ 25C temp is 1.8V, for a red LED. Shall we directly connect a 1.800V constant voltage source across the LED? If we do, then a temp increase takes place, resulting in a larger Is, reverse saturation current. Then If increases, resulting in a further Is increase. We have thermal runaway. Driving an LED w/ constant voltage is not done w/o a resistance in between.

With a constant current source, the Vf is incidental. As long as the current source has more than 1.8V of compliance, it works. Just as If = Is*[(exp(Vf/Vt))-1] it is also true that Vf = Vt*[ln((If/Is)+1)]. If we force 10 mA, Vf becomes 1.80V at 25C temp. When powered on, the temp will increase, so Is increases. But Is going up results in Vf going down. Thus thermal stability is achieved. An LED is inherently stable thermally when driven from constant current w/ the voltage being incidental. That is all I mean by "current controlled". It has nothing to do with causality.

If a power supply with constant voltage is employed to power said LED, if we insert a resistor, we get results like that of constant current drive. If the source is 12V, and the resistor is 1.0 kohm, then at 25C, the current If is (12.0-1.80)/1.0k = 10.2 mA. Should the temp increase, and Is increase, any increase in If results in an increase in the drop across the 1.0k resistor. Thus the LED forward drop Vf decreases. Thermal stability is achieved.

With a constant voltage source plus a large enough resistor, we get stability like that of constant current drive.

The same issues apply for all devices. Some non-linear devices work better when driven from a CVS (constant voltage source), while others are best used with a CCS. That is all implied here.

Does this help at all?
 
Also Claude, the depletion region is not a void, it has an electric field associated with it which is why it exists.

p-n junction - Wikipedia, the free encyclopedia

But it is void of free charge carriers. THe E field in the void does not produce current since no carriers are available. THe reason carriers transit across the depletion region over to the other side of the junction is because they have a velocity, approaching that of saturation. They continue across the junction and encounter lifetime and recombination when reaching the other polarity material. The E field in the bulk of the semiconductor acts on free carriers in the BULK imparting motion upon them. They attain a velocity limited to saturation value. At the junction boundary, the Vbe does not move these carriers. A hole transiting through p type material encounters the junction. The n type emitter has holes at the edge of the depletion region, but the p type base has electrons. A hole at the emitter edge will not attract a hole from the base, and likewise for electrons.

Thus the E field associated with h+ motion in the base, and e- motion in the emitter is due to the E field in the bulk, exerting force on charge carriers in the bulk, which is the only place such carriers are available.

You're convinced that Vbe and its associated E field is responsible for exerting force on the mobile carriers. That is not the case. The bulk region's E field liberates carriers from the bulk region. Ib and Vbe are both created due to the external signal/power source. Ib and Vbe are both indispensable. Neither exists w/o the other. Is this more clear?
 
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The currents cannot exist w/o bias voltage? I've stated that same thing repeatedly. Every electrical device known requires I & V. I can never exist w/o V. We both know that. But, hear me out, V cannot exist w/o I. Neither can exist independently of the other under dynamic conditions.
What about photodiodes? What about batteries?
Maybe the qualification "dynamic conditions" excludes them?
 
I at no point said the e field is responsible for exerting force on mobile carriers, it is responsible for the changes in the material that lets charge carriers become available. Also you need to clarify what you said, there ARE charge carriers in the depletion region they're just not available. An externally applied e-field causes the depletion region to cease to exist, no molecules move but the e-field causes the charge carriers to become available.

What I'm trying to explain is easiest to see in a mosfet. You have to charge the gate/source relative voltage to a specific voltage then the depletion region goes away. Once the initial current to charge the gate is done no charge carriers move and none are required to be supplied to keep the depletion region open which makes it an e-field effect not a moving charge (current) that actually causes the semi conductor effect. The same effect occurs in BJT's but for the e-fields to maintain themseves current has to be flowing because the junctions aren't electrically isolated, this does NOT mean that the current is what's causing the semi conductor effect. That's all I was ever arguing for.
 
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Roff, batteries create their own voltage from the chemical reactions in the cell. Photo diodes get their bias voltage from photons striking the P/N junctions providing enough energy to move the normally tied up charge carries into the conduction band.
 
Roff, batteries create their own voltage from the chemical reactions in the cell. Photo diodes get their bias voltage from photons striking the P/N junctions providing enough energy to move the normally tied up charge carries into the conduction band.
I know that. What I was questioning is the statement,
Every electrical device known requires I & V. I can never exist w/o V. We both know that. But, hear me out, V cannot exist w/o I.
 
What are you questioning? It is a well known property. What needs to be clarified? What is the beef? Just trying to be helpful. Cheers.
A shorted photodiode can generate current. An open-circuit photodiode can have voltage across it. So can a battery, or a capacitor. Your statement seems to be at odds with these facts. I'm not suggesting that you don't know about them.
 
A shorted photodiode can generate current. An open-circuit photodiode can have voltage across it. So can a battery, or a capacitor. Your statement seems to be at odds with these facts. I'm not suggesting that you don't know about them.

I know that. But only under static conditions. I stipulated dynamic conditions in my posts above. Did you catch the word "dynamic"? Under static conditions, I can exist w/o V, such as a superconducting inductor shorted, or V w/o I, as in a charged capacitor. But, only under static conditions. Ditto for a photodiode. But when either I or V changes wrt time, the other quantity cannot be zero. I've stated before the photodiode example exactly as you just did. It's well known.

Under static conditions, like the cap or inductor, the energy is static, i.e. dw/dt = 0. THus an energy static with time has a zero time derivative and hence a zero power. Thus one of the 2, I or V, must be zero.

But in dynamic cases, the energy changes wrt time. Thus dw/dt is non-zero and power is non-zero. Both I and V must be non-zero. So under **dynamic** conditions, I and V are mutually inclusive. In Master Yoda's lingo, "Always both of them will you find. Neither one can be without the other as well."

Master Yoda wouldn't pull your leg now, would he?
 
I don't disagree with anything you said. I had figured that "dynamic" was the key, but I wasn't sure what you meant by it. Now I do.:)
 
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