Wats that supposed 2 mean?Voltage to Current Convertor
First, you must convert the input voltage to a current by using a Voltage to Current Convertor--a resistor.
Current to Voltage Convertor
Next, you convert the output current into a voltage by using a Current to Voltage Convertor in the collector circuit--you guessed it--a resistor.
The base region is narrow and is the least doped of the three regions. So base does not have much charge carriers. Henceapakhira said:1. Talking in terms of conventional current, in a PNP bipolar juntion transistor why doesn't the collector current get out thru the base since the base has lower potential, and instead goes thru the emitter?
It is good to have one. The base emitter region has a certain voltage rating. If you use a resistor in series with the base, it forms a potential divider. A potential diver of the Base-Emitter diode and your resistor. However in biasing circuits, resistors are not used in series with the base. The chief purpose of a transisitor is to amply signals. So it is biased in the active region with the help of a potential divider network. And the signal is applied to the base. This signal that enters the base in an AC(your signal) riding on a DC(the bias current).apakhira said:3. Do i need a resistor b4 the base if the current is low?
apakhira said:why doesn't the collector current get out thru the base since the base has lower potential, and instead goes thru the emitter?
"Reverse" w.r.t the base-collector region, right?Since these have come from another region, they are minority carriers in the base and are swept by the reverse bias field of the base emitter region. Swept from base to emitter.
Could u really xplain it that way? I mean it xplains why there's very low base-current, but it also means current would not flow even 2 emitter (if u try 2 make it look like 2 real diodes back2back)In other words, the transistor works (and is manufactured) much the same as a diode - TWO diodes, actually.
As you probably know, an ideal diode allows currrent to flow only in one direction.
the base-emitter r like the terminals of a short-circuited cell, but with a little resistor between the two, which keeps the PD across the terminals(Vbe) constant at 0.7V by varying its resistance in response 2 current thru the terminals (which is controlled by the biasing circuit). BUt the resistance, tho affecting PD CAN't affect current thru the terminals (wierd!). Am i right?
No. Reverse in it's own absolute sense. Once the electrons are in the base, it has nothing to do with the collector anymore. Since the base emitter region is reverse biased, the charge carriers in this region are swept from base to collector."Reverse" w.r.t the base-collector region, right?Since these have come from another region, they are minority carriers in the base and are swept by the reverse bias field of the base emitter region. Swept from base to emitter.
Actually, i was thinking of the forward biased diode as the wire with the small resistor connected 2 terminals of the imaginary cell. The "constant voltage drop irrespective of Vcc" i imagined 2 be due 2 the dynamically varying small resistor, which can change resistance when current increases (4 eg) 2 keep the voltage drop constant, but in the process it doesn't alter the current thru the terminals (coz its a "special" resistor). I guess it makes it more confusing. Ur POV is betterI am unable to follow what you mean by short sircuited cell... I look at it like a potential divider, where one element(forward biased diode) has a constant voltage drop irrespective of the Vcc or the value of other resistors in the network. This by no means means that you can have Mohms of resistance. You have to bother about the current as well. Over voltage causes breakdown.
I thoght the base emiiter region was fw biased, and the base collector region was reverse-biased? Isn't p connected 2 emitter of a PNP transistor? Pls explain.Since the base emitter region is reverse biased, the charge carriers in this region are swept from base to collector.
I thoght the base emiiter region was fw biased, and the base collector region was reverse-biased? Isn't p connected 2 emitter of a PNP transistor? Pls explain.
Why didn't you think of it as a zener diode instead?Actually, i was thinking of the forward biased diode as the wire with the small resistor connected 2 terminals of the imaginary cell. The "constant voltage drop irrespective of Vcc" i imagined 2 be due 2 the dynamically varying small resistor, which can change resistance when current increases (4 eg) 2 keep the voltage drop constant, but in the process it doesn't alter the current thru the terminals (coz its a "special" resistor).
See? That led 2 1 of the q's i asked b4. But maybe he's just saying, we need a PD across 2 terminals 4 current 2 flow?? What do u say? I'd say, current is more fundamental than voltage. Like, u 2 light a bulb, u need a specified amount of current thru. Put a series resistor in the circuit, and increase the PD 2 compensate 4 the extra voltage drop, so that current remains same, and the bulb'll light up as brightly as b4. The voltage rating in the bulb, is just so that we can put the rated PD across it and not worry about nething else--- otherwise they had 2 specify current requirement and internal resistance. Am i right? (Please, please let me be right this time, i've been wrong every time i wrote that sentence)If (+)voltage is applied to the p-type, to the base wire, while a (-) voltage polarity is applied to the n-type, to the emitter wire, then electrons in the n-type are pushed towards the holes in the p-type. The insulating layer becomes so thin that the clouds of electrons and holes start meeting and combining. A current therefore exists in the base/emitter circuit. But this current is not important to transistor action. What's important to notice is that the *VOLTAGE* across the base/emitter has caused the insulating Depletion Layer to become so thin that the charges can now flow across it.The depletion layer is a voltage-controlled switch which "closes" when the right polarity of voltage is applied.
Certainly Ic = hFE Ib is a useful formula, but if you study how a transistor operates, the collector current is controlled by the base - emitter voltage.apakhira said:2. Why is it said dat the magnitude of current thru the emitter-collector depends on base current and not base voltage (i though and I r interrelated?? OK i know transistors dont obey Ohms law, but its better if u xplained a bit)
Lucky me! They dont call me the best in Physics in my class 4 nothingYeah... you seem to have understood the current and voltage concept quiet well... I understood it this well in 2nd year B.Sc.
See? Thats what i was trying 2 speculate somewhere in the thread--u cant hav current w/o PD. But instead of using that super-big formula, can i just do something like this?:Certainly Ic = hFE Ib is a useful formula, but if you study how a transistor operates, the collector current is controlled by the base - emitter voltage.
From memory, it is Ic = Io(e^qV/(kT) - 1)
Where Io is a constant, q = the electron charge, V is the base emitter voltage, k is Boltzman's constant and T is the temperature in degrees Kelvin.
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