Hi,
The nonlinear transfer curve shows always input current vs. output current.
An emitter follower has 0,6 V less on the emitter referred to the base.
Does that change with increasing collector-emitter current ?
The nonlinear transfer curve shows always input current vs. output current.
An emitter follower has 0,6 V less on the emitter referred to the base.
Does that change with increasing collector-emitter current ?
i dont know exactly what you are asking , if u are asking if the 0.6V voltage drop changes with current then yes it is ...
with higher current u have higher voltage drop 😉
with higher current u have higher voltage drop 😉
Yes, Vbe is a logarithmic funtion of Ic. Approximately, we have
Vbe = Vt * ln(Ic/Is)
where Vt = 26 mV at room temperature and Is is transistor dependent.
It is more common to see the inverse function
Ic = Is*e^(Vbe/Vt)
Vbe = Vt * ln(Ic/Is)
where Vt = 26 mV at room temperature and Is is transistor dependent.
It is more common to see the inverse function
Ic = Is*e^(Vbe/Vt)
Vbe of an emitter follower also changes with Vce, it gets lower as Vce is increased, thus emitter followers doesn't always follow the input signal as well as expected.
Thanks,
so the nonlinearity of the transistor is caused by the current depending
change of the average 0.6V voltage drop ?
I noticed that the transfer curve of a mosfet just goes into the other direction.
Is it possible to combine both to get a more linear device ?
so the nonlinearity of the transistor is caused by the current depending
change of the average 0.6V voltage drop ?
I noticed that the transfer curve of a mosfet just goes into the other direction.
Is it possible to combine both to get a more linear device ?
I recommend that you study the very basics of a transistor and a plain diode.. but a shortcut is to use some SPICE software and simulate, then you'll see how it look like in real life, of course without any forumals.
www.linear.com LTSpice useful freeware
www.linear.com LTSpice useful freeware
There are many different non-linearities in a transistor caused by various factors. There is no simple answer if you want to account for all of these. The equation I stated is the fundamental relationship in the transistor (ie. the BJT). As Eva mentioned, also Vce affects Vbe. That is because Vce, or to be more exact, Vcb, affects the base width and thus modulates the value of the "constant" Is, in the formula above. This effect also modulates hfe, ie. the Ic/Ib realationship, to vary with Vcb. However, hfe also varies with Ic, for at least two different reasons, which is why a plot of hfe against Ic is not a straight line. Then we have the base-collector capacitance which has a value which depends non-linearly on Vcb, making this capacitance effectively be modulated by Vcb. These are probably the major non-linearities.
BJTs and FETs (of whatever kind) will not cancel each others non-linearities, since the fundamental relationship (Ic vs. Vbe and Id vs. Vgs) is exponential for the BJT but polynomial for FETs. What might be possible in certain cases would be to make two BJTs cancel each other (or two FETs), but that is probably difficult to achieve in most cases.
BJTs and FETs (of whatever kind) will not cancel each others non-linearities, since the fundamental relationship (Ic vs. Vbe and Id vs. Vgs) is exponential for the BJT but polynomial for FETs. What might be possible in certain cases would be to make two BJTs cancel each other (or two FETs), but that is probably difficult to achieve in most cases.
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