Questions tagged [ebers-moll]
For questions about the Ebers-Moll model for bipolar junction transistors (BJTs). Always use in conjunction with the "bjt" tag.
23 questions
0
votes
1
answer
141
views
On the gain of an NPN Common-Emitter Amplifier without emitter degeneration
I tried to get the voltage gain (\$ A_v \$) of a Grounded Common-Emitter (GCE) Amplifier (see Fig. 1), which in many electronic textbooks is provided (sometimes without showing some algebra) and is ...
- 11
1
vote
1
answer
68
views
Ebers Moll parameters for MPSA18 and AC128 BJT transistors
First of all, I should mention electronics is not my field so my problem might be trivial for you.
I'm currently working on my thesis and I need to model two BJT transistors: NPN MPSA18 and PNP AC128. ...
- 13
1
vote
1
answer
63
views
Determination of early voltage from the Ebers-Moll equation
I know that it can also be estimated by extrapolation, but I would like to determine the Early voltage from the Ebers-Moll equation.
The equation I want to use is:
Where Is = saturation current. Ut = ...
- 411
3
votes
5
answers
227
views
TAOE3, Exercise 2.13 -> Verify that a 8°C rise will cause grounded emitter BJT to saturate
I have a question about this circuit from the Art Of Electronics by Paul Horowitz & Winfield Hill, 3rd Edition, Figure 2.44 below. For reference, we just learned about the Ebers-Moll equations and ...
- 723
6
votes
6
answers
444
views
Effect of Vbe on Ic for a BJT
I am trying to find out where I have gone wrong in my understanding of BJTs:
According to the Ebers-Moll equation:
$$ I_C = I_S\cdot (e^{ \frac{V_{BE}}{V_T}}-1)$$
So if VBE decreases, then IC should ...
- 61
4
votes
3
answers
802
views
Early effect in simple current mirror
By "simple current mirror" I mean the following circuit.
Due to the Early effect the output current changes to some degree with output voltage. According to The Art of Electronics (3rd ...
- 1,094
5
votes
1
answer
437
views
What are the limits of the Ebers-Moll model for large currents?
I learned that the Ebers-Moll equation Ic = Is(T) ∗ exp(Vbe/Vt) "predicts" the collector current to rise exponentially with the base-emitter Voltage.
Experimenting with LTSpice for a LED ...
- 172
1
vote
2
answers
629
views
On the huge error between LTSPICE and Ebers-Moll when vCE=0 for a BJT
Let us assume that we have a npn BJT with parameters similar to 2N2222 in LTSPICE at T=27 C
The thermal voltage at T=27C is VT=25.865 mV
Let us assume that VCE=0 and VBE=0.85 V
From 2N2222 in LTSPICE ...
- 181
1
vote
3
answers
169
views
The small-signal impedance looking into the emitter when base voltage is not fixed
In section 2.3.2 of the 3rd edition of The Art of Electronics, the small-signal impedance looking into the emitter, \$r_\text{e}\$, for the base held at a fixed voltage is defined as "the ...
- 1,094
1
vote
1
answer
193
views
How do you use an LED's log V/I curve to force an exponential current change in the LED for a linear voltage change?
The info needed to make log and exponential converters with silicon is widely available. The saturation current, intrinsic resistances, and the Ebers-Moll equation are sufficient. A few other numbers ...
- 151
1
vote
1
answer
144
views
Do Ebers-Moll model cover all working modes of BJTs?
I mean the normal working modes (cutoff, forward/reverse active, saturation).
Or an other form of the question: Do Ebers-Moll cover the whole working domain of BJT (in potential and current values)?
- 205
1
vote
0
answers
223
views
What is value of Reverse Saturation Current (Is) for BC547B NPN transistor
I am trying to evaluate Ebers Moll equation for estimating collector current for a given V_BE at DC conditions. The datasheet of BC547B (which I am using) does not mention the Is (i.e. Reverse ...
- 11
1
vote
2
answers
1k
views
How to use Ebers-Moll equation to calculate collector current?
The Ebers-Moll equation is given by:$$I_C = I_S(T) * (e^{V_{BE}/V_T})$$
where \$V_T\$ = \$kT/q\$ = 25.3mV at room temperature. In TAOE (2.3.1), it mentioned
\$I_S(T)\$ is the saturation current of ...
- 1,448
1
vote
1
answer
359
views
Question on Ebers-Moll model
I have what should be a simple misunderstanding of a piece of text from "RF Circuit Design" by Lugwig. I am not in a class, just self-teaching. This book has been quite helpful, and I have not found ...
- 111
3
votes
1
answer
567
views
What part of Ebers-Moll equation shows the decrease of the collector current in saturation region
By looking at the Ebers-Moll equation for a BJT transistor:
Is this formula explicitly showing why Ic starting to decrease towards zero in saturation region. Which part of the equation shows that?
- 4,385
0
votes
0
answers
244
views
Reverse biased diode formula in Ebers-Moll model
As far as I understand in an PNP transistor the base voltage Vb is higher potential than the collector voltage. So since Vb>Vc the base collector junction is then reverse biased:
But in Ebers-Moll ...
- 1,504
5
votes
1
answer
653
views
Operation of BJT with low values of Vbe ("cutoff" region)
Many sources claim that when the base-emitter voltage becomes smaller than approximately 0.6V-0.7V, the bipolar junction transistor goes in the cutoff region and there is zero base and collector ...
- 163
0
votes
1
answer
3k
views
Saturation current in Ebers-Moll equations for BJT: what is it and how to measure it?
In Ebers-Moll Equations for common emitter BJT the inverse saturation current \$I_s\$ appears as a parameter. What is the saturation current \$I_s\$ exactly and how should I measure in a common ...
- 309
1
vote
2
answers
312
views
Ebers–Moll model aF? Where does it come from?
I am just getting back into electronics after a long while. For the life of me I can't figure where the \$\alpha_F\$ variable in the Ebers–Moll model comes from when you are calculating \$I_C\$ or \$...
- 199
3
votes
1
answer
564
views
An NPN BJT - from Spice to Ebers-Moll
Wikipedia reports a simple model for a BJT in active mode (an approximation to the Ebers-Moll model):
\$I_E=-I_{ES}(e^{V_{BE}/V_T}-1)\$
(in the NPN case). Here, \$I_{ES}\$ is the Base-Emitter ...
- 229
1
vote
1
answer
213
views
Which equation of the Ebers-Moll-Model is correct?
I'm confused.
In different sources sometimes I find the equation
\$ I_C = I_S\cdot\left(e^{\frac{U_{BE}}{U_T}}-1\right) \$
or like wikipedia
\$ I_C = I_S\cdot e^{\frac{U_{BE}}{U_T}} \$
Can ...
- 11
1
vote
1
answer
468
views
Collector currents of different BJT Models and Ebers-Moll
Per Horowitz&Hill book, the Ebers-Moll equation for the collector current in a BJT is:
Ic = Is (e ^ (Vbe/Vt) - 1)
where Ic is the collector current and Is is the saturation current.
Now, I am ...
- 31
0
votes
5
answers
1k
views
Can you find an analytic expression for the (beta)hfe of a BJT?
I understand there are two models \$I_c=\beta I_b\$ and $$I_c=I_s \exp \left(\frac{V_{BE}}{V_t}\right)$$ for a bipolar junction transistor.
However (correct me if I am wrong), I have not seen any ...
- 1,831