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Questions tagged [ebers-moll]

For questions about the Ebers-Moll model for bipolar junction transistors (BJTs). Always use in conjunction with the "bjt" tag.

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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 ...
AJ_Smoothie's user avatar
6 votes
6 answers
329 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 ...
Xavier's user avatar
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4 votes
3 answers
690 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 ...
apadana's user avatar
  • 1,052
5 votes
1 answer
395 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 ...
ChristophK's user avatar
1 vote
2 answers
557 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 ...
Aria's user avatar
  • 181
1 vote
3 answers
157 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 ...
apadana's user avatar
  • 1,052
1 vote
1 answer
166 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 ...
KFW's user avatar
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1 vote
1 answer
122 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)?
RobertSzili's user avatar
1 vote
0 answers
213 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 ...
Amit's user avatar
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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 ...
KMC's user avatar
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1 vote
1 answer
331 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 ...
SpacemanScott's user avatar
3 votes
1 answer
520 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?
user1245's user avatar
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0 votes
0 answers
231 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 ...
pnatk's user avatar
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5 votes
1 answer
581 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 ...
Tob Ernack's user avatar
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 ...
Sørën's user avatar
  • 299
1 vote
2 answers
288 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 \$...
Zack Frost's user avatar
3 votes
1 answer
549 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 ...
Enrico's user avatar
  • 229
1 vote
1 answer
207 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 ...
Thomas's user avatar
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1 vote
1 answer
438 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 ...
Victory's user avatar
  • 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 ...
midnightBlue's user avatar
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