# 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 ...
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### 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
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 ...
• 1,052
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### 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
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 ...
• 181
1 vote
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 ...
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1 vote
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 ...
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1 vote
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### 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)?
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### 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 ...
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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 ...
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### 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 ...
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?
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### 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 ...
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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 ...
• 163
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 ...
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