Ebers–Moll model for an NPN transistor. mode are well modeled by an approximation to the Ebers–Moll model. Ebers and Moll created a model between the current and voltages in the transistor terminals. This model is knowned as the Ebers Moll model. The Ebers-Moll model is an ideal model for a bipolar transistor, which can be used, in the forward active mode of.

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The emitter current therefore equals the excess minority carrier charge present in the base region, divided by the time this charge spends in the base. This variation in base width often is called the Early effect after its discoverer James M.

Chapter 5: Bipolar Junction Transistors

Because base—emitter voltage varies as the logarithm of the base—emitter and collector—emitter transisgor, a BJT can also be used to compute logarithms and anti-logarithms. The minority carrier densities on both sides of the base-collector depletion region equal the thermal equilibrium values since V BC was set to zero.

As shown, the h-parameters have lower-case subscripts and hence signify AC conditions or analyses.

This gain is usually or more, but robust circuit designs do not depend on the exact value for example see op-amp. This allows thermally excited electrons to inject from the emitter into the base region. Moll introduced their mathematical model of transistor currents: A cross-section view of a BJT indicates that the collector—base junction has a much larger area than the emitter—base junction.

For other uses, see Junction transistor disambiguation. This section needs expansion. The reason the emitter is heavily doped is to increase the emitter injection efficiency: And the emitter current due to electrons, I E,nsimplifies to: Although these regions are well defined for sufficiently large applied voltage, they overlap somewhat for small less than a few hundred millivolts biases.


The BJT is also the choice for demanding analog circuits, especially for very-high-frequency applications, such as radio-frequency circuits for wireless systems. The current gain then becomes: Small changes in the voltage applied across the base—emitter terminals cause the current between the emitter and the collector to change significantly.

The BJT when operated in normal mode and inverse mode is shown in transisyor figure below. The device thus loses all gain when in this state. In addition, higher doping in the base can improve figures of merit like the Early voltage by lessening base narrowing.

For the specific case where the base-emitter and base-collector ebets are the same and the base doping is uniform, there can be no minority carrier diffusion in the base so that:.

Ebers-moll model of transistor | ECE Tutorials

A bipolar junction transistor bipolar transistor or BJT is a type of transistor that uses both electron and hole charge carriers. Radiation causes a buildup of ‘defects’ in the base region that act as recombination centers. Ebers—Moll model for an NPN transistor.

The thermal runaway process associated with secondary breakdown, once triggered, occurs almost instantly and may transustor damage the transistor package.

The Bipolar Transistor (Ebers Moll Model)

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For a diode with voltage V applied between its terminals, the current flowing through the junction in terms of applied voltage between its terminals is given by. Compact Models of Bipolar Junction Transistors, pp. Since D1 and D2 fbers in series same current should flow through both of them then only currents order of reverse saturation currents flow through their junctions.


This allows BJTs to be used as amplifiers or switches, giving them wide applicability in electronic equipment, including computers, televisions, mobile phones, audio amplifiers, industrial control, and radio transmitters. However, to accurately and reliably design production BJT circuits, the voltage-control for example, Ebers—Moll model is required.

The emitter current due to electrons and holes are obtained using the “short” diode expressions derived in section 4.

Since the carrier mldel can be significantly longer than the base transit time, the turn-off delay causes a large and undesirable asymmetry between turn-on and turn-off time. Now coming to important question of Why two back to back diodes cannot function as a transistor?

Common source Common drain Common gate. The ideal transistor model is based on the ideal p-n diode model and provides a first-order calculation of the dc parameters of a bipolar junction transistor. The emitter efficiency is obtained from: Sedra and Kenneth C.

For this the h oe and h re parameters are neglected that is, they are set to infinity and zero, respectively. It is this gain that allows BJTs to be used as the building blocks of electronic amplifiers. In the discussion below, focus is on the NPN bipolar transistor.

NPN base width for low collector—base reverse bias; Bottom: The h refers to its being an h-parameter, a ttansistor of parameters named for their origin in a hybrid equivalent circuit model.

While this boundary condition is mathematically equivalent to that of an ideal contact, there is an important difference. For high-frequency analyses the inter-electrode capacitances that are important at high frequencies must be added.