Why BJT is not suitable for low temperature?

Bipolar transistors are generally preferred over MOS transis- tors because of their lower spread. However, at deep-cryogenic temperatures, the performance of BJTs deteriorates due to a significant reduction in current gain and a substantial increase in the base resistance.

How does temperature affect BJT?

As temperature increases , Ibo or reverse saturated current through emitter junction increases and hence overall current through Je reducess, and hence Vbe also get reduces proportionally.

How does temperature affect transistor?

An increase in temperature produces an increase in the minority carrier current, but a negative change in V_BE, so both effects lead to an increase in collector current with temperature.

What are the disadvantages of BJT?

Why does Icbo vary with temperature?

This junction being polarized in opposite direction, the current ICBO is due to the minority carriers constituted by the electron-hole pairs. The number of these couples increases when the temperature increases. As a result, the ICBO current also increases.

44 BJT Breakdown and Temperature Effects

Is performance of BJT temperature dependent?

The effect of temperature on a transistor is depend upon type of transistor we are using. If we are using BJT then with increase in temperature the current increases or if we are using FET the current will decrease with increasing temperature.

What happens in base emitter resistance if temperature of a transistor goes up?

Right Answer is: A

Due to an increase in temperature, base-emitter voltage (V_BE) decreases and hence base-emitter resistance decreases.

Why MOSFET is preferred over BJT?

Mosfet provides a very good isolation between the gate and the other two terminals compared to bjt. MOSFET can handle more power compared to BJT. The mosfet has a very low power loss and a high speed. Voltage signals can easily operate a mosfet, so it is used in many digital circuits.

What are the advantages of BJT over PN diode?

There are some advantages of bipolar junction transistor (BJT) are as given below, The bipolar junction transistor (BJT) has a large gain bandwidth. The BJT shows better performance at high frequency. The BJT has a better voltage gain.

What is thermal runaway in BJT?

Thermal runaway

The problem with increasing temperature causing increasing collector current is that more current increase the power dissipated by the transistor which, in turn, increases its temperature. This self-reinforcing cycle is known as thermal run away, which may destroy the transistor.

Why is thermal stability required for a transistor?

Abstract: When the junction temperature of a transistor increases, the collector current increases, as a result of increases in 1) saturation currents and 2) dc conductances. Thermal instability occurs when junction temperature and collector current increase in regenerative and uncontrollable fashion.

Why does beta increase with temperature?

It because of the fact that base transport factor(which constitute mobility and recombination lifetime) reduces with temperature, in turn causing decrease in base current, and therefore an increase in β.

How temperature affects the maximum power output in transistor?

The maximum power output available from a power transistor is closely linked to temperature, and above 25°C falls in a linear manner to zero power output as the maximum permissible temperature is reached.

How does temperature affect Mosfet?

The temperature dependency of various parameters on the MOSFET causes variation in dc characteristics. At higher values of gate to source voltage, the drain current decreases with increase in temperature, ie, the MOSFET exhibits negative temperature coefficient at higher values of gate to source voltage.

Why does VBE decrease with temperature?

It's related to the energy required for the carriers to cross the PN junction. The thermal motion of the carriers reduces the amount of added energy needed, thus as the temperature increases, the forward voltage drop goes down.

Why does base bias Q point change with temperature?

Q Point Instability due to Temperature:

Due to increase in temperature the following parameters of a transistor will change: 1 VBE: The base to emitter voltage decreases at a rate of 2.5 mV/? with increase in temperature. The base current IB will therefore increase and it will force IC to change, and hence the Q point.

What is difference between BJT and Mosfet?

There are many differences between the MOSFET and BJT. The MOSFET (voltage controlled) is a metal-oxide semiconductor whereas the BJT (current controlled) is a bipolar junction transistor.

Where do we use BJT?

Bipolar junction transistors (Also known as BJTs) can be used as an amplifier, filter, rectifier, oscillator, or even a switch, which we cover as an example in the first section. The transistor will operate as an amplifier or other linear circuit if the transistor is biased into the linear region.

Why CMOS is used instead of BJT?

BJT consumes more power whereas CMOS consumes less power and allows you to increase density of transistor in circuit. Also, BJT has positive temperature coefficient that makes it less stable in higher temperature whereas CMOS is more stable in higher temperatures.

Is BJT faster than MOSFET?

Amit Das Hi, BJTs are faster than MOSFETs due to the capacitances at the junctions of MOSFETs are produced by the metal, substrate, and oxide layer.

Why BJT is more noisy than FET?

BJT is more noisy compared to FET at high frequency because BJT is a current current controlled device and sudden change in current direction is not an easy task. It takes some time to invert current direction. While in case of FET, as it is a voltage controlled device so, changing potential externally is much easier.

How does the internal base emitter voltage in a BJT change with the temperature at a constant collector current?

At constant current, the voltage across the emitter–base junction V_BE of a bipolar transistor decreases by 2 mV (silicon) and 1.8 mV (germanium) for each 1 °C rise in temperature (reference being 25 °C).

Does Beta DC increase or decrease with temperature?

So as temperature increases, beta increases.

Why the width of the base region of a transistor is kept very small compared to other regions?

9. Why the width of the base region of a transistor is kept very small compared to other regions? Base region of a transistor is kept very small and very lightly doped so as to pass most of the injected charge carriers to the collector.