Thermal considerations, Electrical Engineering

Assignment Help:

Thermal considerations:

At continuous current, the voltage across the emitter-base junction VBE of a bipolar transistor get decreases 2 mV (silicon) and 1.8mV (germanium) for every 1°C rise in temperature (reference being 25°C). Through the Ebers-Moll model, if the base-emitter voltage VBE that is held constant and the temperature increases, the current by the base-emitter diode IB will raise, and so the collector current IC will as well increase. Depending upon the bias point, power dissipated in the transistor might as well increase that will further increase its temperature and exacerbate the problem. This deleterious positive (+ive) feedback results in thermal runaway. There are various approaches to mitigate bipolar transistor thermal runaway. For instance,

1. Negative feedback can be made into the biasing circuit so that increased collector current directs to decrease base current. Therefore, the increasing collector current throttles its source.

2. Heat sinks can be employed which carry away extra heat and prevent the base-emitter temperature from rising.

3. The transistor can be biased that is why its collector is usually less than half of the power supply voltage that implies that collector-emitter power dissipation is at the maximum value of it. After that runaway is impossible because increasing collector current directs to a decrease in dissipated power; this notion is termed as the half-voltage principle.

The circuits below primarily illustrate the use of negative feedback to avoid thermal runaway.


Related Discussions:- Thermal considerations

Crystal-controlled oscillator circuits, Circuits, which provide sinusoidal ...

Circuits, which provide sinusoidal waveforms, are but useful in themselves and form the basis of many other circuits, such as square and triangular waveform generators, and clocks.

Peak inverse voltage - thyristor, Peak inverse Voltage   Peak  inverse v...

Peak inverse Voltage   Peak  inverse voltage is   important parameter in the design of rectifier circuit. PIV is the maximum  voltage that appears across the device  during its

Find the induced emf across the coil, Q. A coil is formed by connecting 15 ...

Q. A coil is formed by connecting 15 conducting loops, or turns, in series. Each loop has length l = 2.5 m and width w = 10 cm. The 15-turn coil is rotated at a constant speed of 3

Discuss properties and uses of mica and mica products, Discuss important pr...

Discuss important properties and uses of Mica and Mica Products. Mica and Mica Products - Mica is an inorganic material. This is one of the best insulating materials availa

Error in simulink, dear sir, when i am going to simulate my model in matlab...

dear sir, when i am going to simulate my model in matlab i am getting the following error : the derived input for the integrator is inf or nan at time xxxxx. try to reduce the step

Homework, voice signal is measured at 3.21692v and resides in an interval f...

voice signal is measured at 3.21692v and resides in an interval from 3.20v to 3.30. How big is an interval? MAx possible voltage?

memory to register , Memory  to Register This  instruction is used to...

Memory  to Register This  instruction is used to copy the contents of a memory  locations whose  address is specified by the HL register  pair to any register. Before  using th

Give homogeneous matrix quation for b-splive curve, What are the different ...

What are the different kinds of surface entities used in CAD? Give homogeneous Matrix form equation for : (i) B-Splive Curve (ii) Bezier Curve

Determine the maximum power, Determine the maximum power: 1 For the c...

Determine the maximum power: 1 For the circuit shown below, what value of RL will result in maximum power transfer? Determine the maximum power dissipated in RL. You

What is logic gates - microprocessor, What is Logic Gates? The Logic Gat...

What is Logic Gates? The Logic Gates are circuits made up of transistors, diodes, and resistors. The Logic gates process one or more input signals in a logical fashion. Dependin

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd