What is thermal runaway, Electrical Engineering

Assignment Help:

Q. What is thermal runaway? State one method to prevent the same?

The effect of changes in leakage current (ICO)  and current gain(b) on the dc bias point is given by the equation

IC = bIB + (1+b) ICO.

The collector current increases with the increase in temperature since b increases with increase in temperature.

           ICO doubles in value for every 100 C increase in temperature.

This leads to increased power dissipation with further increase in temperature. Being a cumulative process it can lead to thermal runaway resulting in burn-out of the transistor. The self-destruction of an unstabilized transistor is called thermal runaway. However, if by some technique, IB is made to fall with increase in temperature automatically, then decrease in the term bIB can be made to neutralize the increase in the term (1+b)ICO, thereby keeping IC almost constant. This will achieve thermal stability resulting in bias stability.

Stabilization technique makes use of a resistive biasing circuit that permits such a variation of base current (biasing current) IB as to maintain the collector current IC almost constant in spite of variations in reverse saturation current ICO and b.

DT = Tj - TA = θPD

where, PD = power in watts dissipated at the collector junction

TA = ambient temperature

Tj = junction temperature

θ = constant of proportionality called thermal resistance


Related Discussions:- What is thermal runaway

Explain how switching systems are classified, Question 1 Explain how switc...

Question 1 Explain how switching systems are classified Question 2 Explain the function of pulse dialing in rotary dial telephone Question 3 Explain the functioning of crossba

What are shift registers - sequential logic circuit, What are Shift Registe...

What are Shift Registers - Sequential Logic Circuit? The Shift registers are a type of sequential logic circuit that mainly for storage of digital data and they are a group of

Determine the resistivity of the wire, The resistance of 1.5 km of wire of ...

The resistance of 1.5 km of wire of cross-sectional area 0.17 mm 2 is 150Ω. Determine the resistivity of the wire.

Saturation and cutoff in bipolar junction transistor, Saturation and Cutoff...

Saturation and Cutoff in bipolar junction transistor: Saturation : With both of the junctions forward-biased, a BJT is in saturation mode and makes easy high current condu

Electric circuits, How to design a single phase distribution circuit from a...

How to design a single phase distribution circuit from a supply point to a load?

Ic packaging, which type of ic package is more advantageous,suitable and ve...

which type of ic package is more advantageous,suitable and versatile

Determine radius of curvature of concave spherical mirror, The focal length...

The focal length of a concave spherical mirror is equal to 1 meter. What is the radius of curvature of this mirror? Ans: The radius of curvature of this mirror is 2 meter.

Synchronization, Synchronization:  Whatever type of weep is used, it must ...

Synchronization:  Whatever type of weep is used, it must be synchronized with the signal being measured. Synchronization has to be done to obtain a stationary pattern. This requir

Show television waveform, Q. Show television waveform? The television w...

Q. Show television waveform? The television waveform representing one scan is illustrated in Figure. A blanking pulse with a duration of 0.18 of the horizontal - sweep period T

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