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

Diode current -zener region, Diode current: Zener region: when the r...

Diode current: Zener region: when the reverse biased voltage is increase to a very high value then a point is reached where will is suddenly going a very high value. Th

Define explicit - implicit and parametric representations, Give an industri...

Give an industrial look at modern CAM/CAD. Define explicit, implicit and parametric representations. What are the basic advantages of parametric representations over the impli

Explain bios, Explain BIOS The IBM PC has in its ROM a collection of ro...

Explain BIOS The IBM PC has in its ROM a collection of routines, each of which performs some particular function such as reading a character from keyboard, writing character to

Define causal system - discrete time systems, Define Causal System - Discre...

Define Causal System - Discrete Time Systems? A causal system is one which produces an output only when there is an input. All physical systems are causal. In general, a causal

Dsp., fir and iir filter design

fir and iir filter design

Explain magnetostriction, Explain Magnetostriction. Magnetostriction: I...

Explain Magnetostriction. Magnetostriction: If ferromagnetic materials are magnetized a small change of dimensions of the material obtains place. There is a small extension alo

Compute efficiency of transformer in power factor lagging, Q. A 10-kVA, 200...

Q. A 10-kVA, 200:400-V, single-phase transformer gave these test results: • Open-circuit test (LVwinding supplied): 200V, 3.2 A, 450 W • Short-circuit test (HV winding suppli

Show the load current is independent of zl, Q. A negative impedance convert...

Q. A negative impedance converter is used, as shown in Figure. Show that the load current i L is given by v in /R, which is independent of Z L . Note that since the load sees a cu

Optimal voltage control in distribution network with DG, Hi can you help to...

Hi can you help to work on my project...I want you to help me writing my graduation thesis

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