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

Find the effective noise temperature, Q. An antenna with an effective noise...

Q. An antenna with an effective noise temperature of 130 K couples through a waveguide that has a loss of 0.8 dB to a receiver. Find the effective noise temperature presented by th

Drift current density and conductivity, Drift Current Density and Conductiv...

Drift Current Density and Conductivity: Consider a conductor of length / meters and cross sectional area a square meters, as shown in Fig. Let the number of free electrons ava

Digital electronics logic family, For a given logic family, consider VOL = ...

For a given logic family, consider VOL = 0.25V and VOH = 5 V . For a given circuit, VIL = 0.96 V and VIH = 2.18 V. Find the largest positive-going and largest negative-going nois

Slip-power controlled wound-rotor induction-motor drives, Q. Slip-power con...

Q. Slip-power controlled wound-rotor induction-motor drives? Slip power is that portion of the air-gap power that is not converted into mechanical power. The methods involving

Interrupts, how the interrupts are affected by system rest

how the interrupts are affected by system rest

Pass band of the resulting bandpass filter, A bandpass filter design can be...

A bandpass filter design can be accomplished through the cascade connection shown in Figure, where the frequencies between the two cutoffs fall in the passband of both filters and

Port address - address bus , Port Address The port  address  is of 8 bi...

Port Address The port  address  is of 8 bit  it is range from 00H  to FFH. It means  there may be total  i 256 input  ports and 256  output  port which can be accessed by 8085

Determine and sketch il for inductance, Q. For the circuit of Figure, deter...

Q. For the circuit of Figure, determine and sketch i L (t) and vC(t) for inductance values of (a)3/4 H, (b) 2/3 H, and (c) 3/17 H. Note that the inductance values are chosen her

Explain industry standard architecture bus, Explain the term Industry Stand...

Explain the term Industry Standard Architecture Bus. The Industry Standard Architecture, bus has been approximately since the very start of the IBM-compatible personal computer

Determine the value of capacitance to give resonance, Determine the value o...

Determine the value of capacitance to give resonance: A circuit shown in Figure having a resistance of 5 Ω, an inductance of 0.4 H and a variable capacitance in series is conn

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