Thermal considerations, Electrical Engineering

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.

Posted Date: 1/10/2013 7:03:52 AM | Location : United States







Related Discussions:- Thermal considerations, Assignment Help, Ask Question on Thermal considerations, Get Answer, Expert's Help, Thermal considerations Discussions

Write discussion on Thermal considerations
Your posts are moderated
Related Questions
Explain the Cylindrical or Round Rotors? All synchronous machines have a similar stator design and it is actually the rotor construction that makes them different. The rotor is

Q. (a) Consider the amplifier block in the circuit configuration of Figure. Find an expression for v 2 /v 1 in terms of R i , R o , and A of the amplifier. (b) Determine the

A feedback control system with the configuration of Figure has the following parameters: K p = 0.5 V/rad, K a = 100 V/V, K m = 2.7 × 10 -4 N·m/V, J = 1.5 × 10 -5 kg·m 2 , and

Discuss important properties and uses of Rubber. Rubber: It is polymeric material along with high elastic yield strain. The various types of rubber materials are given as-

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

1- Use 4-to-16 decoder and some residue gates to recognize the following functions F1(A,B,C)= S(1,2,4,5,7) F2(A,B,C,D)= S(1,2,4,5,7,10,12,14,15) F3(A,B,C,D,E)= S(1,2,4,5,7,10,12,1

Construct a full wave bridge rectifier circuit and connect it to the transformer output. What is the Output Voltage and Frequency?

How many machine cycles does 8085 have, mention them The 8085 have seven machine cycles. They are Opcode fetch Memory read Memory write I/O read I/O

how to make a matlab program for calculation of AT&C loss for perticular area

Give some applications of constantan. Constantan is an alloy of nickel and copper. It is used in thermocouples, motor starters and precision resistors.