My circuit has a Vcc of 18v and a Vee of -18 ,Rc 330 ,Ic 20 mA ,Vce 8.58V, Re 470, Rb 5.1k, Just want to know the formula for power dissipation for Rc and within the transistor, Please.
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1\$\begingroup\$ Do you mean power dissipation ? \$\endgroup\$– brhansJan 16, 2015 at 20:10
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\$\begingroup\$ yes dissipation \$\endgroup\$– Anthony HoodJan 16, 2015 at 20:19
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\$\begingroup\$ Hint: Since Rc=330 (preumably ohms) and Ic=20 mA right from your problem-statement, what is the power through Rc? \$\endgroup\$– the gods from engineeringJan 17, 2015 at 0:58
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\$\begingroup\$ As for the power through the transistor, there's a worked out example: electronics.stackexchange.com/questions/75140/… \$\endgroup\$– the gods from engineeringJan 17, 2015 at 1:07
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\$\begingroup\$ I am going to try out that equation, But if the transistor's, power' at all those locations is added up than it will most likely be more than the rated, maybe you take all those and then find the average. Or maybe the wattage the transistor has accross it is the dissipation, anyway will have to research it more \$\endgroup\$– Anthony HoodJan 17, 2015 at 8:14
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1 Answer
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I won't do the actual math for you, but here's how to approach it.
The difference between Vcc and Vee is 36 volts. Knowing the collector current and the collector resistance, you can calculate the voltage across Rc. Adding this to Vce, you can subtract this from 36, and you know what the voltage is across Re. You know how to calculate the power being dissipated in a resistor, right? So calculate them. Once you know the voltage across Re, you can compare this to the base drive voltage (which you did not mention). The difference, minus one diode drop, can be used to calculate the base current. Now take this current, combine it with the base/emitter voltage, and you know how much power the base is dissipating. Plus, you know how the calculate the power being dissipated in the collector/emitter path of the transistor, right? (Hint - voltage and current). Add the two to powers, and there you go.
You may want to check for sanity by calculating the current in Re, and you will find there is something wrong with the circuit. You might want to point this out to your professor.
answered Jan 16, 2015 at 20:46