regarding diode

Discussion in 'Homework Help' started by gaya3eeee, Aug 23, 2006.

1. gaya3eeee Thread Starter New Member

Aug 18, 2006
7
0
why resistors used in testing "the forward and reverse characteristics of diode" gets burned when high current is passed?

2. Dave Retired Moderator

Nov 17, 2003
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I'm sorry but I don't understand the question, can you clarify what exactly you are asking? You may benefit from reading this.

Dave

3. n9352527 AAC Fanatic!

Oct 14, 2005
1,198
4
Umm... because the resistor power rating is too low?

4. Papabravo Expert

Feb 24, 2006
10,340
1,850
High current in a resistor causes heat which must be dissipated by conduction, convection, or radiation. To compute the power in a resistor you square the current and multiply by the resistor value. If the current is expressed in Amperes and the resistance is expressed in Ohms then the power will be expressed in Watts.

Example: An IR-LED has the desired brightness at a forward current of 150 mA at a forward voltage drop of 2.2 Volts. The supply is +5 VDC. The resistor for this application is 18 Ohms. Compute the required power dissipation rating of the resistor
Code ( (Unknown Language)):
1.
2. (0.150)*(0.150)*18 = 405 mWatts
3.
If you use a quarter watt resistor in this application the magic smoke will very quickly exit the resistor body with the usual fetid acrid smell.

Remember the following piece of doggerel:

"Twinkle-twinkle little star
Power's equal I squared R"

Jan 10, 2006
613
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What voltages are you using..?

6. Dave Retired Moderator

Nov 17, 2003
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Electronics for pre-schools

Love the ditty.

Dave

7. Papabravo Expert

Feb 24, 2006
10,340
1,850
Twinkle-twinkle little star
Voltage equals I times R

8. Dave Retired Moderator

Nov 17, 2003
6,960
145
Twinkle-twinkle little star
Current equals V by R

I can play this too

Dave

9. Papabravo Expert

Feb 24, 2006
10,340
1,850
Never a dull moment with this crowd. Nothing better than snappy repartee.

10. Dave Retired Moderator

Nov 17, 2003
6,960
145
You know it makes sense

Dave