# regarding diode

#### gaya3eeee

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

#### Dave

Joined Nov 17, 2003
6,969
why resistors used in testing "the forward and reverse characteristics of diode" gets burned when high current is passed?
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

#### n9352527

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

#### Papabravo

Joined Feb 24, 2006
18,849
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
Rich (BB code):
(0.150)*(0.150)*18 = 405 mWatts
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"

Joined Jan 10, 2006
614
What voltages are you using..?

#### Dave

Joined Nov 17, 2003
6,969
Remember the following piece of doggerel:

"Twinkle-twinkle little star
Power's equal I squared R"
Electronics for pre-schools

Love the ditty.

Dave

#### Papabravo

Joined Feb 24, 2006
18,849
Electronics for pre-schools

Love the ditty.

Dave
Twinkle-twinkle little star
Voltage equals I times R

#### Dave

Joined Nov 17, 2003
6,969
Twinkle-twinkle little star
Voltage equals I times R
Twinkle-twinkle little star
Current equals V by R

I can play this too

Dave

#### Papabravo

Joined Feb 24, 2006
18,849
Never a dull moment with this crowd. Nothing better than snappy repartee.

#### Dave

Joined Nov 17, 2003
6,969
Never a dull moment with this crowd. Nothing better than snappy repartee.
You know it makes sense

Dave