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overheating resistors

dirtdiver

Hi, im using the arduino to turn on a relay and complete a curcuit connecting the USB to a curcuit like this one :

 

    The IR's are TSHA203  , 100mA , Vr -5V, 180mW,image

Now one thig i dont understand is how 5 * 0.1 = 0.5 W and not 0.18 W, so I assumed that it could work on lower values like 2 volts or 50 mA and these are the maximum ones.

...But i guess i was wrong couse the resistors are overheating.Can you guys point me in the right direction?

Thanks!

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  • You need to ask yourself "Do I need to drive with 100ma or not?". 100ma is the maximum non pulsed current allowed. As you already know, then the resistors need to dissipate about 500 mW. If the answer is "Yes", then buy ceramic resistors of the value required, but with at least a 2 watt rating.....they will still get warm though and may need some cooling if enclosed.

     

    The Arduino should be able to pulse the output pin and use a PWM method to control the brightness and to actually reduce the power needed to go through the LED.

     

    To learm more look here:- http://arduino.cc/it/Tutorial/PWM

     

    This may or not be appropiate for your application of course, only you know that.

     

    regards

     

    Andy

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  • You need to ask yourself "Do I need to drive with 100ma or not?". 100ma is the maximum non pulsed current allowed. As you already know, then the resistors need to dissipate about 500 mW. If the answer is "Yes", then buy ceramic resistors of the value required, but with at least a 2 watt rating.....they will still get warm though and may need some cooling if enclosed.

     

    The Arduino should be able to pulse the output pin and use a PWM method to control the brightness and to actually reduce the power needed to go through the LED.

     

    To learm more look here:- http://arduino.cc/it/Tutorial/PWM

     

    This may or not be appropiate for your application of course, only you know that.

     

    regards

     

    Andy

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