PC817 overheating problem

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1

ısınmasorunu
ısınmasorunu208×464 1.44 KB

PC817 in this schematic is getting hot, power is 24dcv 5amp. what could be the reason?

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The resistor.

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what should it be worth

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Obviously you did not look at the data sheet. If you had you would know this part cannot take several amps on the LED side. Your 10 Ohm resistor will pass about 2.2A on a 50mA device. The spec is as follows, easy to find with google.

PC817 Features and Specifications

  • Input Diode Forward Voltage: 1.25V
  • Collector-Emitter Voltage: 80V (max)
  • Collector Current: 50mA (max)
  • Cut-off frequency: 80 kHz
  • Rise Time: 18us
  • Fall Time: 18us
5

Try 2.7 kΩ.

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Anywhere from just over 5mA up to 50mA lights the led sufficiently to fully open the photo-transistor. I tend to aim for 10mA
24v = 0.01A * R thus 2.4K, or yes 2.7K or 2.2K, whatever is on hand. 10R really is not enough, How many Watts was the resistor ? what burned, the resistor or the PC817 ?

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pc817 was overheating, i solved the problem with 470R, it doesn't heat up anymore.

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