[SOLVED] Circuit design optocoupler 4N25

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masoud1234

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I'm designing a circuit with optocoupler 4N25 and 24v dc input which output is connected to the microcontroller

Please calculate the resistance

R1=?

R2=?
 

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  • 4N25 CIRCUTE.bmp
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R1 = 450 ohm. It is designed to work for 5 volt. Resistance should be more than 450 and upto 1200.
R2 = 1k ohm or higher. (I guess)
 

thanks

Calculated :
KVL: -24+(R1 *I1)=0

R1=2.4 KΩ It is true؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟

Please calculate R2
 

R2 is 10k as mentioned by tpetar. It is a pull down resistor and are used in a range of 1k to 10k.
 

Hello masoud1234,

for R1 you have to calculate like this:

VF = 1,2V ; IF = 10 mA

R1 = (24V - VF) / IF = (24V - 1,2V) / 10mA = 2200Ω = 2K2

Calculate for R2:

R2 = (5V - VCE(SAT) / IC

From Datasheet: VCE(Sat) = 0,3V

IC = 1mA

Regards

Rainer


R2 = (5V - 0,3V) / 1mA = 4700Ω = 4K7
 

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    Mattooc

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