[SOLVED] Circuit design optocoupler 4N25

[masoud1234]

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=?

 

[Genovator]

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)

 

[tpetar]

R1 = 2k

R2 = 10k


Put resistor before LED anode.

 

[masoud1234]

thanks

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

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

Please calculate R2

 

[masoud1234]

please help me

 

[Genovator]

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

 

[rfredel]

Hello masoud1234,

for R₁ you have to calculate like this:

V_F = 1,2V ; I_F = 10 mA

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

Calculate for R2:

R₂ = (5V - V_CE(SAT) / I_C

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

I_C = 1mA

Regards

Rainer


R₂ = (5V - 0,3V) / 1mA = 4700Ω = 4K7