hi

im wanting to use this opto isolator what is the max voltage i can put on the input side? i want to use 24v just unsure what the max voltage i can put on the input?
thank you

ftp://ftp.elektroda.net/pub/Karty%20katalogowe/pc817xx.pdf

 

Hi,

Why would you want to put that much voltage across an LED?
The max voltage is 3V.
The typical current from the datasheet is 50 mA, and the maximum 1A.
You'll need to use a resistor to drop the current anyway, why not just a voltage divider?

 

The input is an LED (diode) so you need a series resistor at the input to limit the current. For a nominal input current of 20mA you would need a resistor value of (24-1.3) / 20mA ≈ 1.3kΩ

 

The input is an LED (diode) so you need a series resistor at the input to limit the current. For a nominal input current of 20mA you would need a resistor value of (24-1.3) / 20mA ≈ 1.3kΩ

On the datasheet it gives a maximum of 3V as input to the LED, can you drive the LED without a divider to drop the voltage from 24V?

 

On the datasheet it gives a maximum of 3V as input to the LED, can you drive the LED without a divider to drop the voltage from 24V?

That's not a specification for driving the input. Look at it closly: that spec shows the forward voltage for a specified current, and it's given as a characteristic of the input device. What you are worried about is the "Absolute Maximum Ratings" chart. Forward current should be nominally 50mA, and Peak Forward Current is 1A. But don't design for peak forward current. Use the nominal "Forward Current" spec.

 

That's not a specification for driving the input. Look at it closly: that spec shows the forward voltage for a specified current, and it's given as a characteristic of the input device. What you are worried about is the "Absolute Maximum Ratings" chart. Forward current should be nominally 50mA, and Peak Forward Current is 1A. But don't design for peak forward current. Use the nominal "Forward Current" spec.

Oh....Ok...thanks.

So then the input is like any LED, I should be mostly concerned with the current.

Thanks again!

 

The input is an LED (diode) so you need a series resistor at the input to limit the current. For a nominal input current of 20mA you would need a resistor value of (24-1.3) / 20mA ≈ 1.3kΩ

make sure its rated 1W or more.

 

So then the input is like any LED, I should be mostly concerned with the current.

Thanks again!

Yup. Use the equation given by Crutschow above and you'll be fine.