Hi

I could do with some help understanding this data sheet for an optoisolator.

https://toshiba.semicon-storage.com/info/docget.jsp?did=60600&prodName=TLP176AM




I want to calculate the resistor I need for the LED.

I will be powering it from a 4.2v supply. As I read it, on the first page, the current I need to switch the LED on is 3mA - or is this the maximum current? Further down the sheet on table 6 it says maximum current is 30mA.

Then on table 7 it says maximum forward current is 25mA.

Is one of these referring to the current the isolator can carry on the switch side? If so, what is the maximum?

I’m pretty confused ...

 

hi rj,
The 3mA is the turn on threshold current
The 30mA is the Absolute allowed current.
The 25mA is the recommended max current.
I would calc my resistor for 15mA.
E

[4.2v- 1.25Vfwd]/0.015A = Rseries =195R, use a 180R >> 16mA

 

Thanks very much. Where does it say what the maximum carrying current (to be switched) is?

 

hi.
The spec says on state current is 700mA, On state resistance is 2R.
Note: Power dissipation is 300mW
E

 

The opto output on-resistance is tested at an input current of 5mA (below) so you shouldn't need more than that to turn it on.