4N28 to replace 4N26? Will this Work?

[Astroman (Andrew Wall)]

Hello all,

I am building a bulb cable for my Canon 400D using the circuit available on this website http://www.beskeen.com/projects/dslr...r_serial.shtml I have a few 4N28 Opto's but the circuit calls for 4N26 or 4N33. Would there be any harm in using the 4N28's?

[Bassnut (Fred)]

I used a 4n28 for exactly the same purpose, works fine.

[Astroman (Andrew Wall)]

Thanks Fred.

[wasyoungonce (Brendan)]

All the same devices pin compatible and specs.

Only difference is CTR % with I think is reliability degradation factor...aka how long it's life will be.

[Astroman (Andrew Wall)]

Thanks Guys, used the 4N28 and connected it all up, works perfectly. Now I can go longer than 30s and use mirror lockup.

[Scorpius51 (John)]

Main difference is the current transfer ratio (CTR), that is Ic/If @ some Vce. Sort of current gain. The 4N26 (20%) is higher than the 4n28 (10%), and the 4n33 is a darlington output for very high CTR (500%)- i.e. high gain, if you like. The higher the CTR, the lower the LED current required for a given output current. Don't let the output saturate, the performance will degrade.

In your application the substitution should be fine. You may have to fiddle with R1 to optimise it, depending on the input voltage you are using - probably 5V.

[wasyoungonce (Brendan)]

Originally Posted by Scorpius51

Main difference is the current transfer ratio (CTR), ....

excellent thanks