can someone confirm for me

the 4N25 (Vishay) opto bjt is magnitudes faster than the TLP222A (Toshiba) opto fet ??
faster as in the time it takes to turn "on" between collector-emitter or drain-to-drain.

but also correct me if i am wrong here, the TLP222A can switch AC vs 4N25 is DC only.

and is it the case the bjt opto's are usually faster than their fet counterparts?

 

You could look both of these up on Google an get the datasheets, which will answer your question. If you don't understand the datasheets-- then there is a better question to ask, and folks here can help with that, which will help you with every project you work on.

 

You could look both of these up on Google an get the datasheets, which will answer your question. If you don't understand the datasheets-- then there is a better question to ask, and folks here can help with that, which will help you with every project you work on.

i have the datasheets

Ton is not always the same thing in every datasheet. i also posed a couple of other questions if you want to answer them.

 

Yeah, it looks like the 4N25 is a lot faster but that's not saying much. The 4N25 rise and fall times are like 3 uS, not particularly speedy.

AC vs DC? Both have a single LED so they aren't going to light up with reverse current. Might blow out though, depending on the voltage.

 

The TLP222A is quite slow (a tenth of ms or greater) but that's because it's designed to act as an AC/DC relay (SSR) and switch loads up to 60V and a half amp peak where response time is generally not a significant concern.

In contrast, the 4N25 is designed to switch digital signals (although it can be used in a limited analog fashion such as power supply isolated feedback loops) so it is much faster and can switch only single-polarity on the output.

 

thanks crutschow

what i mean by ac/dc, the n-bjt has one direction only, collector-to-emitter. the opto fet that has ganged fets has drain-drain output, so AC can flow when on (current in two directions)

 

what i mean by ac/dc, the n-bjt has one direction only, collector-to-emitter. the opto fet that has ganged fets has drain-drain output, so AC can flow when on (current in two directions)

Yes, that's also what I meant by the AC/DC switching in the opto-fet.

 

i have the datasheets

Ton is not always the same thing in every datasheet. i also posed a couple of other questions if you want to answer them.

Ton refers to the same thing on all data sheets where on or off is based on a transition of voltage levels. In this case the 4n25 is 2.8us, and for the TLP222A, it's 8ms. You answered your own question-- the 4N25 is faster.

As for A/C .v. D/C usage, It is unlikely you can use the FET for A/C-- typically you cannot. It depends on exactly what kind of FET it is, whether or not it has diodes in it, and whether or not they've tied some pins together internally.

However, you can still switch A/C on and off by putting a full-wave bridge rectifier (FWB) in series with the A/C load, and then putting the FET on the D/C side of the FWB. As long as power flows through the FET, the A/C side runs. When it stops, A/C stops. The 4N25 will work this way, as well. It really depends on how much current you need to pass through the optoisolator.

 

look at the TLP222A, the fet's are tied s-to-s, DC can flow in either direction (aka AC).
although 4N25 is 2-3usec, i am using something much faster, 2N4401 which on my scope is about 37nsec.

the 4401 was in my container of mixed NPN's, knocked the dust off and now it has a purpose in life

 

i am using something much faster, 2N4401 which on my scope is about 37nsec.

I don't quite understand what the switching time of a single BJT has to do with the switching time of an opto-isolator.

 

I don't quite understand what the switching time of a single BJT has to do with the switching time of an opto-isolator.

i am using ATtiny85 to control a remote shutter cable on a Canon DSLR. delays across the controller are to be kept to a minimum. the 4401 is rather fast, so i use that instead of the opto-fet i have. on my scope the on time for 4401 about matched that of its spec, low nsec duration, which is good for me.