[sdiy] phototransistor Ic max

[harrybissell]

Unless you connect a resistor to the base terminal, if there
is one...

the max collector current will be the same, its OK for the load to
be in the emitter ~or~ the collector.

Its more common to use a common emitter because the load will
be on the collector side and you can get current gain via the
CTR (current transfer ratio) of the opto.

You could put the load in the emitter... but it will be MUCH
slower and will it will essentially be an emitter follower
(the output transistor will NOT be saturated, and you will
have a voltage drop as well...)

You will not damage the opto, but its a really unusual
configuration...

H^) harry

"." wrote:
> 
> Hello,
> 
> When the specs of a phototransistor says Max collector current = 20mA,
> does it refer to the max current that can go thru CE or the fact that the
> collector cannot be connect straight to the power +15v. (even if the emitter
> has a proper resistor on the other side to limit current below 20 mA) ?
> 
> Mine is the tranny involved in this device:
> http://www.fairchildsemi.com/ds/H2%2FH21A1.pdf
> 
> And i made a mistake soldering a bunch of them, the limiting resistor (in fact
> the load resistor) is on the emitter side :-/
> 
> Sorry for the dumb question, thanks a lot for your time :)
> 
> L.