Open collector npn output

[marjan]

Can someone give a brife explanation and maybe some example (shema) of npn open collector output stage in audio amp?
marijan

 

[richie00boy]

I would have thought that this would only apply to a switching circuit, e.g. comparator, as it is capable only of sinking current not sourcing.

 

[Enzo]

I guess you could do some sort of single ended thing, but why on earth would one want to?

A little more info on your intent or application maybe?

 

[marijan]

I simply can not understand how can npn output stage of an amplifier work without electrical conection (at least I`m not able to determine it using multimeter) from 1 (out of 4) transistor collectors to the rest of the circuit. But mesuring of the voltage (in working set up-sorce and loade on) show`s -45V on colector on that npn.

Marijan

 

[richie00boy]

Ahh, now I see. It's very simple

Basically, the other three transistors are doing the work so the amplifier will appear to be fine until you stress it. You are seeing -45V on the one transistor that is unconnected simply because it's emitter is connected to the -ve rail and the device is turning on = low resistance.

 

[marijan]

Thanks Richie. I draw a quick skatch but I`m not shure, does it make any sense. All npn`s out.