Today was the last day to demonstrate the working cct but I will keep working on it to make it fully work.
@Post 9 and 10:
Yes I've realized that this is a voltage follower photo-BJT (its an optocoupler) which is very limited however I don't understand why the low-side switching (post1) would work in this cct. On falstad it supplies 'high' to the output at all times the same was with the actual physical circuit measured with digital oscilloscope and thus I don't want the output to be on at all times it should be also noted that Opto is PWM driven and we had no time to re-design the low-side switching so we moved to a high-side design.
Why voltage follower:
- non-inverted signal
- I've found post yesterday that not the same rules apply to photo-bjt as for base BJT but I couldn't find exactly how to calculate what voltage will be on the output so I assumed a that its gonna behave like a voltage divider in ON condition.
Today's results:
In cct in post 8 I've replaced 180Ω with 100Ω which 'theoretically' should give me 110mA and 11.07V, this would satisfy the gate of mosfet incredibly well I think, but the result was different.
Testing cct:
View attachment 63024
A voltage drop across LED was 1.2V which was correct however the optos were not ran at full supply current i.e. The LED should be driven at least with 10mA but pulse generator supplied only 8mA that's why we concluded very low output on BJT side of the mosfet.
The output on BJT emitter-side was around 0.8-0.9V and we assumed that its because of the not sufficient current going to opto but this will be further analysed.
The other reason might be the fact as you mentioned above, common collector phototransitor theory might be wrong which need to researched in detail.
View attachment 63021
Output measured at point before the PIN1 but after resistor on optocoupler.
Output measured at the Gate of the mosfet S1
The actual value to the LED was 1.12-1.32V but it just keep giving different values at all times.
The value on Gate leaves many question and was oscillating between 0.1-1.2V which leaves even more questions.
Overall I'm happy that the Gate was supplied in respect with the input impulses, its not the matter of analyzing the circuit and where mistakes has been done.