Battery charger Clarification

[murali_dece]

hi, recently I prepared battery charger schematic from faulty charger and able to fix the problem but theoritically i am unable to clarify myself some sections, Please explain.

functioning of third stage of Op Amp

Functioning and purpose of Q2 and Q3

I am feeling Q2 is biased in saturation region, Please Clarify

Thank You
Regards
murali_dece

 

[leo_o2]

I guess Q2 will work as a switch.

 

[vimalkhanna]

For Q2 the emitter and collector sketches is interchanged .
This works as a an emitter grounded amp with collector working for current limiting when the AC signal is present .
The diodes raise the inverting input of the limiter opamp.
The Q3 works for putting the Q2 base current to cutoff.

 

[murali_dece]

thank you for showing intrest on my query, after seeing replies i have gone through my drawing and found one mistake, corrected and uploaded once again. i have double checked while drawing schematic and found Q2 is biased in such a way collector is grounded and emitter is conneted to positive. positive ripples of fullwave bridge rectifier is applied to base with out filtering through 10K ohm resistor. conecting Q3 collector to Q2 base is my mistake on drawing once again i checked with original card.
thanks & regards
murali

 

[Raza]

Hi murali,
As said by vimal, the Q2 collector and emitter is connected reversely. Means Collector and emitter are interchanged. See the image.