Try to be specific and it will be easier for others to understand and comment. Anyhow in general if the circuit is IC based then directly search those IC's & in their datasheet you may find what is the application and all that, rest is all your electronic understanding and concepts whereby you will conclude the reason behind the use of each capacitor and resistor etc.....
It is a hopeless horrible circuit.
R3 does nothing and can be replaced with a piece of wire.
Since there is no negative supply and no output coupling capacitor then R6 and Q4 also do nothing and can be removed.
It is a hopeless horrible circuit.
R3 does nothing and can be replaced with a piece of wire.
Since there is no negative supply and no output coupling capacitor then R6 and Q4 also do nothing and can be removed.
I don't agree regarding Q4. It might be intended to drive a capacitive load, e.g. cable capacitance.
You can't rate or correct the circuit without a functional specification. In this case input voltage, output load, required output voltage level and switching speed.
About a possible capacitive load:
- Current limiting resistors should be on the collectors of the output transistors.
- The output voltage during switching may exceed the maximum reverse base-emitter voltage on both output transistors which is only 5V.
I think the circuit still needs a bit of work.
(Just an observation. The opto-coupler is slow with a rise and fall time of 5us. No 10Mbits per second or doing anything at a high frequency.)