regarding (d3s ic) dual transistor npn pnp

i need to know why is D3S connected in such a way?

  • analog

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  • d3s

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  • transistor

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  • digital meters

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Thread Starter


Joined Dec 28, 2017
firstly I'm new to electronics project with some basic knowledge.
My project is "DAC controller"
The device is used to adjust the output voltage or current ( in that respective mode,the device works for both modes) based on the input vltg or current . ie as input raises the output should drop based on the scaled value from the microcontroller and vice versa as input drops output raises (can be considered as a comparator also).
Basically to understand in common words we are doing the job of a potentiometer(logic) in a digital meter,
i already have a demo model which is working fine but done by an another person.
I have got some knowledge on this spending these days but now im struck and i hope u guys can help me, thanks in advance.
microcontroller : msp430afe253
and from microcontroller 3 pwm output pins are considered . it is then connected to 3 different optocouplers(EL817,2nd pin input) and from optocoupler(4th pin output) it is connected to the "d3s" transistor mentioned above and the output is fed to opamp(op07cp) non inverting pin and output is fed back to inverting pin. This is the device output(opamp output pin)
i found out that any msp can generate a max of 3.5v (==msp ic vcc) but here in this device the output ranges from 0 to 5 v
from the above optocoupler connection i found out that the input voltage given to it is same as the output voltage(optocouler is mainly used here as a input output circuit isolater)
and opamp in that connection (maybe acts as a voltage follower, not sure)
so my doubt is from 3.5 to 5v how does it change, maybe only way is from the transistor ic i mentiond, but how?

question: What does this d3s actually mean and what happens when connected this way(attached below)
on img it seems like d38 but it is d3s.JPG