Need help with analysing this circuit

[Akshatha Venkatesh]

Details regarding the circuit- the TM+ is a varying voltage signal and VDD5 is a constant signal of 5v . Can anyone please tell me the use of the series diode in the circuit ?

 

[davenn]

Can anyone please tell me the use of the series diode in the circuit ?

there is no series diode

the 2 diodes in the middle of the circuit are acting as a form of voltage limiter

 

[Akshatha Venkatesh]

there is no series diode

the 2 diodes in the middle of the circuit are acting as a form of voltage limiter

Would you please elaborate ?

 

[Harald Kapp]

See e.g. here, figure 1 or read this discussion.

 

[Akshatha Venkatesh]

See e.g. here, figure 1 or read this discussion.

I read the discussion, and the cathode of the first diode is connected to Vdd , which in not the case here, so should I be knowing the voltage at point 4 of T201 (emitter voltage) to analyse the circuit ?

 

[Harald Kapp]

T201's B-E is just another diode.

 

[Akshatha Venkatesh]

Yeah , what will be the volatge at that point ? and how do i determine this ? should I look at the datasheet ?

 

[Harald Kapp]

should I look at the datasheet ?

Always a good idea.
However, for a first estimation you can also use 0.6 V as a typical value for the diode or B-E voltage.