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Sry, english is not my first language. this answer is in regard to which question ?Assume Vce(sat) is 0V and that the other two transistor's input pin is equivalent to their base resistor to ground.
Those conditions lead to a slight overestimate
This calculation of current is trivial and I would be profoundly disappointed if you can't do it.
the current is highly unlikely to exceed 1mA for the first transistor ?The one you asked immediately prior to me posting it, and then repeated immediately after I posted it.
approx 0.7 drop across diode and 0.6 across the transistor . so abt 1.3 volt ,right ? why 1.8 v?No, it's in common emitter config. It's pretty much impossible for these biased transistors to be anything else.
T201 will start turning on when TM+ exceeds Vdd5 by more than about 1.8V.
Isn't it 7.3V- 0.2 V ??I don't know, perhaps you should just say it pulls the output low.
Vbe of 0.7 is not what you need to worry about. Remember that there are not just transistors. You need to use the minimum on voltage from the datasheet.
Vcc5 - 0.2V from memory.
The voltage on the collector of the first transistor is (volatge at Tm+ - diode drop - transistor drop )What is the voltage on the collector of q201a (or whatever the first transistor is)?
I'm working through the "why no more than 1mA" question.
the current then will be the voltage at collector divided by the resistance. oh ok , I guess I had a confusion regarding the Vbe . So I have to assume the Vbe to be 0 ? right ?Yeah, sorry, you're right. I misremembered it.
Now you have that, assume the entire load is the resistor between the input terminals and bases (assume Vbe is 0V).
What current will flow?
Ok , thank you steveYep. It will overestimate the current a bit, but that's fine.
there are two paths , to two base resistors of different transistors. Should I consider those two resistors parallel in connection and use ohm's law ?Can you see a path to any rail?
Would I be right in considering the resistors as in parallel ? (the base resistors of transistors)You can use ohms law if you want to, but you can often consider the current through the transistor to be zero (I think they specify a maximum value of some small fraction of a milliamp, but I can't remember it off the top of my head)
How do I calculate the voltage at the collector of the first transistor ?You can use ohms law if you want to, but you can often consider the current through the transistor to be zero (I think they specify a maximum value of some small fraction of a milliamp, but I can't remember it off the top of my head)