Sunnyrulz
Sunnyrulz
Branch Unspecified
18 Jan 2009

Can't figure out function of transistor in the given circuit

hey...!!
in the given circuit...i cant figure out the function of transistor...!!
ie. is it acting as a switch or an amplifier...??
Its a BJt pnp transistor...!!
If it is acting as a switch...then mode of its operation must be "saturation" or "cutoff"...but it is operating in active mode...??
please help...!!

[​IMG]
reachrkata

reachrkata

Branch Unspecified
10 years ago
I don't see how that is possible. The base current is high enough for the Transistors to go to saturation. Can you tell us the exact voltages that you measured across the 1kOhm resistors, the emitter-collector voltage and the LED forward voltage.

Secondly, the way i understood the circuit, i think all the LEDs are printed reverse.

-Karthik
😁
Rifaa

Rifaa

Branch Unspecified
10 years ago
Sunnyrulz
hey...!!
in the given circuit...i cant figure out the function of transistor...!!
ie. is it acting as a switch or an amplifier...??
Its a BJt pnp transistor...!!
If it is acting as a switch...then mode of its operation must be "saturation" or "cutoff"...but it is operating in active mode...??
please help...!!

[​IMG]

As u can see the the transistors are used to light the led and sound the buzzer which means they will saturate in order to apply enough voltage to forward bias the LED's. If no indicator meaning no LED's are lit then transistors are in cuttoff. So it's simple. The transistor serves as a switch for the 3 liquid levels and the buzzer sounds if it overflows.
Meaning the tr. operates either in cuttoff or saturate. Active region does not apply in these conditions.
If you need the tr. to be in active region then there should be a biasing circuit. Which from the diagram you can clearly see there is nothing of the sort.
Hope you understood me
Rifaa 😁

PS the LED's are in REVERSE. they will not light this way

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