Transistor switching

[Murugesh_89]

In the following circuit,



Supply Voltage at the collector 22k resistor is 5V.

when i input the R1 with the 5v then i get the output as Q1C,V = 0.03V as i expected.

But when i input the R1 with 0V then i did not get the complete 5V at the Q1C instead i am getting 4.15V. I tried with R1 as 1K and R2 as 4.7K then also same problem. This results i am getting in simulation.

When i did it practically i am getting 2V at the Q1C.

When i removed the connection to the mux from transistor then it is working perfectly.

Why it is happening like this when i interface with mux. How do i solve this problem?

Thanks,
Murugesh

 

[iimagine]

Because that mux is loading down the output, try a 220k across the output and the connection to the mux

 

[Murugesh_89]

Loading down means by what value of resistor? Do you have any internal schematic of 74151.

 

[iimagine]

Its pretty much voltage divider law. If the output voltage dropped to 2V then the input resistance of the 74151 mus be around 15k, hence Vout = R2/(R1 + R2) * Vin
Since your collector resistor is 22k, and you dont want the voltage to drop so you must set your output resistance to be 220k or higher

 

[crutschow]

What is the supply voltage to the 74151?

 

[Murugesh_89]

The supply voltage of 74151 is 5V