Hi everyone,

I am trying to boost the output of my TIL38, an IE LED emitter, with the help of an NPN BJT, 2N3904. The maximum current the TIL38 can handle is 150mA according to the datasheet and I am trying to boost the current through it to 100mA.

I connected the circuit below (please ignore the .nxp file as it is not in use):



In real life, I am feeding in to the base of the BJT, a 1kHz sine wave from a Wien Bridge Oscillator, with Vpp of 1.64V, Vmin = 1.8V to Vmax = 3.44V.

The output from simulation above is:



However, I am not getting an output from the oscilloscope in real life.

May I ask if this is due to a difference between simulation and the working of the circuit in real life?

Thank you.

 

What is Q1, 2N7000 or 2N3904 ?
R3 is too low, try 2k2 to 10k. You need around 10 mA base current.

 

What is Q1, 2N7000 or 2N3904 ?
R3 is too low, try 2k2 to 10k. You need around 10 mA base current.

Thank you for your quick reply and help. I am sorry for the confusion. Q1 is 2N3904, an NPN BJT. I see~ I will try your suggestion and see what the output is~ thank you once again! ^^

 

May I ask if this is due to a difference between simulation and the working of the circuit in real life?

Probably.

You have no series base resistor.
In real life that can zap the transistor, which is likely why you are getting no output.
The simulation model doesn't have the maximum limits of the device and will continue to operate under conditions that would cause a real device to fail.

The series base resistor value should be about 270Ω for a 3.44V peak input.

 

Probably.

You have no series base resistor.
In real life that can zap the transistor, which is likely why you are getting no output.
The simulation model doesn't have the maximum limits of the device and will continue to operate under conditions that would cause a real device to fail.

The series base resistor value should be about 270Ω for a 3.44V peak input.

Thank you so much for your input. I have tried your suggestion above based on my project's requirements and managed to get a sensible output which I will show in a later post for verification~

Thank you once again!

 

Hi crutschow~~ I tried your configuration and after some simulations in LTSpice and trial and error, I obtained the graph I wanted for the IR emitters~~ ^^ The graph looks like a normal square wave, except the top was slanting at a +45 degree angle~

I realized that biasing the base of the BJT with a square wave was much easier in controlling/determining the output of the BJT than a sine wave.

Thank you so much for your help once again!