Proper way of triggering LED

[elki]

A very basic question. Naively, the circuit attached should be the most straightforward way to trigger a LED by a TTL-like pulse to the base of a NPN transistor. Somehow, when tested in real life, the input triggering pulse becomes distorted, which looks like a parasitic capacitance effect. Is there any way to secure the input signal shape when pulsing the LED?

[jmelson]

Your R1 (10K) only allows about 0.3 mA to flow through the LED.  Your base resistor R2 (1K) allows at least 3 mA of base current.  R2 should be at least 20 X larger resistance than R1.
Jon

[edavid]

You don't say exactly what problem you are seeing.

The saturated NPN switch will be slow to turn off - is that it?

For a visual indicator, this doesn't matter and your circuit is fine.

If you are trying to generate fast pulses, a different circuit would be better.  In that case, what are your actual speed and current requirements?

When you say it was tested in real life, did you build it, or just simulate it?

[Peabody]

Yes, it looks like the resistors need to be switched.

Also, any distortion in the base drive could also be dependent on the output capabilities of the "In" drive source, which become more important with such a low base resistance.

Could you draw us a picture of what you're seeing?

[kevin.gibbs]

Where are you measuring the distorted signal, and what is the duration of your pulses? Can you share the actual waveform?