Brief Description on S S is a NPN transistor hence the collector and emitter will be left open Reverse biased when the base pin is held at ground and will be closed Forward biased when a signal is provided to base pin. It has a maximum gain value of ; this value determines the amplification capacity of the transistor normally S Since it is very high it is normally used for amplification purposes. However at a normal operating collector current the typical value of gain will be The maximum amount of current that could flow through the Collector pin is mA, hence we cannot drive loads that consume more than mA using this transistor.
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Knowing how your circuit was built and the model of your scope probe and its settings become relevant at this sort of capacitance level. Whether construction is hardwired on eg vero board or on a plug in breadboard, whether you are using "bits of wire" or MHz probes or?
It is likely that the circuit itself is swamping all these effects, but they start to come potentially significant at this level. Did you change them between displayed results? See below. The photos are useful and do a good job of showing us both what is happening AND that you are partially fooling yourself and maybe your viewers by what you show.
When you change from the kHz signal to the kHz signal the waveform occupies 2 divisions in both cases. This means that the rising waveform in the first photo is 5 x slower-rising than is apparent when making visual comparisons.
This makes a difference when you are trying to find out what effects are really happening and where they are occurring. Also, it looks like you have changed the vertical scale as well, with more sensitivity in the last photo compared to the first so that it looks taller. But, this difference may be accounted for by your probe calibration. Have you calibrated your oscilloscope probe?
If the probe does not let you display a square wave response to a low frequency square wave then it will mask the results at higher frequencies. Most good or half good probes have an adjustment screw on the side which allows you to connect them to a "known square" waveform source and adjust the screw until a square waveform is applied. While this may seem to be somewhat cheating by MAKING a waveform look square regardless it is a valid operation as long as the waveform is in fact square.
And also - you do not show the driving source at the transistor base, and it matters. You will usually use a drive resistor from a source of maybe 5 volts, and this resistor value can make an immense difference to the result.
A substantial improvement in frequency response can often be obtained by adding a "speedup capacitor" across the drive resistor.
Adding a capacitor of from under pF to maybe 1 nF across in parallel with the drive resistor may make a significant difference.
10x Transistor S8050 D331 - NPN - TO-92 - 37tran013