I am using this BC807-40 transistor.
My maximum collector current through the transistor is 200mA.
I want to calculate the delay time between the transistor input Vbe and output Ic.
Is there a way or formula to calculate the delay time theoretically? I couldn't find any delay specification mentioned in the datasheet.
Whereas, for a MOSFET which I have used in a different circuit, I was able to find the delay time:
It is mentioned in the datasheet as turn on delay time and turn off delay time.
But this delay parameter is not available for all transistors.
Why don't the manufacturers of transistors mention this delay in their datasheet? Is it because transistors switch slower when compared to MOSFETs? Or which switches much faster between input and output?
Please explain.
Best Answer
That's a general-purpose transistor and specified for slow switching and slow (AF= audio frequency) linear operation. You can find general-purpose transistors specified for faster switching.
The speed of a BJT can also be influenced a lot by the circuit it's in, in an emitter follower configuration usually it doesn't saturate and will switch a lot faster. You can add a Schottky diode clamp to prevent saturation at the expense of a couple hundred mV more "on" voltage. You can use a speed-up capacitor across the base resistor.
Note that the datasheet MOSFET speed is dependent on driving the gate with about 1.5A peak. If you drive it with a high value series resistor or a wimpy drive circuit it will be much slower due to the Miller and input capacitances.