boylesg
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Never mind the 555 and everything to the left of it - have a good understanding of that part.
But I don't understand hoiw the designers of the circuit (below) have come of with the resistor values on the base of the BC327 and the base of the Darlington.
I have had a stab based on a 555 puting out from 50 to 100mA but I have not come remotely near the resitance values they did or the base saturation voltages of the transistors.
So I need a really basic lesson on how to do this and what known values you start off with.
Have had a go at using a BD140 and 2SD2348 from a television.....actually I joined two of the latter as a darlington pair. I just used the resistor values in the below circuit but obviously it didn't work with these different resistors.
Apart from the maximum ratings there doesn't seem to be an aweful lot of difference between the saturation levels of BC327 / BD140 and the darlington / 2SD2348
I get that the idea of the resistors is to set the base current and voltage at the saturation level of each transistor. But I would dearly love to know how to do this for myself with any transistors I might like to try.
But I don't understand hoiw the designers of the circuit (below) have come of with the resistor values on the base of the BC327 and the base of the Darlington.
I have had a stab based on a 555 puting out from 50 to 100mA but I have not come remotely near the resitance values they did or the base saturation voltages of the transistors.
So I need a really basic lesson on how to do this and what known values you start off with.
Have had a go at using a BD140 and 2SD2348 from a television.....actually I joined two of the latter as a darlington pair. I just used the resistor values in the below circuit but obviously it didn't work with these different resistors.
Apart from the maximum ratings there doesn't seem to be an aweful lot of difference between the saturation levels of BC327 / BD140 and the darlington / 2SD2348
I get that the idea of the resistors is to set the base current and voltage at the saturation level of each transistor. But I would dearly love to know how to do this for myself with any transistors I might like to try.