Hi folks,
I am about to build an H-Bridge driver for a small DC motor, I know I could probably buy one but its as much about learning as anything else.
I have bought some Darlington power transistors BD679A and BD680, NPN and PNP respectively, that have an hFE of 750 and contain a reverse bias protection diode and base/emitter resistors within the package.
In the past I have always found the minimum base current that would turn a transistor fully on by experimentation but I would like to learn how to calculate this from the data sheet.
I think I understand that a BJT is a current amplifier and that hFE is its gain in specific conditions but I defiantly dont understand how interpret the datasheet for one.
I have looked at several posts on this subject but still dont get it
If I want to use a BJT or Darlington BJT as a switch (saturated right?), in an open collector configuration, where ICE will effectively be limited by the load, how do I determine the required IB, given that the load and thus ICE may change. (Different motors for example.)
How would I calculate the voltage drop across the transistor for a given IC? Should I be thinking in terms of forward bias threshold like a diode or on resistance like a FET.
If the answer to the question above is forward bias, which I suspect is the case, is that forward voltage drop then proportional to IB when the transistor is partially on.
Any input would be much appreciated
Thanks, Alistair
I am about to build an H-Bridge driver for a small DC motor, I know I could probably buy one but its as much about learning as anything else.
I have bought some Darlington power transistors BD679A and BD680, NPN and PNP respectively, that have an hFE of 750 and contain a reverse bias protection diode and base/emitter resistors within the package.
In the past I have always found the minimum base current that would turn a transistor fully on by experimentation but I would like to learn how to calculate this from the data sheet.
I think I understand that a BJT is a current amplifier and that hFE is its gain in specific conditions but I defiantly dont understand how interpret the datasheet for one.
I have looked at several posts on this subject but still dont get it
If I want to use a BJT or Darlington BJT as a switch (saturated right?), in an open collector configuration, where ICE will effectively be limited by the load, how do I determine the required IB, given that the load and thus ICE may change. (Different motors for example.)
How would I calculate the voltage drop across the transistor for a given IC? Should I be thinking in terms of forward bias threshold like a diode or on resistance like a FET.
If the answer to the question above is forward bias, which I suspect is the case, is that forward voltage drop then proportional to IB when the transistor is partially on.
Any input would be much appreciated
Thanks, Alistair