Hi. I was really confused with what exactly does it mean when there is a positive current running on a N-MOSFET. I build a H-Brigde which works fine but i followed some online guides etc..
The thing is an N-MOSFET is sait to connect Drain and source beacuse the gate is connecting them when there is a positive current on the gate. However i know that a electrons flow from Ground to the positive side. So exactly what is meant by a positive current? Will the N-MOSFET be on with LOW or HIGH on the gate??
N-channel MOSFET typically connects motor 'negative' terminal to Gnd, acting a 'low side' switch. It "sinks" current from the motor.
P-channel MOSFET typically connect motor 'positive' terminal to Supply voltage, actin as a 'high side' switch. It sources current to the motor.
Electrically & physically, electrons may flow from negative to positive. By convention tho, current is discussed as flowing from positive to negative. Follow that convention for current and you will be in sync with everyone else.
N-channel turns on with their Gate driven high(er than their source), while P-channel turns on with their Gate driven low(er than their source). Thus +Vgs to turn on N, and -Vgs to turn on P, with the voltage measured with the Source as the reference point.
In both cases, Gate voltage = Source voltage = MOSFET off (not conducting).
CrossRoads:
N-channel turns on with their Gate driven high(er than their source), while P-channel turns on with their Gate driven low(er than their source). Thus +Vgs to turn on N, and -Vgs to turn on P, with the voltage measured with the Source as the reference point.
In both cases, Gate voltage = Source voltage = MOSFET off (not conducting).
Thanks for clearing that up for me. I just needed to make sure i had understood the theory correctly for future reference!
However i know that a electrons flow from Ground to the positive side.
If you are not doing something that involves chemistry or quantum physics, you will never need to care about exactly what kind of charges are flowing in exactly which direction. All of that is abstracted away with "conventional current". If you have 1 amp of positive charges flowing from + to -, and 1 amp of negative charges flowing from - to +, you don't have to treat them separately. From the perspective of electric and magnetic fields, it is equivalent in every meaningful way to 2 amps of positive charges flowing from + to -.
Conventional current is not "wrong", it is a mathematical abstraction that eliminates unnecessary details.
If you are not doing something that involves chemistry or quantum physics, you will never need to care about exactly what kind of charges are flowing in exactly which direction.
However diodes and transistors have charge carriers or both polarities (electrons and holes), so the sign
of the charge carrier often crops up with semiconductor devices, especially when describing how they work.
A few decades ago the ubiqitous CRT would also make the sign of charge carriers explicit, and prior to
that thermionic valves.
But we stick to the original sign convention because changing it would be completely confusing!
