How can a MOSFET be used to change voltage sources automatically?
At 1.55V gate voltage the LED is barely on, amazing what 5V at 20uA can do! Then at 2.3V the LED is very bright. So we have the relationship of a higher gate voltage allows more current to flow between the drain and source. How can a mosfet be used to change voltage sources automatically? I’ll show you.
What are the characteristics of an enhancement mode MOSFET?
The operation of the enhancement-mode MOSFET, or e-MOSFET, can best be described using its I-V characteristics curves shown below. When the input voltage, ( VIN ) to the gate of the transistor is zero, the MOSFET conducts virtually no current and the output voltage ( VOUT ) is equal to the supply voltage VDD.
Why do you need a VGS for a MOSFET?
In datasheets you see it called Vgs and they provide you a minimum voltage that is needed before the mosfet will allow current to flow through the drain and the source. We can build a simple circuit using a mosfet, LED, 10K and 330 Ohm resistors and a 10K pot to show what happens at different gate voltages.
Why do we need to connect MOSFETs in parallel?
While connecting together various MOSFETS in parallel may enable us to switch high currents or high voltage loads, doing so becomes expensive and impractical in both components and circuit board space. To overcome this problem Power Field Effect Transistors or Power FET’s where developed.V
How is a MOSFET similar to a transistor?
We can think of a mosfet sort of like a transistor, it has a gate, drain and source compared to the transistor which has base, common and emitter. With transistors that we want to act as a simple switch it’s all about adjusting the current at the base however with mosfets it’s actually the voltage at the gate that turns them on.
Is the 10K resistor still on when the MOSFET is off?
You’ll see that the 10K resistor on the left is still actually on however since both voltage sources grounds are separated this means the connection to ground is not through the mosfet so the resistor takes the full 5V voltage drop and the mosfet is now off.
Is there a way to disconnect both power sources?
If both power sources are connected at the same time, I want some kind of electrical switch, that would disconnect the battery and power the circuit just from the 5V USB. But the circuit still has to work, when only one of the sources is present. I tried to design a switch using two mosfets, but I was not able to figure out a working circuit.