What happens when the MOSFET is turned off on a solenoid?
The short answer is that you need a freewheeling diode to conduct the current when the MOSFET turns off; the solenoid has inductance that stores energy in the magnetic field, and when you turn the MOSFET off the inductance will generate however much voltage is necessary to continue flow of that current.
How is a MOSFET switch connected to a supply rail?
In this instance the MOSFET switch is connected between the load and the positive supply rail (high-side switching) as we do with PNP transistors. In a P-channel device the conventional flow of drain current is in the negative direction so a negative gate-source voltage is applied to switch the transistor “ON”.
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
Why are MOSFET switches used in CMOS circuits?
MOSFET’s make very good electronic switches for controlling loads and in CMOS digital circuits as they operate between their cut-off and saturation regions.
What happens when you connect a solenoid valve instead of a led?
But then I connect my solenoid valve instead of the LED. It works for a few seconds, then it stops working and the MOSFET ends up permanently conducting current, regardless the state of the 5V control pin. The MOSFET is permanently damaged, because when I connect the LED again, it doesn’t work anymore. Too much current?
How many milliamps does a solenoid valve draw?
This MOSFET is fine for very small loads like LEDs drawing a few milliamps. But solenoids generally draw tens or hundreds of milliamps, and you need to calculate I2R loss in your MOSFET for the current load it draws, and make sure that it doesn’t cause your transistor to overheat.
Can a voltage pulse cause a MOSFET to breakdown?
The resulting voltage pulse will cause breakdown in the MOSFET which causes the damage you are seeing.
Can a MOSFET be used as a microcontroller power switch?
This is a poor choice for a MOSFET used as a power switch from a microcontroller. First of all, the MOSFET is specified at 10V Vgs. You’re supplying it from a 5V microcontroller. You need to make sure you use MOSFETs that are “logic level” and have on-resistance specified at 4.5V or 3.3V Vgs.