How can I reduce the turn off time of my MOSFET?
A very effective way of reducing the MOSFET turn-off time if you are driving it by a single pull-up (or pull-down, as it is in the case of a P-channel MOSFET) is to use an active pull-down (pull-up in our case circuit). This can be realized simply as follows: The circuit works according to the following points:
Why does a MOSFET turn on at a lower voltage?
As the threshold voltage is between 2 and 4 V the FET might partially turn on for a few microseconds. By adding extra capacitance to the Gate your circuit increases the capacitive division ratio which makes the power-on transient Gate voltage lower, (hopefully) ensuring that the FET stays turned off when an external voltage is applied.
What to do if a MOSFET gate is left floating?
Just like a regular capacitor, the gate holds its charge till it’s removed or leaks away through the very small gate leakage current, to get rid of this charge, the gate must be discharged. This can be done by connecting the gate back to the source terminal. But what if the gate is left floating by the driving circuitry?
When does a n channel MOSFET turn on?
N-channel MOSFETs turn on when the gate voltage is a few volts above the source, the rating for these voltages are mentioned in the datasheet and the drain-source voltage is specified in positive volts. Current flows into the drain and out of the source.
Why does a FET turn off so slowly?
The FET is turning off slowly because the only thing driving the gate at that time is 10 kΩ impedance. That forms a rather large time constant with the effective total gate capacitance, which makes the turn-off slow. The gate of a FET looks capacitive to the driving circuitry.
Why do MOSFETs have a lower your D S?
More expensive MOSFETs can deliver less gate capacitance for a lower R D S ( o n) or maximum current handling ability. Also, don’t use a MOSFET with more current handling ability than necessary; you will pay for it in increased gate capacitance. Most gate driver designs can also benefit from driving the gate to a negative voltage.