Purpose: To control the first MOSFET's on/off state with an IO port, to determine whether the gate of the second MOSFET has 15V applied and thereby control the second MOSFET's rapid on/off state.

Question 1: As shown in Figure 1, the gate of the first MOSFET is connected to an IO port, and the threshold voltage (Vgs(th)) of this MOSFET is between 0.45V and 1V, which should be sufficient for the IO port of the microcontroller to turn it on. However, when the first MOSFET is turned on, the second MOSFET does not turn on; conversely, when the first MOSFET is off, the second one turns on.

Question: When the second MOSFET turns on, since its source-drain voltage is equal to Vin, which is greater than 15V, at this time Vgs is less than 0, does this mean it does not conduct? Or does it remain conducting after it turns on, with the source-drain voltage equal?

Question 2: As shown in Figure 2, mainly by swapping the positions of the voltage divider resistors, when the first MOSFET is off, the second one is also off, which is the effect I want to achieve.

Question: When the second MOSFET turns on, its source voltage rises to around 15V, at which point Vgs is less than 0, does this mean it will turn off again?

Note: The answers to these questions will be noted in the next article.