Hi everyone,

I'm working on a project using an Arduino Pro Mini (3.3V version) and a P-MOSFET IRLML6402 to control power to a module. The MOSFET is wired as shown in the attached schematic.
Setup:

• Arduino Pro Mini (3.3V)
• P-MOSFET: IRLML6402
• Control pin: D10
• Supply voltage: 3.3V

Observed Behavior:

• When I turn the MOSFET on (digitalWrite(pinD10, LOW):
  • Drain (D): 3.3V
  • Gate (G): 0.146V
  • Everything seems to work fine.
• When I turn the MOSFET off (digitalWrite(pinD10, HIGH):
  • Gate (G): 3.3V
  • Drain (D): 0.3V - 0.6V (I expected 0V!)

Even though the MOSFET is supposed to be fully off, there's still some voltage left on the drain.

Questions:

1. Why is the MOSFET not fully turning off?
2. Could this be related to the gate-source voltage threshold (V_GS(th)) of the IRLML6402?

Would appreciate any insights! Thanks in advance.

#define pinA3 A3
#define pinD10 10



void setup() {
  pinMode(pinA3, OUTPUT);
  digitalWrite(pinA3, LOW);

  pinMode(pinD10, OUTPUT);
  digitalWrite(pinD10, HIGH);


}

void loop() {
  Serial.begin(115200);
  Serial.println("Mosfet turn on 5 sec...");

  digitalWrite(pinA3, HIGH);
  digitalWrite(pinD10, LOW);

  delay(5000);

  Serial.println("Mosfet turn off 5 sec...");

  digitalWrite(pinA3, LOW);
  digitalWrite(pinD10, HIGH);

  delay(5000);


}

 

What is the load module?

 

Good question! Currently, there is no load on the module. However, I have connected an SHTC3 sensor, but there is no response. On the other hand, when I connect a Quectel LC86L GPS module, it works fine.

 

Without a load there is sometimes a residual voltage. Try a 10K resistor from Drain to ground.
Check polarity of the SHTC3 sensor? Does it work connected directly to 3.3 volts?

 

Hi, polarity is ok but forgot to initiate the module in arduino ide. I will do it in a moment.

 

Hi, finally I removed MOSFET and instead that put the SHTC3 into sleep mode what is much easier - so thank You for help