[solved] Advice about the resistences

Other Hardware General Electronics
1

Hi everyone, last month I asked some advice to build my system adding mosfet. Now I am wondering if the resistences that I put between and the mosfet are good... I would feed sensors with 5V, the source is 5V and the mosfet that I choose is NDP6020P. (https://www.onsemi.com/pub/Collateral/NDP6020P-D.PDF) .
I followed this guide (https://www.gammon.com.au/motors) and I put 10k resistence and after 150 resistenze before the mosfet.
After some tests i mesure the volt in the drain and they are less than 5V. I ask you what resistence should I put before the mosfet?

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2

2022-12-10_16-12-30
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What was the value ?

3

The values Is 3.95 V

4

What is the voltage across the Drain to Source on the MOSFET ?

5

Mmm the source Is 5V and the drain 3.95.

6

No.

Measure the voltage from the Drain to Source on the MOSFET (i.e. across the MOSFET) when the MOSFET is turned ON.

7

How can i measures It?

8

We assume you have a DMM ?

Also, is the Gate voltage going from 5v to 0V if you toggle the Arduino output pin ?

And, the output pins are indeed set to OUTPUT ?

9

Yes i have

10

Red lead on Source, Black lead on Drain.

Also, is the Gate voltage going from 5v to 0V if you toggle the Arduino output pin ?

And, the output pins are indeed set to OUTPUT ?

11

Okok I put the Red on source and the black on drain but I read 0 on DMM.
Yes the Pin Is setted output but I can t see if the toggle the Arduino :frowning:

12

Can we try this again ?

Red lead on Source, Black lead on Drain, Arduino output pin, which is connected to MOSFET gate, set to give a HIGH (5V).

Also time to show us a good image of the actual wiring, and your sketch.

13

Okok thanks, I change the wire and now It run :blush: I tried a very simple sketch:

  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(12, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  Serial.println("high");
  digitalWrite(12, HIGH);  
  delay(5000);
  Serial.println("low");
  digitalWrite(12, LOW);
  delay(5000);                    
}

I noticed that the drain isn't 0V when the pin is 5V, is it right?
The value is 0,45V

14

Your volt meter is one of your best friends.

:nerd_face:

15

hihihihi yes, thanks :smiley:
i modified my ex post adding more details about output volt from the drain, in your opinion could it be a problem for my sensor?

16

In the guide, he's switching the low side with an N-channel MOSFET. However, on your schematic, you're switching the high side with a P-channel MOSFET. In this case, an NPN transistor should be added between each P-channel MOSFET and the control pin.

I think it would better (and simpler) to switch the low side.

17

In this case, 0V on the Gate of P MOSFET turns the MOSFET on.

The Drain, ideally, should go to 5V when Gate is 0V.

Due to the MOSFET’s internal Rds(on), a small Vds will be seen.

Rds(on) is ≈.041 ohms.

If you are seeing .45V (when the drain current is small) it might be your MOSFET is iffy :thinking:

Try a few different MOSFETs to see if they all act the same.

The same MOSFET here, with the Drain current at 1A, gives a Vds = 0.06V

18

If my pin output is 3.3V how can I run this mosfet?

19

It should work down to 2.5V.

20

Okok thanks, I Will try It with Arduino nano 3.3V