Hi everyone one.

I am right now in my quest to learn electronics. So far so good but I have tripped over this circuit supposed to be a PWM controlled by Arduino.


The MOSFET's gate it already has a + voltage trough RC so it is conducting. What I understand is if the output PIN gives a + voltage, they transistor stars conducting and the gate's voltage drops to 0.

What am I missing?

Thank you

 

I am assuming that when you say "output PIN" you mean the output pin on the Aduino. If that is what mean the all you say is correct. So when the output pin on arduino is high the voltage on the drain of the mosfet is high. The current through R is zero.
If the circuit was controlling the speed of a motor then the motor would be in the place where R is on the circuit. So there would be power to the motor when the output of the arduino pin was low. You would have to write the code in the arduino to pulse the pin low when you wanted drive to the motor.
Les.

 

Hi everyone one.

I am right now in my quest to learn electronics. So far so good but I have tripped over this circuit supposed to be a PWM controlled by Arduino.

View attachment 353233
The MOSFET's gate it already has a + voltage trough RC so it is conducting. What I understand is if the output PIN gives a + voltage, they transistor stars conducting and the gate's voltage drops to 0.

What am I missing?

Thank you

In your circuit, the MOSFET will turn on during the LOW/OFF state of the PWM signal. If you want it inverted, ie, turn on the MOSFET during the HIGH pulse, you can follow the circuit in this tutorial.

 

What am I missing?

Not much.

The presence of the transistor indicates that the output voltage from the Arduino is lower than the turn on voltage of the MOSFET. Otherwise, the gate would be driven directly and the duty cycle would be modified appropriately.

 

THAAAANNNK YOU!!

It was driving me crazy. Just starting to understand the BJTs and the MOSFETs and when I saw this I thought I learnt nothing

 

Consider that in any circuit or system, that includes an arduino, or other processor, suddenly much more than an understanding of electronics is required.
That is the world of software and programming.
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