Schematic Review PWM and MOSFETs

Hi All,

I am working on a fan controller that will be built on a custom board and am looking for any advice on this schematic. Do I need a cap on pin 1?

What it is:

  • Two fan outputs controlled with 4 MOSFETS driven by PWM.
  • Two NTC temp sensors
  • Serial LCD
  • Programing header

Some comments on your "schematic". Reset is active Low, you need it pulled high. Your programming header needs a DTR input, goes to a 0.1uF cap to reset. You need 0.1uF caps on Vcc, Avcc, and Aref as you appear to be using the analog inputs. How are you installing a bootloader/sketch on the chip? I don't think you have two PWM outputs connected.

Thank you CrossRoads,

Oops about butchering "schematic" that's what I get for using my phone's auto correct... :fearful:

Anyway, I have added the cap to pin 1 for DTR. I thought I needed it but was unsure why I have looked into that some more and now understand. Also made it high.

You need 0.1uF caps on Vcc, Avcc, and Aref as you appear to be using the analog inputs.

What are the caps for? (other than filtering input) Also the sensors will be 5v so I was going to not use Aref, do I still need the cap?

How are you installing a bootloader/sketch on the chip?

The chip has the bootloader on it now, and i am using a SparkFun FTDI breakout board to program (now I have a 6 pin header to match)

I don't think you have two PWM outputs connected.

Not sure exactly what you see that I dont but I did find that I was off by one pin, I moved the PWM MOSFET drive to pins 11 and 12, I don't care if they run at the same frequency as long as I can change the duty cycle in the code based on temp. (separately)

The caps provide immediate and close by power source to smooth out high frequency power surges from internal switching.

PortD is D0,1,2,3,4,5,6,7 D3 is PWM, D4 is not. D5, D6 are PWM.

I think this has all the changes.

If anayone has any suggestions bring them on… 8)
I am looking at pulling about 15A from each set of MOSFETS, more than I have ever tried before. each is rated for 30A but it is going in a high ambient temp location.

NOTE: The MOSFETS have diodes in them already, it just does not show it in the drawing.