Circuit Design Review (4 channels of PWM mosfets)

Projects General Guidance
1

Hi All,

Could someone please review my circuit design?

R1, R2, R3, R4 = 10K
Q1, Q2, Q3, Q4 = IRLZ44N (55v, 49a)
D1, D2, D3, D4 = 1N5819RL (40v, 1a Schottky Diodes)
J1, J2, J3, J4 = Screw terminal junction blocks. 1 = Live, 2 = Negative
J5 = 24v Input (1 = Live, 2 = Negative)

This is a simple 4 channel N-Mosfet controller to control 4 x 24v 600ma solenoids with the ability to lower PWM so i can hold the solenoids closed without burning out the coils

Power to the arduino hasnt been implemented in this design, but will come off the 24v in and through a buck converter to arduino 5v.

Schematic:

image
image602×499 4.32 KB

PCB:
(I will add a jumper from arduino to R4 as indicated by the blue line))

image
image575×482 5.79 KB

Software used: DipTrace (First time using it!)

Am i missing anything? Thankyou!

2
  • Why are you shorting the gate to the source ?

image
image602×499 4.32 KB

3

image
image666×528 3.39 KB

2 Likes
4

Arduino PWM Pin to Gate... 10K Pull down resistor... Source through that 10k? Well spotted!

Is this right?

image
image766×271 3.19 KB

5
  • See Post #3 schematic.
6

Sorry just seen that - will take a look - thankyou :slight_smile:

7

image
image766×271 3.19 KB

  • Slow down a bit . . .

  • R4 is shorted out.

1 Like
8

solenoids not driven by pwm in standard use.
R4 wrong in BOTH schematics.
No gate resistor R1.
IRLZ44N already has a built-in freewheeling diode.

9

Ok i think im there?

image
image546×599 6 KB

10

I did not realise IRLZ44N has a built in freewheeling diode - would it hurt leaving the diode in my circuit and have 2? Incase i ever switch IRLZ44N out for a different mosfet?

11

That's the body diode which is part of every MOSFET.

1 Like
12

A body diode conducts during the "dead-time" between MOSFET switching, while a flyback diode prevents voltage spikes when an inductor's current is interrupted.

So i would be correct in thinking i need to keep my flyback diodes?

13
  • DC inductive loads need a kickback diode.
1 Like
14

You can trust the body diode of the complementary MOSFET. Even professional drivers don't add extra flyback diodes.

15

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.