Hi, I'm trying to build some 12V control box using mosfets. The general circuit idea seems pretty easy to me, but there are few things that I'm just not familiar with enough and would like to get some suggestions.

Some general explanation:
I plan on building a circuit(all DC) that gets 12V@10A input, and have a few outputs that will have controlled output with either ON/OFF switching, or power control(e.g 50% pwm to run some device on ~5V).
The devices will take on average 0.5A to 1.5A, but I would like to be able to have a max of 5A for each output.

In theory, I think the circuit logic should be very simple. DC input, multiple mosfets with multiple gate resistor/gate drivers(one, both, idk..), and then connect to the arduino nano and outputs.

The ON/OFF switch will not happen often, so speed etc is not important here, the PWM control would mostly be static, might change once every few minutes or so.

The most important thing for me here is to keep power loss as low as possible, avoid gate ringing, and avoid electromagnetic interference.
If I understand correctly, I should look at higher resistors to have slower switching speed, but this means higher heat dissipation, so not really sure how to know what I really need.
In terms of gate driver, I'm quite clueless, so would love to get suggestions(do I need it, what do I need, what will this achieve, etc...)
I currently own IRF520N and IRF3205, technically I used them in the past with 12V and they both worked, but possibly for this application a different one would be needed.

Hope I explained enough, if more info is needed let me know, would love to get some suggestions on how to optimize it for my needs.
Thanks

 

A gate driver is only necessary if you are switching at high frequencies (above 10KHz).

Use logic level N-channel MOSFETs for low side switching and you can drive them directly from your Arduino.

 

A gate driver is only necessary if you are switching at high frequencies (above 10KHz).

Use logic level N-channel MOSFETs for low side switching and you can drive them directly from your Arduino.

Thanks, in that case I'd only need a gate resistor then?

 

Why do you think you need a gate resistor?

 

Why do you think you need a gate resistor?

Isn't it always recommended due to the initial high current to protect the I/O pins?

 

Isn't it always recommended due to the initial high current to protect the I/O pins?

It is not necessarily recommended. The gate of a MOSFET looks like a capacitor. As you know a capacitor will not pass any DC current. The high AC current will add charge to and remove charge from the gate to source and the gate to drain capacitance. When there is a gate resistor it forms a low pass filter with those capacitors which reduces the speed at which the MOSFET can switch. If you look carefully at gate resistors, you will find they are often low value resistors that do little or anything to restrict current into or out of the gate. They are sometimes useful in damping the ringing that can occur on some gate drive signals.

 

It is not necessarily recommended. The gate of a MOSFET looks like a capacitor. As you know a capacitor will not pass any DC current. The high AC current will add charge to and remove charge from the gate to source and the gate to drain capacitance. When there is a gate resistor it forms a low pass filter with those capacitors which reduces the speed at which the MOSFET can switch. If you look carefully at gate resistors, you will find they are often low value resistors that do little or anything to restrict current into or out of the gate. They are sometimes useful in damping the ringing that can occur on some gate drive signals.

Perhaps it's not necessarily needed, but I guess even a small 10 ohms resistor would be a better practice?
Regarding gate driver, though it might not be needed too, shouldn't it help with ringing and power loss efficiency? At least as far as I could find info on it.

Thanks.

 

Ho fast are you switching?

 

Hi,

I've been told that, some 50+ years ago when MOSFETs became widespread as switches, you had to use a resistor to prevent high frequency oscillations. I joined the party after those early days.

Basically, as far as I know, you use a 10 Ohm gate resistor. If you want to make the switching slower, I generally favour adding a small capacitor between gate and drain ("Miller") as this results in constant dV/dt gate-source voltage rather than an exponential R-C voltage.

I see designs all the time. I've never seen a MOSFET being driven directly from a low impedance output.

Cheers,

Alex