Question about the bed mosfets modules

[hitman47]

Hello guys. Just a general question: I want to know if the common bed mosfets modules that are used in many printers, outside the boards , are N-channel please.

And if there’s no quick answer possible, is there an easy method to check if it is N-channel or not?

Thanks!

[mykepredko]

@hitman47

Just a general question: I want to know if the common bed mosfets modules that are used in many printers, outside the boards , are N-channel please.

The short answer is “Yes”.

The longer answer is they are if the bed is heated using DC current. You may have an issue with if gate “on” voltage of the N-Channel MOSFET is higher than the logic output voltage that is driving it:

Need help for PWM Led and IRF520

Not sure about this. In the end the boards are also just using simple MOSFET circuits and all of them will have some voltage drop. You’re missing the point of what I’ve written. The LED strip and MOSFET are essentially a voltage divider circuit. The higher the effective resistance in the MOSFET, the higher the voltage across it and the lower the voltage across the LED strip. The IF520 (and AOD4184A, which is used in the board that you are using) have an optimal on voltage of 4V or more: …

If the bed is heated using AC then you need to use a Solid State Relay (SSR).

[hitman47]

@mykepredko so according to what you said, my understanding is that the current sent from the control pin to the mosfet should not exceed the current driven by it.

So for example, if I want to drive a 24v module with such 24v bed mosfet module, I must not exceed 24v as signal, right? Or better, using a lower current as the signal?

Thank you for the information. It’s so great to have people with amazing electronics skills like you here to get good advices and not burn down the house.

[EddyMI3D]

@hitman47

so according to what you said, my understanding is that the current sent from the control pin to the mosfet should not exceed the current driven by it.

So for example, if I want to drive a 24v module with such 24v bed mosfet module, I must not exceed 24v as signal, right? Or better, using a lower current as the signal?

Please do not mix up current [measured in Ampere] and tension (commonly called voltage) [measured in Volt]

[mykepredko]

@hitman47

@mykepredko so according to what you said, my understanding is that the current sent from the control pin to the mosfet should not exceed the current driven by it.

No.

Transistors are devices that control the flow of current. The input to an N-Channel MOSFET that controls whether or not current flows through the transistor is voltage.

The higher the voltage, the more current will flow through the transistor up to a maximum.

What I am saying is that you have to understand the voltage that will be used to control the N-Channel MOSFET.

In the link I provided, if the MOSFET board you are using has an IRF520 (which is a common transistor used in these boards) is less than 4V then the transistor will not turn on to the point where the maximum possible current will flow through it.

This is a problem if you are using a 3.3V logic pin as the MOSFET control (which is what was being discussed in the link).

So, when selecting your MOSFET module, look at the N-Channel MOSFET transistor that is built into it and look at it’s datasheet to see what is the “Rated” or “Specified” Vgs and make sure it is less than the logic output of the pin that you are using:

[hitman47]

Thank you for the clarification. It does make sense now.