MOSFET as on/off switch

This post is a summary of my findings on how to use MOSFET as on/off switch.

Below is the configuration of a decoder circuit based on push buttons and I want to automate the pressing of the buttons. For this kind of application, the easiest way to do it is by using relays. However, as relays are bulky* and noisy, they are ruled out for this exercise.

* I was told to consider Reed Relays (http://www.digikey.com/product-detail/en/CRR05-1A/374-1039-1-ND/698050). I think I will give them a try some other time..

I must admit that I didn't do well in Circuitry when I was in school and I found it painful to do circuit analysis. As a result of my own ignorance, I came out with the below design as my 1st design, which, of course, doesn't work. :-(

After further research, I came across Electrical Engineering StackEchange and posted my question there (http://electronics.stackexchange.com/questions/177056/using-arduino-mosfet-to-automate-the-pressing-of-button?noredirect=1#comment362798_177056). To my surprise, I received answers to my questions within hours. I want to give a big thank you to those tirelessly providing support on the forum. THANK YOU...

The solution works perfectly and its behavior is exactly what I need.



If the below behavior is acceptable, there is a simpler solution.

Vin = 0V, Vout = 12V (Vout remains at 12V until Vin = 5V / 12V - because of the pull low resistor)
Vin = 5V** / 12V, Vout = 0V

** Whether Vin = 5V will work or not is dependent upon the specs. of the MOSFET. For example, Vin = 5V doesn't work in the below configuration.

Below is the behavior of the above configuration:

Vin = 0V, Vout = 12V
Vin = 12V, Vout = 0V (Vout remains at 0V until Vin = 0V - because of the pull up resistor)

To drive P-Channel MOSFET with Arduino, use the design below.

Now that I have a working design, the next step is to find the MOSFETs that are more suitable for my applications. I think FQP30N06L and FQP27P06 may be the ideal candidates.


MOSFET as a switch?

MOSFETs and How to Use Them

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