Electronic – Explanation needed on using 2 transistors as a switch

switchestransistors

I'm suggested to use following design to drive a load with a micro-controller. I would like to know that why is it needed to use 2 transistors (n-ch and p-ch) to act as a switch and not only one?

I searched over Google and youtube, and most pages were using one transistor (mostly n-ch) to make a switch, like this page:

http://www.electronics-tutorials.ws/transistor/tran_7.html

Could you please explain me advantages or disadvantages of having such design (2 transistors) over one-transistor switches?

schematic

simulate this circuit – Schematic created using CircuitLab

Best Answer

If the digital signal swing is the full 5 V, then you can use just the final P-channel FET.

The advantage of the two-transistor circuit is that the power voltage being switched and the digital signal power voltage don't need to be the same. The circuit you show would work with the power voltage being up to the maximum G-S voltage the second FET can handle.

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