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I'm new to electronics and was wondering what was the difference between a Mosfet and a voltage regulator?

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    \$\begingroup\$ Short answer would be: Almost everything :) \$\endgroup\$ – XTL Jul 25 '10 at 9:23
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MOSFETs and voltage regulators often come in similar-looking packages and usually have 3 pins each, but their functions are different.

A voltage regulator takes in a high voltage, like 12 V, and puts out a lower voltage, like 5 V. The canonical example of a voltage regulator is the LM7805. They tend to be fairly inefficient (some of the power is lost as heat).

A MOSFET is a semiconductor switch. It varies the resistance between two pins in response to a voltage on a third pin. Inside the MOSFET, the voltage on the third pin (the gate) pulls electrons into a narrow path between the other two pins (the source and drain), allowing electricity to flow. Here's a decent diagram.

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  • \$\begingroup\$ Their inefficiency is directly related to the voltage drop across the regulator. Therefore, the efficiency is entirely a function of application, and it not something you can make a blanket statement about. I regularly use linear regulators to regulate a noisy ~6v down to 5v. That's a efficiency of ~80%, which is as good as a switcher generally gets. \$\endgroup\$ – Connor Wolf Jul 26 '10 at 7:40
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    \$\begingroup\$ @Fake Name: You're right that with a low-dropout regulator, you can get higher efficiency performance. But I think that when you're answering a question about the difference between a MOSFET and voltage regulator, it's reasonable to say that regulators tend to be less efficient compared to switchers, without going into the details. I'll change "half" to "some." \$\endgroup\$ – pingswept Jul 26 '10 at 14:07
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In very basic terms, a voltage regulator is a device for building a power supply, whereas a mosfet is something you use to build an amplifier. A voltage regulator is basically an integrated circuit that has several transistors within it, while a mosfet is exactly a single transistor.

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    \$\begingroup\$ If you view the input power as a signal floating on a DC bias, then a voltage regulator is acting like a filter that attenuates (as opposed to amplifying) fluctuations in the power signal. A poor man's voltage regulator is a single zener diode: en.wikipedia.org/wiki/Zener_diode#Uses \$\endgroup\$ – Eryk Sun Jul 24 '10 at 6:29
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    \$\begingroup\$ @eryksun: indeed, though I was just attempting to split the difference w/o going into all the possibilities. I didn't think describing a regulator as an amplifier with zero bandwidth would help a beginner (note tag) to get oriented. \$\endgroup\$ – JustJeff Jul 24 '10 at 12:52
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A MOSFET is a single transistor that will be able to provide a regulated voltage if used inside of a whole voltage regulator circuit (or IC). To build a (linear) voltage regulator, one needs a pass element (regulated "valve", e.g. MOSFET or biolar transistor), a voltage reference and a circuit that compares the desired, regulated output voltage to the reference voltage and adjusts the pass element such that the output will remain in regulation.

Thus, a MOSFET may act as one part inside of a voltage regulator.

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