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I want to control some 12V solenoids (SH-04215-015) from a Raspberry Pi Zero W. I believe I need to use a MOSFET transistor to switch from the 3.3V of the GPIO to the 12V the solenoids need. I'm not sure what MOSFET I need though; I don't understand most of the terms on the datasheets. I was looking at the 2N7000 MOSFET will that work for going from 3.3V to 12V? If not what do I need to look for on a datasheet to determin if a transistor meets my criteria?

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    \$\begingroup\$ A bipolar junction transistor may be a better choice for this situation. Even many so-called "logic-level" MOSFETs will not be very well turned-on by the 3V that you can expect from your microcontroller's output driver. \$\endgroup\$ – pericynthion Aug 19 '17 at 8:01
  • \$\begingroup\$ I see. I was getting that sense from all the MOSFETs I was looking at. What transistor would I want to use? Would the typical 2N3904 work? Or the 2N2222 maybe since it's optimized at 150mA? Would the large disparity between the 3V at the base and the 12V at the collector cause any problems? (I was under the impression that's why I needed a MOSFET) Sorry for having to ask.... I'm new at this electronics thing. \$\endgroup\$ – RedHatter Aug 19 '17 at 9:18
  • \$\begingroup\$ Ask another question about how to choose a BJT, and no need to apologise - that's what the site is for. Briefly though, either of those could work but I would choose one with a higher rated current so it will run cooler. Voltage disparity no problem. Don't forget base resistor and freewheeling diode. \$\endgroup\$ – pericynthion Aug 19 '17 at 16:58
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As JonRB said, NO.

The parameter to look for in a MOSFET datasheet is the Vgs at which the transistor has an acceptable Rds (series resistance) and can conduct an acceptable current. For your 2N7000 the relevant part is on page 2:

enter image description here

The first line for the Static Drain-Source On-Resistance is for 10V at the gate, which is for 500mA, which sounds OK*. The second line, for 4.5V at the gate, might still be OK for some purposes, but not for your solenoid, which draws 120mA. Note that there is no line for a lower Vgs.

*Never put your trust on a single entry in the datasheet. At 500mA with an Rds of 5 Ohm, the dissipation is 1.25 W, which is far above the 350 mW stated on the first page**. That 500mA/1.25W is probably OK under some very specific circumstances, like keeping the casing at 0 degrees C.

**Never trust a figure on the first page of a datasheet, read it as if it were written by the marketing department, not the engineers. But you can trust that a device will never do better than what is stated on the first page.

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No. The Vgt has a maximum of 3V, which means it is only just turning in. Equally fig1 shows the drain current for that gate voltage

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The link below, shows the FET you are asking about, doing almost exactly what you want. Change the high side voltage to 12V. You will need to know what current your solenoids require and if they require more than the FET you mention then you will either need to change the FET or feed the signal from the FET into another switch of some sort (BJT or FET switch).

http://www.hobbytronics.co.uk/mosfet-voltage-level-converter

There are also other logic level translators that you can use, however be aware of the level of current required by the solenoids as I mentioned before.

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    \$\begingroup\$ That page shows the FET uses as an I2C level shifter, which involves far less current than switching a solenoid. \$\endgroup\$ – Wouter van Ooijen Aug 19 '17 at 7:54
  • \$\begingroup\$ Hence my comment about using a power switch in conjunction with the level shifter. \$\endgroup\$ – JCollins Aug 19 '17 at 9:07
  • \$\begingroup\$ That doesn't make much sense. Level shift + power FET uses one FET too many; level shifter as power switch doesn't work because the source would have to supply the full current. BTW the 2N7000 isn't very good at 3.3V-5V level shifting either, despite it being mentioned in the page you link to. \$\endgroup\$ – Wouter van Ooijen Aug 19 '17 at 9:27

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