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I want to control a 5V valve from my BeagleBone Black.

As a single GPIO port only has 3.3V with 8mA I cannot use common relays.

I found this thread: how to use a 3v output to control a 5v relay which covers the same issue. However I do not understand the result.

Does a single N-Mosfet enough to let this work or do I need all components shown in the circuit?

How do I calculate the values and type of the resistors, diode and N-MOSFET in that type of circuit?

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  • \$\begingroup\$ Yes, you need all the components, the two resistors, the mosfet, and the protection diode. \$\endgroup\$
    – Passerby
    Nov 11, 2013 at 13:16
  • \$\begingroup\$ @Passerby 1x 100 Ohm, 1x 10.000 Ohm but what about the mosfet? \$\endgroup\$
    – bodokaiser
    Nov 11, 2013 at 13:25
  • \$\begingroup\$ The mosfet must be able to handle the current required by the relay, and switch totally on at 3V or lower. \$\endgroup\$ Nov 11, 2013 at 13:26
  • \$\begingroup\$ What actually about the diode? What type does this have to be? \$\endgroup\$
    – bodokaiser
    Nov 11, 2013 at 13:32
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    \$\begingroup\$ To be on the safe side, the diode must be able to handle the relay coil current. For most relays an 1N4148 will do, for very large relays an 1N400x. \$\endgroup\$ Nov 11, 2013 at 14:14

1 Answer 1

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A single MosFet can do what you want, provided you use an appropriate MOSFET.

Because your GPIO can only output 3.3 volts, you need to carefully choose your MOSFET. Look at mosfet gate characteristics for gate threshold voltage. The FQP30N06L mosfet has gate threshold voltage of 1.0 to 2.5 volts, and your 3.3 volt system can easily supply this minimum threshold voltage.

The link you provide does show additional resistors. Without further information from you, just go with the typical resistors shown.

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