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I wish to use a MOSFET to drive a 12V rated LED strip from an Arduino.
The negative side of the LED strip must be connected to ground, so that means that the driving MOSFET must be between +12V and the LED strip.

This is what I have tried so far.

led strip mosfet arduino

The load must be between my mosfet and my car battery GND.

Russell McMahon
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hanoo
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1 Answers1

2

In your existing arrangement.

Swap to P Channel FET
Swap drain and source leads (right hand two).

This will work for up to 5V feed to LEDs.

To get 12v operation you will need to add a driver between the FET gate and the Arduino.
see circuit diagram below.

To operate with FET on the HIGH (V+) side when V+ is greater than the rduino's supply voltage, the FET must either

  • Be P Channel with FET source to +12V and FET drain to load+ or

  • An N Channel with gate drive above V+.

    The gate drive to the FET must go to about +12V to turn it off.
    The Arduino will only drive it to +5V.

As you are unlikely to want to provide an extra high side drive the P channel option is preferred. This could be eg:

  • A "jellybean" bipolar transistor or small FET worth a few cents) and a few resistors, or a small N Channel MOSFET and one resistor

or

  • An opto isolator.

Transistor driver:

Bipolar transistor NPN (BC337 / BC817 or similar)(ANYTHING NPN will work).
R1 = 10k resistor Arduino out to base.
R2 = 10k FET gate to +12.

If an N Channel MOSFET is used for Q1 then R1 is not needed.

This could be a 5LN01SP IF you can get them - no stock Digikey.These have a very low Vgsth (turn on voltage)

Otherwise you can use a 2n2222, VN2222, BS108 or similar logic-gate N channel MOSFET.
eg VN2222. Many variants of these are widely available and low cost.

schematic

simulate this circuit – Schematic created using CircuitLab

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Russell McMahon
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  • won't it drain the 12v battery to have a link beetween +12 and GND throuth R2 ? 2) I have multiple led strips, can i simplify the circuit if i use it multiple times (reuse some components) ?
    • – hanoo Feb 08 '15 at 17:18
  • @hanoo You should be able to work out the current drain answer yourself. Treat all such as a learning exercise and not just blind copying or you will not progress BUT :-) -> (1) R2 is 10k Ohms (see text). Current in 10k is I=V/R = 12/10k = 1.2 mA. Current in LED strip = Power_Watts/V. Here for say 5 Watts = 5/12 = 0.417A = 417 mA. ie R2 current is about 0.3% of LED current at 5 Watts = trivial. (2) You can place any load that works on 12V at output of M1 - so eg N x 12V LED strips as long as the FET current rating is adequate. .... – Russell McMahon Feb 08 '15 at 22:07
  • .... | If you want to drive multiple FETS at once you can connect FET gates to Q1 collector directly. This works if M1 is MOSFET. If M! is a bipolar transistor you need a resistor between Q1 collector and M1 base in each case. – Russell McMahon Feb 08 '15 at 22:08