# MOSFET arduino RGB LED strip problem

I'm trying to control my RGB led strip using my arduino. I'm using the following schematic: http://www.engineerathome.com/upload/rgbledschema.png

For some reason the led strip turns on when I connect the power, so the MOFSET conducts without a voltage from the gate. I've set the pin to the gate on LOW so there should be no voltage to make the MOSFET conduct. I'm using a BUK454 800A, the datasheet can be found here: http://pdf1.alldatasheet.com/datasheet-pdf/view/17129/PHILIPS/BUK454-800A.html

I'm new to MOSFET's so I have no idea what's wrong. Can anyone tell me what could be wrong? I've tested the MOSFET on a single led and it worked fine.

• connect a 100k or even higher value to gate and ground. This avoids the gate to float while Arduino is powering up/Off. Have you checked the turn on condition for MOSFET for the current required?. Share your schematics/wiring diagram. Give a link of the image, somebody can add it into the question Jan 7, 2017 at 9:57

The basic N MOS switch circuit is shown below. Please verify your connections.

VDD in your case 12 V. Vin is the control signal from Arduino.

The schematics you are referring to is a P-MOSFET while, the datasheet you have shared (which you are using) is N-MOSFET.

Below table indicates the gate voltage that is required to turn on the FET. Even for mere 1 mA the gate voltage may sometime needs to be 4 V (Arduino can provide a maximum of 5 V, some Arduinos,like Pro mini, Mega provide only 3.3 V). Since the LED strips datasheet is not available i am assuming at least it expects a few 100 mA for which chosen FET probably will fail to turn on. You have to choose another FET with lower VGS at required LED strip current. You cal also get away with gate drive circuitry to shoo the gate voltage from 5 V of Arduino to higher, but it will be not necessary, if you have access to other MOSFETs.

For some reason the led strip turns on when I connect the power

Possibly due to wiring issue or the FET have already gone bad (failed and D and S pins are internally short). If the FET is still working for single LED then it is time to replace the FET with other FETs which have lower VGS requirement for significant currents that will match LED strip current you are using.
Below is one example of FET, which can be used instead (DMG3420U: datasheet):

http://www.digikey.com/product-detail/en/diodes-incorporated/DMG3420U-7/DMG3420U-7DITR-ND/2279237

• Thanks for the great reply. I found that my strip is common cathode, so that's where the problem was. I bought a common anode and now the setup is working. But what is the setup for a common cathode led strip? Will I need P-channel MOSFET's? Jan 12, 2017 at 18:28
• Do you have part number of LED strips? Jan 12, 2017 at 23:53
• @lukas yes the common cathode strip needs a high side driver. In that case a p - channel mosfet. But since a p - channel mosfet needs a a gate voltage near the VDD, you need a small driver circuit, like a NPN or n channel mosfet to turn it on. The circuit isn't very different or much more complicated. Feb 8, 2017 at 4:02