You project has no description so it is not possible to understand what your project is intended to achieve and under what operating conditions. The BoM information is insufficeint because it does not indicate any manufacturers or suppliers so it is not possible to find datasheets to understand what each component or module is, what it is designed to do and what it should be capable of. Your schematic does not make sense. * Why is the LED strip returned to the gate of the MOSFET? * The step down converter is connected back to front. * You have no power supply decoupling (see: [https://easyeda\.com/andyfierman/Power\_supply\_decoupling\_and\_why\_it\_matters\_\-451e18a0d36b4f208394b2a2ff7642c9](https://easyeda.com/andyfierman/Power_supply_decoupling_and_why_it_matters_-451e18a0d36b4f208394b2a2ff7642c9)) The PCB layout is sub-optimal for a circuit including a switched mode power supply. The traces are very narrow and you have no proper ground or supply plane areas. Assuming that you have corrected the pin mappings between the incorrectly connected schematic symbols and the PCB footprints so that the connectivity of the PCB is actually correct for the parts you have fitted (but of course your schematic still looks wrong because you have corrected the pin mappings without correcting the schematic), then this poor layout and total lack of extra decoupling may be partly responible for the noises that the step down converter is making. What is also likely to be happening is that the step down converter is not well designed for use with zero load current and/or uses poor quality components that generate acoustic noise under certain operating conditions. Without a datasheet and schematic of the step down converter module itself it is not possible to say any more that that about it. You might however be interested to read this: [https://goughlui.com/2018/07/04/tested-mini-360-mp2307-based-3a-buck-converter-module/](https://goughlui.com/2018/07/04/tested-mini-360-mp2307-based-3a-buck-converter-module/)

Before posting back about this project, please read: [https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a) Thanks.

@andyfierman thanks for your response. this is my first project, so my post and my schematics are really bad. sorry. The description: I'm trying to power up a ledstrip with a 12v external power, and with the same supply also power the photon electron. The reason for using the mosfet is to control the ledstrips light. And i'm using a zener diode to make sure that 12v don't enter the electron by the ledstrip. I didn't find the part numbers since i bought most of the parts on banggood. but here are at least the links to them: 3.3 V zener diode: 1W Zener Diode DO-41 3V-30V 15 Values Assortment Kit For Electronic DIY Kit, [https://www.banggood.com/150Pcs-1W-Zener-Diode-DO-41-3V-30V-15-Values-Assortment-Kit-For-Electronic-DIY-Kit-p-1305825.html?rmmds=search&cur_warehouse=CN](https://www.banggood.com/150Pcs-1W-Zener-Diode-DO-41-3V-30V-15-Values-Assortment-Kit-For-Electronic-DIY-Kit-p-1305825.html?rmmds=search&cur_warehouse=CN) 100uf 16v Electrolytic Capacitor: [https://www\.banggood\.com/200pcs\-0\_1\-220uF\-15\-Value\-Electrolytic\-Capacitor\-Assortment\-Box\-Kit\-p\-1032358\.html?rmmds=search&cur\_warehouse=CN](https://www.banggood.com/200pcs-0_1-220uF-15-Value-Electrolytic-Capacitor-Assortment-Box-Kit-p-1032358.html?rmmds=search&cur_warehouse=CN) step down converter: DC-DC 12V 5V to 3.3V Step Down Voltage Regulator Power Module, [https://www\.banggood\.com/DC\-DC\-12V\-5V\-to\-3\_3V\-Step\-Down\-Voltage\-Regulator\-Power\-Module\-p\-1083356\.html?rmmds=search&cur\_warehouse=CN](https://www.banggood.com/DC-DC-12V-5V-to-3_3V-Step-Down-Voltage-Regulator-Power-Module-p-1083356.html?rmmds=search&cur_warehouse=CN) mosfet: IRFZ44N Transistor N-Channel International Rectifier Power Mosfet, [https://www.banggood.com/Wholesale-IRFZ44N-IRFZ44-Transistor-Mosfet-N-Channel-International-Rectifier-Power-Mosfet-p-44871.html?rmmds=search&cur_warehouse=CN](https://www.banggood.com/Wholesale-IRFZ44N-IRFZ44-Transistor-Mosfet-N-Channel-International-Rectifier-Power-Mosfet-p-44871.html?rmmds=search&cur_warehouse=CN) power supply: LUSTREON AC100-240V TO DC12V 2A 24W Power Supply Adapter For Strip Light + Female Connector - EU Plug, [https://www.banggood.com/DC12V-2A-24W-Power-Supply-Adapter-For-Strip-Light-Female-Connector-p-1154361.html?rmmds=search&ID=43101&cur_warehouse=CN](https://www.banggood.com/DC12V-2A-24W-Power-Supply-Adapter-For-Strip-Light-Female-Connector-p-1154361.html?rmmds=search&ID=43101&cur_warehouse=CN) ledstrip: 5M Cool White 3528 SMD LED Strip Light Non-Waterproof 12V DC 300 LED, [https://www.banggood.com/5M-White-3528-SMD-LED-Strip-Light-Non-Waterproof-12V-DC-300-LED-p-77079.html?rmmds=search&cur_warehouse=CN](https://www.banggood.com/5M-White-3528-SMD-LED-Strip-Light-Non-Waterproof-12V-DC-300-LED-p-77079.html?rmmds=search&cur_warehouse=CN) and a electron photon microcontroller. Why is the LED strip returned to the gate of the MOSFET? D0 from the microcontroller is connected to a zener diode, and into the gate. i dont want to have current(12v) flowing from the mosfet into the microcontroller, only the other way to turn the light on or off(or something in between). from D0 to mosfet. where should i connect the gate if not to D0? i cant see that the ledstrip is returned to gate. led strip minus is connected to middle pin which is drain. right? "The step down converter is connected back to front" not sure what you mean by that? "You have no power supply decoupling": i added a uf100 v12 capacitor from plus to minus right after the powersupply, but no change except that i get more stable voltage. is this what is needed to decouple? how wide should the traces be? are there some rules or guidance? i changed them to 0.8mm is that better? "no proper ground or supply plane areas": minus from the powersupply works as gnd right? that's the one i tried to use. and gnd on the microcontroller. since i get light i think i have connected the correct pin mappings between the incorrectly schematic symbols. i guess my design is still poor, can you please take a look at it again and point me in the right direction? i only get this noise when the step down is connected.

forgot to say and also only when pin is set to low digitalWrite(led1, LOW);

Please study your own schematic in: [https://easyeda.com/bernardthedog/led-strip](https://easyeda.com/bernardthedog/led-strip) As described in the Tutorial, in EasyEDA the Schematic is the master document from which the PCB is generated. So, all the info (schematic symbols, pin assignments, package assignments, pin mapping of symbol pins onto the pads of the assigned PCB footprints, BoM manufacturer, BoM manufacturer part number, BoM Supplier and BoM supplier part numbering) should be correct in the Schematic before you try to convert it to a PCB. The Tutorial includes a detailed checklist of everything you have to do before clicking **Convert to PCB...** in the Schematic Editor. There's another for everything you have to do before clicking **Submit** in the PCB Editor. Electronics is not like building with Lego bricks. Bang Good might be cheap but the information they give about the components is minimal. They seem to assume that you know exactly what the part is and it's performance before you buy it. That's fine if you know enough about what you are doing to be able to specify the parts you need correctly from OEM datasheets but for a novice with little or no knowledge of how components actually work or how they are specified then such sites are next to useless. So you need to go away and think about what your circuit is intended to do and then look at how you can achieve that function. Then you can specify the components that you need Then you need to look for appropriate parts and find the original manufacturer datasheets for those parts to verify that they meet your requirements. From there you can select the parts you are going to use which will probably also be governed by their cost and availability. For example, the IRFZ44N MOSFET: [https://www.infineon.com/cms/en/product/power/mosfet/20v-300v-n-channel-power-mosfet/40v-75v-n-channel-power-mosfet/irfz44n/](https://www.infineon.com/cms/en/product/power/mosfet/20v-300v-n-channel-power-mosfet/40v-75v-n-channel-power-mosfet/irfz44n/) [https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d](https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d) is in fact unsuitabe for your circuit because you are trying to control it using a controlled that runs from only a 3.3V supply and the IRFZ44N has a gate threshold voltage of between 2V and 4 V which means for some parts it may not effectively turn on at all. Your circuit is also wrong because if you use a MOSFET with a gate drive of 0V to 3.3V to control the LED strip supplied from 12V then not only is there is no need for the zener diode in series with the controller output but it should not be there at all because it drops about 0.7V off the voltage that should be connected to the gate and then prevents the gate capacitance from being discharged when the controller output drops to 0V because the the reverse voltage across the 12V zener is only about 2.6V so it never goes into reverse breakdown so effectively looks like an open circuit. Looking again at your PCB the pin assignments in the schematic are still wrong because the pad assignments in the PCB are also wrong. See the detail of the TO-220AB Package Outine drawing and pins assignment on page 8 of: [https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d](https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d)

You've said: "The description: I'm trying to power up a ledstrip with a 12v external power, and with the same supply also power the photon electron. The reason for using the mosfet is to control the ledstrips light." OK, it's a start but what do you want your circuit to _actually _do? What's it for? What's the purpose of it? How's it supposed to fulfill that purpose? What is the criterion for turning the LED strip on and off? Why do you need a "electron photon microcontroller" whatever one of those is? Time of day? Under Bluetooth/IR/Wifi/IoT remote control? Fading up and down for some sort of ambient lighting feature? Distributed slave flash illumination? Why do you need to use a complicated and not very well designed or specified 12V to 3.3V SMPS when you could use a simple linear regulator with far fewer problems? Unless of course the "electron photon microcontroller" draws some silly current: and where _is_ the datasheet for that? I just love websites that try to sell you clever stuff and then make it really hard to find out about it... [https://www.particle.io/](https://www.particle.io/) Where's the Search tool on the site? Where's the link to your "electron photon microcontroller".

Well, i'm going to have the ledstrip under my desk, and i want to turn it on and off by my phone, the photon [https://store.particle.io/products/photon](https://store.particle.io/products/photon) is connected to wifi, so i can send commands (functions) or to it, so i can dim the light, turn it on and off. i have full control of the ledstrip by using the photon, and its pretty easy to use. i love it and that why i have it in this setup. here is the datasheet for it [https://docs.particle.io/datasheets/wi-fi/photon-datasheet/](https://docs.particle.io/datasheets/wi-fi/photon-datasheet/) I dont need a complicated and not very well designed smps. if i can choose something else and have less problems im happy to use that. but step downs are also switching regulators. maybe i could have used a LD1117V33 [https://www.sparkfun.com/datasheets/Components/LD1117V33.pdf](https://www.sparkfun.com/datasheets/Components/LD1117V33.pdf) that can handle 12v to 3.3v. when i check other tutorials most of them use mosfets to control the ledstrip. the mosfet is working correctly for me, when it's on, it's about 10v on the strip. when i turn the mosfet off, (if that's the correct wording.), there is 0v on the ledstrip. and it seems like 3.3v from the microcontroller is enough to turn the mosfet on. strange thing is that some current are flowing from the mosfet through the zener diode to the d0 pin, but it's like 0.2v so not much, so you are probably right that the mosfet is like an open circuit and why do this setup work now even if it's all wrong? i'm able to turn on and off the ledstrip and also dim it, just like i wanted it to work? so back to my original question, why is there Whining Noise from my power supply when i connec the step down, and not if i remove it. (when i have it removed i connect usb to the photon) could i ask you to help me out a bit, and make a correct schematic, with components that you think would be better. so i get a better understanding? i know it's a lot to ask for, but it would really help me out.

"the mosfet is working correctly for me, when it's on, it's about 10v on the strip. ...and it seems like 3.3v from the microcontroller is enough to turn the mosfet on." No it's not. In your circuit when you turn the MOSFET on you have only 10V across the led strip from a 12V supply so you have 2V across the MOSFET. With an IRFZ744N is fully on it has an on-resistance of 17.5mOhms. You are not passing 2V/17.5mOhms = 114.3A through it. Therefore that implies that it is not turned fully on. I made a mistake when I was describing the problem you have created by putting the zener dioe in series with the IRFZ744N gate but only in the I mistook the polarity of the zener diode. I also was wrong when I said "Looking again at your PCB the pin assignments in the schematic are still wrong because the pad assignments in the PCB are also wrong." I mistook the orientation of the PCB footprint. My apologies for that: the footprint is correct. However... If you want to use the controller to dim the led strip then you have to use PWM. therefore you need to switch the MOSFET on and off at at least a few 100Hz so you don't see the flicker. With that zener diode in series with the supply to the gate it will slug the turn on so much that you would only be able to turn it on once in a blue moon because of the time it would take to charge the gate capacitance. In other words you could turn the MOSFET off fairly fast but not turn it on fast. That is completely incompatible with PWM. If you want your PWM to work properly then replace the zener with something like a 100 Ohm resistor. Now that you have provided a datasheet for the [https://docs.particle.io/datasheets/wi-fi/photon-datasheet/](https://docs.particle.io/datasheets/wi-fi/photon-datasheet/) then it is clear that you do need an SMPS for the 12V to 3.3V step down because it can draw nearly 500mA which with almost 9V across the regulator would dissipate about 4.5W in a linear regulator. So stick with your extra input capacitor across the 12V rail and you IN- plane but beef up the traces to the IN+ side of the smps module, and both of the output OUT- and the OUT+  tracks to the photon micro. Better: turn them both into copper plane areas. And put the input side IN- and OUT- planes on one side of the board and the 12V in and 3.3V out planes on the other. Note: even though the IN- and OUT- pins of the step down converter module are almost certain to be shorted together on the module PCB, it may be saferl to NOT treat them both as the same ground because it may make the module unstable. Without a PCB layout for the module itself it is not possible to be sure. In other words keep the IN- and OUT- plane separate. As for the whining noise with the leds turned off: as I said earlier, the module is not well specified enough to say with any certainty. It could be caused in a number of ways, none of which you can do much about other than, perhaps, by modifying the module.  If you can track them down, you could try asking the OEM.