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2psus

Please ignore the 2 green and orange lines in the middle and consider the transistors to be IRF mosfets instead.

First of all looking at the setup on the picture: is there any issues with using 2 completely separate power supplies here one supplying 5V to the Arduino and the other supplying 12V to the RGB led strip (the supplies are not connected on any way)?

Second Question: When using 1 single 20v 10A power supply with 2 buck converters connected to it one of them providing 5V and the other one providing 12V I have noticed the following (without using any Arduinos): if I connected the GND of the 2 buck converters which went to the MOSFETS as well and I used the 5V rail to control the mosfets I could measure 0.5-0.7A flowing through the 5V buck (which would ruin the arduino). Why is this happening? When I disconnected the 2 GNDs, aka the 5V rails gnd and + went into the arduino the 12V rails only to the LED strip I did not see any significant power draw on the 5V rail yet all of these guides recommend you to connect the GND of the 12V and 5V rails in case of using 1 power supply, why?

Thx

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Yes, there is a problem. There is no return path for the base drive. You are hoping to pull current from the base of each transistor but there is no return path to the 12 V PSU so it won't work. You need to connect the negative of both PSUs together and to the microcontroller's ground. This would be much easier to see if you had drawn a proper schematic rather than a hybrid wiring diagram.

The second problem is a "high-side fail".

enter image description here

Figure 1. The protection diodes on most logic chips creates a sneak-path to positive supply. This will keep the PNP transistor permanently turned on and may damage the chip. Image source: GPIO high-side driver fail.

If If VSS > VMICRO then the output protection diodes built into the chip provide a sneak path for the base current. The e-b junction of Q1 will be forward biased and current will flow through it, R1 and D1 to the micro supply. Q1 will turn on and LED will light and will not switch off. If the current is high enough the microcontroller will be damaged.

The linked article (mine) shows a fix for that if a high-side driver is required.

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  • \$\begingroup\$ Yes sorry about the bad picture and description but as I said these are MOSFETs not transistors what I have and as far as I know they are not current driven but voltage driven. Namely they are all IRFZ30s because these were the only ones I could salvage for this project. \$\endgroup\$
    – user106458
    Commented May 17, 2020 at 16:18
  • \$\begingroup\$ I suggest that you edit your question and add in a correct schematic. You can add one in using the CircuitLab button on the editor toolbar. Double-click a component to edit its properties. 'R' = rotate, 'H' = horizontal flip. 'V' = vertical flip. Note that when you use the CircuitLab button on the editor toolbar and "Save and Insert" on the editor an editable schematic is saved in your post. That makes it easy for us to copy and edit in our answers. You don't need a CircuitLab account, no screengrabs, no image uploads, no background grid. \$\endgroup\$
    – Transistor
    Commented May 17, 2020 at 16:50
  • \$\begingroup\$ Yeah I started doing the sketch, after 10 mins it require registration. :( \$\endgroup\$
    – user106458
    Commented May 17, 2020 at 17:51
  • \$\begingroup\$ Not if you followed my instructions carefully. Use the CircuitLab button on the editor toolbar. When finished press "Save and Insert". \$\endgroup\$
    – Transistor
    Commented May 17, 2020 at 17:54

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