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I made two LED controllers using an ESP. On the PCB I'm using three 2N2222 transistors + resistor (1k Ohm) at the base to control the 12V circuit powering the LED strips by applying 3.3V from the ESP.
Schematic (Q1, Q2 and Q3 have been replaced by the transistors): enter image description here

Now I've got a problem: On one of the two controllers the Q2 transistor keeps blowing (Q2 is RED, not GREEN, as I accidentally mixed something up). It seems to be the LED strip, because I put it in place of the other controller and now it's working fine.

Could the problem be that the LED strip is too long? Or is there something faulty and I need to replace the whole strip? If more info is needed, I'll gladly provide it.

Edit: I still have the original controller, which uses an IR remote. If there's anything I need to measure while the strip is on, I can do that too.

The resistor soldered to the base of the transistor works, I just checked that. The red LEDs start flickering, and at some point the transistor blows

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  • \$\begingroup\$ A 2n2222 transistor is not rated for particularly high power, so it's entirely possible that you're overtaxing it. \$\endgroup\$ – microtherion Aug 14 at 22:28
  • \$\begingroup\$ @microtherion The thing is, this is the only one blowing out of the 6 I'm using total (3 per board, 2 boards). Also, what would be more critical, the 12V or the amperes (idk how much I have tbh)? \$\endgroup\$ – matthesinator Aug 14 at 22:30
  • \$\begingroup\$ What LED strip? Asking us to figure out why the transistor blowing and then not giving information as to how you set the circuit up (schematic) with part numbers is like asking us to fix a car without telling us who makes it and what model it is. \$\endgroup\$ – Voltage Spike Aug 14 at 22:36
  • \$\begingroup\$ @VoltageSpike it's a 2m smd 5050 strip, some cheap china thing. I ordered two, cut one down to about 1,7m and left the other at 2m. The short one is the one working. They run at 12V \$\endgroup\$ – matthesinator Aug 14 at 22:37
  • \$\begingroup\$ @matthesinator what model number of LED? \$\endgroup\$ – Voltage Spike Aug 14 at 22:39
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Most 2n2222 transistors have a max Ic collector current of 800mA. If each LED (only one color) drew 20mA and you had 60 (usually what a 2m strip has) of them that would be 1.2A which means you'll burn the transistor out. If your using this with a controller, then it could source amps of current which will also kill the transistor.

The other problem with modifying the schematic is NPN's are lossy and generate loads of heat under high currents. It would be better if you stuck with the original irlb8721's as a low side switch. They must be used as a low side switch and not high side.

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  • \$\begingroup\$ So cutting the strip down would solve this problem? How can I measure the amps, I'm pretty new to this. Also, I replaced the mosfets since they didn't output enough volts \$\endgroup\$ – matthesinator Aug 14 at 22:55
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    \$\begingroup\$ Were you planning the load on the source or the drain? \$\endgroup\$ – Voltage Spike Aug 14 at 23:48
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    \$\begingroup\$ @matthesinator Another option would be to use a different transistor, too, of course. A TIP31 would be an easy enough BJT to use for this. Though a FET still seems a better option. \$\endgroup\$ – Hearth Aug 15 at 0:12
  • \$\begingroup\$ @VoltageSpike Gate was connected to the ESP and would get 3.3V or nothing. Drain was connected to the strip, and Source was connected to the ground \$\endgroup\$ – matthesinator Aug 15 at 9:25
  • \$\begingroup\$ @Hearth any tip (hehe) on what FET to get? Or better, a tip on where to look for transistors, in case I need to look for some in the future? thanks \$\endgroup\$ – matthesinator Aug 15 at 9:27

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