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I have an LED strip with 7.2 Wattage/m and the strip is 3 meters long. The led strip has R,G,B,+12v inputs and I have connected a 12V DC 1000mA power supply to the +12v and attached transistors to the R,G,B running to ground. When I run this circuit alternating between dimming the transistors and changing the light combination the Arduino gets hot. What can I do to keep this from happening?

The LED strip says that is requires a 12VDC 3A 36W power supply.

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  • \$\begingroup\$ Please provide a schematic of your circuit. I suspect you're driving the gates of your transistors directly, and this will draw more current that the Arduino is happy about. \$\endgroup\$ – WhatRoughBeast Jan 23 '15 at 2:35
  • \$\begingroup\$ "12V DC 1000mA power supply" aka 12W supply on a 21.6 W load... \$\endgroup\$ – Passerby Jan 23 '15 at 2:38
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    \$\begingroup\$ Yes, my arduino PWM pin is connected directly to the base of the transistor (no components between them) \$\endgroup\$ – user3916570 Jan 23 '15 at 2:44
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    \$\begingroup\$ Stop tormenting your Arduino and start using current limiting resistors and/or MOSFET's. \$\endgroup\$ – jippie Jan 23 '15 at 6:53
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1 - The LED strip says that it needs 12 volts at 3 amps. You are providing 12 volts at 1 amp. I'm tempted to ask, "Do you see a problem?" but you obviously don't. So get at least a 3 amp supply, already.

2 - You are driving the transistor bases directly, rather than through a base resistor. This is causing the Arduino to try to provide way more current than it can, so the Arduino is getting hot.

3 - If you do provide a base resistor which makes the Arduino happy, the transistors will not be driven hard enough to work without a heat sink, and they will get very hot and probably fail if you do it long enough.

4 - Regardless of whether the transistors fail, they will not be able to drive the LEDs to much brightness. A single transistor will not have enough gain. Sergei Grishin has the right idea, but make sure that the MOSFET can drive one amp reliably (some cannot, although most can), and that the maximum "gate threshold voltage" - Vgss - is greater than the output voltage of the Arduino pins. This will not be a problem if your Arduino is putting out 5 volts, but some MOSFETs will not work reliably with 3.3 volts on their gates.

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Use an N-Channel MOSFET instead of a BJT. Make sure to have a pull down resistor on the gate. (10K should work.)

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