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Topic: weird issue with a transistor and an external power supply (Read 625 times) previous topic - next topic


I'm driving a few 10mm LEDs, using an external power supply.  The transistor that I'm using is an MPS2222A.  When I disconnected my microcontroller from the circuit, the LED's were still receiving a small amount of current.  When I place my hand on the power supply, the LED's stop receiving current entirely.  My power supply is composed of a 5 amp pyramid linear power supply and a buck converter to step down the voltage. When I swapped out the linear power supply  for a battery the issue went away.  My best guess is some noise generated by the power supply is partially triggering the transistor and by placing my hand on the power supply I'm grounding it which either attenuates the noise or eliminates it completely.

Does anybody have an easy and safe solution for connecting the case of the power supply to the ground socket of an outlet (the supply only has a 2-prong plug, US mains)?


Hi, not an expert here, but try placing a 10 K Ohms resistor from the Base to Ground.


Thanks, I tried that.  It did reduce the current, but there is still a little current flowing to the LEDs.

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