I'm wanting to drive a NeoPixel from a CMOS device. The power for the neopixel is a 4v LiPo battery and will fall from around 3.9v to 3v before it cuts off. I have a few PN2222 NPN transistors, I'm not sure what kind of circuit I should be building out of them. The neopixel needs around 0.4us timing.


The CMOS device will have a step up/down regulator. It's output will be a steady 3.3v. I will be powering the neopixels from the battery directly (3.9-3v is in it's operating range). I need to ensure the signal the CMOS device is sending to the neopixels matches the neopixel's input voltage.


  • \$\begingroup\$ PN2222 is an NPN transistor. onsemi.com/pub/Collateral/PN2222-D.PDF \$\endgroup\$ – caveman Jan 17 '15 at 6:48
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    \$\begingroup\$ If your load requires a constant 3.3V from a battery that will drop to 3V and you want maximum operating life then you'll need a buck-boost SMPS that will put out 3.3V from any input between 3 and 4V. If your load can take work down to about 2.8V, or you can accept a shorter working life, then you can get away with a much smaller, simpler & cheaper low dropout voltage regulator. \$\endgroup\$ – markt Jan 17 '15 at 6:48
  • \$\begingroup\$ Why not giving a try to a low side driver? Use npn transistor. \$\endgroup\$ – Sergey Sukhotinsky Jan 17 '15 at 10:46
  • \$\begingroup\$ Whoops, I do have NPN transistors not pnp. \$\endgroup\$ – reconbot Jan 17 '15 at 17:29
  • \$\begingroup\$ I have a low amperage power source for the cmos device. I'd like to power the LED's from the Lipo battery but need to ensure it's signal pin gets the same as VCC.. I'll update my question. \$\endgroup\$ – reconbot Jan 17 '15 at 17:31

This isn't perfect, but it gives me an almost 0.3v and VCC output from a 0v and 3.3v input.

NPN transistor level shifter

  • \$\begingroup\$ @sergey-sukhotinsky is this what you were talking about? \$\endgroup\$ – reconbot Jan 18 '15 at 5:06

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