Power conservation with neopixel strip

[jgilbert]

I have a strip of 30 neopixels as part of a battery operated project, cut from a strip purchased here. My goal is that the device is "on" all of the time, but I only plan to have the neopixels light up when someone is interacting with it. I discovered that even with the MCU powered down, the neopixels themselves draw close to 1mA each even when not lit when powered by a 350ma lipo from the AF store.

After googling the problem and not getting anywhere beyond the data sheet, I decided to put an N-channel mosfet between the strip GND and the project ground (product 355). I discovered that when ground is disconnected, the strips actually use more current and seem to get warm (some sort of short?).

Can someone recommend a better way to shut down the strip? I am at an extreme space premium, so smaller = better.

[adafruit_support_rick]

Have you tried putting the transistor on +5? I would think that would work better than putting it on GND.

[jgilbert]

Thanks for the suggestion. This did occur to me. However, wouldn't I need a P channel MOSFET? Wouldn't I have trouble triggering the gate with 3.3V logic?

[adafruit_support_mike]

You can use an NPN transistor (or an N-mosfet) to control the P-mosfet:

p-mosfet.jpg (14.73 KiB) Viewed 423 times

When the NPN is turned off, the 100k resistor pulls the P-mosfet's gate to 5v, keeping it shut off. When the NPN turns on, it pulls the P-mosfet's gate to GND, turning it on as well.