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I,m trying to find the right mosfet or transistor to switch on-off a neopixel strip to safe battery power on a Lipo 3.7v using a pro mini 3.3v.

My Animation-Setup and Power Comsumption with 35 Neopixels is :

  • Sparkel : 20mA
  • Knight Rider : 80mA
  • Pulse : 600mA

So the maximum current for the ledstrip is 600mA @ 3.7v My first thought was to use the 2N 2222 - Transistor NPN TO-18 60V 0,8A 0,5W.

But then i realize the worst case: What happens if the all 35 Neopixels turn full white caused by a software glitch or a bug in the code. Full white means every neopixles consumes 60mA.

Total power comsumption: 35 X 60mA = 2.1A

Would be destroyed the 2N2222? Because it could handle only 800mA drain current?

How can I avoid this situation. So I read about Mosfet like this one FQP30N06L :

N channel power MOSFET
TO-220 Package
Vds = 30V max
Max current = 62A
Vgs = 2.35V max
Rds_on = as low as 8.7 milliohm - depending on Vgs

What do you think will it work to switch on/off the led if:

  • the drain current is between 20mA - 600mA - 2.1A
  • ledstrip Vcc is 3.7v
  • pro mini out 3.3V at max 40mA

Or is there an other suitable Mosfet for this problem than the FQP30N06L with 62 Ampere for these hardware setup with only 2.1 Ampere Peak @ 3.7v ?

Jupiter Moll
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1 Answers1

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You refer to a 2N2222 handling 800 mA. However, the 2N2222 datasheet shows 600 mA as its maximum rating for Collector Current – Continuous. Moreover, from the On Characteristics table, Collector – Emitter Saturation Voltage at 500 mA current could be as high as 1 V. In typical circuits with high base drive it usually is less, eg about 0.2 V typical with 50 mA base drive, which is more current than a typical AVR output is rated for. Anyhow, the Neopixels won't operate if your switch drops any significant voltage from the supply. Using a 2N2222 might work ok, or briefly, or intermittently, or not at all – depending on the quality of the 2N2222 and the amount of base drive.

You refer to a FQP30N06L handling 62 Amperes. However, the FQP30N06L datasheet shows 32 A as its rating for Drain Current - Continuous (vs 128 A for Drain Current - Pulsed, which is irrelevant here).

Using a FQP30N06L at its maximum 32 A continuous drain current would require careful heatsinking and perhaps 10 V of VGS drive to achieve low RDS(on), like 27 mΩ. With low VGS of say 3.3 V, RDS(on) might be twice as much. For example, if it were 45 mΩ, going above 4 or 5 A current would be problematic without careful heatsinking: 4 A → P = 4²·0.045 = 0.72 W, enough to heat up a not-heatsinked unit's junction by about 45℃ or 80℉.

But the FQP30N06L should work ok for your 600 mA typical-case scenario, and also should be ok with the 2 A worst-case as well.

James Waldby - jwpat7
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