NeoPixel-UserGuide-Alimenter

Alimenter des NéoPixels

NeoPixels are usually described as “5 Volt devices,” but the reality is a little more nuanced than that.

Some (not all) NeoPixel products can work with slightly higher voltages. This depends on the additional support components around the chip, based on available space, cost and the most likely application. Refer to the specific product description page for guidance on acceptable voltage limits for each type. When in doubt, aim for 5 Volts.

Lower voltages are always acceptable, with the caveat that the LEDs will be slightly dimmer. There’s a limit below which the LED will fail to light, or will start to show the wrong color.

450px	Before connecting a NeoPixel strip to ANY source of power, we very strongly recommend adding a large capacitor (1000 µF, 6.3V or higher) across the + and – terminals. This prevents the initial onrush of current from damaging the pixels.
	For many wearable projects we recommend a lithium-polymer battery. These deliver 3.7 Volts — perfect for directly feeding low-power microcontrollers such as the Adafruit Flora, yet enough voltage to run a short length of NeoPixels.
	Three alkaline cells (such as AA batteries) can be installed in a battery holder to provide 4.5 Volts. Though larger and heaver than the fancy lithium-polymer pack, they’re inexpensive and readily available.
	Four nickel-metal hydride (NiMH) rechargeable cells can similarly be used in a 4-cell battery holder to provide 4.8 Volts. Make sure you only use NiMH cells in this configuration. Four alkaline cells (the disposable type) will output 6V total — that’s too high for some NeoPixels, and definitely too much for the microcontroller!

Battery-operated LED project planning is discussed in greater detail in Piles et accus pour alimenter les LEDs et Rubans NéoPixels.

	For most non-portable “desktop” projects, a 5V DC switching power supply is ideal. This small 2 Amp supply is good for a a meter or so of NeoPixel strip. We’ll explain larger projects in a moment.
	Be extremely cautious with bench power supplies. Some — even reputable, well-regarded brands — can produce a large voltage spike when initially switched on, instantly destroying your NeoPixels! If you use a bench supply, do not connect NeoPixels directly. Turn on the power supply first, let the voltage stabilize, then connect the pixels (GND first).

Estimation de la puissance nécessaire

Each individual NeoPixel draws up to 60 milliamps at maximum brightness white (red + green + blue). In actual use though, it’s rare for all pixels to be turned on that way. When mixing colors and displaying animations, the current draw will be much less. It’s impossible to estimate a single number for all circumstances, but we’ve been using 1/3 this (20 mA per pixel) as a gross rule of thumb with no ill effects. But if you know for a fact that you need every pixel on at maximum brightness, use the full 60 mA figure.

To estimate power supply needs, multiply the number of pixels by 20, then divide the result by 1,000 for the “rule of thumb” power supply rating in Amps. Or use 60 (instead of 20) if you want to guarantee an absolute margin of safety for all situations. For example:

• 60 NeoPixels × 20 mA ÷ 1,000 = 1.2 Amps minimum
• 60 NeoPixels × 60 mA ÷ 1,000 = 3.6 Amps minimum

The choice of "overhead" in your power supply is up to you. Maximum safety and reliability are achieved with a more generously-sized power supply, and this is what we recommend. Most power supplies can briefly push a little extra current for short periods. Many contain a thermal fuse and will simply shut down if overworked. So they may technically work, but this is the electronics equivalent of abusing a rental car.

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Source: NeoPixel UserGuide créé par Phillip Burgess pour AdaFruit Industries. Crédit AdaFruit Industries

Traduit par Meurisse D. pour MCHobby.be

Traduit avec l'autorisation d'AdaFruit Industries - Translated with the permission from Adafruit Industries - www.adafruit.com

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