When to use a LED driver?

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1

Hi there,

I am switching 5 LEDs in parallel powered using a 3.7V lipo battery using a single transistor. I have seen LED driver ICs, but when should i use this? Is my current setup sufficient? I am using a lipo fuel gauge to monitor the battery.

Cheers

2

Jeffro_Aus:
I am switching 5 LEDs in parallel powered using a 3.7V lipo battery using a single transistor. I have seen LED driver ICs, but when should i use this?

Always.

Jeffro_Aus:
Is my current setup sufficient?

No. At the very least you should have a resistor for each LED.

3

At the very least you should have a resistor for each LED.

Ok, if i have a resistor also, will i still need a LED driver and what type would be suitable for parallel LEDs?

Thanks

4

Jeffro_Aus:

At the very least you should have a resistor for each LED.

Ok, if i have a resistor also, will i still need a LED driver

No.

A LED driver is better but you can use either. The idea is to limit the current.

PS: You also need a resistor for your transistor.

Jeffro_Aus:
what type would be suitable for parallel LEDs?

For five LEDs in parallel this is perfect: an6884 for sale | eBay

You won't even need a transistor. You can switch it directly from an Arduino pin (connect to pin 7 of that chip).

5

Quote from: Jeffro_Aus on Today at 10:06:10 am
what type would be suitable for parallel LEDs?

For five LEDs in parallel this is perfect: an6884 for sale | eBay

You won't even need a transistor. You can switch it directly from an Arduino pin (connect to pin 7 of that chip).

This is exactly what i am after. Thanks

Should each LED have a resistor? I couldn't find any good Arduino wiring diagrams.

6

Actually how should the AN6884 be wired also?

7

Jeffro_Aus:
This is exactly what i am after. Thanks

Should each LED have a resistor?

Nope. All you need is that chip, nothing more.

Jeffro_Aus:
Actually how should the AN6884 be wired also?

Connect the anodes of the LEDs to the battery, cathodes to the chip.

Use pin 7 to switch them on/off, don't connect pin 8.

8

A quick diagram I just made.

(nb. Don't worry about the "+5V", the chip works down to 3V...)

AN6884.png
AN6884.png730×490 5.43 KB

9

Nope. All you need is that chip, nothing more.

Connect the anodes of the LEDs to the battery, cathodes to the chip.

Use pin 7 to switch them on/off, don't connect pin 8.

Please check my attached diagram. The LEDs i will use are rated at 3.2V 20mA, and the battery voltage will vary a bit as it is a lipo 3.5-4.2V.

Is this setup fine now?

Thanks

AN6884.bmp (307 KB)