Constant current ICs that provide 15-20 mA?

seanspotatobusiness

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I'm looking for constant current drivers in the form of single ICs with maybe only one or two external components required that will take power from a lithium-ion battery and drive one SMD LED at 15 or 20 mA. The AMC7113 (correction: AMC7135) is kind of what I want except that it does 350 mA. I'm hoping to find equivalent ICs that do 15-20 mA.
 
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seanspotatobusiness

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I found the AMC711X which provides 15 mA or 20 mA to upto three or four LEDs depending on which version you get and requires only an external capacitor (not sure if this is mandatory nor why they couldn't include it in the IC?). Alternatively there's the CN5711 and CN5611 which are variable from 30 mA to 1.5 A or 800 mA respectively, requiring only an external resistor to set the current. The CN5711 is the cheapest available option and I can just put two LEDs in parallel to take 15 mA each.
 

DIWdiver

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Sounds like the AMC711x is what you want. You could probably get away without the capacitor in a small battery powered device. If you have long wires between the battery and the driver, you should include the cap to ensure it performs reliably. Otherwise it could oscillate, draw a lot of power, and not give you the output you want. A small 0.1 uF ceramic cap should be fine.

The reason they don't include it in the chip is that even that small value is orders of magnitude larger than what they can put on a silicon wafer of any reasonable size.

I know you want me to define 'long' but I'm not going to. It varies from one part to another, and depends on your layout, battery, and other things. Generally up to a few inches you are okay, possibly quite a bit longer. What you would see if you need the cap but don't have it is that the chip would get hotter than normal. The LED current is likely to be low, but could even be high. If you put an oscilloscope on it you would see the LED current oscillating at a frequency in the tens or hundreds of kiloHertz.

Did you find a good place to buy these? I found lots of datasheets, but no actual parts for sale, except for a couple of questionable listings on eBay.

By the way, I think there's a typo in your first post. It's the 7135 that does 350 mA. The 7113 does 15 mA.
 

iamlucky13

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I've never tried it before, but the Luxdrive DynaOhm sounds like it could fit your need without any other external components. They have a 20mA version.

I'm not sure how they make it work with only two leads, but it wires in line with your LED like a sort of smart resistor, and it's not much bigger than a typical resistor. LED Supply has them.
 

DIWdiver

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The Luxdrive DynaOhm parts look really cool, and pretty useful in some situations, but they require an input voltage of 2.6V + Vf of the LED. Even for a red LED with very low Vf of 1.7V, this is a minimum of 4.3V, and not possible with a LiIon battery specified by the OP.
 

seanspotatobusiness

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I think that has the same problem as the DynaOhm, requiring a higher voltage than my cell will provide (and kind of wasting it?).


Sounds like the AMC711x is what you want. You could probably get away without the capacitor in a small battery powered device. If you have long wires between the battery and the driver, you should include the cap to ensure it performs reliably. Otherwise it could oscillate, draw a lot of power, and not give you the output you want. A small 0.1 uF ceramic cap should be fine.

The reason they don't include it in the chip is that even that small value is orders of magnitude larger than what they can put on a silicon wafer of any reasonable size.

I know you want me to define 'long' but I'm not going to. It varies from one part to another, and depends on your layout, battery, and other things. Generally up to a few inches you are okay, possibly quite a bit longer. What you would see if you need the cap but don't have it is that the chip would get hotter than normal. The LED current is likely to be low, but could even be high. If you put an oscilloscope on it you would see the LED current oscillating at a frequency in the tens or hundreds of kiloHertz.

Did you find a good place to buy these? I found lots of datasheets, but no actual parts for sale, except for a couple of questionable listings on eBay.

By the way, I think there's a typo in your first post. It's the 7135 that does 350 mA. The 7113 does 15 mA.


Questionable vendors are my specialty. The cheapest I found source for:

CN5611: https://www.aliexpress.com/item/10p...1bf11e5&transAbTest=ae803_1&priceBeautifyAB=0

CN5711: https://www.aliexpress.com/item/10P...927.html?spm=a2g0s.8937460.0.0.71c42e0eSald9K

AMC7111DNFT: https://www.aliexpress.com/item/AMC...e44fe40&transAbTest=ae803_1&priceBeautifyAB=0


The CN5711 is the cheapest considering I want a couple to use immediately and some for future projects. I have a bunch of random ceramic disk capacitors that I think I can use. Thanks very much for everyone's input!
 

iamlucky13

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The Luxdrive DynaOhm parts look really cool, and pretty useful in some situations, but they require an input voltage of 2.6V + Vf of the LED. Even for a red LED with very low Vf of 1.7V, this is a minimum of 4.3V, and not possible with a LiIon battery specified by the OP.

Good catch. Thanks for pointing that out.
 

jykelly

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This is very interesting. I hope you'll keep us informed about what your final choice(s) turns out to be.
 
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