AMC7140 vs. LM713 current drivers

Hi tried searching a bit, but cant find any advantages of using one over the other as a constant current driver for high power LED's. Can anyone shed some light on pros and cons of each?

amc7135 ground-sinks 350mA, give or take a few tens of milliAmps. low dropout voltage, and it's on the ground-side of the load. Only usable with a single Li-Ion, though some have taken it over the 6V max by heatsinking the chip, and others speculate that you can drop the Vcc with diodes while keeping the supply to the load still high. Doesn't need external components unless LED is more than 2 inches away from the driver.

LM317 regulates voltage, but can be rewired to regulate current. Not just at a constant 350mA, but at a range of currents. Has much higher dropout voltage, though, so need more voltage for it to work. Also needs more external components, like resistors and capacitors.

7135's are the easiest to work with, but if you want to be able to set the current to anything, not just multiples of 350mA, then go for the lm317.

Thanks for the reply. I will be using the LED's for an automotive application, is there one that would be better than the other for that application? Also you mentioned capacitors, where would they need to go and for what purpose?

The LM317 isn't really useful as a current regulator for many applications, particularly portable applications, due to the dropout voltage mentioned by bshanahan14rulz, and the relatively high voltage it uses for current sensing.

Though there are some niches where one might be useful, there aren't many places where an LM317 (or lower-dropout equivalents like the LM1085/1086) would be the best choice.

What kind of applications did you have in mind (supply voltage, LED number, LED current, etc)?

Also both drivers can be used only with relatively low dropout voltage, as maximum power dissipation is key limiting factor. For AMC7140 maximum dropout voltage is about 1V for SOT-89 package and 1.3V for TO-252 package on the typical FR4 board. For LM317 this limit depends of the programmed current.

Some more linear constant-current LED drivers for power LEDs from different manufacturers:
CAT4101 - up to 1A current, PWM input, TO-263, up to 25V
http://www.onsemi.com/PowerSolutions/product.do?id=CAT4101TV-T75
MBI1801 - up to 1.2A current, PWM input, TO-263, up to 17V
http://www.dhes.co.kr/pdf/MBI1801PreliminaryDatasheetV1[2].02-EnglishSMD.pdf
NUD4001 - up to 0.5A, SO-8, up to 28V
http://www.onsemi.com/PowerSolutions/product.do?id=NUD4001
STCS05A - up to 0.5A, PWM input, SO-8, up to 40V
http://www.st.com/stonline/products/literature/ds/14510/stcs05a.htm
STCS1A - up to 1.5A, PWM input, SO-8/DFN-8, up to 40V
http://www.st.com/stonline/products/literature/ds/14455/stcs1a.htm
STCS2 - up to 2A, PWM input, powerSO-10, up to 40V
http://www.st.com/stonline/products/literature/ds/14456/stcs2a.htm

Thanks for the replies. I will be using this in an automotive application so voltage is around 12.6V-14.8V (car running). Is there one or the other that would work better? Also capacitors were mentioned, where would i need to put those and for what purpose?

88supraT said:

will be using this in an automotive application so voltage is around 12.6V-14.8V (car running). Is there one or the other that would work better?

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It depends of the required number of the LEDs, type of the LEDs and LEDs current. Could you please be more specific ?
For example, STCSxx linear drivers family listed above specially designed for simple automotive applications.
AMC7140 can not be used in your application, as it's maximum input voltage is only 6V.

I will be using Cree XP-G running at about 1000 ma. Possibly 2 or 3.

88supraT said:

I will be using Cree XP-G running at about 1000 ma. Possibly 2 or 3.

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Three XP-G in serial with STCS2A will work well in your application. You only need enough heat-sink for LEDs and driver IC. MCPCB is the best solution. 0.5mm double-side FR4, attached to the heatsink, also will work.
You will need to dissipate up to 15W in this setup.

If you only need 2 LEDs, or prefer to dissipate less power, buck converter is the way to go. Some examples:
MBI6650
http://www.dhes.co.kr/pdf/MBI6650_Advance_Information_V0_2_20070627.pdf
MBI6651
http://www.mblock.com.tw/en_download_file/datasheet/MBI6651PDV100.pdf
MBI6653
http://www.mblock.com.tw/en_download_file/MBI6653 Preliminary Datasheet V1.00_英文 繁中 簡中.pdf
PT4105
http://www.lesliewong.us/images/0808/PT4105E.pdf
AX2002
http://www.micro-bridge.com/data/Axelite/AX2002.pdf
AX2003
http://www.micro-bridge.com/data/Axelite/AX2003.pdf
ST1S03
http://www.st.com/stonline/books/pdf/docs/10992.pdf
LM3406
http://www.national.com/pf/LM/LM3406.html
AP8802
http://www.diodes.com/datasheets/AP8802.pdf
AP8803
http://www.diodes.com/datasheets/AP8803.pdf

You can also find ready-made driver boards, based on some of the IC listed above. Check this exellent drivers list:
http://www.videofoundry.co.nz/ianman/laboratory/research/driverlist.php

Another option - you can take assembled MCPCB board with LEDs and buck driver on board. Example:
http://www.led-tech.de/en/High-Powe...on-round-PCB-with-driver-LT-1544_120_117.html

for 1 white led 3.6v 20ma to work off automobile dc system, it needs 330ohm resistor.
in reality there is no need for fancy regulator unless you want it to dim via pwm. for simple on\off resistor is good enough, in a car mounted leds, you don't need to think of efficiency and run time.
i build many led modules for cars, all using 330ohm resistor for 1 led, all work just fine some for many years now, (you can also wire 3 in series with smaller value resistor, but i just had thousand or so 330ohm resistors, so i use them as much as i can).

alpg88 said:

for 1 white led 3.6v 20ma to work off automobile dc system, it needs 330ohm resistor.

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Sorry alpg88, 88supraT plan to use modern LEDs with 1000mA current, it is 50 times more, than with your LEDs. In this case efficient driver is essential.

lol, yea, i missed that little detail.

i would wire 3 in series, 4ohm 10w sand resistor would work just fine, voltage in car sys is relatively constant, if it is not, that he got bigger problems than dimming leds, if it was battery operated device than yes driver is important, for a car, you can do without.

though wouldn't he need a cap for the voltage spikes from the regulator?

alpg88 said:

i would wire 3 in series, 4ohm 10w sand resistor would work just fine, voltage in car sys is relatively constant

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Probably you will kill LEDs soon with this setup for several reasons.
First reason - voltage spikes on the power line due to ignition/starter work. Modern LEDs is very sensitive to overcurrent, so they will degrade quickly with this spikes. Confirmed by own experiments...
Second reason - as LEDs heat up, the forward voltage drops and the current passing through the LED increases. The increased current generates additional heating of the junction.

So, for typical XP-G LED running at 1000mA forward voltage is about 3.3V at 25C. If you have limiting resistor 4Ohm for 3 series LEDs, you will have the following LED currents:
As you see, with this resistor you will have more than 2 times different LED current, depending of the input voltage and LED temperature. For real cars voltage can vary from 7...8 till 15...16V, so you will have even greater LED current and LED flux differences.

Could he use a buck driver like this one?

http://www.dealextreme.com/details.dx/sku.13557

With some modifications...

oh, my bad, i thought they are 3.6v,
well anyway 5ohm than.

What about using a high quality, high efficiency, proven, true current regulated LED drivers from www.taskled.com?

Eltehs said:

Probably you will kill LEDs soon with this setup for several reasons. First reason - voltage spikes on the power line due to ignition/starter work. Modern LEDs is very sensitive to overcurrent, so they will degrade quickly with this spikes. Confirmed by own experiments....

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Your car must have a lousy electrical system.

For over a year I've had LED interior, Park and Brake lights using just series resistors with no problems - except the front Park lights.

These are in the same housing as HID Headlights and it seems the heat causes all that I've tried to fail aftr a few months.

Eltehs said:

AMC7140 can not be used in your application, as it's maximum input voltage is only 6V.

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No, the AMC7140 is designed for Power supplies from 5 to 50 volts, but the maximum current is 700mA.

The minimum voltage drop is 0.5 volt.

http://www.micro-bridge.com/AMC7140.asp

I'm surprised by the lack of drivers available that can power directly off a car battery's 12.8-14v.

The AMC 7135 is pretty popular. Why no drivers made with the AMC7140 or AMC7150?

The only option that I see to light several LEDs at once using 13.8v of car power with a 7135 is drivers in series:
https://www.candlepowerforums.com/threads/220768
https://www.candlepowerforums.com/threads/201392

Efficiency curve:
https://www.candlepowerforums.com/threads/192925