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I need to design a board like this:

![![enter image description here

Each LED is an SMD 5730 type with a maximum current of 150 mA in three line and the input voltage is 3.2 × 7 ≈ 23 V.

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I have seen this circuit:

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But I found the AMS1117 which is more stable on stress by this datasheet part:

Unlike older regulators, the AMS1117 family does not need any protection diodes between the adjustment pin and the output and from the output to the input to prevent over-stressing the die. Internal resistors are limiting the internal current paths on the AMS1117 adjustment pin, therefore even with capacitors on the adjustment pin no protection diode is needed to ensure device safety under short-circuit conditions. Diodes between the input and output are not usually needed. Microsecond surge currents of 50A to 100A can be handled by the internal diode between the input and output pins of the device. In normal operations it is difficult to get those values of surge currents even with the use of large output capacitances. If high value output capacitors are used, such as 1000μF to 5000μF and the input pin is instantaneously shorted to ground, damage can occur. A diode from output to input is recommended, when a crowbar circuit at the input of the AMS1117 is used (Figure 1).

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It could give me almost 1 A at almost a 1.3 V drop and a max. Vin of 15 V, so by this connection type:

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I would like to know if the LM317 is better than the AMS1117 by some factors. I care about its price; the AMS1117 price is almost 1/3 of the LM317's price, and maximum voltage offers (which I don't think I need here because the open loop doesn't pass any voltage on an adjustable voltage IC).

I have also seen this question:

LM317 Constant Current vs Transistor Current Limiter

I think the LM317 or AMS1117 are better for this usage, am I right?

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    \$\begingroup\$ for this usage, it really should make little difference. Both are wrong here. Don't just copy circuits from somewhere else without understanding what they're doing. \$\endgroup\$ Mar 26, 2020 at 10:48

3 Answers 3

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If your voltage drop is 15V, and your current is 450 mA, then your linear regulator, no matter whether it's just a transistor, a LM317 or an AMS1117, will have to dissipate 7W.

That's an insane amount of power you waste and convert to heat. They will all overheat.

So, you're wrong, and all your solutions are inadequate; they are wrong "by the same amount".

In fact, you're also misinterpreting what "current limit" is here. But that's been asked multiple times on here...

You need a switch-mode power supply here. And you don't want a constant-voltage supply, but a constant-current supply, so design accordingly. Actually, I'd argue you'd really want three constant current supplies, one for each string, to avoid thermal runaway if any of your LEDs has a lower forward voltage than the others.

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  • \$\begingroup\$ I agree; I would also add 'open LED' sensing for the supplies. \$\endgroup\$ Mar 26, 2020 at 11:05
  • \$\begingroup\$ I wonder if Class-A audiophiles would agree that 7 W is an insane amount of power to waste as heat… \$\endgroup\$
    – pipe
    Mar 26, 2020 at 21:59
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    \$\begingroup\$ @pipe well, assuming that someone who builds Class-A amplifiers can read an LM317 datasheet... \$\endgroup\$ Mar 26, 2020 at 22:44
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AMS1117 is better . because the voltage drop of it is only 1.25v . it is an LDO it needs only 1.1-1.3v more than the output to work . the 317 is ldo also but needs more than 2v.

and with this drop and 450mA it will dissipate only about 600mW .

those people saying 7w is maybe confusing with the 15v which is the maximum voltage that it support between (vin - vout) , and in the case of using to reg current like that the vin-vout will be always 1.25v .

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    \$\begingroup\$ The voltage applied to this circuit is never specified by the OP. It could be 2V more than what the LED strip requires, or it could be 15V. You are assuming a minimum regulation condition, but the maximum input voltage is the worst case. The LM317 is not a low-dropout (LDO) regulator. \$\endgroup\$
    – W5VO
    Feb 22, 2023 at 21:07
  • \$\begingroup\$ Downvoting because the last sentence is wrong (and correct answers have already been provided almost three years ago). \$\endgroup\$
    – PStechPaul
    Feb 22, 2023 at 22:01
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Use constant current IC like LT3092. It can configure for 200mA of current. If this IC is not compatible then search for any other constant current IC. Voltage regulators like AMS1117 are not designed for constant current operation for LEDs.

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  • \$\begingroup\$ The LM317 and AMS1117 and other adjustable linear voltage regulators are well suited for constant current LED drivers as long as voltage drop and power dissipation are within appropriate limits. Also, the LT3092 analog.com/media/en/technical-documentation/data-sheets/… costs about $6 and can dissipate only a couple watts. Please read the OP's question and the answers that have already been provided before posting a non-helpful answer. Sorry to seem harsh - I know you are a new contributor - but criticism is to be expected. \$\endgroup\$
    – PStechPaul
    Feb 22, 2023 at 21:58

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