i need to design some board like this:
each led is SMD 5730 type with current max 150mA in three line and input voltage almost 3.2×7~23V, to create some SMD led board like this:
so i have seen this circuit:
bu at this post somebody introduced this circuit, SO there said some other method like this:
and at other post said this:
but i fond the AMS1117 with 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).
and could give me almost 1A by almost 1.3V drop and max Vin 15V,so by this connection type :
So i like to know is LM317 better than AMS1117 by some factors and care about its price AMS1117 price is almost 1/3 amount of LM317 price, and maximum voltage offers (which i dont think have any needs here because of open loop dont past any voltage on Adjustable voltage IC)?
Also i have also seen this question :
LM317 Constant Current vs Transistor Current Limiter
And think the LM317 or AMS1117 or better for this usage, am i right?
Thanks.
Best Answer
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.