I have a circuit that will need to power different loads at different voltage levels (because they are LEDs of different colors). Can I use several cheap MP1584 modules in parallel (as in: same input, different outputs), or will this have adverse effects (e.g. because they are not synchronized, they all draw current at the same time)? in this case, will a series inductor (on the input) be any help in smoothing the current draw?

The input source will be a supercapacitor (or maybe a small lithium battery), itself powered by a bike dynamo. In particular the input voltage will be low (maximum 6V).

  • \$\begingroup\$ What is the current load you are expecting? What is the vorlage range? Why not give higher voltage which can make both LEDs work? \$\endgroup\$ – User323693 Sep 18 '20 at 14:30
  • \$\begingroup\$ - I do not want all LEDs on, all the time (e.g. braking lights); - all LEDs do not draw the same current, so I can't wire them in series; - the dynamo produces only 6V-ish, which is not enough to power about 5 or 6 LEDs in series. The total load is bounded at 3W (dynamo output), so about 1A. Given the array of LEDs that I will be using, I expect to use about half of this. Also, preventively: I don't want to power them all at the same voltage and use limiting resistors, because the energy source (me) needs a somewhat power-efficient circuit. \$\endgroup\$ – Circonflexe Sep 18 '20 at 16:12
  • \$\begingroup\$ you are better with a LED current driver IC. What is your thought on that? \$\endgroup\$ – User323693 Sep 18 '20 at 17:53
  • \$\begingroup\$ I've been reading some datasheets and as I understand it, most of these ICs (at least the 2-terminal ones) are current limiters and not constant-current drivers; thus they regulate by dissipating, which is exactly what I want to avoid. Is there a “classic” constant-current driver that you would recommend? (that would work with low input voltages). (also, one advantage of those tiny MP1584 modules is that I can adjust the voltage, and hence the luminosity, by turning a potentiometer, which is handy). \$\endgroup\$ – Circonflexe Sep 18 '20 at 20:27

The principle of all led circuits is based on current limiters. Usually a resistor. In your case several step-down constant current supplies, in parallel, one for each led or series of leds, will be more energy efficient than resistors. Especially since your supply voltage is about double that of the leds. And it will give a constent output no matter the voltage of the dynamo which flucuates.

EDITO: I looked at the size of the step down board and I think they can be a very good solution given their compact size. They will stop working if voltage falls under 4.5V.
(how they can sell them that cheap is a mystery: Bellow the cost of components)

But it will complicate you circuit too much for such low power lights. Resistors will be much smaller. You can use SMD resistors on prototype board. And much more robust against shocks and weather hazards. Search for LED circuits, resistor led circuits, led resistor power dissipation to know which resistors to chose. 1W resistor should be safe. Resistance depends on supply voltage and the desired number of amperes.

Make your choice.

  • \$\begingroup\$ Here is another one with fixed voltage (1.8V 2.5V 3.3V 5V 9V 12V) aliexpress.com/item/… \$\endgroup\$ – Fredled Sep 18 '20 at 21:30

In theory you can connect any load in parallel with any other load. So all your buck converters will act as loads to the super-capacitor and the bike dynamo.

Most of this kind of buck converters work by switching the current through an inductor. This switching may produce some ripple and interfere with the other converters.

Now since you have a super-capacitor providing the power it should smooth out all this ripple.

Generally it's a good idea to add some low ESR bypass capacitors in parallel as close as possible to each load.


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