Small doubt about power supply

Hello :)

Let's say I've got a 7.5V 2A power supply and I reduce the output voltage to 5V, can it provide (7.5V / 5V) * 2A = 3A ?

In a perfect world.

The 7.5v 2A power supply can provide 15 watts of power. If something converts that power to a different voltage potential then a higher current can theoretically be drawn (from that device not the power supply).

If you had a 100 percent efficient regulator that was also rated to handle that current then nothing would be lost from that original 15 watts of power and can be used at a lower potential 5 volts 3 amps. This would still only use 15 watts at the power supply. The same current from the wall.

In the real world, due to efficiencies and current limitations of the regulation/transformation devices there is a great loss of that power. Sometimes a hard physical limit to its current capability because of its package. The loss in power is dissipated as heat. Sometimes multiple watts.

Just altering the voltage output of the supply does not neccesarily increase the current handling capacity of its circuity. There is a reduction in heat dissipated in the supply output though so a higher current can be drawn from that part circuit to be under the same thermal limits.

Thanks :)

Why I asked this:

I have a project which requires 24 WS2812B rgb leds and an arduino. When all the leds are fully on, they draw just a little less than 1A @ 5V.

I though I could use a 7.5V 1A power supply, to power the arduino, and reduce to 5V with a LM2596 step down module from ebay to power the leds. The leds will rarely be all fully on at the same time, but can be, for a few seconds.

Do you think this could work without overheating the power supply?

Anyway, I think I will just buy a higher current power supply so that I don't play with fire... :P

Well the supply can output 7.5 watts. The LEDS use 5 watts. The arduino and regulators maybe 0.5 watts.

It depends on the quality of the power supply. I would keep an eye on it. Try it for a while and if it stays relatively cool then you may be ok. I would try to aim for little more headroom than that.

Ok ;)

guix: Hello :)

Let's say I've got a 7.5V 2A power supply and I reduce the output voltage to 5V, can it provide (7.5V / 5V) * 2A = 3A ?

With a 100% efficient buck converter, that's the theory. In practice you wouldn't run it at the limit in the first place, perhaps 1.5A, giving some margin for startup surges and permitting cooler running.

If you wanted 5V for analog circuitry (audio amp for instance) you might consider a linear regulator even though that wastes power, as there is then much less noise on the supply from the switching (as a linear regulator doesn't switch)