How to lower USB voltage from computer?

Question

Iron

Description:
I have a Spire noa1100 keyboard, it was bought for $20, over time it turned out that it eats batteries (AAA) for about a couple of days in a constantly on state (it feels like sleep mode does not work) (off. condition is not meant to be used). It is impossible to use the keyboard in this case, as it quickly sits down.
I took it apart and saw two power wires (black, red). I had an idea, but what if we make it wired, at least power. (for example, from a computer usb). There was a problem, as I understand it, all usb use 5v, and the keyboard needs 3v (maximum 3.2v, minimum 2v).
And accordingly, the question itself is how to lower usb or PS / 2 power to 3v so that you can connect a keyboard?
PS! there is also a battery from iphone 3gs (3.7v)

Answer 1

You can simply choose a resistor.
But it's best to assemble just such a simple circuit
. In general, if the keyboard is now disassembled, look at the name of the microcircuit that is in it. There is a possibility that it can be powered from 5 volts

Answer 2

I can advise LF33C.
There was a similar situation.
It turned out such an adapter.

Answer 3

It is also possible to connect 2 or 3 diodes in series. On each diode there is a drop of approximately 0.6 to 1.4 volts (depending on the characteristics of the diode).
but the best option is with a stabilizer. And I do not advise using one USB connector, at least two. Each normal USB is rated for 500mA load. Plus, it is possible to set it programmatically depending on the requirements of the USB device. And due to the fact that you obviously do not have enough batteries for it, it may require much more current.

Answer 4

can you advise exactly what capacitors or diodes are needed. I just don't understand electricity, but I can understand.
There was such an idea, but what if somewhere at the beginning we insert a diode bulb or a fan with 12v in series like this: Red (+) valve. -> keyboard -> (-) black ??

Answer 5

s019.radikal.ru/i607/1403/1a/7b10521b6272.jpg

Answer 6

In general, after digging around, I directly connected the wires from USB directly to the keyboard power wires and voila, everything works fine. Windows recognizes everything is ok. But the question arose, is it forever or not, on the other hand, the fact that other keyboards with batteries seem to be powered by USB is spinning in my head.

Answer 7

Still, try to look for the name of the microcircuits (as you were advised above) and the "datasheet" for them. They will indicate whether this model is adaptive to + 5V power supply.

Answer 8

In general, having touched the chip (I don’t know which one, probably the bluetooth), I almost burned my finger. I decided to add a light bulb as described above. Now it doesn't seem to get hot. Now the question is when it will break.
This is what the whole thing looks like.