Can LM1117-5V Be Used for USB Charging?

This post was flagged by the community and is temporarily hidden.

Can’t do this.

because the internal resistance of the battery will change during the charging process. When the battery voltage is very low, the current will be very large. If the current-limiting circuit is not added, 1117 may be burned, causing unexpected danger.

Disagree. The 1117 does have current limiting and overheating protection build in. I see no major problem charging USB devices with it if you can live with the relatively low current of 800mA and the low efficiency.

Phones have all the charging circuitry and battery protection built in and any 5Vdc power supply connected to the USB port should work.

For fast charging there are some tricks with connecting resistors to the USB data lines to tell the phone it can draw more current, and with USB-C there can be complicated binary handshakes to set current limits and voltage and there are specialized IC’s for that.

I’ve had phone batteries drained by a charger that was unplugged from the mains power supply but connected to the phone with the USB plug.

Also, having a Li-Ion battery connected continuously to a charger is not optimal for the battery.

One of my project idea’s is to make a phone charging station, but I never got around to actually making it. If I would make it, I would roughly do it like this:

  1. Put some cloth over the phone.
  2. Plug in an USB cable in the phone (through a hole in the cloth).
  3. Pour some sludge over the connector and cloth. (Gypsum, silicone, epoxy, hot glue or similar)
  4. Mold the cloth into something visually attractive.
  5. Let dry.

And then for the electronic parts I would use a 5V power supply and a microcontroller based timer which turns on the relay for a few hours every 4 days or so.

Some extra Idea’s I have not worked out is to add a switch for phone insertion detection, and maybe some extra feedback with a LED or a LCD, to give feedback that he phone is properly inserted. Maybe a switch to start a charging cycle. You can add lot’s of extra’s to a microcontroller.

But this forum is primarily for discussing the KiCad software itself and not for electronics projects. For such a forum like EEVblog is more suitable, or others such as for example diyaudio for audio related stuff.

2 Likes

My first choice for 5V regulator is 7805. There are 1A nad 1.5A versions:
https://www.ti.com/product/LM7800
Fast 5V USB chargers starts from 2A up I think. Even faster use higher voltage to not burn the USB cable with higher current.

What have you been doing so far? Have you used your charger as well as your computer to charge the phone. Is there any difference in charging speed?

It all depends on your phone and charger. If the charger is smart and the phone can take advantage of it, they can negotiate a turbocharge mode. Especially for USB-C chargers. But if your charger and phone have no such refinements, then you can do no worse with your project than with your computer.

So it all depends. Is there a reason you are using a regulator for this? Are you getting the power from a battery or something? You haven’t told us everything.

Charge speed can vary a lot by just the quality of the USB cable. There are a lot of bad quality USB cables with too high a resistance for 1A. “USB Chargers” often have an output voltage that is a little bit higher, for example 5.2V to make it a little bit easier to get some decent amount of current through the cable. With a voltage regulator such as an LM317 (which is very common) you can set the output voltage with a resistor and a trim potmeter.

1 Like

When using a linear regulator like the LM1117, bear in mind that the excess voltage is lost in the form of heat.

Let’s assume for the moment that you wanted to be able to source a current of 1A. Dropping your 8V battery to 5V is means the regulator has to dissipate 3V x 1A = 3 Watts. In the US, the classic incandescent night light bulb was rated at 4W, and it got far too hot to touch. What sort of heat sink are you planning on using with that regulator?

There’s a reason that most such chargers use switching regulators rather than linear.

(If you hadn’t considered this, don’t feel too bad. I had this exact conversation with some electrical engineers at a large defense contractor a few years ago. The only difference was their battery put out over 13V!)

1 Like

Thank u!Paul !
These are very useful. and I think I got it!

Good idea! I will have a try! Thanks!

Hello @KAKU

Another question: What source is your 8V supply? What current can it supply? How reliable is the voltage out?

Just curious to know in case it would cause problems with a linear regulator.

It is better (from learning point of view) to find out about the problems yourself than to be informed about them.