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I am building a 5 V PSU to charge my phone. I am using a 7805 regulator. When I connect to the phone the Android Charger Tester app reports a charge current of only 100 mA or less. This is confirmed by measuring the current with my multimeter connected in series with the +5V line. I am expecting much more. The phone's battery state indicator shows charging but not increasing battery level.

This is the diagram enter image description here

Link: https://www.electronicshub.org/understanding-7805-ic-voltage-regulator/

Beginner Dude
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  • I suppose you mean 100mA instead of 100amps in your question. How did you measure the output current ? What sort of load did you connect to it? – vtolentino Mar 22 '20 at 09:54
  • Sorry my bad. You are correct 100mA. I measured it using a digital multi tester. I connected a USB cable to the USB female pin out to my phone. My phone is a 5v 2A required charger. – Beginner Dude Mar 22 '20 at 09:54
  • How did you measure the current? What sort of load did you connect to it? – vtolentino Mar 22 '20 at 09:56
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    (1) What does "*When I tested it, the amp is too low.*" mean? (2) How did you test it? (3) Did you calculate how much power will be dissipated in the 7805 and how much of a heatsink you will require? (4) Do you understand that you shouldn't measure current by connecting the ammeter between +5 V and 0 V? – Transistor Mar 22 '20 at 09:56
  • No I really don't understand. Now that you have mentioned it. I now understand. Another way that I tested the current is I downloaded an android app called Charger Tester. I found out in the app that the output current is less than 100 mA and sometimes less than 0. – Beginner Dude Mar 22 '20 at 10:01
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    You are asking us to guess a lot of what you are doing. Please edit your question to say something like: "I am building a 5 V PSU to charge my phone. (You might want to explain why you are risking damage to your phone by doing this.) I am using a 7805 regulator. When I connect to the phone the Android Charger Tester app reports a charge current of only 100 mA. This is confirmed by measuring the current with my multimeter connected in series with the +5V line. I am expecting much more. The phone's battery state indicator is showing xx% charge." – Transistor Mar 22 '20 at 10:23
  • How can the current be less than zero – Andy aka Mar 22 '20 at 10:28
  • @Transistor I have edited my question. Thank you for helping me out on this. – Beginner Dude Mar 22 '20 at 10:43
  • You have pretty much copied my text into your question. I hope I guessed correctly. You haven't explained (1) Why you are risking damaging your phone by doing this. (2) What did the multimeter show. (3) What is the battery state of charge. Android can tell you this. – Transistor Mar 22 '20 at 10:43
  • I just did this for just an experiment. The multi meter showed 100mA or less than 100mA. The battery's state of charge is charging but not increasing battery level. – Beginner Dude Mar 22 '20 at 10:45
  • What is your input voltage to the regulator? Are you aware that no USB device are allowed to draw more than 100mA, unless the device detects via the data pins that it is allowed to draw more? What do you have on USB data pins? – Justme Mar 22 '20 at 10:51
  • Maybe your phone is already full and does not need more than 100mA. A phone will generally not attempt to charge more than 500mA from a source that it cannot determine the maximum current of (like in your case). Some phones will not charge from a "naked" 5V source but need (for example) their USB D+ and D- lines connected or at a certain predetermined voltage to attempt to charge. [This](https://electronics.stackexchange.com/questions/130559/how-does-a-usb-2-0-wall-charger-negotiate-current-output) explains some technical details. – StarCat Mar 22 '20 at 10:52
  • I tested the input voltage for a 9v and 12v battery still result are the same. I am really not aware. No data pins were connected. – Beginner Dude Mar 22 '20 at 10:53
  • A 9V battery can not supply high current. It is intended for low current (less than 100mA) use. – JRE Mar 22 '20 at 11:20

2 Answers2

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I am building a 5 V PSU to charge my phone. I am using a 7805 regulator.

This is risky. For example, if you loose the connection to the centre pin (GND) the output may go close to VIN and permanently damage your phone.

When I connect to the phone the Android Charger Tester app reports a charge current of only 100 mA or less.

Charge management is done internally in the phone. You can't force charge into it. Your phone's "charger" is typically a 5 V supply and the battery monitor in the phone manages the amount of charge current into the battery.

This is confirmed by measuring the current with my multimeter connected in series with the +5V line. I am expecting much more.

Why are you expecting more?

The phone's battery state indicator shows charging but not increasing battery level.

I asked for the % charge so that we could determine whether or not the battery was close to fully charged. Without that we can't guess where in the charge cycle you are.

Be aware that the phone will assume that the PSU can only supply 500 mA unless certain voltages appear on the D+ and D- lines. Depending on the voltages it will know if the PSU can supply 1 A, 1.5 A, 2 A, etc. You should be able to find this information in a web search.

You also need to be aware that the 7805 is a "linear" voltage regulator so any voltage dropped by it will cause heating in the regulator and the power dissipated is given by P = VI so if your supply is 12 V in and 5 V out you have 7 V across the regulator. At 0.5 A out that will dissipate 7 x 0.5 = 3.5 W and the regulator will require a decent heatsink. Without that the regulator will heat up and shut down or start to limit current by reducing the output voltage.

Transistor
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  • the battery's charge is 61% .. I did not connect the D+ and D- on the female pin out. I will try to put a heatsink on it. – Beginner Dude Mar 22 '20 at 11:01
  • First measure the output voltage. If it's 5 V and the heatsink is not hot then you don't need one yet. How much is your phone worth? – Transistor Mar 22 '20 at 11:16
  • Are your sure it'll assume it can supply 500 mA? It's been a while since I've looked but I always thought before enumeration (if resistors aren't in place to indicate a charger) that a device shouldn't draw more than 100 mA. – PeterJ Mar 22 '20 at 12:24
  • I was going from memory so you may be correct. According to [100 mA is a myth](https://www.medo64.com/2016/11/100-ma-is-a-myth/), "Unless you are making device that has to be certified, stop worrying about the power negotiation. If your device already has an USB transceiver onboard and you need to program it anyhow, go for the standard and configure current you need. But if you don’t have such chip or programming is just too much of a hassle, simply ignore it and world is not going to self-destruct. I promise." – Transistor Mar 22 '20 at 12:30
  • I've done the same and done a few things that charge Li-Ion at 500 mA and never had a problem, but at the same time they've never been certified whereas I guess all cell phone manufacturers would go down that path. – PeterJ Mar 22 '20 at 12:38
  • Thanks guys and especially to Transistor. It is working now. What I did was I removed the USB female pin out and connected the output with a micro USB cable. As what Transistor said the IC tends to get hot and needs a heatsink. I guess I need a larger heatsink. Also the USB Female pinout will just only draw less than or equal to 100mA. As I checked the Charger Tester App it is now drawing 600-900mA. – Beginner Dude Mar 25 '20 at 03:20
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How is this circuit being connected to the phone? Are you connecting this straight to the USB port? If so I believe the phone will limit to one USB unit of power which is 100mA.

Carl Gilbert
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