Why I can't charge an Android phone properly with 7805 regulator IC? - Page 1
Forum section: electronics / projects

author: sbdada
author_rank: Contributor
timestamp: March 18, 2016, 07:32:05 am
content: Hi... my question may seems silly but it is making me naughts. Plz if you know then answer it. I have made a regulator circuit using 7805 (1 Amp version) to charge my Android phone (which has 5v 1A adapter). But the problem is... Phone is showing it is taking charge but in reality it is not..(!).I have also measured the current and it shows the phone is taking about 400 mA. I have searched all over the internet and various forums but didn't get any proper reason or explanation about it.Please suggest me. Thanks in advance.

author: sleemanj
author_rank: Super Contributor
timestamp: March 18, 2016, 07:42:06 am
content: You need to signal to the phone that it can take more than 500mA.If you don't signal to the phone, it will think it is connected to a low-current USB port and will only draw up to about 500mA.For Android, it is generally sufficient to connect D+ and D- pins of the USB going into the device, the device sees D+ and D- are connected togethor and, for an Android device, will know it can attempt to draw more current. For iPhones it is more complicated.Make sure your 7805 is appropriately heatsunk

author: Fungus
author_rank: Super Contributor
timestamp: March 18, 2016, 11:33:36 am
content: Quote from: sbdada on March 18, 2016, 07:32:05 amDid you use a heatsink? The "1 amp" numbers in datasheets are only under ideal conditions. If it overheats is might shut down.Quote from: sbdada on March 18, 2016, 07:32:05 amIf you've got a multimeter (or two) connected properly and they show "400mA" and "5V" then the phone must be charging.

author: Ian.M
author_rank: Super Contributor
timestamp: March 18, 2016, 11:43:39 am
content: Make sure the regulator has enough 'headroom' 78XX series regulators generally need about 2V higher input input voltage than their rated output. Excess ripple on the input voltage that compromises the headroom will cause it to drop out of regulation. The capacitors in the sample application circuit in the datasheet are *REQUIRED* and mus be as close as possible to the regulator.Ignoring any of these issues can result in an unstable output voltage and failure to charge.N.B. more headroom = more heat. Make sure you have enough heatsinking and keep the input voltage fairly low or you wont get anywhere near the nominal 1A rating. The 78S05 is rated at 2A, and is more likely to be able to actually deliver 1A on a good heatsink.

author: j.a.mcguire
author_rank: Contributor
timestamp: March 18, 2016, 12:43:22 pm
content: Instead of using a linear regulator you should consider using a buck converter as they are more efficient, can provide a few amps and generate less heat. There are many available for this specific application on eBay.

author: wolf32d
author_rank: Contributor
timestamp: March 18, 2016, 02:18:07 pm
content: Quote from: sbdada on March 18, 2016, 07:32:05 amUsually the other two USB pins (D+ and D-) are involved: each charger manufacturer applies a specific voltage to these pin (usually with a couple or voltage dividers). Android phone and Apple devices have different standards.See this very nice article:http://www.eetimes.com/document.asp?doc_id=1279469

author: KL27x
author_rank: Super Contributor
timestamp: March 18, 2016, 10:48:33 pm
content: Android phone: take D+ and D- and short them together. (On your charger, not your phone.) This will solve the problem of the phone showing it's charging, "but it is really not" (really it is charging, just very slow!).If you don't get any charging symbol at all, then you need to keep troubleshooting.If the D+ D- doesn't increase your charge rate to over an amp, you need to work on your circuit.

author: ovnr
author_rank: Frequent Contributor
timestamp: March 18, 2016, 11:22:17 pm
content: Also, some Android phones will not show the charging symbol if they don't detect a proper supply. So get to shorting that data pair!

author: technix
author_rank: Super Contributor
timestamp: March 20, 2016, 11:05:48 pm
content: You need to implement some kind of USB Power Delivery (USB PD) protocol to tell the phone your board is a charger and it can supply up to an amp of current, assuming your 7805 have adequate headroom and cooling.For the recent release phones that uses the USB Type C port you need to implement the public USB PD2 protocol, probably using either an ASIC or a microcontroller.Phones using USB Micro-B have different protocols and you need to research them on a case-by-case basis. (the public USB PD protocol is followed by some, but not all devices, especially Apple devices, which have their own Apple USB PD protocol)

author: davelectronic
author_rank: Frequent Contributor
timestamp: March 23, 2016, 07:35:52 pm
content: We charge androids from atx supplys +5 Volts rail, most phones respond well if you short the data pins in the lead, as mentioned above. Be sure you have a stable +5 Volts, last thing you won't is a cooked phone.

author: stmdude
author_rank: Frequent Contributor
timestamp: March 25, 2016, 06:17:09 pm
content: Quote from: davelectronic on March 23, 2016, 07:35:52 pmBwahaha.. At least at the manufacturer we worked with, we tested the shit out of the rigidity of the VBUS-in circuitry. They'll take a good licking, and come back asking for more.Why? Well, people connect just about any cheap crap they've found buried in some Chinese rice-field, and expect it to work. If it doesn't, they blame us...Worst charger I've tested with was an early charger for a Kindle e-Reader. That f***er gave out 9V _square-wave_ at 50Hz... Nope, we actually couldn't charge with that, but at least the circuitry didn't break.But, as others have said. Connect D+ and D- together, and your 7805 becomes an actual "USB Dedicated Charging Port" (DCP). Spec-compliant and everything. When the phone sees a DCP on the other side, it'll try and draw up to 1.5A @ 5V, and "back off" the amperage when it sees the voltage drop.Keep in mind that just about any modern phone today can charge with well over 1A, so your 7805 will be pushed to its limit. I.e, (as others have mentioned), make sure you have a nice heatsink on it, and properly sized decoupling caps.

author: eneuro
author_rank: Super Contributor
timestamp: March 31, 2016, 07:41:40 pm
content: Quote from: j.a.mcguire on March 18, 2016, 12:43:22 pmIn my Sun powered cell phone this tinyLTC3539/LTC3539-2 - 2A, 1MHz/2MHz Synchronous Step-Up DC/DC Convertersmentioned also in other thread works fineQuoteI've removed oryginal flamable battery and... provide 4.15V instead of battery and... crappy phone thinks it has full charged batteryQuoteNo Batterizer needed while it can operate even at 0.5V when operation starts with 0.7V.Additionally tolerates Vin > Vout which is what I was looking forNo need to charge cell phone anymore... just use when needed using Sun light