Car USB Charger circuit

Apple Hi-current charge resistorsHow many devices do you have that charge over USB? How many devices require you to do something special, or have a special adapter to do it?

The last few cell phones I’ve had have USB micro or mini ports to charge from. I figure I can take a USB A Male to USB micro/mini Male cable and just plug it into a USB port and get power… except that doesn’t work some times. Then there are the Apple devices. You’ve got your iPods, iPhones and iPads. They do their own thing as well. What’s a geek to do?

Well, the Chinese started mandating a specific configuration for cell phone charging via USB (shorting DATA- and DATA+ pins together) back in 2007. The EU got the big cell phone manufacturers onboard in 2009, with the US wireless industry coming along also. The bad news is that the EU standard doesn’t have to be implemented until 2012.

So that problem is resolved, right? That’s just cell phones. Others will probably jump on the band wagon, but there will be hold outs. So, how do you design a USB charger in the mean time? The Chinese standard is here, but that leaves our device non-apple compliant.Hybrid Charging Resistors We don’t want to miss out on the apple market do we? I hear you say, “but that means another product, and that’s expensive.” We’ve got a handy generic circuit to allow you to use the same design for both charging standards by just replacing a couple resistors. First, let’s look at the standards.

I don’t have the Chinese standard, but all articles agree that it is just shorting the D+ and D- lines together. Easy enough. Now, the Europeans did their own thing… sort of… not really. They supported the USB Battery Charging Specification, which instead of shorting D+ to D-, puts a 200 Ohm resistor between them. It’s practically the same thing. So we can meet those two standards with a 200 Ohm resistor, or if you really want to short it out, a zero Ohm resistor.

2D Charging Circuit layout

Now onto Apple’s USB charging setup. Luckily, there are intrepid explorers who did the hard work there. There’s two Apple USB charging circuits, low and high current. To change between the two we just need to switch out the resistors. Here’s the circuit for the high current resistors.

Now, we just need to combine the two. Merging the two circuits we get:

Now realize, that installing all five resistors will not meet either of the charging standards. However, if we install R2, R3, R8 & R9, we will have an Apple format charging port. If we install just R6, we will have an EU standard charging port. If we replace R6 with a zero Ohm resistor and leave the other resistors off, we will have a Chinese standard charging port.

Now, instead of two different boards, we can use the same board with two or three assembly variants to support different devices. First, here’s the layout for the resistors connected to a USB A Female board mount connector:

Car Charger, WirelessFinest, Dual Port 3.1A USB Car Charger Adapter for Apple iPhone 6/6 Plus/5s/5c/5/4s/4, Apple iPad 4/3/2/Mini/Air/2, Apple iPod, Samsung Galaxy S6/S5/S4/S3/Tab 4, Motorola, HTC Phone and other USB powered devices (Black)
Wireless (WirelessFinest)
  • Up to 3.1A Output Current when use both USB ports
  • Fast Charging for multiple devices
  • Smartchip with short circuit protection never heats or overcharges battery
  • LED indicator light lets you know the status of the charge
Meagoes Fast USB Car Charger Adapter (4.8A / 24W), with Dual Smart Ports for Apple Iphone 7/6s/6/Plus/5s/5c/5, Ipad, Ipod, Samsung Galaxy S8/S8+/S7/S6/Edge/S5/S4 ,Note, LG, HTC, and More [Space Gray]
Wireless (Meagoes)
  • ERGONOMIC & STYLISH DESIGN - Combining circular soft blue LED light and Multi-annular design of appearance, to create convenient for you to pull and plug USB...
  • UNCOMPROMISED RELIABILITY - Meagoes intelligent circuit design protects against short circuiting, over-heating, over-current, and over-charging. This dual USB car...
  • AUTOMATICALLY IDENTIFY YOUR DEVICES - 2 smart USB ports can automatically identify your cell phone model to provide stable current output, you can charge up 2 mobile...
  • FAST CHARGING WITH HIGH OUTPUT - This Car charger have 4.8amp output, shared by 2 smart USB port; Each USB port has 2.4A max output to quickly charge your phones...
  • IMPORTANT NOTICE - This series CC001 car adapter does not support Qualcomm Quick Charge 2.0/3.0 technology, if you need much faster charging speed for Samsung Galaxy...
USB Car Charger, TeckNet PowerDash D2 9.6A/48W 4-Port Rapid USB Car Charger with BLUETEK Technology For Apple iPhone 6 / 6 Plus, iPad Air 2 / Mini 4,Samsung Galaxy S6 / S6 Edge and More
  • Tecknet PowerDash D2 USB Car Charger with BLUETEK technology maximizes compatibility with Android, Apple and other devices to ensure recharging at maximum speed (5V...
  • 4 Smart USB charge ports allow you to recharge 4 phones, iPads or other devices simultaneously, quickly and easily in your car. Input: DC 12-24V; Output: 5V 9.6A/48W
  • Lightweight, compact design for improved portability (only 57x39.5x26mm, 40g); Easy-to-read LED indicator helps to confirm whether the USB car charger is properly...
  • Use your existing USB charging cables to recharge most USB powered devices, including iPad Air 2, Mini 3, iPhone 6S, 6, 5SE, 5S, 5, Samsung Galaxy S7, S6 Edge Plus...
  • TeckNet s advanced multi-level safety system and intelligent circuit design protects you and your device from short-circuit, over-heating, over-current and over-charging. 
1byone 1byone 7.2A / 36W 3-Port USB Car Charger with Smart IC Adapts, Safety Protection for Apple and Android Devices, Red & Black
Wireless (1byone)
  • Top Performance - Smart IC chip intelligently communicates with connected devices to maximize both compatibility and charging speed (up to 2.4 Amp).
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  • LED Light - Internal LED power indicator is build-in. The dimmed LED indicator helps visualize the connection status and does not distract you while driving.
  • Compact Dimension - 65 x 37 x 23 mm, fits nicely into the recess and firmly into power socket to make sure your digital devices are always charged.
RAVPower Car Charger RAVPower 36W Dual USB Car Charger with Quick Charge 3.0 (4X Faster) and iSmart 2.0
Wireless (RAVPower)
  • Quick Charge 3.0 for 4x Faster Charging: Witness a whole new charging experience that s 4x faster than conventional chargers with the latest Qualcomm Quick Charge...
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  • 36w Via 2 Usb Outputs: Let the dual Quick Charge 3.0 and iSmart USB ports charge up to 2 smartphones, tablets, or QC compatible devices at full speed and simultaneously.
  • Wider Stainless Steel Contacts: Experience a more stable and efficient charge even on bumpy roads thanks to the wider circuitry contacts made of stainless steel.
  • 360° Protection: Safely charge your devices thanks to the charger s built-in protections to prevent overheating, overcharging, and short-circuit.

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