USB charger design help

[Sunny55]

Hi, i am planning to make some usb chargers to charge electronic devices like smartphones.

I have the following questions to ask:

(1) Is it better to use switching regulator or linear regulator ICs? The ICs will convert 12Vdc to 5Vdc. I know that switching regulator ICs have better operating efficiency but linear regulator(7805) is low cost.

(2) After selecting the right IC and assembling the circuit, we can just directly plug in the usb charging cable or we have to consider other factors such as the cable's resistance ?

Thanks.

 

[DarkMoon]

Hey!

I've done both and switching is way way better than linear, but it was kinda hard to get it working right.
And about the cables I don't think it matters much if you are using a standard USB cable, just test the device before plugging it to charge something.

 

[BabaYaga]

Ans-1 --> Use switching Regulator, you can get cheaper ones from Linear technology or national semiconductors, since the current rating is small(500mA).

Ans-2 -->No need to consider cable resistance and all unless the length of the cable is longer than half a meter, use short circuit protection circuitry at the output of the circuit for safety.

 

[Sunny55]

Hey!

I've done both and switching is way way better than linear, but it was kinda hard to get it working right.
And about the cables I don't think it matters much if you are using a standard USB cable, just test the device before plugging it to charge something.

Hi, what kind of testing did you do before connecting the usb cable to the phone?

- - - Updated - - -

Ans-2 -->No need to consider cable resistance and all unless the length of the cable is longer than half a meter, use short circuit protection circuitry at the output of the circuit for safety.

Can you provide me with the schematic of the short circuit protection circuitry please? As i known, both the two data ports will be left open or connected to ground. So its just two ports being use which are the 5V and ground ports.

 

[DarkMoon]

Hi, what kind of testing did you do before connecting the usb cable to the phone?

Well mainly for noise with an o-scope, and with a dummy load to see if the output was nominal, nothing special.

 

[Sunny55]

Hi, i have read about supplying some voltage to both the data ports in the usb is needed to drive the device to start charging. Is that true and is applicable for most devices like mp3 players to smartphones?

 

[omega6]

Hi, i have read about supplying some voltage to both the data ports in the usb is needed to drive the device to start charging. Is that true and is applicable for most devices like mp3 players to smartphones?

That is correct. Some smart phones like Apple IPhone need some voltage on the data lines to make the phone recognize the charging device as a charger. Not sure whether it's applicable for all devices but you can try.

 

[tpetar]

Hi, i am planning to make some usb chargers to charge electronic devices like smartphones.

I have the following questions to ask:

(1) Is it better to use switching regulator or linear regulator ICs? The ICs will convert 12Vdc to 5Vdc. I know that switching regulator ICs have better operating efficiency but linear regulator(7805) is low cost.

(2) After selecting the right IC and assembling the circuit, we can just directly plug in the usb charging cable or we have to consider other factors such as the cable's resistance ?

Thanks.

All depends from many things, in some cases linear is better.


Linear
=======
- Low cost
- Simple design, no need for inductive parts
- Bad efficiency, but can be satisfactory if input voltage is around 3-4V above output voltage, not more.
.
.
.


Switcher
=======
- In lots of cases, bad ripple on output, and need additional capacitors-inductors
- Some switcher are expensive
- Need inductive parts
- Better efficiency
- Possible greater the difference between input and output
.
.
.



For your need I guess you will power this charger from mains, in that case you can use linear freely (78S05 2A, 78T05 3A). If you have free time, why not play with switchers.

 

[Sunny55]

Hi, i want to design a simple USB port that allows me to connect and charge my external rechargeable battery pack. I am not sure how to connect the data + and data - pins. For smartphones, i know that there are some setups like both pins shorted or connected to a voltage divider but what about for charging external battery packs?

Can someone help me please?

Thanks.

 

[tpetar]

Dont play with data + and data - you can be in situation to search new phone. Double check what you doing.

Yes its true some devices check data +/- to ensure that you use device on PC, and not over some cheap Chinese power source, also when PC is in standby mode some peripherals such USB ports are under power, to provide awakening from standby mode and charging some devices like this phones,...

https://thecustomgeek.com/2011/08/03/charging-an-ipad-iphone-or-ipod/

https://www.extremetech.com/computi...ks-or-how-to-avoid-blowing-up-your-smartphone

 

[RCinFLA]

You best to try and find out the particulars of the devices you intend to charge with regard to D+ and D- lines. A smartphone or tablet can draw a charging current beyond the official USB max. spec of 500 mA. The charge may be limited, by the device, to 100 mA if it doesn't recognize the USB charger. Many manufacturer have their own scheme for recognizing their USB charger before the device will draw its full charge current that can be well beyond 500 mA.

Some chargers, like Motorola, have current limiting function in the charger so the heat generated in the series pass device is taken by the external charger instead of heating up the phone. The phone's series pass regulator goes into switching state (totally ON or OFF) instead of linear mode when a computer's fixed 5 vdc supply is the source. When it must operate in linear mode the charging current is modulated to keep the generated heat down.

There are three possible charge rates depending on the device and its recognition or lack of recognition of device specific USB charger.

1) Full charge current, typically 50% to 80% of the battery's mAH rating in mA's, for LiIon batteries.
2) Drop to 100 mA which is USB OTG max. without handshake to go to 500 mA. Some laptops and On-The-Go USB devices limit to this level of draw from their USB ports.
3) No charging engaged, due to unknown source capability.

 

[tpetar]

Additional to my Post #8:

**broken link removed**

**broken link removed**

**broken link removed**



**broken link removed**

 

[Sunny55]

Thanks for the replies. I wonder if it would be possible to make a universal USB charger which is suitable for charging all electronic devices such as iPhones, iPads, Android devices, mp3 players and rechargeable battery packs?( as different devices needs different D- and D+ settings).

I am doing some findings on this problem and i hope i can get a solution to this problem.

 

[tpetar]

You can use dedicated connectors for each phone/device and resistor adjusted for that device is solder inside each connector. If device not need data +/- then you will not add this resistors in connector.

Use SMD 1206 or 0805 resistors. Connectors should have ability to be open.

 

[Sunny55]

You can use dedicated connectors for each phone/device and resistor adjusted for that device is solder inside each connector. If device not need data +/- then you will not add this resistors in connector.

Use SMD 1206 or 0805 resistors. Connectors should have ability to be open.

Thanks for the suggestion. I am planning to use IC as i am not sure about the Data - and Data + lines settings. There are some ICs that provide automatic detection of the Data - and Data + settings for different devices.