USB charging reaching current limit of regulator

[Hawaslsh]

Hello,

I had a question regarding a potential USB charging circuit and what happens when a voltage regulator reaches its current limit. For example, if I have a 5V regulator that is speced 500mA and I plug in a phone which is capable of charging at 1A. What would happen?

Are most devices “smart” enough to limit their own current draw to maintain 5V? Is it usually incumbent the voltage regulator have its own current limiting circuitry to prevent overheating?

I’ve seen a lot of cheap chargers out there with low current limits, just wondering how it’s done.

Thanks in advance!

 

[cupoftea]

Are most devices “smart” enough to limit their own current draw to maintain 5V?

They should be ,and could be, but they are not.

If you try and draw 1A from a 500mA SMPS then it will most likely go into overload protection and shutdown. Or hiccup on and off which is pretty useless for your charging.

It would be easy to design a charger in the phone which could simmer down its current draw so that the vin stayed at 5V....but it would likely have to be 4.9V or so...and then the upstream SMPS would again likely trip out on time-out-overload-protection. ..unless it was designed not to......but they arent designed like this.

It could all be so easily done...but is not.

 

[plouf]

the smartphones when connected to USB with JUST + and - cables draws maximun of 500mA
in order to draw more, there is identifier resistor between D+ and D-. a simple D+-> D- shortcut says ,usually a MAX of 1.5A
otehr restistor and custom IDentification exist between manufacturer choice,

now USUALLY computer ports have protection and detection, if draw too much just shut down port

 

[KlausST]

Are most devices “smart” enough to limit their own current draw

As already said: they should be.

There are clear specifications how devices should behave - also regarding current draw - when conneted to USB.
There is a good reason why the USB.org continously spends time and effort to work and update specifications.

There also are charging controller ICs that care for the allowed current.

So it´s well defined. But it´s a pity that many device manufacturers don´t care about these specifications ... and thus risk damage of customer devices.
Host devices as well as power supplies and slave devices.



Klaus

 

[GreenTech0621]

Hello,

I had a question regarding a potential USB charging circuit and what happens when a voltage regulator reaches its current limit. For example, if I have a 5V regulator that is speced 500mA and I plug in a phone which is capable of charging at 1A. What would happen?

Are most devices “smart” enough to limit their own current draw to maintain 5V? Is it usually incumbent the voltage regulator have its own current limiting circuitry to prevent overheating?

I’ve seen a lot of cheap chargers out there with low current limits, just wondering how it’s done.

Thanks in advance!

Hello,

I had a question regarding a potential USB charging circuit and what happens when a voltage regulator reaches its current limit. For example, if I have a 5V regulator that is speced 500mA and I plug in a phone which is capable of charging at 1A. What would happen?

Are most devices “smart” enough to limit their own current draw to maintain 5V? Is it usually incumbent the voltage regulator have its own current limiting circuitry to prevent overheating?

I’ve seen a lot of cheap chargers out there with low current limits, just wondering how it’s done.

Thanks in advance!

Common Phone charger uses protocol to mange the Power/Current/Voltage limits such as PD, QC, if you are using typical voltage regulator without any USB Com interfaces ( CC1, CC2, DM, DP) it's better to have Constant Current control in the Voltage regulator, Phone might sink current higher than regulator max current.

Please see attached IC that can work with or without protocol, No protocol default 5V Constant current.