I just come across the situation to cutoff the power when mobile battery full is detected (by breaking the +5v line) .I planned to implement this using high side current sensing method.When the battery is full it draws very less current, so when the current goes less than 100mA I would like to cutoff the power on +5v line (as shown in the figure). The problem is once if the current goes less than 100mA the output of second comparator activates the switch to break the connection.
How can I detect the plug in/out of the USB cable when there is no power on +5v line as I have to reset the switch position on every plugin/out action so that if a new phone is connected to charge it.
Also is there any better method to detect battery full and turn off the power on +5v line.
Also I dont want to use any microcontroller as i'm making this project at absolutely minimum BOM.
2 Answers
If the mobile is just sleeping and wakes up on its own it will draw more current not going to charge the battery. For this reason the responsibility of charging the mobile battery must be internal to the mobile and not as you would like. The mobile will also be responsible for indicating when it is full.
So the problem has no need for a solution and no way to detect where the load current is going.. to power the mobile charger or the rest of the mobile loads.
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\$\begingroup\$ Ofcourse when mobile wakes up it draws more current, but after few seconds it goes off. From the tests I have conducted on charging different mobile phones, the current falls to less than 100mA when almost fully charged. So on an overnight charge when current falls below 100mA I just want to disconnect the V_Bus. \$\endgroup\$ Commented Feb 23, 2018 at 22:50
cutoff the power when mobile battery full is detected (by breaking the +5v line)
This is the function that almost any USB power banks do: disconnect when consumption drops below 30-50 mA. The solution is to periodically (say, once per second) re-connect the source, and see if someone draws any significant current, then disconnect back if nobody is there. Another method is to sense the capacitive load of device (every USB device must have at least 1 uF cap on VBUS), there will be a short spike of current when a device is plugged in.
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\$\begingroup\$ I can't go for the first method as reconnecting source periodically will consume some charge, also there is no point if I'm powering it again for every 1 or 2 sec. I would like to turn off the power bank after 3 seconds when +5v line is disconnected. Can you brief me how can I implement the second method? Thank you. \$\endgroup\$ Commented Feb 23, 2018 at 22:39