Hi All,
Recently one of my USB battery chargers died and instead of messing around ordering a new one I decided to build my own based on the circuit inside the dead charger.
After opening up the charger I found it was all surface mount tech... No big deal, I have a USB microscope and the knowledge to decipher the circuits, here is what I found along the way.
The Battery is a 3.7v in a bag, I am not sure atm what it really is LI, NM, NC, ETC.
The main control of the charger is an LM393 comparator, very common and available at any circuit supply place in non-surface mount configuration, the rest is all resistors and capacitors.
The Function of the charger compares voltage and varies the amperage based on it.
A Battery that is discharged will cause the charger to feed around 100ma to the battery and light the red LED.
As the battery nears full charge, the ma will reduce.
At about 26ma the green LED will start to flicker on and the red LED will flicker off.
At about 20ma, the green LED will be full on and the red one will be off.
The charger will slowly (about 2 min) reduce the ma push to a 10ma maintenance trickle.
For those that wish to build their own, here is the data you will need.
As a Special note;
The PCB layout was set up to be transfered via UV photo etch so the IC is flipped.
The PCB image has 2 views shown, one with just the traces and one with the silkscreen shown.
Recently one of my USB battery chargers died and instead of messing around ordering a new one I decided to build my own based on the circuit inside the dead charger.
After opening up the charger I found it was all surface mount tech... No big deal, I have a USB microscope and the knowledge to decipher the circuits, here is what I found along the way.
The Battery is a 3.7v in a bag, I am not sure atm what it really is LI, NM, NC, ETC.
The main control of the charger is an LM393 comparator, very common and available at any circuit supply place in non-surface mount configuration, the rest is all resistors and capacitors.
The Function of the charger compares voltage and varies the amperage based on it.
A Battery that is discharged will cause the charger to feed around 100ma to the battery and light the red LED.
As the battery nears full charge, the ma will reduce.
At about 26ma the green LED will start to flicker on and the red LED will flicker off.
At about 20ma, the green LED will be full on and the red one will be off.
The charger will slowly (about 2 min) reduce the ma push to a 10ma maintenance trickle.
For those that wish to build their own, here is the data you will need.
As a Special note;
The PCB layout was set up to be transfered via UV photo etch so the IC is flipped.
The PCB image has 2 views shown, one with just the traces and one with the silkscreen shown.
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