Description
This is a sample cell phone charger which converts a single AA battery output to a 5.5V output. The output cannot supply a current like 500mA for handling USB loads. The charger is very compact as seen in the picture below.
Internals
Opening up the top transparent cap where the charger is connected we see the circuit board:
Below are some close up pictures of the circuit board from both sides:
On the side we have the connector mounted there is a wirewound inductor a couple of resistors, cap and a LED
On the other side we have 3 components with top markings:
- E2HD
- B14
- STVD
Circuit Diagram
The circuit diagram after tracing out the PCB traces is like this:
Components
After searching on the internet the prospective components for the top marked components are:- B14 is a schottky rectifier like MBRS140
- E2HD is a switching transistor like FDV305N
- STVD is a boost controller like S8352
As for the small RC circuit and LED it seems that since the regulator runs in PFM mode when there are sufficient cycles of charging the output the cap has enough charge to light up the LED and hence indicate a load. The LED lights up whenever a load is connected.