Hello, this is my very first instructable, i am often reading instructables, but until now i haven't written any.
Many times in our electronics project we need 3.3V or even less and most popular and cheapest phone chargers seems to be the first choice for powering our micrcontrollers or chips. But you will need voltage regulator or additional components. I have been looking for other's instructables to hack an USB phone charger in order to modify the output voltage to 3.3V, but haven't found any suitable for me, because i bought a cheap one, which doesn't have a PWM controller and no TL431, just 2 transistors and opto feedback.
You will need very low electronics knowledge to make this modification, just unsolder a 2 pin diode and solder another one.
Step 1: Locate the Zener Diode
After opening the plastic case, you will have to find the diode, usually is placed close to optocoupler's led, on the secondary winding side of the transformer.
I placed the schematics only to have an ideea about how things are on the pcb and better understand of the modification, but is not the schematic of my PCB.
Step 2: Replace the Zener Diode
Simply place the new diode and solder it. Be careful when place the new diode, it should have the anode connected to GND.
It seems that the output voltage is dependent to the zener voltage + voltage drop over the resistor of the optocoupler's led.
In my case to get 3.24V output, i used 2.4V zener.