I wanted to learn more about voltage regulator, power sources, the components used in such circuits, especially the transformers, type of capacitor, inductor and resistors used etc. I had many damaged mobile phone adapter or charger and I thought I could learn how voltage converter works from its circuits. I watched some youtube videos to learn how to repair a mobile phone charger before I actually do that. I checked the components. Using digital multi-meter, I checked the resistors, capacitors, diodes and the transistor in continuity mode. Found out that one of the resistor was not working.
This resistor is called the inrush current limiting resistor and is located at the input AC main side in the SMPS(Switch Mode Power Supply) circuit. More specifically, it is between the ac input and the diode rectifier circuit. The function of this resistor is slow down or limit the rush current that otherwise would flood into the capacitors located at the DC circuit part, charge them quickly drawing huge surge current. Such huge surge current can cause the electrolytic capacitor to explode and destroy other part of the circuit including the resistor itself, as shown in the figure below.
This happened when I replaced the original 10 ohm inrush current limiting resistor with an unknown resistor taken from another similar mobile adapter and changed the original 3uF electrolytic capacitor with 2.2uF capacitor. This 2.2uF capacitor is seen exploded in the above picture with its outer metallic cylinder. The explosion sound was quite high like loud pop sound. Now the explosion can be caused by either the wrong capacitor or the inrush current limiting resistor value.
