I salvaged many components from older PC ATX SMPS(Switched Mode Power Supply). One of the component I salvaged is the MJE13001 or 2SC13001 transistor among othes like SBL3040 diode, PC817 optocoupler, LM358N op-amp, LM339N op-amp, TL494 (KA7500) PWM controller IC.
The MJE13001 or 2SC13001, is a high voltage NPN bipolar junction transistor(BJT) that is widely used in small, inexpensive power supplies. You will usually find it in low cost phone chargers, LED bulb drivers, and simple adapter circuits. It is popular in these designs because it can handle the high voltages that appear after rectifying AC mains while still being cheap and easy to implement.
The transistor typically has a collector-emitter voltage rating of around 400 volts and can handle about 0.3 to 0.5 amperes of current continuously, with higher values possible in short pulses. Its current gain is fairly low, so it is not suited for amplification but rather for switching applications. Depending on the version, it comes in packages like TO-92, TO-126, or SOT-89.
In power supply circuits, the 13001 often acts as the main switch on the primary side of a transformer in a flyback converter. The rectified AC mains supply a high voltage DC rail, and the transistor chops this DC into pulses that drive the transformer. Many of these circuits are designed to be self-oscillating, which means they do not require a dedicated PWM controller chip. Instead, a feedback winding on the transformer, together with a few resistors and capacitors, provides the necessary drive to keep the transistor switching.
This approach is very common in cheap USB chargers and LED drivers. The 13001 is well suited for such applications because it is inexpensive, can tolerate the high voltages of rectified mains, and is adequate for low wattage power supplies in the range of two to ten watts.
Would you like me to walk you through a real charger circuit that uses the 13001 so you can see how the components are connected around it?
