MPSA92 BJT is another component I have salvaged from my old ATX power supply circuit. Other components used are PC817 optocoupler, 2SC13001, TL431 adjustable voltage regulator, 2SC1815 small signal BJT transistor and SBL3040PT schottky barrier rectifier. The MPSA92 is a high-voltage PNP transistor often found in ATX power supplies, mainly in the primary side circuitry. It is used in control, switching, and regulation functions where high voltage handling is required, since it can withstand up to 300 V across collector-emitter. In a PSU, it may be part of the startup circuit, snubber network, or feedback regulation, helping to manage the switching operation of the main power transistors. Its role is usually not to deliver high current, but to handle high voltages reliably in support and driver circuits.
When salvaged from a power supply, the MPSA92 can be a very useful part for DIY electronics. It is particularly suited for circuits that need to switch or amplify high voltages at relatively low currents, such as in pre-driver stages of inverters, high-voltage sensor circuits, or the front end of CRT driver boards. Its modest current capacity (up to about 500 mA) and moderate gain mean it is not designed for heavy loads, but it performs well in signal or voltage-level control roles.
In hobby projects, MPSA92 transistors can be reused in audio amplifier stages, voltage regulation feedback loops, oscillator circuits, and DIY DC-AC inverter designs where high voltage tolerance is necessary. They are also handy in experimental high-voltage projects like neon driver circuits or Geiger counter interfaces, where other general-purpose BJTs might break down. For a DIYer, keeping a few MPSA92s salvaged from old PSUs provides a versatile option for circuits that need both reliability and high-voltage endurance.
