The MPS A42 (also commonly referred to as MPSA42) is a high‑voltage NPN bipolar junction transistor (BJT) typically used in switching and high‑voltage amplifier applications. It comes in a through‑hole TO‑92 package, making it easy to use in prototype boards and soldered circuits.
 
Key Specifications
 
Feature
Value
Transistor Type
NPN BJT
Package
TO‑92 (through‑hole)
Collector‑Emitter Voltage (V<sub>CEO</sub>)
300 V
Collector‑Base Voltage (V<sub>CBO</sub>)
300 V
Emitter‑Base Voltage (V<sub>EBO</sub>)
~6 V
Max Collector Current (I<sub>C</sub>)
0.5 A (500 mA)
DC Current Gain (h<sub>FE</sub>)
Typically ~25–40 (varies with bias)
Power Dissipation (P<sub>tot</sub>)
625 mW
Transition Frequency (f<sub>T</sub>)
~50 MHz
Operating Temp Range
-55 °C to +150 °C
Pins
3 (Emitter, Base, Collector)
 
Note: Because of its high voltage rating, it’s preferred where typical small signal transistors (e.g., 2N3904, BC547) aren’t suitable due to lower breakdown voltages.
 
Pinout (TO‑92)
When looking at the flat side of the transistor with pins pointed down:
1 Emitter
2 Base
3 Collector
 
Common Uses
High‑voltage switching circuits
CRT/video output stages
Driving relays & moderate loads
Audio amplifier stages at high voltages
General high‑voltage electronics designs
 
Equivalent / Similar Parts
Parts with similar specifications include:
MMBTA42 / KST42 / PZTA42 (similar high‑voltage NPN BJTs)
2N5551 (lower voltage, sometimes acceptable in lower‑voltage designs)