MPSA42 NPN Transistor

MPSA42 is an NPN typically used transistor that has been widely used for high voltage switching and amplification applications. It is an advanced form of an amplifier with extra over-voltage and breaks down voltage protection property. It is highly adequate with a low collector current amplifier as compared to conventional type amplifiers such as LM741 OP-AMP etc. It is made of silicon material and easily available in a dip TO-92 package. The identical family members of this MPSA42 are MPSA42G, MPSA42RL1G, MPSA42RLRAG, and MPSA42RLRAG, etc. These have a little bit differ specifications and characteristics form each other. MPSA42 has 300volts emitter to collector voltage.

MPSA42 Pinout Explanation

MPSA42 consists of three basic segments emitter-base and collector. Because it is an NPN transistor, therefore, current flows from collector to emitter. It works at dc operating voltage range 30 to 300votls. Its pinout configuration is shown in figure 1

The figure below Pinout configuration diagram of MPSA42 NPN Transistor

MPSA42 NPN transistor pinout diagram

Emitter -Pin1 This pin is for basing the emitter-base junction
Base – -Pin2This pin is for controlling the current that flow from emitter to collector.
Collector – -Pin3This pin is for providing the junction current to output load.

Other alternative options are 2N3906, MPSA55, MPSA90

MPSA42 Features

All Features of this NPN transistor are mentioned as per the datahseet. Unlike other transistors, it offers a high collector to emitter voltage. But you can drive a dc load with a maximum output current of 500mA.

  • Type: NPN bipolar transistor.
  • Dc current Gain: 40.
  • Collector- emitter voltage: 300V
  • Collector -base voltage: 300V
  • Emitter- base voltage: 6V
  • Transition frequency: 50MHz
  • Maximum operating junction temperature: +150C0
  • Collector base capacitance: 3pF
  • Minimum forward current transfer ratio: 25
  • Continuous collector current : 500mA
  • Maximum collector power dissipation : 0.625W
  • Junction to ambient thermal resistance: 200C0/W
  • Collector cut off current: 0.1μA

Download MPSA42 DataSheet

Where and How to Use MPSA42

MPSA42 transistor is specifically designed for high voltage switching and amplifications. But mostly it is used for that load which has high voltage at the output side. When it is used as a switch then it works in two regions such as cut off and saturation region. In cut off region, it acts as an open switch no current flows from collector to emitter. Similarly in the saturation region, it acts as a close switch then current flows from collector to emitter. One thing that should be kept in mind by using this transistor its collector current is only 500mA so don’t connect the load which has greater current


In this example, we will design a motor control circuit where the NPN transistor is used as a switch. MPSA42 transistor is commonly used for high voltage switching therefore here we will explain how it is used for turning on and off the high voltage dc motor(48V). This NPN transistor is connected to the motor according to the below diagram

.MPSA42 Example used as switch to control motor

5V dc voltages are applied at the base pin through a 1KΩ resistor. The value of this resistor is calculated by the formula, RB= VBE / IB. where we know when VBE is 5V and IB is 500mA then RB would be 1KΩ. when 5Votls are applied at base pin then current flows and transistor connect to the ground then the motor turns on. Similarly when zero volts are applied at base pin then no current flows then transistor does not connect to ground and the motor does not turn on.

MPSA42 Applications

  • Hight voltage switching
  • In Audio amplifiers
  • Low current motor drive circuits
  • High power LED diver circuits
  • Speed control stepper motor circuits
  • Various temperature control circuits
  • Communication circuits
  • Analog to digital converters.

NPN Transistor 2D Model Diagram

MPSA42 transistor is typically used in PCB (printed circuit boards) boards. These boards are designed with the help of software therefore its 2D model diagram understanding is so much necessary. These transistors are available in T-92 packing therefore its 2D model dimension figure is below here. For other packages, the user consults the datasheet of the required package.

NPN transistor 2D model


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