MPSA42 Transistor : Pin Configuration & Its Applications

The MPSA42 transistor is a high voltage-based NPN transistor. Generally, a transistor is used like an amplifier & a switch, although this MPSA42 transistor is frequently used for only switching purposes because it includes a less gain value like 30. It can control the loads with upto 300 voltages.

Once this transistor is completely biased with 6V of base-emitter voltage (VBE), then it holds upto 500mA of collector current. As a result, if you want to switch high voltages using decent enough current then the NPN transistor is the best choice for you. This article discusses an overview of the MPSA42 transistor and its working.

What is MPSA42 Transistor?

MPSA42 transistor is an NPN bipolar junction transistor, used in high voltage-based applications like high voltage amplification and switching. The transistor’s CE (collector-emitter) voltage is 300V, so it can be used in applications where a general-purpose transistor cannot be used due to the max collector-emitter voltage like 100V.

In addition, the feature of CE voltage of MPSA42 transistor will make it to utilize in circuits wherever there is a sudden voltage risk with fluctuations. When the base terminal of this transistor is connected to GND, the collector and emitter terminals are connected in reverse bias. MPSA42 is an NPN transistor hence the collector & emitter will be left open (Reverse biased) when the base pin is held at the ground. The CE terminals will be forward biased or closed once a signal is given to the base pin.

MPSA42 Transistor
MPSA42 Transistor

The gain value of this transistor will decide the capacity of amplification for the transistor. So due to less gain value, it will not be utilized in the amplification. It has a gain value of 30; this value determines the amplification capacity of the transistor normally MPSA42 is not used for amplification due to its low gain value.

Here the maximum current supply throughout the collector pin of this transistor is 500mA, so above 500mA of loads cannot drive. This transistor is biased by providing the 5mA of limited current supply to the base terminal. Once this transistor is completely biased then it allows max current flow like 500mA across the emitter & collector terminals so, this phase is called the saturation region.


The typical voltage supplied across the CB & CE could be 300V correspondingly. Once the supply is detached at the base terminal then it will turn off, so this is called the cut-off region.

Pin Configuration

The pin configuration of the MPSA42 transistor is shown below.

MPSA42 Transistor Pin Configuration
MPSA42 Transistor Pin Configuration
  • Pin1 (Emitter): This terminal drains out the current
  • Pin2 (Base): The base terminal controls the transistor biasing
  • Pin3 (Collector): Current supplies throughout this terminal

Specifications & Features

The specifications and features of the MPSA42 transistor include the following.

  • The package of this transistor is TO-92
  • Operating and storage temperature (Max) must be -55 to +150 C
  • The type of transistor is NPN
  • Max & min DC gain is 40
  • Collector current max is 500mA
  • Transition frequency (Max) is 50 MHz
  • VCE or Collector emitter voltage (Max) is 300V
  • Collector dissipation (Max) is 625 mW
  • VCB or Collector base voltage (Max) is 300V
  • VEB or emitter-base voltage (Max) is 6V
  • High voltage & Bipolar NPN transistor

Alternative MPSA42 transistors are SS8550, S9014, SS8050, 2N3904, BC547, 2N2369, 2N3055, 2N3906, 2N3904. Equivalent MPSA42 transistors are MMBTA42, KST42 & PZTA42.

How to use MPSA42 Transistor/Circuit Diagram

MPSA42 transistor is specifically designed for amplifications & high voltage switching. However, it is mostly used where the load at the output side has high voltage.

Once this transistor is used as a switch afterward it works within two regions like saturation & cut off. In the saturation region, the transistor works like a close switch so that the current supply will be from collector terminal (C) to emitter(E) whereas in cut off region, this transistor behaves like an open switch, so there is no current flow from two terminals like a collector to emitter.

DC Motor Controlling with MPSA42 Transistor
DC Motor Controlling with MPSA42 Transistor

Here, one thing we have to notice that is, the collector current must be 500mA while connecting to load. If this current is higher than this, don’t connect to load otherwise it will damage the circuit.

Here, a circuit is designed with the MPSA42 transistor to control a motor where the transistor is used as a switch. Generally, this transistor is used in high voltage switching. The following circuit is used to control a high voltage-based DC motor by connecting an NPN transistor.

Here, this resistor value is measured through the formula like RB= VBE / IB. where VBE = 5V & IB = 500mA & RB = 1KΩ. At the base pin of this transistor, 5V DC voltage is applied with the help of a 1KΩ resistor then-current supply & transistor is connected to the GND then the DC motor will turn ON.
Likewise, once 0V is applied at the base terminal of this transistor then there is no flow of current, so this transistor does not connect to GND & the DC motor does not activate.

Where to use/Applications

The applications of the MPSA42 transistor include the following.

  • MPSA42 transistor is used in high voltage-based applications like Telephonic, video communications, etc.
  • This transistor can also be used for high voltage-based switching.
  • If this transistor is used as a switch then it can drive up to 500mA of loads to control LEDs, relays, medium & high power transistors.
  • This transistor can be used as an amplifier in audio based applications
  • Inverter based applications
  • Low current based motors speed control
  • Circuits like UPS, battery charger, etc.
  • Drive LEDs, stepper motors, etc
  • High voltage based power supplies
  • Audio amplifiers & their stages
  • Controllers of motor
  • To switch different loads which work with high voltage
  • Drive LEDs which operates with high power
  • High peak voltage based loads can be controlled
  • Drive stepper motors with high voltage
  • Low current motors speed can be controlled

Thus,  this is all about an overview of the MPSA42 transistor datasheet which includes its pin configuration, specifications, features, circuit working & its applications. MPSA42 is a small signal-based NPN transistor that is used in different high voltage applications like telephone dialers and video amplifiers. Here is a question for you, what are different NPN transistors available in the market?