What is 2P4M SCR : Pin Configuration & Its Applications

The electronic component called 2P4M SCR (Silicon Controlled Rectifier) is a 4-layered PNPN 3-terminal thyristor used to control the AC of the device. It is a unidirectional device because it allows the current flow only in one direction. It is used in various power converters, regulators, rectification, switching applications, and many more. These can resist high currents and voltages.


In 1957, Gordon Hall and Frank W. Bill Gutzwiller developed the SCR at Bell laboratories. This article gives a brief description of pin configuration, specifications, and circuit diagram of 2P4M SCR, which is one of the SCR types used in various switching and power control applications.

What is 2P4M SCR?

The semiconductor device is designed to have a trigger level with high sensitivity and it is used in specific applications with limited gate currents called 2P4M SCR. It is a solid-state semiconductor device and belongs to the family of SCR (Silicon Controlled Rectifier) or Thyristor. The basic 2P4M SCR device is shown in the figure below.

2P4M Silicon Controlled Rectifier
2P4M Silicon Controlled Rectifier

This rectifier is used in various electronic applications where limited gate currents are produced. For example, a 2P4M SCR device is employed in applications such as ignitions of capacitive discharge, controlling of motors in kitchen appliances, and high/over-voltage protection in low power supply circuits. This type of SCR is used in AC rectifiers with low voltage and applications of RMS voltage controllers.

Pin Configuration/Pin Diagram

This is a 3-terminal semiconductor device. The 3 terminals are Anode, Cathode, and Gate. The 2P4M SCR pin configuration/pin diagram is illustrated in the figure below.

2P4M SCR Pin Configuration
2P4M SCR Pin Configuration
  • Pin 1 represents the Cathode terminal
  • Pin 2 represents the Anode terminal
  • Pin 3 represents the Gate terminal

Pin 1 Cathode: This terminal is connected to the neutral point. It is common to both input and output and connected to common ground.

Pin 2 Anode: This terminal is connected to the load to obtain the output. It is also known as the output terminal.

Pin 3 Gate: To turn ON the 2P4M SCR, a trigger pulse with low voltage is applied to this terminal. It controls the input given to the SCR.

2P4M SCR Specifications

The 2P4M SCR specifications or features according to the datasheet are as follows,

  • Installation in any circuit is easy due to its thin electrodes and small size.
  • It is available in the TO-202AA type of package.
  • It is available at a low cost
  • Free application design is provided by the low holding distribution current
  • The voltage of peak reverse blocking is 500 Volts
  • The Peak current of the gate terminal is 0.2 Amps.
  • The peak On-State Current is 2 Amps
  • The peak reverse gate voltage is 6 Volts
  • The triggered gate voltage is 0.8 Volts
  • The surge peak On-State current (non-repetitive) is 20 Amps
  • The range of operating temperature of the junction is between -40°C and +120°C
  • The range of storage temperature is between -55°C and +150°C.

Circuit Diagram/How to use

To understand the working and to learn how to use the 2P4M SCR device, consider an example of the switching device as explained in this section. The application with a simple circuit diagram using the 2P4M SCR is illustrated in the figure below. The components required for this application circuit of the device are; 2P4M SCR, Buttons -2, Resistors & Voltage source.


Circuit Diagram
Circuit Diagram
  • From the above circuit diagram we can observe that the DC voltage source is represented as V1;
  • The gate voltage, which is the trigger voltage at the gate of the device;
  • The load resistor is in series connection with the SCR;
  • Once the button B2 is pressed, by default it will be closed and break the circuit.
  • The anode terminal of the SCR is connected to the load
  • The cathode terminal of the SCR is connected to the other end of the source.

In the initial stage, the button B1 is not pressed and the absence of gate voltage leads to the SCR being in a non-conducting state. When Vg= 0V or no trigger is given to the gate terminal of the SCR, the total voltage drop will appear across the device and the voltage at the load will be 0V (Vload=0V). This is illustrated in the above graph. This state is continued till the voltage pulse is applied to the gate of the device. This state is possible only when the button B1 is pressed.

Now consider at time T1, the button B1 is pressed. In this state, the 2P4M SCR conducts and the total voltage will appear across the load as illustrated in the above graph. Due to the DC power supply, the SCR is triggered ON and stays in the conducting mode. The device conducts even though the gate voltage is removed after triggering the SCR.

Now to recover the 2P4M SCR in a high resistance state, the current flowing through the device should be ‘0’ for some time. When the current is ‘0’ or cutoff, the stored charge in the device is dissipated to recover to its initial state, that is forward blocking state.

To bring the current flowing through the device to ‘0’, the button B2 should be pressed. By pressing the button B2 once, the loop of the circuit breaks, and the current flowing in the device becomes ‘0’. Therefore the voltage across the load also becomes ‘0’ and the device starts to recover its state as shown in the above graph. This is due to the loop breakdown when the B2 is pressed.

Waveform Representation
Waveform Representation

After releasing button B2, the device blocks the forward DC voltage and waits for the trigger voltage (gate pulse). The load voltage will be ‘0’ till the button B2 is pressed. The above graph illustrates the load voltage after the first and second trigger pulses. This triggering and breaking cycle continues.

This whole operation shows how to use the 2P4M SCR as the switching device. In the same way, it is used in other applications.

Where to Use/Applications of 2P4M SCR

In the above section, we have learned how to use the 2P4M SCR with a small circuit. Now, let’s know where to use it. The applications of 2P4M SCR include the following.

  • Light dimmer
  • Battery chargers
  • Motor controllers
  • Capacitor discharge ignition
  • Different temperature-controlled devices
  • AC rectifiers
  • RMS voltage switching circuits
  • Industrial switching applications
  • Power converters
  • Electric blankets
  • Electronic jars
  • Sewing machines (electric)
  • Light display systems
  • Gas lighter (automatic)
  • Alternative 2P4M SCR
  • SN102, BT169, TIC206D, TYN604, 2N1595, 2N1596 are the alternative 2P4M SCRs

Thus, this is all about an overview of 2P4M SCR, which is one of the types of SCR or thyristor. This article includes- what is 2P4M SCR, pin configuration/pin diagram, technical specifications, circuit diagram/how to use, where to use/applications of 2P4M SCR. This is a general-purpose SCR in the p-gate type of diffused plastic model used in various applications of power control. Here is a question for you, “What are the disadvantages of Silicon Controlled Rectifier or Thyristor?”

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