BT151 SCR : Pin Configuration, Circuit & Its Applications

The term “SCR” stands for “Silicon Controlled Rectifier” and this is an essential & most frequently used 3-terminal semiconductor device in different applications like power regulation & inversion, rectification, etc. This component comes under the family of the thyristor. Similar to a diode, silicon controlled rectifier is a unidirectional component that permits the flow of current in only one direction & restricts it in another direction. This article discusses an overview of BT151 SCR & its working with applications.

What is BT15 SCR?

BT151 SCR is a Semiconductor device and it is also called a thyristor. So this component includes four alternating N layers & P-type material. BT151 SCR IC is available in a plastic envelope. The main intention of this component is to use in applications where high thermal cycling performance & high bidirectional blocking voltage capacity is necessary.

The working principle of a silicon-controlled rectifier is, once the biasing or triggering is given at the gate terminal of the SCR, the conduction will start immediately. It is a uni-directional component, so the flow of current will be in a single direction.


The BT151 is a 12A medium power SCR that is available in a TO-220 package. This kind of SCR is used to switch standard power AC or DC loads & manages high DC signals. This is a medium power silicon controlled rectifier and it is mainly used for power switching purposes.

SCRs are transistors however they can latch once triggered, even if the gate signal is detached. They wait in conduction until the anode-cathode current drops under a fixed value known as the holding current. Silicon-controlled rectifiers in several methods act like diodes with the same forward drops, therefore the name is called a controlled rectifier.

BT151 SCR Pin Configuration

The pin configuration of BT15 SCR is shown below. This component includes four terminals where each terminal and its purpose are discussed below.

BT151 SCR Pin Configuration
BT151 SCR Pin Configuration
  • Pin1 (Cathode): Current supplies out from this terminal
  • Pin2 (Anode): Current supplies into this terminal
  • Pin3 (Gate): Conduction can be controlled among the two terminals like anode & cathode.
  • Pin4 (Tab): This pin is connected electrically toward the anode terminal.

Features & Specifications

The features & specifications of BT15 SCR include the following.

  • BT151 Part number
  • Functions like Thyristor & SCR
  • Manufactures are Philips, NXP
  • Blocking voltage capacity in bidirectional is good
  • The capacity of surge current is high
  • Thermal cycling performance is high
  • Reliability is high
  • Peak off-state voltage is 650V
  • The Standard on-state current is 7.5A
  • RMS on-state current is 12A
  • Trigger current of gate terminal ranges from 1mA – 15mA
  • Thermal cycling performance is high
  • Blocking voltage is high & bidirectional
  • The rating of surge current is 132 Amp
  • Gate trigger current max is 15 mA
  • Holding current max is 20 mA
  • Peak off current repetitive is 0.5 mA
  • Max reverse voltage repetitive is 500V
  • Gate trigger voltage max is 1.5 Volts
  • Max on-state voltage is 1.75 Volts
  • Repetitive max forward blocking voltage is 500 Volts
  • Equivalent BT151 SCRs are TYN208, BT152, 2N6508 and an alternative BT151SCRs are BTA16, S6010, BTB12600B, etc.

How to Test an SCR?

An SCR can be tested with a multimeter quite efficiently. The primary process is to verify the action of the diode in between the gate & cathode terminals of the silicon-controlled rectifier. First, we need to fix the multimeter selector switch within the position of high resistance.

Connect the anode terminal of an SCR to the multimeter’s positive terminal whereas the negative terminal to the cathode. The multimeter device will display like an open circuit. Now the connections must be reversed then again the multimeter device will show an open circuit.

After that connect the two terminals of the SCR like anode & gate to the +ve terminal of the multimeter whereas the cathode terminal to the negative terminal.

The multimeter will illustrate less resistance that indicates the activation of an SCR. At present detach the gate terminal carefully from the two terminals like anode & again of the multimeter that will display a less resistance reading & indicates the latching condition. Here the battery of the multimeter supplies the holding current mainly for the SCR.

Silicon Controlled Rectifiers in DC Circuits

SCR is used for controlling AC or DC loads, switchless voltage & current devices & extremely large currents at line voltages. The best application of SCR-controlled DC motor is shown below. The load in the circuit-like DC motor is allied to a 12V DC supply with the help of a BT151 SCR, however, it does not perform until the SCR is made to conduct.

DC Circuit using BT151 SCR
DC Circuit using BT151 SCR

This can be obtained by momentarily locking the start switch. This switch provides a current signal toward the thyristor’s gate terminal. Now the DC motor runs because the thyristor turns ON & its resistance will be extremely low.

Once the start switch comes to its normally open (NO) condition, then there is no flow of any gate current however the thyristor conducts continuously. In a DC circuit, the continuous current supply will be there & the DC motor runs continuously. The thyristor will simply turn OFF if the current supply decreases to a value under the holding current threshold of SCR.

This can be attained by shorting out the SCR by turn OFF the ‘stop’ switch momentarily. Now the flow of current in the circuit throughout the stop switch rather than throughout the SCR, which directly switch OFF, because now the thyristor current is decreased to low than the value of holding current.

The DC motor working could be attained with a normally closed (NC) switch within series through the thyristor. Once the switch is pressed, it will prevent the flow of current temporarily throughout the SCR to switch OFF. By using this circuit, motor control can be done easily.

Where to use BT151 SCR?

The applications of BT151 SCR include the following.

  • Controlling of Motors
  • Ignition & Protection Circuits
  • Static Switching
  • In industries for domestic lighting, static switching & heating.
  • It is used in applications where maximum thermal cycling performance & blocking voltage capacity in bidirectional is necessary.
  • CDI (Capacitive Discharge Ignition)
  • Protection of Crowbar & Inrush
  • Regulation of voltage
  • High junction working temperature capacity

Thus, this is all about an overview of the BT151 SCR datasheet which includes its pin configuration, features, specifications, working, and applications. This is a medium power silicon controlled rectifier mainly used for power switching. These are similar to transistors however they can stay on when triggered, even if the signal at the gate terminal is detached. They wait in conduction till the flow of current from anode to cathode falls under a fixed value known as holding current. Here is a question for you, what is the main function of a silicon-controlled rectifier or SCR?