BT151 SCR Features, Pin Configuration, Working Principle and Applications
27 November 2023
Ⅰ. What is a one-way thyristor?
Ⅲ. What are the features of BT151?
Ⅳ. Footprint and pin configuration of BT151
Ⅴ. Technical parameters of BT151
Ⅵ. How to measure the quality of BT151 thyristor?
Ⅶ. How does the BT151 SCR work?
Ⅷ. What are the applications of BT151?
One-way thyristor generally refers to silicon controlled rectifier (SCR). It is a core power control appliance based on thyristors and integrated with intelligent digital control circuits. It has many advantages such as high efficiency, small size, light weight, fast response speed, and no mechanical noise and wear.
It consists of anode, cathode and gate. Among them, the anode and cathode are P-type semiconductors, and the gate is an N-type semiconductor. When a voltage is applied between the anode and cathode, current can flow freely between the anode and cathode. At the same time, the gate control voltage can control the current on and off.
The operational of a unidirectional thyristor involves regulating the flow of current between the cathode and anode by manipulating the gate. In the absence of gate voltage (when it is 0), the PN junction between the cathode and anode is in a reverse-biased state, preventing any current from flowing between them. Conversely, when the gate voltage exceeds 0, the PN junction between the gate and the cathode becomes forward-biased. This forward bias enables a current to traverse the PN junction between the cathode and anode, facilitating the passage of current between the two.
BT151 is a 12A medium power SCR in TO-220 package. This type of thyristor is used for switching standard mains AC or DC loads and managing high DC signals, primarily for power switching purposes. SCRs are similar to transistors but have latching capabilities. Once triggered, it will remain on even if the gate signal disappears. This property makes SCR very useful in many applications. However, when the current drops to a certain value (called the holding current), the SCR will stop conducting.
Replacements and equivalents:
• BTA16
• CR10AM
• 2N2222
• 2N3904
• 2N2907
• It has low voltage drop and high current capability to provide high quality power amplification.
• It exhibits excellent thermal cycling capabilities, ensuring consistent and dependable performance across numerous thermal cycles.
• BT151 has a lower voltage drop during conduction, which can reduce power loss and improve circuit efficiency.
• BT151 has a four-layer PNPN structure, which can realize the switching function of controlling current and has bidirectional conduction characteristics. It is capable of controlling two half cycles of alternating current. It can trigger during both positive and negative half cycles.
The footprint and pin configuration of BT151 are shown below.
BT151 typically consists of three pins, namely the control electrode, anode, and cathode. The control electrode is used to control the current switch, while the anode and cathode are used to conduct the current. Their names and descriptions are as follows.
Pin 1 (Anode): Current is supplied to this terminal.
Pin 2 (Cathode): Conventional current flows out of the cathode.
Pin 3 (Gate): It can control conduction between the anode and cathode terminals.
• Package: TO-252
• Peak gate power: 5W
• Peak gate current: 2A
• Off-state repetitive peak voltage : 650V
• Average gate power consumption PG: 0.5W
• Repetitive peak reverse voltage: 650V
• RMS on-current IT: 12A
• Working contact temperature range: -40 ~ 125℃
• Storage contact temperature range: -40 ~ 150℃
• Non-repetitive surge peak on-state current: 120A
First, we need to ensure that the test instrument is set to the appropriate measurement range and that it is disconnected from the power supply. We use a multimeter and turn it into diode test mode. In this mode, the meter applies a small voltage and measures the current through the thyristor. We connect the red test probe to the anode (A) of the BT151 and the black test probe to the cathode (K).
At this time, if the thyristor is normal, the multimeter should show a forward conducting voltage value, usually between 0.6V and 0.8V. This indicates that the thyristor is in a normal conduction state. If your multimeter shows an open circuit or reverse conduction, it may indicate a faulty or damaged thyristor.
Thyristors can switch extremely high currents at low voltage, low current equipment and mains (line) voltages, and they can regulate AC or DC loads. In the DC circuit, the use of BT151 SCR can refer to the circuit diagram below.
A BT151 thyristor connects the motor to the 12V DC supply. However, the motor will not run until the thyristor conducts. This is accomplished by briefly closing the start switch, which sends a current pulse to the gate terminal of the thyristor. Once the thyristor is switched on, the motor starts running and its resistance plummets.
When the start switch is in the normally open state, although the thyristor continues to conduct, there is no gate current. In a DC circuit, current will continue to flow and the motor will continue to drive. Any operation on the starting switch has no effect and the thyristor switches off only when the current drops below the holding current threshold of the thyristor.
This is accomplished by briefly closing the stop switch, at which point the thyristor short-circuits. Since the current of the thyristor is already less than the holding current value, the circuit current will pass through the stop switch, causing the thyristor to turn off immediately. At the same time, a normally closed switch in series with a thyristor can also be used to stop the motor. When the switch is pressed, the normally closed switch temporarily cuts off the current flowing through the thyristor, causing the thyristor to turn off.
• Leakage protector: When leakage occurs in the circuit, BT151 thyristor can detect the abnormal current and immediately cut off the power supply to protect the safety of the circuit and equipment. This automatic cut-off function can effectively avoid safety accidents such as fires and electric shocks caused by electric leakage.
• Power tools: The BT151 can be employed to regulate the electric motor's speed. By manipulating the firing angle of the BT151, the motor's duty cycle can be adjusted, consequently altering the rotational speed of the tool.
• AC voltage regulation: By introducing BT151 in the circuit and controlling its firing angle, we can adjust the effective voltage in the circuit.
• Motor drive: This component finds application in motor drive circuits, including those for DC motors and stepper motors. The manipulation of on and off times allows us to regulate both the speed and direction of the motor.
• Electric and induction cooktops: Apart from this, BT151 can also be used to control heating elements in electric and induction cooktops. By controlling the firing angle of BT151, it can adjust the power of the heating element and achieve temperature regulation.
• Power switch: BT151 thyristor can be used in various power switch circuits, such as chargers, power adapters, etc., to achieve efficient power transmission and utilization.
Frequently Asked Questions
1. What is the function of BT151?
The BT-151 is a medium power SCR used for power switching. SCRs are like transistors but have the ability to latch, i.e. stay on once triggered, even if the gate signal is removed. They stay in conduction till the anode-cathode current drops below a certain value called the holding current.
2. What is BT151?
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.
3. Is BT151 a triac?
BT151 is a sensitive gate triac suitable for direct coupling to TTL, HTL, CMOS, and applications such as various logic functions, low power AC switching applications, such as fan speed, small light controllers, and home appliances equipment.
4. What is the equivalent of BT151 thyristor?
Equivalent BT151 SCRs are TYN208, BT152, 2N6508 and an alternative BT151SCRs are BTA16, S6010, BTB12600B, etc.
5. How do you test a BT151 with a multimeter?
(1) Turn on the multimeter and switch it to the 'diode' mode.
(2) Refer to the BT151 datasheet to verify the pin connection of the SCR.
(3) Attach the black (negative) terminal with the Cathode pin and the red (positive) with the Anode pin.
