BU931T - 15A, 400V NPN Power Darlington Transistor | STMicroelectronics
MPN: BU931T β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.25 | $1.25 |
| 10 | $1.1 | $11.00 |
| 100 | $0.95 | $95.00 |
| 500 | $0.85 | $425.00 |
| 1,000 | $0.75 | $750.00 |
Drop-in alternatives for BU931T β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
BU931
β Drop-Inπ Reference alternative (not in catalog)
TIP140
β Drop-Inπ Reference alternative (not in catalog)
MJ10015
β Drop-Inπ Reference alternative (not in catalog)
MJE13009
β Drop-Inπ Reference alternative (not in catalog)
2N6547
β Drop-Inπ Reference alternative (not in catalog)
BU931T Maximum Ratings & Electrical Characteristics
| Transistor Type | NPN Darlington |
| Collector-Emitter Voltage (VCEO) | 400 V |
| Collector-Base Voltage (VCBO) | 500 V |
| Emitter-Base Voltage (VEBO) | 5 V |
| Continuous Collector Current (IC) | 15 A |
| Peak Collector Current (ICM) | 30 A |
| Power Dissipation (PC) | 125 W |
| DC Current Gain (hFE) | 500 min at IC=10A, VCE=5V |
| Collector-Emitter Saturation Voltage (VCE(sat)) | 2.0 V max at IC=10A, IB=40mA |
| Base-Emitter Saturation Voltage (VBE(sat)) | 2.5 V max at IC=10A, IB=40mA |
| Fall Time (tf) | 1.5 Β΅s |
| Storage Time (ts) | 2.5 Β΅s |
| Thermal Resistance (RthJC) | 1.0 Β°C/W |
| Operating Junction Temperature | -65Β°C to +150Β°C |
| Package | TO-220 |
| Mounting Type | Through Hole |
| RoHS Status | Compliant |
BU931T Pin Configuration
| Pin 1 | Base β Base terminal for controlling the transistor |
| Pin 2 | Collector β Collector terminal, connected to the load |
| Pin 3 | Emitter β Emitter terminal, connected to ground |
Safe Operating Area (DC)
Typical Applications
BU931T is suitable for 6 applications: Motor Control, Switching Power Supplies, Automotive Ignition Systems, Solenoid Drivers, Battery Chargers, Welding Equipment.
Motor Control
The BU931T is ideal for motor control applications due to its high current rating (15A) and voltage rating (400V). It can switch DC motors directly, providing reliable on/off control. In PWM motor control, the BU931T's fast switching speed (fall time 1.5Β΅s) allows efficient operation at frequencies up to 10 kHz. The low saturation voltage (2.0V) minimizes power loss, improving overall system efficiency. For inductive loads, a flyback diode is recommended to protect the transistor from voltage spikes. The TO-220 package allows easy mounting on a heatsink for thermal management. Compared to MOSFETs, the Darlington transistor offers higher current gain, simplifying the drive circuit. However, for high-frequency PWM above 10 kHz, a MOSFET may be more suitable due to lower switching losses. The BU931T is commonly used in industrial motor control panels, robotics, and automotive applications.
Recommended
Switching Power Supplies
In switching power supplies, the BU931T is used as a high-voltage switch in the primary side of flyback or forward converters. Its 400V VCEO rating allows it to handle rectified 240V AC mains (approximately 340V DC). The high current gain (hFE 500) enables direct driving from PWM controller ICs without additional driver stages. The fast switching speed ensures efficient operation at typical switching frequencies of 50-100 kHz, though the BU931T is more suited for lower frequencies due to its storage time. The low saturation voltage reduces conduction losses, improving efficiency. Thermal management is critical, as power dissipation can be significant at high currents. A heatsink with adequate thermal resistance is required. The BU931T is often used in offline power supplies for consumer electronics, industrial equipment, and battery chargers. For higher efficiency, a MOSFET or IGBT may be preferred, but the BU931T offers a cost-effective solution for moderate power levels.
Recommended
Automotive Ignition Systems
The BU931T is well-suited for automotive ignition systems, where it switches the ignition coil to generate high-voltage sparks. Its 400V VCEO rating is sufficient to handle the back-EMF from the ignition coil, which can exceed 300V. The high current rating (15A) allows it to handle the coil's primary current, typically 5-10A. The fast switching speed ensures precise timing of the spark, improving engine performance and fuel efficiency. The device's ruggedness and wide operating temperature range (-65Β°C to +150Β°C) make it suitable for the harsh automotive environment. The TO-220 package can be mounted on a heatsink or directly on the engine block for thermal management. The integrated base-emitter resistor and diode provide protection against spurious turn-on due to electrical noise. The BU931T is used in both conventional and electronic ignition systems, offering reliable performance in demanding conditions.
Recommended
Solenoid Drivers
The BU931T is an excellent choice for driving solenoids in industrial automation, vending machines, and locking systems. Solenoids require a high inrush current to actuate, which the BU931T can provide with its 15A continuous and 30A peak current ratings. The high voltage rating (400V) ensures compatibility with various supply voltages, including 24V, 48V, and 120V systems. The low saturation voltage minimizes power dissipation during the hold phase, reducing heat generation. The fast switching speed allows rapid actuation and release, improving system response time. For inductive loads, a flyback diode is essential to clamp voltage spikes. The BU931T can be driven directly from a microcontroller via a base resistor, thanks to its high current gain. The TO-220 package is easy to mount on a PCB or heatsink. This application is common in factory automation, where reliability and long life are critical.
Recommended
Battery Chargers
The BU931T is used in battery charger circuits for switching the charging current. Its high current rating (15A) allows it to handle charging currents for lead-acid, NiMH, and Li-ion batteries. The 400V VCEO rating makes it suitable for chargers connected to AC mains, where the rectified voltage can be high. The low saturation voltage reduces power loss, improving charging efficiency. The fast switching speed enables PWM-based charging algorithms for precise current control. The device's ruggedness ensures reliable operation in harsh environments. Thermal management is important, as high charging currents can cause significant power dissipation. A heatsink is recommended. The BU931T is commonly used in automotive battery chargers, industrial charging stations, and portable chargers. For higher efficiency, a synchronous rectifier MOSFET may be used, but the BU931T offers a simple and cost-effective solution.
Recommended
Welding Equipment
The BU931T is used in welding equipment for switching the high current required for arc welding. Its 15A continuous and 30A peak current ratings can handle the welding current, which can be several hundred amps when using multiple transistors in parallel. The 400V VCEO rating ensures compatibility with the high voltages present in welding circuits. The low saturation voltage minimizes power loss, improving efficiency and reducing heat generation. The fast switching speed enables precise control of the welding arc. The device's ruggedness and wide operating temperature range make it suitable for the demanding welding environment. The TO-220 package can be mounted on a heatsink for thermal management. The BU931T is used in both inverter-based and traditional transformer-based welding machines. For high-frequency inverter welders, an IGBT may be preferred, but the BU931T offers a cost-effective solution for lower-frequency applications.
Recommended
Recommended Products Summary
Engineering reference data for BU931T β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BU931 | TIP140 | MJ10015 | MJE13009 | 2N6547 |
|---|---|---|---|---|---|---|
| Package | TO-220 | TO-220 | TO-220 | TO-220 | TO-220 | TO-220 |
| Brand | STMicroelectronics | STMicroelectronics | STMicroelectronics | ON Semiconductor | ON Semiconductor | STMicroelectronics |
| Collector-Emitter Voltage (VCEO) | 400 V | 400 V | 400 V | 400 V | 400 V | 400 V |
| Continuous Collector Current (IC) | 15 A | 15 A | 15 A | 15 A | 12 A | 10 A |
| Power Dissipation (PC) | 125 W | 125 W | 125 W | 125 W | 100 W | 100 W |
| DC Current Gain (hFE) | 500 min at 10A | 500 min at 10A | 500 min at 10A | 500 min at 10A | 500 min at 8A | 500 min at 5A |
| Collector-Emitter Saturation Voltage (VCE(sat)) | 2.0 V max at 10A | 2.0 V max at 10A | 2.0 V max at 10A | 2.0 V max at 10A | 2.0 V max at 8A | 2.0 V max at 5A |
| Fall Time (tf) | 1.5 Β΅s | 1.5 Β΅s | 1.5 Β΅s | 1.5 Β΅s | 1.0 Β΅s | 1.5 Β΅s |
Key Differentiators
- High current gain (hFE 500 min) simplifies drive circuitry (vs MJE13009)
- Higher power dissipation (125W) allows more robust designs (vs 2N6547)
- Same-brand drop-in compatibility with BU931 (vs BU931)
Design Notes
The BU931T dissipates up to 125W, requiring a heatsink with a thermal resistance of less than 1.0Β°C/W to keep the junction temperature below 150Β°C. For example, at 50W dissipation, the junction-to-case temperature rise is 50Β°C, so the case must be kept below 100Β°C. Use thermal compound and a proper mounting torque to ensure good thermal contact.
When driving inductive loads such as motors or solenoids, always place a flyback diode (e.g., 1N4007) across the load to clamp voltage spikes. Without it, the collector-emitter voltage can exceed the 400V rating, damaging the transistor. Also, ensure the base drive current is sufficient (at least IC/250) to achieve low saturation voltage.
For TO-220 packages, ensure the leads are properly inserted into the PCB and soldered with adequate solder fillets. The tab is connected to the collector, so if it is mounted on a heatsink, ensure electrical isolation if the heatsink is grounded. Use a mica washer and insulating bushing if needed.
Compliance Information
RoHS compliant per STMicroelectronics datasheet. Not AEC-Q100 qualified as it is a discrete transistor, not an IC.
