STMicroelectronics 2ST501T

Overview

2ST501T from STMicroelectronics is a high-voltage NPN power transistor in monolithic Darlington configuration, rated for 500 V V_CES, 4 A continuous collector current, and 100 W total dissipation at T_C = 25 °C, designed for rugged solenoid, relay, and DC motor driver stages in industrial control systems.

For engineers reviewing the 2ST501T datasheet, 2ST501T pinout, 2ST501T application, or 2ST501T equivalent, key selection criteria include V_CEO = 350 V, h_FE ≥ 2000 at I_C = 2 A, t_s = 15 ms storage time under inductive switching, and TO-220 thermal resistance R_thj-case = 1.25 °C/W.

Technical Context

The 2ST501T integrates two cascaded NPN transistors in a single silicon die to achieve high DC current gain (h_FE ≥ 2000) while maintaining high breakdown voltage (V_CES = 500 V). Its Darlington structure enables low base drive requirements-only 2 mA IB needed to saturate at I_C = 2 A-with V_CE(sat) = 1.5 V and V_BE(sat) = 2 V.

Designed for inductive load switching, it features specified storage time (t_s = 15 ms) and fall time (t_f = 1.5 ms) under V_CC = 12 V, V_clamp = 250 V, L = 4 mH, and reverse base bias (V_BE = −3 V), supporting reliable turn-off in relay/solenoid drivers.

Key Specifications

Pinout & Package

Supplied in JEDEC-standard TO-220 plastic package (3-lead, vertical mounting, metal tab connected to collector), with pin 1 = emitter, pin 2 = base, pin 3 = collector (tab). Thermal path optimized via direct metal tab contact to heatsink.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage Darlington transistor applications.

Compared with BUX87 and TIP142, the 2ST501T uniquely balances 500 V blocking, 2000 h_FE, and 1.25 °C/W thermal resistance-making it optimal for 24–48 V industrial actuators where logic-compatible drive and snubberless inductive switching are mandatory.

Availability

2ST501T is available at Aetrix Electronics and suitable for industrial relay drivers, DC solenoid actuators, small DC motor controllers, and high-voltage lamp ballasts requiring stable component supply across multi-year production cycles.

Supply support for 2ST501T includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in power management, analog, MEMS, and microcontrollers for industrial, automotive, and consumer markets.

The 2ST501T belongs to ST's high-voltage bipolar power transistor family, engineered specifically for robust, high-reliability switching in industrial actuation and control systems operating up to 150 °C junction temperature.

FAQ

Is the 2ST501T pin-compatible with standard TO-220 NPN transistors?

No-the 2ST501T uses emitter-base-collector (E-B-C) pinout (pin 1 = emitter, pin 2 = base, pin 3 = collector), whereas many generic TO-220 NPNs use E-C-B or C-B-E arrangements. Always verify pin assignment using Figure 1 and Table 2 in the official STMicroelectronics datasheet Rev. 1.

Can the 2ST501T replace a MOSFET in a 24 V relay driver?

Yes, but with trade-offs: it offers higher V_CES and inherent ruggedness against voltage transients, yet requires ~2 mA base drive versus MOSFET gate charge. Its 1.5 V V_CE(sat) yields similar conduction loss to a 30 mΩ MOSFET at 2 A, but switching speed is slower due to minority-carrier storage.

What is the maximum safe operating current at 85 °C case temperature?

At T_C = 85 °C, derating from 100 W (at 25 °C) gives P_tot ≈ 62.5 W. With V_CE(sat) = 1.5 V, max continuous I_C ≈ 41.7 A is thermally impossible-practical limit is ~3.2 A, constrained by I_C = 4 A absolute rating and safe SOA boundaries defined in Figure 4 of the datasheet.

Does the 2ST501T require a base resistor when driven by a 5 V microcontroller GPIO?

Yes-a series base resistor is mandatory. For I_B = 2 mA at V_GPIO = 5 V and V_BE(sat) = 2 V, R_B = (5 − 2) V / 2 mA = 1.5 kΩ. Use 1.2–1.8 kΩ standard value to ensure saturation across process and temperature variation.