Diodes Incorporated BF621TA

Overview

BF621TA from NXP Semiconductors is a PNP silicon planar high-voltage transistor in SOT89 package, rated for V_CEO = −300 V and I_C = −50 mA continuous, with V_CE(sat) = −0.6 V at −30 mA/−5 mA drive, used in video output stages of CRT TV sets and flyback switching power supplies.

For engineers reviewing the BF621TA datasheet, BF621TA pinout, BF621TA application, or BF621TA equivalent, key selection criteria include high-voltage blocking capability (−300 V), low saturation voltage under pulsed video load conditions, thermal stability up to +150 °C junction temperature, and complementary pairing with BF620 for push-pull stage design.

Technical Context

This device operates as a high-voltage PNP switching transistor optimized for linear video output amplification and quasi-resonant SMPS switching. Its −300 V V_CEO rating enables direct use across CRT anode supply rails, while f_T = 100 MHz supports stable operation in horizontal deflection timing circuits.

The SOT89 package provides enhanced thermal dissipation (P_tot = 1 W at T_amb = 25 °C) and low-inductance emitter connection critical for fast turn-off in video linearity-critical applications. C_obo = 0.8 pF at −30 V ensures minimal Miller effect distortion during high-slew-rate transitions.

Key Specifications

Pinout & Package

SOT89 package: surface-mount, 3-lead, single-ended heatsink tab (pin 3), JEDEC TO-243AA compliant, thermal resistance R_θJA ≈ 125 K/W (standard PCB layout).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BF621TA, BF620TA serves as its polarity-matched counterpart in symmetric designs, while MJD2955T4 trades voltage capability for current capacity and thermal mass-making it unsuitable for video or high-voltage SMPS where −300 V blocking and 100 MHz f_T are essential.

Availability

BF621TA is available at Aetrix Electronics and suitable for CRT television repair, legacy flyback power supply replacement, and high-voltage analog signal amplifier refurbishment requiring stable component supply and long-lifecycle support.

Supply support for BF621TA 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

NXP Semiconductors is a global semiconductor company headquartered in Eindhoven, Netherlands, specializing in high-reliability analog, logic, and RF components for industrial, automotive, and consumer electronics.

The BF621TA belongs to NXP's legacy high-voltage bipolar transistor product line, designed specifically for analog video output and horizontal deflection circuits in CRT-based display systems and compact offline power supplies.

FAQ

What is the maximum safe operating voltage for BF621TA in continuous DC mode?

The BF621TA is rated for continuous collector-emitter voltage V_CEO = −300 V at T_j ≤ +150 °C. Operation above this value risks avalanche breakdown even with current limiting. Derating is required above +70 °C ambient per NXP's thermal curves; at 100 °C case temperature, max V_CEO drops to −240 V.

Can BF621TA be used as a direct replacement for BF620TA in a circuit?

No-BF621TA is PNP while BF620TA is NPN. Swapping them without inverting biasing, signal polarity, and load connections will prevent circuit operation and may damage surrounding components. They are complementary, not interchangeable, devices intended for paired use in push-pull topologies.

Does BF621TA require a heatsink in standard TV video output applications?

In typical CRT video output use (30–50 mA peak, 15.625 kHz duty cycle), the SOT89 package dissipates <0.8 W average. A small copper pour (≥1 cm²) on the collector pad suffices; no external heatsink is needed unless ambient exceeds +60 °C or duty cycle exceeds 40%. Thermal resistance to ambient is ~125 K/W with standard 2-layer FR4.

What is the typical h_FE spread across production lots, and how does it affect video linearity?

NXP specifies h_FE = 50 min at −25 mA/−20 V, with typical lot mean near 85 and ±25% variation. In video output stages, this spread is mitigated by emitter degeneration resistors and feedback networks; linearity depends more critically on V_CE(sat) consistency and thermal tracking than h_FE absolute value.