Diodes Incorporated ZTX549STOB

Overview

ZTX549STOB from Diodes Incorporated is a PNP silicon planar medium-power transistor designed for linear amplification and switching in industrial control, power supply regulation, and relay driver circuits. It features V_CEO = −30 V, I_C = −1 A continuous, P_tot = 1 W at T_amb = 25°C, h_FE = 100–300 at I_C = −500 mA, and f_T = 100 MHz - enabling robust low-frequency gain and fast turn-off in discrete power stages.

For engineers reviewing the ZTX549STOB datasheet, ZTX549STOB pinout, ZTX549STOB application, or ZTX549STOB equivalent, key selection criteria include verified PNP polarity, TO-92-compatible E-Line package thermal derating (5.7 mW/°C above 25°C), safe operating area up to 100 V/1 A pulsed, and confirmed V_CE(sat) ≤ −0.5 V at I_C = −1 A / I_B = −100 mA under pulsed conditions.

Technical Context

This device operates as a medium-power PNP bipolar junction transistor with fixed emitter-base and collector-base breakdown limits (V_EB0 = −5 V, V_CB0 = −35 V) and specified saturation behavior across three current tiers: −100 mA, −500 mA, and −1 A. Its h_FE variation with I_C (100–300 at −500 mA; 70–130 at −1 A) supports predictable DC bias design in Class-A amplifiers and saturated-switch configurations.

Switching performance is characterized by t_on = 300 ns and t_off = 50 ns under defined load (I_C = −500 mA, V_CC = −10 V, I_B1 = I_B2 = −50 mA), and C_obo = 25 pF at V_CB = −10 V enables stable high-speed operation without unintended resonance in snubberless designs.

Key Specifications

Pinout & Package

Supplied in an E-Line TO-92-compatible plastic package with standard lead configuration: Emitter (pin 1), Base (pin 2), Collector (pin 3). The package provides 1 W thermal dissipation capability at 25°C ambient and requires PCB copper area or external heatsinking for >500 mW continuous use.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP medium-power transistor applications.

Compared with BC327-40 and MPSA92, ZTX549STOB uniquely balances 1 A continuous current, −30 V V_CEO, and tight h_FE spread (100–300) - making it optimal for industrial 24 V control loads requiring both current headroom and predictable base drive.

Availability

ZTX549STOB is available at Aetrix Electronics and suitable for industrial relay drivers, linear regulator pass elements, DC motor direction control circuits, and audio preamplifier stages requiring stable component supply across multi-year production cycles.

Supply support for ZTX549STOB 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, specializing in high-reliability components for industrial, computing, and consumer applications.

ZTX549STOB belongs to the ZTX series of medium-power bipolar transistors engineered for ruggedized switching and linear amplification in harsh-environment control systems - emphasizing thermal stability, consistent gain, and TO-92 mechanical compatibility.

FAQ

Is ZTX549STOB RoHS compliant and halogen-free?

Yes, ZTX549STOB meets RoHS Directive 2011/65/EU and is certified halogen-free per IEC 61249-2-21. The device carries the "HF" suffix in its full ordering code (ZTX549STOBHF) to denote halogen-free construction, with all materials verified to contain <900 ppm bromine and <900 ppm chlorine.

What is the maximum safe operating area (SOA) for ZTX549STOB at 100°C case temperature?

At T_c = 100°C, the SOA is bounded by I_C ≤ 0.5 A at V_CE = −30 V (single-pulse, 1 ms), derived from the 5.7 mW/°C derating curve and published SOA graph (Fig. 3-193). Operation beyond this boundary risks second breakdown and permanent degradation.

Can ZTX549STOB be used in parallel for higher current handling?

No - ZTX549STOB lacks built-in emitter ballasting or matched h_FE bins for forced current sharing. Parallel operation without external emitter resistors will cause thermal runaway due to positive temperature coefficient of V_BE(sat) and gain mismatch. Use a single higher-rated device instead.

Does ZTX549STOB require a base resistor in switching applications?

Yes - a base resistor is mandatory to limit I_B and ensure saturation. For I_C = −1 A and minimum h_FE = 100, I_B ≥ −10 mA is required; with V_BE(sat) ≈ −1.0 V and 3.3 V logic drive, R_B = (3.3 V − (−1.0 V)) / 10 mA = 430 Ω is recommended.