Diodes Incorporated ZTX949STOB

Overview

ZTX949STOB from Diodes Incorporated is a PNP silicon planar medium-power high-current transistor rated for −4.5 A continuous collector current, −30 V V_CEO, and 1.2 W power dissipation at T_amb = 25°C, with V_CE(sat) as low as −60 mV at I_C = −0.5 A / I_B = −20 mA - used in industrial DC-DC converter output stages and linear regulator pass elements.

For engineers reviewing the ZTX949STOB datasheet, ZTX949STOB pinout, ZTX949STOB application, or ZTX949STOB equivalent, key selection criteria include verified PNP polarity, TO-92-compatible E-Line package thermal resistance (R_th(j–amb) = 150 °C/W), gain linearity down to 10 mA, low leakage (<1 nA at 100°C), and Spice model availability for switching transient validation.

Technical Context

This PNP bipolar junction transistor operates in active, saturation, and cutoff regions with guaranteed h_FE ≥ 100 at I_C = −10 mA and ≥ 75 at I_C = −5 A under V_CE = −1 V. Its f_T of 100 MHz supports moderate-speed switching up to ~10 MHz square-wave operation with controlled turn-on/turn-off times (t_on/t_off = 120/130 ns).

The device features low V_BE(sat) (−960 mV typ. at I_C = −5 A) and exceptional V_CE(sat) stability across temperature (−55°C to +175°C junction), enabling reliable performance in thermally constrained PCB-mounted applications without forced cooling.

Key Specifications

Pinout & Package

Package: E-Line TO-92-compatible plastic package (3-312 outline), lead-free, RoHS-compliant, with emitter (E), base (B), and collector (C) terminals arranged in linear C–B–E order when viewed from flat side with leads down.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD2955G and ZTX951, ZTX949STOB uniquely balances TO-92 mountability, sub-100 mV saturation, and verified gain linearity - making it optimal for thermally limited, medium-current linear and switching roles where footprint and thermal simplicity are prioritized over ultimate power rating or voltage headroom.

Availability

ZTX949STOB is available at Aetrix Electronics and suitable for industrial linear regulators, DC-DC converter output stages, thermal protection circuits, and high-current LED drivers requiring stable component supply with consistent parametric performance across production lots.

Supply support for ZTX949STOB 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, automotive, and computing markets.

ZTX949STOB belongs to the ZTX series of high-current bipolar transistors designed specifically for medium-power linear regulation and switching in thermally constrained environments without heatsinks.

FAQ

Is ZTX949STOB suitable for surface-mount assembly?

No - ZTX949STOB uses an axial-leaded E-Line TO-92-compatible package intended for through-hole PCB mounting. Its lead spacing and body geometry do not comply with standard SMT reflow profiles or pick-and-place tolerances. Hand-soldering or wave soldering is required.

What is the maximum safe operating temperature for continuous operation?

The junction temperature must not exceed +200°C, but continuous operation at rated I_C = −4.5 A is only possible up to +75°C ambient when mounted on a 1-inch² copper area. Derating begins at +25°C per the 150 °C/W R_th(j–amb) curve, reaching zero derated current at ~105°C ambient.

Does ZTX949STOB have built-in ESD protection?

No - ZTX949STOB is an unprotected bipolar transistor with no integrated ESD structures. Standard handling precautions (grounded workstations, anti-static packaging) are mandatory. Input pins (base/emitter) are susceptible to damage from >2 kV HBM events.

Can ZTX949STOB replace NPN transistors in existing designs?

No - ZTX949STOB is a PNP device with inverted polarity and complementary biasing requirements. Direct substitution for NPN types (e.g., ZTX450) would reverse current flow and disable circuit operation unless the entire bias network, feedback path, and power topology are redesigned.