Diodes Incorporated ZTX849STOB

Overview

ZTX849STOB from Diodes Incorporated is an NPN silicon planar medium-power high-current transistor rated for 5 A continuous collector current, 30 V V_CEO, and 1.2 W power dissipation at 25°C ambient. It features low saturation voltages (e.g., 50 mV at I_C=1 A, I_B=20 mA), high h_FE (100–300 depending on bias), and 100 MHz f_T, making it suitable for switching in LCD backlight converters and battery-powered motor drivers.

For engineers reviewing the ZTX849STOB datasheet, ZTX849STOB pinout, ZTX849STOB application, or ZTX849STOB equivalent, key selection criteria include verified V_CE(sat) performance at high I_C, thermal resistance (R_th(j-amb) = 150 °C/W), safe operating area under pulsed loads, and TO-92-compatible lead form factor for through-hole PCB integration.

Technical Context

This discrete NPN bipolar junction transistor operates as a medium-power switch with robust pulse handling (20 A peak) and low V_CE(sat) across 0.5–5 A load range. Its h_FE remains stable up to 5 A (min 100 at I_C=5 A, V_CE=1 V), supporting reliable base-driven switching without excessive drive loss.

The device uses a planar epitaxial structure with E-Line TO-92-compatible mechanical outline (3-291), enabling direct replacement in legacy designs. Thermal design must account for R_th(j-amb) = 150 °C/W and derating above 25°C - e.g., full 1.2 W only at T_amb ≤ 25°C, dropping to zero at 150°C.

Key Specifications

Pinout & Package

Package: E-Line TO-92-compatible (3-291), through-hole, plastic case with leads identified as Collector (C), Base (B), Emitter (E) - pin configuration matches standard TO-92 orientation when viewed with flat side facing user and leads downward: left = E, center = C, right = B.

Key Features

Applications

Availability

ZTX849STOB is available at Aetrix Electronics and suitable for LCD backlight converters, flash gun converters, and battery-powered motor drivers requiring stable component supply with consistent TO-92 mechanical fit and electrical performance.

Supply support for ZTX849STOB 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, headquartered in Plano, Texas, with design and manufacturing operations across Asia and the Americas.

The ZTX series targets medium-power discrete switching applications, emphasizing ruggedness, thermal reliability, and pin-for-pin compatibility with industry-standard TO-92 footprints for cost-sensitive industrial and consumer designs.

FAQ

What is the maximum safe continuous collector current for ZTX849STOB at 70°C ambient?

At 70°C ambient, the maximum continuous collector current is approximately 3.2 A. This is derived from the 1.2 W P_tot rating at 25°C and R_th(j-amb) = 150 °C/W: allowable power drops linearly to ~0.5 W at 70°C, limiting I_C based on V_CE(sat) and thermal constraints.

Is ZTX849STOB pin-compatible with ZTX851 or ZTX853?

Yes - ZTX849STOB uses the same E-Line TO-92 package (3-291) and identical pinout (E-C-B, flat side facing, leads down). Electrical differences exist (e.g., ZTX851 has higher V_CEO = 60 V), but mechanical replacement is direct in existing footprints.

Can ZTX849STOB be used in linear amplifier applications?

It can operate in linear mode, but its design emphasizes switching: h_FE variation (100–300), limited f_T linearity, and thermal limitations make it less optimal than dedicated audio transistors. Use is viable only for low-fidelity, low-power Class-B stages with careful bias and heatsinking.

What is the recommended base resistor value for switching a 2 A load with 5 V logic drive?

For I_C = 2 A and h_FE ≥ 100, minimum I_B = 20 mA. With 5 V drive and V_BE(sat) ≈ 1.05 V, R_B = (5 − 1.05) V / 0.02 A = 197.5 Ω - a standard 180 Ω or 220 Ω resistor ensures reliable saturation while limiting base current to safe levels.