Diodes Incorporated ZTX694BSTOB

Overview

ZTX694BSTOB from Diodes Incorporated is an NPN silicon planar medium-power high-gain transistor with V_CEO = 120 V, h_FE = 400 at I_C = 200 mA, and V_CE(sat) = 0.25 V (typ.) at I_C = 100 mA / I_B = 0.5 mA. It serves as a Darlington pair driver in relay/solenoid control and battery-powered motor interfaces.

For engineers reviewing the ZTX694BSTOB datasheet, ZTX694BSTOB pinout, ZTX694BSTOB application, or ZTX694BSTOB equivalent, key selection criteria include its 120 V breakdown rating, low 0.25 V saturation voltage under moderate drive, 130 MHz f_T, TO-92-compatible E-Line package, and thermal resistance of 175 °C/W (junction-to-ambient, PCB-mounted).

Technical Context

This NPN bipolar junction transistor operates in linear and switching modes with verified gain stability across I_C = 100–400 mA and V_CE = 2 V. Its 130 MHz transition frequency and 200 pF input capacitance support medium-speed switching up to ~100 kHz in inductive load drivers.

The device features low V_CE(sat) (0.25–0.5 V) under two distinct drive conditions (I_B/I_C = 0.005 and 0.0125), enabling efficient operation in battery-constrained solenoid and small DC motor circuits without external heat sinking.

Key Specifications

Pinout & Package

Package: TO-92-compatible E-Line (3-lead, straight lead form, epoxy molded). Pin identification follows standard B-C-E sequence when viewed with flat side facing user and leads downward.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN medium-power switching applications.

Compared with ZTX653BSTOB and MJD122G, the ZTX694BSTOB uniquely balances 120 V robustness, 400 h_FE, and TO-92 usability-making it optimal for space-constrained, battery-fed 24–48 V switching where gain and voltage margin are critical.

Availability

ZTX694BSTOB is available at Aetrix Electronics and suitable for relay drivers, solenoid controllers, battery-powered motor interfaces, and Darlington pre-driver circuits requiring stable component supply across industrial and embedded OEM programs.

Supply support for ZTX694BSTOB 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 power management, signal integrity, and protection solutions.

The ZTX series targets medium-power bipolar switching applications, emphasizing high gain, low saturation voltage, and rugged voltage ratings for industrial control and electromechanical interface design.

FAQ

What is the maximum continuous collector current for ZTX694BSTOB at 70°C ambient?

At T_amb = 70°C, derating begins at 25°C using R_th(j-amb) = 175 °C/W. With T_j(max) = 200°C, allowable ΔT = 130°C → P_diss(max) = 130 / 175 ≈ 0.74 W. At V_CE(sat) ≈ 0.3 V, I_C(max) ≈ 0.74 / 0.3 ≈ 2.47 A - but absolute max I_C remains 0.5 A per datasheet rating. Therefore, max continuous I_C is 0.5 A regardless of temperature.

Can ZTX694BSTOB replace BC337 in a 24 V relay driver?

Yes - ZTX694BSTOB offers higher V_CEO (120 V vs. 45 V), higher h_FE (400 vs. 100–630), and lower V_CE(sat) (0.25 V vs. 0.5 V). Its TO-92 pinout matches BC337 (E-B-C), and it drives the same relay coil with reduced base current and improved flyback tolerance.

Is a base resistor required when driving ZTX694BSTOB from a 3.3 V MCU GPIO?

Yes - a series base resistor is mandatory. For I_C = 100 mA and h_FE = 400, minimum I_B = 0.25 mA. With V_BE(sat) ≈ 0.9 V, R_B = (3.3 − 0.9) / 0.00025 = 9.6 kΩ. A standard 10 kΩ resistor ensures reliable saturation while limiting GPIO current to safe levels.

Does ZTX694BSTOB require a flyback diode when switching inductive loads?

Yes - although V_CEO = 120 V provides margin, repetitive flyback voltage spikes exceeding this rating will cause avalanche failure. A 1N4007 or similar diode connected cathode-to-V_CC, anode-to-collector is required for all relay, solenoid, and motor applications to clamp inductive kick and protect the transistor.