Diodes Incorporated ZTX694B

Overview

ZTX694B 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 - used in relay/solenoid drivers and battery-powered motor control circuits.

For engineers reviewing the ZTX694B datasheet, ZTX694B pinout, ZTX694B application, or ZTX694B equivalent, key selection criteria include breakdown voltage margin, saturation voltage under load, DC current gain stability across I_C, thermal resistance to ambient (175 °C/W), and TO-92 mechanical compatibility for legacy board replacement.

Technical Context

The ZTX694B operates as a medium-power switching and linear amplification device with robust 120 V collector-emitter and collector-base standoff capability. Its h_FE spans 150–500 across I_C = 100–400 mA, supporting stable biasing in Darlington configurations and low-loss switching in inductive loads.

With f_T = 130 MHz at I_C = 50 mA / V_CE = 5 V and C_obo = 9 pF, it supports moderate-speed switching (t_on = 80 ns, t_off = 2900 ns) while maintaining low output capacitance and thermal impedance (R_th(j-amb) = 175 °C/W on 1-inch² PCB copper).

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible, 3-lead plastic). Lead identification per standard TO-92 orientation: viewed from flat side with leads down, left-to-right = Emitter (E), Base (B), Collector (C).

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX653 and MPSA42, the ZTX694B uniquely balances 120 V standoff, 400 h_FE at operational current, and sub-0.3 V saturation - making it optimal for space-constrained, thermally sensitive 24–48 V industrial switching where both gain stability and conduction loss matter.

Availability

ZTX694B is available at Aetrix Electronics and suitable for relay drivers, battery-powered motor controllers, Darlington pre-drivers, and industrial sensor interfaces requiring stable component supply and long-term obsolescence management.

Supply support for ZTX694B 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 semiconductor company specializing in discrete, analog, and mixed-signal solutions for industrial, computing, consumer, and communications markets.

The ZTX694B belongs to Diodes' high-reliability bipolar transistor portfolio, engineered for robust switching and amplification in harsh-environment industrial controls and power management subsystems.

FAQ

What is the maximum continuous collector current for ZTX694B at 25°C ambient?

The ZTX694B supports I_C = 500 mA continuously at T_amb = 25°C with adequate PCB copper area (≥1 inch²). Derating begins above 25°C at 5.7 mW/°C, reducing usable current to ~350 mA at 70°C ambient with standard mounting.

Can ZTX694B replace ZTX650 in existing designs?

Yes - ZTX694B shares identical TO-92 package, pinout (E-B-C), and electrical specifications exceeding ZTX650 (V_CEO = 100 V, h_FE = 250). Its higher gain and lower V_CE(sat) improve efficiency without layout changes.

Is a base resistor required when driving ZTX694B from a 3.3 V MCU GPIO?

Yes - a series base resistor is mandatory. For I_C = 200 mA and h_FE = 400, minimum I_B = 0.5 mA is needed. With 3.3 V GPIO and V_BE(sat) ≈ 0.9 V, a 4.7 kΩ resistor delivers ~0.51 mA, ensuring reliable saturation.

Does ZTX694B require a flyback diode when switching inductive loads?

Yes - although V_CEO = 120 V provides margin, inductive energy from relays or motors can generate voltage spikes exceeding this rating. A parallel flyback diode (e.g., 1N4007) is essential to clamp reverse EMF and prevent junction breakdown.