Diodes Incorporated ZTX325

Overview

ZTX325 from Zetex Semiconductors (now Diodes Incorporated) is an NPN silicon planar RF transistor optimized for VHF/UHF small-signal amplification and oscillator applications. It delivers 1.3 GHz transition frequency, <5 dB noise figure at 500 MHz, and >175 mW output power at 500 MHz under 13.5 V/22.5 mA bias, commonly used in FM receiver front-ends and low-power RF transmitters.

For engineers reviewing the ZTX325 datasheet, ZTX325 pinout, ZTX325 application, or ZTX325 equivalent, key selection criteria include its 1.3 GHz f_T, 5 dB noise figure at 500 MHz, 15 V V_CEO, TO-92 package thermal limits, and suitability for narrowband amplifier stages requiring stable gain and low phase noise.

Technical Context

The ZTX325 employs a planar epitaxial structure with optimized base doping and emitter geometry to achieve high f_T while maintaining low C_re (0.85 pF) and r_bb'C_b'c (2–12 ps), enabling stable gain up to 500 MHz. Its 2.5 V V_EBO rating and 5 V V_(BR)EBO reflect tight emitter-base junction control for reliable biasing in common-emitter configurations.

Thermal design is constrained by P_tot = 350 mW at T_amb = 25°C and T_j range of –55°C to +200°C, requiring careful derating above 25°C ambient. The device operates with IC ≤ 25 mA average (100 µs pulse width), limiting continuous-duty Class-A use without heatsinking.

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible, 3-161 outline), through-hole, epoxy-molded plastic case with 1.27 mm lead pitch. Thermal resistance θ_JA ≈ 350°C/W (free air).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN RF transistor applications.

Compared with BC547B and MPSH10, the ZTX325 provides 2.1× higher f_T and 0.5 dB lower noise than MPSH10, enabling wider bandwidth and improved dynamic range in 400–500 MHz receiver front-ends without changing PCB layout.

Availability

ZTX325 is available at Aetrix Electronics and suitable for FM receiver front-ends, VHF oscillator cores, and portable two-way radio IF stages requiring stable component supply across production lifecycles.

Supply support for ZTX325 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

Zetex Semiconductors, acquired by Diodes Incorporated in 2008, specialized in high-performance discrete semiconductors for analog and RF signal conditioning.

The ZTX series was developed for demanding RF amplification and switching applications where gain-bandwidth, noise, and thermal reliability exceed standard general-purpose transistor requirements.

FAQ

What is the maximum safe DC collector current for continuous operation?

The ZTX325 specifies I_AV = 25 mA averaged over 100 µs pulses. For continuous DC operation, limit I_C to ≤15 mA at T_amb = 25°C to maintain junction temperature below 150°C, given P_tot = 350 mW and typical V_CE = 5 V. Derate linearly above 25°C ambient using θ_JA ≈ 350°C/W.

Can ZTX325 be used in Class-C amplifier configurations?

Yes - its 50 mA I_CM peak rating and 1.3 GHz f_T support efficient Class-C operation at 100–500 MHz. However, ensure base drive remains within V_EBO = 2.5 V during negative swing, and use low-inductance emitter bypassing to maintain switching integrity and minimize second-harmonic generation.

How does the 2.5 V V_EBO rating impact bias network design?

The 2.5 V emitter-base reverse breakdown voltage requires base bias networks to avoid exceeding this limit during signal swing or power-up transients. In common-emitter amplifiers, use emitter resistors ≥100 Ω and clamp diodes if AC-coupled inputs risk reverse-biasing the BE junction beyond 2.5 V.

Is ZTX325 RoHS-compliant and halogen-free?

Yes - Diodes Incorporated certifies ZTX325 as RoHS-compliant (2011/65/EU) and halogen-free per IEC 61249-2-21. The TO-92 package uses matte tin-plated leads and bromine-free epoxy molding compound, with full material declarations available under Diodes' PPAP documentation.