onsemi BZX55C3V9_T50R

Overview

BZX55C3V9_T50R from Fairchild Semiconductor is a 3.9 V, ±5% tolerance Zener diode in DO-35 glass package, rated for 500 mW power dissipation at 75°C with 95 mA maximum zener current and 85 Ω dynamic impedance at 5 mA test current. It serves as a precision voltage reference or overvoltage clamp in low-power analog circuits, power supply feedback loops, and signal conditioning stages.

For engineers reviewing the BZX55C3V9_T50R datasheet, pinout, applications, or equivalent options, key selection criteria include its 3.9 V nominal zener voltage, 5 mA test current, 85 Ω impedance, -65°C to +200°C operating temperature range, and DO-35 mechanical compatibility with legacy through-hole designs.

Technical Context

The BZX55C3V9_T50R operates as a silicon planar Zener diode with sharp reverse breakdown at 3.9 V, designed for stable voltage regulation under DC or low-frequency transient conditions. Its 5% tolerance and 85 Ω dynamic impedance at 5 mA ensure predictable clamping behavior in feedback networks and reference dividers.

Thermal derating begins above 75°C at 4.0 mW/°C, and it maintains leakage current ≤2 μA at 1 V reverse bias. The device meets JEDEC DO-35 mechanical standards with cathode band marking and supports operation up to +200°C junction temperature.

Key Specifications

Pinout & Package

DO-35 glass axial package with cathode indicated by color band; two-terminal device requiring no orientation-specific PCB layout beyond cathode/anode polarity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Zener diode applications.

Compared with 1N4730A and BZX55C3V9 (ON Semi), the BZX55C3V9_T50R offers identical zener characteristics and DO-35 form factor but with Fairchild's legacy thermal derating curve and marking convention-making it optimal for maintaining legacy board builds while enabling direct substitution where sourcing constraints exist.

Availability

BZX55C3V9_T50R is available at Aetrix Electronics and suitable for power supply feedback, overvoltage protection, and reference divider applications requiring stable component supply across industrial automation, consumer electronics, and automotive subsystems.

Supply support for BZX55C3V9_T50R 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.

The BZX55C series was developed as a general-purpose, low-cost Zener diode family targeting voltage regulation and protection in cost-sensitive, high-volume applications such as AC-DC adapters, battery chargers, and sensor signal conditioning.

FAQ

What is the zener voltage tolerance of BZX55C3V9_T50R?

The BZX55C3V9_T50R has a nominal zener voltage of 3.9 V with a ±5% tolerance, meaning its actual breakdown voltage falls between 3.7 V and 4.1 V when measured at 5 mA test current and 25°C ambient. This tolerance is guaranteed per the Fairchild datasheet Rev. D1 and applies across the full operating temperature range.

Does BZX55C3V9_T50R support surface-mount assembly?

No, the BZX55C3V9_T50R uses a DO-35 glass axial package with 0.4 mm diameter leads intended for through-hole mounting only. It lacks solder pads or terminations compatible with reflow or wave soldering processes used for SMT. For surface-mount equivalents, consider SMA- or SOD-123-packaged Zeners like BZT52-B3V9.

What is the maximum reverse leakage current for BZX55C3V9_T50R?

The BZX55C3V9_T50R exhibits a maximum reverse leakage current of 2 μA when biased at 1 V reverse voltage and tested at 25°C. At elevated temperatures (e.g., 125°C), leakage remains ≤2 μA per the datasheet, ensuring minimal loading in high-impedance reference circuits.

Can BZX55C3V9_T50R replace BZX55C3V6 or BZX55C4V3 in existing designs?

No-BZX55C3V9_T50R is not a drop-in replacement for BZX55C3V6 (3.6 V) or BZX55C4V3 (4.3 V), as their zener voltages differ by ≥0.3 V. Substituting alters regulation thresholds and may cause system-level overvoltage or undervoltage faults. Always verify target voltage match before interchange.

What is the thermal derating behavior of BZX55C3V9_T50R above 75°C?

The BZX55C3V9_T50R derates linearly at 4.0 mW/°C above 75°C lead temperature. At 100°C, its usable power drops to 400 mW (500 mW − [25°C × 4.0 mW/°C]); at 125°C, it falls to 300 mW. This derating ensures safe junction temperature operation within the -65°C to +200°C specified range.