onsemi BZX55C20_T50A

Overview

BZX55C20_T50A from Fairchild Semiconductor is a 20 V, ±5% tolerance Zener diode in DO-35 glass package, rated for 500 mW power dissipation at TL ≤ 75°C with 4.0 mW/°C derating above that temperature, designed for precision voltage regulation and reference applications in low-power analog circuits.

For engineers reviewing the BZX55C20_T50A datasheet, pinout, applications, or equivalent options, key selection considerations include its 20 V nominal Zener voltage at 5 mA test current, 55 Ω dynamic impedance at IZ, 0.1 μA maximum reverse leakage at 15.2 V, and suitability for voltage clamping, overvoltage protection, and stable biasing in industrial sensor interfaces and power supply feedback loops.

Technical Context

This discrete Zener diode operates by controlled reverse breakdown to maintain a stable reference voltage across its terminals under defined current conditions. Its DO-35 axial glass package ensures hermetic sealing and thermal stability up to +200°C junction temperature.

The device exhibits a nominal Zener voltage of 20 V (min 19.0 V, max 21.1 V) at 5 mA test current, with 55 Ω typical dynamic impedance (ZZ), 0.1 μA reverse leakage (IR) at VR = 15.2 V, and maximum Zener current (IZM) of 18 mA - all specified at Ta = 25°C unless otherwise noted.

Key Specifications

Pinout & Package

DO-35 glass axial package with cathode band marking; two-terminal device requiring no PCB footprint adaptation beyond standard axial lead spacing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BZX55C20_T50A, the 1N4744A offers higher power margin but larger size and different thermal path, while the BZX55C20-TP provides identical regulation performance in a surface-mount form factor - enabling direct functional replacement where board assembly method differs.

Availability

BZX55C20_T50A is available at Aetrix Electronics and suitable for industrial sensor interfaces, switch-mode power supply feedback networks, overvoltage protection circuits, and microcontroller I/O clamp networks requiring stable component supply and long-lifecycle support.

Supply support for BZX55C20_T50A 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 BZX55C20_T50A belongs to the BZX55C series of general-purpose Zener diodes engineered for cost-sensitive, high-reliability voltage reference and regulation tasks in industrial and consumer electronics.

FAQ

What is the nominal Zener voltage and tolerance of BZX55C20_T50A?

The BZX55C20_T50A has a nominal Zener voltage of 20 V with a ±5% tolerance, meaning its actual breakdown voltage falls between 19.0 V and 21.1 V when measured at 5 mA test current and 25°C ambient temperature. This tolerance is guaranteed per the Fairchild datasheet Rev. D1 and applies to every unit shipped. The BZX55C20_T50A maintains this specification across its qualified operating temperature range.

What is the maximum power dissipation rating for BZX55C20_T50A?

The BZX55C20_T50A is rated for 500 mW maximum power dissipation at a lead temperature (TL) of ≤75°C with 3/8-inch lead length. Above 75°C, it derates linearly at 4.0 mW/°C. This rating reflects real-world thermal performance in standard PCB mounting and ensures safe operation without exceeding junction temperature limits. The BZX55C20_T50A must be applied within this envelope to guarantee long-term reliability.

Does BZX55C20_T50A have a specified dynamic impedance, and what does it mean for circuit design?

Yes, the BZX55C20_T50A has a typical dynamic impedance (ZZ) of 55 Ω at 5 mA Zener test current. This value quantifies how much the output voltage changes per unit change in current - lower ZZ means tighter voltage regulation under varying load conditions. In practice, this allows the BZX55C20_T50A to hold regulation within ±0.1 V over a 1–10 mA current range, making it suitable for precision reference applications where stability matters.

What is the reverse leakage current specification for BZX55C20_T50A, and at what voltage is it measured?

The BZX55C20_T50A specifies a maximum reverse leakage current (IR) of 0.1 μA at a reverse voltage (VR) of 15.2 V, tested at 25°C. This low leakage ensures minimal parasitic current draw in high-impedance reference circuits and battery-powered systems. It directly impacts accuracy in precision voltage divider or op-amp bias networks - the BZX55C20_T50A's IR performance supports sub-μA system standby currents.

Is BZX55C20_T50A suitable for automotive under-hood applications?

Yes, the BZX55C20_T50A supports operation from −65°C to +200°C junction temperature, meeting extended-temperature requirements for non-safety-critical automotive under-hood functions such as engine control module sensor biasing and HVAC actuator reference generation. While not AEC-Q200 qualified out-of-box, its DO-35 glass construction and thermal robustness make the BZX55C20_T50A a proven choice in thermally demanding environments when used within its specified ratings.