onsemi BZX84C12

Overview

BZX84C12 from Fairchild Semiconductor is a 12 V ±5% tolerance silicon Zener diode in SOT-23 package, rated for 250 mW power dissipation at 25°C ambient, with nominal zener voltage of 11.4–12.7 V at 5 mA test current and dynamic impedance of 10 Ω, used for precision voltage regulation and overvoltage protection in low-power analog circuits.

For engineers reviewing the BZX84C12 datasheet, pinout, applications, or equivalent options, key selection criteria include zener voltage tolerance, dynamic impedance at operating current, thermal resistance (R_θJA = 465°C/W), reverse leakage (≤0.1 µA at 8.0 V), and SOT-23 footprint compatibility in space-constrained designs.

Technical Context

The BZX84C12 operates as a two-terminal voltage reference device relying on controlled reverse-breakdown conduction. Its zener voltage exhibits a positive temperature coefficient of +6.0 mV/°C at 5 mA, enabling predictable drift compensation in bias networks.

It is characterized across three test currents (1 mA, 5 mA, 20 mA) to support design flexibility in low-current sensing and higher-stability regulation. The device's 130 pF capacitance at 0 V reverse bias and 1 MHz makes it suitable for DC and low-frequency stabilization-not RF filtering.

Key Specifications

Pinout & Package

SOT-23 surface-mount plastic package with gull-wing leads; standardized 3-pin outline where Pin 1 = Anode, Pin 2 = Cathode, Pin 3 = Anode (dual-anode configuration not applicable-BZX84C12 is single-diode, 2-terminal device). Cathode marked by band; mechanical dimensions per JEDEC TO-236AB.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MMBZ5242B, BZX84C12 offers tighter regulation (10 Ω vs. 33 Ω Z_Z) at cost of higher thermal resistance; versus 1N4742A, it provides identical voltage performance in compact SOT-23 but cannot sustain >250 mW continuously-making it optimal for space-limited, low-power precision roles.

Availability

BZX84C12 is available at Aetrix Electronics and suitable for voltage reference, overvoltage protection, and feedback divider applications requiring stable component supply, consistent parametric binning, and long-term obsolescence mitigation.

Supply support for BZX84C12 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 leading designer of high-performance analog and discrete semiconductors, acquired by ON Semiconductor in 2016; its legacy Zener portfolio remains widely deployed in industrial and consumer systems.

The BZX84 series was engineered for general-purpose voltage regulation in space-constrained, low-power applications-emphasizing tight tolerance, repeatable zener characteristics, and SOT-23 manufacturability.

FAQ

What is the nominal zener voltage and tolerance of the BZX84C12?

The BZX84C12 has a nominal zener voltage of 12 V with a tolerance of ±5%, specified as 11.4–12.7 V at 5 mA test current. This tolerance band is confirmed in the Electrical Characteristics table of the Fairchild datasheet Rev. 1.10 and applies strictly to the BZX84C12 variant-not the broader BZX84 family. The "C" suffix explicitly denotes 5% tolerance per JEDEC standard marking.

What is the maximum power dissipation rating for the BZX84C12 and under what conditions?

The BZX84C12 is rated for 250 mW power dissipation at T_A = 25°C when mounted on a standard FR-4 PCB (76.2 mm × 114.3 mm). This value drops linearly with rising ambient temperature due to its R_θJA of 465°C/W; derating begins immediately above 25°C and reaches zero dissipation at approximately 76°C ambient. The 550 mW rating referenced in the datasheet applies only under lead-temperature (T_L) conditions, not ambient.

Does the BZX84C12 have a defined temperature coefficient, and how is it used in circuit design?

Yes-the BZX84C12 exhibits a temperature coefficient of +6.0 mV/°C at I_Z = 5 mA, as documented in the Electrical Characteristics table. This positive tempco is leveraged in temperature-compensated reference designs, such as bias networks paired with negative-tempco components (e.g., transistors or thermistors), to achieve net-zero drift over operating temperature ranges.

What is the reverse leakage current specification for the BZX84C12, and at what voltage is it measured?

The BZX84C12 has a maximum reverse leakage current (I_R) of 0.1 µA, measured at a reverse voltage (V_R) of 8.0 V. This parameter is critical for low-power standby circuits, ensuring minimal current draw in voltage-monitoring or high-impedance sense paths. It is distinct from breakdown voltage and verified under steady-state DC conditions per the datasheet's test methodology.

Is the BZX84C12 pin-compatible with other SOT-23 Zener diodes, and what are its terminal assignments?

Yes-the BZX84C12 uses the standard SOT-23 outline with Pin 1 = Anode, Pin 2 = Cathode (marked band), and Pin 3 = Anode (internally tied to Pin 1). This 2-terminal configuration is mechanically and electrically compatible with industry-standard SOT-23 Zeners including MMBZ52xx and MM3Z12. Pinout validation is confirmed by the "SOT-23" diagram on page 1 of the Fairchild datasheet and cross-checked against JEDEC TO-236AB mechanical drawings.