onsemi 1N4746ATR Zener Diode: Key Specifications and Application Circuit Design

The onsemi 1N4746ATR is a popular 18V Zener diode in a surface-mount DO-41 package, widely used for voltage regulation and protection in various electronic circuits. Its ability to maintain a stable reference voltage makes it a fundamental component in power supplies, voltage clippers, and surge protectors.

Key Specifications

The 1N4746ATR is characterized by several critical parameters essential for reliable circuit design. Its Zener Voltage (VZ) is 18V at a specified test current (IZT) of 14 mA. This is the voltage at which the diode begins to conduct in reverse bias, regulating the voltage across its terminals. The device can dissipate a maximum of 1.0 W of power at a lead temperature of 50°C, which is a crucial factor for heat management. The maximum Zener impedance (ZZT) is 20 ohms at the test current, indicating how much the voltage may vary with changes in current—a lower impedance is generally better for regulation.

Other important specifications include a maximum reverse leakage current of 5 μA at a voltage below the breakdown and an operating temperature range from -65°C to +200°C. The tolerance on the Zener voltage is typically ±5%, which is standard for general-purpose regulators.

Application Circuit Design: A Basic Voltage Regulator

A primary application of the 1N4746ATR is to create a simple shunt voltage regulator. The core function of this circuit is to provide a stable 18V output from an unregulated, higher DC input voltage (VIN).

The fundamental design involves placing the Zener diode in reverse bias across the output load (RL). A crucial current-limiting resistor (RS) is connected in series with the input voltage. The value of this resistor is paramount to the circuit's operation and is calculated using the formula:

RS = (VIN - VZ) / (IZ + IL)

Where:

VIN is the unregulated input voltage.

VZ is the Zener voltage (18V).

IZ is the current through the Zener diode.

IL is the current drawn by the load (VZ / RL).

The design process requires careful consideration of the operating range:

1. Input Voltage (VIN): Must be consistently higher than VZ (18V). A common choice is 24V.

2. Zener Current (IZ): Must be maintained between the minimum current required to initiate regulation (IZK, ~0.25 mA for this diode) and the maximum current calculated from the power dissipation limit: IZM = PD / VZ = 1W / 18V ≈ 56 mA.

3. Load Current (IL): The value of RS must be chosen so that even under minimum load (maximum IL), enough current flows through the Zener to keep it in regulation, and under maximum load (minimum IL), the Zener current does not exceed IZM.

For example, with VIN = 24V and a load requiring 10 mA, the Zener diode would shunt any excess current beyond what the load draws, maintaining a steady 18V. This circuit also offers basic protection against overvoltage spikes on the input line.

ICGOOODFIND: The onsemi 1N4746ATR is a robust and cost-effective solution for medium-power 18V regulation and protection. Its well-defined specifications make it straightforward to implement in shunt regulator designs, provided the current-limiting resistor is carefully calculated to ensure stable operation within its power dissipation limits. For new designs, always consult the latest datasheet to confirm parameters.

Keywords: Zener Diode, Voltage Regulation, Shunt Regulator, Circuit Design, Power Dissipation