Onsemi 1N5349BG 15V Zener Diode: Key Specifications and Application Circuit Design
The Onsemi 1N5349BG is a robust 5 W Zener diode designed for voltage regulation and protection in a wide range of electronic circuits. With its nominal Zener voltage (Vz) of 15V, this component is a fundamental building block for managing power supply stability and suppressing voltage transients. Its construction in a solid DO-15 package makes it suitable for both through-hole PCB mounting and various industrial environments.
Key Electrical Specifications
Understanding the device's parameters is crucial for reliable circuit design. The most critical specifications include:
Zener Voltage (Vz): 15V @ Izt (Test Current). The voltage across the diode remains relatively constant at this value when it is operating in its reverse breakdown region. The actual voltage has a tolerance, typically ±5%.
Rated Zener Test Current (Izt): 220 mA. This is the current at which the Vz is specified and tested.
Maximum Power Dissipation (Pd): 5 Watts. This defines the maximum amount of power the diode can safely dissipate without being damaged. Exceeding this value will lead to thermal runaway and destruction.
Maximum Reverse Leakage Current (Ir): This is the small current that flows when the voltage applied is below the Zener voltage. It is typically in the microamp range.
Dynamic Impedance (Zzt): Measured at the test current, this low impedance value (typically around 2 ohms) indicates the diode's ability to maintain a stable voltage despite changes in current.
Application Circuit Design: A Basic 15V Voltage Regulator
A primary application of the 1N5349BG is to create a simple shunt voltage regulator. The schematic below illustrates a basic circuit for deriving a stable 15V DC output from a higher, unregulated input voltage (e.g., 18V-24V).
R
Unregulated |
Vin o-----/\/\/\----+-----> Vout (15V Regulated)
|
|
/ \ 1N5349BG
˅ ˅
|
GND o--------------+----------------- GND
Design Calculations:
1. Input Voltage (Vin): Must be higher than the desired output voltage (Vout = 15V). A common design choice is for Vin to be at least 20-30% greater than Vz.
2. Series Current-Limiting Resistor (R): This resistor is critical. It limits the current through the Zener diode to a safe level, ensuring the power rating is not exceeded. Its value is calculated based on the input voltage, Zener voltage, and the total load current.
Formula: R = (Vin - Vz) / (Iload + Iz)
Where:
`Vin` is the unregulated input voltage.
`Vz` is the Zener voltage (15V).
`Iload` is the current required by the load connected to Vout.
`Iz` is the current flowing through the Zener diode.
3. Power Rating of Resistor (R): The resistor must be sized to handle the power it will dissipate.
Formula: P_R = (Vin - Vz) (Iload + Iz)
Select a resistor with a power rating significantly higher than the calculated value (e.g., 2x higher) for safety and reliability.
Design Example:
Assume Vin = 20V, and the load requires Iload = 100 mA.
We want a minimum Zener current (Iz) of 20 mA to ensure good regulation.
R = (20V - 15V) / (0.1A + 0.02A) = 5V / 0.12A ≈ 41.7 Ω (use a standard 39 Ω or 43 Ω resistor).
P_R = (20V - 15V) 0.12A = 0.6 W. A 1W or 2W resistor should be selected.
Important Considerations:
This regulator's efficiency is low because current constantly flows through the Zener diode, making it unsuitable for high-power or battery-operated applications.
Regulation accuracy is affected by changes in load current and input voltage due to the dynamic impedance. For lighter loads, regulation is less precise.
For higher current requirements or better efficiency, a Zener diode is often used to provide a reference voltage for the base of a series pass transistor, creating a more powerful linear regulator.
ICGOOODFIND: The Onsemi 1N5349BG is a highly reliable and simple solution for medium-power voltage regulation and over-voltage protection tasks. Its 5W power rating and stable 15V breakdown make it ideal for industrial power supplies, automotive electronics, and as a voltage reference. While simple shunt regulators are inefficient for high-current applications, their simplicity and robustness ensure the 1N5349BG remains a vital component in a designer's toolkit.
Keywords:
Zener Voltage Regulation
Power Dissipation
Shunt Regulator
Voltage Reference
Circuit Protection
