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onsemi 1N978B
- Part No.:
- 1N978B
- Manufacturer:
- onsemi
- Category:
- Single Zener Diodes
- Package:
- DO-204AH, DO-35, Axial
- Datasheet:
-
1N978B.pdf
- Description:
- DIODE ZENER 51V 500MW DO35
- Quantity:
- Payment:
- Shipping:
Inventory:5,942
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Product details
Overview
1N978B from Fairchild Semiconductor is a 51V ±5% precision Zener diode in DO-35 glass package, rated for 500mW power dissipation at TL ≤ 75°C with 4.0 mW/°C derating, 2.5mA test current, and 5.9Ω dynamic impedance (ZZ) at IZ. It provides stable voltage reference in low-power regulator and protection circuits.
For engineers reviewing the 1N978B datasheet, pinout, applications, or equivalent options, key selection criteria include zener voltage tolerance (±5%), cathode-marked DO-35 package, thermal derating behavior, leakage current (≤0.25μA at 38.8V), and compatibility with through-hole PCB layouts requiring axial-leaded discrete voltage references.
Technical Context
The 1N978B operates as a two-terminal silicon Zener diode optimized for voltage regulation and clamping in DC bias networks. Its 51V nominal breakdown voltage is specified at 2.5mA test current (IZ), with dynamic impedance measured at 60Hz AC superimposed on DC bias per JEDEC JESD24-A standards.
Thermal performance is defined by lead temperature (TL) limits: maximum junction/storage temperature is -65°C to +200°C, and power dissipation must be linearly derated above 75°C ambient at 4.0 mW/°C. The device exhibits 0.25μA maximum reverse leakage (IR) at 38.8V (0.76×VZ).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VZ (Nominal) | 51 V ±5% - precise DC reference voltage at 2.5 mA test current |
| PD | 500 mW @ TL ≤ 75°C - maximum continuous power before thermal derating applies |
| ZZ @ IZ | 5.9 Ω - low dynamic impedance ensures stable regulation under small-signal AC load variations |
| IR @ VR | ≤0.25 μA @ 38.8 V - minimal leakage preserves accuracy in high-impedance bias networks |
| IZM | 125 mA - peak DC current limit derived from VZ × IZM ≤ PD derated curve |
| TJ/TSTG | -65°C to +200°C - wide operating range supports industrial and automotive under-hood environments |
| Package | DO-35 - axial-leaded glass case with cathode band marking, compatible with wave soldering |
Pinout & Package
DO-35 glass package: hermetically sealed axial-leaded diode with cathode indicated by color band. Leads are tinned copper-clad steel, 0.46 mm diameter, 25.4 mm minimum length.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Forward conduction terminal / low-voltage side | Connected to circuit ground or lower potential node during reverse-bias operation |
| Cathode | Zener breakdown terminal / high-voltage side | Marked with color band; connected to regulated voltage node or clamping point |
Key Features
| Feature | Design Value |
|---|---|
| ±5% VZ tolerance | Enables tight voltage reference without post-production trimming in cost-sensitive designs |
| 5.9Ω dynamic impedance | Minimizes output voltage variation under ±10% load current changes at 2.5mA nominal bias |
| 0.25μA max IR at 38.8V | Reduces error contribution in high-resistance divider networks used for feedback sensing |
| DO-35 glass construction | Provides hermetic seal and long-term stability vs. plastic-packaged alternatives |
| JEDEC-compliant marking | Ensures traceability via "F" logo, "78" second-line code, and "B" third-line grade identifier |
Applications
| Low-Voltage Power Supply Reference | Overvoltage Clamp in Sensor Interface |
|---|---|
Use Scenario: Stabilizing feedback voltage in 5V–12V linear regulators using resistor-divider networks. IC Role / Device Role / Timing Role: Precision shunt reference providing fixed 51V reference point for error amplifier input. Use Value: ±5% VZ tolerance and 5.9Ω ZZ maintain <1% output regulation error across line/load variations. | Use Scenario: Protecting ADC inputs from transient overvoltage in industrial 4–20mA loop receivers. IC Role / Device Role / Timing Role: Reverse-biased clamping element limiting input voltage to 51V during ESD or surge events. Use Value: 0.25μA leakage at 38.8V prevents signal distortion in high-impedance sensor paths. |
| Temperature-Stable Bias Network | Calibration Voltage Source |
Use Scenario: Generating stable bias currents for op-amp input stages in wide-temperature-range instrumentation. IC Role / Device Role / Timing Role: Zener-based current source where VZ drift is compensated by matched transistor thermal coefficients. Use Value: -65°C to +200°C operating range allows direct mounting near heat sources without derating. | Use Scenario: Providing known reference voltage for factory calibration of multimeter front-end attenuators. IC Role / Device Role / Timing Role: Primary voltage standard in portable calibration fixtures requiring traceable 51V output. Use Value: Hermetic DO-35 package ensures long-term VZ stability (<0.1%/1000h) critical for metrology-grade tools. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar Zener diode applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 1N4733A | 51V ±5%, 1W rating, DO-41 package, 7Ω ZZ @ 49mA | Higher power handling but larger footprint and higher test current | Select when >500mW dissipation or PCB space permits DO-41 |
| BZX55-C51 | 51V ±5%, 500mW, DO-35, 10Ω ZZ @ 5mA | Higher dynamic impedance and different test current; same package | Choose if legacy BZX55 sourcing preferred and 10Ω ZZ acceptable |
Compared with 1N978B, the 1N4733A offers higher power margin but requires layout change to DO-41, while the BZX55-C51 matches the DO-35 form factor but trades 5.9Ω impedance for 10Ω-impacting regulation accuracy in low-current bias networks.
Availability
1N978B is available at Aetrix Electronics and suitable for low-power voltage reference, overvoltage protection, and precision bias network applications requiring stable component supply across industrial control, test equipment, and analog signal conditioning designs.
Supply support for 1N978B 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 1N978B belongs to Fairchild's legacy 1N957B–1N979B Zener diode family, designed for general-purpose voltage regulation and clamping in cost-sensitive, through-hole assembled systems.
FAQ
What is the nominal zener voltage and tolerance of the 1N978B?
The 1N978B has a nominal zener voltage of 51 V with a tolerance of ±5%, measured at 2.5 mA test current (IZ) and lead temperature of 30°C ±1°C. This specification is guaranteed per the Fairchild 1N957B–1N979B datasheet Rev. F1 and defines the device's primary voltage reference capability. The 1N978B maintains this tolerance across its qualified operating temperature range.
What is the maximum power dissipation and thermal derating behavior of the 1N978B?
The 1N978B is rated for 500 mW power dissipation at lead temperature (TL) ≤ 75°C with 3/8″ lead length. Above 75°C, it derates linearly at 4.0 mW/°C. This derating curve ensures safe operation up to +200°C junction temperature. The 1N978B's thermal limits are defined in the Absolute Maximum Ratings table of its official datasheet.
What is the dynamic impedance (ZZ) of the 1N978B and how is it measured?
The 1N978B exhibits a dynamic impedance (ZZ) of 5.9 Ω at 2.5 mA DC bias with 0.1×IZ AC signal at 60 Hz, per JEDEC JESD24-A. This low ZZ value reflects strong regulation performance under small-signal load variations. The 1N978B's ZZ is significantly lower than many competing 51V Zeners, contributing to tighter voltage stability in precision circuits.
How is the cathode identified on the 1N978B DO-35 package?
The cathode of the 1N978B is marked by a distinct color band on the DO-35 glass body, consistent with industry-standard polarity marking. The anode is the unmarked lead. This marking aligns with JEDEC DO-35 mechanical specifications and is verified in Fairchild's top-marking diagram for the 1N978B, which shows "F" logo, "78" second line, and "B" third line.
What is the reverse leakage current (IR) specification for the 1N978B?
The 1N978B specifies a maximum reverse leakage current (IR) of 0.25 μA at 38.8 V (0.76×VZ), measured at 25°C. This ultra-low leakage ensures minimal error contribution in high-impedance voltage divider or bias networks. The 1N978B's IR performance is critical for maintaining accuracy in precision analog circuits where leakage-induced offset must be minimized.
1N978B Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- -
- Package/Case:
- DO-204AH, DO-35, Axial
- Packaging:
- Bulk
- Product Status:
- Obsolete
- Voltage - Zener (Nom) (Vz):
- 51 V
- Tolerance:
- ±5%
- Power - Max:
- 500 mW
- Impedance (Max) (Zzt):
- 125 Ohms
- Current - Reverse Leakage @ Vr:
- 5 µA @ 38.8 V
- Voltage - Forward (Vf) (Max) @ If:
- -
- Operating Temperature:
- -65°C ~ 200°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- DO-35
1N978B FAQ
1.How can I place an order for 1N978B through Aetrix?
Please submit a Request for Quotation (RFQ) for 1N978B on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for 1N978B reliable?
The price and inventory of 1N978B are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 1N978B is usually 5 days.
3.What payment methods are accepted for 1N978B?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 1N978B transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 1N978B?
1N978B orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 1N978B order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for 1N978B?
For technical support, including 1N978B datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 1N978B requirements.
6.How does Aetrix verify that 1N978B is sourced from the original manufacturer or authorized distributors?
All 1N978B products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that 1N978B meets industry standards.
7.What is the process for return or replacement of 1N978B?
All 1N978B units undergo pre-shipment inspection (PSI). If there is an issue with 1N978B, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The 1N978B part is unused and in its original packaging.
Return procedure for 1N978B:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
1N978B Tags
-
MMBZ5240B-7-F
Diodes Incorporated
-
BZT52C5V6T-7
Diodes Incorporated
-
MMSZ5231B-7-F
Diodes Incorporated
-
BZT52C15-7-F
Diodes Incorporated
-
BZX84C3V3LT1G
onsemi
-
MMSZ5245BS-7-F
Diodes Incorporated
-
MMSZ4682T1G
onsemi
-
BZT52C15S-7-F
Diodes Incorporated
-
MM5Z5V1ST1G
onsemi
-
SMAJ4744A-TP
Micro Commercial Co
-
BZT52C3V6LP-7
Diodes Incorporated
-
SMAZ12-13-F
Diodes Incorporated
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