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onsemi SA78A
- Part No.:
- SA78A
- Manufacturer:
- onsemi
- Category:
- TVS Diodes
- Package:
- DO-204AC, DO-15, Axial
- Datasheet:
-
SA78A.pdf
- Description:
- TVS DIODE 78VWM 126VC DO15
- Quantity:
- Payment:
- Shipping:
Inventory:8,927
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Product details
Overview
SA78A from Fairchild Semiconductor is a unidirectional 500 W transient voltage suppressor (TVS) diode in DO-15 package, with 78 V reverse stand-off voltage (VRWM), 86.7–95.8 V breakdown voltage (VBR), 126 V clamping voltage at peak pulse current, and 4.0 μA maximum reverse leakage at VRWM. It protects DC power rails and signal lines in industrial motor drives and automotive body electronics against ESD and lightning-induced surges.
For engineers reviewing the SA78A datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, DO-15 terminal mapping, bidirectional variant context (SA78CA), clamping performance under 10/1000 μs waveform, and real-world surge protection use cases in 24 V and 48 V systems.
Technical Context
The SA78A employs a glass-passivated junction for stable avalanche behavior and low incremental surge resistance. Its fast response time-less than 1.0 ps from 0 V to breakdown-enables effective suppression of sub-nanosecond ESD transients in sensitive analog and digital interfaces.
Designed for unidirectional operation, it conducts only during negative transients relative to cathode, with clamping action defined by its 126 V VC at IPPM = 3.97 A (calculated from 500 W / 126 V). The device operates up to +175 °C junction temperature and supports 70 A non-repetitive forward surge current per JEDEC method.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Peak Pulse Power (10/1000 μs) | 500 W - sustains single high-energy surges common in automotive load-dump and industrial switching events |
| Reverse Stand-off Voltage (VRWM) | 78 V - defines maximum continuous DC operating voltage before significant leakage begins |
| Breakdown Voltage (VBR) | 86.7–95.8 V at 1.0 mA - ensures reliable avalanche initiation within specified tolerance band |
| Clamping Voltage (VC) | 126 V at IPPM - limits downstream voltage stress to safe levels during full-rated surge |
| Reverse Leakage (IR) | ≤4.0 μA at 78 V - minimizes standby power loss in always-on 24 V/48 V control circuits |
| Junction Temperature (TJ) | +175 °C - enables deployment in under-hood automotive and high-ambient industrial environments |
| Package | DO-15 - industry-standard axial leaded package with cathode band marking, compatible with through-hole assembly |
Pinout & Package
SA78A uses the DO-15 package: axial-leaded, glass-passivated, epoxy-bodied diode with cathode indicated by a color band on the unidirectional version. Lead length is standardized at 0.375 inches for thermal derating compliance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Surge return path | Connected to system ground or low-impedance reference; carries full IPPM during clamping |
| Cathode | Protected line connection | Connected to line being protected (e.g., 24 V rail); voltage referenced to anode during conduction |
Key Features
| Feature | Design Value |
|---|---|
| Glass-passivated junction | Ensures long-term stability of VBR and low parameter drift across temperature and life cycles |
| 500 W peak pulse rating (10/1000 μs) | Matches IEC 61000-4-5 Level 4 surge immunity requirements for industrial equipment |
| Clamping ratio (VC/VBR) ≈ 1.31 | Indicates low dynamic impedance (~31.7 Ω), enabling efficient energy diversion without excessive voltage overshoot |
| Response time < 1.0 ps | Provides effective suppression of fast-rising ESD events (IEC 61000-4-2) before IC damage occurs |
| Low IR ≤ 4.0 μA at VRWM | Reduces quiescent current draw in battery-backed or energy-sensitive applications |
Applications
| Industrial Motor Drives | Automotive Body Control Modules |
|---|---|
Use Scenario: Protection of 24 V DC input stage against load dump and inductive kickback from solenoids and relays. IC Role / Device Role: Primary overvoltage clamp placed between supply rail and ground, upstream of DC-DC converters and microcontrollers. Use Value: Limits transient voltage to ≤126 V, preventing latch-up or permanent damage to 36 V-rated power management ICs. |
Use Scenario: Safeguarding LIN bus transceivers and door module MCUs from battery voltage spikes during jump-start or alternator regulation faults. IC Role / Device Role: Unidirectional TVS connected between LIN line and chassis ground, suppressing negative-going transients. Use Value: Maintains signal integrity below 12 V threshold while adding <1 nF capacitance, avoiding data corruption at 20 kbps. |
| Telecom Power Feeds | Renewable Energy Charge Controllers |
Use Scenario: Input-stage protection on 48 V PoE-powered remote units exposed to induced lightning surges on outdoor cabling. IC Role / Device Role: First-line defense in series with feed-through capacitor, shunting surge energy to earth ground. Use Value: Withstands 500 W pulses without degradation, preserving MTBF in outdoor telecom enclosures rated IP65+ |
Use Scenario: Protection of MOSFET gate drivers and sense amplifiers in solar charge controllers subjected to PV array arcing events. IC Role / Device Role: Bidirectional clamping (via SA78CA variant) across differential voltage inputs measuring panel open-circuit voltage. Use Value: Clamps both polarities to ±126 V, ensuring ADC input stays within 0–5 V range via resistive divider scaling. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar transient voltage suppression applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMBJ78A (ON Semiconductor) | Same VRWM (78 V), lower VC = 121 V, SMB package (surface-mount), 600 W rating | Requires PCB rework for SMT layout; better suited for space-constrained designs with automated assembly | Select when board area is limited and thermal pad access is available; verify solder joint reliability under thermal cycling |
| P6SMB78A (Littelfuse) | Identical VRWM and VC (126 V), same DO-15 package, but rated at 600 W peak pulse power | Higher surge margin allows extended lifetime in high-cycle industrial environments (e.g., factory automation) | Prefer for mission-critical systems where 20% extra pulse energy headroom improves field failure rate metrics |
Compared with SA78A, SMBJ78A offers superior power density and modern packaging but requires layout change, while P6SMB78A delivers identical form-factor compatibility with enhanced 600 W surge handling-ideal for upgrading legacy designs without hardware revision.
Availability
SA78A is available at Aetrix Electronics and suitable for industrial motor drives, automotive body electronics, telecom power feeds, and renewable energy charge controllers requiring stable component supply and long-term obsolescence management.
Supply support for SA78A 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 devices, acquired by ON Semiconductor in 2016. Its TVS portfolio emphasized ruggedness, consistency, and broad voltage coverage.
The SAxxA series was developed for cost-effective, high-reliability transient suppression in harsh-environment applications-particularly targeting 24 V and 48 V industrial and transportation systems where DO-15 through-hole robustness remains critical.
FAQ
What is the clamping voltage of the SA78A under full-rated surge conditions?
The SA78A exhibits a maximum clamping voltage (VC) of 126 V when subjected to its rated 500 W peak pulse power on the standard 10/1000 μs waveform. This value is measured at the peak pulse current (IPPM ≈ 3.97 A) and defines the upper voltage limit imposed on protected circuitry during transient events. The SA78A maintains this clamping performance across its qualified operating temperature range.
Is the SA78A suitable for bidirectional transient suppression?
No-the SA78A is a unidirectional TVS diode intended for suppression of positive transients only (cathode-to-anode conduction). For bidirectional protection, the SA78CA variant must be used. SA78CA shares identical VRWM, VBR, and VC ratings but conducts symmetrically in both directions, making it appropriate for AC lines or differential buses like RS-485 where polarity reversal occurs.
What is the maximum junction temperature rating for the SA78A?
The SA78A has a maximum operating junction temperature (TJ) of +175 °C, as specified in Fairchild's official datasheet. This rating enables reliable operation in high-ambient environments such as engine compartments, industrial control cabinets, and solar inverters. Derating curves confirm usable power dissipation down to 0 W at 175 °C ambient when mounted with 0.375" lead length.
How does the SA78A compare to the SA78CA in terms of leakage current?
At its 78 V reverse stand-off voltage, the SA78A specifies ≤4.0 μA maximum reverse leakage (IR) at 25 °C. The SA78CA exhibits identical IR performance-≤4.0 μA-because both share the same silicon die and passivation process. The only functional difference lies in internal connection topology: SA78A is a single PN junction, while SA78CA integrates two back-to-back junctions for bidirectional behavior.
Can the SA78A be used in place of the P6SMB78A without board modifications?
Yes-both SA78A and P6SMB78A use the DO-15 package with identical pinout, lead spacing, and cathode band marking. They are mechanically interchangeable in through-hole assemblies. However, P6SMB78A is rated for 600 W peak pulse power versus 500 W for SA78A, offering higher surge margin. Electrical compatibility is confirmed across VRWM, VBR, VC, and IR specifications.
SA78A Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Package/Case:
- DO-204AC, DO-15, Axial
- Series:
- -
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- Zener
- Unidirectional Channels:
- 1
- Bidirectional Channels:
- -
- Voltage - Reverse Standoff (Typ):
- 78V
- Voltage - Breakdown (Min):
- 86.7V
- Voltage - Clamping (Max) @ Ipp:
- 126V
- Current - Peak Pulse (10/1000µs):
- 4A
- Power - Peak Pulse:
- 500W
- Power Line Protection:
- No
- Applications:
- General Purpose
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- DO-15
SA78A FAQ
1.How can I place an order for SA78A through Aetrix?
Please submit a Request for Quotation (RFQ) for SA78A 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 SA78A reliable?
The price and inventory of SA78A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SA78A is usually 5 days.
3.What payment methods are accepted for SA78A?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SA78A transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SA78A?
SA78A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SA78A 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 SA78A?
For technical support, including SA78A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SA78A requirements.
6.How does Aetrix verify that SA78A is sourced from the original manufacturer or authorized distributors?
All SA78A 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 SA78A meets industry standards.
7.What is the process for return or replacement of SA78A?
All SA78A units undergo pre-shipment inspection (PSI). If there is an issue with SA78A, 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 SA78A part is unused and in its original packaging.
Return procedure for SA78A:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SA78A Tags
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