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Taiwan Semiconductor Corporation SMAJ78
- Part No.:
- SMAJ78
- Manufacturer:
- Taiwan Semiconductor Corporation
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SMAJ78.pdf
- Description:
- 300W, 96.4V, 10%, UNIDIRECTIONAL
- Quantity:
- Payment:
- Shipping:
Inventory:7,187
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Product details
Overview
SMAJ78 from Taiwan Semiconductor is a unidirectional surface-mount transient voltage suppressor (TVS) diode in DO-214AC (SMA) package, designed for overvoltage protection in DC power rails. It features a 78 V working stand-off voltage (VWM), 86.7–106 V breakdown voltage (VBR) at 1 mA test current, 139 V maximum clamping voltage (VC) at 2.9 A peak impulse current, and 400 W peak pulse power rating with 10/1000 µs waveform - suitable for automotive load-dump and ISO 7637-2 Pulse 1/2a/2b/3a/3b compliance.
For engineers reviewing the SMAJ78 datasheet, SMAJ78 pinout, SMAJ78 application, or SMAJ78 equivalent, key selection criteria include clamping performance under 10/1000 µs transients, junction temperature derating above 25°C, unidirectional polarity marking, and compatibility with automated SMT placement on 7500-piece tape-and-reel reels.
Technical Context
The SMAJ78 operates as a silicon avalanche diode with glass-passivated junction, delivering sub-1 ps response time from 0 V to VBR(min). Its unidirectional configuration enables asymmetric protection-blocking reverse conduction until breakdown while maintaining low leakage (<1 µA at 78 V) in normal operation.
Thermal design relies on its 150°C maximum junction temperature and 1 W steady-state power dissipation, with pulse power derated linearly above 25°C ambient per Fig.2. The device meets JESD201 Class 2 whisker resistance and UL 94V-0 flammability requirements for high-reliability PCB mounting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VWM | 78 V - Maximum continuous reverse operating voltage before significant leakage begins; defines safe DC rail margin. |
| VBR @ IT=1 mA | 86.7–106 V - Breakdown onset range; ensures reliable triggering above nominal system voltage. |
| VC @ IPPM=2.9 A | 139 V - Clamped voltage during 10/1000 µs surge; determines protected circuit's peak stress level. |
| PPPM (10/1000 µs) | 400 W - Peak transient energy handling capacity; supports single-event load dump up to 2.9 A. |
| IR @ VWM | <1 µA - Reverse leakage at rated stand-off; negligible power loss and signal interference in standby. |
| TJ max | 150 °C - Maximum junction temperature; sets thermal design limit for board layout and airflow. |
| Package | DO-214AC (SMA) - Standard surface-mount outline with cathode band marking; compatible with IPC-7351B footprint. |
Pinout & Package
DO-214AC (SMA) package: molded plastic case with matte tin-plated leads, polarity indicated by cathode band. Weight ≈ 0.060 g. Moisture sensitivity level (MSL) = 1 per J-STD-020.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Forward conduction terminal | Connected to lower-potential side (e.g., GND) in unidirectional configuration; conducts during forward surge. |
| Cathode | Reverse-biased protection terminal | Connected to protected line (e.g., +12 V rail); avalanches into conduction when reverse voltage exceeds VBR. |
Key Features
| Feature | Design Value |
|---|---|
| Glass-passivated junction | Ensures stable VBR over temperature and long-term reliability in humid environments. |
| Fast response time <1 ps | Clamps ESD and fast transients before sensitive downstream ICs experience overstress. |
| ISO 7637-2 compliance | Validated for automotive Pulse 1 (inductive switch-off), Pulse 2a/2b (battery disconnect), and Pulse 3a/3b (line transients). |
| RoHS & halogen-free | Meets IEC 61249-2-21 and EU RoHS Directive 2011/65/EU for green manufacturing. |
| Automated placement compatibility | Standard DO-214AC geometry and tape-and-reel packaging support high-speed pick-and-place assembly. |
Applications
| Automotive Power Distribution | Industrial DC/DC Converters |
|---|---|
Use Scenario: Protecting 24 V battery-fed ECUs against load dump and alternator transients per ISO 7637-2. IC Role / Device Role / Timing Role: Unidirectional TVS placed between battery rail and input filter capacitor to clamp surges to ≤139 V. Use Value: Prevents damage to upstream regulators and downstream microcontrollers during 100 V/100 ms load dump events. | Use Scenario: Safeguarding isolated 48 V-to-12 V DC/DC converter inputs in factory automation systems. IC Role / Device Role / Timing Role: Standoff-rated TVS absorbing repetitive switching noise and lightning-induced surges on primary-side bus. Use Value: Maintains <1 µA leakage at 78 V, avoiding efficiency loss while enabling 400 W transient suppression without derating. |
| LED Driver Power Inputs | Telecom Power Feeds |
Use Scenario: Overvoltage protection for constant-current LED drivers powered from 72 V telecom rectifiers. IC Role / Device Role / Timing Role: Primary-line TVS absorbing 10/1000 µs surges induced by nearby relay switching or cable coupling. Use Value: Clamps to 139 V within <1 ps, limiting stress on MOSFET gate drivers and current-sense amplifiers. | Use Scenario: Input-stage surge suppression on -48 V DC power feeds in base station remote radio units. IC Role / Device Role / Timing Role: Unidirectional TVS referenced to chassis ground, protecting PoE-like power entry circuits. Use Value: Withstands 2.9 A peak impulse current while maintaining MSL-1 moisture robustness for outdoor deployment. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar transient voltage suppression applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMAJ78A | Narrower VBR range (86.7–95.8 V) and lower VC (126 V at 3.2 A); tighter tolerance improves clamping consistency. | Better suited for precision-rail systems where clamping voltage margin is critical (e.g., 100 V-rated capacitors). | Select SMAJ78A when tighter VBR distribution and reduced clamping voltage outweigh minor peak current reduction. |
| SMBJ78 | Same VWM/VBR/VC specs but in larger DO-214AA (SMB) package; higher thermal mass allows greater pulse repetition rate. | Preferred in high-duty-cycle industrial environments where sustained surge energy exceeds SMAJ78's thermal limits. | Choose SMBJ78 when board space permits and thermal management requires >1 W average power handling. |
Compared with SMAJ78, SMAJ78A offers tighter VBR control and lower clamping for improved system margin, while SMBJ78 trades footprint size for enhanced thermal endurance - both require review of PCB layout and surge duty cycle.
Availability
SMAJ78 is available at Aetrix Electronics and suitable for automotive electronics, industrial DC/DC converters, and LED lighting systems requiring stable component supply across extended temperature ranges and high-volume production cycles.
Supply support for SMAJ78 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
Taiwan Semiconductor Corporation (TSC) is a vertically integrated analog and discrete semiconductor manufacturer headquartered in Hsinchu, Taiwan, specializing in TVS diodes, rectifiers, and power MOSFETs since 1979.
The SMAJ series was developed specifically for surface-mount overvoltage protection in automotive and industrial power systems, emphasizing ISO 7637-2 compliance, automated assembly readiness, and high-reliability packaging.
FAQ
What is the maximum clamping voltage of SMAJ78 under standard 10/1000 µs surge conditions?
The SMAJ78 has a maximum clamping voltage (VC) of 139 V when subjected to a 2.9 A peak impulse current with a 10/1000 µs waveform. This value is measured per Fig.5 in the official TSC datasheet (U2102) and defines the upper voltage limit imposed on protected circuitry during transient events.
Is SMAJ78 suitable for bidirectional transient protection?
No, SMAJ78 is a unidirectional TVS diode, intended only for protection against reverse-polarity surges on positive rails. For bidirectional applications, use SMAJ78C or SMAJ78CA - the 'C' or 'CA' suffix denotes symmetrical breakdown in both directions, as confirmed in TSC's bipolar applications note on page 2 of U2102.
What is the thermal derating behavior of SMAJ78 above 25°C ambient temperature?
SMAJ78's peak pulse power (400 W) is linearly derated above 25°C ambient per Fig.2 in the TSC datasheet. At 75°C, it retains ~70% of rated power (~280 W); at 125°C, ~30% (~120 W). Steady-state power dissipation remains fixed at 1 W regardless of ambient.
Does SMAJ78 meet automotive qualification standards beyond ISO 7637-2?
SMAJ78 meets ISO 7637-2 Pulse 1/2a/2b/3a/3b for electrical transients, but is not AEC-Q200 qualified. It is rated for -55°C to +150°C operating junction temperature and passes JESD201 Class 2 whisker testing - sufficient for many non-safety-critical automotive modules when validated per OEM-specific requirements.
What is the marking code for SMAJ78 on the DO-214AC package?
The SMAJ78 is marked with code "RS" on the device body, as specified in the Electrical Specifications table on page 3 of the TSC U2102 datasheet. The cathode is indicated by a band adjacent to the marking, confirming unidirectional polarity orientation during PCB layout.
SMAJ78 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Taiwan Semiconductor Corporation
- Package/Case:
- DO-214AC, SMA
- Series:
- SMAJ
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Zener
- Unidirectional Channels:
- 1
- Bidirectional Channels:
- -
- Voltage - Reverse Standoff (Typ):
- 78V
- Voltage - Breakdown (Min):
- 86.7V
- Voltage - Clamping (Max) @ Ipp:
- 139V
- Current - Peak Pulse (10/1000µs):
- 2.9A
- Power - Peak Pulse:
- 400W
- Power Line Protection:
- No
- Applications:
- General Purpose
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -55°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- DO-214AC (SMA)
SMAJ78 FAQ
1.How can I place an order for SMAJ78 through Aetrix?
Please submit a Request for Quotation (RFQ) for SMAJ78 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 SMAJ78 reliable?
The price and inventory of SMAJ78 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SMAJ78 is usually 5 days.
3.What payment methods are accepted for SMAJ78?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SMAJ78 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SMAJ78?
SMAJ78 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SMAJ78 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 SMAJ78?
For technical support, including SMAJ78 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SMAJ78 requirements.
6.How does Aetrix verify that SMAJ78 is sourced from the original manufacturer or authorized distributors?
All SMAJ78 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 SMAJ78 meets industry standards.
7.What is the process for return or replacement of SMAJ78?
All SMAJ78 units undergo pre-shipment inspection (PSI). If there is an issue with SMAJ78, 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 SMAJ78 part is unused and in its original packaging.
Return procedure for SMAJ78:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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