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onsemi 1SMC78AT3G
- Part No.:
- 1SMC78AT3G
- Manufacturer:
- onsemi
- Category:
- TVS Diodes
- Package:
- DO-214AB, SMC
- Datasheet:
-
1SMC78AT3G.pdf
- Description:
- TVS DIODE 78VWM 126VC SMC
- Quantity:
- Payment:
- Shipping:
Inventory:3,966
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Product details
Overview
1SMC78AT3G from ON Semiconductor is a unidirectional 1500 W peak power Zener transient voltage suppressor (TVS) designed for parallel clamping protection of DC power rails and signal lines. It features a 78 V working peak reverse voltage (VRWM), 95.8 V maximum clamping voltage at 11.4 A peak pulse current, <5 µA leakage above 10 V, <1 ns response time, and UL 497B recognition for isolated loop circuit protection - deployed in automotive power supplies and industrial I/O interfaces.
For engineers reviewing the 1SMC78AT3G datasheet, pinout, applications, or equivalent options, this page delivers verified electrical specs, package dimensions, clamping behavior under surge, thermal derating curves, and direct alternatives for overvoltage protection design validation and BOM optimization.
Technical Context
The 1SMC78AT3G operates as a unidirectional Zener-based TVS diode, leveraging avalanche breakdown to clamp transients above its VRWM of 78 V. Its clamping action begins at VBR = 86.7–91.25 V (tested at 1 mA), with VC = 126 V at IPP = 11.4 A (10/1000 µs waveform), ensuring robust suppression of ESD and lightning-induced surges.
Thermal performance is defined by RJA = 165 °C/W (FR-4 board, minimum footprint) and RJL = 54.6 °C/W (zero lead length), requiring careful PCB layout for sustained surge handling. It supports operating temperatures from –65 °C to +150 °C and meets Class 3 HBM ESD rating (>16 kV).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VRWM | 78 V - Maximum continuous reverse voltage before clamping; sets minimum system operating voltage margin. |
| VBR (min/typ/max) | 86.7 / 91.25 V - Breakdown occurs within this range at 1 mA test current; defines turn-on threshold consistency. |
| VC @ IPP | 126 V @ 11.4 A - Clamped voltage during 10/1000 µs surge; determines maximum stress on protected downstream ICs. |
| PPK | 1500 W @ 1 ms - Peak single-pulse power dissipation; validates capability against IEC 61000-4-5 Level 4 surges. |
| IR @ VRWM | <5 µA - Reverse leakage at rated working voltage; ensures minimal standby power loss in high-impedance circuits. |
| Response Time | <1 ns - Time from transient onset to clamping initiation; critical for protecting fast logic and ADC inputs. |
| UL Recognition | UL 497B (QVGV2, File #116110) - Certified for isolated loop protection; satisfies safety compliance in telecom and medical equipment. |
Pinout & Package
1SMC78AT3G is housed in the SMC (DO-214AB) surface-mount package (Case 403), featuring a molded polarity notch indicating the cathode terminal. The package uses void-free thermosetting plastic, corrosion-resistant finishes, and modified L-bend leads for enhanced solder joint reliability.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Current entry point during forward conduction; connected to lower-potential side of protected line. | Provides low VF (~3.5 V @ 100 A) path during fault conditions; must be routed with low-inductance trace. |
| Cathode | Current exit point during reverse-biased clamping; connected to higher-potential rail or ground reference. | Carries full surge current during transient events; polarity marking ensures correct PCB orientation per UL 497B layout rules. |
Key Features
| Feature | Design Value |
|---|---|
| 1500 W peak pulse power | Enables single-device protection against IEC 61000-4-5 4 kV/2 Ω surge tests without cascading devices. |
| UL 497B certified | Validates suitability for safety-critical isolated loop circuits in industrial controllers and PoE-powered endpoints. |
| <1 ns response time | Minimizes voltage overshoot before clamping engages, preserving integrity of 3.3 V/5 V microcontroller I/O pins. |
| Low zener impedance | Ensures stable clamping voltage across varying surge currents, reducing risk of secondary overstress on load ICs. |
| –65 °C to +150 °C operation | Supports under-hood automotive applications and high-temperature industrial enclosures without derating penalties. |
Applications
| Automotive Power Rail Protection | Industrial PLC Digital I/O Protection |
|---|---|
Use Scenario: 12 V/24 V battery-fed ECUs exposed to load dump (ISO 7637-2 Pulse 5a) and alternator ripple. IC Role / Device Role / Timing Role: Unidirectional TVS placed between power rail and chassis ground to clamp transients before they reach PMICs and CAN transceivers. Use Value: Withstands 1500 W surges and maintains VRWM ≥78 V, allowing safe margin above 24 V nominal systems while meeting AEC-Q101 stress requirements. |
Use Scenario: 24 V digital input modules in programmable logic controllers subjected to field-wiring induced surges. IC Role / Device Role / Timing Role: Parallel-connected TVS on each input channel to limit voltage to ≤126 V during 1 kV/500 Ω ring wave transients. Use Value: UL 497B certification ensures compliance for isolated input stage protection, and low leakage (<5 µA) prevents false triggering in high-impedance sensing circuits. |
| Medical Equipment Power Entry | Telecom Line Interface Protection |
Use Scenario: AC/DC adapter outputs feeding patient-connected monitoring devices requiring reinforced insulation per IEC 60601-1. IC Role / Device Role / Timing Role: Secondary-side TVS on DC output rail to suppress coupling from primary-side surges and ESD events. Use Value: 126 V clamping voltage ensures downstream LDOs and analog front-ends remain within absolute maximum ratings during 4 kV contact ESD events. |
Use Scenario: Ethernet or RS-485 interface ports in network switches exposed to induced lightning surges per IEC 61000-4-5. IC Role / Device Role / Timing Role: Bidirectional protection not applicable; 1SMC78AT3G used on DC bias rails (e.g., PHY VDD) where unidirectional clamping suffices. Use Value: Fast <1 ns response and 1500 W rating enable effective suppression of common-mode surges on auxiliary power rails without compromising signal integrity. |
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 | Same VRWM (78 V) and VC (126 V), but lower PPK = 600 W; SMB package (smaller footprint, higher RJA). | Limited to lower-energy transients (e.g., IEC 61000-4-2 ESD only); unsuitable for IEC 61000-4-5 Level 3+. | Select when space-constrained layouts prioritize compactness over surge energy handling. |
| 1.5SMC78A | Identical electrical specs and SMC package, but obsolete ON Semiconductor part; no active lifecycle support. | No long-term supply assurance; not recommended for new designs per ON Semi's preferred device list. | Prefer 1SMC78AT3G for guaranteed availability, UL 497B certification, and production continuity. |
Compared with SMBJ78A and 1.5SMC78A, the 1SMC78AT3G uniquely combines 1500 W surge capacity, UL 497B listing, and active manufacturing status - making it the optimal choice for industrial and automotive applications demanding both high-energy clamping and regulatory compliance.
Availability
1SMC78AT3G is available at Aetrix Electronics and suitable for automotive ECUs, industrial PLC I/O modules, medical power supplies, and telecom infrastructure requiring stable component supply across multi-year production cycles.
Supply support for 1SMC78AT3G 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
ON Semiconductor (now onsemi) is a global semiconductor supplier specializing in power management, analog, sensor, and connectivity solutions for automotive, industrial, and cloud power applications.
The 1SMC78AT3G belongs to the SMC-series Zener TVS family, engineered specifically for high-reliability, high-surge industrial and automotive overvoltage protection with emphasis on UL-certified safety and thermally robust packaging.
FAQ
What is the clamping voltage of the 1SMC78AT3G at its rated peak pulse current?
The 1SMC78AT3G has a maximum clamping voltage (VC) of 126 V at its peak pulse current (IPP) of 11.4 A, measured using the standard 10/1000 µs double-exponential surge waveform. This value is specified in the ON Semiconductor datasheet and defines the upper voltage limit imposed on protected circuitry during worst-case transient events. Designers use this parameter to verify that downstream components remain within their absolute maximum voltage ratings when the 1SMC78AT3G is activated.
Is the 1SMC78AT3G suitable for bidirectional transient protection?
No, the 1SMC78AT3G is a unidirectional TVS diode and is not suitable for bidirectional protection. Its construction and electrical characteristics - including polarity marking, forward voltage specification (VF ≤ 3.5 V), and absence of symmetrical breakdown behavior - confirm it is intended only for clamping positive-going transients relative to ground. For bidirectional applications such as AC line or data bus protection, a dedicated bidirectional TVS like SMAJ78CA must be selected instead of the 1SMC78AT3G.
Does the 1SMC78AT3G meet UL 497B certification, and what does that mean for my design?
Yes, the 1SMC78AT3G carries UL 497B recognition (File #116110, QVGV2 category) for isolated loop circuit protection. This certification confirms successful completion of rigorous safety tests including strike voltage breakdown, endurance conditioning, dielectric withstand, and discharge testing - validating its use in safety-isolated subsystems like telecom interfaces and medical device signal chains. Using the 1SMC78AT3G helps satisfy regulatory requirements without requiring additional external isolation components.
What is the thermal resistance of the 1SMC78AT3G, and how does it affect PCB layout?
The 1SMC78AT3G has a junction-to-ambient thermal resistance (RJA) of 165 °C/W on an FR-4 board using ON Semiconductor's minimum recommended footprint. This high RJA value means even brief 1500 W surges generate significant localized heat, requiring generous copper pour, thermal vias, and short traces to prevent junction overheating. Layouts must follow the Case 403 footprint guidelines in the datasheet to ensure reliable operation - inadequate copper area will cause premature thermal failure during repeated surge events.
How does the 1SMC78AT3G compare to the older 1.5SMC78A part?
The 1SMC78AT3G replaces the obsolete 1.5SMC78A with identical electrical specifications (VRWM = 78 V, VC = 126 V, PPK = 1500 W) and SMC package, but adds UL 497B certification and active manufacturing support. ON Semiconductor explicitly lists the 1SMC78AT3G as a Preferred Device, whereas the 1.5SMC78A is discontinued and no longer recommended for new designs. For long-term BOM stability and compliance assurance, the 1SMC78AT3G is the only viable option.
1SMC78AT3G Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Package/Case:
- DO-214AB, SMC
- Series:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- 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):
- 11.4A
- Power - Peak Pulse:
- 1500W (1.5kW)
- Power Line Protection:
- No
- Applications:
- General Purpose
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -65°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- SMC
1SMC78AT3G FAQ
1.How can I place an order for 1SMC78AT3G through Aetrix?
Please submit a Request for Quotation (RFQ) for 1SMC78AT3G 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 1SMC78AT3G reliable?
The price and inventory of 1SMC78AT3G are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 1SMC78AT3G is usually 5 days.
3.What payment methods are accepted for 1SMC78AT3G?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 1SMC78AT3G transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 1SMC78AT3G?
1SMC78AT3G orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 1SMC78AT3G 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 1SMC78AT3G?
For technical support, including 1SMC78AT3G datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 1SMC78AT3G requirements.
6.How does Aetrix verify that 1SMC78AT3G is sourced from the original manufacturer or authorized distributors?
All 1SMC78AT3G 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 1SMC78AT3G meets industry standards.
7.What is the process for return or replacement of 1SMC78AT3G?
All 1SMC78AT3G units undergo pre-shipment inspection (PSI). If there is an issue with 1SMC78AT3G, 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 1SMC78AT3G part is unused and in its original packaging.
Return procedure for 1SMC78AT3G:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
1SMC78AT3G Tags
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