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Taiwan Semiconductor Corporation SMAJ78C
- Part No.:
- SMAJ78C
- Manufacturer:
- Taiwan Semiconductor Corporation
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SMAJ78C.pdf
- Description:
- 300W, 96.4V, 10%, BIDIRECTIONAL,
- Quantity:
- Payment:
- Shipping:
Inventory:5,840
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Product details
Overview
SMAJ78C from Taiwan Semiconductor is a unidirectional surface-mount transient voltage suppressor (TVS) diode designed for robust overvoltage protection in DC power rails and signal lines. It features a 78 V working stand-off voltage (VWM), 86.7–106 V breakdown voltage (VBR), 139 V maximum clamping voltage (VC) at 2.9 A peak impulse current, and 400 W peak pulse power rating (10/1000 µs waveform). It is commonly deployed in on-board DC/DC converters and industrial SMPS inputs to absorb ESD and load-dump transients.
For engineers reviewing the SMAJ78C datasheet, SMAJ78C pinout, SMAJ78C application, or SMAJ78C equivalent, key selection criteria include its DO-214AC (SMA) package compatibility with automated placement, ISO 7637-2 Pulse 1/2a/2b/3a/3b compliance, <1 µA reverse leakage at 78 V, and verified clamping performance under 10/1000 µs surge conditions.
Technical Context
The SMAJ78C operates as a unidirectional avalanche diode, leveraging glass-passivated junction technology for stable breakdown behavior and fast response (<1.0 ps from 0 V to VBR(min)). Its single-die DO-214AC construction supports bidirectional use only when paired with a companion device or configured in back-to-back topology - the "C" suffix denotes unidirectional polarity with cathode band marking.
Thermal derating follows Fig.2 in the datasheet: peak pulse power drops linearly above 25°C ambient, maintaining 100% rating up to TA = 25°C and reducing to ~50% at 100°C. Junction temperature is rated from –55°C to +150°C, with steady-state power dissipation limited to 1 W.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VWM | 78 V - Maximum continuous reverse operating voltage before significant leakage; defines safe DC rail margin. |
| VBR @ IT = 1 mA | 86.7–106 V - Breakdown threshold range; ensures reliable turn-on during transients exceeding 78 V. |
| VC @ IPPM = 2.9 A | 139 V - Clamped voltage under 10/1000 µs surge; determines protected circuit's maximum stress level. |
| PPPM | 400 W - Peak pulse power handling (10/1000 µs); sufficient for automotive load-dump and industrial surge immunity. |
| IR @ VWM | <1 µA - Reverse leakage at stand-off voltage; minimizes standby power loss in high-impedance circuits. |
| Package | DO-214AC (SMA) - Standard surface-mount outline with matte tin-plated leads; compatible with J-STD-002 soldering. |
Pinout & Package
DO-214AC (SMA) package: molded epoxy case meeting UL 94V-0 flammability rating; polarity indicated by cathode band on unidirectional devices; weight ≈ 0.060 g.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Low-side reference terminal | Connected to ground or low-voltage return path; forms clamping path during positive transients. |
| Cathode | High-side input terminal | Connected to protected line (e.g., 78 V rail); conducts avalanche current when VIN > VC. |
Key Features
| Feature | Design Value |
|---|---|
| Glass-passivated junction | Ensures stable VBR tolerance and long-term reliability under thermal cycling and humidity exposure. |
| Fast response time <1.0 ps | Enables suppression of nanosecond-scale ESD events before downstream ICs experience overstress. |
| ISO 7637-2 compliance (Pulse 1/2a/2b/3a/3b) | Validates suitability for automotive 12 V and 24 V system-level transient immunity testing. |
| Moisture sensitivity level 1 (J-STD-020) | Permits standard SMT reflow without baking; eliminates moisture-related popcorning risk. |
Applications
| Automotive Power Input Protection | Industrial DC/DC Converter Input |
|---|---|
Use Scenario: Protecting 12 V/24 V vehicle electronics against load dump (ISO 7637-2 Pulse 5a) and alternator transients. IC Role / Device Role / Timing Role: Unidirectional TVS placed between battery rail and DC/DC converter input to clamp surges above 78 V. Use Value: Limits peak voltage to 139 V during 400 W transients, preventing damage to upstream regulators and microcontrollers. |
Use Scenario: Safeguarding isolated DC/DC modules in programmable logic controllers (PLCs) and motor drives. IC Role / Device Role / Timing Role: Standoff-rated TVS on primary-side input to absorb switching noise and coupling-induced spikes. Use Value: Maintains <1 µA leakage at 78 V, avoiding unnecessary quiescent current draw while delivering sub-100 ns clamping response. |
| Telecom Power Adapter Interface | LED Driver Supply Rail Protection |
Use Scenario: Secondary-side overvoltage protection in AC/DC adapters powering telecom baseband units. IC Role / Device Role / Timing Role: Unidirectional clamping device across regulated 78 V output bus to absorb capacitor discharge transients. Use Value: Withstands 2.9 A peak impulse current (10/1000 µs), ensuring survival through repeated adapter plug/unplug events. |
Use Scenario: Protecting constant-current LED drivers from inductive kickback during MOSFET switching. IC Role / Device Role / Timing Role: TVS placed across driver output to clamp flyback voltages exceeding 78 V during turn-off. Use Value: 139 V clamping voltage prevents LED string overvoltage failure while supporting automated SMA placement on high-volume PCBs. |
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 | Lower VBR range (86.7–95.8 V) and lower VC (126 V @ 3.2 A); same DO-214AC package. | Better suited for tighter clamping margins where 13 V lower VC improves downstream component safety margin. | Select SMAJ78A if design requires lower clamping voltage and can accommodate slightly reduced surge current rating (3.2 A vs. 2.9 A). |
| SMBJ78A | Same VWM/VBR specs but higher PPPM = 600 W (10/1000 µs); SMB package (DO-214AA), larger footprint. | Preferred for higher-energy transients where 400 W is insufficient; requires PCB layout change due to different pad geometry. | Choose SMBJ78A only when surge energy exceeds SMAJ78C capability and board space allows DO-214AA footprint. |
Compared with SMAJ78C, SMAJ78A offers tighter clamping at lower test current but reduced peak current capacity, while SMBJ78A delivers higher surge robustness in a physically larger package - neither is pin-compatible, requiring layout revision for substitution.
Availability
SMAJ78C is available at Aetrix Electronics and suitable for automotive power input protection, industrial DC/DC converter input stages, and LED driver supply rail protection requiring stable component supply and full traceability.
Supply support for SMAJ78C 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 semiconductor manufacturer specializing in discrete power devices, TVS diodes, rectifiers, and MOSFETs for industrial and automotive markets.
The SMAJ series was developed specifically for surface-mount transient suppression in harsh environments, emphasizing ISO 7637-2 compliance, high surge robustness, and J-STD-020 Level 1 moisture resistance.
FAQ
What is the polarity configuration of SMAJ78C?
The SMAJ78C is a unidirectional TVS diode, marked with a cathode band indicating the high-side terminal. When reverse-biased beyond its 78 V stand-off voltage, it avalanches from cathode to anode, clamping transients on the protected line. It is not rated for bidirectional operation unless paired with another SMAJ78C in anti-parallel configuration.
Does SMAJ78C meet automotive transient immunity standards?
Yes, SMAJ78C meets ISO 7637-2 requirements for Pulse 1 (inductive load disconnect), Pulse 2a (sudden load removal), Pulse 2b (supply line inductive spike), Pulse 3a (capacitive coupled noise), and Pulse 3b (power line noise), making it suitable for 12 V and 24 V automotive subsystems per the manufacturer's validation.
What is the maximum clamping voltage of SMAJ78C under surge conditions?
The maximum clamping voltage of SMAJ78C is 139 V, measured at 2.9 A peak impulse current using the standardized 10/1000 µs double-exponential waveform. This value defines the upper voltage limit imposed on protected circuitry during a 400 W transient event.
Can SMAJ78C be used in bidirectional applications?
No - SMAJ78C is unidirectional only. For bidirectional protection, select the SMAJ78CA variant (not SMAJ78C), which integrates two opposing diodes in one DO-214AC package and is explicitly rated for symmetrical clamping in both polarities.
What is the thermal derating behavior of SMAJ78C above 25°C ambient?
SMAJ78C's peak pulse power rating decreases linearly above 25°C ambient temperature per Figure 2 in the datasheet: at 75°C, it retains ~75% of its 400 W rating; at 100°C, ~50%; and at 125°C, ~25%. Derating must be applied in thermally constrained layouts or high-temperature enclosures.
SMAJ78C 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:
- -
- Bidirectional Channels:
- 1
- 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)
SMAJ78C FAQ
1.How can I place an order for SMAJ78C through Aetrix?
Please submit a Request for Quotation (RFQ) for SMAJ78C 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 SMAJ78C reliable?
The price and inventory of SMAJ78C are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SMAJ78C is usually 5 days.
3.What payment methods are accepted for SMAJ78C?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SMAJ78C transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SMAJ78C?
SMAJ78C orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SMAJ78C 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 SMAJ78C?
For technical support, including SMAJ78C datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SMAJ78C requirements.
6.How does Aetrix verify that SMAJ78C is sourced from the original manufacturer or authorized distributors?
All SMAJ78C 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 SMAJ78C meets industry standards.
7.What is the process for return or replacement of SMAJ78C?
All SMAJ78C units undergo pre-shipment inspection (PSI). If there is an issue with SMAJ78C, 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 SMAJ78C part is unused and in its original packaging.
Return procedure for SMAJ78C:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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