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Taiwan Semiconductor Corporation SMAJ78CH
- Part No.:
- SMAJ78CH
- Manufacturer:
- Taiwan Semiconductor Corporation
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SMAJ78CH.pdf
- Description:
- TVS DIODE 78VWM 139VC DO214AC
- Quantity:
- Payment:
- Shipping:
Inventory:9,135
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Product details
Overview
SMAJ78CH from Taiwan Semiconductor is a unidirectional surface-mount transient voltage suppressor (TVS) diode in DO-214AC (SMA) package, designed for automotive-grade overvoltage protection. 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 AEC-Q101 qualified and meets ISO 7637-2 Pulse 1/2a/2b/3a/3b for robust vehicle electrical system protection.
For engineers reviewing the SMAJ78CH datasheet, SMAJ78CH pinout, SMAJ78CH application, or SMAJ78CH equivalent, key selection criteria include its unidirectional polarity, 139 V clamping performance under 2.9 A surge, compliance with automotive transients, moisture sensitivity level 1 handling, and DO-214AC thermal and mechanical compatibility with high-density PCB layouts.
Technical Context
The SMAJ78CH operates as a unidirectional avalanche diode, leveraging glass-passivated junction technology for stable breakdown behavior and low leakage (<1 µA at 78 V). Its fast response time (<1.0 ps from 0 V to VBR min) enables effective suppression of ESD and load-dump transients before downstream circuitry is damaged.
It is rated for TJ = –55 °C to +150 °C operation and supports peak forward surge current up to 40 A (8.3 ms half-sine), making it suitable for DC/DC converter input rails and SMPS primary-side protection where sustained thermal reliability and transient immunity are critical.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VWM | 78 V - Maximum continuous reverse operating voltage before clamping begins |
| VBR min/max | 86.7 V / 106 V @ 1 mA - Confirmed avalanche onset range ensuring predictable turn-on margin |
| VC @ IPPM | 139 V @ 2.9 A - Clamped voltage during 10/1000 µs surge, limiting stress on protected ICs |
| PPPM | 400 W - Peak pulse power handling per standard 10/1000 µs waveform |
| IR @ VWM | <1 µA - Minimal leakage at rated stand-off, preserving efficiency in high-impedance circuits |
| Package | DO-214AC (SMA) - Industry-standard surface-mount outline with 0.060 g mass and UL 94V-0 molding |
| AEC-Q101 | Qualified - Validated for automotive underhood and powertrain applications per stress test requirements |
Pinout & Package
DO-214AC (SMA) package: molded plastic case with matte tin-plated leads, cathode band marking polarity, JESD201 Class 2 whisker resistance, and moisture sensitivity level 1 (MSL-1) per J-STD-020.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Forward conduction terminal | Connected to lower-potential side (e.g., ground or return path) in unidirectional configuration |
| Cathode | Reverse-biased clamping terminal | Connected to protected line (e.g., 78 V rail); conducts only during overvoltage events |
Key Features
| Feature | Design Value |
|---|---|
| AEC-Q101 qualification | Validated for automotive temperature cycling, humidity, and mechanical shock per industry standard |
| Glass-passivated junction | Enhances long-term stability and reduces parameter drift under thermal stress and humidity exposure |
| Fast response time <1.0 ps | Enables clamping before ESD or fast transients propagate into sensitive analog/digital circuitry |
| ISO 7637-2 compliance | Meets Pulse 1 (inductive load dump), Pulse 2a/2b (switching transients), and Pulse 3a/3b (line capacitance discharge) |
| Low IR <1 µA @ VWM | Minimizes standby power loss and avoids false triggering in high-impedance monitoring circuits |
Applications
| On-board DC/DC Converter Protection | Automotive Lighting Driver Input |
|---|---|
Use Scenario: Protects buck controller ICs and gate drivers on 12 V/24 V input rails against load dump and jump-start surges. IC Role / Device Role / Timing Role: Unidirectional TVS placed between input rail and ground, clamping transients before they reach switching MOSFETs or PWM controllers. Use Value: Limits voltage to ≤139 V during 2.9 A surge, preventing latch-up or oxide breakdown in 30–60 V rated control ICs. | Use Scenario: Shields LED driver ICs in headlamp modules from battery line transients during ignition and alternator regulation events. IC Role / Device Role / Timing Role: Standoff-rated TVS on supply input, activated only during ISO 7637-2 Pulse 1 (−100 V/100 ms) or Pulse 2b (−100 V/200 ms). Use Value: Maintains <1 µA leakage at 78 V, avoiding interference with current-sense accuracy in constant-current LED regulation. |
| Industrial SMPS Primary-Side Clamp | Adapter Input Surge Suppression |
Use Scenario: Used across bulk capacitor inputs in 100–200 W industrial switch-mode power supplies subjected to AC line surges and lightning-induced transients. IC Role / Device Role / Timing Role: Parallel-connected unidirectional clamp absorbing energy during 10/1000 µs surges, coordinated with MOV or fuse upstream. Use Value: Delivers 400 W peak pulse power without degradation, enabling compact layout vs. higher-capacity alternatives requiring larger footprints. | Use Scenario: Integrated into universal-input AC/DC adapters to meet IEC 61000-4-5 Level 3 surge immunity (2 kV line-earth). IC Role / Device Role / Timing Role: First-line transient suppressor on DC output side, protecting downstream USB-PD or QC controllers from reflected surges. Use Value: MSL-1 packaging and reflow-compatible terminals support automated assembly without baking or special handling. |
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), tighter tolerance; clamps at 126 V @ 3.2 A | Better suited for systems requiring tighter voltage margin control near 78 V rail | Select SMAJ78A when clamping voltage headroom must be minimized without sacrificing surge rating |
| SMBJ78A | Same VWM/VBR specs but in DO-214AA (SMB) package; 600 W peak power rating | Higher power handling requires larger PCB footprint and different thermal management | Choose SMBJ78A only if system-level surge testing exceeds 400 W and board space allows SMB outline |
Compared with SMAJ78CH, SMAJ78A offers lower clamping voltage (126 V vs. 139 V) at slightly reduced surge current (3.2 A vs. 2.9 A), while SMBJ78A provides 50% higher peak power but demands larger layout area-making SMAJ78CH optimal for space-constrained automotive modules needing AEC-Q101 validation and precise 78 V standoff.
Availability
SMAJ78CH is available at Aetrix Electronics and suitable for automotive lighting systems, on-board DC/DC converters, and industrial SMPS designs requiring stable component supply, AEC-Q101 compliance, and consistent 78 V transient protection performance.
Supply support for SMAJ78CH 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 automotive, industrial, and consumer markets.
The SMAJ series is engineered specifically for AEC-Q101-compliant transient suppression in harsh automotive environments, emphasizing reliability under temperature cycling, humidity, and repetitive surge stress.
FAQ
What is the clamping voltage of SMAJ78CH and how is it measured?
The SMAJ78CH has a maximum clamping voltage (VC) of 139 V, measured at 2.9 A peak impulse current using the standardized 10/1000 µs double-exponential surge waveform. This value is guaranteed per the datasheet's Electrical Specifications table and reflects worst-case voltage seen by protected circuitry during a defined transient event. The SMAJ78CH maintains this clamping performance across its full operating junction temperature range (–55 °C to +150 °C), with derating applied above 25 °C ambient per the Pulse Derating Curve.
Is SMAJ78CH unidirectional or bidirectional, and how is polarity identified?
SMAJ78CH is a unidirectional TVS diode, indicated by the "H" suffix and absence of "CH" or "CAH" designation in its part number. Polarity is marked by a cathode band on the DO-214AC (SMA) package body, aligning with the cathode terminal. In circuit implementation, the cathode connects to the protected line (e.g., 78 V rail) and the anode to ground-ensuring conduction only during positive overvoltage events. Bidirectional variants use "CH" or "CAH" suffixes and exhibit symmetrical clamping in both directions.
Does SMAJ78CH meet automotive transient standards beyond AEC-Q101?
Yes, SMAJ78CH meets ISO 7637-2 Pulse 1 (inductive load dump), Pulse 2a (supply disconnection), Pulse 2b (switching transients), and Pulse 3a/3b (capacitive line discharge) requirements. These tests validate its ability to suppress real-world automotive transients without failure or parameter shift. Compliance is confirmed in the datasheet's FEATURES section and supported by TSC's AEC-Q101 qualification report, which includes extended temperature cycling and humidity testing relevant to under-hood deployment.
What is the maximum steady-state power dissipation for SMAJ78CH?
The SMAJ78CH has a steady-state power dissipation (PD) rating of 1 W at TA = 25 °C, as specified in the Absolute Maximum Ratings table. This value applies to continuous DC or low-frequency reverse-bias conditions-not transient events. In normal operation, reverse leakage remains below 1 µA at 78 V, resulting in negligible steady-state power (≤78 µW). The 1 W rating defines the upper thermal limit for non-pulsed operation and informs heatsinking decisions in high-ambient or high-reliability applications.
Can SMAJ78CH be used in place of SMAJ78A, and what is the key trade-off?
SMAJ78CH and SMAJ78A are not direct replacements due to differing clamping and breakdown characteristics: SMAJ78CH clamps at 139 V @ 2.9 A, while SMAJ78A clamps at 126 V @ 3.2 A. The CH version offers higher surge voltage tolerance but lower current capacity; the A version provides tighter clamping at higher current. Substitution requires verifying that the protected circuit can tolerate the 13 V higher clamping voltage of SMAJ78CH-or that the lower 3.2 A surge capability of SMAJ78A still satisfies system-level transient testing. No PCB changes are required, as both share identical DO-214AC (SMA) footprint and polarity marking.
SMAJ78CH 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:
- -
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -55°C ~ 150°C (TJ)
- Grade:
- Automotive
- Qualification:
- AEC-Q101
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- DO-214AC (SMA)
SMAJ78CH FAQ
1.How can I place an order for SMAJ78CH through Aetrix?
Please submit a Request for Quotation (RFQ) for SMAJ78CH 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 SMAJ78CH reliable?
The price and inventory of SMAJ78CH are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SMAJ78CH is usually 5 days.
3.What payment methods are accepted for SMAJ78CH?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SMAJ78CH transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SMAJ78CH?
SMAJ78CH orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SMAJ78CH 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 SMAJ78CH?
For technical support, including SMAJ78CH datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SMAJ78CH requirements.
6.How does Aetrix verify that SMAJ78CH is sourced from the original manufacturer or authorized distributors?
All SMAJ78CH 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 SMAJ78CH meets industry standards.
7.What is the process for return or replacement of SMAJ78CH?
All SMAJ78CH units undergo pre-shipment inspection (PSI). If there is an issue with SMAJ78CH, 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 SMAJ78CH part is unused and in its original packaging.
Return procedure for SMAJ78CH:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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