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Taiwan Semiconductor Corporation SMAJ78AH
- Part No.:
- SMAJ78AH
- Manufacturer:
- Taiwan Semiconductor Corporation
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SMAJ78AH.pdf
- Description:
- TVS DIODE 78VWM 126VC DO214AC
- Quantity:
- Payment:
- Shipping:
Inventory:2,101
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Product details
Overview
SMAJ78AH 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), 86.7–95.8 V breakdown voltage (VBR), 126 V maximum clamping voltage (VC) at 3.2 A peak impulse current, and 400 W peak pulse power rating (10/1000 µs waveform) - suitable for automotive-grade DC/DC converters and industrial SMPS input stages.
For engineers reviewing the SMAJ78AH datasheet, SMAJ78AH pinout, SMAJ78AH application, or SMAJ78AH equivalent, key selection criteria include its AEC-Q101 qualification, DO-214AC (SMA) package compatibility with automated placement, low leakage (<1 µA @ 78 V), and ISO 7637-2 Pulse 1/2a/2b/3a/3b compliance for automotive load-dump and inductive-switching immunity.
Technical Context
The SMAJ78AH 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 clamping action begins at VBR = 86.7 V (min) under 1 mA test current and limits transient energy to ≤126 V at 3.2 A (10/1000 µs), enabling reliable protection of downstream MOSFETs and controllers.
It is rated for continuous operation from −55 °C to +150 °C junction temperature, supports 40 A non-repetitive forward surge (8.3 ms half-sine), and meets JESD201 Class 2 whisker resistance and J-STD-020 Moisture Sensitivity Level 1 - confirming suitability for high-reliability reflow assembly without preconditioning.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VWM | 78 V - Maximum continuous reverse operating voltage before significant leakage; defines safe DC rail margin for 72–80 V systems. |
| VBR @ IT=1 mA | 86.7–95.8 V - Breakdown onset range; ensures predictable turn-on during transients without premature conduction. |
| VC @ IPPM=3.2 A | 126 V - Clamped voltage under 10/1000 µs surge; determines maximum stress on protected ICs or FETs. |
| PPPM | 400 W - Peak pulse power handling (10/1000 µs); sufficient for ISO 7637-2 Pulse 1 (−150 V/2 Ω) and Pulse 2b (−100 V). |
| IR @ VWM | <1 µA - Reverse leakage at rated stand-off; minimizes quiescent power loss and avoids false triggering. |
| TJ max | +150 °C - Maximum junction temperature; enables use in under-hood automotive environments and high-ambient industrial enclosures. |
Pinout & Package
Package: DO-214AC (SMA), surface-mount, single-diode configuration with cathode band marking. Matte tin-plated leads meet J-STD-002 solderability; weight ≈0.060 g.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Positive terminal for reverse-biased operation | Connected to protected circuit ground or low-side return path; forms cathode-to-rail clamp topology. |
| Cathode | Negative terminal (marked by band) | Connected to protected line (e.g., 78 V supply rail); conducts avalanche current during overvoltage events. |
Key Features
| Feature | Design Value |
|---|---|
| AEC-Q101 qualified | Validated for automotive electronics per stress-test requirements including HTOL, TCT, and ESD - enables use in engine control, body electronics, and ADAS power supplies. |
| Glass passivated junction | Stable VBR tolerance and low leakage across temperature; eliminates risk of parametric drift in long-life industrial applications. |
| ISO 7637-2 compliance | Withstands standardized automotive transients (Pulse 1: −150 V/2 Ω; Pulse 2b: −100 V; Pulse 3a/b: ±200 V) without degradation. |
| Fast response time | <1.0 ps rise-to-breakdown - clamps before sensitive logic or gate drivers experience damaging overvoltage. |
Applications
| Automotive On-Board DC/DC Converter | Industrial Switching Mode Power Supply (SMPS) |
|---|---|
Use Scenario: Protects primary-side controller ICs and MOSFET gates against load-dump transients (ISO 7637-2 Pulse 5a) in 24 V vehicle DC/DC modules. IC Role / Device Role / Timing Role: Unidirectional TVS placed between 78 V intermediate bus and chassis ground to clamp negative spikes. Use Value: Limits clamped voltage to 126 V, ensuring gate oxide integrity of 150 V-rated SiC MOSFETs and preventing controller latch-up. | Use Scenario: Shields feedback optocoupler inputs and PWM controller VCC pins from switching noise and line surges in telecom rectifiers. IC Role / Device Role / Timing Role: Standoff-rated TVS on auxiliary 78 V bias rail, absorbing repetitive 10/1000 µs transients from transformer leakage inductance. Use Value: 400 W pulse rating sustains >10,000 cycles without parameter shift; <1 µA leakage avoids bias current error in precision feedback networks. |
| LED Driver Input Stage | Factory Automation Sensor Interface |
Use Scenario: Guards constant-current LED driver ICs against inductive kickback from relay-controlled 72–80 V lighting strings. IC Role / Device Role / Timing Role: Cathode-to-rail connection on input capacitor node; clamps positive transients generated during relay coil de-energization. Use Value: 126 V clamping prevents overvoltage damage to internal LDOs and current-sense amplifiers rated for ≤130 V absolute maximum. | Use Scenario: Protects RS-485 transceiver VCC and data lines in PLC I/O modules exposed to 24 V field wiring surges. IC Role / Device Role / Timing Role: Primary rail protector upstream of local LDOs; absorbs common-mode transients coupled onto 24 V supply from motor drives. Use Value: AEC-Q101 qualification ensures reliability in vibration-prone factory floors; DO-214AC footprint allows compact layout near connector entry points. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar transient suppression applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMAJ78H | Higher VBR range (86.7–106 V) and higher VC (139 V @ 2.9 A); same package and PPPM. | Less precise clamping; higher let-through voltage may stress marginally rated downstream components. | Select SMAJ78H only when tighter clamping is not required and cost is prioritized over voltage margin. |
| SMBJ78A | Same VWM/VBR specs but in DO-214AA (SMB) package; 600 W PPPM rating (10/1000 µs). | Larger footprint and higher surge capacity; unsuitable for space-constrained SMA layouts. | Choose SMBJ78A only if board area permits and 600 W surge headroom is needed beyond 400 W. |
Compared with SMAJ78H and SMBJ78A, the SMAJ78AH delivers tighter VBR tolerance (±5.2% vs ±10.9% for SMAJ78H) and lower clamping voltage (126 V vs 139 V), making it preferable for protecting 130 V-maximum devices - while retaining full DO-214AC compatibility and AEC-Q101 qualification.
Availability
SMAJ78AH is available at Aetrix Electronics and suitable for automotive on-board DC/DC converters, industrial switching mode power supplies, and LED driver input stages requiring stable component supply with AEC-Q101 assurance and ISO 7637-2 compliance.
Supply support for SMAJ78AH 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 for automotive and industrial markets.
The SMAJ series was developed specifically for AEC-Q101-compliant transient suppression in harsh-environment 12 V/24 V/48 V automotive and industrial power systems, emphasizing low clamping voltage, tight VBR tolerance, and high surge robustness in compact DO-214AC packaging.
FAQ
What is the clamping voltage of the SMAJ78AH under standard 10/1000 µs surge conditions?
The SMAJ78AH has a maximum clamping voltage (VC) of 126 V when subjected to a 3.2 A peak impulse current with a 10/1000 µs waveform. This value is measured per Figure 5 in the official Taiwan Semiconductor datasheet (Version A2102) and defines the upper voltage limit imposed on protected circuits during transient events - critical for ensuring compatibility with 130 V-rated downstream components.
Is the SMAJ78AH suitable for bidirectional transient protection?
No, the SMAJ78AH is a unidirectional TVS diode intended for DC rail protection where polarity is fixed. For bidirectional applications (e.g., AC lines or data buses), Taiwan Semiconductor specifies parts with CH or CAH suffixes (e.g., SMAJ78CH). Using SMAJ78AH in reverse-biased configurations risks permanent damage due to lack of symmetrical breakdown capability.
Does the SMAJ78AH require derating at elevated ambient temperatures?
Yes, the SMAJ78AH's peak pulse power must be derated above 25 °C ambient, per Figure 2 in the datasheet. At 85 °C, its 400 W rating drops to approximately 260 W; at 125 °C, it falls to ~140 W. Designers must apply this derating curve when sizing for high-temperature environments such as under-hood automotive locations or enclosed industrial power supplies.
What is the marking code for the SMAJ78AH on the device body?
The SMAJ78AH is marked with the code "RT" on its DO-214AC (SMA) package, as confirmed in the Electrical Specifications table on page 3 of the Taiwan Semiconductor datasheet (Version A2102). This two-character laser marking identifies both the voltage grade and the "A" variant (tighter VBR tolerance) - distinguishing it from the standard SMAJ78H (marked "RS").
How does the SMAJ78AH meet automotive reliability standards?
The SMAJ78AH is AEC-Q101 qualified and meets ISO 7637-2 Pulse 1/2a/2b/3a/3b requirements. It undergoes accelerated stress testing including high-temperature operating life (HTOL), temperature cycling (TCT), and human-body-model ESD (≥8 kV contact). These validations confirm its suitability for automotive power electronics where long-term reliability under thermal and electrical stress is mandatory - as documented in Taiwan Semiconductor's AEC-Q101 certificate for the SMAJx(A)H family.
SMAJ78AH 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:
- 126V
- Current - Peak Pulse (10/1000µs):
- 3.2A
- 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)
SMAJ78AH FAQ
1.How can I place an order for SMAJ78AH through Aetrix?
Please submit a Request for Quotation (RFQ) for SMAJ78AH 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 SMAJ78AH reliable?
The price and inventory of SMAJ78AH are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SMAJ78AH is usually 5 days.
3.What payment methods are accepted for SMAJ78AH?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SMAJ78AH transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SMAJ78AH?
SMAJ78AH orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SMAJ78AH 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 SMAJ78AH?
For technical support, including SMAJ78AH datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SMAJ78AH requirements.
6.How does Aetrix verify that SMAJ78AH is sourced from the original manufacturer or authorized distributors?
All SMAJ78AH 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 SMAJ78AH meets industry standards.
7.What is the process for return or replacement of SMAJ78AH?
All SMAJ78AH units undergo pre-shipment inspection (PSI). If there is an issue with SMAJ78AH, 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 SMAJ78AH part is unused and in its original packaging.
Return procedure for SMAJ78AH:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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