My Inquiry
My Account
Taiwan Semiconductor Corporation SMAJ78A
- Part No.:
- SMAJ78A
- Manufacturer:
- Taiwan Semiconductor Corporation
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SMAJ78A.pdf
- Description:
- TVS DIODE 78VWM 126VC DO214AC
- Quantity:
- Payment:
- Shipping:
Inventory:8,753
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SMAJ78A from Taiwan Semiconductor is a unidirectional surface-mount transient voltage suppressor (TVS) diode in DO-214AC (SMA) package, designed for overvoltage protection of DC power lines and signal interfaces. 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 load-dump and ISO 7637-2 Pulse 1/2a/2b/3a/3b compliance.
For engineers reviewing the SMAJ78A datasheet, SMAJ78A pinout, SMAJ78A application, or SMAJ78A equivalent, key selection considerations include its unidirectional polarity, 1 µA max reverse leakage at 78 V, 150 °C junction temperature rating, DO-214AC mechanical compatibility, and clamping performance under fast transients (<1 ps response).
Technical Context
The SMAJ78A operates as a silicon avalanche diode with glass-passivated junction, enabling precise breakdown behavior and stable clamping during ESD and surge events. Its unidirectional configuration provides forward conduction path only in one direction, requiring correct cathode orientation on PCB layout.
It delivers 400 W peak pulse power at 25 °C (derated linearly above that ambient), supports 40 A non-repetitive forward surge (8.3 ms half-sine), and maintains <3.5 V forward voltage at 25 A - critical for low-loss crowbar operation in high-current protection circuits.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VWM | 78 V - Maximum continuous reverse operating voltage before significant leakage; defines safe DC bus margin. |
| VBR @ IT=1 mA | 86.7–95.8 V - Breakdown onset range; ensures reliable triggering above nominal line voltage. |
| VC @ IPPM=3.2 A | 126 V - Clamped voltage during 10/1000 µs surge; limits downstream IC stress to safe level. |
| PPPM | 400 W - Peak pulse power handling (10/1000 µs); meets automotive ISO 7637-2 Pulse 2b requirements. |
| IR @ VWM | ≤1 µA - Reverse leakage at stand-off voltage; minimizes standby power loss in battery-powered systems. |
| TJ max | 150 °C - Maximum junction temperature; enables operation in under-hood automotive environments. |
| Package | DO-214AC (SMA) - Standard surface-mount outline with 0.060 g mass; compatible with automated pick-and-place. |
Pinout & Package
DO-214AC (SMA) package: molded epoxy case with matte tin-plated leads, polarity indicated by cathode band (band end = cathode). Complies with UL 94V-0 flammability and JESD201 Class 2 whisker resistance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Forward current entry / Surge return path | Connected to protected line side; conducts during reverse transient to shunt energy to ground. |
| Cathode | Clamping reference / Ground connection | Connected to system ground or low-impedance return; defines clamping threshold relative to this node. |
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 | Activates before sensitive downstream circuitry sustains damage from ESD or lightning-induced transients. |
| ISO 7637-2 compliant | Validated for automotive electrical system immunity testing (Pulse 1, 2a, 2b, 3a, 3b), supporting OEM qualification. |
| Moisture sensitivity level 1 | Zero bake requirement prior to reflow; compatible with standard SMT assembly without special handling. |
| Halogen-free & RoHS compliant | Meets IEC 61249-2-21 and EU RoHS directives; supports green manufacturing and end-of-life recycling. |
Applications
| Automotive Power Distribution | Industrial DC/DC Converters |
|---|---|
Use Scenario: Protection of 24 V supply rail in vehicle body control modules against load dump and alternator transients. IC Role / Device Role / Timing Role: Unidirectional TVS clamp placed between battery input and upstream fuse, referenced to chassis ground. Use Value: Limits transient voltage to ≤126 V, preventing damage to MCU power supplies and CAN transceivers rated for 36 V absolute max. |
Use Scenario: Input-side surge suppression for isolated 48 V-to-12 V DC/DC converters in factory automation PLCs. IC Role / Device Role / Timing Role: Primary-side TVS connected across input capacitor terminals to absorb 10/1000 µs surges from shared industrial power buses. Use Value: Withstands 400 W pulses without degradation, maintaining converter uptime during brownout recovery and switching noise events. |
| LED Driver Power Inputs | Telecom Power Feeds |
Use Scenario: Overvoltage protection for constant-current LED drivers in streetlight applications exposed to lightning-induced surges. IC Role / Device Role / Timing Role: Series-connected unidirectional TVS on AC-DC rectified output, clamping transients before buck controller input. Use Value: 126 V clamping ensures driver ICs (e.g., LM3409HV) remain within 65 V absolute maximum rating during 1 kV/µs transients. |
Use Scenario: Secondary-side protection of -48 V telecom power feeds feeding remote radio units (RRUs) on cell towers. IC Role / Device Role / Timing Role: Cathode-to-ground configuration on -48 V rail to clamp positive-going surges while blocking normal negative bias. Use Value: 1 µA leakage at -78 V prevents excessive quiescent current draw in always-on base station subsystems. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar transient voltage suppression applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMAJ78CA | Bidirectional variant; symmetric VBR (86.7–106 V) and same VC (139 V); higher IR (1 µA) but no polarity constraint. | Required where AC-coupled or bidirectional signal lines (e.g., RS-485, CAN FD) need symmetrical clamping. | Select SMAJ78CA only when polarity-agnostic protection is needed; SMAJ78A offers tighter VC (126 V vs. 139 V) for DC rails. |
| SMBJ78A | Same VWM/VBR/VC specs but in larger DO-214AA (SMB) package; 600 W PPPM, higher IFSM (100 A), 0.115 g mass. | Preferred for high-energy surge environments (e.g., outdoor PoE injectors) where board space allows larger footprint. | Choose SMBJ78A if surge energy exceeds 400 W capability or if thermal derating margin is critical; SMAJ78A saves PCB area in space-constrained modules. |
Compared with SMAJ78CA and SMBJ78A, the SMAJ78A provides optimal balance of compact DO-214AC footprint, 126 V clamping, and automotive-grade surge robustness - making it ideal for cost-sensitive, space-limited 24 V/48 V DC power protection where unidirectional polarity is known and controlled.
Availability
SMAJ78A is available at Aetrix Electronics and suitable for automotive electronics, industrial power supplies, LED lighting drivers, and telecom infrastructure requiring stable component supply and full traceability.
Supply support for SMAJ78A 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, MOSFETs, and power management devices.
The SMAJ series was developed specifically for high-reliability transient suppression in automotive and industrial power systems, emphasizing tight VBR tolerance, low clamping ratio, and AEC-Q101 readiness.
FAQ
What is the polarity configuration of the SMAJ78A?
The SMAJ78A is a unidirectional TVS diode, with cathode marked by a band on the DO-214AC package. It conducts only when the cathode is at higher potential than the anode - essential for DC rail protection where polarity is fixed. This differs from bidirectional variants like SMAJ78CA, which protect both polarities equally. The SMAJ78A's unidirectional design yields lower clamping voltage (126 V) versus 139 V for the CA version.
Does the SMAJ78A meet automotive surge immunity standards?
Yes, the SMAJ78A meets ISO 7637-2 Pulse 1, 2a, 2b, 3a, and 3b test requirements for automotive electronic components. Its 400 W peak pulse power rating (10/1000 µs), 126 V clamping at 3.2 A, and 150 °C junction rating enable robust protection against load dump, jump-start, and inductive switching transients in 24 V vehicle systems. The SMAJ78A is commonly used in BCMs and ADAS ECUs.
What is the maximum clamping voltage of the SMAJ78A and under what conditions is it specified?
The SMAJ78A has a maximum clamping voltage (VC) of 126 V, measured at a peak impulse current (IPPM) of 3.2 A using the standardized 10/1000 µs double-exponential waveform. This value is guaranteed across temperature and lifetime per Taiwan Semiconductor's U2102 datasheet. It reflects worst-case voltage seen by downstream circuitry during surge events - critical for ensuring ICs with 36 V or 40 V absolute maximum ratings remain undamaged.
How does the SMAJ78A compare to the SMAJ78 (non-A) variant?
The SMAJ78A offers tighter breakdown voltage tolerance (86.7–95.8 V) versus SMAJ78 (86.7–106 V), resulting in more predictable turn-on behavior and lower clamping variation. Both share identical VWM (78 V), package (DO-214AC), and PPPM (400 W), but the "A" suffix denotes enhanced VBR consistency - important for designs requiring precise overvoltage thresholds. The SMAJ78A is preferred in safety-critical or high-volume automotive applications.
Is the SMAJ78A suitable for use in lead-free reflow processes?
Yes, the SMAJ78A is fully compatible with lead-free reflow soldering profiles, including JEDEC J-STD-020-compliant ramp rates and peak temperatures up to 260 °C. Its matte tin-plated leads meet J-STD-002 solderability requirements, and its moisture sensitivity level (MSL) is rated Level 1 - meaning no baking is required prior to assembly. This simplifies manufacturing and ensures consistent joint integrity in high-reliability production lines.
SMAJ78A 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:
- General Purpose
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -55°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- DO-214AC (SMA)
SMAJ78A FAQ
1.How can I place an order for SMAJ78A through Aetrix?
Please submit a Request for Quotation (RFQ) for SMAJ78A 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 SMAJ78A reliable?
The price and inventory of SMAJ78A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SMAJ78A is usually 5 days.
3.What payment methods are accepted for SMAJ78A?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SMAJ78A transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SMAJ78A?
SMAJ78A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SMAJ78A 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 SMAJ78A?
For technical support, including SMAJ78A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SMAJ78A requirements.
6.How does Aetrix verify that SMAJ78A is sourced from the original manufacturer or authorized distributors?
All SMAJ78A 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 SMAJ78A meets industry standards.
7.What is the process for return or replacement of SMAJ78A?
All SMAJ78A units undergo pre-shipment inspection (PSI). If there is an issue with SMAJ78A, 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 SMAJ78A part is unused and in its original packaging.
Return procedure for SMAJ78A:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SMAJ78A Tags
-
ESD9B5.0ST5G
onsemi
-
DESD3V3E1BL-7B
Diodes Incorporated
-
ESD5Z3.3T1G
onsemi
-
D5V0H1B2LP-7B
Diodes Incorporated
-
D5V0P1B2LP-7B
Diodes Incorporated
-
DESD5V0U1BA-7
Diodes Incorporated
-
ESD5Z5.0T1G
onsemi
-
DESD5V0U1BB-7
Diodes Incorporated
-
D12V0L1B2LP-7B
Diodes Incorporated
-
PESD2V0Y1BSFYL
Nexperia USA Inc.
-
DF2S5M4CT,L3F
Toshiba Semiconductor and Storage
-
D5V0L1B2WS-7
Diodes Incorporated
Tech Hub
Comparator circuit design covering voltage thresholds, input limits, open-collector outputs, LM393 wiring, op-amp differences, hysteresis, timing, window detection and practical fault diagnosis.
Schmitt triggers use separate rising and falling thresholds to stabilize slow or noisy signals. This guide covers hysteresis, 74HC14 and 74HCT14 selection, comparator calculations, RC oscillators and p…
Counterfeit components can hide behind convincing markings and passing basic function tests. This engineering reference covers source traceability, external inspection, X-ray, XRF, electrical testing, …
A practical engineering and sourcing framework covering lifecycle verification, lifetime-buy calculations, replacement qualification, supplier checks and counterfeit-risk controls.
TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
