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Microchip Technology 1N4991US/TR
- Part No.:
- 1N4991US/TR
- Manufacturer:
- Microchip Technology
- Category:
- Single Zener Diodes
- Package:
- SQ-MELF, E
- Datasheet:
-
1N4991US/TR.pdf
- Description:
- DIODE ZENER 240V 5W E-MELF
- Quantity:
- Payment:
- Shipping:
Inventory:95
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Product details
Overview
1N4991US/TR from Microsemi is a surface-mount, voidless-hermetically-sealed glass Zener diode rated for 5 W power dissipation at 140 °C end-cap temperature, with nominal Zener voltage of 240 V at 5 mA test current, ±5% tolerance, and maximum dynamic impedance of 650 Ω at IZT - used in high-reliability voltage regulation for aerospace power conditioning and radiation-hardened instrumentation.
For engineers reviewing the 1N4991US/TR datasheet, 1N4991US/TR pinout, 1N4991US/TR application, or 1N4991US/TR equivalent, key selection criteria include its hermetic glass package (E/D-5B), -65 °C to +175 °C operating range, 0.4 μA max reverse leakage at 182 V, and MIL-PRF-19500/356 qualification for mission-critical analog reference and overvoltage clamping.
Technical Context
This device operates as a precision voltage reference and shunt regulator in high-temperature, high-reliability circuits where long-term stability under thermal cycling and radiation exposure is required. It exhibits a temperature coefficient of +0.115 %/°C and maintains regulation across 10%–50% of IZM (22 mA), with ΔVZ ≤ 22 V over that range.
The 1N4991US/TR uses a tungsten-slug glass package with copper end caps and Sn/Pb termination, enabling robust thermal conduction (7 °C/W junction-to-end-cap) and ESD immunity per MIL-STD-750 Method 1020. Its voidless construction eliminates internal delamination risks common in epoxy-packaged Zeners.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Zener Voltage (VZ) | 240 V at IZT = 5 mA - defines stable regulation point for high-voltage biasing and reference generation |
| Power Dissipation | 5 W @ TEC = 140 °C - enables sustained operation in compact, thermally constrained military enclosures |
| Dynamic Impedance (ZZ) | 650 Ω @ IZT - limits output voltage variation under load transients in precision feedback loops |
| Reverse Leakage (IR) | 0.4 μA @ VR = 182 V - ensures minimal parasitic current in high-impedance sensing nodes |
| Temp Coefficient (αVZ) | +0.115 %/°C @ IZT - quantifies drift magnitude for temperature-compensated reference designs |
| Max Surge Current | 19.8 A @ 8.3 ms - supports transient overvoltage suppression without failure in power rail protection |
| Operating Temperature | -65 °C to +175 °C - validated for extended-range deployment in space-grade and downhole electronics |
Pinout & Package
Package: Hermetically sealed voidless hard glass case (E package / D-5B outline), with copper end caps and Sn/Pb finish; cathode indicated by band; weight 539 mg; tape-and-reel compliant per EIA-481-B.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Forward conduction terminal | Connected to lower-potential node; carries forward current up to 1.0 A (VF ≤ 1.5 V) |
| Cathode | Zener breakdown terminal | Marked with band; connected to higher-potential node; regulates voltage when reverse-biased above 240 V |
Key Features
| Feature | Design Value |
|---|---|
| Voidless hermetic glass construction | Eliminates moisture ingress and internal delamination, ensuring >20-year reliability in vacuum and humid environments |
| MIL-PRF-19500/356 qualification | Validated for JAN, JANTX, JANTXV, and JANS screening levels - mandatory for DoD and NASA flight hardware |
| Triple-layer passivation | Prevents surface conduction paths and leakage growth under high humidity or ionizing radiation |
| Category I metallurgical bond | Internal tungsten-copper interface withstands >1000 thermal cycles between -65 °C and +175 °C without bond fatigue |
| Nonsensitive to ESD | Passes MIL-STD-750 Method 1020 - no handling precautions needed beyond standard static-safe protocols |
Applications
| Aerospace Power Conditioning | Radiation-Hardened Instrumentation |
|---|---|
Use Scenario: Regulating auxiliary supply rails in satellite power distribution units exposed to thermal vacuum and total ionizing dose. IC Role / Device Role / Timing Role: Shunt voltage reference and overvoltage clamp protecting downstream DC-DC converters. Use Value: Maintains 240 V regulation within ±5% across -65 °C to +175 °C and after 100 krad(Si) TID exposure. |
Use Scenario: Providing stable bias voltage for charge-sensitive amplifiers in nuclear detection systems deployed in reactor containment zones. IC Role / Device Role / Timing Role: Precision Zener reference source for low-noise analog front-end calibration. Use Value: Delivers <0.4 μA leakage at 182 V and +0.115 %/°C TC - minimizing gain drift in high-impedance sensor interfaces. |
| Military Avionics Reference | Downhole Oilfield Electronics |
Use Scenario: Generating reference voltages for ADCs and DACs in radar warning receivers operating in jet engine bays. IC Role / Device Role / Timing Role: High-stability shunt regulator for analog signal chain biasing. Use Value: Survives 1000+ g shock and 20 g vibration per MIL-STD-810G while maintaining regulation integrity. |
Use Scenario: Voltage clamping and rail stabilization in logging-while-drilling (LWD) tools operating at 175 °C ambient. IC Role / Device Role / Timing Role: Overvoltage protector and reference element in high-temperature telemetry modules. Use Value: Operates continuously at 140 °C end-cap temperature with 5 W dissipation - no derating required below 175 °C junction limit. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar Zener regulation applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 1N4991US | Same electrical specs and package; differs only in TR (tape-and-reel) vs. bulk packaging | No functional difference; identical use in automated SMT assembly lines | Select 1N4991US/TR for pick-and-place compatibility and traceable reel-based procurement |
| 1N4991 | Same die and specs but axial-leaded DO-41 package; no "US" suffix indicates through-hole variant | Requires PCB through-hole mounting; unsuitable for surface-mount-only designs | Choose 1N4991 only if legacy board layout mandates axial leads or manual assembly |
Compared with 1N4991US and 1N4991, the 1N4991US/TR offers identical Zener performance and reliability in a surface-mount E-package optimized for automated production, while avoiding mechanical stress risks associated with axial lead bending or solder joint fatigue in high-vibration environments.
Availability
1N4991US/TR is available at Aetrix Electronics and suitable for aerospace power conditioning, radiation-hardened instrumentation, and military avionics requiring stable component supply with full MIL-PRF-19500 traceability and lot-level documentation.
Supply support for 1N4991US/TR 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
Microsemi (now part of Microchip Technology) is a U.S.-based semiconductor company specializing in high-reliability, radiation-tolerant, and defense-grade analog and mixed-signal components.
The 1N4991US/TR belongs to Microsemi's legacy MIL-qualified Zener series designed specifically for mission-critical voltage regulation in aerospace, defense, and nuclear instrumentation where failure is not an option.
FAQ
What is the Zener voltage tolerance for 1N4991US/TR?
The 1N4991US/TR has a nominal Zener voltage of 240 V with a standard tolerance of ±5%, as specified in the Microsemi SD44A datasheet. No suffix letter (e.g., "C" or "D") appears on the part number, confirming the 5% tolerance grade. This tolerance applies at 25 °C and IZT = 5 mA, and remains valid across the full -65 °C to +175 °C operating range per MIL-PRF-19500/356 requirements.
Does 1N4991US/TR require derating above 140 °C?
Yes - the 1N4991US/TR is rated for 5 W power dissipation only at an end-cap temperature (TEC) of 140 °C. Above that, power must be linearly derated to zero at 175 °C, per the absolute maximum ratings table. This derating reflects thermal resistance of 7 °C/W junction-to-end-cap and ensures safe operation without exceeding the 175 °C maximum junction temperature.
Is 1N4991US/TR compatible with lead-free reflow processes?
No - the 1N4991US/TR features Sn/Pb (tin/lead) terminations on copper end caps, as confirmed in the mechanical specifications. It is not RoHS-compliant and is incompatible with Pb-free reflow profiles. For lead-free assembly, Microsemi recommends evaluating qualified alternatives such as the 1N4991US-TR-LF (if available) or contacting Microchip for updated qualified variants.
What is the surge current rating for 1N4991US/TR?
The 1N4991US/TR supports a nonrepetitive peak Zener surge current (IZSM) of 19.8 A for an 8.3 ms half-sine waveform, as listed in the Electrical Characteristics table. This rating enables reliable clamping of transient overvoltages in power supply inputs and sensor protection circuits without degradation or parametric shift.
How is polarity identified on 1N4991US/TR?
Polarity on the 1N4991US/TR is indicated by a visible cathode band on the glass body - the banded end is the cathode, which must be connected to the higher-potential node during reverse-bias Zener operation. The unmarked end is the anode. This marking is consistent across all 1N49xxUS devices and aligns with JEDEC-standard diode polarity conventions.
1N4991US/TR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Microchip Technology
- Series:
- -
- Package/Case:
- SQ-MELF, E
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Voltage - Zener (Nom) (Vz):
- 240 V
- Tolerance:
- ±5%
- Power - Max:
- 5 W
- Impedance (Max) (Zzt):
- 650 Ohms
- Current - Reverse Leakage @ Vr:
- 2 µA @ 182 V
- Voltage - Forward (Vf) (Max) @ If:
- 1.5 V @ 1 A
- Operating Temperature:
- -65°C ~ 175°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- E-MELF
1N4991US/TR FAQ
1.How can I place an order for 1N4991US/TR through Aetrix?
Please submit a Request for Quotation (RFQ) for 1N4991US/TR 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 1N4991US/TR reliable?
The price and inventory of 1N4991US/TR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 1N4991US/TR is usually 5 days.
3.What payment methods are accepted for 1N4991US/TR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 1N4991US/TR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 1N4991US/TR?
1N4991US/TR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 1N4991US/TR 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 1N4991US/TR?
For technical support, including 1N4991US/TR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 1N4991US/TR requirements.
6.How does Aetrix verify that 1N4991US/TR is sourced from the original manufacturer or authorized distributors?
All 1N4991US/TR 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 1N4991US/TR meets industry standards.
7.What is the process for return or replacement of 1N4991US/TR?
All 1N4991US/TR units undergo pre-shipment inspection (PSI). If there is an issue with 1N4991US/TR, 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 1N4991US/TR part is unused and in its original packaging.
Return procedure for 1N4991US/TR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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