Microchip Technology 1N975A

Overview

1N975A from Microsemi is a silicon 500 mW axial-leaded Zener diode in DO-35 (DO-204AH) package, rated for 39 V nominal Zener voltage with ±10% tolerance, 3.2 mA Zener test current, 80 Ω dynamic impedance at I_ZT, and maximum 9.5 mA DC Zener current. It operates across –65°C to +175°C and serves as a precision voltage reference or shunt regulator in low-power analog circuits.

For engineers reviewing the 1N975A datasheet, 1N975A pinout, 1N975A application, or 1N975A equivalent, key selection criteria include its 39 V regulation point, ±10% tolerance (A suffix), 80 Ω Zener impedance at 3.2 mA, thermal resistance of 250 °C/W (junction-to-lead), and DO-35 glass-body construction suitable for through-hole mounting in industrial power supplies and sensor conditioning circuits.

Technical Context

The 1N975A functions as a shunt voltage regulator by maintaining a stable 39 V across its terminals when reverse-biased above its breakdown threshold. Its Zener knee is characterized at 3.2 mA test current with 80 Ω dynamic impedance, and it exhibits a +0.094 %/°C temperature coefficient - typical for mid-voltage Zeners in this family.

It is designed for operation in ambient or lead-temperature-limited conditions: rated for 480 mW at T_L < 50°C (3/8″ from body), derating linearly to zero at 175°C, with thermal resistance of 250 °C/W junction-to-lead and 310 °C/W junction-to-ambient on FR4 board.

Key Specifications

Pinout & Package

DO-35 (DO-204AH) glass axial-leaded package: hermetically sealed, tin-lead or RoHS-compliant matte-tin plating, cathode indicated by colored band; polarity must be observed - banded end is cathode (positive during Zener operation).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Zener regulation applications.

Compared with 1N975B and MMBZ5259BLT1G, the 1N975A delivers cost-effective ±10% regulation in through-hole DO-35 form, supporting higher surge capability and wider temperature range than SMT alternatives, while offering lower precision than the B-suffix variant.

Availability

1N975A is available at Aetrix Electronics and suitable for industrial power supplies, sensor signal conditioning, and legacy equipment voltage monitoring requiring stable component supply and long-term obsolescence management.

Supply support for 1N975A 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-hardened, and precision analog components for aerospace, defense, and industrial markets.

The 1N957B–1N992B series was engineered to deliver JEDEC-standardized, glass-encapsulated Zener regulation with extended temperature range and proven reliability in harsh environments - particularly for legacy system support and high-stability references.

FAQ

What is the Zener voltage tolerance for 1N975A?

The 1N975A has a nominal Zener voltage of 39 V with a tolerance of ±10%, as indicated by the "A" suffix per Microsemi's documentation. This tolerance applies under standard test conditions at 25°C with 3.2 mA test current. The 1N975A is not rated for tighter tolerances like ±5% (B suffix) or ±2% (C suffix); those require different part numbers in the same family.

What is the maximum power dissipation for 1N975A at room temperature?

The 1N975A is rated for 500 mW steady-state power dissipation at lead temperature (T_L) < 50°C measured 3/8″ from the body. When mounted on an FR4 PCB with specified copper area, its derated power is 480 mW at T_A < 25°C. Exceeding these limits risks thermal runaway or parametric shift; actual safe operating current depends on ambient and heatsinking conditions.

Is 1N975A RoHS compliant?

The base 1N975A is not inherently RoHS compliant; RoHS compliance requires the "e3" suffix (e.g., 1N975Ae3), indicating annealed matte-tin plating per Microsemi's packaging specification. Standard 1N975A uses traditional tin-lead plating. Always verify suffix and ordering code to confirm compliance status for your specific shipment.

What does the cathode band indicate on 1N975A?

The colored band on the 1N975A marks the cathode terminal. During Zener regulation, the banded end must be held at a higher potential than the anode (non-banded end). Forward conduction occurs when the anode is positive relative to the cathode, with V_F ≤1.3 V at 200 mA - though forward operation is not the intended use case for this device.

Can 1N975A replace 1N975B in existing designs?

The 1N975A can functionally replace 1N975B in applications tolerant of ±10% vs. ±5% Zener voltage variation, but not as a guaranteed drop-in substitute. Both share identical package (DO-35), pinout, thermal specs, and Zener impedance (80 Ω), but the wider tolerance may affect circuit accuracy in precision references or tight-threshold detectors.