Microchip Technology 688-18

Overview

688-18 from Microsemi is a high-voltage silicon stack diode rated for 18 kV working peak reverse voltage (VRWM), 0.35 A average rectified forward current at 100 °C, 30 V max forward voltage at 0.4 A per leg, 500 ns maximum reverse recovery time (trr), and 150 °C junction temperature - used in high-reliability DC power supplies for industrial X-ray and pulsed radar systems.

For engineers reviewing the 688-18 datasheet, 688-18 pinout, 688-18 application, or 688-18 equivalent, key selection criteria include VRWM tolerance, thermal resistance (R_θJC = 25 °C/W per package), surge rating (20 A IFSM), voidless glass construction, and RoHS-compliant matte tin termination.

Technical Context

This device is a multi-die series-connected high-voltage stack built with voidless glass-encapsulated diodes in an epoxy-filled plastic case. It delivers controlled avalanche behavior and fast recovery (trr ≤ 500 ns) under 10 mA forward/10 mA reverse test conditions, enabling stable operation in high-dV/dt switching environments.

Thermal management relies on bonded plate mounting via brass 10-32 tapped inserts, supporting junction-to-case thermal resistance of 25 °C/W per package and continuous operation up to 150 °C. The device meets MIL-PRF-19500 similarity requirements and is marked with anode/cathode polarity and date code.

Key Specifications

Pinout & Package

Package: Epoxy-filled plastic housing with voidless glass diode elements; brass 10-32 tapped mounting inserts on bottom; gold-plated brass terminals with RoHS-compliant matte tin finish; weight ≈ 70 g; overall dimensions: 75.82–76.58 mm (B) × 53.59–54.36 mm (C) × 18.80–19.56 mm (D).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage rectifier applications.

Compared with 688-18, the 688-20(R) offers higher voltage margin but less current drive, while the 688-15(R) trades voltage rating for increased current capacity - both share identical mechanical form factor and fast-recovery performance.

Availability

688-18 is available at Aetrix Electronics and suitable for industrial X-ray power supplies, pulsed radar transmitters, and capacitor charging systems requiring stable component supply across extended production lifecycles.

Supply support for 688-18 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 Corporation (now part of Microchip Technology) designs high-reliability analog and RF semiconductors for aerospace, defense, and industrial markets.

The 688-series high-voltage stacks were developed specifically for ruggedized DC power conversion in mission-critical pulsed-power and radiation-generating equipment.

FAQ

What is the maximum working peak reverse voltage (VRWM) specification for the 688-18?

The 688-18 has a VRWM rating of 18 kV, meaning it is designed to block up to 18,000 volts DC or peak AC reverse voltage continuously without breakdown. This value is confirmed in the Electrical Characteristics table on page 3 of RF01099 Rev A and defines the upper limit for safe operation in high-voltage hold-off applications such as X-ray generator supplies.

Does the 688-18 have fast recovery characteristics, and what is its trr value?

Yes, the 688-18 includes the "R" suffix indicating fast recovery with a maximum reverse recovery time (trr) of 500 ns, measured under IF = 10 mA, IRM = 10 mA, and IR(REC) = 5 mA conditions. This parameter is essential for minimizing switching losses and preventing false triggering in high-frequency pulsed power circuits using the 688-18.

What is the average forward current rating for the 688-18 at 100 °C case temperature?

The 688-18 is rated for 0.35 A average rectified forward current (IO) when the case temperature is maintained at 100 °C, as specified in the Maximum Ratings table on page 1 of RF01099 Rev A. This value reflects real-world thermal derating and must be used with the 25 °C/W R_θJC to calculate required heatsink performance.

Is the 688-18 RoHS compliant, and how is compliance indicated in the part number?

Yes, the 688-18 is RoHS compliant, indicated by the "e3" suffix in the full orderable part number 688-18(R)(e3). The device uses matte tin plating on brass terminals instead of Sn/Pb, satisfying EU Directive 2011/65/EU requirements - confirmed in the Mechanical and Packaging section of RF01099 Rev A.

How is thermal management implemented for the 688-18, and what is its junction-to-case thermal resistance?

The 688-18 uses a bonded plate mounting interface with brass 10-32 tapped inserts on the bottom surface to maximize heat transfer. Its junction-to-case thermal resistance is 25 °C/W per package, enabling effective conduction cooling when mounted to a heatsink. This value is critical for calculating junction temperature rise and ensuring operation remains within the +150 °C absolute maximum limit.