Sanrex FRD100CA120 | Fast Recovery Diode Power Module — 1200V Vrrm, 100A Ifa, 1.80V Forward Drop, 16600A²s I²t, DCB Isolated Base Plate, 2500V Isolation

Overview

The Sanrex FRD100CA120 is a 1200V / 100A fast recovery diode power module — one of Sanrex's established high-current diode module offerings for industrial power electronics.

In power conversion circuits, not all diodes are equal. Standard rectifier diodes (designed for 50/60Hz mains rectification) store charge in their junction when forward biased and release it as a reverse current when the voltage across them reverses — a phenomenon called reverse recovery. 

For slow rectification at mains frequency, this reverse recovery current is brief relative to the cycle time and has little practical consequence. 

For high-frequency switching circuits, where the applied voltage reverses in microseconds, a slow-recovery diode's reverse current pulse can be as large as the forward current and last long enough to short-circuit the supply rail through the switch, generating destructive current spikes and dissipating significant power.

Fast recovery diodes are built with different semiconductor structures — optimised junction doping profiles, narrow base widths, and controlled lifetimes — to reduce the stored charge and accelerate the reverse recovery process.

The result is a diode that stops conducting in the reverse direction in a fraction of a microsecond rather than multiple microseconds.

The FRD100CA120's 1200V blocking voltage covers the standard DC link bus voltage of 3-phase 400VAC-fed drives (with the approximately 560VDC rectified bus plus derating margin), and the 100A current rating places it in the territory of medium-power variable-frequency drive freewheeling and rectifier applications.

Sanrex (a Shindengen company) has been producing power semiconductor modules for industrial automation since the 1970s, and their FRD series diode modules are recognised in the servo drive and inverter maintenance community as reliable components with predictable electrical characteristics.

The FRD100CA120 fits standard international package footprints used by Semikron, Infineon, Powerex, and other major module manufacturers — a practical advantage for system maintenance when the original module type is unavailable.

Key Specifications

Why 1200V and 100A — Understanding the Application Boundary

The 1200V Vrrm rating defines the maximum voltage the diode blocks when reverse-biased without avalanche breakdown.

In a 3-phase 400VAC system, the rectified DC bus voltage is approximately 565VDC. With standard safety derating (the device voltage rating should be at least 1.5–2× the applied blocking voltage in normal operation, with additional margin for transients), 1200V is the appropriate voltage class for 400–480VAC systems. 

A 600V device would have insufficient margin for transient overvoltages caused by load switching, motor ground faults, and line perturbations. An 1700V device provides more margin but at higher cost and typically slightly higher forward voltage.

The 100A Ifa rating — specified at Tc = 78°C case temperature — defines the continuous forward current the module handles without exceeding the junction temperature limit. The case temperature condition is critical: a diode module's current capacity depends entirely on how well its heat is removed.

At Tc = 78°C (a case temperature that requires adequate thermal management — heat sink, thermal interface material, and adequate air or liquid cooling), the diode conducts 100A continuously.

If the case temperature rises above 78°C because of inadequate cooling, the rated current must be derated according to the module's derating curve.

The Ifsm of 2000A defines the module's ability to survive a short-duration fault current — for example, the discharge of a large DC link capacitor bank through a failed switch in a drive inverter. The I²t of 16,600A²s is the energy absorption limit the diode can withstand without destruction — used to select the appropriate fuse for overcurrent protection.

DCB Technology — What Makes the Module Reliable

The DCB (Direct Copper Bonded) substrate is the foundation of the module's reliability. In a power semiconductor module, the silicon die generates heat during conduction, and this heat must flow through the substrate to the base plate and then to the heat sink.

Any thermal resistance in this path increases the junction temperature for a given power dissipation.

DCB substrate bonds copper layers directly to a ceramic insulator (typically alumina Al₂O₃ or aluminium nitride AlN) using a high-temperature diffusion process, creating a metallurgical bond — not solder, not adhesive — between the copper and ceramic.

This direct bond has lower thermal resistance and better resistance to thermal cycling fatigue than older soldered or epoxy-bonded ceramic substrates.

As the module heats and cools through many operating cycles over years of service, the DCB substrate maintains its thermal connection while solder-bonded structures can develop voids and delaminations that increase thermal resistance and eventually cause premature failure.

The DCB substrate also provides the 2500V isolation between the semiconductor devices (which operate at the DC bus potential) and the base plate (which is mounted to the heat sink, typically at ground potential in the system).

This isolation allows the module to be mounted directly on a metallic heat sink without an additional isolating pad in most installations.

Fast Recovery Diode Applications in Motor Drive Systems

The FRD100CA120's typical applications in variable-frequency drive and servo drive power electronics include several distinct circuit positions:

Freewheeling diodes in the inverter bridge: In a three-phase PWM inverter, each IGBT switch is paired with a freewheeling (anti-parallel) diode. When the IGBT switches off during PWM operation, the motor's inductive current continues flowing through the freewheeling diode until the next switching event.

These diodes must recover quickly from their forward conduction state when the IGBT turns on again — if their recovery is slow, the reverse current flows through the IGBT for the recovery duration, increasing switching losses and stress on the IGBT. 

Fast recovery is therefore a basic requirement for inverter freewheeling diodes.

Boost stage freewheeling in PFC circuits: Active power factor correction circuits use a boost converter topology where a fast diode in the boost output stage blocks the rectified voltage and conducts the inductor current. The diode switches at the boost converter's switching frequency — typically 20–100kHz — requiring fast recovery to minimise losses and conducted EMI.

Brake chopper freewheeling: In drive systems with a brake chopper (a switch that dissipates braking energy in a resistor when the DC link voltage rises), a freewheeling diode is connected across the chopper switch to allow the braking resistor's inductor current to recirculate during the chopper's off period.

FAQ

Q1: What is the difference between a fast recovery diode and an ultrafast diode, and which category does the FRD100CA120 fall into?

The distinction is primarily in the reverse recovery time (trr) — the time from when the diode's current reverses to when the diode fully blocks. Fast recovery diodes typically have trr values in the range of 100–500 nanoseconds, while ultrafast diodes achieve trr below 100ns.

The FRD100CA120's exact trr is specified in the Sanrex datasheet — the FRD series designation indicates fast recovery. For switching frequencies up to approximately 20kHz (common in industrial drive PWM), fast recovery diodes are generally adequate.

For higher frequencies (above 50kHz) in high-performance converters, ultrafast or SiC Schottky diodes may be preferred to reduce switching losses further.

Q2: The Ifsm is 2000A. Can this diode withstand a DC link short circuit without protection?

No. The Ifsm (Non-Repetitive Peak Forward Surge Current) represents the diode's ability to survive a single, brief current pulse — typically defined for a half-cycle sine-wave pulse of specific duration (usually 8.3ms or 10ms per IEC standards).

A DC link short circuit in a drive system can deliver sustained fault currents far exceeding 2000A, and the I²t value (16,600A²s) defines the energy limit the diode absorbs before destruction. 

The semiconductor protection system — upstream fuses, IGBT gate driver desaturation detection, or current-limiting reactors — must clear the fault before the energy through the diode exceeds its I²t rating.

Fuse selection for diode protection uses the I²t value to choose a fuse with a lower I²t let-through value than the diode's rating.

Q3: Is the FRD100CA120 a direct equivalent to similar modules from other manufacturers such as Semikron, Infineon, or Powerex?

The FRD100CA120's electrical ratings (1200V, 100A, 1.80V forward voltage) and standard package footprint with 34mm base width are compatible with the international standard package used by modules from Semikron (SKE100/16, for example), Infineon (DD100N12K), and Powerex in the same rating class.

Mechanical mounting dimensions and terminal positions within this standard package are generally consistent across manufacturers, facilitating cross-replacement.

However, electrical parameters — particularly the reverse recovery time (trr), recovery charge (Qrr), and thermal resistance junction-to-case (Rth(j-c)) — should be compared between the original specification and the replacement module to confirm compatibility in the specific application circuit. 

Different manufacturers' modules in the same rating class may have different dynamic characteristics.

Q4: How should the FRD100CA120 module be mounted to achieve rated current capacity?

The 100A rating at Tc = 78°C requires that the module's base plate temperature is maintained at or below 78°C under full-load operating conditions.

Achieving this requires: thermal interface material (thermal grease or a pre-cut thermal pad) between the module base plate and the heat sink to minimise contact thermal resistance; adequate heat sink thermal resistance for the total power dissipation (at 100A forward current with Vfm = 1.80V, the conduction loss is approximately 180W); and sufficient airflow over the heat sink fins.

The mounting screws should be tightened to the torque specified in Sanrex's datasheet to ensure uniform thermal contact pressure without damaging the module's ceramic substrate.

Q5: The datasheet specifies I²t of 16,600A²s. How is this value used in practice?

The I²t (integral of current squared with respect to time) is the thermal energy that the diode's silicon junction absorbs during an overcurrent event. Fuses are rated with a maximum let-through I²t — the energy they pass during their clearing time.

For the diode to survive a fault cleared by its upstream fuse, the fuse's I²t let-through value must be less than the diode's I²t rating of 16,600A²s.

Fuse selection tables in manufacturer catalogs list I²t let-through values for different fuse ratings and fault current levels, allowing the protection engineer to verify that the selected fuse protects the diode.

A fuse with I²t greater than 16,600A²s would allow enough energy through the diode during clearing to destroy it before the circuit opens.