By Why Device Selection Deserves Care
The power device is the most consequential component in a converter. It sets the voltage class, the losses, the heatsink size and, in many cases, the reliability of the whole product. IXYS offers a broad portfolio across four device families, and choosing the wrong type or rating costs time and money. This guide walks through a repeatable method for selecting an IXYS power MOSFET, IGBT, thyristor module or fast recovery diode.
Step 1: Fix the Voltage Class
Start with the DC bus. A 380 to 480 V AC supply rectifies to roughly 560 to 680 V, and switching overshoot adds more, so a 600 V or higher device provides the necessary margin for the switch. Lower-voltage systems may use a lower class. Never choose the voltage class from the nominal bus alone; include the switching overshoot you expect, because the device must survive the peak, not the average.
Overshoot and Margin
The commutation loop inductance and the switching speed set the overshoot. Leave at least fifteen percent margin between the worst-case peak and the blocking voltage, and measure overshoot at the device terminals during validation, not at the bus.
Step 2: Set the Current
Continuous current plus overload sets the current rating. A motor drive may draw 150 percent of rated current during acceleration, and a welder draws repetitive pulses. Choose a device whose rated current covers the worst case at the expected case temperature, then verify junction temperature with the thermal path. Current ratings are specified at a case temperature, so a hot environment requires derating.
Switching Frequency
Switching frequency is the next filter. Below about 15 kHz, conduction loss dominates, so a low saturation voltage IGBT is efficient. Above that, switching loss grows quickly, so a HiPerFAST IGBT or a fast power MOSFET becomes attractive. This is the single most important decision between device families.
Step 3: Choose the Device Type for the Function
Each position in a circuit wants a particular device. The active switch is a MOSFET or an IGBT: a MOSFET for fast switching and a simple gate, an IGBT for high-voltage, high-current switching. The freewheeling path wants a fast recovery diode, with the DSEI version for the shortest recovery and the DSEP version for softer behavior and lower EMI. Phase control, soft-start and rectification want a thyristor, whose latch-on behavior and high surge capability are advantages rather than limitations.
Packages and Isolation
Packages matter as much as the chip. The isolated TO-247AD and SOT-227B packages let several devices share a common heatsink without an extra insulating layer, which simplifies the mechanical design and improves heat transfer. The TO-240AA thyristor package does the same for phase-control modules. Choose the package for your cooling and board, not just for convenience.
Step 4: Confirm the Thermal Design
Thermal design decides reliability. Begin from the datasheet junction-to-case thermal resistance, add the interface and heatsink resistance, and verify junction temperature at worst-case current and ambient. For a MOSFET or IGBT, use the hot on-resistance or saturation voltage; for a thyristor, account for the average current plus surge duty. Use a thin, uniform thermal interface material and the specified mounting torque.
Step 5: Validate on the Bench
Before committing to volume, build a prototype and measure gate waveforms, turn-off overshoot and case temperature under load. Compare the measured loss with the datasheet estimate and adjust the gate resistor, snubber and heatsink as needed. Measured data removes the guesswork and prevents late-stage surprises. BeiLuo's FAE team can support this validation and compare candidate devices on your operating point.
Documentation and Supply
Every IXYS device BeiLuo ships is factory-traceable and includes an import declaration, a certificate of origin and a RoHS compliance file. Mainstream devices are held in regional stock, so a validated design moves smoothly from prototype to production. Selecting the right device is the first step; keeping it supplied is the second, and BeiLuo supports both.