Introduction

An IXYS IGBT combines a MOSFET-like voltage-driven gate with the low saturation voltage of a bipolar transistor, so it drives simply and conducts efficiently at high current. That makes it the default switch for medium-frequency, high-power converters such as motor drives, UPS, choppers and high-frequency supplies. This application note explains the practical rules for driving and cooling an IXYS IGBT, covering the gate drive, the dead time, the freewheeling path and the thermal design.

Gate Drive

An IGBT is driven with a gate voltage, but the gate resistor sets the switching speed and therefore the balance between switching loss and overshoot. Start from the datasheet value, then tune the resistor until ringing and overshoot fall within your limits, and reduce it if switching loss is too high. A negative off-state supply improves robustness at high dv/dt and prevents false turn-on in a half bridge. Keep the gate loop short and place the driver close to the device.

Dead Time

In a half bridge, dead time must be long enough to prevent cross-conduction but short enough to avoid output distortion. Verify it on the bench with a current probe on the phase output, and account for the gate-drive propagation delay and the reverse recovery of the freewheeling diode, which effectively extends the commutation time. Too little dead time causes a shoot-through current; too much distorts the output and reduces efficiency.

Choosing the IGBT Variant

IXYS offers both HiPerFAST and ultra-low VCE(sat) IGBTs, and the choice follows from the operating point. Below about 15 kHz, conduction loss dominates, so an ultra-low saturation voltage device such as the IXGH38N60, with a typical VCE(sat) of 1.8 V, is efficient. Above that, switching loss grows quickly, so a HiPerFAST device such as the IXGH30N60C2, with a square reverse-bias safe operating area, is the better choice. Estimating both loss components at the actual frequency is essential.

Ruggedness

The square RBSOA of the IXYS IGBTs provides margin under clamped inductive switching, which is the condition a motor drive or a supply sees when the load is interrupted. Keep the current density within the datasheet rating and respect the short-circuit withstand time, and the device tolerates the transients of real equipment.

The Freewheeling Path

Every IGBT bridge has a freewheeling path, and its diode affects both loss and EMI. The DSEI60-06A fast recovery diode has a very short recovery time for low loss, while the softer DSEP60-06A trades a little recovery time for lower overshoot and EMI. Match the diode's forward current and recovery charge to the switch so the freewheeling path does not dominate losses.

Layout of the Power Loop

The commutation loop formed by the DC-link capacitor and the switching devices dominates overshoot and EMI. Keep the loop tight, place the capacitor close to the devices and measure overshoot at the device terminals, not at the bus. The isolated TO-247AD package helps by shortening the internal connections, but the external layout still decides the switching quality.

Thermal Design

Start from the datasheet junction-to-case thermal resistance, add the interface and heatsink resistance, and verify junction temperature at the worst-case current and ambient. The isolated TO-247AD package mounts with a single screw and a defined thermal path, and several devices can share a common heatsink. Use a thin, uniform interface material and confirm case temperature under load.

Derating in a Hot Environment

Current ratings are specified at a case temperature, so a hot enclosure requires derating. Estimate the actual case temperature from the loss and the thermal path, and confirm the device still meets the current target with margin. A conservative thermal design lowers the failure rate and extends the life of the surrounding components.

Conclusion

An IXYS IGBT rewards a disciplined design: a gate drive with a tuned resistor and a negative off-state supply, correct dead time, a matched freewheeling diode and a conservative thermal path. Get those right, and the converter reaches production with predictable efficiency and reliability.