High-insulation gate-drive transformer for automotive power MOSFETs

July 31, 2015 // By Graham Prophet
Designed for use in automotive converter circuits, Premo’s GDAU series of transformersoffers high insulation, greater than 3kV, and supports double-transistor control in a reduced-size SMD package.

Embedded AC/DC and DC/DC converters are a growing technology in the automotive marketplace. For EV and HEV cars onboard battery chargers and 14V power supplies are required to ensure the transfer of energy from the 50/60Hz mains when charging, [through to] the equipments used during a drive (ECUs, radio-GPS systems, lighting…). The related power electronics involves not only transformers and filtering chokes built in half- or full-bridge topologies but also switches such as IGBTs or MOSFETs that have to be accurately driven to deliver the expected output voltage. The control-loop often requires a high level of insulation between the primary side connected to the HV DC-bus (typically 350-800V) and the gate of the transistors (10-15V).

Premo (Málaga, España has developed a high isolated gate-drive transformer for such applications. The GDAU series is intended for use where a small, insulated SMD transformer is required to control the MOS transistors. This less-than-8mm height device guarantees an insulation level of 3 kV and a creepage distance greater than 5 mm. The use of special insulated wire and special construction lower the parasitic elements to values (the leakage inductance is 2 µH max and the primary-secondary stray capacitance is less than 12 pF) for a switching frequency in the 90-125 kHz range. The GDAU-001 variant provides a 1:1+1 turn-ratio that can drive two transistors of the same polarity at once. It can withstand 150 V µsec without any noticeable saturation (15V control at 100 kHz for example).

The GDAU series shows a magnetising inductance value of no less than 400 µH to prevent the output control voltage from any noticeable droop. The low DC resistance values of the windings ensure its capability to drive currents up to 0.5 Arms continuous without overheating. It is produced in SMD compatible form. The series is a design fully compliant with the automotive AEC-Q200 standard. It has been validated in operation from -40 to +155°C. With only