Integrated Coreless Transformer

Even though semiconductor manufacturers routinely integrate several hundred thousand transistors on an IC, adding a single inductor has been nearly impossible. A technique developed by Infineon Technologies integrates two windings to provide a coreless transformer (CLT). Additional easily integrated circuitry allows the technique to provide a high level of isolation in high-voltage circuits.

Typical isolation techniques for high-voltage switches with a half-bridge topology (a high-side and low-side switch) include high-voltage ICs with level shifters, optocouplers or isolation transformers. If galvanic isolation is required, the most common technique uses optocouplers to achieve low cost. However, optocouplers have slow transfer characteristics that degrade over time. The more expensive alternative is a pulse transformer. Integrating the windings of a planar transformer in an IC reduces the cost and maintains the high isolation capability.

A sufficiently thick layer of silicon oxide separates the planar primary and secondary windings of the CLT. Because of the size and spacing of the coils, a transformer core is not required to concentrate the flux. However, the transformer can only transmit narrow pulses, so the design uses a transmitter for the primary side with a receiver on the secondary side. The transmitter is on a separate chip than the CLT and the receiver with wirebonds connecting the two units.

To take advantage of this isolation capability, the CLT circuitry has been integrated into a half-bridge driver IC. As part of Infineon’s EiceDRIVER family, the 2ED020I12-F dual-channel IGBT driver handles dv/dt’s up to 50 kV per ìsec and drives IGBT and MOSFET power stages with up to 1,200V breakdown voltage. The specially encoded signals transmitted between the transmitter and receiver suppress EMI that could be generated by variations of the high-side supply ground or the magnetic flux density. A propagation delay introduced into the low-side driver assures a maximum difference of the propagation delay time of 10 nsec between the transmitter, coreless transformer and receiver.

Targeted applications for the half-bridge driver IC include ac-standalone drives, uninterruptible power supplies (UPS), welding and various applications using 600 and 1,200V transistors.

CONTACT: Mario Campello, Infineon Technologies, Tel.: 908-236-5603; e-mail: Mario.Campello@infineon.com

Get more information on Infineon Technologies’ 2ED020I12-F dual-channel IGBT driver IC.

	Integrated Transformer: A transmitter on the primary side and receiver on the secondary side allow a coreless transformer to provide over 1,200V isolation. The initial application of this circuitry is in a high-voltage half-bridge gate driver.