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Insulating IGBT driver with PCB integrated capacitive coupling elements

Isolierter IGBT-Treiber mit PCB integrierten kapazitiven Koppelelemente
: Zeltner, S.

Energietechnische Gesellschaft -ETG-:
CIPS 2010, 6th International Conference on Integrated Power Electronics Systems. Proceedings : March, 16 - 18, 2010 Nuremberg/Germany
Berlin: VDE-Verlag, 2010 (ETG-Fachbericht 121)
ISBN: 978-3-8007-3212-8
ISSN: 0341-3934
International Conference on Integrated Power Electronics Systems (CIPS) <6, 2010, Nuremberg>
Conference Paper
Fraunhofer IISB ()
gate; driver; IGBT

In many power electronic applications galvanic isolated IGBT/MOSFET drivers are advantageously used. The main reasons are safety issues, driving high voltage power semiconductors with blocking voltages of typically 600 V or above and avoiding or minimizing unwanted ground current loops. The last can disturb the driver or the whole power electronic system. In this paper a new method for achieving galvanic isolation in high voltage drivers based on printed circuit board (PCB) integrated capacitive coupling elements will be described. The suggested coupling element consists of a pair of plate capacitors by using copper layers and prepregs of a PCB. First, the influence of the isolation barrier coupling capacitance, which is one of the main important parameters of a galvanic isolated d river, is illustrated by a simple model of the capacitive current loop. As a result it is stated that the coupling capacitance should be lower than 5 pF to achieve high dU/dt levels of at least 100 kV/μs with the modeled driver circuit. Hereby and taking into account the isolation characteristics of the commonly used FR4 PCB material, an integrated capacitive coupling element is designed. With 360 μm isolation distance, and a plate surface of approximately 8 mm², a capacitance of about 1 pF is achieved. A comparison of the developed capacitive coupling element with a comparable inductive coupling element (transformer) shows that the former has advantages due to a much lower current consumption and less dependency on parasitic inductancies. Therefore using galvanic isolat ed drivers in system integrated power electronics means achieving very small solutions. On the other side high isolation voltages on PCBs require wide creepage and clearance distances, especially at higher humidity levels. For solving this conflict a special layout is suggested, were the both sides behind the isolation barrier of the driver are placed on different sides on the PCB by using blind and buried vias. In addition a method for transmitting the switching signal over the isolation barrier is suggested. The well known Manchester coding is applied to use the advantages of phase modulated signals. Reducing the complexity for decoding the switching signal, it is suggested to transmit the carrier frequency by a second capacitive coupling element. Hereby, coder as well as decode r could be realized by a simple exclusive logic or gate. To verify the new isolation method a half bridge driver was built up. With that a bidirectional buck-boost DC/DC converter, operating at a DC link voltage of 300 V, was successfully controlled. Moreover measurements with a standardized burst generator show, that failure free operation of the driver are possible up to high dU/dt levels.