Selecting the Best Power Device for Power Electronics Circuit Design through Gate Charge Characterization

Focus:

Optimal selection of a superjunction MOSFET, IGBT, or one of the emerging higher-voltage GaN FETs requires evaluation of device losses in the intended application, which in turn requires measurement of a device’s gate charge (Qg) curve. But as this article describes, there are challenges to measuring Qg of these high voltage power semiconductors arising mainly from the requirements for a stable power supply that can provide high voltage and high current (ex. 600 V and 200 A.) Although power semiconductor device manufacturers can afford and have space for the required test systems, many power supply designers do not. To address this problem, Agilent has introduced a new benchtop instrument, the B1506A, for measuring Qg. It employs a new technique for deriving Qg curves, which is described in this article. Example measurements are shown and the instrument’s other measurement capabilities are also described. However, most of the article is devoted to an explanation of gate charge and its relationship to various device parameters; how Qg is used in designing drive circuits including the calculation of driving loss; how switching times are calculated from gate charge and other parameters, and how gate charge is used to calculate switching loss.

What you’ll learn:

• How to understand the role of gate charge in the calculation of driving loss and switching loss for power transistors
• How to understand the meaning of the gate charge curve for power transistors
• How to understand a new measurement technique used by a benchtop instrument to measure the gate charge curve of (high-voltage) superjunction MOSFETs and IGBTs and eventually GanFETs.

Notes:

This article appeared in the May 2014 issue of Bodo’s Power Systems. The print version of the article can be accessed by registered users at http://www.bodospower.com/.

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Author & Publication:

Hisao Kakitani and Ryo Takeda, Agilent Technologies International, Japan Ltd., Bodo's Power Systems, May 12 2014

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