For determining the dynamic ON-resistance R dyn,on of a power transistor, the voltage and current waveforms have to be measured during the switching operation. The novel heterostructure wide-bandgap (e.g., AlGaN/GaN) transistors inherently suffer from the current collapse phenomenon, causing the dynamic ON-resistance to be different from the static. Measuring voltage waveforms using an oscilloscope distorts the characteristics of an amplifier inside the oscilloscope when the range of the measurement channel is not set wide enough to measure both ON-state and OFF-state voltage levels, resulting in failure to accurately measure the voltage waveforms. A novel voltage clamp circuit improving the accuracy of the transistor's ON-state voltage measurement is presented. Unlike the traditional clamping circuit, the presented voltage clamp circuit does not introduce delay caused by RC time constants, keeping the voltage waveform clear, even during state transitions of the device under test. The performance of the presented circuit is illustrated by measurements on a 2-MHz inverted buck converter.

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Wide-bandgap (WBG) semiconductors, such as gallium nitride (GaN), are more and more being used in switching power devices. An AlGaN/GaN/AlGaN Double Heterojunction Field Effect transistor (DHFET) was developed in previous work and needed to be tested. The used test circuit was a buck converter. This type of converter, in addition with the normally-on switching behaviour of the GaN-based transistors, requires dedicated gate drive circuitry, resulting in the development of three types of gatedrivers. This paper presents the topology and performance of these drivers. Because of the type of converter, the drivers need to be galvanically isolated. Furthermore, because the experimental GaN transistors are normally-on, the drivers need to be robust so that they apply a negative gate-to-source voltage to switch off the transistor in case an error occurs in the driver. A third requirement for the drivers is that it has to be easy to adjust the voltage levels, in order to test the devices at different gate-to-source voltage conditions. A final requirement is that it has to be possible to construct the drivers with readily available electronic components. Because the drivers are galvanically isolated, there is a parasitic isolation capacitance in the DC-DC-converter of the drivers. This gives rise to a common-mode current which possibly can disturb the operation of the driver. The article also discusses this common-mode problem.

This paper calculates the electric and magnetic fields and the Poynting vector around two infinitely long parallel cylindrical conductors, carrying a DC current. Also the charges on the surface of the wire are calculated, and their distribution is visualized. The wire is assumed to be perfectly electrically conducting. Furthermore, the Hall effect is ignored. In literature [1], the problem of determining the electric field is usually tackled using an equivalent model consisting of two line charge densities, producing the same electric field. In this work, the Laplace equation is rigorously solved. The authors found no work explaining the solution of the Laplace equation with boundary conditions for this problem and hence thought it was useful to dedicate a paper to this topic. The method of separation of variables is employed and a bipolar coordinate system is used. After solving the appropriate Sturm-Liouville problems, the scalar potential is obtained. Taking the gradient yields the electric field.

A method for solving the full equations of Maxwell for circuits with discrete non-linear, non-ideal elements is presented. To this end the method of moments is used in combination with a classical circuit simulator. Both operate in the frequency domain. A few methods to greatly accelerate the calculations are also presented. The methods are implemented and tested in Matlab®.