Transmission line losses—driven by skin effect and dielectric properties—play a critical role in degrading high-speed signal integrity and eye performance.
Transmission line loss directly affects eye diagram quality, with around −12 dB at Nyquist marking the limit before signal integrity rapidly degrades without equalization.
Power conversion relies on fast-switching MOSFETs and IGBTs that use low-voltage gate-drive signals to control high-voltage, high-current switching efficiently.
There are a multitude of circumstances that make power conversion a necessity. Power conversion, of course, is the converting of electric power from one form to another, from one voltage to another, or one frequency to another; it also encompasses any/all combinations of these.
Power conversion can take various forms:
AC-AC: AC line voltage conversion to another voltage and/or frequency
AC-DC or DC-AC: AC line voltage conversion to a specified DC voltage or vice versa
DC-DC: DC voltage conversion to a different specified DC voltage
At the heart of any power-conversion scheme are fast-switching power semiconductor devices to enable the conversion in the most efficient manner. These devices typically operate at switching frequencies from 1 to 100 kHz. Note that power conversion does not encompass typical 50/60-Hz core/coil devices such as conventional utility step-up or distribution transformers.
Figure 1: The basic building blocks of power conversion circuits are the power MOSFET and the IGBT; shown are (left) an N-channel enhancement-mode MOSFET and (right) a P-channel (minority carrier) IGBT
The mainstay building blocks of power conversion are the power MOSFET and the IGBT (Figure 1). These devices both operate in essentially the same way: a gate drive controls switching of current that flows between the drain and source (in the power MOSFET) or the collector and emitter (in the IGBT).
In the context of a power-conversion system, the power semiconductor can be thought of as a very fast switch that can withstand a rated blocking voltage, typically in the hundreds of volts or even more than 1 kV. They can conduct a large amount of current with very low resistance (low forward-voltage drop). Switching rates are in the kilohertz range (Figure 2).
Figure 2: Power semiconductors are very fast-switching devices with high blocking voltages and low forward-voltage drops
As mentioned earlier, switching in the power-semiconductor device is controlled through the gate-drive signal. A pulse-width-modulated (PWM) signal is applied to the device's gate lead to control the switching. This signal, which is typically from 3 to 24 V in amplitude, activates the device's switching at the rate governed by the gate-drive signal (Figure 3). Thus, a low-voltage signal on the gate drive controls switching of very high voltages on the output side of the device.
Figure 3: The gate-drive signal controls the switching activity of the power semiconductor
Because the gate-drive signal is floating at the full (or half, depending on topology) DC bus voltage, there are some probing concerns. For very low-voltage drives of ~50 V or less, passive probes might be feasible. For higher voltages, use a high-voltage differential probe with isolation of 1000 VRMS from channel to channel and from channel to ground. Connecting a passive probe to a 600-V inverter circuit to look at the gate-drive signal will not turn out well for your oscilloscope.
Ken Johnson presented a webinar series titled Essential Principles of Power. Part 2 of that series Power Conversion Fundamentals - From Semiconductor Devices to Complex Drives covers more details on this topic. Click the button below to watch the webinar, or download the transcript to preview the webinar content.
Kenneth Johnson has managed oscilloscope and probe product lines, power applications and HV T&M equipment. He holds a B.S.E.E. from Rensselaer Polytechnic Institute. He enjoys playing ice hockey, cross-country skiing and bicycling in his spare time.
Electrical power spans generation, distribution, and consumption—where motors and modern power electronics dominate global energy use and measurement challenges.
AC line power is a rotating voltage vector measured in RMS terms, with peak, peak-to-peak, and rectified values that differ significantly from the familiar “120 VAC” rating.
Three-phase AC voltages consist of three balanced sinusoidal vectors separated by 120°, with measurable differences between line-to-line and line-to-neutral values.
AC line current is a rotating sinusoidal vector—single- or three-phase—whose accurate measurement depends on system configuration and the right choice of current sensor.
