Micsig | Application of Optical Isolated Probes in Testing High-Power DC Power Supplies

Third-generation semiconductor materials, especially Silicon Carbide (SiC) and Gallium Nitride (GaN), show great market prospects in electric vehicles, renewable energy, industrial power supplies, military and aerospace, fast charging technology, wireless communication, consumer electronics, and other fields. These materials have advantages such as high thermal conductivity, high breakdown field strength, high saturation electron drift velocity, and high bond energy, making them perform well under harsh conditions of high temperature, high pressure, high frequency, and radiation resistance. Although these materials have significant performance advantages, their fast switching speed also poses considerable challenges for testing and measurement.

In practical applications, the measurement of the Vgs of SiC MOSFETs is a technical pain point. The switching speed of SiC devices is very fast, which leads to a significant amount of harmonic energy in the high-frequency harmonic components. During actual development and debugging, oscillations in the Vgs signal of the upper tube are observed, and engineers are unable to determine the authenticity of the signal. This requires testing equipment to have high common-mode rejection capabilities even in the high-frequency range.

• Device Under Test: A high-power DC power supply project from a major power supply factory in Guangdong
• Test Points: Full-bridge circuit upper tube voltage waveform (Vgs) & upper tube Id current
• Customer Pain Point: When developing power supply products with SiC devices, traditional differential probes are used to measure the upper tube Vgs, resulting in signal oscillations that are difficult to analyse and locate problems.

• Optical Isolation Probe MOIP Series： MOIP1000P
• High-Resolution Oscilloscope MHO3 Series： MHO3-5004
•  Flexible Current Probe RCP Series： RCP600XS

The following on-site testing image shows Micsig’s high-resolution oscilloscope MHO3 series MHO3-5004, optical isolation probe MOIP series MOIP1000P, flexible current probe RCP series RCP600XS, and the device under test.

The following test point connection diagram shows the optical isolation MOIP1000P connected to the upper tube Vgs signal with MMCX coaxial cable, and the Rogowski coil RCP600XS monitoring the upper tube Id current signal by passing through the chip pins.

The following oscilloscope display shows the upper tube Vgs and Id test waveforms, with channel 4 (green waveform) displaying the upper tube Vgs signal and channel 2 (blue waveform) displaying the upper tube Id current signal.

Before coming into contact with Micsig’s optical isolation probe, we used differential probes for testing. The waveforms did indeed show some oscillations when the upper tube was turned on/off; due to lack of experience, our engineers did not suspect the testing equipment and spent a lot of time changing circuits, adjusting parameters, etc., but the oscillation problem still existed. This time, using Micsig’s optical isolation probe, we started with a try-it-out mentality, and the actual test results were very good. The waveforms at the test points were very similar to our theories, solving a major problem in our research and development.

Micsig (Micsig), based on its exclusive SigOFIT™ technology, has an optical isolation probe MOIP1000P with a common-mode rejection ratio as high as 180dB, still reaching over 100dB in the 1GHz frequency band. Using it can more effectively perform circuit testing and verification for power supply designs with SiC and GaN as core devices, allowing engineers to capture the real upper tube Vgs voltage waveforms, helping engineers accurately analyse whether their circuit designs meet the requirements, ensuring the high performance and reliability of the products. This not only improves their product quality but also strengthens market competitiveness. Micsig’s innovative technologies and solutions provide strong support for more power supply design companies, jointly promoting the progress and development of the industry’s technology.