Application example of an optically isolated probe in the double-pulse testing of engine control units for new energy vehicles
Case Introduction
Dual-pulse tests allow engineers to accurately evaluate the key performance parameters of power components in motor controllers, such as switching speed, switching losses, voltage response, and current characteristics. This information is crucial for optimizing controller design and improving overall system efficiency.
However, measuring the upper switch gate-source voltage (Vgs) during a double-pulse test presents a significant technical challenge. The measurement system must not only offer a wide bandwidth to capture rapid switching operations, but also exhibit exceptionally high common-mode rejection to suppress interference generated during high-speed operation.
Test example
Device to be tested:
Core control board of an engine control unit for a new energy vehicle
Checkpoints:
Upper switch Vgs and upper switch Vds in the bridge circuit of the engine control unit
Customer challenge:
When conventional differential probes were previously used to measure upper switch Vgs, strong signal fluctuations occurred. These distortions made it extremely difficult to accurately analyze the signal waveforms or to determine the cause of circuit problems.
Test site
The on-site test setup included the Micsig high-resolution oscilloscope (MHO3 series - MHO3-5004), an optically isolated probe (MOIP series - MOIP1000P), a high-voltage differential probe (DP1502) and the device under test.
During the double-pulse test, the optical isolation probe was used to measure the upper switch Vgs. This part of the motor control is the core component of the switching module and operates at extremely high speeds, often in the nanosecond range. Under such conditions, strong electromagnetic interference (EMI) is generated due to the rapid voltage and current transitions.
The high common-mode rejection ratio (CMRR) of the optical isolation probe effectively suppresses these disturbances, allowing the true waveform characteristics to become visible. Even in environments with strong EMI, the probe delivers clean, stable voltage signals.
In comparison, the disturbances acting on the lower switch are relatively weaker, so differential probes can meet the measurement requirements in this part of the circuit. Currently, differential probes with a bandwidth of approximately 200 MHz and an isolation of 1500 V are used for most dual-pulse tests.
Since the chip pins of power devices are often very thin, conventional contact-based current measurement methods may not be suitable. Therefore, a Rogowski coil is recommended for measuring the lower switch leakage current (Id). As a non-contact current measurement solution, the Rogowski coil enables accurate current sensing without stressing or damaging the delicate device pins, while also simplifying the test setup.
The actual measured waveforms are shown below: The optical isolation probe measures the upper switch Vgs, the differential probe detects the lower switch Vds and Vgs, and the Micsig Rogowski coil RCP1200XS is recommended for measuring the lower switch Id.
Customer feedback
In previous dual-pulse tests, the upper switch Vgs signal exhibited significant common-mode noise. Due to limited knowledge of the CMRR performance of differential switches, the initial test results were not questioned. It was assumed that the observed oscillations originated from the system design itself, leading to repeated circuit modifications and validation efforts—but the problem remained unresolved.
After switching to the optically isolated probe from Micsig, the measurement quality improved dramatically. The probe exhibited a high CMRR even in the high-frequency range, and the previously observed oscillations in the waveform disappeared. The acquired signals corresponded exactly with the theoretical expectations and the simulation results, confirming the actual behavior of the circuit.
About Micsig Shenzhen Micsig Technology Co., Ltd.
is a leading manufacturer and solution provider specializing in signal testing and measurement equipment. As a recognized national high-tech enterprise and innovation-driven company, Micsig is dedicated to advancing cutting-edge measurement technologies. With a strong focus on oscilloscopes and oscilloscope probes, Micsig has consistently remained at the forefront of industry innovation. The company is recognized as a pioneer in flat-panel oscilloscopes and a market leader in optical isolation probe technology. Guided by professionalism and a clear mission, Micsig continuously pushes the boundaries of technology to help engineers and businesses achieve greater efficiency and performance. Every innovation reflects the commitment to exploring new possibilities and helping to shape future trends in electronic measurement technology.
Conclusion
The MOIP1000P optical isolation probe from Micsig offers an extremely high common-mode rejection ratio (CMRR) of up to 180 dB and a CMRR of more than 100 dB at 1 GHz bandwidth. This outstanding performance enables highly accurate and reliable testing and validation of circuits built with SiC and GaN power devices.
By accurately capturing the real upper voltage waveform of the switch Vgs, engineers can confidently assess whether motor control designs meet performance requirements and ensure both high efficiency and long-term reliability in new energy vehicle applications.
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