This page explains how high-voltage differential probes are applied in switching characteristic testing of power semiconductor devices, covering switching time, switching loss, dv/dt and di/dt measurement, along with practical cases involving SiC MOSFETs, IGBTs, GaN HEMTs, three-phase inverters, and automotive high-voltage systems.
The switching characteristics of power semiconductor devices directly determine the efficiency, power density, and reliability of power electronic systems. As third-generation semiconductor technologies represented by silicon carbide (SiC) and gallium nitride (GaN) continue to advance, device switching speeds are entering the nanosecond range, while dv/dt can exceed 50-100V/ns. This creates unprecedented challenges for switching characteristic testing. According to T/CASAS 033-2024, accurate switching measurements require instruments with high bandwidth, high common-mode rejection ratio, and low input capacitance.
High-voltage differential probes are core measurement tools in switching characteristic testing because they effectively solve common-mode interference problems in floating measurements and accurately capture fast transient waveforms. Compared with ordinary single-ended probes, they offer stronger common-mode rejection, wider bandwidth, lower input capacitance, and higher isolation voltage.
In double pulse testing, three-phase inverter debugging, and electric vehicle high-voltage system validation, high-voltage differential probes have become indispensable. This page focuses on their technical advantages, representative application cases, and test setup recommendations.
For fast wide-bandgap devices such as SiC and GaN, the challenge is no longer simply whether the signal can be measured, but whether it can be measured accurately under high common-mode voltage, high dv/dt, and demanding safety constraints. High-voltage differential probes are the key to solving that problem.
Switching time, switching loss, dv/dt and di/dt, floating measurement behavior, and measurement-device matching are the most critical dimensions in switching characteristic testing of power semiconductors.
According to T/CASAS 033-2024, switching time parameters include turn-on delay td(on), rise time tr, turn-off delay td(off), and fall time tf. For wide-bandgap devices such as SiC MOSFETs and GaN HEMTs, these times are often in the nanosecond to tens-of-nanoseconds range, which means the measurement system must have sufficient bandwidth.
Bandwidth selection must be matched to the switching speed of the target device.
Switching losses include turn-on loss Eon and turn-off loss Eoff, calculated by integrating instantaneous power over time.
SiC MOSFETs can reach 50-100V/ns dv/dt, while GaN HEMTs can reach 100-200V/ns, far beyond conventional silicon devices. Accurate dv/dt measurement requires enough bandwidth to preserve high-frequency components, while probe leads should be kept as short as possible to reduce parasitic inductance. For 100V/ns signals, a bandwidth of 500MHz or more is typically recommended.
In half-bridge topologies and three-phase inverters, the reference potential of the high-side device switches rapidly relative to system ground, creating high common-mode voltage. Ordinary single-ended probes can form ground loops, introduce severe common-mode interference, and even damage the oscilloscope or the DUT. High-voltage differential probes are ideal for high-side measurements because they can directly measure floating signals through differential input structure and strong common-mode rejection design.
The value of a high-voltage differential probe is not limited to measuring high voltage. Its real strength lies in maintaining stable and low-distortion measurement in high common-mode, high-speed switching, and high-safety test environments.
Typical high-voltage differential probes can achieve 80-120dB CMRR at DC to low frequency and still maintain more than 60dB at 100kHz. Even if common-mode voltage reaches 1000V, the residual interference presented to the oscilloscope can be suppressed to only 0.1V-1V.
Modern high-voltage differential probes can provide bandwidth from 100MHz to beyond 1GHz, with rise time below 3.5ns, enabling complete capture of nanosecond-level switching transients in SiC and GaN devices.
Input capacitance is typically below 5pF, and premium models can achieve 1-2pF. Low input capacitance minimizes probe disturbance to the measured node and reduces resonance and waveform distortion during fast switching.
High input impedance significantly reduces current diversion and measurement loading, which is especially important for high-impedance nodes and gate-drive waveform observation.
High-voltage differential probes provide electrical isolation between the measurement channel and the oscilloscope. Typical insulation ranges from 1500V to 7000V, which supports medium- and high-voltage power device testing as well as automotive high-voltage platforms.
Specially designed high-voltage differential probes can withstand dv/dt beyond 50V/ns without front-end saturation or severe distortion, making them suitable for high-speed SiC and GaN measurements.
Different devices and systems place different demands on probe bandwidth, voltage rating, CMRR, and connection methods. The following cases show how high-voltage differential probes perform in representative real-world scenarios.
Background: A photovoltaic inverter manufacturer developed a 650V/80A SiC MOSFET half-bridge module and needed to test its switching characteristics at 380V bus voltage and 40A load current.
Challenge: Extremely fast switching, high-side floating measurement, and obvious voltage overshoot caused by parasitic inductance.
Solution: A 100MHz, 1500V high-voltage differential probe with CMRR >80dB@50Hz was used to measure Vds, together with a high-frequency Rogowski coil for drain current.
Result: The full Vds trajectory was captured, including a 39V overshoot. Measured turn-off dv/dt reached 58V/ns and Eoff was 1.8mJ.
Background: A rail transit traction-system manufacturer needed to evaluate a 1200V/100A IGBT module under double pulse test conditions.
Challenge: Tail current during turn-off increases loss, voltage is high, and Vce, Ic, and Vge must all be measured synchronously.
Solution: A 50MHz, 2000V high-voltage differential probe was used for Vce, together with a current probe for Ic.
Result: The turn-off process was clearly divided into three stages, and calculated losses were Eon = 2.5mJ and Eoff = 3.8mJ, with the tail-current stage contributing about 40% of Eoff.
Background: A fast-charger manufacturer developed an MHz-class converter based on 650V GaN HEMTs.
Challenge: Rise time down to 4-5ns and turn-off dv/dt beyond 100V/ns demand very high probe bandwidth and extremely low input capacitance.
Solution: A high-voltage differential probe with bandwidth ≥500MHz and input capacitance below 2pF was used, together with the shortest possible leads and grounding accessories.
Result: The probe successfully captured a 4.2ns turn-on transition, about 80V/ns turn-on dv/dt, and total switching loss of only 15μJ.
Background: A motor-drive manufacturer developed a 10kW three-phase inverter using SiC MOSFET modules.
Challenge: High-side source potential switches between 0V and bus voltage, PWM introduces strong common-mode noise, and multi-phase comparison is required.
Solution: A multi-channel high-voltage differential probe setup was used to measure each phase-leg high-side Vds independently and synchronously.
Result: Clear three-phase high-side waveforms were captured, allowing verification of switching consistency and dead-time settings while supporting EMI optimization.
Background: A new-energy vehicle manufacturer developed an 800V platform and needed to perform high-voltage insulation monitoring and fault diagnostics.
Challenge: The test environment involves electric-shock risk, transient voltage spikes during charge and discharge, and strict EMC constraints.
Solution: A CAT III/CAT IV-rated high-voltage differential probe with isolation above 6000Vrms was used.
Result: The probe captured bus ripple and transient spikes with accuracy meeting ±2%, while avoiding measurable loading on insulation-monitoring circuits.
Probe selection should be based on device type, operating voltage, switching speed, CMRR requirement, and voltage withstand capability, rather than relying on a single bandwidth value alone.
| Device Type | Typical Voltage | Switching Speed | Recommended Bandwidth | CMRR Requirement | Recommended Voltage Rating |
|---|---|---|---|---|---|
| Si MOSFET | ≤900V | Medium (10-30ns) | ≥100MHz | >60dB@1MHz | 1500V |
| IGBT | 600-3300V | Slow (50-200ns) | ≥50MHz | >60dB@1MHz | 2000-7000V |
| SiC MOSFET | 650-1700V | Fast (5-20ns) | ≥200MHz | >80dB@1MHz | 1500-2000V |
| GaN HEMT | 650V | Ultra-fast (2-10ns) | ≥500MHz | >60dB@1MHz | 1500V |
High-voltage measurement is not only about accuracy, but also about safety and repeatability. Operating discipline, error control, and probe calibration are equally important.
High-voltage differential probes play an irreplaceable role in switching characteristic testing of SiC MOSFETs, IGBTs, and GaN HEMTs because of their high common-mode rejection, high bandwidth, low input capacitance, high input impedance, and electrical isolation. As third-generation semiconductor technology and 800V high-voltage platforms continue to expand, proper probe selection, correct test setup, and disciplined operating procedures will remain essential to accurate and safe switching measurements.
