In February 2026, IECEE issued CTL Provisional decision PDSH 2302, which establishes unified technical specifications for the equipment used to measure the working voltage of switch-mode power supplies (SMPS). The requirements are as follows:

General Measurement Requirements:

Unless otherwise specified in the applicable product-specific standard, when measuring non-sinusoidal working voltages, measurement equipment with suitable bandwidth, capable of covering the crest factor of the signal under test, shall be used.

SMPS Measurement Requirements:

For measuring the working voltage of switch-mode power supplies (SMPS), an oscilloscope with a bandwidth of ≥ 100MHz, equipped with a high-impedance test probe having an input impedance of ≥ 100MΩ, shall be used. The probe must not impair the accuracy of the measurement results.

Core Rationale:

1. SMPS typically operate at switching frequencies above 30kHz. The switching action generates voltages with high crest factors (Upeak / URMS) and contain high-order harmonics. Therefore, equipment with sufficient bandwidth must be used.

2. Conventional multimeters have insufficient bandwidth to fully capture high-frequency harmonics and are limited to crest factors ≤3. This can lead to a significant underestimation of the true working voltage, resulting in measured values that are much lower than the actual values and fail to reflect the true working voltage.

3. Statistical data from the IECEE Proficiency Testing Programs (PTP) project Working Voltage 23e37-1 shows that 90% of participating laboratories used oscilloscopes, while less than 10% used multimeters. Excluding the multimeter data significantly narrowed the statistically acceptable range of measurement results and greatly improved data validity.

This resolution unifies the specifications for working voltage measurement equipment, resolves disputes over the selection of equipment for measuring SMPS working voltages, and effectively improves the accuracy and industry consistency of test results. Manufacturers performing in-house testing are advised to ensure that they use compliant instrumentation to guarantee the accuracy and consistency of their test results.

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