How to prevent the PMS (Power Measurement System) from malfunctioning when the voltage drops?

The power management system (PMS) should remain operational and data-free during short-term voltage dips or interruptions (according to IEC 61000-4-11). This requires the power supply system to have sufficient hold-up time and rapid switching capability.

First, the hold-up time of the large-capacity energy storage capacitor (e.g., electrolytic capacitor) at the main power input needs to be calculated. For example, under full-load power P, the capacitor C must satisfy C > (2 * P * t) / (V1^2 - V2^2), where t is the hold-up time (e.g., 20ms), V1 is the normal voltage, and V2 is the minimum operating voltage.

Second, a wide-input-range switching power supply module (e.g., 85-265VAC) should be used, ensuring fast dynamic response. Critical circuits (e.g., MCU, memory chips) are powered by backup batteries or supercapacitors, automatically switching in case of main power failure. On the software side, upon detecting a voltage dip, critical data should be immediately saved to non-volatile memory (e.g., FRAM), and a low-power mode should be entered; operation should resume in an orderly manner after voltage recovery. Simultaneously, all digital output drives should have power-off retention or preset safety state functions.

By design, the PMS can withstand a 100% voltage drop for 0.5 cycles (10ms) without malfunctioning, ensuring continuous and reliable operation.