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The USB-A port's power bus (VBUS) experiences fluctuations for a period of time before the system's BIOS boots up. The temporary VBUS on and off during boot-up are expected. Affected Monitors: Dell U4025QW
The USB HUB and KVM switch initialization cause this behavior.
Power Fluctuation Explanations: During the system bootup, the host requests the monitor USB hub to reset power and reinitialize following by monitor firmware flow to set KVM accordingly. The user may experience some attached USB devices that flash or go off and on due to the VBUS fluctuation. This happens two to five times usually and in an extreme scenario that it keeps fluctuating until the computer enters the Operating System (OS). This depends on how fast the computer boots up into the OS. The USB VBUS fluctuation during the computer boot-up does not affect or damage the functionality of the plugged devices on the downstream ports as it is not over the 5-volt specification and each port has an overcurrent protection device. USB devices should deploy Under-Voltage Lockout (UVLO) to protect circuits from a power supply fluctuation, this is the fundamental of electronic circuit design. BIOS Update This issue was fixed in firmware version M3T105, A04. Download and install firmware version M3T105 or newer from the Dell Website, Dell U4025QW Download and Drivers. Back to Top
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