Electrical Failures Caused by Voltage Fluctuation

Today I encountered a strange problem while using my computer and spent quite a long time troubleshooting before finally solving it.

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The Incident

At home I plugged my electric scooter charger into the same power strip as my computer.
After a while I left for something. When I came back and tried to use the computer:

• Mouse had no response
• Keyboard had no response
• The monitor showed extremely slight flickering (almost unnoticeable)
  
  

I began troubleshooting:

• Reseated and cleaned the RAM — no effect
• Updated drivers in Device Manager — no effect
• Added a ground wire to the computer — no effect
• Replaced monitor, keyboard, and mouse — no effect
• Replugged USB devices slowly — still no effect
  
  

After more than two hours with no solution, I suddenly suspected unstable voltage.
I changed the power strip — still no effect.

Then I noticed the electric scooter was charging.

The moment I unplugged the scooter charger, the computer instantly returned to normal.

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Root Cause Analysis

This was a typical but not obvious electrical fault in daily life.

1. Charger Creates Power Line Disturbance

During operation, the scooter charger produces high-frequency pulsed current, which pollutes the AC waveform and causes unstable voltage.

2. Electromagnetic Interference (EMI)

Low-quality chargers often have poor filtering, introducing strong high-frequency noise into the power line.

3. Computers Are Sensitive to Voltage Stability

Even though a computer has a power supply circuit, unstable input voltage can cause:

• Monitor flickering (unstable GPU/backlight supply)
• Keyboard and mouse detection failure (USB voltage drop)
• System lag or reboot (motherboard and CPU power affected)
  
  

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Why the Charger Produces Pulses

Charging circuit working principle:

PWM controller → Gate (G)
→ MOSFET switching channel
→ High-frequency switching current (chopping)
→ Battery charging

The MOSFET repeatedly turns on and off at high frequency, producing pulsed current and electrical noise.

MOSFET Structure

• Gate
• Drain
• Source
• Oxide insulation layer (semiconductor channel)
  
  

It is essentially a semiconductor switching device designed specifically for high-speed switching.

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Conclusion

This was not a computer hardware failure but a power quality problem caused by a switching charger sharing the same outlet.

A key lesson:

Some electrical faults are actually power interference problems, not equipment problems.

Careful and systematic troubleshooting prevented secondary damage and helped accurately identify the real cause — voltage fluctuation and electromagnetic interference from the charger.