The biggest plague of electronics: Common Mode disturbances caused by switch-mode power supplies

It’s in German so switch to English subs or read the ai summary below.

The biggest plague of electronics: Common Mode disturbances caused by switch-mode power supplies

AI generated summary

  • Electrical engineering plagued by Common Mode (Gleichtakt) disturbances, unnoticed by many.

  • Common Mode disturbances in switch-mode power supplies can cause significant harm, including destructive voltages to sensitive components.

  • Common Mode disturbances originate from parasitic capacities within switch-mode power supply windings or cooling bodies.

  • Switch-mode power supplies (USB chargers, laptop chargers) have deceptive voltages not directly measurable on the output.

  • To detect Common Mode disturbances, a multimeter must be set to AC voltage measurement, which can reveal unexpected high voltages with respect to ground. Up to 100V AC Common Mode disturbances!

  • Such disturbances are present on laptops and various chargers, potentially damaging connected sensitive equipment through USB or other interfaces.

  • Damage can occur when working with hardware tools or development boards (e.g., Raspberry Pi, STM32, FPGA) if the ground potential is affected by laptop-supplied voltages.

  • Grounding or using a benchtop power supply does not safeguard against Common Mode disturbances; connecting the negative terminal to ground is necessary to protect hardware.

  • Working with desktop PCs avoids Common Mode disturbances due to the grounded chassis.

  • Devices with two-prong plugs lacking ground connection (e.g., certain laptops, monitors, game consoles) are more susceptible to Common Mode disturbances.

  • Devices with a three-prong plug ensuring proper grounding (e.g., PC power supplies) are safer from Common Mode disturbances.

  • Awareness of Common Mode disturbances is necessary, especially for beginners working with laptops or sensitive equipment, to prevent damaging valuable hardware.

  • The video urges sharing of information about Common Mode disturbances to help others avoid costly hardware damage.


Very informative video! I was just thinking the other day what a better power source for my Schiit Magni Heretic would be, versus the wall-wart that it comes with. I do have it on a grounded power strip but I am sure there are better power supplies out there.

I guess a question I’d pose to others who are more experienced in this area would be, what are some (affordable) recommendations and what are you using? :thinking: