I've noticed for a while that my iPad had a tingling sensation when I brushed my hand along the back of the casing. I found out today that it was because the charger is not grounded, and this was intended by design.

I'm curious though, how did we avoid electrocution even though there is no ground? Why do other chargers like Samsung's need a ground, given they are both handheld electronics with probably similar power ratings? Does that mean it's unwise to use an iPad while charging when wet, even if we avoid touching the lightning cable?



simulate this circuit – Schematic created using CircuitLab

Here there is DC isolation and some CM ferrite chokes (lightning immunity and EMI reduction) not shown and many regulator details missing, but the main cause is ferrite transformer capacitance coupling that induces a differential impedance coupling to hot that is high but low enough to conduct up to 250uA by Safety Stds.

In other words even if you were 0 Ohms to ground the current would be limited by Vin/ total series Capacitance in SMPS XFMR or Imax=250uA = Vin * ωC

Can you calc. Cmax?


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