This is because the dedicated charging IC has enough capacity to charge the battery, while the battery simultaneously feeds power into the motherboard. If you have a lower end Surface Pro 4, you may find that the “charger” diode is not populated. Conversely if you leave the charger connected but not powered on, the charger won’t cause the battery to drain. For example, with the charger connected, the charger will power the unit, without feeding the battery and potentially over-charging it. The use of diodes means that whichever input is higher voltage will feed power to the unit, without feeding power backwards into the other input. These diodes allow either the battery or the charger to power the device. In most cases though, one of the diodes pictured here will fail. In reality, any of them have the potential to fail. The Surface Pro 4 has an abundance of Schottky Diodes on the motherboard. Schottky diodes have a lower forward voltage compared to their silicon counterparts, are available with higher current ratings, are more efficient, and as a result allow for higher switching speeds. These are commonly found in all kinds of electronics. Either the forward voltage increases substantially (sometimes infinitely), or the diode effectively turns into a wire, allowing current to flow in both directions.Ī Schottky Diode is a slightly “better” diode. Exceeding that current (say by overloading or short circuiting) can result in failure.
This effect worsens the more current the diode passes.ĭiodes also have a rated maximum current.
This is generally not ideal or efficient, and the voltage that is lost results in heat dissipation. Unfortunately, a diode also causes a drop in voltage as power passes through it (known as the “forward voltage”). It allows power to travel in one direction, and blocks it from traveling in the other. If you made it here from a search engine, you’ve probably already seen this failure 10 times over.Ī diode is effectively a one-way valve.
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