whit3rd wrote:
On Jan 25, 10:51 am, "pimpom" wrote:
Does anyone have specific information about the protection
device
at the power supply inputs of hard disks?

The most important reason a hard disk would need a protection
device, is that the two power connections (motor power, 12V,
and logic power, 5V) have a sequence condition requirement.

So, the diode might clamp +12 to +5V so that a drop in the
motor power (like, normal power turnoff) doesn't result in
any short time during which the "+12" is actually at lower
voltage than the "+5". Or, it might ensure that the +12
supply never goes negative (which could happen if a
motor is active when power is removed).

Probably this diode is NOT a Zener type, which is
relatively important: high current Zeners often fail
short-circuit
(which would halt the computer until disconnected).

I rather expect that it is similar to a zener diode in action but
more sophisticated than a simple discrete zener, perhaps with
more precise breakdown voltage, lower dynamic resistance and more
surge current capacity. And a shorted device is not uncommon.