Jim Yanik wrote:
"Arfa Daily" wrote in
:


"pimpom" wrote in message
...
Does anyone have specific information about the protection
device at
the power supply inputs of hard disks?

I assume that it's a zener diode or something similar in
action such
as an IC that acts like a precision zener diode. It's not
difficult
to see how such a device would provide protection against
spikes,
over-voltage and reverse voltage by shorting the power rail
to
ground and thereby triggering PSU shutdown.

Devices in the BUX C*** series seem to be widely used, but I
have
not been able to find a datasheet or other detailed info. Can
anybody shed some light on the matter?



BUX * devices are usually high voltage transistors

Arfa




the PSU itself usually has overvoltage protection,where it
really
counts;on the +5 volt supply. The +12 is loosely regulated,and
only
runs the motor drive.some have "balance" nodes,that trigger SD
if one
or more of the supplies go too far outside a window.

Then you don't need the expense of OV protection on every hard
drive.

But there *are* such devices on every hard disk I've examined. At
least, I can't think of any other purpose (counting inductive
spikes as an OV condition). And not all PSUs are created equal. I
have seen such devices burnt out on several HDDs, even to the
extent of being literally blown apart.