Hard disk protection diode?

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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?



Re: Hard disk protection diode?
I know I'm not directly answering your question, but...

The socket and power cords are polarized. It would be extremely difficulty
to insert the plug the wrong way.



Re: Hard disk protection diode?
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Thanks for the reply. Yes, I expect that reverse voltage
protection would be a secondary consideration. Its primary
function would be protection against over-voltage, transient or
sustained. Something like a crowbar or TVS device, but without
the need for very low capacitance. A datasheet or identifying the
manufacturer would be a big help.



Re: Hard disk protection diode?
On Sun, 25 Jan 2009 11:07:31 -0800, "William Sommerwerck"

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It would require a very heavy hand, but I *have* seen it done.

- Franc Zabkar
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Please remove one 'i' from my address when replying by email.

Re: Hard disk protection diode?
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In any case, reversing a 4-pin Molex connector will not reverse
the polarity. It will just juxtapose the +5 and +12V lines.



Re: Hard disk protection diode?
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I have come across these shorted protection diodes on 2 occasions now,
both on Digital Audio Recorders powered by external wall warts.  If
the wrong polarity wall wart is used, you can get the wrong polarity
12Volts to the Hard Drive.  This is shorted out by the diode, which
eventually burns to a dead short protecting the drive.  On both
occasions replacing the diode restored the unit to fully operational.
Good job they are there IMHO.



Gareth.

Re: Hard disk protection diode?
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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).

Re: Hard disk protection diode?
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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.



Re: Hard disk protection diode?

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BUX * devices are usually high voltage transistors

Arfa



Re: Hard disk protection diode?

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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.

--
Jim Yanik
jyanik
at
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Re: Hard disk protection diode?
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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.



Re: Hard disk protection diode?
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Yes. But transistors have the BUX followed by numeric characters.
These devices have a "C" before numerals.



Re: Hard disk protection diode?
put finger to keyboard and composed:

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The BU? marking code appears to be used by ST Microelectronics in
their SMBJ series 600W Transil (TVS) range.

See page 2 of the datasheet:
http://www.st.com/stonline/products/literature/ds/5616.pdf

The BUX marking isn't listed, but it would appear that the "U"
designates a unidirectional device.

The "C" appears to be the manufacturing location, followed by a
numeric YWW date code.

- Franc Zabkar
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Please remove one 'i' from my address when replying by email.

Re: Hard disk protection diode?
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Is it a transient voltage suppression diode?
http://en.wikipedia.org/wiki/Transient_voltage_suppression_diode

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Hard disk protection diode?
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Could be. In fact, I mentioned that in my second post. What I
find surprising and frustrating is that I have not been able to
find any data on the BUX C*** series.




Re: Hard disk protection diode?
put finger to keyboard and composed:

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This forum discussion is about TVS devices in hard drives:
http://forum.hddguru.com/seagate-barracuda-7200-st3300622a-300gb-ide-t9356.html

The above discussion refers to this photo of a Seagate HDD with two
TVS devices made by ON Semiconductor:
http://forum.hddguru.com/download/file.php?id56%2

The parts have the following markings:

 ON logo QE
 R617

 ON logo 620
 LEM .

I can't find exactly the same parts in ON's datasheets, but here are a
few similar looking devices:

Unidirectional Zener TVS 13V 600W (marking = LEN):
http://www.onsemi.com/pub/Collateral/NSB13AN-D.PDF

Zener Transient Voltage Suppressor 12V 600W (marking = LEK):
http://www.onsemi.com/pub/Collateral/NSB12A-D.PDF

400W Peak Power Zener Transient Voltage Suppressor 5V (marking = QA):
http://www.onsemi.com/pub/Collateral/NSA5.0A-D.PDF

600 Watt Peak Power Zener Transient Voltage Suppressor 5V (marking =
6QE):
http://www.onsemi.com/pub/Collateral/NS6A5.0A-D.PDF

Here is a Vishay patent that discusses TVS devices with particular
reference to their application in hard drives:
http://www.freepatentsonline.com/WO2008002421.html

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Hard disk protection diode?
On Tue, 27 Jan 2009 06:13:23 +1100, Franc Zabkar

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600 Watt Peak Power Zener Transient Voltage Suppressor, 12V,
Unidirectional, p/n SMBJ12AON (marking = LEM):
http://www.icbase.com/English/ic_search/just.asp?urlftp=/ONS/ONS26380605.pdf

The "QE" marking belongs to a 1SMA5.0AT3, 400 Watt Peak Power Zener
Transient Voltage Suppressor:
http://www.datasheetarchive.com/pdf-datasheets/Datasheets-23/DSA-454313.html

ON TVS/Zener Device Data Book:
http://www.mosaico-eng.com.br/arquivos/Data-Sheet%20Zener.pdf

- Franc Zabkar
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Please remove one 'i' from my address when replying by email.

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