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Microchip's TB008 Reprise

Discussion in 'Electronic Basics' started by Phil Allison, May 13, 2008.

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  1. Phil Allison

    Phil Allison Guest

    **Hi to all:

    On March 13 this year - poster " Hammy" raised a few valid questions about
    Tech Bulletin " TB 008 " on the Microchip web site ( and quoted widely
    elsewhere) on the subject of "Transformerless Power Supplies".

    http://ww1.microchip.com/downloads/en/AppNotes/91008b.pdf

    This prompted Mr Rod Elliot of ESP to contact Microchip with a view to
    having them retract and withdraw TB008 from publication. As feared but
    expected, this was not successful.

    The ESP site now has an outline of what happened when he complained and
    includes the email reply received from Microchip's Tech Support Group.

    http://sound.westhost.com/articles/power-supplies2.htm#s7

    A second, even stronger worded email from Mr Elliot went unanswered.

    Microchip's anonymous tech support guy was clearly WAAAY out of his depth on
    the topic of AC mains and appliance electrocution hazards - as was that
    fool Stan D'Souza who wrote the infamous tech bulletin.

    D'Souza is now a "Technical Fellow " at Microchip - so I guess the dude
    walks on water and his word is Gospel round the place.

    IME - people like him will * NEVER * admit to even the most grievous of
    errors nor allow any error of theirs to be publicly corrected.

    Shame there appears to be no way to make direct contact.



    ...... Phil
     
  2. Unbelievable!

    There is a way to make direct contact though, and right to the TOP.
    Steve Sanghi is Microchip's CEO, his direct email address is (spambot
    friendly):
    steve DOT sanghi AT microchip DOT com

    Well, maybe his personal secretary vets every email first, but it should at
    least get that far.

    Dave.
     
  3. and tell him how much you love his book:
    http://www.drivingexcellence.biz/

    Dave.
     
  4. and tell him how much you love his book:
    http://www.drivingexcellence.biz/

    Dave.
     
  5. default

    default Guest

    That supply is very dangerous in the wrong hands. But I've been using
    caps to run LED pilot lights on 120 with no problems. It is just not
    suitable for any application where the user might come in contact with
    the "low voltage" derived from a capacitive reactance power supply.

    I've got one in my electric range - powers a microchip pic to modulate
    the range heater - no more dangerous than the 240 VAC mechanical
    switch it replaces.

    The problem is in the application, not the circuit I'd recommend for
    anyone just starting out in electronics. After a couple of "sit down"
    shocks you gain the proper respect for mains.

    I'm pretty sure he didn't become a technical fellow because of this
    circuit - it appears in a 70's Fairchild publication.
     
  6. Bob Monsen

    Bob Monsen Guest


    Well, they should clearly be more responsive about these kinds of things.
    However, I'm still somewhat confused as to why the original tech note is
    considered harmful.

    It seems to be a fairly standard transformerless power supply. I've built
    lots of them. The only problem with it is that it lacks a fuse (other than
    the silly one between neutral and earth). The circuit needs to be isolated
    from the user, of course.

    I wonder if Australian and US standards are different in this respect?

    Regards,
    Bob Monsen
     
  7. Here is my thread in the Microchip forum. I posted it in their "Tips 'n
    Tricks", but under the development tools rather than a more
    hardware-oriented area. Still, it is usually read by their technical
    people, and I think it should be addressed.

    http://forum.microchip.com/tm.aspx?m=322529

    Maybe someone should contact a lawyer and tell them they tried a circuit
    recommended by Microchip, and got a bad shock, and now they have
    neurological problems. It would be hard to disprove, if you actually built
    the circuit and just claim to have touched it. You could also offer to
    submit a design to Microchip for one of their contests as "The Next Killer
    App"!

    I like Microchip, but that App Note needs some major revision or
    retraction.

    There is also a bad circuit in:
    http://ww1.microchip.com/downloads/en/DeviceDoc/41283A.pdf. It is Tip #8,
    and it shows the AC line directly connected to the +5VDC supply, and the
    dropping capacitor and resistor on neutral!

    This sort of supply is reasonably safe if dropping resistors and capacitors
    are used in both legs (if line/neutral polarity cannot be guaranteed), or
    for 220 VAC applications, AND if the maximum current to ground (or into a
    person connected to ground) is less than about 10-20 mA. The 0.47 uF
    capacitor shown in their circuit will limit current to about 21 mA at 60
    Hz, so if there were one on each leg, it would be reasonably safe.

    Paul
     
  8. Phil Allison

    Phil Allison Guest

    "Bob Monsen"

    ** Yes - killing people is not a very nice thing to do, is it ?


    ** You must be an utter moron.

    ** No it ain't !!

    Read the FUCKING link - you colossal jerk !!

    You are JUST AS BAD as bloody Microchip.



    ....... Phil
     
  9. default

    default Guest

    What!!?? the world doesn't rotate at your colossal command, who's the
    jerk, idiot.
     
  10. Phil Allison

    Phil Allison Guest

    "default"

    ** Those words were NOT written to you - but you removed all the
    context & altered the text to make it look as if they were.

    Clearly - YOUR gross incomprehension of extreme electrocution hazard here
    is just as bad as any of the fuckwits at Microchip.

    **** off and die - you vile pile of shit.



    ...... Phil
     
  11. default

    default Guest

    The simpering wimp doth speak. Let me guess, you are one of the
    children who never got to be playground monitor and it has affected
    you this way. You'd probably be wetting yourself if you had to
    confront some of these people in person.
     
  12. Phil Allison

    Phil Allison Guest

    "default = some anonymous mental retard "


    ** **** off and die

    - you vile, autistic pile of shit.





    ...... Phil
     
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