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Dropping 1V from a Regulated 6V Wall Wart

Discussion in 'Electronic Repair' started by Watson A.Name - Watt Sun, Dark Remover, Dec 29, 2003.

  1. Bill Garber

    Bill Garber Guest

    :
    : Fred Bloggs wrote:
    : >
    : > Watson A.Name - Watt Sun, Dark Remover wrote:
    : >
    : >> I needed to drop 1V from a 6VDC 200 mA regulated wall wart,
    so I tried
    : >> a 3 amp rectifier, but it varied by more than .2V over a
    range of
    : >> loads. So I tried this: (view with courier font)
    : >>
    : >> + From
    : >> wall
    : >> wart >--+ |
    : >> +---+------+
    : >> | |
    : >> | |
    : >> 400 \ / 2SC2334 or TIP31
    : >> ohm / |/ NPN power TO-220
    : >> WW \<-----| Heatsink optional
    : >> pot / |\
    : >> | E\ | |
    : >> | |
    : >> +----+-----+
    : >> | |
    : >> +------> + output
    : >> to load
    : >> - >--------------> -
    : >> From wall wart
    : >>
    : >> This has some advantages and disadvantages. It's simple and
    cheap,
    : >> and keeps the output at 5V within a tenth of a volt over a
    current
    : >> range. But it has a minimum current below which it loses
    regulation
    : >> and the output starts to go up to 6V, because the transistor
    is not
    : >> conducting and the current is being supplied thru the ww
    pot. This
    : >> circuit is sometimes used in the bias circuit for the output
    : >> transistors in high powered amplifiers. Also Win Hill
    showed us here
    : >> how to use a similar circuit to maintain the voltage steady
    for a
    : >> current regulator circuit used on four AA cell rechargeable
    batteries.
    : >>
    : >> I'm thinking about putting a 5.1V zener on the output so
    that if the
    : >> voltage climbs above that, it just shunts the excess
    current. Oh,
    : >> yeah, I set the pot to various values to see what the output
    voltage
    : >> was with various loads. The two resistances were 120 ohms
    for the
    : >> upper and 280 ohms for the lower. I suppose the 400 ohms
    total could
    : >> be raised to a higher value, but the transistor needs enough
    base
    : >> current to do its job. There's only 1V available minus the
    ..6V E-B
    : >> voltage, so even at 400 ohms, that's not a lot of current.
    : >>
    : >>
    : >
    : > You almost had it- put the Vbe multiplier inside the feedback
    loop and
    : > buffer like so:
    : >
    : > Please view in a fixed-width font such as Courier.
    : >
    : >
    : > 6V >---+------+---------+
    : > | | |
    : > | / |
    : > | 22 |
    : > | / |
    : > | \ c
    : > | | |/
    : > | +-------| TIP31
    : > | | |\
    : > | | e----+--> 5V
    : > | | |
    : > === | +----+
    : > | c | |
    : > | \| / |
    : > | |-----> \ |
    : > | /| / ===
    : > | e \ 1000U
    : > | | | |
    : > | | | |
    : > | | | |
    : > GND>--+------+---------+----+--> GND
    : >
    :
    : Then you can work a common 5.1V zener into the equation like
    so:
    : Use a 2N3906 for the pnp for Vbe,max=6V rating.
    :
    : Please view in a fixed-width font such as Courier.
    :
    :
    :
    :
    :
    : 6V >---+--------+----------+-------------+
    : | | | |
    : | / / |
    : | 22 51 |
    : | / / |
    : | \ \ c
    : | | | |/
    : | +----------|-----------| TIP31
    : | | | |\
    : | | | e----+--> 5V
    : | c | |
    : | \| | pnp |
    : | npn |--+-----|-------- c e---+
    : | /| | | \ / |
    : | e | | ---- |
    : === | | | 180 | |
    : | | | +----/\/\---+ |
    : | | | | | |
    : | | | | | |
    : | | / _/ / ===
    : | | 1K /^ 5.1v 1.2K 1000U
    : | | / - / |
    : | | \ | \ |
    : | | | | | |
    : GND>--+--------+----+-----+-----------+------+--> GND

    It's getting bigger. Soon he'll need a 2nd
    breadboard to build and test this thing. ;-)

    Bill @ GarberStreet Enterprizez };-)
    Web Site - http://garberstreet.netfirms.com
    Email -
    Remove - SPAM and X to contact me
     
  2. Fred Bloggs

    Fred Bloggs Guest

    Fred Bloggs wrote:
    [snip]

    This one will make the output tempco essentially that of the zener which
    is not bad for the 5.1V's. Ripple rejection is lacking due to the low
    overhead -at 14dB, but your 6V is regulated anyway.

    Please view in a fixed-width font such as Courier.


    6V >---+--------+----------+-------------+
    | | | |
    | / / |
    | 22 51 |
    | / / |
    | \ \ c
    | | | |/
    | +----------|-----------| TIP31
    | | | |\
    | | | e----+--> 5V
    | c | |
    | \| | pnp |
    | npn |--+-----|-------- c e---+
    | /| | | \ / |
    | e | | ---- |
    === | | | 1N4148 | |
    | | | +----|>|----+ |
    | | | | | |
    | | | | | |
    | | / _/ / ===
    | | 1K /^ 5.1v 1.2K 1000U
    | | / - / |
    | | \ | \ |
    | | | | | |
    GND>--+--------+----+-----+-----------+------+--> GND
     
  3. Active8

    Active8 Guest

    Ah! So, you mean R2 = 5*R1 or 5.R1 in K.A. notation.
     
  4. Active8

    Active8 Guest

    That's a diskette. A floppy disk has no hub. The old joke
    originated way back then.

    I (oops! can't read again) went to google's S.E.D. and searched on
    Magnet lifting floppy. It returned

    soc.sexuality.spanking

    as a related site (?!)

    "You see, Timmy (usee2me), when Mommy and Daddy..."

    "You're weird, Mom! I don't like spankings."
     
  5. mike

    mike Guest

    I've tried to do this on numerous occasions. If you need any amount
    of current at all, the big lump of stuff makes it too unweildy, even if you
    do bite the bullet and put in a complex circuit that works.

    Now, for regulated warts, I crack the case and shunt a resistor inside
    the wall wart. You can add a switch if you have multiple applications.
    If you need both voltages at once, it's still easier to use two
    warts than to have this lump of regulator stuff hanging about.

    I'm a little confused by your requirements. If you even considered a
    diode, you can't be too concerned about the actual voltage...but you're
    concerned about the .2V variability. Sounds like there's something
    in there that's important but not disclosed???
    mike

    --
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    TEK Sampling Sweep Plugin and RM564
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    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  6. news.ops.worldnet.att.net>,
    mentioned...
    Well, the output of the wall wart is already regulated to 6V at 200
    mA. But 1V at 200 mA is going to require a 5 ohm resistor. And the
    zener will have to dissipate a lot of wasted power. And the wall wart
    may not like being run at its max and overheat. Using the 1 amp
    rectifier in series with the output dropped about .6 to .8V, depending
    on current, which isn't all that bad a regulation. But the circuit I
    drew above gives a voltage closer to 5V over a wider range of load
    currents. I suppose I could've used a LDO 5V regulator, but then the
    output's already regulated.

    --
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  7. Thanks, but I think someone snipped the part where I said that I was
    trying to get this to fit across the pins of the RF modulator, and
    that the wall wart was already regulated. I guess I could do it if it
    was surface mount parts, but I'm not experienced with those. What
    kind of opamp works down to only 6V? A LM358? In order to put out 5V
    at the emitter, it would have to swing the base to 5.7 or more volts
    at 200 mA, so the opamp would have to swing close to the positive
    rail. Maybe a better idea would be to use a PNP for the emitter
    follower.



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    Don't be ripped off by the big book dealers. Go to the URL
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  8. Man, what did I start? Buncha pedants.

    BTW, I scrapped a couple old half gig hard drives, and took out the
    magnets. Those things are powerfull little devils! Made out of
    Nicodemus or some other exotic sounding materials. ;-) But I held
    the magnet to the platter and it literally won't even attract the
    plated coating on the aluminum. I guess it's so thin that it's like
    it's not even there!

    --
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    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
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  9. I think the emitter to base voltage will be something like .6 to .75V,
    and this has to be subtracted from the 1V diff, leaving something like
    ..4 to .25V. This very low voltage is what you have to work with when
    coming up with the resistor value to limit the current to the zener.

    --
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    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
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  10. I'll toss one together, but what value should I use for the Pot? 10k?
    Lower?

    This looks a lot like the current limiter circuit, 'cept for the pot.
    I'm wondering if it's such a good idea to have such a large cap on the
    output. When the wall wart is powered off, all that current tries to
    go backwards thru the pass transistor.


    --
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    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
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  11. Active8

    Active8 Guest

    On Tue, 30 Dec 2003 02:46:55 -0800, Watson A.Name - "Watt Sun, Dark
    can't find that spec anywhere.
     
  12. Active8

    Active8 Guest

    <snip massive headers. christ on a crutch! did we need all that
    info? :) >
    Nyuk, nyuk, nyuk.
    LOL i love it! Neodymium or Neodium (either a misspell or a TM).
    Good one, man.

    Nostrildumbass. I love playing with woids.

    Bone swar, moan sewer.
    Yup. I read an article about IBM developing a new process where
    it's so excruciatingly absoposifriggintutely thin that it doubles
    the density. They should've been out by now. Another article/AD
    (EDN or something) described a process to photoetch(?) the R/W
    heads, too. I think it was a matrix of heads.

    BTW. I said I was "thinking" series pass reg b4. I think I've never
    seen one drop 6V to 5V, either. I figgered since you already had a
    trans and a hulking ww pot and were thinking zener...

    Now you're talking about size and RF modulator which you never
    mentioned. What gives, Watson?
     
  13. Active8

    Active8 Guest

    On Tue, 30 Dec 2003 03:19:37 -0800, Watson A.Name - "Watt Sun, Dark
    Rough guess...



    ---+------------------+
    | |
    | 10 |
    | ___ |/
    +---|___|---+----|
    | |>
    | |
    - |
    5.6 500mW ^ +---------
    |
    -------------+----------------


    I kinda like JT's deal with the programmable zener which ain't much
    different.
     
  14. John Fields

    John Fields Guest

     
  15. Asimov

    Asimov Guest

    "Spehro Pefhany" bravely wrote to "All" (29 Dec 03 20:16:37)
    --- on the heady topic of "Re: Dropping 1V from a Regulated 6V Wall Wart"

    SP> Xref: aeinews sci.electronics.misc:8735 sci.electronics.design:31375
    SP> sci.electronics.repair:16164 alt.binaries.schematics.electronic:7314

    Would "you people", please, stop crossposting into sci.electronics.repair?
    Thanks In Advance!

    .... # <--- electrocuted tribble
     
  16. John Fields

    John Fields Guest

    ---
    Closer guess:

    Ib ~ Ie/ß = 200mA/100 = 2mA

    IZt = 20mA

    R = (Vin-VZ)/(IZt+Ib) = 0.4V/0.022A = 18.18...R ~ 20R
     
  17. Yeah, I was thinking something really low like that.

    But these approaches have been to establish a new regulated voltage,
    dependent on the value of the zener. There's nothing wrong with this,
    but it would be simpler to just use a LDO 5V regulator as someone
    suggested.

    I figured that since the 6V input was already well regulated, that it
    would be easy to just drop a single volt. My subject: line kind of
    said that. And if I use a 1N4002 inline with the input, it gives me
    5.4 to 5.2V or so, over most of the current range, which is not all
    that bad. And I did say I wanted to keep it simple. It's not that
    I'm unappreciative of all the input others have given, it's been a
    good learning experience seeing these neat little circuits. I've
    saved many of them to disk, to experiment with later. So I thank all
    who contributed.

    --
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    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  18. Active8

    Active8 Guest

    Ok, I incorrectly guessed Beta (Chaos Master told me how to get
    special characters and it doesn't work here) of 200 and set Iz at
    40mA (a waste) to get the 500mW zener to operate at about half it's
    rating. I know, I only needed 10mA if Ib really were 10mA.
     
  19. Wade Hassler

    Wade Hassler Guest

    I did this a while back. Replaced the 7806 in the wall wart with a 7805.
    Wade
     
  20. Active8

    Active8 Guest

    On Tue, 30 Dec 2003 08:28:53 -0800, Watson A.Name - "Watt Sun, Dark
    I'll trade a pot for a zener and R anyday, but I haven't looked at
    what this thing will do over the full current range. It's so close
    to what you started with, I thought it would be a snap to check
    out.
    I'm just glad to find an electronics post or 2 lately. Lots of long
    OT stuff I'm guilty! I feed it, but it's fun.
     
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