Dropping 1V from a Regulated 6V Wall Wart

[Bill Garber]

:
: 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 - [email protected]
Remove - SPAM and X to contact me

 

[Fred Bloggs]

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

 

[Active8]

<GROANNNN...>

OK, it arteried: "In order to assure a voltage of 5VDC across Rl the
resistance of R2 should be five times the resistance of R1." ?^)

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

 

[Active8]

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."

 

[mike]

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.

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

--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Watson A.Name - Watt Sun, Dark Remover]

news.ops.worldnet.att.net>, [email protected]
mentioned...

Why not a 5volt zener and a resistor?....Just a thought...

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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[Watson A.Name - Watt Sun, Dark Remover]

I needed to drop 1V from a 6VDC 200 mA regulated wall wart,

...


6VDC>------+-----------------+
| |
[R1] |
| |
+-----|+\ C
| | >------B
| +--| / E
| | |
| +----+---------+
| |+ |
[R2] [C1] [RL]
| | |
GND>-------+-------+---------+

R1/R2 = 5

C1 = Whatever you need to keep the thing from oscillating; 100µF is
probably a good guess.

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
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
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[Watson A.Name - Watt Sun, Dark Remover]

But Mr. Wizard, this *package* says 502 and this one's on
psychedelics.

Why won't this magnet pick up this floppy disk?

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!

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
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goes directly to the trash unless you add NOSPAM in the
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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
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Watson A.Name - Watt Sun, Dark Remover]

NEver mind. I tried to cancel this but Gravity thinks I didn't post
this.

Still at TARFU level, I guess.

OK 5.6V zener, solly.

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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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
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Watson A.Name - Watt Sun, Dark Remover]

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

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.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
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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
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Active8]

On Tue, 30 Dec 2003 02:46:55 -0800, Watson A.Name - "Watt Sun, Dark

I needed to drop 1V from a 6VDC 200 mA regulated wall wart,

...


6VDC>------+-----------------+
| |
[R1] |
| |
+-----|+\ C
| | >------B
| +--| / E
| | |
| +----+---------+
| |+ |
[R2] [C1] [RL]
| | |
GND>-------+-------+---------+

R1/R2 = 5

C1 = Whatever you need to keep the thing from oscillating; 100µF is
probably a good guess.

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,

can't find that spec anywhere.

 

[Active8]

<snip massive headers. christ on a crutch! did we need all that
info? >

Man, what did I start? Buncha pedants.

Nyuk, nyuk, nyuk.

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

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.

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!

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?

 

[Active8]

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

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.

Rough guess...



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


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

 

[John Fields]

I suppose I could've used a LDO 5V regulator, but then the
output's already regulated.

 

[Asimov]

"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

 

[John Fields]

Rough guess...



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

---
Closer guess:

Ib ~ Ie/ß = 200mA/100 = 2mA

IZt = 20mA

R = (Vin-VZ)/(IZt+Ib) = 0.4V/0.022A = 18.18...R ~ 20R

 

[Watson A.Name - Watt Sun, Dark Remover]

---
Closer guess:

Ib ~ Ie/ß = 200mA/100 = 2mA

IZt = 20mA

R = (Vin-VZ)/(IZt+Ib) = 0.4V/0.022A = 18.18...R ~ 20R

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.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
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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
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Active8]

---
Closer guess:

Ib ~ Ie/ß = 200mA/100 = 2mA

IZt = 20mA

R = (Vin-VZ)/(IZt+Ib) = 0.4V/0.022A = 18.18...R ~ 20R

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.

 

[Wade Hassler]

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.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###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
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

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

 

[Active8]

On Tue, 30 Dec 2003 08:28:53 -0800, Watson A.Name - "Watt Sun, Dark

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.

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.

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.

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.