voltage regulator accuracy

I

Isaac

Guest
hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!
 
Isaac wrote:
hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

NTE buys floor-sweepings from the semiconductor fabs, then marks them
Click to expand...
with their own numbers.

_Any_ voltage regulator will be inaccurate. The more you spend, the
better accuracy you'll get.

Not knowing the voltage regulator that you used its hard to say how much
your design could impact the output voltage. Any 3-terminal voltage
regulator will drop out of regulation if your input voltage is too low.
How much is too low depends on the regulator: a garden variety
regulator will have a drop out voltage as high as 2V, "low drop-out"
regulators are specifically designed to work down to a few hundreds or
tens of millivolts differential.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
 
On Oct 23, 3:35 pm, Tim Wescott <t...@seemywebsite.com> wrote:
Isaac wrote:
hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

NTE buys floor-sweepings from the semiconductor fabs, then marks them
with their own numbers.

_Any_ voltage regulator will be inaccurate. The more you spend, the
better accuracy you'll get.

Not knowing the voltage regulator that you used its hard to say how much
your design could impact the output voltage. Any 3-terminal voltage
regulator will drop out of regulation if your input voltage is too low.
How much is too low depends on the regulator: a garden variety
regulator will have a drop out voltage as high as 2V, "low drop-out"
regulators are specifically designed to work down to a few hundreds or
tens of millivolts differential.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details athttp://www.wescottdesign.com/actfes/actfes.html
Click to expand...
thanks, tim... i can't recall the part number at the moment... do you
have any recommendations for a more accurate regulator?... at the
moment, i'm at the mercy of dozens of cryptic numbers in digikey et
al. catalogs or a local fry's (who seem to sell only nte products)...

thanks
 
"Isaac" <isaacdover@gmail.com> wrote in message
news:1193164957.514869.292400@z24g2000prh.googlegroups.com...
hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!
Click to expand...
Most "logic level" devices are quite happy anywhere between 4.75V & 5.25V,
many modern devices are even more forgiving.
 
Isaac wrote:
On Oct 23, 3:35 pm, Tim Wescott <t...@seemywebsite.com> wrote:
Isaac wrote:
hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..
thanks!
NTE buys floor-sweepings from the semiconductor fabs, then marks them
with their own numbers.

_Any_ voltage regulator will be inaccurate. The more you spend, the
better accuracy you'll get.

Not knowing the voltage regulator that you used its hard to say how much
your design could impact the output voltage. Any 3-terminal voltage
regulator will drop out of regulation if your input voltage is too low.
How much is too low depends on the regulator: a garden variety
regulator will have a drop out voltage as high as 2V, "low drop-out"
regulators are specifically designed to work down to a few hundreds or
tens of millivolts differential.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details athttp://www.wescottdesign.com/actfes/actfes.html

thanks, tim... i can't recall the part number at the moment... do you
have any recommendations for a more accurate regulator?... at the
moment, i'm at the mercy of dozens of cryptic numbers in digikey et
al. catalogs or a local fry's (who seem to sell only nte products)...

I forgot to mention: The necessary accuracy of the voltage regulator
Click to expand...
depends on what you're driving. Check the data sheets (they're on the
manufacturer's web sites) for the required input voltages, then make
sure your regulator accuracy matches.

Generally you'll find that it's easy to get regulators that are good for
+/-5% over temperature, and that that's good enough for most digital logic.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
 
Isaac wrote:
hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

4.91 would be in tolerance in my opinion but any regulated power supply
Click to expand...
you can't adjust is a piece of crap.
 
Isaac wrote:

hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

nah, just cheap regulators NTE got their hands on that didn't pass the
Click to expand...
precise 5 volts out test or drifted a bit.
It's close enough for what it was designed for. Most likely well with
in the limits of generic specs. Now if you were talking about mill specs
then, that could be an issue.



--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
 
On Oct 24, 4:42 am, Isaac <isaacdo...@gmail.com> wrote:
hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..
Click to expand...
A typical 7805 regular has +/- 4% accuracy over the working
temperature range, that's 4.8V to 5.2V.
You can get better "grade" devices with better accuracy, see the
datasheet of a typical device:
http://www.fairchildsemi.com/ds/LM%2FLM7805.pdf
This one is available in +/-4% and +/-2% versions.

5V components are usually specified to work over +/- 5% range, so
4.75V to 5.25V, so all of your 5V projects will work just fine with
whatever regulator error you have.

Your basic stamp board is spot on 5V due to luck, nothing more.
Another basic stamp board could be 5.1V or whatever.

Dave.
 
On Tue, 23 Oct 2007 18:42:37 -0000, Isaac <isaacdover@gmail.com>
wrote:

hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!
Click to expand...
The regulator may be inaccurate NTE parts are not the best.

NTE doesn't manufacture parts - they buy large lots of parts
(sometimes surplus and seconds) and put their brand on them They are
intended for consumer repair shops - hence the large cross reference
directories for NTE parts. A single NTE transistor may "replace"
100's of regular branded and specified parts. Good enough for fixing
the TV or radio.

LM7805 would be a garden variety 5V reg. It requires about 9 volts
input to stay in regulation - and that also means you need to keep the
"valley of the ripple" above 9 volts - a good rule of thumb is 1,000
microfarads of filter cap for each 1/2 amp of current, for around 10%
ripple, with a full wave bridge rectifier.

You also need to allow for the .6 volt diode drop in the rectifiers -
a four diode bridge will loose 1.2 volts in the rectifiers alone.

If you don't have a scope you have to guess at how much ripple is on
the input - too much ripple and it would be dropping out of regulation
- 120 times a second with a FWB and 60 cycle mains. Your meter may
average that and be giving you a 4.9 reading.

Some low drop out (LDO) regulators will only need .6 volts across the
regulator so they might work with only 5.6 volts input.

- allowing again for transformer loss or transformer regulation
(~10%), line regulation (power company accuracy in delivering 120 (or
105-125 volts), diode loss, ripple voltage, etc..

Even a simple three terminal regulator takes a bit of arm waving and
head scratching to apply. Read about it, then read some of the data
sheets for the regulators. They spell out what is considered good and
what the tolerance limits for the parts are, and how they behave under
other environmental conditions.
--

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On Oct 24, 6:12 pm, default <defa...@defaulter.net> wrote:
On Tue, 23 Oct 2007 18:42:37 -0000, Isaac <isaacdo...@gmail.com
wrote:

hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

The regulator may be inaccurate NTE parts are not the best.

NTE doesn't manufacture parts - they buy large lots of parts
(sometimes surplus and seconds) and put their brand on them They are
intended for consumer repair shops - hence the large cross reference
directories for NTE parts. A single NTE transistor may "replace"
100's of regular branded and specified parts. Good enough for fixing
the TV or radio.

LM7805 would be a garden variety 5V reg. It requires about 9 volts
input to stay in regulation - and that also means you need to keep the
"valley of the ripple" above 9 volts
Click to expand...
Incorrect. It's about 7V. The "dropout" voltage of a typical 7805 is
around 2V

Dave.
 
On Wed, 24 Oct 2007 02:01:00 -0700, "David L. Jones"
<altzone@gmail.com> wrote:

Incorrect. It's about 7V. The "dropout" voltage of a typical 7805 is
around 2V
Click to expand...
National Semiconductor gives it as 7.5 volts input to maintain line
regulation and yet they give the dropout voltage as 2.0 volts.

So you are correct it is 2 volts for reasonable temperatures

Fairchild just says 2 volts

ST Micro says 2 volts then runs all their specifications at 8 volts
minimum . . . They also give two specifications on minimum voltage.
no current minimum is 4.9, and at currents of 5ma to one amp 4.65 with
a power dissipation equal or below 15 watts
--

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On Wed, 24 Oct 2007 09:19:43 -0400, default <default@defaulter.net>
wrote:

On Wed, 24 Oct 2007 02:01:00 -0700, "David L. Jones"
altzone@gmail.com> wrote:


Incorrect. It's about 7V. The "dropout" voltage of a typical 7805 is
around 2V

National Semiconductor gives it as 7.5 volts input to maintain line
regulation and yet they give the dropout voltage as 2.0 volts.

So you are correct it is 2 volts for reasonable temperatures

Fairchild just says 2 volts

ST Micro says 2 volts then runs all their specifications at 8 volts
minimum . . . They also give two specifications on minimum voltage.
no current minimum is 4.9, and at currents of 5ma to one amp 4.65 with
a power dissipation equal or below 15 watts
Click to expand...
Its load and temperature dependent.
I'm using a 7808 from ST. Its delivering 1A pulses, it drops out at
about 10.7V.
 
On Oct 24, 4:12 am, default <defa...@defaulter.net> wrote:
On Tue, 23 Oct 2007 18:42:37 -0000, Isaac <isaacdo...@gmail.com
wrote:

hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

The regulator may be inaccurate NTE parts are not the best.

NTE doesn't manufacture parts - they buy large lots of parts
(sometimes surplus and seconds) and put their brand on them They are
intended for consumer repair shops - hence the large cross reference
directories for NTE parts. A single NTE transistor may "replace"
100's of regular branded and specified parts. Good enough for fixing
the TV or radio.

LM7805 would be a garden variety 5V reg. It requires about 9 volts
input to stay in regulation - and that also means you need to keep the
"valley of the ripple" above 9 volts - a good rule of thumb is 1,000
microfarads of filter cap for each 1/2 amp of current, for around 10%
ripple, with a full wave bridge rectifier.

You also need to allow for the .6 volt diode drop in the rectifiers -
a four diode bridge will loose 1.2 volts in the rectifiers alone.

If you don't have a scope you have to guess at how much ripple is on
the input - too much ripple and it would be dropping out of regulation
- 120 times a second with a FWB and 60 cycle mains. Your meter may
average that and be giving you a 4.9 reading.

Some low drop out (LDO) regulators will only need .6 volts across the
regulator so they might work with only 5.6 volts input.

- allowing again for transformer loss or transformer regulation
(~10%), line regulation (power company accuracy in delivering 120 (or
105-125 volts), diode loss, ripple voltage, etc..

Even a simple three terminal regulator takes a bit of arm waving and
head scratching to apply. Read about it, then read some of the data
sheets for the regulators. They spell out what is considered good and
what the tolerance limits for the parts are, and how they behave under
other environmental conditions.
--

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Click to expand...
thank you for the info... i'm using a cheap wall wart in place of
building a transformer into my project... what i currently have is
very simple, nothing more than the 5v regulator, a 10mf capacitor, and
an led to let me know it's powered... my goal was more to practice
soldering, which certainly needs as much time as i can offer... i have
been working under the assumption that with the wall wart, i didn't
have to worry about a transformer or bridge rectifier?... i don't have
a scope, too expensive for me as a beginning hobbyist...

i'm currently using a book i found online, "Lessons in Electric
Circuits - DC"... is this a good resource?... for free, it certainly
seems so..

thanks again..
 
On Wed, 24 Oct 2007 07:41:08 -0700, Isaac <isaacdover@gmail.com>
wrote:

On Oct 24, 4:12 am, default <defa...@defaulter.net> wrote:
On Tue, 23 Oct 2007 18:42:37 -0000, Isaac <isaacdo...@gmail.com
wrote:

hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

The regulator may be inaccurate NTE parts are not the best.

NTE doesn't manufacture parts - they buy large lots of parts
(sometimes surplus and seconds) and put their brand on them They are
intended for consumer repair shops - hence the large cross reference
directories for NTE parts. A single NTE transistor may "replace"
100's of regular branded and specified parts. Good enough for fixing
the TV or radio.

LM7805 would be a garden variety 5V reg. It requires about 9 volts
input to stay in regulation - and that also means you need to keep the
"valley of the ripple" above 9 volts - a good rule of thumb is 1,000
microfarads of filter cap for each 1/2 amp of current, for around 10%
ripple, with a full wave bridge rectifier.

You also need to allow for the .6 volt diode drop in the rectifiers -
a four diode bridge will loose 1.2 volts in the rectifiers alone.

If you don't have a scope you have to guess at how much ripple is on
the input - too much ripple and it would be dropping out of regulation
- 120 times a second with a FWB and 60 cycle mains. Your meter may
average that and be giving you a 4.9 reading.

Some low drop out (LDO) regulators will only need .6 volts across the
regulator so they might work with only 5.6 volts input.

- allowing again for transformer loss or transformer regulation
(~10%), line regulation (power company accuracy in delivering 120 (or
105-125 volts), diode loss, ripple voltage, etc..

Even a simple three terminal regulator takes a bit of arm waving and
head scratching to apply. Read about it, then read some of the data
sheets for the regulators. They spell out what is considered good and
what the tolerance limits for the parts are, and how they behave under
other environmental conditions.
--

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----= East and West-Coast Server Farms - Total Privacy via Encryption =----

thank you for the info... i'm using a cheap wall wart in place of
building a transformer into my project... what i currently have is
very simple, nothing more than the 5v regulator, a 10mf capacitor, and
an led to let me know it's powered... my goal was more to practice
soldering, which certainly needs as much time as i can offer... i have
been working under the assumption that with the wall wart, i didn't
have to worry about a transformer or bridge rectifier?... i don't have
a scope, too expensive for me as a beginning hobbyist...

i'm currently using a book i found online, "Lessons in Electric
Circuits - DC"... is this a good resource?... for free, it certainly
seems so..

thanks again..
Click to expand...
Wall warts . . . they can good or bad quality most of the run of the
mill stuff is of questionable quality - they are cheaply made.

In the case of wall warts designed to recharge batteries - they
sometimes incorporate a scheme where they intentionally have poor
regulation to avoid overcharging and to protect them from high
currents (shorted or very low batteries).

Wall warts are generic. They don't all meet some standard, or the
same standard. They do usually meet some safety standard, designed to
fail without starting a fire and designed to provide a high degree of
isolation from the full voltage of the power mains. - but not all of
them fail safe.

Wall warts are likely to be transformers (or switching regulators).
The fact that you don't mention things getting hot or blowing up
suggests the rectification is already inside the wall wart (they can
be either AC or DC warts). Three terminal regs die with overheating
on AC or reversed polarity.

10 ufd is bound to be too small for filtering. You'd want 200 or 1000
on the input to the regulator and maybe a 10 on the output. - and
again some wall warts include a capacitor inside the case for
filtering. What is your input voltage?

Polarized Electrolytic capacitors connected to AC or reverse connected
tend to "vent." Sounds like a firecracker as the case splits open or
the rubber plug on the positive lead flies out. Collateral Damage is
usually minimal but you wouldn't want your eyes close to it. The cap
dies permanently.

I looked at the indexes and one chapter of the book - it looks very
good
http://www.ibiblio.org/obp/electricCircuits/index.htm

Problem is, chapter one won't cover the stuff you need to know about
transformers and power supplies. That comes along in chapter two and
three for transformers rectifiers and filters.

I started electronics in high school. They gave us meters, signal
generators, power supplies and breadboards. You might have to lay out
a few bucks for a "trainer" but if you plan to stay with it that
might be a good way to go.

A lot of the "train at home" schools offered trainers as part of the
tuition costs and there might be some on Ebay for less money.

Jameco has one for $439 (Ouch!) Seems to me I've seen them for much
less $70-200 range. The jameco one comes with two variable supplies,
two fixed 5 volt supplies, and a function generator and mounted pots
switches leds etc as well as a breadboard space. Not a good deal in
my opinion, but they aren't the only people selling them.

digital trainer for $129-159
http://www.omnitronelectronics.net/phpstore/html/XK-550--AnalogDigital-Trainer-assembled-version.html

Elenco stuff is OK - I've had one of their scopes for years more than
I can say for the Tektronics Sony I had . . .

Search on phrase "analog digital trainer"

Digitals cost less because they usually only give you two or three
fixed supplies.

Ebay had may still have lots of the old Hewlett Packard lab quality
supplies with meters and adjustable voltage and current for $30 (and
worth a whole lot more)

Stay safe, good luck
--

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Jamie wrote:
Isaac wrote:

hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

nah, just cheap regulators NTE got their hands on that didn't pass the
precise 5 volts out test or drifted a bit.
It's close enough for what it was designed for. Most likely well with
in the limits of generic specs. Now if you were talking about mill specs
then, that could be an issue.
Click to expand...

You obviously don't know the difference between a voltage regulator,
and a voltage reference.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
Michael A. Terrell wrote:

Jamie wrote:

Isaac wrote:


hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!


nah, just cheap regulators NTE got their hands on that didn't pass the
precise 5 volts out test or drifted a bit.
It's close enough for what it was designed for. Most likely well with
in the limits of generic specs. Now if you were talking about mill specs
then, that could be an issue.



You obviously don't know the difference between a voltage regulator,
and a voltage reference.


Excuse me ?
Click to expand...

You obviously don't know how to read and follow the thread?

Yes, I know what a voltage reference is which wasn't part of the
original post as a concern?

Should I start calling you Eeyore JR. ? That last remark resembles
kinship.

I hope you don't hang out with him at that Turkish bathe house
he adores so much.

--
"I'm never wrong, once I thought I was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
 
On Oct 24, 12:23 pm, default <defa...@defaulter.net> wrote:
On Wed, 24 Oct 2007 07:41:08 -0700, Isaac <isaacdo...@gmail.com
wrote:





On Oct 24, 4:12 am, default <defa...@defaulter.net> wrote:
On Tue, 23 Oct 2007 18:42:37 -0000, Isaac <isaacdo...@gmail.com
wrote:

hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!

The regulator may be inaccurate NTE parts are not the best.

NTE doesn't manufacture parts - they buy large lots of parts
(sometimes surplus and seconds) and put their brand on them They are
intended for consumer repair shops - hence the large cross reference
directories for NTE parts. A single NTE transistor may "replace"
100's of regular branded and specified parts. Good enough for fixing
the TV or radio.

LM7805 would be a garden variety 5V reg. It requires about 9 volts
input to stay in regulation - and that also means you need to keep the
"valley of the ripple" above 9 volts - a good rule of thumb is 1,000
microfarads of filter cap for each 1/2 amp of current, for around 10%
ripple, with a full wave bridge rectifier.

You also need to allow for the .6 volt diode drop in the rectifiers -
a four diode bridge will loose 1.2 volts in the rectifiers alone.

If you don't have a scope you have to guess at how much ripple is on
the input - too much ripple and it would be dropping out of regulation
- 120 times a second with a FWB and 60 cycle mains. Your meter may
average that and be giving you a 4.9 reading.

Some low drop out (LDO) regulators will only need .6 volts across the
regulator so they might work with only 5.6 volts input.

- allowing again for transformer loss or transformer regulation
(~10%), line regulation (power company accuracy in delivering 120 (or
105-125 volts), diode loss, ripple voltage, etc..

Even a simple three terminal regulator takes a bit of arm waving and
head scratching to apply. Read about it, then read some of the data
sheets for the regulators. They spell out what is considered good and
what the tolerance limits for the parts are, and how they behave under
other environmental conditions.
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thank you for the info... i'm using a cheap wall wart in place of
building a transformer into my project... what i currently have is
very simple, nothing more than the 5v regulator, a 10mf capacitor, and
an led to let me know it's powered... my goal was more to practice
soldering, which certainly needs as much time as i can offer... i have
been working under the assumption that with the wall wart, i didn't
have to worry about a transformer or bridge rectifier?... i don't have
a scope, too expensive for me as a beginning hobbyist...

i'm currently using a book i found online, "Lessons in Electric
Circuits - DC"... is this a good resource?... for free, it certainly
seems so..

thanks again..

Wall warts . . . they can good or bad quality most of the run of the
mill stuff is of questionable quality - they are cheaply made.

In the case of wall warts designed to recharge batteries - they
sometimes incorporate a scheme where they intentionally have poor
regulation to avoid overcharging and to protect them from high
currents (shorted or very low batteries).

Wall warts are generic. They don't all meet some standard, or the
same standard. They do usually meet some safety standard, designed to
fail without starting a fire and designed to provide a high degree of
isolation from the full voltage of the power mains. - but not all of
them fail safe.

Wall warts are likely to be transformers (or switching regulators).
The fact that you don't mention things getting hot or blowing up
suggests the rectification is already inside the wall wart (they can
be either AC or DC warts). Three terminal regs die with overheating
on AC or reversed polarity.

10 ufd is bound to be too small for filtering. You'd want 200 or 1000
on the input to the regulator and maybe a 10 on the output. - and
again some wall warts include a capacitor inside the case for
filtering. What is your input voltage?

Polarized Electrolytic capacitors connected to AC or reverse connected
tend to "vent." Sounds like a firecracker as the case splits open or
the rubber plug on the positive lead flies out. Collateral Damage is
usually minimal but you wouldn't want your eyes close to it. The cap
dies permanently.

I looked at the indexes and one chapter of the book - it looks very
goodhttp://www.ibiblio.org/obp/electricCircuits/index.htm

Problem is, chapter one won't cover the stuff you need to know about
transformers and power supplies. That comes along in chapter two and
three for transformers rectifiers and filters.

I started electronics in high school. They gave us meters, signal
generators, power supplies and breadboards. You might have to lay out
a few bucks for a "trainer" but if you plan to stay with it that
might be a good way to go.

A lot of the "train at home" schools offered trainers as part of the
tuition costs and there might be some on Ebay for less money.

Jameco has one for $439 (Ouch!) Seems to me I've seen them for much
less $70-200 range. The jameco one comes with two variable supplies,
two fixed 5 volt supplies, and a function generator and mounted pots
switches leds etc as well as a breadboard space. Not a good deal in
my opinion, but they aren't the only people selling them.

digital trainer for $129-159http://www.omnitronelectronics.net/phpstore/html/XK-550--AnalogDigita...

Elenco stuff is OK - I've had one of their scopes for years more than
I can say for the Tektronics Sony I had . . .

Search on phrase "analog digital trainer"

Digitals cost less because they usually only give you two or three
fixed supplies.

Ebay had may still have lots of the old Hewlett Packard lab quality
supplies with meters and adjustable voltage and current for $30 (and
worth a whole lot more)

Stay safe, good luck
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- Show quoted text -
Click to expand...
thanks for all of the info!... the wall wart was suggested with one of
the simple schematics i downloaded... i ended up buying a coby, the
cheapest of the cheap, which switches from 3v to 12v... though, as
cheap as it is, my hope is that with knowing how to build a proper 5v
supply, i can forget about the input (is this reasonable?)... i
actually have a breadboard that i used to build the power supply, then
transferred it to a small, more permanent strip board... the original
actually had a 100 mf cap on the input, but my poor planning led to a
disaster that forced me to remove it, leaving only the 10mf on the
output... the sad part is that i understand how the capacitors work to
smooth the signal, but i don't really understand how the input
capacitor can help smooth since there is no load on the input and
ground... though, the fact that i don't understand that may be a sign
that i don't really understand this simple circuit with only a few
components... thanks for the trainer info and links, but i'm not ready
to shell out that much yet... i have a basic stamp, but am already
losing interest simply because of the language... i'm a seasoned
programmer, having started in c, and the basic language annoys me
without cessation... i'm now looking at an arduino... though, i wonder
if it makes better sense to spend the money on a more basic "learn
electric circuits" kit?... now, i think i'll send up a flare for help
in the immediate atlanta area... maybe someone will have time to take
under his wing :)...

thanks,
isaac
 
Jamie wrote:
Michael A. Terrell wrote:

Jamie wrote:

Isaac wrote:


hi all, i'm teaching myself via books and online material just for the
fun of electronics... i have built from spare parts a simple +5v power
supply using an NTE 5v regulator... however, when i measure the
voltage output, it is at 4.91v... i also have a basic stamp board...
on the basic stamp board the voltage regulator is a precise 5v... is
this due to the manufacturing or possibly my design?... what will the
impact be on my projects if the voltage is slightly less than 5v?..

thanks!


nah, just cheap regulators NTE got their hands on that didn't pass the
precise 5 volts out test or drifted a bit.
It's close enough for what it was designed for. Most likely well with
in the limits of generic specs. Now if you were talking about mill specs
then, that could be an issue.



You obviously don't know the difference between a voltage regulator,
and a voltage reference.


Excuse me ?

You obviously don't know how to read and follow the thread?

Yes, I know what a voltage reference is which wasn't part of the
original post as a concern?

Should I start calling you Eeyore JR. ? That last remark resembles
kinship.

I hope you don't hang out with him at that Turkish bathe house
he adores so much.
Click to expand...


You are the one damming NTE parts for being out of spec, without
checking the specs, donkey.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
On Thu, 25 Oct 2007 04:18:30 -0000, Isaac <isaacdover@gmail.com>
wrote:

snip
thanks for all of the info!... the wall wart was suggested with one of
the simple schematics i downloaded... i ended up buying a coby, the
cheapest of the cheap, which switches from 3v to 12v... though, as
cheap as it is, my hope is that with knowing how to build a proper 5v
supply, i can forget about the input (is this reasonable?)... i
actually have a breadboard that i used to build the power supply, then
transferred it to a small, more permanent strip board... the original
actually had a 100 mf cap on the input, but my poor planning led to a
disaster that forced me to remove it, leaving only the 10mf on the
output... the sad part is that i understand how the capacitors work to
smooth the signal, but i don't really understand how the input
capacitor can help smooth since there is no load on the input and
ground... though, the fact that i don't understand that may be a sign
that i don't really understand this simple circuit with only a few
components... thanks for the trainer info and links, but i'm not ready
to shell out that much yet... i have a basic stamp, but am already
losing interest simply because of the language... i'm a seasoned
programmer, having started in c, and the basic language annoys me
without cessation... i'm now looking at an arduino... though, i wonder
if it makes better sense to spend the money on a more basic "learn
electric circuits" kit?... now, i think i'll send up a flare for help
in the immediate atlanta area... maybe someone will have time to take
under his wing :)...

thanks,
isaac
Click to expand...
Here is some free info on regulators.

ON Semiconductor

http://www.onsemi.com/pub/Collateral/HB206-D.PDF


http://elearning.algonquincollege.com/coursemat/saurioc/ELE-3/ELE-3-NOTES/VOLT-REG.pdf

You can also look here

http://elearning.algonquincollege.com/coursemat/saurioc/electron-3.htm
 
On Thu, 25 Oct 2007 04:18:30 -0000, Isaac <isaacdover@gmail.com>
wrote:

pruned

thanks for all of the info!... the wall wart was suggested with one of
the simple schematics i downloaded... i ended up buying a coby, the
cheapest of the cheap, which switches from 3v to 12v... though, as
cheap as it is, my hope is that with knowing how to build a proper 5v
supply, i can forget about the input (is this reasonable?)
Click to expand...
Reasonable if you stay within the confines of the absolute maximum
specifications of the chip.

Cheapest of the cheap doesn't necessarily mean it is a transformer
since they do make universal switching supplies in a wall wart case
these days. I make the distinction because a switcher would certainly
have a built in filter cap.

From what you've said so far, I couldn't guess whether you need a
filter or not . . . Cheap - suggests yes since they are usually only
transformers and the manufacturer doesn't spend more money than
absolutely necessary.

Coby brands a lot of DVD mp3 and other consumer electronics.

actually have a breadboard that i used to build the power supply, then
transferred it to a small, more permanent strip board... the original
actually had a 100 mf cap on the input, but my poor planning led to a
disaster that forced me to remove it, leaving only the 10mf on the
output... the sad part is that i understand how the capacitors work to
smooth the signal, but i don't really understand how the input
capacitor can help smooth since there is no load on the input and
ground...
Click to expand...
The output of a mains powered transformer/rectifier is a sine wave
with every other peak missing in the case of "half wave" rectification
and every peak but with the peaks all of one polarity with full wave
(versus AC which has both positive and negative peaks).

Now that changing signal going into the regulator will still be on the
output if there is no filter since it goes from zero volts to 1.4142 X
the RMS value of the AC every 8 or 16 milliseconds (at 60 cycles
mains). You need to filter it before the regulator if you expect the
regulator to stay in regulation. The cap sits there and provides
energy while the rectifier would be at zero volts. The bigger the cap
the more energy it can supply - and the higher the "valley of the
ripple" - low part of the ripple, in volts, on a scope.

If you filter after the regulator the regulator isn't really doing
regulation just clipping the peaks in the rectified supply to a
uniform five volts. Apply a load and the output ripple will skyrocket
with only a 10 ufd on the output alone. Your meter will average that
(ripple) value and show you a lower voltage. Digital circuits and
analog circuits will have problems with a lot of ripple on the supply.

They usually use a small cap on the output of three terminal
regulators - strictly speaking it is unnecessary. It is there to keep
the regulator from oscillating as it tries to compensate for a high
inductance load (AC theory)

You need to understand Inductance, Capacitance, Inductive Reactance,
Capacitive Reactance, Resistance, Inductance, Impedance, and how it
all ties together with RMS AC and frequency of the AC. Then this
stuff makes sense - that would be chapter two? They aren't hard
concepts to understand, but without it, a lot of what you are doing
won't make sense.

though, the fact that i don't understand that may be a sign
that i don't really understand this simple circuit with only a few
components... thanks for the trainer info and links, but i'm not ready
to shell out that much yet... i have a basic stamp, but am already
losing interest simply because of the language... i'm a seasoned
programmer, having started in c, and the basic language annoys me
without cessation... i'm now looking at an arduino... though, i wonder
if it makes better sense to spend the money on a more basic "learn
electric circuits" kit?... now, i think i'll send up a flare for help
in the immediate atlanta area... maybe someone will have time to take
under his wing :)...
Click to expand...
Microprocessors and controllers can't do everything. It is an analog
world and they don't groke that. There are lots of companies taking
advantage of the fact to provide sensors that already do the
conversions and output a serial stream of data - but that tends to be
expensive, and ignores the multi channel A/D capability already built
into things like the one board controllers or chips.


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