On May 24, 9:34=A0am, NT <meow2...@care2.com> wrote:
> On May 22, 5:27=A0pm, Father Haskell <fatherhask...@yahoo.com> wrote:
>
> > Low current (< 100 mA) power supply regulator. =A0Any reason I'd want t=
o
> > use 7809s instead of cheaper 9.1v zeners?
>
> This suggests you want a regulated voltage, but presumably don't care
> about energy waste. So probably mains power, but what needs regulated
> 9v? reg v zener is already covered, so what about other options. Would
> smoothed unregulated do? Is it an option to tweak the circuit so it
> doesnt need a clean supply?
>
> NT
Guitar pedal supply -- pedals are supposed to sound better
if you run them from separate regulators. Most draw less than
20 mA, so cheaper zeners should power them fine and allow
more branches per dollar.
Reply by NT●May 24, 20122012-05-24
On May 22, 5:27=A0pm, Father Haskell <fatherhask...@yahoo.com> wrote:
> Low current (< 100 mA) power supply regulator. =A0Any reason I'd want to
> use 7809s instead of cheaper 9.1v zeners?
This suggests you want a regulated voltage, but presumably don't care
about energy waste. So probably mains power, but what needs regulated
9v? reg v zener is already covered, so what about other options. Would
smoothed unregulated do? Is it an option to tweak the circuit so it
doesnt need a clean supply?
NT
Reply by Jamie●May 22, 20122012-05-22
Father Haskell wrote:
> Low current (< 100 mA) power supply regulator. Any reason I'd want to
> use 7809s instead of cheaper 9.1v zeners?
You can use a 78L09 which is a small 100 ma regulator however, you do
need a little head way before that. These types of regulators require a
minimum above the regulated output voltage to work. Like 2 volts or more
to be on the safe side.
A zener is ok of you can live with the wasted power. you'll find a
integrated solution is more stable and uses less power why it's laying
around doing nothing. (quiescent current).
Now I like something like this..
http://www.ti.com/lit/ds/symlink/mc33063a.pdf
It'll handle up to 40 volts in and start at very low
voltage. It has its own internal ref 2.5V that you can use
with the voltage divider to configure for the voltage you need.
You can use it as a step up, step down, voltage to voltage. etc..
It handles up to 1.5 A on chip and it's cheap!
It's up to you. Most people these days are very conscientious about
power usage, especially when it comes to batteries as the supply.
Jamie
Reply by Spehro Pefhany●May 22, 20122012-05-22
On Tue, 22 May 2012 11:44:36 -0500, Tim Wescott <tim@seemywebsite.com>
wrote:
>On Tue, 22 May 2012 09:27:27 -0700, Father Haskell wrote:
>
>> Low current (< 100 mA) power supply regulator. Any reason I'd want to
>> use 7809s instead of cheaper 9.1v zeners?
>
>Because the 7809 will give you better regulation and significantly less
>current wasted to achieve it than the Zener will -- particularly if your
>current requirements vary. And it's easier to use, once you've verified
>that you won't burn it up.
>
>A 1N4739A from DigiKey will run you $14.40 if you buy 100 of 'em. An
>MC78L09 will run $22.00. That's a $0.076 difference, you still have to
>buy the resistor to make the Zener work, you have to _always_ present it
>with about 105mA, even when the circuit downstream isn't pulling any
>current at all, and the regulation won't be nearly as good as the 7809.
>And if your input voltage varies much then you won't be able to reliably
>hold the Zener current down enough to use a 1W diode, which means you'll
>have to spend even more.
>
>If you can stand 9.3 to 9.4V, then a 1N5240 is only $7.32/100, a PMBT2222A
>is only $7.42/100, and a resistor is something like $0.48/100 -- that
>gives you much better regulation than a Zener alone, about the same or
>better dropout characteristics than a 7809, and should cost less than a
>penny more than your bare nekkid Zener, once you buy the resistor to bias
>that honkin' big thing.
Simple zeners are cheap in quantity- you can probably get all three
parts for 2-3 cents. But a small transistor does not have the power
dissipation capacity of a TO220. If you have a 12V input and need 9V
at 100mA, that's 420mW at +10% in, which is too much for an SOT-23.
If you're making a Chinese-assembled gewgaw that doesn't have to work
over a wide temperature range or for decades, you can stick an 8050 in
there and still stay at less than 3 cents, which is probably less than
1/5 the cost of a 7809.
Reply by Phil Hobbs●May 22, 20122012-05-22
Father Haskell wrote:
>
> Low current (< 100 mA) power supply regulator. Any reason I'd want to
> use 7809s instead of cheaper 9.1v zeners?
Better regulation
Lower power dissipation
Better ripple rejection, probably
Lower output impedance.
Otherwise, not really. ;)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Reply by John Larkin●May 22, 20122012-05-22
On Tue, 22 May 2012 11:44:36 -0500, Tim Wescott <tim@seemywebsite.com>
wrote:
>On Tue, 22 May 2012 09:27:27 -0700, Father Haskell wrote:
>
>> Low current (< 100 mA) power supply regulator. Any reason I'd want to
>> use 7809s instead of cheaper 9.1v zeners?
>
>Because the 7809 will give you better regulation and significantly less
>current wasted to achieve it than the Zener will -- particularly if your
>current requirements vary. And it's easier to use, once you've verified
>that you won't burn it up.
>
>A 1N4739A from DigiKey will run you $14.40 if you buy 100 of 'em. An
>MC78L09 will run $22.00. That's a $0.076 difference, you still have to
>buy the resistor to make the Zener work, you have to _always_ present it
>with about 105mA, even when the circuit downstream isn't pulling any
>current at all, and the regulation won't be nearly as good as the 7809.
>And if your input voltage varies much then you won't be able to reliably
>hold the Zener current down enough to use a 1W diode, which means you'll
>have to spend even more.
>
>If you can stand 9.3 to 9.4V, then a 1N5240 is only $7.32/100, a PMBT2222A
>is only $7.42/100, and a resistor is something like $0.48/100 -- that
>gives you much better regulation than a Zener alone, about the same or
>better dropout characteristics than a 7809, and should cost less than a
>penny more than your bare nekkid Zener, once you buy the resistor to bias
>that honkin' big thing.
A BCX70J is only 4 cents, and has a huge, bracketed beta!
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Reply by Tim Wescott●May 22, 20122012-05-22
On Tue, 22 May 2012 09:27:27 -0700, Father Haskell wrote:
> Low current (< 100 mA) power supply regulator. Any reason I'd want to
> use 7809s instead of cheaper 9.1v zeners?
Because the 7809 will give you better regulation and significantly less
current wasted to achieve it than the Zener will -- particularly if your
current requirements vary. And it's easier to use, once you've verified
that you won't burn it up.
A 1N4739A from DigiKey will run you $14.40 if you buy 100 of 'em. An
MC78L09 will run $22.00. That's a $0.076 difference, you still have to
buy the resistor to make the Zener work, you have to _always_ present it
with about 105mA, even when the circuit downstream isn't pulling any
current at all, and the regulation won't be nearly as good as the 7809.
And if your input voltage varies much then you won't be able to reliably
hold the Zener current down enough to use a 1W diode, which means you'll
have to spend even more.
If you can stand 9.3 to 9.4V, then a 1N5240 is only $7.32/100, a PMBT2222A
is only $7.42/100, and a resistor is something like $0.48/100 -- that
gives you much better regulation than a Zener alone, about the same or
better dropout characteristics than a 7809, and should cost less than a
penny more than your bare nekkid Zener, once you buy the resistor to bias
that honkin' big thing.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Reply by Father Haskell●May 22, 20122012-05-22
Low current (< 100 mA) power supply regulator. Any reason I'd want to
use 7809s instead of cheaper 9.1v zeners?