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Topic: Your latest purchase (Read 124559 times) previous topic - next topic

SirNickity

#780
Dec 31, 2013, 10:03 pm Last Edit: Dec 31, 2013, 10:11 pm by SirNickity Reason: 1
Using a resistor in series with a Zener is a common way to get a voltage reference, but it's of limited value as a regulator.  Basically the current draw has to be exceedingly small, because as you pull variable current from the supply, there will be a corresponding voltage drop.  If you follow this with a traditional linear regulator, sourced from the junction between R1 and D1, the regulator will drop the remaining voltage.  This could be anywhere from the entire voltage difference (at no load) to being already well below the desired regulated voltage (at heavy loads).  If you calculate the max allowable current draw and size the resistor so this load corresponds to the point where its voltage drop results in a perfect Vin for the linear regulator, you can probably make it work, but it's a kludge.

In addition to being dependent on current, using a resistor is not at all an efficient way to drop voltage -- it becomes wasted heat.  However, it's essentially how all linear regulators work (except the resistance is variable depending on the load) and also what makes linear regulators inherently inefficient.

None of that really takes the Zener into much consideration.  For that, you have competing goals:  Keep the resistance high to avoid dumping tons of current through the Zener, which would overheat it and burn it out; and keep the resistance low so you can draw current from the PSU without simultaneously dropping all available voltage through the resistor.  There's a fairly small window where you can satisfy both criteria.

Your line of thinking is how to reduce the heat load on one regulator, correct?.  The simple solution to this is to spread that load among other devices.  One such way is to use a regulator as a controller, and have the load pass through a heftier transistor (and/or parallel transistors).  You can also pre-regulate the voltage so the drop is shared between two or more regulators.  This works, but it's usually not the best approach.

GoForSmoke

Would an LM317 get around all that? I think I have however many a dollar or two cost from where I fleshed out an order with cheap, interesting-looking parts to justify shipping... in one of my past purchases (back OT?).
Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

SirNickity

No, an LM317 is still a linear regulator -- it's just designed to output an adjustable voltage.  You can force a 78xx or 79xx to change their regulated voltage too, if you step outside the typical application design in the data sheet.

Many of the linear regulator datasheets do include schematics for using external transistors though.  Then you're designing a linear regulator that has much in common with a Class B power amplifier, with the same flaws... namely, that Class D amps and switching regulators can be much more efficient for high-current loads, at the expense of being more complicated and not as well behaved if poorly designed or poorly matched to the load.

waterlubber

Air, and some RGB LEDs for my Mood Light (look meh up on Instructables)
waterlubber
Codes in: C++, Python, some VB, winDOS, YAML
Likes cake and arduino. And minecraft.

retrolefty

A 99 cent, 12vdc @ 2 amp switching regulated wall transformer with 10 foot cable with standard arduino like connector at a local charity store. Can't have too many of these.

Lefty

nightcrawler218

2mm & 5mm heat shrink cable.
"Imagination is more important than knowledge."
-Einstein

TomGeorge

Hi, just used my work bonus to goto Bunnings (DIY) to get materials to build proper shelving to sit on work bench.
Hope to get LED string under lower shelf to light bench area and hooks and bars on side to fasten clip leads, gluegun and heatgun.
Also want to run leads from LAB supply to a series of terminals along front of shelf, sick and tired of banana plug on banana plug on banana plug etc etc..to get juice from supply and provide gnd ref for  test gear.
Have made design so as little timber cutting as possible.
Will let you know how I go.

Tom..... :)  (damn forgot to check if drill is charged..) Have circular saw will attempt carpentry.
Everything runs on smoke, let the smoke out, it stops running......VK3DMK

Peter_I

A bunch of LEDs in jolly colors from evilbay.

I'm a sucker for LEDs.......they are just so pretty! They shine, they smile to me, they illuminate me!

(or maybe it is just the memories of the anemic green and red LEDs of the late seventies and eighties?)
"Nothing is foolproof to a sufficiently talented fool"

MAS3

Quote from: TomGeorge

..to build proper shelving to sit on work bench.


You know this calls for a picture after completing this, don't you ?
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

SirNickity

I was thinking the same thing.  Maybe someone should start a "show off your cool work bench" thread.  I could use some inspiration.

(My work bench is the shield plate from an old LCD monitor, sitting on one of the three unoccupied square feet of floor in my spare room.  But some day...)

JimboZA

Ordered the laser cut parts for the uFactory robot arm....
"Could you do the egg bacon spam and sausage without the spam then? "

No PMs for help please.
DO NOT power servos from Arduino 5V: give them their own power and connect the grounds.

TomGeorge

Quote
"show off your cool work bench" thread.

Good idea, it would show the hideous, depressing, uplifting, inspiring places that our ideas and projects have to take form and succeed.

Tom.... :) (Got it together, just a bit of white paint, fit the LEDs, 10 packs of Ibrufen to fix the back) :smiley-sweat:
Everything runs on smoke, let the smoke out, it stops running......VK3DMK

justjed

Hello all!

Okay, my Arduino activity has been zero for a while. Other stuff taking up too much room in my head. Just got my ham technician's license, and bought a Yaesu FT-60R. But what I dropped in to share with you is this, purchased for $45 at the NCARC ham fest today. I have yet to plug it in. Didn't come with probes. I think you can see in the pic that the "B (DLY'D) Trigger Slope" pot stem is bent and the collar is broken. It does turn, so maybe the pot is still OK. Seems to not quite have a full range of motion. Seller said the the pots all need cleaning. So, I have a project.  :D
... it is poor civic hygiene to install technologies that could someday
facilitate a police state. -- Bruce Schneier

GoForSmoke

Congrats on the tech license!
Good to know that ham fests still live. 
Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

justjed

Thanks!

Yes, ham fests live. We have 3 more this year that I can think of off the top of my head, here in Colorado.

Landlord came down and gave me a quick intro to scope usage. Seems this one is working fine, other than dirt in the pots and switches. W00T! He also gave me a 10x probe passed along from a friend of his who was at the show when I bought the scope.

The part that really tickles me, now that I'm looking into this? It's apparently worth a lot more than I paid.  ]:) Okay,mine hasn't been refurbed. Do I care? No.
... it is poor civic hygiene to install technologies that could someday
facilitate a police state. -- Bruce Schneier

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