Hi Jim. Replied.
A single 19.25v Zener might be better than three in series although if in series they will all pass the same amount of current. The earth connection is probably OK as it is.
Printable View
Hi Jim. Replied.
A single 19.25v Zener might be better than three in series although if in series they will all pass the same amount of current. The earth connection is probably OK as it is.
A 19.25V Zener would be a great improvement do to the simplification, no doubt. However I can't find any 1W in that voltage.
Jim -
I have compleated my layout:
http://www.jkwynn.co.uk/Project_Imag..._Regulator.pdf
I will wait to see what the out come is for Zener choice and resistor value before going any further.
The layout is optimised for straight line point to point soldering of uninsulated wire.
Further space could be saved if it was optimised for PCB tracks :eyebrows:
I see what you mean! Although there are some 19V SMD available. How about using a TL431, lower impedance still and much quieter as well...something like this:Quote:
Originally Posted by 6L6
http://i94.photobucket.com/albums/l8...17_Control.png
This is for a 5v output from a 9v battery. The Cathode needs a min of 1mA for the TL431 to work hence the 8K2 resistor. I would also bypass the TL431 Cathode to ground just as with the Zener and also bypass the VRef pin (lower resistor) to ground with a small cap, say 0.1uF.
VOut=1+(R1/R2) x 2.5
Make R1 and R2 1% or better.
Ken, That looks sharp! I like it. :)
What output voltage do you want? Depending on which schematic you look at, the regulator's output is 20V to 21V. So anywhere in that range will be fine.
This circuit's voltage will be the summed voltage of the Zener string plus 1.25V. (The 1.25 is the voltage that the 317 will keep between the adjust and out pins) So assuming for a second you want the output to be 20.5V, you will need 19.25V in the Zener string, as 19.25 + 1.25 = 20.5
So what voltage Zeners to use? Well, 19.25/3 = 6.41V, and 3 in series will get you back to 19.2. That's great!
But can you get 6.4V Zeners? That's the issue. You might not be able to. So perhaps you can find (for example) 5.6V and 8V Zeners. Use 2 of the smaller and one of the bigger, they will add up to the 19.2 reference voltage you need and all is good. Or some other combination.
If you can find (2) 9.6V Zener, Robert will in fact be your sister's brother.
Upon the suggestion of NRG (Neal), making the resistor a smaller value, perhaps 100ohm, will keep more current flowing through the Zener string, making it more linear. That seems like a fine idea. Use any resistor value you have between 100-240 ohm, lower is probably better.
Neal - There is something about using a 431 that I don't care for in this. I don't like the idea of having one voltage dependent regulator as the reference for another. (Although I do know that the 431 is a shunt, not a linear regulator) There is a certain elegance to standing the 317 on a Zener stack that I am attracted to.
However - As I have some 431 in my bits box, I will give this configuration a go additionally when I try the 'tracking pre-regulator' scheme. It might be fantastic. :)
No Problem Jim but I see the TL431 as a much better solution that a Zener string! ;) Anyhow if you do go this route you'll need about a 10mA draw on the LM317 so R1 at 1K8 and R2 at 240R would get you close to 21v and draw just over 10mA...
Jim –
20.5v should do, I think that’s what the KAB board puts out.
Will this pair of zeners fit the bill, one 11v + one 8.2v both are 1w with specs as below:
http://uk.farnell.com/fairchild-semi...-41/dp/1467575
http://uk.farnell.com/fairchild-semi...11v/dp/1651545
If ok, I will re-jig the layout for a pair of zeners and go for the 100 Ohm resistor.
Although I have never made one before, I am seriously thinking of making a PCB for this project, using the laser jet toner transfer method. (Iron on acid resist). I am looking into it further as it would appear all you need is access to a laser printer and a design of course, plus some FR4 board and Ferric Chloride to etch it, which can both be had off Flebay for about £10. Probably get 8 boards out of the 100 x 160mm sheet. Mmnn…. May just take the plunge.
Yes, the zeners are fine.
If you make a PCB, put me down for one! (Get a couple spare Zeners and send them on as well, if you are going to make the PCB for two) I'll PayPal you reimbursement.
OK Jim - bear with me as its a new process for me so I won't be as rapid as someone that is familier and I need to send away for the materials.
I've started looking it the track layout, I looked at some of the free PCB design software but it all seems to have a steep learning curve. I am a CAD designer by profession but don't see the point in getting too deeply involved, for something so simple and chances are I will have forgoten how to use it before the next project comes around. I am going to do this very basic layout in Corel Draw, it will do the task just fine.
I'll purchase a bunch of Zenners, at 7pence each its a waste of the parcel space not to. :D
Take your time, I'm certainly in no rush!