linear regulators

Hi,
I have a project with power circuit (24V) completly isolated from the arduino. to power my mega pro I need 6 to 9 V So I drew up a cirquit for a linear regulator to give me 9V from my second 12V power supply:

12V-9V.png1050×246 3.69 KB

for the power part I might need to use shift registers, which need 5V supply. Since it can not be connected to the arduino can I use the same circuit for the 2 shift registers just with the 7805 and 24V input and 5V output? I dont need much power just to power 2 x a 74HC 165.

12V-9V.png1050×246 3.69 KB

What's your current requirements? I would suggest go for Linear regulators if your current requirements are below 200mA range, otherwise a buck converter is better.

A buc converter produces emi if badly designed. and I don't want to have another daughter board. I don't need a lot of power just guessing for logic (worst case: mega ~40mA + 16 *10 to 15mA so roughly 300mA) if all outputs are used at the same time (which should not happen).
for the shift registers it should be even less (DC Input Diode Current 20mA maximum) so worse case would be 40mA. but I am going down from 24V.

24volt to 9volt at 250mA is (24 - 9) * 0.25A = 3.75watt.

The 7809 would need a heatsink the the size of a matchbox, and get hot.

A 5volt Pololu buck converter would fit inside a matchbox.
Leo..

I bet I could get get 20 Pololu 300ma 9V converters into the matchbox.

Sry I havent been clear: I want to have 9V roughly (worst case) 300mA from a 12V supply. and 5V roughly 50mA from a 24V power supply.
So using your calculation: (12 - 9) * 0.30A = 0.9watt.
and (24-5)*0.05=0.95W
I just have no idea what the maximum would be.

My second question what caps should I choose and why?
third question: should I use 2 linear regulators for the 5 V to dissipate the heat over 2 devices? like a 15 and than a 5V?

If you have noise sensitive analog stuff ( microphone amps, RF below 100MHz etc) use a linear reg.

If not, buck convertors are cheap and efficient - see eg ebay.

Allan

KOR:
So using your calculation: (12 - 9) * 0.30A = 0.9watt.
and (24-5)*0.05=0.95W

1watt could raise the temp of an uncooled TO-220 package by about 60C (above ambient).
Leo..

I found this cool little guy:tiny buck converter

but I still feel very uncomfortable having 2 additional emi sources next to my logic electronics.

buying a bug converter locally is more expensive than a linear regulator circuit.

should I use caps with this aswell?

using 1 of those as the logic supply 12v to 6v (lower limit of the mega pro) I should have plenty of power. Or is it better to use a 5V directly?
edit: @noobian: thanks I was to slow typing found exactly the same one

KOR:
I found this cool little guy:tiny buck converter

but I still feel very uncomfortable having 2 additional emi sources next to my logic electronics.

CMOS is very noise immune, so that probably won't be a problem. 100nF ceramic despiking capacitors on each VDD pin, as close as possible to the chip. And a low ESR, 10 to 47 uF cap at the point where the +5V is connected to the logic circuit board. Besides, logic circuits are powered by SMPS' all the time. It's not an issue. If this were some sort of analog circuit, then extra filtering might be called for.

KOR:
buying a bug converter locally is more expensive than a linear regulator circuit.

What's a "Bug Converter"? UPDATE: I Googled it and realized you probably meant "Buck Converter"

KOR:
using 1 of those as the logic supply 12v to 6v (lower limit of the mega pro) I should have plenty of power. Or is it better to use a 5V directly?

Probably not a good idea to go as low as 6V at Vin. The documentation warns against that, mainly because that is the Absolute Bare Minimum, so that 6V better be VERY stable and truly at 6V [tolerances on regulators could result in less than 6V, even if the regulator is called "6V" -- that's a nominal value -- the reality might be different!] The recommended minimum is 7V.

KOR:
I found this cool little guy:tiny buck converter

It occurs to me that I'm a bit confused about what it is that will be functioning with those shift registers. Apparently it's something other than the Mega, right? So why 6V? At first I thought is was to kill two birds by powering your Mega at 6V and also powering your TTL devices off that same 6V, but, that can't be right, since the Shift Registers are on a separate circuit [powered by the 24V supply], right?

Is this correct: you have two separate circuits:

• An Arduino Mega Pro, that will be powered from a 12V supply [that presumably, also, powers one or more LEDs/LED strings/?? -- based on the MeanWell notation]. AND, there needs to, also, be a 9V supply for some other stuff (consuming around 260mA) -- also from the 12V supply. And, so, the idea is to power both the Mega, AND the other stuff from that 9V regulator.
• You want to power a couple of 74HC165's from the 24V supply (which is isolated from the Mega circuit).

What will the shift registers be doing [i.e. what will connect to them (i.e. Data and Clock, etc.), and what will they be connecting to]?

BTW: expect the Mega to use more like a minimum of 70 to 80mA

yes I meant buck converter^^

yes it is for the same project 24V IO.

It occurs to me that I'm a bit confused about what it is that will be functioning with those shift registers. Apparently it's something other than the Mega, right?

If I have the logic and the 24V io powered from the same supply I don't need the optos, as far as I know.
So I looked at the powersupplies I had access to and found this meanwell 20W 12V which I will be using for logic power and the 24V powersupply for the IO.
I got a tip to use those shift registers for Outputs so I can safe a couple optos. Since they need a decent 5V and they are on the 24V side of the optos they need 5V from 24V.

Is this correct: you have two separate circuits:

An Arduino Mega Pro that will be powered from a 12V supply [that presumably, also, powers one or more LEDs/LED strings/?? -- based on the MeanWell notation]. AND, there needs to, also, be a 9V supply for some other stuff (consuming around 260mA) -- also from the 12V supply. And, so, the idea is to power both the Mega, AND the other stuff from that 9V regulator.
You want to power a couple of 74HC165's from the 24V supply (which is isolated from the Mega circuit).

thats mostly correct. There are 2 supplies one 24V(IO side) and one 12V(logic side).
The mega pro(Mega pro) has a recommended input voltage of 6-9V. So I need to lower the voltage to something between 6-9V on the logic side.
on the power side there might be some of those shift registers, at least I ordered them for breadboarding.
so they need to run on the IO side powered by the 24V supply.

hope this was not more confusing.

Yup, It's more confusing!

KOR:
yes it is for the same project 24V IO.

You're making me work, here ... what is "for the same project 24V IO"? Define "it".

If I have the logic and the 24V io powered from the same supply I don't need the optos, as far as I know.

What "optos"?!? When did you ever mention "optos"?!! You seem to be assuming I can read minds

So I looked at the powersupplies I had access to and found this meanwell 20W 12V which I will be using for logic power and the 24V powersupply for the IO.

Wait! I thought you said that the Logic [i.e. the 74HC165(s)] will be powered from the 24V supply! So, now you're referring to the Mega side as the "logic" side, and the 74HC165 side as the "IO" side?!? Please make your language more consistent and less ambiguous!!!

I got a tip to use those shift registers for Outputs so I can safe a couple optos.

You seem to be assuming that I was privy to that conversation! Again, I can't read your mind!!

Since they need a decent 5V and they are on the 24V side of the optos they need 5V from 24V.

WHAT OPTOS?!? What needs a decent 5V ... and how did you arrive at that?

The mega pro has a recommended input voltage of 6-9V. So I need to lower the voltage to something between 6-9V on the logic side.

Do you mean "Mega" (what's a "Mega Pro"?). Assuming you mean "Mega", then False. The recommended input voltage range is 7-12V.

Do you see the problem I'm having, here? You are making assumptions, expecting me to know things there is no way I can know [like what "Optos" have to do with anything, and what "tip" you're referring to], etc. Please, when you write up a post, read it back, to yourself, and ask the following questions:

• Have I supplied enough informaiton
• Have I made my language clear, consistent and unambiguous.
• If I were the one reading this, and trying to help me, would I know what the heck I was talking about?
• You might also catch a typo--or two--thus making it even easier for us to read -- those of us who are giving you our time, for free!

It is always good to refer to the datasheets just for a start.

http://tronixstuff.com/wp-content/uploads/2010/06/fairchild-lm7805c.pdf

It lists the input and output capacitors, suggested, at 0.33uF and 0.1uF respectively.

In my experience, the values you have will work just fine. In general, put the 0.1uF capacitors close to the LM7809. If your power source has capacitors, the larger capacitor on the input side is not really necessary unless you have long wires between it and the LM7809.

For the output side, put the larger capacitor closer to the circuits drawing power.

FYI, the LM780x series has a dropout voltage of 2V, so your input voltage can only drop to about 11V before the 9V starts to droop. Also on the datasheet.

I can't figure out what is connected where to provide a useful comment. I'm thinking a block diagram is in order here now.

ReverseEMF:
Do you mean "Mega" (what's a "Mega Pro"?). Assuming you mean "Mega", then False. The recommended input voltage range is 7-12V.

KOR:
The mega pro (Mega pro) has a recommended input voltage of 6-9V.

That at least clears up the Pro Mega, question.

Here is the diagram hopes this clears my confusing texts

Sorry not really. We know the voltages involved, but not what section of the project they are for.

What is "second power supply"? What is the voltage and what does it power?

The Mega Pro box shows that it needs two power supplies but does not show why. What inside requires 12V and 6-9V (obviously the Pro Mega, anything else?).

Similar for shift register box. What inside boxes requires 24V vs 5V?

In my current project, they call this a single line power distribution drawing. Each box has one voltage going to it. If a module requires two voltages then there are two "touching" boxes. This works very well to verify if the modules requires 24VDC and 110VAC are being wired with the correct voltages (instead of 24VDC and 220VAC ).

KOR:
Here is the diagram hopes this clears my confusing texts

Nope. Still not clear enough.

• Why does the Mega need a "second powersupply[sic]"? Is that "second powersupply[sic]", the 9V supply? Why does it need to be 9V?
• There is an "Opto bridge" AND more other optos somehow associated with the Mega?
• What is the Shift Register for? Why is it "24V output"? Or is this a punctuation issue? Since I recall we were powering the Shift Registers at 5V.
• It's NOT 6-9V! It's 7-12V!!

And, frankly, because you have yet to collect ALL the information in one place (like expected current demands for each supply, and a clearer breakdown of ALL the pathways, and circuitry, so I don't have to keep scrolling around to get all the fiddly little details), I shall back away. Saying "needs 6-9V and second powersupply[sic]" all in the same box is nebulous and "blackbox". And, having to scroll to another part of the conversation to collect all the other bits of information, hoping that I've properly fit all the pieces together, is just too tedious! I need you to meet me halfway, and present this stuff in a way that makes it easy for me to examine. In other words, clear, complete & concise!

OR

Just take the short answer, and use Switch Mode regulators for anything above, say 50mA, and otherwise, use Linear regulators. That is, unless there is some "noise sensitive" component in your "blackbox" [refer to previous replies for a definition of "noise sensitive"]. And many of the answers you probably need, have already been presented on this thread. If you don't understand a particular reply, quote it and ask about it in particular, in a way that is clear, complete & concise.

KOR:
Sry I havent been clear: I want to have 9V roughly (worst case) 300mA from a 12V supply. and 5V roughly en clear: I want to have 9V roughly (worst case) 300mA from a 12V supply. and 5V roughly

12V to 9V regulator, to 9V connect 5V regulator