I know, that's not what I meant.
I'm making a controller board which is suppposed to be able to accept 5-12V. Some of the subsystems require 9V and 6V, but at logic levels these are not needed, i.e if 5V are put in, those systems can't be used and shouldn't. If I daisy-chain the input, a 7809 and a 7806, what would happen if 5V instead of 12V are put in? I want to be able use the 5V systems if 5V are put in.
Rafael
With only 5V into a 7809, will only result in GIGO (garbage in, garbage out.)
The input of a 78xx regulator must be at least 3.5V greater than its corresponding output.· That's called the drop-out voltage (it's in/on the data sheet.)
There's a LM1084-5V, a low drop-out type, and its input can be as little as 6.5V· There·are 12V and ADJustable versions, too.· (You can get the LM1084-ADJ from bgmicro.com for $1.95.· They have the same pin-out as a LM317.)
I believe there are similar LDO Regulators that will still pass lower voltages through them.· I just can't think of the part # off the top of my head, but if someone knows what I mean, please type...·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Chris Savage Parallax Tech Support csavage@parallax.com
Basically speaking, if the input voltage is less than the minimum usable voltage, the voltage you get out is the voltage in minus the internal dropout. If the regulator series drops 2.2V internally (like the 78xx), you get 2.2V less then the input. Thus, put in 5V to a 7805, get 2.8V out. I have no idea if·2.2v is the·dropout for a 7809 or 7806, but I imagine it's going to be in that range. Go check a data sheet or two. The 294x series has low drop out, only 0.7V, so 5V in gets 4.3V out.
Go to page 13, where you'll find the schematic for a supply that can use 3V to 11V in, and put out 5V/500mA! These are available in DIP-8, at DigiKey for $4.45 each, one piece.
How much voltage can I put into a 7805 and/or 7809 without heating them up to the thermal shutoff?
If I can put 12-13V through the 7805 for >45min then I won't need any of that more complex stuff. I have max, 1 square inch of board space for my regulators and I need 5 and 9V from anything between 5 and 12V (if it's under 9, I wont be needing that.). To cap it, I have very limited soldering and breadboarding experience, so I tend to do rather space-consuming designs...
Rafael
flyingfishfinger said...
How much voltage can I put into a 7805 and/or 7809 without heating them up to the thermal shutoff?
If I can put 12-13V through the 7805 for >45min then I won't need any of that more complex stuff. I have max, 1 square inch of board space for my regulators and I need 5 and 9V from anything between 5 and 12V (if it's under 9, I wont be needing that.). To cap it, I have very limited soldering and breadboarding experience, so I tend to do rather space-consuming designs...
Rafael
Don't use any linear voltage regulator, as they DO heat up, and waste energy...
The National LM2574 series switcher are a better choice,
A) they would easily fit in 1 square inch board area they are switchers, so heat is minimal..
C) they can supply up to 500ma, and come in fixed, plus a variable output..
Or the TI 78st100 series of switchers that have a to220 pinout, and an output of up to 1500ma
These are my favorite.
I'll have a look. How do they behave when powered below output voltage?
BTW, I just cheked and found that the ones you prefer must be powered by at least 7V in any case for any output voltage(?????)
Thanks
Rafael
Post Edited (flyingfishfinger) : 11/9/2005 12:14:59 AM GMT
flyingfishfinger said...
I'll have a look. How do they behave when powered below output voltage?
BTW, I just cheked and found that the ones you prefer must be powered by at least 7V in any case for any output voltage(?????)
Thanks
Rafael
Wellllll, you said that you needed a possible 9v-5v in your design....
You need to narrow down and fix your voltage requirements, then design a circuit that will do what you require.....
Either a low dropout regulator, or a switcher.....
You still need a common supply voltage thats HIGHER than your highest v required...
flyingfishfinger said...
How much voltage can I put into a 7805 and/or 7809 without heating them up to the thermal shutoff?
If I can put 12-13V through the 7805 for >45min then I won't need any of that more complex stuff. I have max, 1 square inch of board space for my regulators and I need 5 and 9V from anything between 5 and 12V (if it's under 9, I wont be needing that.). To cap it, I have very limited soldering and breadboarding experience, so I tend to do rather space-consuming designs...
Rafael
To answer that question, it'll depend on how much heatsinking you have setup. And I think, the amount of current you need for your project.
As previously mentioned, these devices basically "burn" up the extra energy. They are very inefficient. I know the simplicity of them is really appealing, but there are some other similiar devices with the same simplicity, without the wasted energy. (The switching type.)
Imagine this, and I'll have to make sure my values are right... but imagine you use a 7805 with a 12V input, and no heat sinking. This means you have to get rid of 7 volts right? 7 volts * 1 amp is 7 watts.... So, you're having to waste 7 watts to get your 5V. There are some soldering irons that run off of 15watts, so you're at half of the power of a soldering iron. Get the idea of hte amont of possible heat (and thus wasted energy) here?
You need a 5V and a 9V supply? What's the 9V for? Could it be 12V? If so, considering using a hacked computer power supply. They are cheap, and offer 5V, and 12V power supplys, as well as 3.3V, and -5V and -12V. I use a hacked computer power supply as my bench test power supply, and it works excellent. I realize it's NOT without the 1 inch requirment.
Knight.
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This message transmitted with 100% recycled electrons.
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Light the man on fire, and he will be warm for the rest of his life.
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Well, I'm running the 9V into the LEGO Mindstoms RCX computer as a coprocessor, and I imagine that would burn up on 9V. Although I have to admit I won't be using it right yet, I do want to reserve that option for later. But if my board is full, I won't have space for the regulator later (LOL) so I just want to put it in now.
Rafael
Danke. Ich schaetze mal ich habe die Wahl zwischen ineffizienten 78xx'n oder diese kleinen Platinen die aber wiederum mehr Teile mit sich bringen, nicht wahr?
Rafael
Mouser.com has switching regulators suited to your needs. Goto www.mouser.com/micrel, search for "803-" in the search part# or mouser # box. a good part # for you would be " 803-mic2172bn " it's a DIP 8 pkg, input from 4-14V output is adj from 1.23-37V, drives i belive either 1.3A or 1.3mA (the book doesn't specify), and costs under $3.
FlyingFishFinger
Posts: 461
Comments
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Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html
·
I'm making a controller board which is suppposed to be able to accept 5-12V. Some of the subsystems require 9V and 6V, but at logic levels these are not needed, i.e if 5V are put in, those systems can't be used and shouldn't. If I daisy-chain the input, a 7809 and a 7806, what would happen if 5V instead of 12V are put in? I want to be able use the 5V systems if 5V are put in.
Rafael
The input of a 78xx regulator must be at least 3.5V greater than its corresponding output.· That's called the drop-out voltage (it's in/on the data sheet.)
There's a LM1084-5V, a low drop-out type, and its input can be as little as 6.5V· There·are 12V and ADJustable versions, too.· (You can get the LM1084-ADJ from bgmicro.com for $1.95.· They have the same pin-out as a LM317.)
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Chris Savage
Parallax Tech Support
csavage@parallax.com
If you want to put in a wide range of voltages and reliably keep 5V for the digital logic, consider using a DC-DC converter. Here's the site for a data sheet for the MAX1771:
http://rocky.digikey.com/WebLib/Maxim/Web%20Data/MAX1771.pdf
Go to page 13, where you'll find the schematic for a supply that can use 3V to 11V in, and put out 5V/500mA! These are available in DIP-8, at DigiKey for $4.45 each, one piece.
Later!
kenjj
If I can put 12-13V through the 7805 for >45min then I won't need any of that more complex stuff. I have max, 1 square inch of board space for my regulators and I need 5 and 9V from anything between 5 and 12V (if it's under 9, I wont be needing that.). To cap it, I have very limited soldering and breadboarding experience, so I tend to do rather space-consuming designs...
Rafael
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Jon Williams
Applications Engineer, Parallax
Don't use any linear voltage regulator, as they DO heat up, and waste energy...
The National LM2574 series switcher are a better choice,
A) they would easily fit in 1 square inch board area
C) they can supply up to 500ma, and come in fixed, plus a variable output..
Or the TI 78st100 series of switchers that have a to220 pinout, and an output of up to 1500ma
These are my favorite.
Bob N9LVU
BTW, I just cheked and found that the ones you prefer must be powered by at least 7V in any case for any output voltage(?????)
Thanks
Rafael
Post Edited (flyingfishfinger) : 11/9/2005 12:14:59 AM GMT
Wellllll, you said that you needed a possible 9v-5v in your design....
You need to narrow down and fix your voltage requirements, then design a circuit that will do what you require.....
Either a low dropout regulator, or a switcher.....
You still need a common supply voltage thats HIGHER than your highest v required...
Bob N9LVU
To answer that question, it'll depend on how much heatsinking you have setup. And I think, the amount of current you need for your project.
As previously mentioned, these devices basically "burn" up the extra energy. They are very inefficient. I know the simplicity of them is really appealing, but there are some other similiar devices with the same simplicity, without the wasted energy. (The switching type.)
Imagine this, and I'll have to make sure my values are right... but imagine you use a 7805 with a 12V input, and no heat sinking. This means you have to get rid of 7 volts right? 7 volts * 1 amp is 7 watts.... So, you're having to waste 7 watts to get your 5V. There are some soldering irons that run off of 15watts, so you're at half of the power of a soldering iron. Get the idea of hte amont of possible heat (and thus wasted energy) here?
You need a 5V and a 9V supply? What's the 9V for? Could it be 12V? If so, considering using a hacked computer power supply. They are cheap, and offer 5V, and 12V power supplys, as well as 3.3V, and -5V and -12V. I use a hacked computer power supply as my bench test power supply, and it works excellent. I realize it's NOT without the 1 inch requirment.
Knight.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-=-=-=-=-=-=-=-=-=-=-
This message transmitted with 100% recycled electrons.
-=-=-=-=-=-
Gravity doesn't exist. The Earth sucks.
-=-=-=-=-=-
Make a man a fire, and he will be warm for the night.
Light the man on fire, and he will be warm for the rest of his life.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-=-=-=-=-=-=-=-=-=-=-
Rafael
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Greetings from Germany,
G
Rafael
Is that circuit the same as the example circuit on the product specs pdf from national semi?
Bob N9LVU
Rafael,
die Teile m