Please make me undestand how to read "Datasheets" and how to obtain the required info

[netfreak]

Dear Sirs,
i have been through a lot of datasheets of a lot of ics but am not able to understand a single of them. Like lets suppose the data sheet of IC LM7805, LM317T. I cant get anything out of the datasheet like how much output current it will give how much input voltage is required, how much output voltage will be given and things like this, Please make me understand on understanding how to read data sheets

 

[MrAl]

Hi,

For those two ic's you mentioned dont they give the output current right on the data sheet, such as "1 amp" or "1.5 amps" ?

 

[tvtech]

Dear Sirs,
i have been through a lot of datasheets of a lot of ics but am not able to understand a single of them. Like lets suppose the data sheet of IC LM7805, LM317T. I cant get anything out of the datasheet like how much output current it will give how much input voltage is required, how much output voltage will be given and things like this, Please make me understand on understanding how to read data sheets

You need to learn the basics of Electronics. Without the basics, you are in the wild and clueless. And nobody here can try and teach you everything.

I don't know what else to say.

TV Tech

 

[Ian Rogers]

Believe it or not.. You get more info when buying... Take the LM7805.... Put that into ebay and voila... all the data.. current ... voltage... pinout.

There can be pitfalls... RS sells a LM2576T-5, stating a massive 5amp rating..... (it's only 3).... Tvtech is correct.. experience prevails..

 

[unclejed613]

rule #1- the ABSOLUTE MAXIMUM ratings are exactly that.... stay away from those voltage, current, and temperature levels, as they are guaranteed to make the device fail.

 

[simonbramble]

learn a little bit of theory, then build a project based on the theory. You learn by doing. Build a basic power supply with a 7805 regulator on the output to give a stabilised 5V supply. Then add some bells and whistles to it, learning as you go. As the previous guys have said, you need to know the theory before you can understand datasheets, but the only way to learn is to wire something up

 

[unclejed613]

you will also notice that depending what the device is, and who the manufacturer is, determines a lot of what information is included in a data sheet, and how it's presented (and there are parameters that are named one thing in one data sheet, and has a different name in another)

but i would definitely do what others have said here.... try building a few simple things and learn how they work, and this will (along with learning some basic theory) begin to help you understand data sheets, and why some things are more important than others in a data sheet. also, you can get a SPICE program and use it to see what certain devices do in a circuit. i recommend you get a basic electronics textbook and start at the beginning. learning how electricity behaves, and what simple components do will give you some insight into how things work. another good place to look is in publications like the ARRL Radio Amateur's Handbook, which contains basic theory as well as simple, intermediate and advanced projects. when i was young, my grandfather gave me his collection of several year's worth of these (1955-1964). the chapters on theory didn't change much (except for the addition of transistor theory), but most of the projects were different from year to year.

 

[tvtech]

Here is a little something. Very basic roots to start you off on a solid understanding of Electronics.

I don't work for Mantech BTW...I just buy my parts from them. Never had a dud part yet. Like RS but @ least 50% cheaper.

Please see attachments.

Cheers,
TV Tech

 

[crutschow]

Let's look at this LM317 data sheet.

The very first sentence says it is capable of supplying currents in excess of 1.5A over a 1.2V to 37V output range. That tells you the maximum current it can deliver and that is has an adjustable voltage output. The current does depend upon the package as shown by the Package Option table on the same page.

If you look at page 4, it lists the Absolute Maximum Ratings. You always want to operate below those values with a comfortable margin to avoid zapping the device. Among other things, you see that the maximum input-output voltage differential is 40V so, for most applications, you should keep the input (supply) voltage below this value.

If you look at the curve labeled Dropout Voltage on page 6 you will see the minimum voltage drop across the regulator required for it to work properly. The input voltage always needs to be equal to or above the programmed output voltage by that amount or the regulator will cease to regulate.

If you look at Figure 1 on page 9 you will see a typical circuit for the regulator and how to generate the desired output voltage.

Linear regulators typically generate significant heat (equal to the output current times the voltage difference between the input and output) so there is a section called Heatsink Requirements that must be read and understood to provide proper heat dissipation for your particular application.

There is obviously a lot more info in the data sheet and you just have to look at what is particularly important for your application. The Application Hints section is usually very good at showing you how to use the part.

 

[netfreak]

Thankyou . Thankyou very very very much for all you guys. Specially "crutschow" as with your guidance I've been able to get a lot of things which I never had knowledge of before.

I myself am a fresh graduate and have done Bachelors in Electrical(Power) Engineering. We did use to make circuits and projects etc but those all had ready made diagrams available on the internet so we just used to make the hardware which used to work guaranteed.
Now at home I am trying to make things myself which is putting me into trouble ( as on the other hand I do have bookish knowledge but not practical experience or I would say the appropriate knowledge)

 

[tvtech]

Never mind. (Post edited......)

Quoted by netfreak:

"myself am a fresh graduate and have done Bachelors in Electrical(Power) Engineering. We did use to make circuits and projects etc but those all had ready made diagrams available on the internet so we just used to make the hardware which used to work guaranteed.
Now at home I am trying to make things myself which is putting me into trouble ( as on the other hand I do have bookish knowledge but not practical experience or I would say the appropriate knowledge)"

 

[netfreak]

Thankyou Tvtech
And yes its ofcourse great for me to have so much positive response from you experts here It wuld be a greattt help

 

[netfreak]

One thing . . about LM 317T
How am I going to get to know that for what input I give to this IC, am going to have what value of output?
As in what I did practically was I connected LM317T IC and gave it an input of 52.4V DC , at its output terminal I obtained 51.9V DC .. . this was what i measured with the help of DMM
So how am I going to know these values from the datasheet? that for which value of input am i going to obtain that particular range of output? Please help me out here so that I may get to start to know how to actually use this IC and know which one is of my use

 

[tvtech]

@ netfreak

You probably could see my post above....Stop, think, learn please

As a Bachelor in Electrical(Power) Engineering, you should know better......I really cannot believe you are that clueless ????
Surely your degree would have provided you with some knowledge.

You having me on right????

If so, you have picked the wrong person to play games with.

 

[MrAl]

Hi,

I dont think you can input 50 volts to the LM317 and then reference the output to ground because i think the maximum is thirty something volts. Too much voltage (referenced to ground) will blow the device out.

It sounds to me like you should be experimenting with circuits that only take 12v or less for now until you get some more hands on experience.

 

[Ian Rogers]

The trusty 317 has a MAXIMUM voltage drop of 40v ... But you can't run it at this limit without a heatsink the size of a doorstep... 40v @1.5A is 60W ... It would make a great heater.

You should keep the voltage drop to "as low as possible"...

What voltage output do you need... and what current will your circuit take?... I will show you the settings in the datasheet that are relevant.. (hopefully before you do tvtech's head in)...

 

[tvtech]

Hi,

I dont think you can input 50 volts to the LM317 and then reference the output to ground because i think the maximum is thirty something volts. Too much voltage (referenced to ground) will blow the device out.

It sounds to me like you should be experimenting with circuits that only take 12v or less for now until you get some more hands on experience.

Agreed there

Thing is, the LM317 only sees input/output differential voltage. As long as the difference is not more than around 30 Volts or so, it is happy and good to go....The LM317HV is a prime example. Not the time or place, but anyway

Cheers,
TV Tech

 

[bountyhunter]

Hi,

For those two ic's you mentioned dont they give the output current right on the data sheet, such as "1 amp" or "1.5 amps" ?

Yes, but that's very misleading. The actual current is dependent on the input-output voltage differential.

 

[bountyhunter]

Agreed there

Thing is, the LM317 only sees input/output differential voltage. As long as the difference is not more than around 30 Volts or so, it is happy and good to go....
Cheers,
TV Tech

Actually, the SOA current limiting starts cutting the current back at an input-output differential of about 12V. At 30V differential, current is about 40% of peak value.

 

[bountyhunter]

The trusty 317 has a MAXIMUM voltage drop of 40v ... But you can't run it at this limit without a heatsink the size of a doorstep... 40v @1.5A is 60W ... It would make a great heater.

It will only put out about 300 mA at a 40V differential.