5 VDC voltage Ragulator

[maxchirag]

Hello,

I am very new to this stuff, so please bare with me.

I am trying to make my first micro controller based circuit (basically trying to power my microcontroller for first time).

What i have now is,
1. 230 V AC (mains) to 24v DC/1.5A Converter.
2. 7805 - 5v DC ragulator.

Is that possible to give direct input 24v DC/1.5A to 7805 and the output will be 5v Ragulated DC that i can give in my microcontroller Vcc?

I tried to check in the the datasheet of 7805 but the table looks very confusing. their test condition says their input is 8 to 20v and nothing specified for current (atleast what i understand).

Thanks in Advance!

 

[MrAl]

Hi,

The Fairchild version will take up to 35v on the input. You just have to watch power dissipation, which shouldnt be too much of a problem with the small current a uC chip draws.

 

[maxchirag]

Thanks for a quick reply!,

What you said is correct, i will check with power dissipation.

but another question, i m going to use this for long time (for other micro controller based projects).

in that case, what is the most efficient, Reliable and cost effective way to convert 24vDC to 5vDC. i mean with minimum power dissipation and all

 

[cowana]

That would be using a switching regulator. What current draw do you expect?

 

[MrAl]

Hi again,


Well, it depends on how much current you need to draw from the 5vdc supply. For just running one micro controller chip at 1ma the power dissipation will not be very much at all, very very low in fact, using a device like the 7805 or the 78L05.
If you intend to power other circuits that need much more current, then you may have to go to a switcher like a Simple Switcher from National Semiconductor.
Maybe you should mention here how much current you really need to draw from the 5vdc supply for any project, or what you need for several projects if they are very different.

 

[erendesh]

Hello,

I am very new to this stuff, so please bare with me.

I am trying to make my first micro controller based circuit (basically trying to power my microcontroller for first time).

What i have now is,
1. 230 V AC (mains) to 24v DC/1.5A Converter.
2. 7805 - 5v DC ragulator.

Is that possible to give direct input 24v DC/1.5A to 7805 and the output will be 5v Ragulated DC that i can give in my microcontroller Vcc?

I tried to check in the the datasheet of 7805 but the table looks very confusing. their test condition says their input is 8 to 20v and nothing specified for current (atleast what i understand).

Thanks in Advance!

While consulting datasheet, for those kind of stuffs, you should always jump into "Absolute Maximum Rating" part of the datasheet. 7805 is manufactured by different manufacturer, so i request you to refer to datasheet of which that paticular 7805 is made by. When i checked datasheet for LM78XX from National Semiconductor it says, absolute max is 35V DC input.
So it is ok for that.
But be warned, for Linear DC/DC converter Efficiency is given by Vout/Vin ( 5/25 = 20% ). So the efficiency of your circuit will not be great due to massive voltage difference. and if you circuit is pumping large DC current, there might be thermal issues.

I hope this helps.
Sandesh

 

[maxchirag]

Thank you all for your replies,

@sandesh, i did the same, jumped direct to the Absolute maximum rating section, but that was also bit confusing(as i said in my first post), anyway but now i have figured out what it basically says, thanks anyway for directing.

as far as the other questions, like how much current i expect to draw in my circuit, then the answer is, i m new to electronics, but good with microcontroller programming (as i m a software engineer), i m learning electronics, trying to make setup my environment for big project (like making a complete board, its bootloader, and operating system for that). that's why i have started with basic controllers so i can learn the basics quickly and then move to the higher controllers and bigger circuits.

Thanks all!

 

[MikeMl]

With 5V wall warts this cheap, why screw with the 24V one?