NerdKits - electronics education for a digital generation

You are not logged in. [log in]

NEW: Learning electronics? Ask your questions on the new Electronics Questions & Answers site hosted by CircuitLab.

Basic Electronics » Voltage Regulators and Efficiency...

January 24, 2012
by JimFrederickson
JimFrederickson's Avatar

Given -

I compare the following running on a 12v battery source

A circuit running on a 7833 voltage regulator at 200ma, (so .66 watts drain)

A circuit running on a 7805 voltage regulator at 200ma, (so 1 watt drain)

**

Expectations -

The 7833 voltage regulator will run cooler

The circuit running on the 7833 voltage regulator will run about 50% longer

**

Reality -

The 7833 voltage regulator runs a little warmer

The circuit lasts longer, but not 50% longer

So my conclusion is -

The 78xx Series of voltage regulators 'bleed off', maybe dissipate as heat is better phrasing, most of the excess input voltage in order to get their rated output voltage.

(As I thought I was just 'casually validating what I thought', I wasn't as exact as I could have been but I did run the tests several times...)


So...

Is my conclusion true?

Are the 'Linear 78xx Series of Voltage Regulators' dissipating excess input voltage primarily as heat?

Is this 'power loss' referenced on the datasheet somewhere? (I have looked and it seems, maybe, the "quiescent current" is part of the puzzle, but it doesn't seem to account for the whole thing...)

Lastly...

Is my assumption correct that the switching voltage regulators, like the TI L2575, would be more efficient? (Although they do require a couple extra parts to get the job done...)

January 24, 2012
by Ralphxyz
Ralphxyz's Avatar

This is one of the questions asked in the Nerdkit User Guide, page 24:

"You might be curious as to what impact the voltage regulator has on power... Can you figure out what happens to the voltage that's dropped between the input and the output?"

It's also one of my first questions here on the forum.

Are the 'Linear 78xx Series of Voltage Regulators' dissipating excess input voltage primarily as heat?

Yes

Is my assumption correct that the switching voltage regulators, like the TI L2575, would be more efficient?

Yes as far as I know (which is limited).

Which leads to some really good discussions, what is the effective cost of efficiency? and what is the justifiable cost of efficiency?

Would the Nerdkit be "better" if it had/used a more efficient voltage regulator?

Would the cost justify the efficiency?

Ralph

January 24, 2012
by JimFrederickson
JimFrederickson's Avatar

Ralph,

While that 'question' is asked in the guide, I didn't see a real definitive answer...

I will check for your post shortly and review the answers you received as well... :)

From my point of view I am quite sure that the 7805 voltage regulator was the best choice for the Nerdkits.

I have used them for years, and still do. They are pretty robust, easy to come by, multiple sources, cost effective, and quite easy to hookup.

Using one of the Switching Voltage Regulators would provide more points of potential problems, since there are a few more parts to connect there are more connections. (Perhaps resulting in chip damage as well.)

But...

I am still quite curious, at least for some operations, what the potential 'efficiencies are'...

I have a couple of things that I want to run on battery. Likely the efficiency is not much of an issue, except one is to run 3v LED Lights and of course the sole reason for that is to 'be efficient'... So that is how my 'investigation' began.

So now I am trying to make a 'determination'.

Basically, I always use a separate voltage regulator for each board just because it gives me good testing flexibility. (Also if I am rushing around I don't end up 'suffering as much' if I plug the wrong voltage into a board! ;) )

But...

What I find out may end up affecting the voltage I will be supplying to my AVR boards used in my projects.

Post a Reply

Please log in to post a reply.

Did you know that you can turn a $20 digital scale into a live weight sensor using our kit with a few extra parts? Learn more...