Finally Measured 7805 Regulator!

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MrAl
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Finally Measured 7805 Regulator!

Post by MrAl »

Hello,

I finally got around to measuring the standard 7805 regulator to see just how far off it can be sometimes, even at room temperature. We talked about this in another thread but im not sure where that thread is now, so here is a pic to prove it.

Image

As we can see this one was quite a bit off already. It's the one in the TO3 package. For a little better performance the LM317 with appropriate resistors works better over the full temperature range.

Ignore the Yuengling beer package in the background :smile:
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Bob Scott
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Re: Finally Measured 7805 Regulator!

Post by Bob Scott »

MrAl wrote:As we can see this one was quite a bit off already. It's the one in the TO3 package. For a little better performance the LM317 with appropriate resistors works better over the full temperature range.
The 78 and 79 regulators that I use are usually TO-220's. The ones that I have measured are always 4.99 to 5.01 volts. I noticed that the data sheets do not guarantee such good tolerance.
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Robert Reed
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Re: Finally Measured 7805 Regulator!

Post by Robert Reed »

My 78xx's I have used have always been extremely close to the mark.The 79xx's stray a little bit. However the 78Lxx and 79Lxx rarely come within 1% and generally average +/- 4% error. As far as stability vs. temperature, I have not followed up on that, only to say that when the occasion warranted checks on established equipment, they were still very close to the mark.
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Re: Finally Measured 7805 Regulator!

Post by Dean Huster »

The regulators that were bought as prime stock from companies such as Digi-Key, Allied, Mouser, Newark, etc. have always been dead-on. It's the ones that were bought from the "surplus electronics" places that tended to vary -- hence the term we used to give such products sold by the old Poly-Pacs and such as being "floor sweepings". When you buy ICs that have been overmarked with new IDs, he original ID sanded off and remarked or the IC being totally blank, you can be suspect of its quality.
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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MrAl
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Re: Finally Measured 7805 Regulator!

Post by MrAl »

Hi again,


Yes i think i should have measured more packages than just that one, but that shows just how far off one can be even at room temperature. A little interesting i think. The spec is plus or minus 5 percent, so that's 4.75v to 5.25v which might be too wide of a spread for measuring circuits that depend on Vcc for their voltage reference. This is another reason why i always suggest using a voltage reference diode for measuring circuits.
The LM317's track better over temperature too but still not as good as a voltage reference diode.
I've used 317's in several measuring circuits but only those where the temperature is always going to be stable like when using a circuit indoors only.

As a side note, the new PIC's due to ship this month have a voltage reference built in, but im not sure if they are as super stable as a reference diode though. I dont think they are.
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Re: Finally Measured 7805 Regulator!

Post by Robert Reed »

MrAl
Interesting to hear you mention reference diodes. Most people think in terms of zener diodes with a 2,5 or 10 percent tolerance. Although the 'reference' diode is a zener, it is tabbed by its name because of its extreme accuracy. I have 6 of these tucked away for that special project that hasn't occurred yet which is going on 15 years now. These are so accurate and stable that they are rated in parts per million rather than percentage. Needless to say they are very expensive and that is why they are being saved for a special project . Back to the 78xx series. I have noticed that the 7805's are the most accurate of all that series and I have rarely had one that wasn't within 1% of its stated value. Since zeners have their best temperature coefficient at about six volts, I have always thought that the 7805 internal reference might be close to this and thus their superior accuracy. Oddly enough, the 'reference' diodes I have come across seem to be rated in the low 8 volt ranges.
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MrAl
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Re: Finally Measured 7805 Regulator!

Post by MrAl »

Hi Robert,

Well, i dont like to call the reference diodes 'zeners' because they are made very differently using transistors instead of a single junction and operate under different principles. They do behave a lot like zeners though i have to agree.
Yeah, many people just like to throw a zener at a project but i wonder if they would rather use a reference diode with just a little more trouble.

i too have a super reference diode around here in stock somewhere which has it's own internal heater to maintain junction temperatures. It's amazing that it's all in one metal can IC too. Made by National Semi.
Believe it or not i got one of these a long long time ago for 1 dollar US as a parts store i was visiting was selling them for 1 dollar each. I only bought one too, geeze. I dont think that parts store is around anymore either. Today i think they sell for about 14 dollars US in other places.
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Re: Finally Measured 7805 Regulator!

Post by Robert Reed »

I think mine were about $15-$20 each the last time I checked. What a dilemma - holding on to the ones I have because if I use them, I can't justify the cost of purchasing replacements for the 'stock on hand' bin :smile: >
I just hope a worthwhile project comes up before I am too old to hold a soldering iron: ha-ha.
Your metal can IC's number should be suffixed with an "H" (denoting metal). I have always jokingly thought of the H as high priced And they are, rarely seeing any configuration under $10. And even if one can purchase them in single lot.
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MrAl
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Re: Finally Measured 7805 Regulator!

Post by MrAl »

Hi Robert,

Yeah they get pretty expensive. I have found that the dollar ones work pretty well too. They have a slight curve but not much. Good enough for most stuff.
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Re: Finally Measured 7805 Regulator!

Post by cnc002 »

I have always used the TO-220 packages WITH heatsinks. I always have good performance and the voltage stays between 4.99 and 5.02 volts, never had one outside of that range with between 9 and 24 volts going into the regulator. I realize that sometimes space is a consideration and the TO-220 package, especially with a heatsink, can take up a considerable amount of real estate. However, I think a TO-220 would take no more room than a TO-3 would. They do make heatsinks for the TO-3, in case you didn't use one. I couldn't tell from the image. Just my experience with them.

Rick
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