LM7809 regulator woes...

[JKowalski]

Alright - I am putting together a homemade spyder-type pedal power supply. I rewound the secondaries of a hefty wall wart transformer to use for this project, and extensively tested it and determined that that part works perfectly fine through extensive use. It gives me eight 10-11VAC outputs.

Now, I built a regulator board, quite conventional - each of the eight sections has your standard rectifier, into 1000uF filter cap, into a LM7809 regulator, into a final 100uF cap and then out. Since I decided to do this whole thing on a whim, I made use of all the parts I had lying around in my parts collection - in which were four LM7809 regulators. I built the PCB, put everything on it except for the four regulators I did not have yet, and tested it with the transformer.

The regulators outputs were:
9.02v, 9.04v, 9.06v, and - the odd one out - 8.92v.

But that's not my concern, of course. The big problem is that I took a trip down to Fry's electronics and bought myself four more regulators, NTE1910. I installed those yesterday - but, for some reason, on testing them, their voltages were:

11.24v, 11.28v, 11.26v, and one that seems obviously fried as the voltage rises slowly from 12V to almost the same as the filtered dc on the input.




As for construction, None of the parts were excessively heated in soldering (pretty darn sure of it, periodic checks of temp), and all were put in with care and in a similar fashion.

Also, for this testing I am using the same VAC output winding on the transformer for all the regulators.

Traces are totally fine, I went over them with a magnifying glass and a file and took out anything that looked remotely suspicious.



Ideas??? I mean, the regulators could be fried, but what are the chances that 3 of them, newly bought in the store, and carefully put in, could be all damaged in the same way so that they regulate an output of 11.2 volts each instead of 9v?

[R.G.]

Once is an accident. Twice is a coincidence. Three times is enemy action.

If an NTE replacement functions differently than a manufacturer-marked part, I would go back to Frys and demand a refund. The simplest explanation is that NTE marked the wrong part as a 7809. There are other explanations, but Occam would feel that this one was sharp.

[head_spaz]

Do your NTE1910's have a *dash 12* in the part number?
Fixed voltage regulators are often numbered that way.

Also, are your supplies loaded when you're measuring them?
They need at least a few milliamps load in order to stabilize.
A 1k5 ohm resistor directly across the output should do it.

Also, you should make sure that you have a small cap across the output
smack dabb on reg's output pin to ground... to prevent it from oscillating.
You'll have to read the manufacturer's datasheet to find out what value cap they
recommend, but usually a 0.1uf to 10uf is sufficient.

[doitle]

Are you sure they are 7809s and not 78L09s? The 78L09s can only output 100mA before going bonkers.

[R.G.]

Are you sure they are 7809s and not 78L09s? The 78L09s can only output 100mA before going bonkers.

... not to mention not having the same pinout. 

[JKowalski]

Thanks for all the quick replies, guys.

Once is an accident. Twice is a coincidence. Three times is enemy action.

If an NTE replacement functions differently than a manufacturer-marked part, I would go back to Frys and demand a refund. The simplest explanation is that NTE marked the wrong part as a 7809. There are other explanations, but Occam would feel that this one was sharp.

Hmm... My understanding is that there are no 11.2v regulators, only 12, and that's quite a margin of consistent error for a regulator is it was that mistake.  And the problem is, I seriously doubt Fry's would accept a regulator that has been soldered to a board, as they would likely simply claim that I have damaged it myself.

Do your NTE1910's have a *dash 12* in the part number?
Fixed voltage regulators are often numbered that way.

Also, are your supplies loaded when you're measuring them?
They need at least a few milliamps load in order to stabilize.
A 1k5 ohm resistor directly across the output should do it.

Also, you should make sure that you have a small cap across the output
smack dabb on reg's output pin to ground... to prevent it from oscillating.
You'll have to read the manufacturer's datasheet to find out what value cap they
recommend, but usually a 0.1uf to 10uf is sufficient.

The NTE's do not have a dash 12, they simply read NTE1910 - which comes up in Google as the right thing for the job.

I typically do not load the supplies as I test them, as till now I have had no problems with this kind of thing. I did however load the strange regulators as part of my troubleshooting, and no change.

I will consider that cap - I have not had any problems with any regulators I have used that have necessitated the use of a small cap on the output, so I haven't really bothered to put any in my projects. Also - if you were implying that oscillation may be the cause of this weird problem, I assure you it is not, since I have checked the output on a scope and it is well-regulated DC, just 2.2 volts higher then it should be! 

Are you sure they are 7809s and not 78L09s? The 78L09s can only output 100mA before going bonkers.

They are NTE1910's, which can handle 1A - and if searching up the product data sheet does not convince you, they are in TO-220 packages.

[Ripthorn]

Are you sure they are 7809s and not 78L09s? The 78L09s can only output 100mA before going bonkers.

... not to mention not having the same pinout. 

I was going to mention the pinout thing because the same thing happened to me on a recent project.  I just mixed up which pin was which.  Probably not 78L09's unless they are in a TO92 package, and then they would be markedly different just on sight.  I would check the pinout.

[Gus]

As posted above by head_spaz measure with a load.  3 terms can measure high without a load.  1K, 1.5K etc.

[JKowalski]

I would check the pinout.

Pinout is correct.


I suppose I should just give up with this sometime soon - It's not like these things are that expensive, and I was going to order a selection of parts from mouser soon anyways. That way I can bypass frys ( ) too and get some LM's.