Re: Alun's low voltage alarm

[Guest Alun]

Sorry MP I can see your point but I agree with audioguru on this one.

If I building and I will assume the worst case scenario for all the factors that I'm taking into consideration. At work my boss told me to use a 5V regulator because I was planning to power a chip with 15V even though it was rated for a 5V – 15V power supply, he said “the 15V power supply has a tolerance of 5%, now what would happen if it was on the upper end of it's tolerance you would get 15.75V and while this is highly unlikely to cause any damage it's far more reliable to run well within the absolute maximum ratings!

[audioguru]

Thanks Alun,
MP and I have had many disagreements about spec's like this.  ;D

[MP]

...You don't believe what is stated in datasheets and you operate ICs above their ratings.
..... I design and use parts within their ratings for assurance that every circuit will work...

I have never said I do not believe a data sheet. I have also never exceeded the specs. However, when a data sheet only gives you specs on a device for 24 degree C at 1 volt and you plan to use a different voltage and run the device over the complete temperature range, there is not much use from what you have in the data sheet. A data sheet is never a complete story. It is only a beginning. Just like theory is never a complete story. It is only a starting place to push something to the bench. Engineers look at this from a different angle than audioguru. I am sure you have very good results with limiting yourself to the min values in data sheets and never using different voltages or temperature range than used in the test specs in a data sheet. But then, if the Engineering world did this, technology would be about 50 years behind what it is now.
Go beyond the paper...... A data sheet in many cases will not give you enough information for your specific use of the product. In some cases it might. Data sheets are not made to limit you. They are there to give you an initial start.

This thread started with a comment that a specific project would not work. I think audioguru is trying to save his reputation by still finding a problem with it. In the beginning, he did not look at the data sheet. Now he seems to be looking at it too hard to still find fault.
I have breadboarded this project and it works fine. No problem turning on the LED and no problem buzzing the buzzer. You are not reading the data sheets for these parts in the true perspective that they were written.
Just to let you know- I had to take a course specifically on data sheets before I got my degree in Engineering. These are the worst nightmare for most technicians and Engineers alike. No two are written alike.
To give you a little background, I own an electronics business which designs, builds and ships worlwide. I have never had a problem with specs in a design. But then I also take into consideration, as a general rule, altitude, barometric pressure, temperature, and humidity. Look at the data sheet and tell me how to be safe with these unknowns. Most components are effected by some or more of these parameters as well. This is the basis behind further testing on my bench. Not in trying to push a part beyond the spec sheet.

BTW- your boss made a bad decision. First, he added too much cost to the device. For safety, you could have clamped the supply pin of the chip with a zener rated lower than the max value and saved board space and component costs. If you need to worry about temperature compensation, you could use one of the many temperature compensated zeners which are sold in packages that look like a transistor and called reference voltage chips. Your regulator is just dumping 10 volts to ground and converting it to heat unnecessarily. Two thirds of your potential is being dumped to ground.

MP

[audioguru]

I have breadboarded this project and it works fine. No problem turning on the LED and no problem buzzing the buzzer.

Maybe you should tell National Semi to raise their minimum spec rating because you breadboarded a single circuit and it worked! They will raise their spec only when their production yield is good enough for them to throw away the weak ones.  :P
What would you do with the assemblies with LM339's that give only 6mA, 10mA and 16mA to your 22mA load?  ???

.....you could have clamped the supply pin of the chip with a zener.....
Your regulator is just dumping 10 volts to ground and converting it to heat unnecessarily. Two thirds of your potential is being dumped to ground.

Zeners dump current to ground and heat unnecessarily, not series voltage regulators. He, he.  ::)

[MP]

Maybe you should tell National Semi to raise their minimum spec rating because.....

Current spec isn't something that you program into a device. It is about what is connected to it. The data sheet says you can connect to 20 mA as a maximum. This is the maximum rating at which they no longer guarantee it to work anymore. My bench tests have provided the same results.

.....you could have clamped the supply pin of the chip with a zener.....
Your regulator is just dumping 10 volts to ground and converting it to heat unnecessarily. Two thirds of your potential is being dumped to ground.

Zeners dump current to ground and heat unnecessarily, not series voltage regulators. He, he.

[Guest Alun]

I can still see MPs point, the same board had a current sensor on with a temperature range of 0^oC to 85^oC, but the board needed to be rated down to -30^oC so we asked the manufacturer  if it would be damaged by the cold they said it wouldn't but the accuracy would degrade from 2% to 5%. We tested it in a climatic control chamber and there were no problems.

But this is still different than exceeding the maximum voltage, current ratings or gain etc. If a circuit requires a transistor with a gain of at least 100 then we use a transistor with a mimimum gain of 100. What if we used a transistor with amimimum gain of 60 and a typical gain of 120? A lot of the circuits we build simply wouldn't work so it would be silly.

An another thing MP, the circuit required at least 5mA and the current consumption would've gone down slightly with a lower voltage anyway, so a 14V zener would have used more power.

[audioguru]

Hi Alun,
Your boss told you to use a 5V regulator to power a chip with a 5V to 15V rating, so it isn't damaged and doesn't become unreliable when the 15V supply is high. It's a voltage reduction that's too extreme. Will the chip even work if the 5V is actually 4.8V?

Did you notice the typo error in the datasheet for the LM339? It says, "if the output is shorted to ground, the maximum current is approximately 20mA" (or less for a weak one). Hey, it has an open-collector NPN transistor so an output short to ground won't do anything to it. I think they mean an output shorted to the positive supply. He, he.

[Guest Alun]

While it was specified work down to 4.5V, 5V was the prefered normal mimimum voltage, but the absolute maximum was 15V, and 5V gave the best current consumption too.

LOL!  ;D I maybe they mean short circuit to the +V rail, that would mean 20mA if the maximum current nowI could power a buzzer and two LEDs. ;)

[Guest Alun]

Mike has fixed it for us!

http://www.electronics-lab.com/projects/sensors/023/

Thanks Mike!

[audioguru]

A really strong LM339 would provide 20mA into a dead short and about 16mA with a 1.5V saturation loss. A weak one will provide only 6mA with a 1.5V saturation loss. Even less if it heats up.

You might be unlucky if some of the weak ones are sent to your country like they send to mine. It's still winter, maybe the strong ones are made only in summer. Who knows?

Did you notice that even the LM139A, which has better spec's and costs more, also has only a 6mA minimum current rating? You can't even pay them to select strong ones for you. I guess that's why they call it Low Power.

I wouldn't use a 6mA part in a 20mA circuit. Unfortunately they don't make the much stronger LM311 anymore. 

[Guest Alun]

A really strong LM339 would provide 20mA into a dead short and about 16mA with a 1.5V saturation loss. A weak one will provide only 6mA with a 1.5V saturation loss. Even less if it heats up.

I was joking in the last post.  ;D

I would use a transistor buffer, to power anything above 6mA, maybe even >5mA.

You might be unlucky if some of the weak ones are sent to your country like they send to mine. It's still winter, maybe the strong ones are made only in summer. Who knows?

Well it may still be Winter over in Canada  ;D , but spring sprung over here in England a good few weeks ago - our garden's certainly in full bloom. ;D

But how can the changing of the season affect component quality, perhaps it depends on the phase of the moon too. ;D

Did you notice that even the LM139A, which has better spec's and costs more, also has only a 6mA minimum current rating? You can't even pay them to select strong ones for you. I guess that's why they call it Low Power.

I wouldn't use a 6mA part in a 20mA circuit. Unfortunately they don't make the much stronger LM311 anymore. 

They don't make them how they used to. ;D

[audioguru]

Hi Alun,
Nobody could wait for the phase of the moon and the season to be correct for Low-Power comparators to give any output current. So they started using transistor buffers with them like you. They also didn't use or buy the strong ones which became extinct.  ;D

[Guest Alun]

Old thread again, I'm bored this evening so wtf. ;D

I wouldn't use a 6mA part in a 20mA circuit. Unfortunately they don't make the much stronger LM311 anymore.

[audioguru]

Thanks Alun,
Horray! They still make the strong-output LM311. It has about 10 times the wimpy output current of a low-power LM339. ;D