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solar3000
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LM1084 power supply

Mon Nov 27, 2017 2:33 am

I don't see a matching Hardware category so...

Building my own power supply here.

I have a chip that says LM1084. Not sure which version it is. I know there are 3.3, 5, 12, and adjustable voltage. I know there are different Amp variations too. I am holding the adjustable one, I don't know which amperage.

Specs say the input max voltage is 29 volts.

I am using a 25.2 volt AC transformer. Passing the secondary through a bridge rectifier and then a large capacitor ( 63 volts, 470uF electrolytic metal can ) I get 37 volts DC. I guess it is buffering the peak voltage. I put an LED circuit on it to drop the voltage, but it only dropped it down to 35.6 volts.

Is this unsafe for the LM1084.
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davidcoton
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Re: LM1084 power supply

Mon Nov 27, 2017 9:46 am

solar3000 wrote:
Mon Nov 27, 2017 2:33 am
Is this unsafe for the LM1084.
Yes, it is unsafe. It is also wasteful, the LM1084 is a linear regulator so the voltage difference between its input and output is converted to heat. More than 10V in (for 5V out) wastes more power than it provides, less than 50% efficient. At 35V in and 5V out, you are wasting six times what you use. At 5A, thats 25W used, 150W as heat. You'll need a good an extreme heatsink too.

Get a switching regulator module that will take 40V in and provide the output (V and A) that you need, it will be 90% or more efficient.
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Re: LM1084 power supply

Mon Nov 27, 2017 10:14 am

davidcoton wrote:
Mon Nov 27, 2017 9:46 am
solar3000 wrote:
Mon Nov 27, 2017 2:33 am
Is this unsafe for the LM1084.
Yes, it is unsafe. It is also wasteful, the LM1084 is a linear regulator so the voltage difference between its input and output is converted to heat. More than 10V in (for 5V out) wastes more power than it provides, less than 50% efficient. At 35V in and 5V out, you are wasting six times what you use. At 5A, thats 25W used, 150W as heat. You'll need a good an extreme heatsink too.

Get a switching regulator module that will take 40V in and provide the output (V and A) that you need, it will be 90% or more efficient.
Unsafe is beyond. It would be something that can be built for educational purposes for a test bench setup. I would not trust the Power Supply, without a Oscilloscope. The sad thing is that I was in the U.S. Navy as a Interior Communications and because our part of the dept. for Electrical would have all of our work done by Thursday before lunch. We had to go run audits and even setup these type of Breadboard experiments, due to some type of gear that the ET (Acted like Gods, but did very little on the boat and never got dirty).

We can only learn if we do these projects and respect that snake that bites, called current.
Ren: Now listen, Cadet. I've got a job for you. See this button? Ren: Don't touch it! It's the History Eraser button, you fool! Stimpy: So what'll happen? Ren: That's just it. We don't know. Maybe something bad, maybe something good.

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Re: LM1084 power supply

Mon Nov 27, 2017 4:21 pm

broe23 wrote: Unsafe is beyond. It would be something that can be built for educational purposes for a test bench setup.
No, it is NOT safe. You cannot safely apply 37V to a device with a 29V limit. The result would be escaping smoke, not just the magic stuff.
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Re: LM1084 power supply

Mon Nov 27, 2017 5:31 pm

broe23 wrote:
Mon Nov 27, 2017 10:14 am
We can only learn if we do these projects and respect that snake that bites, called current.
We could also learn from other people's errors, other people's advice, even books!
Life's too short to make all the mistakes ourselves!

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Re: LM1084 power supply

Mon Nov 27, 2017 5:50 pm

Burngate wrote:
Mon Nov 27, 2017 5:31 pm
broe23 wrote:
Mon Nov 27, 2017 10:14 am
We can only learn if we do these projects and respect that snake that bites, called current.
We could also learn from other people's errors, other people's advice, even books!
Life's too short to make all the mistakes ourselves!
Why do you think that Edison stated that he did not fail. He proved that his success was learned while creating the perfect light bulb. Learning from our's and other's mistakes, is why the Home Brew Computer Club became what it was and now we are seeing a new revolution with the SBC experiments. You even can have a computer stick the size of a Amazon Fire Stick or Roku. Those came from learning and listening.

The best thing for the OP to do is use one of the schematic drawing programs or even paint to lay out the circuit board. I though would not use any more than a cheap USB voltage tester, with a fuse on the positive side from the Power Supply to the load. At the power cord end, I would use a fuse to protect the electronics in it, rated no more than +/- 5% to 10% of what you expect a surge may happen and could potentially cause a issue, even though a Ammeter would show voltage, to test input power, a Kill-a-Watt.
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Re: LM1084 power supply

Mon Nov 27, 2017 5:54 pm

I'm not sure why this is a question. The absolute ratings in the datasheet are clear enough.

If you wanted to lift 37 tons with a steel cable would select a cable that was specified to only stand a maximum of 29 tons?

I'm kind of with broe23 here. Sometimes you just have to blow things up. Just for the learning experience. But it's better to do such things with some idea of the dangers involved.

For example: Years ago I pushed a 5mm red LED to the limit. The thing did not just fail, it exploded. The shrapnel could have done serious eye damage. Except for the safety glasses I was wearing.

In this case, I say no. A linear regulator is not appropriate.

Even if it could safely drop 37 volts down to 5 for the Pi. That is 32 volts to be rubbed off. Even at one amp that is 32 watts to be dissipated. That is twice as much as my soldering iron!
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Re: LM1084 power supply

Mon Nov 27, 2017 6:14 pm

Apart from Edison not inventing the light bulb (Swan did that) and in my opinion being a wazzock of the ninth order, I tend to agree with Broe23's sentiments.
But I'm not going to admit that. It'd make me look like a wazzock.

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Re: LM1084 power supply

Mon Nov 27, 2017 6:17 pm

What I'm not sure about is why Solar3000 wants to use a 25.2V transformer. Surely he could obtain something more reasonable?

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Re: LM1084 power supply

Mon Nov 27, 2017 6:22 pm

broe23,
Why do you think that Edison stated that he did not fail.
What, you believe that Edison invented the light bulb?

Sure his company perfected it, and he got the patent:

For example:

"Where Edison succeeded and surpassed his competition was in developing a practical and inexpensive light bulb, according to the DOE. Edison and his team of researchers in Edison's laboratory in Menlo Park, N.J., tested more than 3,000 designs for bulbs between 1878 and 1880"

See here for the real history: https://www.livescience.com/43424-who-i ... -bulb.html

He invented nothing. With his showmanship he raised money to hire a team to perfect stuff.

Kind of like Bill Gates. Who did not invent BASIC or computers, as seems to be the common understanding today, and rode on the work of the Home Brew Computer Club in the early days.

Edison failed. Today we use Tesla's means of power generation, distribution, motors etc. We use LEDs for lighting. Thank you Nick Holonyak!
Memory in C++ is a leaky abstraction .

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Re: LM1084 power supply

Mon Nov 27, 2017 6:28 pm

Burngate,

Speaking as one wazzock to another, like I said, I'm all for wazzock broe23's suggestion to blow stuff up. What more fun could be had? And it's a great way to learn stuff.

On the other hand, if you want to build a power supply that is not going to burn the house down whilst you sleep and kill all your family, it's probably a good idea to find out what you are doing first, take precautions and pay attention.
Memory in C++ is a leaky abstraction .

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davidcoton
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Re: LM1084 power supply

Mon Nov 27, 2017 9:13 pm

broe23 wrote: The best thing for the OP to do is use one of the schematic drawing programs or even paint to lay out the circuit board. I though would not use any more than a cheap USB voltage tester, with a fuse on the positive side from the Power Supply to the load. At the power cord end, I would use a fuse to protect the electronics in it, rated no more than +/- 5% to 10% of what you expect a surge may happen and could potentially cause a issue, even though a Ammeter would show voltage, to test input power, a Kill-a-Watt.
That may, in some ways, be the best thing -- if your aim is a memorable smoke generator, with possible fire and explosive elements, possibly releasing potentially harmful materials from the IC into your environment.That does not make it safe.
A fuse offers no protection to the electronics, thopugh it mat reduce the consequential damage following a failure.
What on earth do you mean about the fuse rating compared to "what you expect a surge may happen"? It makes no physical or engineering sense.
An ammeter would show voltage? Not normally, though it is possible in combination with a series resistor.
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Re: LM1084 power supply

Mon Nov 27, 2017 9:27 pm

broe23 is suggesting our OP take the time to design a PCB layout and presumably get it made somehow.

Then blow it up.

I don't get the idea.

I have a better idea. Put your safety glasses on. Have a fire extinguisher at hand. Be sure any onlookers are far away.

Now, connect that LM1084, as per the schematic in it's data sheet, to your rectified, and smoothed, transformer output. Preferably with a Pi attached to the output as a load.

Oh, be sure to video the proceedings and post the resulting video to youtube.

That Kill-a-Watt will not even register anything before everything has been killed!
Memory in C++ is a leaky abstraction .

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Re: LM1084 power supply

Mon Nov 27, 2017 9:53 pm

By the way, by the logic above, the Wright Brothers did not invent the airplane. They just perfected it.

It was invented by Da Vinci, centuries earlier. I assume that's also the case in regards to this "Swan" fellow...
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Re: LM1084 power supply

Mon Nov 27, 2017 10:10 pm

n67,
...Wright Brothers did not invent the airplane. They just perfected it.
Well there is the thing. Never mind Da Vinci. At the time the Wright Brothers were doing their thing it was known that flying machines were possible. Many were trying to do it. There were conferences and expos about it. Everyone was snooping on everyone else in the hope of being the first.

Basically it relied on the development of some kind of motor to provide the power in a light weight format and a structure strong enough not to collapse under the power and weight of it all.

The Wright Brothers perhaps did it first. Woopy doo.

I think the guys who built the motor deserve more credit. With that, pretty much anyone with a bunch sticks and sheets could have got off the ground as long as the Wright brothers first flight.
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Re: LM1084 power supply

Tue Nov 28, 2017 11:12 am

n67 wrote:
Mon Nov 27, 2017 9:53 pm
... this "Swan" fellow...
https://en.wikipedia.org/wiki/Joseph_Swan
Both he and Edison were into stage lighting. They both took out patents (1879), but Swan got there first.
They both used carbon filaments, with tungsten not being used until the 1920s

https://en.wikipedia.org/wiki/Incandescent_light_bulb is also interesting.

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Re: LM1084 power supply

Tue Nov 28, 2017 9:43 pm

Burngate wrote:
Mon Nov 27, 2017 6:14 pm
Apart from Edison not inventing the light bulb (Swan did that) and in my opinion being a wazzock of the ninth order, I tend to agree with Broe23's sentiments. But I'm not going to admit that. It'd make me look like a wazzock.
Never really thought about it. It seems that we tend to believe what we were taught in grade-school, and usually never revisit the ideas. So, today was educational. From random posts I read about the subject (there are surprisingly many) - I get:

1800s (early) - various arc lamps
1840 - Warren de la Rue - platinum filament (works, too expensive)
1860 - Swan - carbonized paper filament (too short life)
1879 - Swan - carbonized cotton, vacuum pump (better life)
1879 - Edison - thinner carbonized cotton filament, better vacuum (longer life)
1879 - Edison - carbonized bamboo and vacuum (800 hours life)
1904 - Sandor Just/Franjo Hanaman - tungsten (better life)
1906 - General electric - improved, ductile tungsten (today's bulb)

Whew! In my youth I watched TV educational shows that showed Edison "inventing" tungsten bulb.

History is twistier than a person thinks.
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Re: LM1084 power supply

Tue Nov 28, 2017 9:48 pm

1906 - General electric - improved, ductile tungsten (today's bulb)
Keep in mind who founded GE...
"L'enfer, c'est les autres"

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Re: LM1084 power supply

Wed Nov 29, 2017 10:25 am

solar3000 wrote:
Mon Nov 27, 2017 2:33 am
I don't see a matching Hardware category so...

Building my own power supply here.

I have a chip that says LM1084. Not sure which version it is. I know there are 3.3, 5, 12, and adjustable voltage. I know there are different Amp variations too. I am holding the adjustable one, I don't know which amperage.

Specs say the input max voltage is 29 volts.

I am using a 25.2 volt AC transformer. Passing the secondary through a bridge rectifier and then a large capacitor ( 63 volts, 470uF electrolytic metal can ) I get 37 volts DC. I guess it is buffering the peak voltage. I put an LED circuit on it to drop the voltage, but it only dropped it down to 35.6 volts.

Is this unsafe for the LM1084.
The first step to designing any circuit is a basic understanding of circuit theory.
A full wave rectified AC will produce an output √2 times the RMS voltage.

Even if you did not exceed the input voltage of the regulator, if you did succeed in dropping the voltage to 5V the power dissipation of the regulator would be exceeded.

In short this is doomed to failure!

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Re: LM1084 power supply

Wed Nov 29, 2017 10:44 am

n67,
Keep in mind who founded GE...
So? That was in 1989 or so. Years after the invention of the light bullb.

We can give credit to Edison for hiring a bunch of guys, using J.P. Morgan and the Vanderbilt families money, to work on improving the technology.

Oddly enough if you check the GE Wikipedia page there is no mention of light bulbs. Only LED lighting. https://en.wikipedia.org/wiki/General_Electric

I guess feeding 50v into an LM1084 to power a Pi might be an experiment into a new form of lighting :)
Memory in C++ is a leaky abstraction .

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Re: LM1084 power supply

Wed Nov 29, 2017 12:54 pm

So? That was in 1989 or so. Years after the invention of the light bullb.
1989? Really?
"L'enfer, c'est les autres"

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Epmu Sn!

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Re: LM1084 power supply

Wed Nov 29, 2017 1:06 pm

n67 wrote:
Wed Nov 29, 2017 12:54 pm
So? That was in 1989 or so. Years after the invention of the light bullb.
1989? Really?
Not to be confused with the former British company General Electric Company, or the musical project General Elektriks
https://en.wikipedia.org/wiki/General_E ... ompany_plc
Founded 1886
Defunct 1999
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Re: LM1084 power supply

Wed Nov 29, 2017 2:46 pm

n67,
1989? Really?
Well, Wikipedia does not lie to me. Does it?

"In 1889, Drexel, Morgan & Co., a company founded by J.P. Morgan and Anthony J. Drexel, financed Edison's research and helped merge those companies under one corporation to form Edison General Electric Company which was incorporated in New York on April 24, 1889. The new company also acquired Sprague Electric Railway & Motor Company in the same year."

Swan's light bulb dates from 1878, patented in 1880.

He started with the idea in 1850.

The idea of getting light from a current passed through a wire goes back to Ebenezer Kinnersley in 1761.

Perhaps Kinnersley was the first one to let out the "magic smoke" :)
Memory in C++ is a leaky abstraction .

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Re: LM1084 power supply

Wed Nov 29, 2017 9:04 pm

Milliways wrote:
Wed Nov 29, 2017 10:25 am
A full wave rectified AC will produce an output √2 times the RMS voltage.
The missing link.
That is the piece I needed.
I would never have guessed √2 * v . That did give me the a value near the 37 volts I measured.

Milliways wrote:
Wed Nov 29, 2017 10:25 am
In short this is doomed to failure!
This part you got wrong.
I never said I connected the LM1084. I didn't start because of the absolute max values stopped me.


A lot of doom and gloom here against linear voltage regulators. Distributors like seller Digikey lists thousands of kinds of transformers and 3 and 5 pin linear voltage regulators. People are still buying them. Must be a good reason. Anyway, I am not buying anything. I am using what I already have.
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Re: LM1084 power supply

Wed Nov 29, 2017 9:27 pm

solar3000,

I don't have any "doom and gloom" about linear regulators. They are great:

1) Very cheap. Especially if you have a load of them in the junk box already.

2) Very simple.

3) Low noise.

4) Sometimes even more efficient than switched mode solutions.

All components are good, in the suitable place.

Yep, I'm all in favor of using up what you have to hand. If it fits the application.
Memory in C++ is a leaky abstraction .

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