Voltage regulating.

[dinosquirrel]

Hi everyone! I'm new here and need some help.

I've been looking for a voltage regulator that will run off of a battery, BUT will keep the output voltage the same as the voltage on the battery drops.

I have a lot of electronics experience, I know what most parts are, I solder on a regular basis, but I'm not an expert and there's is a lot that I don't know and I'm not afraid to admit it.

I need to adjust for 5-8volts out at 3 amps ( i know it's a lot) and the battery inputs are 9-16volts. I need a few of these for quite a few different projects. I am more than happy to build this myself if someone knows the schematic and although I've never etched a board, I'm sure willing to try. I'm trying to keep my cost down, but I'm willing to spend some cash to get started.

I've looked on ebay, but I can't see things in person so I don't know if I've found what I'm looking for.

The output voltage has to be specific within a volt because it's running a camera or transmission equipment, or lights. Just a lot of devices can't deviate much.

I searched and hope I didn't re-post something.

Thank you in advance.

 

[davenn]

hi there
welcome to the forums

do a google search on Low Voltage Dropout Regulators
they can go down as low as ~ 1.25V difference between input and output
you would then have a look at the datasheets to find one that could handle 3Amps
ot it may give circuit examples of using current pass transistors

cheers
Dave

 

[dinosquirrel]

ok, looked for some stuff like that and I got to thinking - I have a kit that I bought from radio shack, and it's rated for 1 amp. Can I just replace the semiconductor to something like a LM338T? Using this as a reference

http://www.ebay.com/itm/5AMP-Adjust...=320901010625&ps=63&clkid=8326029521616618982

The RS kit had a 4 way bridge, i think a 50v 500uf cap and not much more.

 

[War_Spigot]

What Dave said. I have some LDO Regulators that I think can regulate from an input that's only ~.5V above the output(under ideal conditions). They sold them in 3.3V, 5V, 9V, and adjustable versions. Buck converters are more efficient than linear ones, but I don't think they're typically made for high current applications, so a linear regulator would probably be better(and easier)

 

[davenn]

The LM338 is a good adjustable regulator and has great current capabilities specially when using the steel cased version ( not the aluminiun cased one) on a good heatsink

I have used a good few of them over the years where I wanted adjustable supplies.
that kit you linked to on ebay would be a good way to do some experimenting with the unit and see if it provides your needs.

cheers
Dave

 

[War_Spigot]

That seller provided the schematic, part numbers AND PCB layout? That's pretty sweet. I'm saving them for sure.

 

[dinosquirrel]

That seller provided the schematic, part numbers AND PCB layout? That's pretty sweet. I'm saving them for sure.

Yeah, I was kind of thinking the same thing. Why don't I just build that one? I need about 5 of those, so that price point is a little high for me. You know, considering I'm ebaying and building specifically to save money.

 

[dinosquirrel]

What do you mean steel lm338 vs aluminum? Is the steel one the circular?

 

[davenn]

What do you mean steel lm338 vs aluminum? Is the steel one the circular?

they look the same TO3 style case, just one is made of aluminium the other of steel
the steel one is better

Dave

 

[BobK]

Check this out. A buck converter is much more efficient than a linear regulator and you can't beat the price.

http://www.ebay.com/itm/4-40V-to-1-...933?pt=LH_DefaultDomain_0&hash=item20c521fadd

Bob

 

[dinosquirrel]

A while ago I bought some regulators, that from what I've been reading from you guys, seem to be buck converters. Here's a link

http://www.ebay.com/itm/1pcs-DC-DC-...=160800480328&ps=63&clkid=8445410710828786625

Instead of a 3 pin semi, this has a 5 pin, so am i correct in saying I see a parallel with the buck converter vs linear regulator?

 

[BobK]

Well, the description calls it buck converter, why would think it is not?

 

[dinosquirrel]

ah... because that's not the exact listing. That one looks exactly like the one I have, I found the original listing and but can't find it now. It didn't say buck anywhere on it. It was very vague but did say it would handle 3 amps without a heatsink and 5 with. But that means I would have to desolder the semiconductor from the board and add the sink.

 

[(*steve*)]

Look at the chip it uses and search out the datasheet.

OR notice if it has an inductor on the board. (could also indicate a boost regulator, but you can tell that by output voltage > input voltage)

OR measure input and output current and note that output current > input current

 

[dinosquirrel]

Played with my regulator a little - It appears to be a buck converter (based on the others I see) and it handles my application no problem.

Questions -
What is BUCK vs Linear?
I ran the app over night and my batteries dropped from 12.9 to 10.2 and my output voltage went from 5.53 to 5.52 <- is that what the buck converter does, keep it where you set it to?

can you tell me a little on why they use capacitors on this, and what their focus is? If I change them would it be beneficial for current spikes?

I added a heatsink to the lm2596 (that's what it is BTW) and it was fine, warm, but not hot. Is that technically called a transistor? I feel I'm wrong for some reason.

 

[dinosquirrel]

Adding more info to the above.

Obviously you know what BUCK does, but I tried to find a simple explanation and I didn't (can't say I looked very hard though). I did a test, where I increased the input voltage and lo, the output stayed the same. So I think I answered my own questions. But now I want to know what it stands for.

Also, if I rectified the outputs on two of them, and placed the outputs on a parallel line would I theoretically increase the current? ie from 3a to 6a

 

[BobK]

A linear regulator acts like a variable resistor, it changes its resistance to make its output at the regulated voltage independent of the current being drawn. For any linear regulator all of the difference in voltage is wasted as heat in the variable resistor. So given an input voltage Vin and an output voltage Vout the efficiency of a linear regulator is at best Vout / Vin. So if you are dropping 10V to 5V you are wasting exactly half the energy: 50% efficiency.


A buck converter is also called a switch mode regulator, it uses an inductor and capacitor to to keep the output at a stable voltage by switching the input on and off rapidly, typically 100 kHz or so. The inductor can limit current (for a very short period of time) without losing any power. So constantly turning it on and off to keep the capacitor charged to the correct voltage loses no energy. The capacitor supplies the current when the switch is off. So a switch mode regulator is typically in the range of 80 to 90% efficient, with the rest of the energy wasted in, for instance the DC resistance of the inductor.

Bob

 

[dinosquirrel]

Very happy with my bucky boys. Theyre doin the trick! What does buck stand for? Does it stand for anything? I read something where they were using certain caps in order to filter out noise - Any suggestions as to switch to? I have a tekkeon battery that is so noisy it's not even funny. Not to the ear, just when I plug in audio equipment, it picks it up too well.

 

[dinosquirrel]

got my buck answer, now I need a little help from anyone reading this.


Someone broke into my truck and stole my project, they have no idea what it is but I guess the grid antenna impressed them. Now I'm out power - They took my home made wires with regulators and now I don't have any power, so if anyone has any of the buck converters we've all linked to, and is selling them for a reasonable price, let me know. China would take too long.

 

[(*steve*)]

There's a word that describes people who do that. I'm afraid if I used it the forum software would replace it with asterisks.