Voltage regulator question (Buck) LM2574 5V 0.5A DIP8

When replying before to your question of measuring caps and inductors, I was not under the impression you where thinking of using them for the buck regulator, Michaels points are all very valid and to make an efficient and reliable module need to be followed.

I was simply providing some basic info on how you could determine their values and perhaps create a fun project along the way with a measurement tool for yourself at the end of it.

it is also fun to experiment with inductors and capacitors while you learn their properties, there is something very satisfying in buildin an LC oscillator, doing the math and finding it running at the calculated frequency

a thing to note with the buck regulators btw is that you can get the complete unit from ebay for about 4$ or less, not sure what your paying for the inductor, diode and cap but it is worth considering and is much simpler, unless your wanting to learn how to build buck regulators of course, I always keep a few on hand for projects and when i get low, i simply get a pack of 5-10 from ebay to re-stock

never had an issue with them so far except having to wait a few weeks for them to arrive.

check out http://www.ebay.com/sch/i.html?_trksid=p2053587.m570.l1313.TR3.TRC2.A0.H0.XDC-DC+Buck+Converter+Step+Down&_nkw=DC-DC+Buck+Converter+Step+Down&_sacat=0&_from=R40

I do have some complete units on order

I have some of these coming:

http://www.ebay.com/itm/141255711343?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

The questions were more related to using the ICs I have, even if it is just experimental

I really enjoy being a hardware experimenter but I don't know a lot of things about electronics.

I figure the more I do and the more I ask the more I will learn.

So that Boost regulator says it is a 2A max continuous

for 10 350mA LEDs would I not need something that can handle 3.5A continuous?

I am looking to see if I can find a more powerful one.

I suppose I could get 4 of those and run 2 per fixture that is 5 350mA LEDs per boost module.

Just run the 5v power to the fixture and split it out to the 2 boards there.

I am not interested in dimming these, so I do not need any other control

The question is do I run all 5 LEDs in series then?

I am still foggy as to how to use a constant current regulator when running LEDs in series.

if you had the LEDs in parallel, yes, the whole idea of this is they can be in series and therefore if you had 5 in series on one sconce and 5 in series in the other, that will only be 700mA but at 5* the LED voltage which would be about 15V

up the boost to 30V and you can have all in series and only have to drive 350mA on the output, the input would consume the same power but at the 5V * 3.5 amp instead of 30V * .350A approximately

boost at t he power supply, not the sconce and then you distribute 15 or 30V instead at way less current, put the LEDS in series

The other option is to use 4.7 ohm resistors and figure the voltage is less than 5v.

The reality is the drop over 40 ft of 1.5A rated mains cable is not going to be that great, but you could always measure the resistance and adjust accordingly.

note sure what cable ratings you guys use, but this might help

Voltage Drop Calculator

mark

The reality is one sconce is right on the other side of the wall from the power supply and control enclosure, so in a poor execution of cable running that sconce will have at most 5 feet of wire running to it.

The other one is on the other side of the door.

So I need to drop down under the floor or up through the ceiling, but I will say that either way probably less than 12 feet.

I will probably go through the ceiling since there is already a chase there from running wire for the strip lights.

I am not thinking I am going to have much to worry about in the way of voltage drop.

There is a whole mess of 16ga stranded wire there that I think I am going to use for the run, probably ridiculously overkill, but at least then I don't have anything to worry about.

I was looking for boost modules for this and ran across someone's spec of a LM2577 module and they stated that:

An input of 5V and an output of 12V will be stable up to 800mA

That worried me about having to boost all the way to 30V

So I think simplicity is my answer, it is easy and cheap to replace a resistor if something stops working I only lose one LED, if I lose one of those boost modules I lose an entire fixture.

Just my thought.

So I think simplicity is my answer

An often overlooked quantity.

If it doesn't work out, you can always go with plan B and try 5 in series at 350mA. which is about 20v give or take.

Mark

totally agree, if those are the distances and your using 16AWG wire and can deal with the heat of the resistors... why not.

I have to remind myself your using commonly available parts you have around too so my suggestion while viable and more efficient is perhaps over kill in this situation

btw, would be great to see some pictures or even better a video once your done

Good luck, if you need more help, you know where we are

peter

Oh, the buck regulator I linked to was to show you an example, to show an idea of what could be done to mitigate the power drops if it proved to be an issue, it was not necessarily the best one for your situation

it looks like your good to go

So do you think 16ga is heavy enough or should I go to 12ga?

I do have both in ample quantity.

The other question is how can you figure out the rated heat dissipation of a heatsink?

I know there is some function of mass and surface area, but I have no idea how that works.

I am hoping that the ones that I have will be sufficient for the 1 or so watt per resistor of heat that will be generated. I don't mind having a small space heater and since it is open both above and below it there is plenty of opportunity for convection, I am just curious.

It may be a couple weeks before I get to actually implementing this project, I will be leaving Alaska for the summer in a couple days to go visit for the summer and at some point complete this job which was started last summer. LOL I will try to get back here and at least report on the success of the on the plan.

Andrew

The link I gave was in guage size, so plug some figures in.

Heatsinks are rated in deg C/W, however finding out what you have is nearly impossible.

Video cards produce lots of heat, so its likely they are pretty efficient, but usually they have forced air as well.

Google it and you might find http://www.sm0vpo.com/begin/heat-0.htm

You could do an experiment .... or use the imperically derived method  ... ie try it and see.

Mark

Andrew

The link I gave was in guage size, so plug some figures in.

Heatsinks are rated in deg C/W, however finding out what you have is nearly impossible.

Video cards produce lots of heat, so its likely they are pretty efficient, but usually they have forced air as well.

Google it and you might find http://www.sm0vpo.com/begin/heat-0.htm

You could do an experiment .... or use the imperically derived method  ... ie try it and see.

Mark