LM2596 & fluctuating input

Can a ‘LM2596 DC Step-Down Voltage Adjustable Converter’ give a steady output from a fluctuating input ?
The one I have doesn’t, but is that because it just doesn’t or because its faulty
If its not able to cope with a fluctuating input can anyone suggest something that can.
The fluctuating input is from a 6v solar panel, I’d like to limit the top end to 6v

Any help gratefully received

Hi, if the input voltage is high enough you should be able to get constant regulated output voltage, BUT it depends on your circuit and LOAD and what you are supplying the converter with.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?

Tom...... :)

thanks for the answer

I just knew that sooner or latter someone would ask me for a circuit diagram.

Thats (i know) a really good idea, and i have started to look for a program to allow me to produce such a thing - an ordinary drawing program like say Paint.net isn’t up to it.
I’ve downloaded Fritzing which looks ok but doesn’t have all the ‘parts’ I’m using - like the LM2596.
There’s something called Eagle - haven’t looked at yet.
Could you suggest something thats easy to use that allows grouping of parts so changers can be made.
Do you have any thoughts on such programs as Fritzing and Eagle are they worth learning.

You did mention input voltage being high enough, bottom end would be about 5v for a 6v out put, does there have to be a marked difference between the input and output

I use Eagle for all my design work. If symbols don't exist, they can often be found at www.newark.com (free download after registering), or you can make your own. http://www.newark.com/webapp/wcs/stores/servlet/Search?st=lm2596&catalogId=15003&categoryId=800000037003&langId=-1&storeId=10194 The chip symbol indicates an eagle library is available to download.

I also use www.expresspcb.com schematic capture software for putting together a quick design for posting in the forum for discussion. Also very easy to make a new symbol.

It's rare to see a readable schematic from fritzing posted here.

Hi,

Can you please post a copy of your circuit, in CAD or a [u]picture of a hand drawn circuit[/u] in jpg, png or pdf?

Most phones produce a good picture of an A4 size sheet. Use paint to resize to 1000 pixel width.

Tom... :) I heartily recommend ExpressPCB, google it, not a big download and it will allow you to produce a BMP image of your work.

I really hate Fritzing…

My attempt at a circuit diagram – using expresspcb, thanks CrossRoads
expresspcb producers a .bmp image I can post the .sch if required.

Its not the complete circuit just the section giving me problem. The relay is switched by a voltage sensor across the solar panel output, if the output falls bellow 6v then it switchers to the 9v transformer. The Arduino and voltage sensor and other parts seem to be working ok.
I had hopped to route both outputs through the LM2596 to give a steady 6v, but this final bit isn’t happening.
With this setup what happens is:
Switched to transformer power
I set the 9v transformer to (through the LM2596) to produce 6v
If I then switch to solar power (6v or greater) at 6v I can only get the LM2596 to produce 5.4v

I’m thinking of changing the circuit so that ony the transformer is routed through the LM2596, assuming that the solar pannel will not produce much more than 6v – and I know the pump is ok with that. Just means on a sunny day the pump flow will be a bit greater than wanted.

Fritzing doesn’t look like a contender
Eagle a rather expensive paid for – uummm yes there are ways round, I’ll do a bit more reading first
expresspcb i’ve probably not used it as it should be but it will probably do

Hi, what is the LM2596, is it an IC, or is it a board that has LM2596 and associated components with it. The Solar panel will have no chance of keeping that circuit running, what power rating is the panel, and the motor. The solar panel is not like a power supply or battery, and will need some sort of storage , like a capacitor to help it out.

Tom.... :)

DesignSpark PCB is free for any use.

IGraham: Can a 'LM2596 DC Step-Down Voltage Adjustable Converter' give a steady output from a fluctuating input ? The one I have doesn’t, but is that because it just doesn’t or because its faulty If its not able to cope with a fluctuating input can anyone suggest something that can. The fluctuating input is from a 6v solar panel, I'd like to limit the top end to 6v

Any help gratefully received

Solar panels are roughly speaking a current source, not a voltage source, so won't drive a chip expecting a voltage source well (or at all). Or put another way as soon as the chip demands too much current the voltage will drop and everything resets.

I'd suggest adding a large amount of decoupling. Feed the solar panel via a schottky to a large (1000uF or more) electrolytic to the DC-DC converter. This should make the thing stable, but it won't address the problem of the panel producing insufficient power for the load, that's fundamental and may require some rethinking. Solar panels are often used to charge batteries for a reason...

Hello again & a Happy New Year

Tom, MarkT, yes its a board like this

The solar panel does not power the Arduino and related parts, the power is provided by a 9v 2a transformer, the same transformer that provides the alternative power to the pump. The solar panel only powers the pump when its providing sufficient power to do so.

My original question (i tried to keep it simple and focused) is mostly moot as I've changed the circuit so that only the transformer supplied 9v goes through the LM2596 now. The solar panel provided 6v is now not trimmed and in full sunshine will go over 6v (not really the time of year to stick a meter on and measure by how much). I'd still like a way to limit that but as i dont have a spare LM2596 i cant test that.

I've been 'tinkering' with the thing today and completing the coding and all 'seems' to work - with simulated solar input. Time to move off the test bed.

polymorph, thanks i shall have a look at DesignSpark PCB

Thanks for your help people the answers and questions were appropriated - an aid to thinking

polymorph: DesignSpark PCB is free for any use.

does it have an autorouter ?