DC to DC Voltage Regulation

Well DC/DC power supply design is often at least a full semester study in a post graduate curriculum. You would probably be best served by just buying the appropriate DC/DC converter module. But if you wish to delve into the realm of designing the circuit yourself, On semiconductor has a decentslide presentation on the topic.

The slide presentation was lovely and very well done, and if I was an electrical engineer, I would probably find it very informative, but -

Let me rephrase. I have no intention of reinventing the wheel, or electronic circuits. That has already been done and units like the LM-317 have been around for years.

If anyone has no better suggestions, I'll probably go with the LM-2670, 3 amps and 94% efficiency.

or the EZ1584CT, rated at 7 amp output and "high efficiency", whatever that means.

Most of them are between $2 and $10 each.

I did not intend to discourage you at all with the link, but I did want you to at least to see that unlike a simple linear regulator, LM-317, any switching supply circuit can get to be much more complicated than many expect. Having said that, the LM-2670 is a good controller. Keep in mind that you will find that your choice of inductors and capacitors will effect the efficiency of your final design.

From the NS Datasheet:

As Redfred indicated, it is not 'just a couple of resistors' needed for the circuit, but you are correct that it should be more efficient to avoid the 120VAC up and down conversions.

A couple of notes: 1. It would probably be worth your time to design and build a printed circuit to mount the parts on. keep all leads as short and wide as possible, paying attention to the notes shown. (I was surprised and disappointed to see that they did NOT provide a suggested layout). If you design the layout correctly, the same circuit board could be used for both fixed and variable voltage devices, assuming you will not use the sync input. 2. Obtain, use, and LABEL correct sockets for each device to be connected; pay attention to polarity.

You have very little to loose and a lot to learn plus significant extension of your battery time, so GO for it!

The efficiency is "AFTER" the transformer/rectifier only.

In a pure DC to DC situation, you should achieve the efficiency.

Another good chip is the LT1074/LT1076 DC to DC family.

I have a schematic and build infos (PCB can be ordered in the US or Europe) for an excellent power supply that uses two of them to produce up to 10 amps at 85% efficiency. Let me know if you wish to have a copy.....look up the chip first to see if its interesting for you though!

Andy,

Could you send me your schematic and PCB layout of LT1074/LT1076 you mentioned.

I'd appreciate it.

Thanks.

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Here is some "think outside the box" ideas.

Instead of a single 6/12 volt battery, how about using several (ok maybe lots) of 1.5 volt rechargeable D-cell batteries in a series-parallel arrangement? By having multiple tap points you can get any voltage in 1.5 increments with zero efficiency losses from a power supply.

Or can you open the case of your lead-acid battery (preferably before filling with acid) and solder on multiple taps?

That will guarantee that some cells die before others, unless you have a system that charges each individual cell according to its condition. Even in that case some cells would get greater use than others, so would die sooner.

Good post.

I wrote much the same after you, but before I read your post, sorry!!!

Also this is not solely about charging batteries, it's about maximizing efficiencies in using a solar array to charge a deep cycle system and not adding the additional power loss of going from DC to AC (low frequency) to DC.

The problem with the D-Cell idea means that different cells will be di´scharged at different rates. This will quickly lead to cell damage and consequent costs.

All cells in ANY battery need to be treated exactly the same way, and of course properly!!!

Charging of single cells MUST be made on an individual basis too.

Chargers that charge 2 or more cells together are just killing the cells, unless many special precautions are made.

Instead of a single 6/12 volt battery, how about using several (ok maybe lots) of 1.5 volt rechargeable D-cell batteries in a series-parallel arrangement? By having multiple tap points you can get any voltage in 1.5 increments with zero efficiency losses

A clump of D cells is nowhere near enough power to run a dozen or more warts 24/7.

As for dissecting a battery and tapping into it, that is a great idea if it was simple to do, but I don't care to start cutting open batteries.