OK, I will do my best. Much of my downloaded info was lost with a computer crash. I have much of the info backed up but where I got it is questionable. Start with jaycar's pdf called dcdcconv.pdf for a primer.
Microchip has a document called buck converter design example. If you want to calculate outputs this download will help you.
International rectifier has circuits like the ir2117 that likely have design data sheets with more on dc to dc converters. If not look online on their site. Someplace there I found information on converters, because I have some of that in my info.
Arduino has a project listing for a power supply using dc to dc converter that I used to build my first circuit of a dc to dc converter. My circuit was used to charge batteries at a rate of 50amps. The design was a three stage charger. That design was unfortunately lost in the crash.
Much of the information I have has a copyright on it so I can't just post it.
Problem as I stated earlier, I am having trouble finding all my files. Because I need to build another project, I will be re-locating much of the old sources, but this may take a while if still published online. I am thinking a Cuk converter the next time around for the low ripple.
For the record. Computers have taken a lot of the calculation out of making one of these. I am using AI fuzzy logic when I program the controller. I start with a smaller PWM number than required and check the output voltage with the voltage divider then increase the pwm number till the desired voltage is reached. This takes a little time to stablize but never has overvoltaged on me.
My variable voltage power supply is set to the desired voltage and I program the arduino to send the reading to my computer via usb. This number I then program as a constant to compare to my reading from the divider.
If you wonder how to use the PWM output, it is the analog output of the arduino/wiring programming language for the arduino IDE. Note that the freq. Is much lower as programmed with the analog out command than is normal for dc to dc converters. You can change this with avrcpp with a few instructions in C by changing the counter/divider timer values. Or just use larger components. I have done both and find the larger components the easer method for a one off project. This is also why my next project will be of the Cuk design. I need the ripple free output for that project. You also have got the benefit of my past posts. My new 12v system will be a bank of capacitors rather than a battery. The thought of wasting power to charge a battery when the power to do it is comming from a off grid battery bank and sources makes no sense.
Oh! Almost forgot, spice is a development started with the development of the IC, at Berkeley University in California, then released to opensource. It is used as a lab to test circuits without having to build a prototype. I use the opensource version. Topspice is a windows version of spice that has a trial version that can be used for personal use. The website referenced at the start of this thread has a link to download it. As well as a script to run in it to see how the dc to dc circuit will respond to different components you may already have in your junk drawer.
Tutorials for arduino system show how to configure components and drive transistors. Driving any kind of load from a micro processor pin will only serve to distroy the processor. Read the tutorials online before you get started. Driving high voltage (over 5volts) loads without opto-couplers is a bad practice. This includes my voltage divider. To protect the processor the high side resistor is 1/8w and the low side resistor is1/2 w when I build one. My idea is should a resistor burn out it will likely be the lower watt one. This in turn will keep the pin from ever getting the full high side voltage. It will instead go to ground. This to has a bad side effect. The output will peg unless you program a failsafe. For me this is done by turning off the PWM pin should the voltage go to 0 after checking for an input voltage.
Kevin
P.S. as I recall ecircuits an online site has a study course on dc to dc converters. Yes I think that is one of my references. I seldom follow a course to the end, I just get what I need. My guess is they have a ICR channel for discussion where you can get the answers you need real time. If not I bet you can find an IRC easily enough. Of course if you don't mind waiting on my responses keep this topic here, but remember I am not a teacher or engineer, just a hobbiest.
Kevin,
I would also like to add my appreciation for the hints you provided!
That project looks very interesting to start with and begin tinkering. I saw an article on wikipedia about boost circuits and pumps. The described the basic circuit, but didn't show how easy it was to implement with a controller, and I don't recall seeing the diode configuration shown in the Arduino project. In my previous google searches for tutorials and circuits, the references you (Kevin) suggested didn't pop up. Thank you!
Wayne's project is unfortunately limited by using the controller pins to directly charge the capacitors. So I can see that he can get from 5V to 12 or even 18V at no load, or very little load. I'm guessing that I could add switches (transistors) between the controller and the capacitors to get it to boost the current capacity a bit. One question I would have on that would be whether only (+) needed to be switched, or if (gnd) would also have to be switched (2x transistors per connection). I haven't had a chance to play with it yet....
But I'm also guessing that there's a limit to how far this can be pushed. I'm skeptical that this can be practically scaled up to the 10-15A range.
And, as you mentioned in other emails - there's definitely a limit to how much power you can suck out of one battery to produce the desired voltage.
I haven't had a chance to tinker with voltage pumps yet. They look cool, and would certainly solve some problems. But it would be no surprise to run into practical limits....
John
Kevin, I'm fascinated by this subject but it would be very helpful if you could share a little more of what you've found in your own research. For example, I don't know what Top Spice is, or where to find it. Also the particular on line sources for other information about high current PWM DC:DC converters using Arduino would be super helpful. If you have actually gotten far enough into this to design a particular DC:DC converter using the approach, would you be willing to share the schematic and maybe a few design notes that would be helpful to others of us interested in doing a similar project? I have tinkered with analog approaches but for one reason or another, most of my attempts have shown one or more design flaws and I can't really claim to have been totally successful, esp when trying to draw 10-15 Amps of current.
On Wed, Mar 19, 2014 at 2:42 PM, Kevin Pemberton
<pembertonkevin@gmail.com> wrote:
Because many of you have wanted to know more about dc to dc power supplys I have looked up some things that helped me learn more about them.
Most engineers use black box devices to put a system together rather than build from scratch. We will not build from scratch but will open the case on the blackbox.
Building an a PWM source can be troublesome so I use the arduino project to feed the buck circuit to avoid many problems. Fact is the play area of the arduino website has published a project for a buck supply with a circuit we will use.
Other tools we will use include TopSpice just download the free version.
Next we will use the text file found in the tutorial on the ecircuit website files named basic buck. Much more can be gleened there but that can get you started.
Using a p channel fet driven by a npn small signal transistor with the PWM signal, and following the project published on the arduino site, you can have any size dc to dc supply you care to build.
Use the ecircuit site to learn why it works. See the results in action using the spice file supplied in the file from ecircuit in the downloaded TopSpice program.
You will find much on voltage dividers and a voltage divider calculator online. Build a divider and test it before you connect it to the arduino board. This input is feed to an analog pin on the board. It is used to read the output of the circuit so the program can adjust the output via the PWM duty cycle.
The output voltage can be 1/4 of the supply voltage. This means that a 48 volt supply can provide 12volts.
Have fun,
Kevin
--
All the best,
Dave Steere
dcsteere@dcsteere.com 850-234-2540 office
850-319-6010 cell phone
