DC-DC converter construction - Page 1
Forum section: electronics / projects

author: lipovi
author_rank: Newbie
timestamp: June 28, 2013, 07:05:41 pm
content: Hello to all the people!I've been following the EEV YouTube channel from #300 (no pun intended) and every time, Dave said: "if you have a question, comment below or go to EEVblog.com". So here I am with a question for the, as the title says, converter build.I've been trying to make one for quite some time now and never had time to build it actually so I thought, let's get to work.I've found a small DC-DC 12V to 24V converter and actually built it but, for the application I needed it for, it isn't doing what I want it to do.I've added the schematic pic.The author described it like this:This simple DC-DC converter can provide up to 24V from a 12V source. It can be used to run radios, small lights, relays, horns and other 24V accessories from a 12V vehicle with a maximum draw of about 800mA. It can be used to charge one 12V battery from another, or step up the voltage just enough to provide necessary overhead for a 12V linear regulator. Using one op-amp as a squarewave oscillator to ring an inductor and another op-amp in a feedback loop, it won't drift around under varying loads, providing a stable 24V source for many applications. With a wide adjustment in output this circuit has many uses.The component list is:R1, R2, R3, R4, R8, R7 6 100K 1/4W ResistorR5 1 470 Ohm 1/2W ResistorR6 1 10K Linear PotC1 1 0.01uF Mylar CapacitorC2 1 0.1uF Ceramic Disc CapacitorC3 1 470uF 63V Electrolytic CapacitorD1 1 1N4004 Rectifier Diode (REPLACED WITH 1N4007)D2 1 Y229-400 Fast Recovery DiodeQ1 1 BC337 NPN Power TransistorU1 1 LM358 Dual Op Amp ICL1 1 See NotesThat L1 was a bit of a brain overload because the author of that schematic described this for it:L1 is made by winding 60 turns of 0.63MM magnet wire on a toroidial core measuring 15MM (OD) by 8MM (ID) by 6MM (H).Now, I noticed that the was no permeability specified so I went to my local garbage depot, found a destroyed PC, opened it and yanked a 24 mm(OD) by 17 mm (ID) by 8 mm (H) toroidal rind painted one side white and everything else yellow (I could have gone to Ebay and bought a toroidial ring with u = 2500 and Bsat = 500mT), took 0.6 MM magnet wire and made a winding of 60 turns too.But after all of this work and testing on phone charger adapter (12V, 1A), car battery (5 and 55Ah) and car battery charger (12V, 6A), the only rise in voltage was to 18V and ridiculous current of 10mA.Do I swap the ring with the EBay one and would it make any difference?I also have found some more schematics and trough Texas Instruments, found another schematic for a 150W supply. Here's a link to my Dropbox for schematic:https://www.dropbox.com/s/o5h78sirq1t39tl/webench_design_3772936_5_382117264.pdfThis looked neat and pretty simple but the average current input of 14.059A was a bit jaw dropping moment which brings me to another question:Can I combine this with something (any schematic) so I don't have that much of current drain?I wanted to make myself a 150W to 200W (yes, I know that the first schematic isn't what I need but to try at least to make one) so I can install it on my scooter along with 2 x 70W LED's (the Chinese ones) and have a go with them.My concept was that the 5Ah scooter battery would power the LED's while the engine is working and main lights are on (a relay can fix that) with a converter or a power supply that COULD drain 2-4 A and 5 A max. along with voltage being increased to at least 30-35V.Which is the next question: can this be pulled off? Thinking and thinking it over and over, it doesn't seem possible but wanted to be sure by asking you people here.And lastly, I found this beast:http://www.conrad-uk.com/ce/en/product/511533/VOLTCRAFT-SDC-245-Voltage-Reducer-DCDC-Converter-Synchronised-550-W-24-Vdc-138-Vdchttps://www.dropbox.com/s/wbrydfnhwdjutfj/511533-sp-01-en-Spannungswandler_24_12V_40A.pdfA 24V to 13.8V voltage reducer with 40A output.I think this is a overkill but more power does sound GOOOOOOOOOOD.So my final question is this:Can I make something from the first, second, third or one combined with each other to make a good converter so I can power my LED's?I would really appreciate comments and suggestions on this.....

author: c4757p
author_rank: Super Contributor
timestamp: June 28, 2013, 07:53:52 pm
content: Sorry - your post is long and I'm squinting at it through my previous two hours of sleep, so I'll just point out a bit about the first section:1) The toroids you find on PC motherboards often have quite a high permeability. 60 turns could easily be well into the mH range, and I doubt this circuit is designed for that. Try taking off a bunch of turns. I've got some high permeability toroids and it takes only 20 turns or so to reach 1mH.2) This is 2013, you can buy inductors.Look for 100uH or so.