fever16 Posted September 3, 2006 Report Share Posted September 3, 2006 hello all,i need 5v supply from my vehicle 12v battery.i know i can use 7805 but the problem is my circuit drives 20 LEDs continuously which roughly needs more than 400ma of current(over all).and the area is so conjusted i can't mount a big heat sink.so can i use dc-dc converter for this purpose.which chip is best for automotive project (if it is from MAXIM i can order a sample ::) )thanks Quote Link to comment Share on other sites More sharing options...
hotwaterwizard Posted September 3, 2006 Report Share Posted September 3, 2006 Just add a Transistor that can handle the load. 1 To3 Style 2N3055 would handle it with a small heatsink.The Datasheet Has a circuit for the Job.LM78xx.pdf Quote Link to comment Share on other sites More sharing options...
fever16 Posted September 3, 2006 Author Report Share Posted September 3, 2006 is it efficient than 7805?imean if we compare heat produced by these 2(7805 and transistor based circuit)which one is good Quote Link to comment Share on other sites More sharing options...
hotwaterwizard Posted September 3, 2006 Report Share Posted September 3, 2006 Sorry I modified my post the Datasheet showes the best circuit with the Short circuit Protection. Quote Link to comment Share on other sites More sharing options...
hotwaterwizard Posted September 3, 2006 Report Share Posted September 3, 2006 or you could just use an LM323 Regulator 5 volts 3 ampsLM123_LM323.pdf Quote Link to comment Share on other sites More sharing options...
Cabwood Posted September 3, 2006 Report Share Posted September 3, 2006 Or, you could get a tiny switcher from this site's advertisers here:http://www.dimensionengineering.com/DE-SW0XX.htm80% efficient, 1A output, and a tiny drop in replacement for the 7805! I haven't tried any, but they sure look good to me.If they really are over 80% efficient, these units would only dissipate half a Watt when supplying 400mA at 5V. Quote Link to comment Share on other sites More sharing options...
ante Posted September 3, 2006 Report Share Posted September 3, 2006 Here is another possible solution:http://datasheets.maxim-ic.com/en/ds/MAX724-MAX726.pdfHigh current, high efficiency, no heatsink, low part count, free samples and no fuzz! ;) Quote Link to comment Share on other sites More sharing options...
fever16 Posted September 3, 2006 Author Report Share Posted September 3, 2006 Here is another possible solution:http://datasheets.maxim-ic.com/en/ds/MAX724-MAX726.pdfHigh current, high efficiency, no heatsink, low part count, free samples and no fuzz! ;)yes i saw those.but no samples for these chips :(any other maxim chips.@hotwaterwizardthanks i'll try these too Quote Link to comment Share on other sites More sharing options...
ante Posted September 3, 2006 Report Share Posted September 3, 2006 Woops! :-[The MXL1074CT-SL is available as sample and works the same way as the MAX724-26 (max 2A). ;) Quote Link to comment Share on other sites More sharing options...
fever16 Posted September 3, 2006 Author Report Share Posted September 3, 2006 yes it is available.and in TO-220 package.thanks ante.**if it is so efficient can i place it in a closed box(with small hest sink) for my motorcycle project?? Quote Link to comment Share on other sites More sharing options...
ante Posted September 3, 2006 Report Share Posted September 3, 2006 If I got it right here you need less than 500mA and this should be fine with almost no heatsink at all. If you fit it in a metal box just bolt it to the box and you’ll be fine. The tab of the MXL1074CT-SL is common ground so you don’t need any insulation for it if you don’t want to. (I presume your bike has negative ground connected to the frame)!? Quote Link to comment Share on other sites More sharing options...
mugsby Posted September 6, 2006 Report Share Posted September 6, 2006 a cheap way would be to use one of the to-220 TIP series with a zener to bias it. Quote Link to comment Share on other sites More sharing options...
hotwaterwizard Posted September 6, 2006 Report Share Posted September 6, 2006 Here are a couple more Quote Link to comment Share on other sites More sharing options...
nickagian Posted September 11, 2006 Report Share Posted September 11, 2006 or you could just use an LM323 Regulator 5 volts 3 ampsCan I ask something about that? Does the output current of 3 amps (or 1.5 amps for LM117) depend on the input current or it is provided even if the input current is less? Quote Link to comment Share on other sites More sharing options...
ante Posted September 11, 2006 Report Share Posted September 11, 2006 Hi Nick,It depends on the power dissipation in the LM323 and the available current on the input side! Quote Link to comment Share on other sites More sharing options...
mvs sarma Posted October 12, 2006 Report Share Posted October 12, 2006 if you can accomodate more parts go for MC34063C, the datasheet you may study. of late there are 4 pin swichable regulators providing for economical space saving and efficent ones. perhaps nationa semi has few of them. for all linear methods you will have to loose energy acroos the set up. sarma Quote Link to comment Share on other sites More sharing options...
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