audioguru Posted May 26, 2007 Report Share Posted May 26, 2007 My bright red wide-angle LEDs are these ones:MV8191.pdf Quote Link to comment Share on other sites More sharing options...
pier Posted May 28, 2007 Author Report Share Posted May 28, 2007 In one of their page (pdf) i found white with the part number : 'MV8W0O'http://www.fairchildsemi.com/collateral/psg04_opto.pdf#page=28 Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 28, 2007 Report Share Posted May 28, 2007 Fairchild's MV8W00 white LED is narrow angle and is not as bright as modern LEDs.Digikey don't have any in stock so maybe it is not made anymore.Fairchild's website has old catalogs like the one you found.I don't think Fairchild makes LEDs anymore. Quote Link to comment Share on other sites More sharing options...
pier Posted May 28, 2007 Author Report Share Posted May 28, 2007 Hi AG Which manufacturer would be your next choice ? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 28, 2007 Report Share Posted May 28, 2007 I used Hewlett-Packard's LEDs for many years. Then their opto business was sold to Agilent who sold it to Avago. Digikey sell these excellent Avago LEDs at a pretty good price.There are forums for guys who eat and breath LEDs. They talk about the good and new brands of LEDs better than me. Quote Link to comment Share on other sites More sharing options...
pier Posted May 30, 2007 Author Report Share Posted May 30, 2007 While testing the board (old project with 52 led's) i applied just about +50 volts and found all the LED's start to work with a very dim light but around 4 of them were very very dim than the other 48 ones which were uniform in brightness. Is this because of the forward voltage rating or will those 4 of them fail fast ? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 30, 2007 Report Share Posted May 30, 2007 If the LEDs are in series and are the same make then they should all be the same brightness because in series the all have the same current. I guess your dim ones are not good. Quote Link to comment Share on other sites More sharing options...
pier Posted June 2, 2007 Author Report Share Posted June 2, 2007 I fixed them with good ones, but the capacitors are still charged even after the led's are off . They give small shocks . I took the pcb in my hand after the led's were off, thinking they would be discharged . Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 2, 2007 Report Share Posted June 2, 2007 Shocking!A white LED can have about 2.5V across it and not pass any current.You have 70 LEDs in series? Then the capacitor will be charged to at least 175V which will bite you. Quote Link to comment Share on other sites More sharing options...
pier Posted June 4, 2007 Author Report Share Posted June 4, 2007 So should i put a resistor across it to discharge it when it is put off ? Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 4, 2007 Report Share Posted June 4, 2007 So should i put a resistor across it to discharge it when it is put off ?Yes, but I can't remember the voltage across it and the capacitance value to calculate the resistor value and power rating. Quote Link to comment Share on other sites More sharing options...
pier Posted June 5, 2007 Author Report Share Posted June 5, 2007 Hello AG Do you mean the voltage across the led string when the mains voltage is disconnected and the led's are put off ? Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 5, 2007 Report Share Posted June 5, 2007 Hello AG Do you mean the voltage across the led string when the mains voltage is disconnected and the led's are put off ?Yes. I can't remember how many volts is across the capacitor that bites you. Quote Link to comment Share on other sites More sharing options...
pier Posted June 5, 2007 Author Report Share Posted June 5, 2007 when the mains is off and all leds are also off the voltage across the capacitor is 117 volts DC (reducing very very slowly) . The capacitors i used is 10uF/450volts, 3nos in parallel which makes 30uF. Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 5, 2007 Report Share Posted June 5, 2007 A 100k resistor will nearly fully discharge 30uF in 15 seconds.It will use only 1.2mA and dissipate only 137mW with the power connected. Use a 1/2W resistor for its high voltage rating. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 3, 2009 Report Share Posted April 3, 2009 Hi Pier,The circuit has 300mA, not 960mA.A 2N3055 power transistor can dissipate up to about 70W if it has a huge heatsink.Why do you have battery-powered LEDs in your room? Don't you have electricity?Or do you live in a tree? ::) Quote Link to comment Share on other sites More sharing options...
pier Posted April 3, 2009 Author Report Share Posted April 3, 2009 Hi AG :D :D :D ;D I dont live in a tree. I have a 13.5 volt 1.5A battery charger so that charges the battery and also lights up the leds. So when the power goes off it lights for some time taking back up from the battery. My previous image had some wrong calculations. In the image shown here i plan to have 4 such modules(led board 4nos and current regulator 4 numbers). So which would be the best power transistor to use ? the current of one module is 240mA. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 3, 2009 Report Share Posted April 3, 2009 If the LEDs are actually all 3.0V and divide the current equally then each 33 ohm resistor will have a voltage drop of 0.99V. Then if the battery is max at 13.55V the power transistor has a voltage drop of 13.55V - 9V - 0.99V= 3.56V. It will dissipate 3.56V x 0.96A= 3.4W. Any power transistor will work fine with a small heatsink.Why does your power go off? Can't they fix it so it is on all the time like mine? Quote Link to comment Share on other sites More sharing options...
pier Posted April 7, 2009 Author Report Share Posted April 7, 2009 Due to summer season there is power cuts here . They call it load shedding. So need to prepare for it. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 7, 2009 Report Share Posted April 7, 2009 Due to summer season there is power cuts here . They call it load shedding. So need to prepare for it. It must be difficult to live in a tree. :oMy home is on the ground and my electrical utility company keeps the electricity running for 99.999999% of the time. They also keep the voltage and frequency accurate.Of course it is not as hot here in summer as it is in your country but we still use air conditioning in summer.Our electricity use was maximum just before Christmas because of millions of old high current incandescent Christmas tree lights. So the electrical utility traded new low current LED Christmas tree lights for the old ones and now the electicity use is less. Quote Link to comment Share on other sites More sharing options...
pier Posted April 7, 2009 Author Report Share Posted April 7, 2009 Me too live on the ground ;D. Water here reduces a lot in summer and Hydro stations are affected. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 7, 2009 Report Share Posted April 7, 2009 My electricity is supplied by a hydro generator station between the largest lakes in the world (The Great Lakes) at Niagara Falls. The lakes never run out of water.There are two or three nuclear generating stations nearby.My electrical utility company plans for future growth. Quote Link to comment Share on other sites More sharing options...
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