RAVIKORIBILLI Posted October 30, 2009 Report Share Posted October 30, 2009 i try t built a emergency light by the project by community which name is low cast emergency automatic light i copied the entire crkt as per and made project but it did not work at all the led are built around bd 140 pnp transistor when apply a positive voltage to emitter the out put will go to base only because forward bias ckt says output to led are taken through collector where there is no voltage. kindly confirm the ckt and component (tr bd 140 is correct at the or not reply me as soon as possible Quote Link to comment Share on other sites More sharing options...
Hero999 Posted October 30, 2009 Report Share Posted October 30, 2009 How are we supposed to know when you haven't provided the schematic? Quote Link to comment Share on other sites More sharing options...
RAVIKORIBILLI Posted October 30, 2009 Author Report Share Posted October 30, 2009 it there in projects Quote Link to comment Share on other sites More sharing options...
Hero999 Posted October 30, 2009 Report Share Posted October 30, 2009 There are hundreds of projects on this site.Please provide a link to the one you're talking about. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 30, 2009 Report Share Posted October 30, 2009 You are correct, the circuit does not work. Nothing turns on the BD140 transistor.Many circuits posted here from that author do not work. Quote Link to comment Share on other sites More sharing options...
Hero999 Posted October 31, 2009 Report Share Posted October 31, 2009 Nothing turns on the BD140 transistor.That's not completely true, it will turn on a little bit, just not enough to power the LEDs, they might glow dimly.I have a couple of possible solutions:1) Replace the BD140 with a P-channel MOSFET, remove the 1k resistor and connect a 10k resistor across the bridge rectifier.2) Omit the 1k resistor and replace the BD140 with a Sziklai pair, the rest of the circuit should leak enough current to turn it on, if in doubt connect a 3k9 resistor across the rectifierAs shown the LEDs will draw about 25mA per diode, if fix #1 is used which might be too much, I'd recommend increasing the series resistors.If fix #2 is used, the current will only be 19mA per diode so the resistors can stay as it. Quote Link to comment Share on other sites More sharing options...
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