ameya Posted January 1, 2005 Report Share Posted January 1, 2005 can any 1 help me i need some information about DOME LAMP DIMMER. i got few points regarding it but i want more information. i am giving the list of componunts,ic 555,1k&47K resistor,0.01uf capacitor,MOSFET,2diodes,1potect.pls if u have any information pls mail me. my id is [email protected] Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 2, 2005 Report Share Posted January 2, 2005 Hi Ameya,Welcome to our forum.Our Dome Lamp Dimmer project uses a standard Pulse Width Modulation circuit. The schematic is missing a wire: Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 2, 2005 Report Share Posted January 2, 2005 Pulse with modulation is ok but pulse position modulation will achieve the same effect but is a lot easier. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 2, 2005 Report Share Posted January 2, 2005 Hi Alun,Your Pulse Position circuit basically changes only the frequency of the oscillator. With your 10:1 timing resistor values, its duty-cycle will remain about 50:50 for most of its range so the lightbulb will always be at half brightness.Try a 555 this way, make the timing resistors equal value:1) With a high control voltage the timing cap will charge from both resistors for a long time and the 555's output is high and therefore the lightbulb is off. The cap discharges though a single resistor for a shorter time when the lighbulb is on. Therefore the lightbulb's average brightness will be a bit dim.2) With a low control voltage the timing cap will charge through both resistors as before, but the voltage across the resistors is much higher so the cap charges much quicker. The cap charges quicker also because it charges to a lower voltage. The cap also discharges quicker because its discharge voltage range is less. Therefore the lightbulb's average brightness will be near half brightness or a little brighter.Your Pulse Position circuit won't have anywhere near the 100:1 or more range needed to fully dim a lightbulb. My LED PWM dimmers have a 1000:1 range and you can still see the LEDs dimly glowing. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 2, 2005 Report Share Posted January 2, 2005 audioguru, I think you might be confusing pulse position with frequency modulation, with pulse position modulation the length & amplitude of the pulse remains constant but the interval between is varied, the longer the interval between pulses the lower the duty cycle and the lower the power.For more info see: http://www.argospress.com/Resources/CommunicationsSystems/pulpositimodula.htmAlso altering the control voltage alters both the threshold and trigger voltages, as illustrated by the internal block diagram as well as voltages on the capacitor show on the graph at the bottom.The circuit below (set up for 50% duty cycle) shows inverted pulse position modulation since the space between the pulses is constant and the length of each pulse is varied, in the first circuit I posted the PNP transistor inverted this output to give normal pulse position modulation. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 3, 2005 Report Share Posted January 3, 2005 Hi Alun,I see how Pulse Position Modulation changes the pulse width somewhat, but I don't think that a pulse width range from 10% to 70% is enough to dim a lightbulb. It is more suitable for motor speed control. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 5, 2005 Report Share Posted January 5, 2005 Well the computer simulation on the lamp dimmer suggests <25% to >99%, and I've tested the circuit as a lamp dimmer and it proved satisfactory. I don't have access to an oscilloscope at the moment, but I'm also building it on a PCB and if it works expect some pretty pictures. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 5, 2005 Report Share Posted January 5, 2005 Hi Alun,I suppose that an incandescent lightbulb dims OK with PWM from 99% to 25% since when it is dimmed, more of the reduced power goes into making heat, not light.I was thinking about dimming Ultra-Bright LEDs with PWM where the LED is still glowing when the duty-cycle is 1000:1. Half the current in an LED makes it just a bit dimmer. Half it again and it is still pretty bright. Then you have your 99:25 ratio. If you invert the pulses then you'll have a PWM range from 75% to 1% which still isn't enough for fully dimming LEDs.My PWM dimmed LEDs were still glowing when the PWM pulses were so narrow that I couldn't see them on my 'scope. I squashed those narrow pulses with a small filter cap at the base of the driver transistor to dim my LEDs down to zero. Quote Link to comment Share on other sites More sharing options...
ante Posted January 5, 2005 Report Share Posted January 5, 2005 Hi Guys,Here is a dimmer circuit with MOSFET: Quote Link to comment Share on other sites More sharing options...
ante Posted January 5, 2005 Report Share Posted January 5, 2005 And here is a way to get almost 0 to 100% adjustable pulse width: Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 8, 2005 Report Share Posted January 8, 2005 Ante, that's a very good idea, it only has one disadvantage - you can't use an external voltage signal to control the brightness.I've tweaked the values in the circuit and manage to borrow an oscilloscope, as shown the output on pin 3 goes from off completely (or too small to be seen on the scope), to about 95% on. I replaced the PNP transistor for a P-Channel power MOSFET to increase the efficiency further with a 20W bulb the heat-sink barely gets warm. The bulb goes from 5% to 100% on, with the 20W bulb it's completely off at 5% but a torch bulb will glow very dimly.Audioguru, if you want to use this circuit to power white LEDs you could connect them directly to pin 3 of the 555 and you wouldn't need it to turn on more than 75% or so (use the previous 50-50 circuit). This would allow you to save power by using a lower value ballast resistor (you might be able to get away with no resistor at all if the LED's internal resistance is high enough). If the LED doesn't turn completely off then you could always use one of those variable resistors with a built in switch to interrupt the power. I shall get hold of some of these white LEDs and try this myself.When I get hold of a digital camera I will post some pictures. Quote Link to comment Share on other sites More sharing options...
ante Posted January 8, 2005 Report Share Posted January 8, 2005 Hi Alun,As far as I can see you are not using an external voltage to control your circuit? And there is no reason to do this in a dimmer circuit. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 8, 2005 Report Share Posted January 8, 2005 Oh, I agree, I was just being picky. ;DIt could be useful though if you wanted to connect is to a control circuit so the light would come on slowly, or connect it to an audio amplifier to make it flash to the beat of the music, but for this application your circuit is perfect. Quote Link to comment Share on other sites More sharing options...
ante Posted January 8, 2005 Report Share Posted January 8, 2005 Well since you are the picky kind; the component count would increase of course but with the help of an op-amp and some resistors it could be changed to voltage control.[move] ;D ;D ;D [/move] Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 9, 2005 Report Share Posted January 9, 2005 I'm going to build your circuit, wish me luck, If its better than the other circuits here it should replace the one currently used. I will also post a diagram of alll the parts I used and if you're lucky a picture too. Quote Link to comment Share on other sites More sharing options...
ante Posted January 9, 2005 Report Share Posted January 9, 2005 I wish you all the luck in the world my friend! Looking forward to hear (and see) about your results! ;D Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 15, 2005 Report Share Posted January 15, 2005 Hi ante, I've buit your dimmer on a PCB using the transfer method and it works very well indeed! the PCB is perfect and the circuit isn't that bad either. ;DThe bulb goes from all the way off to all the way on.I looked at the waveform on a scope and there were some small pulses of a few us when it was on minimum but there wer none whent it was alll the way on.Here is the complete circuit with the exact component values, when I get round to it I will take some picrures. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 15, 2005 Report Share Posted January 15, 2005 Hi Alun,Good, you have made a nice lamp dimmer circuit. Also try it as a DC motor speed control with a reversed diode across the motor. Quote Link to comment Share on other sites More sharing options...
ante Posted January 16, 2005 Report Share Posted January 16, 2005 Hi Alun,I am very honoured to have a circuit named after me! ;D Good job Alun! As Audioguru says a diode for protection and the circuit will run DC-motors too! Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 18, 2005 Report Share Posted January 18, 2005 I have just tried a motor and it works very well indeed!The motor stops when on the lowest power level and the current consumption is <6mA. I could hear a very faint squeaky sound coming from the motor but when I turned the shaft I felt no resistance, so whilst this is a very good motor controller it just won't do for white LEDs.When on full power the motor runs at full speed, and when I bypass the transistor by connecting the drain to the source the motor doesn't run any faster.Although I haven't built the circuit originally posted, I would rather use this circuit because it's cheaper and easier to build and you stand a far greater chance of success.I strongly recommend this circuit, you should replace the original circuit with this one! Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted January 19, 2005 Report Share Posted January 19, 2005 I heard you could make a motor sing. Any Ideas? Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 19, 2005 Report Share Posted January 19, 2005 I've done that before, just connect the motor to the speaker output of a radio. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 19, 2005 Report Share Posted January 19, 2005 Poor radio with an inductive load. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted January 19, 2005 Report Share Posted January 19, 2005 Aren't speakers inductive anyway? Quote Link to comment Share on other sites More sharing options...
ante Posted January 19, 2005 Report Share Posted January 19, 2005 Yes a speaker is inductive, any coil is! ;D Quote Link to comment Share on other sites More sharing options...
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