Tobes49 Posted March 28, 2008 Report Share Posted March 28, 2008 I'm making some LED lights for the rear of my trike, I've brought some Osram Linearlight modules (PDF document). They look great the only problem is they need a 10volt supply. Whats the best way of dropping 14 Volts down to a stable 10 Volts Link to comment Share on other sites More sharing options...
craigyb Posted March 28, 2008 Report Share Posted March 28, 2008 Work out the forward current and use Ohms law to calculate how to drop 3V (cars are 13.8) and the operating is 10-11Volts. SO 3 volts would be 10.8 Volts operating. Link to comment Share on other sites More sharing options...
Tobes49 Posted March 28, 2008 Author Report Share Posted March 28, 2008 So 0.4A current draw with 3 volts is 7.5Ohms. So a 7.5ohm resistor should do the job, Cheers Link to comment Share on other sites More sharing options...
paulrstaylor Posted March 29, 2008 Report Share Posted March 29, 2008 Personally I'd go for a voltage regulator rather than a resistor..... MC7810 or something like that Link to comment Share on other sites More sharing options...
Tobes49 Posted March 29, 2008 Author Report Share Posted March 29, 2008 [ QUOTE ] Personally I'd go for a voltage regulator rather than a resistor..... MC7810 or something like that [/ QUOTE ] Is that the same as a LM317? I had been reading about them and in the spec sheet it shows a stable 10v schematic. Progress so far Main Red light bar (Full 440mm length) This can be cut into sections 55mm long with 4 led's With a 10ohm resistor (Didn't have any 7.5 laying around) Next challenge is to locate a osram OTDIM unit, This will let me dim the LED's to provide sidelights and then full power for stop lamps. Well that's what I'm hoping to do! Link to comment Share on other sites More sharing options...
paulrstaylor Posted March 29, 2008 Report Share Posted March 29, 2008 [ QUOTE ] [ QUOTE ] Personally I'd go for a voltage regulator rather than a resistor..... MC7810 or something like that [/ QUOTE ] Is that the same as a LM317? I had been reading about them and in the spec sheet it shows a stable 10v schematic. [/ QUOTE ] Similar.... LM317 is a variable output regulator, you need external components in order to set the output voltage. The MC78XX series are fixed voltage regulators, they require no additional external components and provide a fixed voltage output, 78'10' = 10V Paul Link to comment Share on other sites More sharing options...
davidhodgkinson Posted March 29, 2008 Report Share Posted March 29, 2008 Looking at the data sheet on the OTDIM. The OTDIM wont allow you to feed 13.8V (Max battery voltage) into it,so a 7810 regulator & heatsink will be needed. The OTDIM will provide 1 to 10Vdc to feed the LED light string. You will just need to "switch in" 2 different resistor values into the control pins to set the brightness levels. Looking at the system (but never used one) I think you should have a 100k resistor across the control signal pins to give zero light output (maybe even just an open circuit might do the same), 50k to give 1/2 brightness level and 0 ohms to give full brightness level. You should also fit a relay (or power transistor) into the power circuit to disconnect the controller when the ignition is turned off. Link to comment Share on other sites More sharing options...
Tobes49 Posted March 29, 2008 Author Report Share Posted March 29, 2008 [ QUOTE ] [ QUOTE ] [ QUOTE ] Personally I'd go for a voltage regulator rather than a resistor..... MC7810 or something like that [/ QUOTE ] Is that the same as a LM317? I had been reading about them and in the spec sheet it shows a stable 10v schematic. [/ QUOTE ] Similar.... LM317 is a variable output regulator, you need external components in order to set the output voltage. The MC78XX series are fixed voltage regulators, they require no additional external components and provide a fixed voltage output, 78'10' = 10V Paul [/ QUOTE ] I did a quick seach on some local suppliers websites but nothing came up for MC7810? I'll have a search later. It sounds like what I need. Link to comment Share on other sites More sharing options...
Tobes49 Posted March 29, 2008 Author Report Share Posted March 29, 2008 [ QUOTE ] Looking at the data sheet on the OTDIM. The OTDIM wont allow you to feed 13.8V (Max battery voltage) into it,so a 7810 regulator & heatsink will be needed. The OTDIM will provide 1 to 10Vdc to feed the LED light string. You will just need to "switch in" 2 different resistor values into the control pins to set the brightness levels. Looking at the system (but never used one) I think you should have a 100k resistor across the control signal pins to give zero light output (maybe even just an open circuit might do the same), 50k to give 1/2 brightness level and 0 ohms to give full brightness level. You should also fit a relay (or power transistor) into the power circuit to disconnect the controller when the ignition is turned off. [/ QUOTE ] I know I need a stable 10V in, I will look into the voltage regulators. Thats what I was thinking if I could switch in a sidelight/Brakelight feed to the unit to change it from 50% to 100% it means I can run one light bar for side and stop lamps. I should have the OTDIM unit but order the OT9/10-24/350DIM by accident I've also got a white 6700K linearlight unit, this looks like Audi DLR lights, I'll post a picture up tomorrow. Cheers for everyone that helped so far Link to comment Share on other sites More sharing options...
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