I am attempting to build my first LED light string... yes yes I know it can be very simple, but everyone has to start somewhere!
Ok here we go!
Power Source: old laptop ac adapter rated output of 19v 4.74A
LED's: http://www.mouser.com/ProductDetail...=sGAEpiMZZMu4Prknbu83y1kHJl487Qqnh7qFW6eM39A=
I will be running the LED's at 500mA instead of the 1A it says on the datasheet for longer life and lower heat.
Schematic: http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/?ALLSTEPS#step7
Questions:
1. Im having trouble finding out how to calculate R1 in this schematic. I am somewhat familiar with ohms law but im having trouble visualizing how to apply it to get my R variable. The poster of the schematic lists a 1/4 watt 100k ohm resistor, and I'm not sure if this needs to be adjusted as I will be using more led's then the poster, but he seems fairly confident that his schematic only needs the addition of the zener diode or r2 to beef it up.
2. Im not sure what the advantage of using the zener diode over R2 is
3. How can I calculate the optimal amount of 500mA LED's I can put onto this circuit? I know my adapter is capable of pushing 4.74A so theoretically I should be able to get 9 on to the circuit, but I've read some posts about reducing the load to half of the maximum output to avoid burning out the adapter. Is this something I should be concerned about?
4. It looks like R3 would be exactly 1 ohm and .25 watts to set the current at 500mA. Should I leave headroom in this calculation?
5. Should I upgrade Q2's voltage capacity? He says the schematic should handle up to 60V with the zener diode or r2 added but this is a grey area for me.
Thanks!
Ok here we go!
Power Source: old laptop ac adapter rated output of 19v 4.74A
LED's: http://www.mouser.com/ProductDetail...=sGAEpiMZZMu4Prknbu83y1kHJl487Qqnh7qFW6eM39A=
I will be running the LED's at 500mA instead of the 1A it says on the datasheet for longer life and lower heat.
Schematic: http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/?ALLSTEPS#step7
Questions:
1. Im having trouble finding out how to calculate R1 in this schematic. I am somewhat familiar with ohms law but im having trouble visualizing how to apply it to get my R variable. The poster of the schematic lists a 1/4 watt 100k ohm resistor, and I'm not sure if this needs to be adjusted as I will be using more led's then the poster, but he seems fairly confident that his schematic only needs the addition of the zener diode or r2 to beef it up.
2. Im not sure what the advantage of using the zener diode over R2 is
3. How can I calculate the optimal amount of 500mA LED's I can put onto this circuit? I know my adapter is capable of pushing 4.74A so theoretically I should be able to get 9 on to the circuit, but I've read some posts about reducing the load to half of the maximum output to avoid burning out the adapter. Is this something I should be concerned about?
4. It looks like R3 would be exactly 1 ohm and .25 watts to set the current at 500mA. Should I leave headroom in this calculation?
5. Should I upgrade Q2's voltage capacity? He says the schematic should handle up to 60V with the zener diode or r2 added but this is a grey area for me.
Thanks!