FINAL : LED driver
5/26
Components
- CL6808
http://akizukidenshi.com/download/ds/chiplink/CL6808_p.pdf
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Capacitor 4.7uF (Fablab inventory)
http://www.comchiptech.com/cms/UserFiles/CDBM120-G%20Thru934798.%20CDBM1150-G%20RevD.pdf -
Inductor 68uH
SMD power inductor : NR10050T680M
http://akizukidenshi.com/download/ds/taiyouyuden/NR10050T680M.pdf -
Resistor 100Ω (Fablab inventory)
Rs can be calculated with the formula:
Iout nom = 0.1/Rs
To set Iout to 1A, Rs suppose to be 100Ω. -
Freewheeling diode (Fablab inventory)
http://www.comchiptech.com/cms/UserFiles/CDBM120-G%20Thru934798.%20CDBM1150-G%20RevD.pdf
flyback diode is used across Inductive load basically sometimes called a snubber diode, freewheeling diode, suppressor diode, or catch diode is a diode used to eliminate flyback, the sudden voltage spike seen across an inductive load when its supply voltage is suddenly reduced or removed.
Freewheeling Diode Selection (Datasheet)
The forward voltage of the freewheeling diode should be as low as possible for better efficiency. A Schottky diode is a good choice as long as the breakdown voltage is high enough to withstand the maximum operating voltage. The forward current rating of the diode must be at least equal to the maximum LED current.
- LEDs to drive
Making PCB - Eagle
Add CL6808 to the library
Download XC6210B332PR.lbr
Edit pins, tabs and connections.
Add NR10050T680M to the library
Created new component library according to Recommended Land Patterns in the datasheet.
Added a terminal block library
The design for LED driver
Assembling components
- D1 : anode / cathode direction
*Fablab inventory SMD size : 1206 EIA = 3216 JIS.
Problems
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Current varies depends on the VCC voltage. e.g.) 340mA@12V and 550mA@7V
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Output current suppose to be 1A according to the equation ( IOUTnom = 0.1/Rs ).
Assuming that something is going wrong with Rsense as the resistance voltage changes according to VCC voltage, but I am not sure…
Another doubt was ADJ logic level might be affected by VCC voltage, but turned out it always keeps 5V.
Anyway, although output current does not fit the calculation, it still function as constant current LED driver and could be dimmed from 10 to 100%, I decided to move on.