Constant current LED driver using step up regulator from Ebay.
This constant current LED driver drives string of LEDs that require a higher voltage than the available power source. For example one of the 10 watt 30 volt LED's (These actually consist of 9 LEDs in series.) can be driven from a 12 volt supply. It is based on one of the step up regulator modules that are sold by may different sellers on Ebay.
This is a picture of this type of regulator
This is a picture of this type of regulator
This is the schematic of the unmodified module.
This is the modified version of the module.
Modifications
First remove the trimmer R4. Now calculate the value required for the current sense resistor. (R3 and R4 in parallel.) The value of the current sense resistor should give 1.25 volts with the required LED current flowing through it. (R sense = 1.25/LED current.) The voltage rating of the zener diode D2 should be a couple of volts more than the voltage required across the string of LEDs. This zener diode prevents the regulator destroying itself in the event of the string of LEDs becoming open circuit.
First remove the trimmer R4. Now calculate the value required for the current sense resistor. (R3 and R4 in parallel.) The value of the current sense resistor should give 1.25 volts with the required LED current flowing through it. (R sense = 1.25/LED current.) The voltage rating of the zener diode D2 should be a couple of volts more than the voltage required across the string of LEDs. This zener diode prevents the regulator destroying itself in the event of the string of LEDs becoming open circuit.