I cobbled together a solar powered joule thief circuit from through hole components I had (1st picture). It consists of 3 x BPW34 photodiodes, 100uF electrolytic capacitor, 2 x 470uH axial inductors, 2n2222, and a red LED. The open voltage of a BPW34 is .4V, and the loaded voltage of all 3 combined under the same conditions is .463V (as measured with a Fluke 27 DMM). The intent is to use this for an indoor project.
The joule thief works in the sense that the LED blinks in low light, and is dimly lit in bright light. I would like for the LED to be brighter. I experimented with switching out components. I found that the circuit will not work with a capacitance below 47uF, and blinks slower as the capacitance gets larger. The axial inductors looked like they performed the same at 220uH, 330uH, 470uH, and 680uH. However, the base and collector inductors had to be the same size.
Also, I tried adding another capacitor in parallel with the LED, but that caused the LED not to light up at all after I left the circuit in bright light for an hour. Then, I added a 1.2V 80mAh NiMH battery in parallel with the LED along with a Schottky diode to prevent battery discharge back into the circuit (2nd picture). The LED did not light up either in that configuration after I let it sit overnight.
Any ideas how to make the LED brighter using minimal components? I'm trying to keep the footprint small.
The joule thief works in the sense that the LED blinks in low light, and is dimly lit in bright light. I would like for the LED to be brighter. I experimented with switching out components. I found that the circuit will not work with a capacitance below 47uF, and blinks slower as the capacitance gets larger. The axial inductors looked like they performed the same at 220uH, 330uH, 470uH, and 680uH. However, the base and collector inductors had to be the same size.
Also, I tried adding another capacitor in parallel with the LED, but that caused the LED not to light up at all after I left the circuit in bright light for an hour. Then, I added a 1.2V 80mAh NiMH battery in parallel with the LED along with a Schottky diode to prevent battery discharge back into the circuit (2nd picture). The LED did not light up either in that configuration after I let it sit overnight.
Any ideas how to make the LED brighter using minimal components? I'm trying to keep the footprint small.
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