Hi, im working on a small lighting project. I need 3 circuits. 2 that simply turn on with 12V power and put a string of 3 LED's to 60mA, and one dual stage circuit that turns on 5 strings of 2 led pairs from 16mA to 60mA.
Using 2.5v, 70mA Cree P4 leds, I have prototyped just a simple circuit with LM regulators and resistor strings, i have tried using an LM337 with a voltage divider on the ADJ/OUT pin, and i have tried the ON-Semi method of transistor controlled strings using a LM317T with my own addition of a 2n7000 mosfet to introduce another resistor in parallel to get dual stage.
All have worked but i have been wanting something more efficient. Being the device is battery powered i dismissed the first 2 ideas (one with 7809 regulators, and the other using 5 LM337's) due to them being too hungry for use on a battery. The third idea is better, using only 3 LM317's in total, but still not quite there for me.
Earlier i entertained the idea of using a 555 for PWM and controlling a TLC5947, but it only outputs about 30mA max, and i cant find anywhere if i can parallel mode 2 of the output pins to get 60mA like a few of the TI LED devices say.
Any ideas? I can use eagle cad, and have a very god understanding of electrical. Just a little out of the loop for products/IC's on the market that can be used.
I have attached my current plan. I put some other things on the same eagle file (will be on the board with other things in the end), the 7809 with the 150ohm is extra. Thanks.
Using 2.5v, 70mA Cree P4 leds, I have prototyped just a simple circuit with LM regulators and resistor strings, i have tried using an LM337 with a voltage divider on the ADJ/OUT pin, and i have tried the ON-Semi method of transistor controlled strings using a LM317T with my own addition of a 2n7000 mosfet to introduce another resistor in parallel to get dual stage.
All have worked but i have been wanting something more efficient. Being the device is battery powered i dismissed the first 2 ideas (one with 7809 regulators, and the other using 5 LM337's) due to them being too hungry for use on a battery. The third idea is better, using only 3 LM317's in total, but still not quite there for me.
Earlier i entertained the idea of using a 555 for PWM and controlling a TLC5947, but it only outputs about 30mA max, and i cant find anywhere if i can parallel mode 2 of the output pins to get 60mA like a few of the TI LED devices say.
Any ideas? I can use eagle cad, and have a very god understanding of electrical. Just a little out of the loop for products/IC's on the market that can be used.
I have attached my current plan. I put some other things on the same eagle file (will be on the board with other things in the end), the 7809 with the 150ohm is extra. Thanks.
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