R2 and R3 divide down the voltage developed across R1 before its sensed by the LM317.
Lm317 Laser Diode Circuit Full Detail OnNote how R3 is connected, with the wiper going to R2 - this is the upside down version of the grounded-wiper potentiometer feedback circuit I described in full detail on this page.It results in perfectly linear adjustment and, if the potentiometer wiper loses contact with the track, the output current is forced to the low end of the adjustment range for safety.With the values shown above, the maximum power dissipation is 1.6W, so a 3W rating is quite safe.
Basically, exactly the same Ive shown both circuits below - you can see how the LM337 circuit has the same connections; Ive just flipped it upside-down for ease of viewing, since thats usually now negative regulators are depicted. Lm317 Laser Diode Circuit Professional Engineers ToThese tools allow students, hobbyists, and professional engineers to design and analyze analog and digital systems before ever building a prototype. Online schematic capture lets hobbyists easily share and discuss their designs, while online circuit simulation allows for quick design iteration and accelerated learning about electronics. IMO input filtering is more essential than output coupling with these type of drivers. Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers. For a better experience, please enable JavaScript in your browser before proceeding. I am having readings that do not agree with the instructions. I am not getting the 1.25V reference voltage across the middle pin of the 317 to after the resistors. I am getting the full input voltage at the output from the driver circuit, where the LD will sit. I am confused about the two diagrams, the assembly, and the testing diagrams. I think there might be a discrepancy between the two diagrams. And on the Veroboard layout the resistor is before the pot with the first and middle pins commoned. Am I reading these diagrams incorrectly Which one is correct Heres a link to his page just incase, Laser driver - It can be done if you need me to circle the parts of the circuit that I think are different, Ill do that and post them here later on tonight. Anyway, I think the problem stems from people who dont normally look at schematics not knowing exactly what the schematics mean. Lm317 Laser Diode Circuit Driver Configuration OnTo alieviate this I have drawn up a schematic with the common LM317 Constant Current Driver configuration on it twice; 1) Shown how it normally is, with explanation of where the different voltages are. Shown arranged differently but electrically the same. It may look very different to the laymans eyes, but it is really exactly the same. This time it should eliminate errors commonly run in to by those who just replace the lines on the schematic with wires. A common mistake is to put the load between OUT and GROUND when it should really be between ADJUST and GROUND. When using a Pot as a VARIABLE RESISTOR and not as a VOLTAGE DIVIDER you only need TWO PINS. You can choose which outer pin you want based on which way you want the pot to turn to increase resistance. With the part you turn facing up at you and the pins facing towards you, if you use the left and center pin, resistance will increase when you turn it clockwise. If you use the center pin and the right pin, resistance will decrease when you turn it clockwise. So, if you wanted to use a pot on a constant current driver like for a laser diode, you could use the center pin as in and the right pin as out of the pot, and when you turn the knob to the right (clockwise) it will increase the current being supplied. Sigurthr: thanks for the tips about pots, I did not know that. Heres a macro of my build sofar, compactness was my prime concern, hehe. Even though it will shunt most of the current in the event of a polarity reversal, there will still be a reversed voltage across the diode that way, and that is enough to kill some LDs. You will incur a 0.7v drop though, so you would need to provide 3.7V higher than your laser diodes Vf. I would also add a second cap before the LM317 for input filtering.
0 Comments
Leave a Reply. |