LaserDriver - A6211
Recently, a friend of mine talked to me about his new hobby - handheld lasers. A big downside of the cheap lasers purchased from China turns out to be the design of their laser diode driver boards. Most of them are based on the LM358 operational amplifier and use a bipolar transistor to regulate the current. There is one major problem with this configuration - the transistor dissipates a lot of heat - especially if the voltage of the batteries is significantly larger than the forward voltage of the laser diode. I decided to build a custom board based on a buck DC/DC converter which is more efficient and runs at a significantly lower temperature. After some searching on the Internet, I chose the A6211 driver from Allegro.
The board is designed to provide a maximum of 2.5A of current to the laser diode. On the markings of the board, I specified a very conservative maximum current of 2A, so that there is some margin for fault tolerance and experimentation. The board has a trimmer pot which is used to tweak the current after the components have been soldered on. In my case, I am using an Osram PL TB450B blue laser diode and the resistor values specified in the schematic allow a current between 1A and 2.22A depending on the position of the trimmer pot. At the moment, I am using the laser diode at 1.5A - the maximum recommended datasheet value - and everything functions very well. The current regulation is stable and the laser diode works fine.
The board uses up to five 1206 resistors to measure the current flow and has a schottky diode protecting the electronics from accidental reverse polarity. The source voltage should be larger than 6V. The practical bottleneck for the maximum voltage value is the voltage limit of C3 and the two schottky diodes. For my laser, I used a 25V capacitor C3 but you may use a capacitor rated for 50V to extend the source voltage range. The A6211 driver itself can go up to 48V. On the whole, I obtained best results with 3-4 protected Li-Ion batteries (types 18650 or 16340).
As a host/body for the laser diode, I used one from a cheap laser from China (~ 10 USD). My friend gave me the body and helped me to make it longer so that it can house more batteries.
The schematic diagram and the BOM of the board are given below:
The board is designed for hand soldering. It is manufactured locally in Bulgaria (EU). If you wish to know more about the board or you want to experiment with it and get a board or a development kit, please drop me a note using the about page.