Current amplifier for digital output
This is simply done if you're not looking for extremely high speed or power efficiency.







simulate this circuit &ndash; Schematic created using CircuitLab

M1 is almost any logic-level n-type MOSFET, such as an IRLIZ44N, which is available at Digikey for about 1.20 ea.

If you can't find a source of logic-level FETs, you can make a level shifter easily







simulate this circuit

with the note that a high on the 6501 output will turn the diode off, rather than on.

The FET in this case is any n-type MOSFET with a voltage rating of 20 volts or more and a current rating of 0.5 amps or more, and that's pretty much all of them.

R1 needs to be at least 2 watts, and more is probably better up to about 5 watts, but make sure the resistor is not a wirewound unit. A really good way to do it is to put 2 100-ohm 2-watt resistors in parallel.

The combination of 12 volts and 50 ohms will give a very consistent diode current of a bit less than 200 mA without requiring precision in the resistor value and voltage level. As a plus, you don't have to worry about the effects of ripple voltage on the supply. The price for this simplicity is the power dissipation in the 50 ohm resistor, which will dissipate about 2 watts when the laser is on. You can reduce this by dropping both the supply voltage and the resistor value, but if you get sloppy you may wind up with inappropriate current levels.

The 12-volt supply, of course, must provide at least 200 mA, and give yourself a bit of margin.