Thank you all for motivating me to make a guide like this one. I hope this answers any questions and clears any confusions. If anyone requires any further support please do not hesitate to ask questions. 
One of the best items to be able to build yourself is the laser diode driver. The driver is supposed to regulate voltage and current. One of the best things to have in a laser diode driver is variable voltage AND current supply. This is sure to be an item that many would like to replicate and use on all of their home made projects. Also, given the very low component count in this driver, it could probably easily be made to fit into a regular L.E.D. flashlight be using SMD parts and rebuilding the circuit already in the flashlight.
Since voltage is already being provided by the regular battery, let's start with what we really need the circuit to do for the diode.
Regulate voltage:
What?
The voltage source that this circuit is designed to regulate is one supplied by an alkaline/lithium battery. An AA/AAA/AAAA battery supplies approximately 1.5 Volts DC(usually more around 1.2 for lithiums, but I've had a few at about 1.6-1.8!!). A CR123A battery supplies 3.0 or 3.6 Volts DC depending on the battery. This is very useful and very stable for the most part. When a battery is left unused for a while, the first burst of energy dispelled from the battery can spike up to 10 times the average power of the battery! Therefore, for a 1.5V battery, this would add up to approximately 15V. This burst is very small and very short that in most situations would not even kill the laser diode, but there are times when the burst packs some power along with it, supplying well over a watt of energy to the diode. This can spell instant death for most diodes!
How?
To regulate the voltage we can either use a voltage regulator and set it up in voltage regulation mode and limit the supplied voltage(This would still miss some of this spike and still pass it on to the diode) or we can use a capacitor. Capacitors work by charging up when there is a change in voltage. Direct Current voltage turns a capacitor into an open-circuit (a cut wire), and thus any spike or change in line regulation would work first on charging up this capacitor. Capacitors have 2 readings on them that correspond to maximum voltage and capacitance. For most of my applications I use a 47uF 16V capacitor. To be more on the safe side, you can get a higher capacitance and a higher voltage rating, but it all depends on personal preference. A capacitor will work to regulate the line up to the maximum power that it can soak up as fast as it could. Capacitors ADD up when connected in PARALLEL. Therefore, if you want to use mutiple capacitors with different benefits (Max voltage and big capacitance for instance) you need to make sure that BOTH positive and negative leads on the capacitors are connected together. I will explain more detail later on.
Regulate current:
What?
The current supplied by the battery is rather stable, but in most cases, is too much to drive a laser diode. For instance, a DVD-burner laser diode would need about 200-250mA of power at about 2.5-3 volts(for any long life span to actually be expected of the diode). Laser diodes are, unfortunately, a very light load when wired directly to a battery, and an alkaline battery would easily put out about 500mA or more, and lithiums put out 2 or 3 times that much! This too is an instant death situation for our beloved laser diode. Although very simplistic, it is not that common to find a flashlight with the right current regulation, and most of us would like to be able to control the current supply by using a potentiometer.
How?
Current regulation is the tricky part of this circuit. The chip that I like most for current regulation is the LM317. The chip can be used as a voltage regulator and as a current regulator. This guide will use a capacitor as a voltage regulator since the battery's voltage is, for the most part, already regulated and stable, while all we need to do is limit the current that we let flow into the diode.
Required components:
It has been suggested by Xenodius to use THIS potentiometer. This is a great alternative and a very easily acquired item from most local RadioShack stores. This circuit can completely be bought from your local RadioShack now
Thanx Xenodius
This diode driver would be able to drive all kinds of diodes and at all power levels. The LM317 can easily control current up to 1.5Amps but would require sufficient cooling to actually remain operational for a reasonable time. With a respectable regulated power supply, this circuit could power a laser diode without the need for any batteries.
The potentiometers in the bundle package MAY have a 100-Ohm pot. I have bought 2 of them and have not found any, but it’s not that difficult to get some from DigiKey…
As about the resistors, I actually prefer getting the package from RadioShack over getting individual resistors from DigiKey.
The LM317T from RadioShack is the same as the one from DigiKey. I personally prefer the smaller package from DigiKey only because it is much easier to pack into small spaces. The downside is that the bigger package has a small heat sink already on the LM317T, thus making it more usable for higher power ratings.
So... let's build it
The easiest way to learn about the LM317 voltage regulator itself is to read the data sheet available here.
Following is the schematic diagram for the laser diode driver.
The pins are not how your LM317 will be... note the labels and not the pin numbers...
One of the best items to be able to build yourself is the laser diode driver. The driver is supposed to regulate voltage and current. One of the best things to have in a laser diode driver is variable voltage AND current supply. This is sure to be an item that many would like to replicate and use on all of their home made projects. Also, given the very low component count in this driver, it could probably easily be made to fit into a regular L.E.D. flashlight be using SMD parts and rebuilding the circuit already in the flashlight.
Since voltage is already being provided by the regular battery, let's start with what we really need the circuit to do for the diode.
Regulate voltage:
What?
The voltage source that this circuit is designed to regulate is one supplied by an alkaline/lithium battery. An AA/AAA/AAAA battery supplies approximately 1.5 Volts DC(usually more around 1.2 for lithiums, but I've had a few at about 1.6-1.8!!). A CR123A battery supplies 3.0 or 3.6 Volts DC depending on the battery. This is very useful and very stable for the most part. When a battery is left unused for a while, the first burst of energy dispelled from the battery can spike up to 10 times the average power of the battery! Therefore, for a 1.5V battery, this would add up to approximately 15V. This burst is very small and very short that in most situations would not even kill the laser diode, but there are times when the burst packs some power along with it, supplying well over a watt of energy to the diode. This can spell instant death for most diodes!
How?
To regulate the voltage we can either use a voltage regulator and set it up in voltage regulation mode and limit the supplied voltage(This would still miss some of this spike and still pass it on to the diode) or we can use a capacitor. Capacitors work by charging up when there is a change in voltage. Direct Current voltage turns a capacitor into an open-circuit (a cut wire), and thus any spike or change in line regulation would work first on charging up this capacitor. Capacitors have 2 readings on them that correspond to maximum voltage and capacitance. For most of my applications I use a 47uF 16V capacitor. To be more on the safe side, you can get a higher capacitance and a higher voltage rating, but it all depends on personal preference. A capacitor will work to regulate the line up to the maximum power that it can soak up as fast as it could. Capacitors ADD up when connected in PARALLEL. Therefore, if you want to use mutiple capacitors with different benefits (Max voltage and big capacitance for instance) you need to make sure that BOTH positive and negative leads on the capacitors are connected together. I will explain more detail later on.
Regulate current:
What?
The current supplied by the battery is rather stable, but in most cases, is too much to drive a laser diode. For instance, a DVD-burner laser diode would need about 200-250mA of power at about 2.5-3 volts(for any long life span to actually be expected of the diode). Laser diodes are, unfortunately, a very light load when wired directly to a battery, and an alkaline battery would easily put out about 500mA or more, and lithiums put out 2 or 3 times that much! This too is an instant death situation for our beloved laser diode. Although very simplistic, it is not that common to find a flashlight with the right current regulation, and most of us would like to be able to control the current supply by using a potentiometer.
How?
Current regulation is the tricky part of this circuit. The chip that I like most for current regulation is the LM317. The chip can be used as a voltage regulator and as a current regulator. This guide will use a capacitor as a voltage regulator since the battery's voltage is, for the most part, already regulated and stable, while all we need to do is limit the current that we let flow into the diode.
Required components:
| Component | DigiKey | RadioShack | Approximate Price |
| Capacitor | 1 2 | 1 | ~ $1 |
| LM317 | 1 2 | 1 | ~ $2 |
| Potentiometer | 1 | 1 | ~ $1 |
| Resistors | 1 | 1 | Pennies |
| Silicon Diodes | 1 | 1 | Pennies |
It has been suggested by Xenodius to use THIS potentiometer. This is a great alternative and a very easily acquired item from most local RadioShack stores. This circuit can completely be bought from your local RadioShack now
Thanx XenodiusThis diode driver would be able to drive all kinds of diodes and at all power levels. The LM317 can easily control current up to 1.5Amps but would require sufficient cooling to actually remain operational for a reasonable time. With a respectable regulated power supply, this circuit could power a laser diode without the need for any batteries.
The potentiometers in the bundle package MAY have a 100-Ohm pot. I have bought 2 of them and have not found any, but it’s not that difficult to get some from DigiKey…
As about the resistors, I actually prefer getting the package from RadioShack over getting individual resistors from DigiKey.
The LM317T from RadioShack is the same as the one from DigiKey. I personally prefer the smaller package from DigiKey only because it is much easier to pack into small spaces. The downside is that the bigger package has a small heat sink already on the LM317T, thus making it more usable for higher power ratings.
So... let's build it
The easiest way to learn about the LM317 voltage regulator itself is to read the data sheet available here.
Following is the schematic diagram for the laser diode driver.
The pins are not how your LM317 will be... note the labels and not the pin numbers...
