The chip that I like most for current regulation is the LM317. Following is the schematic diagram for the laser diode driver.
The current controlled circuit of a laser pointer power supply explained in the following post was requested by Mr. Steven Chiverton ([email protected]), who himself is an intense electronic hobbyist and researcher.
1Technical Specifications
Technical Specifications
Dear swagatam,
I'm emailing you to ask you for your expertise, and you being one of India's finest electronics engineers I thought you be the best man in the world to know, bear with me my friend its a bit of a long story.
I brought some 10 milliwats laser diodes from xxxx electronics here, the data on them isn't much but maybe enough to go by, they are 2.4 volts and the threshold current is 24 milliamps and the maximum current is 40 milliamps
now I've looked all over the net for a power supply circuit using the lm317 regulator for this diode but there's circuits for other diodes only but there voltage and currents are different
so trying to find a simple lm317 regulator circuit that will deliver 2.4 volts dc at up to or near 40 milliamps is hard . so I used an lm317 regulator calculator for voltage and
so I breadboarded it only to find out the voltage output was no where near the output of 2.4 volts I wanted , despite what the lm317 regulator calculator says
so I wanted 40 milliamps or to be safe just under it so I used the lm317 current regulator calculator and the resistor I entered got me 40 milliamps
but when I bread boarded it I got no where near it . so the best way to go is may be to modify an already existing laser power supply for a laser diode
I know nothing about to try get the 2.4 volts at near 40 milliamps so ill include one here can you modify the circuit to deliver 2.4 volts dc at near 40 milliamps for me and powered from a nine volts battery .
thank you swagatam I hope you can get it right where I've failed .
The Design
The required laser pointer driver circuit was actually very easy to design, thanks to the versatile 317 IC, you can do almost anything with this chip.
As shown in the figure, a single LM317 is used for acquiring the required precise 2.4V output at 24mA current.
It's a standard 317 variable power supply design. The preset P1 is used for setting up the 2.4V output.
Or alternatively P1 may be replaced with a fixed resistor of 110 Ohms, which would yield exactly 2.4 volts at the output
R3 is adjusted for getting the 24mA threshold current limit.
As per the formula, the current control resistor R3 may be calculated in the following manner:
R3 = 0.7/0.024 = 29 ohms.
Feedback
thank you very much swagatam ill give that circuit a go to just have to round up the resistors I need out of a draw full of them and the 110 ohms isn't an easy one
but resistors are never the exact values these days that's why they have the gold tolerance bands they are either above or below there values ,
and also due to the various calibrations of digital meters they don't all read the same values so anyhow 110 ohms is close to 120 ohms is a try and electronic calculators and theory circuits don't calculate values using the gold tolerance bands
so the actual results are not known till the actual circuit build is done or the resistors are measured to the present calibration of the meter you use to test them with ,
thanks swagatam pal ill get back to you soon hopefully the red 10milliwats laser diodes hold up ok and at just over 6 dollars each I have 2 only so ill try them soon.
More Feedbacks from Mr. Steven
here's a copy of the modified laser driver circuit you once emailed my back can you modify it again to be adjustable up to 1.2 amps max and minimum of as low as you can get it , as I want to build another but with a higher adjustable current
DDL Laser Circuit
here's a new printed circuit version I made from a schematic from the laser pointer site this is for the ddl laser driver circuit , its a test load circuit for that so you can adjust the ddl laser diode driver and use the next circuit the test load circuit for that to tune this ddl laser diode driver I think its for 2.8 volts laser diode or near that
Improving the Laser Circuit Further
here's the latest swagatam,
I've made a printed circuit of another ddl laser diode driver from the laser pointer forum
so I've added a new feature to it to solve the laser diode damage problem caused by an undischarged electrolytic capacitor in the circuit near the output to the laser diode
even though I got the same thing when I blew my test laser diode when I forgot all about the 10 uf 16 volts electrolytic that caused it .
so here is my solution , look at the picture and next to the electrolytic capacitor is a plain dc input socket and I've used just 2 out of its 3 pins so it bridges the capacitor and forms a short to discharge it
so to unshort it just put any plug into it and it opens the short so the capacitor can charge during use of the driver and when you finish pull the plug out to shorten the capacitor again fail to do so would result in the charge left in the capacitor being dumped into the laser diode and thus over volting it and blowing it
In this project, we will show how to connect up and build a laser diode circuit.
A laser diode is a diode which outputs a laser beam.
Unlike LED light, a laser's light output is more concentrated, meaning it has a smaller and more narrowviewing angle. This means it must be directed at its source more directly in order to be picked up. Laser light is alsomonochromatic, meaning laser light isn't composed of several lights combined together, but one light of the same wavelength and energy. Normally with LEDs, the different light outputs are based upon different colors combined. One such example is green light. To output green light, blue and yellow lights are combined to give green. Lasers, for the most part, do not follow this. Laser lights have a single spectral color and is almost the purest monochromatic light available.
Laser diodes are used in CD players, CD-ROM drives, and other optical storage drives. They are used in laser printers, laser faxmachines, laser pointers, measurement equipment, bar-code and UPC scanners, and in high-performance imagers, as well as various other applications. These are just the most popular and used aspects of them.
To build a laser diode circuit, we must create a driver circuit for the laser diode.
A driver circuit is a circuit which can limit appropriately the amount of current being fed into the laser diode, so thatit can function correctly. Too much current and the laser diode will blow. Too little current and the laser diode will not have sufficient power to turn on and operate. Therefore, a driver circuit is needed to give precisely the correct range of current needed so that our diode will operate.
To build the driver circuit, we are going to need a voltage source, a voltage regulator, a diode, an electrolytic capacitor, and a few resistors.
All these parts will be explained below:
Components Needed for Laser Diode Circuit
- Laser diode
- LM317 Voltage Regulator IC
- 1µF electrolytic capacitor
- 0.1µF ceramic capacitor
- 240Ω Resistor
- 300Ω Resistor
- Heatsink
- 4 AA batteries or DC power supply
The laser diode we will use in this case is a 650Nm red laser diode made by US-Lasers Inc.
The type of regulator we will use is the LM317 adjustable voltage regulator. The reason we need a heat sink is to dissipateexcess heat created by the regulator. For example, if we input 6V into the regulator and it only regulators out 3V, this means that 6V-3V= 3V is dissipated as heat energy. To safely get rid of this excess heat energy, we connect the voltage regulator to a heat sink so that the excess heat dissipates into the air rather than damage sensitive electronic components.
For our input DC voltage, we can use anywhere from 5V-6V as our DC input. With a heatsink, even more voltage can be usedsuch as up to 9V, since the heatsink will ensure that the difference in input and output voltage will be safely dissipated away as heat. For this DC input, we can either use a DC power supply and set it to output 5V or we can use 4 'AA' batteries for 6V input or a 9V battery if used with a heatsink.
Laser Diode Circuit Schematic
The circuit we will build is shown below:
The circuit is actually pretty simple in nature.
The first capacitor, the 0.1µF ceramic capacitor, serves to filter out high-frequency noise from the DC power supply. The second capacitor, the 1µF electrolytic, serves as a power load balancer to smooth out fluctuating signals. The 2 resistors R1 and R2 serve to determine the output voltage of the LM317 regulator. Usually R1 is a fixed 240Ω resistor, as specified by the manufacturer. R2, on the other hand, is decided by the design engineer, basedon the amount of voltage he wants the regulator to output. In this case, with the laser diode we have selected, it has an operating voltage of about 2.7V. Therefore, we want the LM317 to output around 2.7V or a little higher. Therefore, we must choose the R2resistor value so that it outputs this desired voltage.
Since VOUT= 1.25V(1 + R2/R1) and R1= 240Ω, a 300Ω resistor for R2will output approximately 2.8V. So a 300Ω resistor will be perfect for our application for demonstration purposes. Later on, you can swap out this resistor for a potentiometer to vary the laser diode voltage to increase the brightness or dim it, as to how desired.
However, if you are using a different laser diode, it may have different voltage and current requirements. To calculatoethe output voltage needed output from the LM317 regulator, see the LM317 Voltage and Resistor Calculator. This calculator can find the R2 resistor value needed for the voltage that is desired to be output.
Just so that you can see the operating requirements of the laser diode, these are snippets of the datasheet. If you want to see the PDF of the datasheet, click on the datasheet link below.
To check the current flowing through the circuit, you an take a multimeter and place it in the DC ammeter setting. Break the circuit opening right at the anode of the laser diode and the anode of the capacitor and measure the amount of current flowing through. At least 20mA is needed for the laser diode to turn on. This is called the threshold current; it again representsthe minimum amount of current needed for the diode to function. However, more typically, the operating current is used for a decentamount of power output. For this diode, the typical operating current is 40mA. So 40mA should be fed. To increase or decrease resistance, you can change the value of resistance R2. Increasing this resistance value increases current. Conversely, decreasing this value decreases current. The maximum amount of current which the laser diode should receive is specified by its maximum operating current, which in with this diode is 60mA. No more than 60mA should be fed into the diode or the diode may be destroyed.So make sure to always follow the datasheet specifications.
And this is a simple, yet effective, laser diode driver circuit.
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