Design of diode laser lifetime test device
Lehtinen, Mikko (2019)
2019
Sähkötekniikan DI-ohjelma - Degree Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2019-12-18
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-201911065775
https://urn.fi/URN:NBN:fi:tuni-201911065775
Tiivistelmä
The objective of this thesis was to design and assemble a device for diode laser lifetime testing. This thesis also introduce briefly the history, basics of operation, some applications and manufacturing methods of diode lasers. This thesis was done to Modulight Oy.
At my responsibility was to design the electronics and mechanics of the device. At the beginning of the project some requirements were set to the device. The device had to be able to measure eight diodes simultaneously, setup had to be easily scaled for more simultaneous measurements, it had to be able to drive at least 15 amps of current to a load of 2.5 volts with each channel, it had to monitor and log the current and voltage of each channel and it had to be able to control the temperatures of each channel between 10 and 50 degrees Celsius.
The design started from the schematic of the electronics. For this I used a software called EAGLE. I chose this software because it was a standard design tool at Modulight. The main component of the device was a constant current driver. For this case the best option was to choose predesigned and manufactured ATLS6A201D from Analog Technologies. It was already familiar to me from previous projects so it was a natural choice for me. Analog Technologies also provided comprehensive instructions on how to use their driver in different situations so those could be easily be used as a base of the design.
The next step was to design the layout for the electronics. At this stage the placement of the components and the physical dimensions of the PCB was determined. The main feature to be considered with this design was the large amount of current that the PCB had to withstand. Each channel needed to be able to drive 15 amps of current so the PCB and the connectors on it had to be able to withstand 120 amps. To manage this, I designed six layers to the PCB. This way I could use a full layer of copper for just conducting the current. In the design of the layout I also had to consider the physical shape of the PCB and the attachment of it to the mechanics.
After the layout was designed, the next phase was to design the mechanics. For this I used a software called SolidWorks. One of the requirements was that the device should be easily scalable for more simultaneous measurements. To achieve this, I decided to design the device on a rack self. This way the scaling would be easy just by adding more selves to the set. Most of the component manufacturers offers 3D-models of their product free of charge so basically I just had to combine all these ready-made designs in to one assembly. One of the most important things in the mechanics design was to consider the heat control. Powerful drivers and lasers would both produce a lot of heat that needed to be led away from the setup. I executed the cooling by adding to big heatsinks under the PCB and to fans to blow cool air through both of them. Everything combined the device consisted of rack self, rack frame, PCB, eight peltier elements that were used to control the temperatures of the channels, four fans, two heatsinks and two AC/DC sonverters that were used to provide the DC current for the PCB.
After the designs were done, the PCBs were ordered from a manufacturer. In this case the PCBs were ordered without the assembly of the components because there were relatively few components on the board and we only ordered five of them so it was cheaper and faster to order and solder the components myself.
After all of the parts had arrived I started to assemble the device. The premade 3D-model helped a lot at this stage. After everything was assembled, I did some test to make sure that the device was working as designed. First test was the stability test of the current drivers. For this I used a programmable digital load. Unfortunately the loads maximum current was 14 A so I wasn’t able to test the stability at the maximum current. During 200 minute test the current varied only 8 mA which means 0.06%. This kind of stability is really good and is sufficient for this application.
Next feature to test was the heat control. For this I connected load diodes to all of the channels. These diodes turn all of the electrical power driven through them to heat and this way it is good way of testing the worst case scenario where all of the lasers are broken down and isn’t producing light anymore. During the test the ambient temperature in the room was 20.3 °C and the test time was 114 minutes. During the test the temperature of the heat sinks rose to 33 °C where it stabilized. All of the channels was set to 25 °C and the real temperatures varied between 24.9 °C and 25.22 °C. This kind of stability was moderate but large enough to affect the output power and the wavelength of the lasers.
All in all I think that the project was a success. The device met all of the requirements and it is in use daily at Modulight. Naturally there are also some improvements to be made in the future. The stability of the temperature control should be improved. This could be done for example by improving the thermal contact between the lasers and the heatsinks. I also hadn’t considered the placement of the wiring during the design of the device. This led to a fact that the wires looked quite messy in the device and were little bit on the way when using the device. This could be solved by designing some designated routes for the wiring in the mechanics. I had also forgotten to fire one of the connections in schematic and it had to be added by hand with jump wires to the PCB.
At this moment there are already second version of this device done where the thermal contact between lasers and heat sinks was improved. A third version is also being designed where the scalability is going to be further improved and some designated paths for wiring to be added.
At my responsibility was to design the electronics and mechanics of the device. At the beginning of the project some requirements were set to the device. The device had to be able to measure eight diodes simultaneously, setup had to be easily scaled for more simultaneous measurements, it had to be able to drive at least 15 amps of current to a load of 2.5 volts with each channel, it had to monitor and log the current and voltage of each channel and it had to be able to control the temperatures of each channel between 10 and 50 degrees Celsius.
The design started from the schematic of the electronics. For this I used a software called EAGLE. I chose this software because it was a standard design tool at Modulight. The main component of the device was a constant current driver. For this case the best option was to choose predesigned and manufactured ATLS6A201D from Analog Technologies. It was already familiar to me from previous projects so it was a natural choice for me. Analog Technologies also provided comprehensive instructions on how to use their driver in different situations so those could be easily be used as a base of the design.
The next step was to design the layout for the electronics. At this stage the placement of the components and the physical dimensions of the PCB was determined. The main feature to be considered with this design was the large amount of current that the PCB had to withstand. Each channel needed to be able to drive 15 amps of current so the PCB and the connectors on it had to be able to withstand 120 amps. To manage this, I designed six layers to the PCB. This way I could use a full layer of copper for just conducting the current. In the design of the layout I also had to consider the physical shape of the PCB and the attachment of it to the mechanics.
After the layout was designed, the next phase was to design the mechanics. For this I used a software called SolidWorks. One of the requirements was that the device should be easily scalable for more simultaneous measurements. To achieve this, I decided to design the device on a rack self. This way the scaling would be easy just by adding more selves to the set. Most of the component manufacturers offers 3D-models of their product free of charge so basically I just had to combine all these ready-made designs in to one assembly. One of the most important things in the mechanics design was to consider the heat control. Powerful drivers and lasers would both produce a lot of heat that needed to be led away from the setup. I executed the cooling by adding to big heatsinks under the PCB and to fans to blow cool air through both of them. Everything combined the device consisted of rack self, rack frame, PCB, eight peltier elements that were used to control the temperatures of the channels, four fans, two heatsinks and two AC/DC sonverters that were used to provide the DC current for the PCB.
After the designs were done, the PCBs were ordered from a manufacturer. In this case the PCBs were ordered without the assembly of the components because there were relatively few components on the board and we only ordered five of them so it was cheaper and faster to order and solder the components myself.
After all of the parts had arrived I started to assemble the device. The premade 3D-model helped a lot at this stage. After everything was assembled, I did some test to make sure that the device was working as designed. First test was the stability test of the current drivers. For this I used a programmable digital load. Unfortunately the loads maximum current was 14 A so I wasn’t able to test the stability at the maximum current. During 200 minute test the current varied only 8 mA which means 0.06%. This kind of stability is really good and is sufficient for this application.
Next feature to test was the heat control. For this I connected load diodes to all of the channels. These diodes turn all of the electrical power driven through them to heat and this way it is good way of testing the worst case scenario where all of the lasers are broken down and isn’t producing light anymore. During the test the ambient temperature in the room was 20.3 °C and the test time was 114 minutes. During the test the temperature of the heat sinks rose to 33 °C where it stabilized. All of the channels was set to 25 °C and the real temperatures varied between 24.9 °C and 25.22 °C. This kind of stability was moderate but large enough to affect the output power and the wavelength of the lasers.
All in all I think that the project was a success. The device met all of the requirements and it is in use daily at Modulight. Naturally there are also some improvements to be made in the future. The stability of the temperature control should be improved. This could be done for example by improving the thermal contact between the lasers and the heatsinks. I also hadn’t considered the placement of the wiring during the design of the device. This led to a fact that the wires looked quite messy in the device and were little bit on the way when using the device. This could be solved by designing some designated routes for the wiring in the mechanics. I had also forgotten to fire one of the connections in schematic and it had to be added by hand with jump wires to the PCB.
At this moment there are already second version of this device done where the thermal contact between lasers and heat sinks was improved. A third version is also being designed where the scalability is going to be further improved and some designated paths for wiring to be added.