I have designed a boost driver circuit for my 2D Mag light which I installed the Tri-star LED heatsink in. I wanted all 3 LED's to be in series (equal current to all of them). I couldn't find anything that I knew for sure would work. It seemed there were some that were close but I wasn't sure about all technical parameters so I designed one from scratch. It's easier to do one of these if the voltage is higher than 2 cells but I wanted one that would run off of the standard 20,000 mAhr alkaline D cells and down to a voltage of 1.8volts. (It will also work with 3D and 4D mag lights too)
When it came to putting in an aftermarket LED such as Mag's or Terralux, I wanted something that would wow people. Since the D size batteries have more capacity than AA's why not utilize the D Mag light into something that really shines. At least that was my justification.
The problem with boosting the voltage up to around 10volts and 6oomA of current to run these 3 leds in series is that power in = power out, minus efficiency of the converter. This means around 4 to 5 amps of input current on 2 D cells. I'd expect to get 4 to 5 hours continous use on the D cells but I'm not sure about current handling capability on the stock Mag light switch. Maybe someone can enlighten me there?
I decided to use Linear Technologies LT1619 low voltage current mode pwm controller because of its ability to work down to 1.8 volts. I sized up a n-channel mosfet with a balance of low RDSon resistance and also low Vgs threshold to work at 1.8 volts. The inductor is probably a little bigger than needed but wanted to make sure it could handle a variety of current capability. Anyhow I've simulated it on Linear's switcher cad, have layed out the pcb to a 2-sided 1"x1" board. I know its not the smalest thing but its robust and there is lots of room within the cavaty of the 'D' size Mag light.
I'm curious to know if anyone would be interested in this driver board. For me to get the fab (NRE) done on the gerber files is $140 and the unpopulated pcb boards are $8 ea in quantites of 12. So if I buy 12 of them my first batch is $20/ea. All of the parts can be bought at Mouser and Digikey. I'd provide a schematic and parts list but I don't have the resources to assemble. With the schematic you'd always be able to repair if needed. I did choose parts that can be hand soldered for the most part. Resistors and caps are 0805 instead of 0603 and the mosfet and pwm converter are SO-8 size. I think it's workable by hand. I know at work I have a gal do all of my small soldering becuase I can't. There is one small sot-6 transisor which I use as a current to voltage converter to save efficiency instead of a power hungry current sense resitor.
Now I haven't built this but I have worked with DC-DC power supplies and I believe it will work fine. Let me know if anyone is interested as I'm interested not in making money but in amortizing the cost to me.
One other thought. A lot of you guys probably have that LaCross BC-900 battery charger. The required input power to it is 3Vdc with 4amp capability. The power supply adapter that comes with it plugs into 120vac. I have always wanted to make an a dc-dc converter so that I could plug into my 12v outlet on a vehicle. If I don't get much interest in the boost converter mentioned above I may actually combine this project (which is also already designed) onto the same pcb fabrication so that I share the NRE charges.
Comments, suggestions, or questions welcome.
Jeff
When it came to putting in an aftermarket LED such as Mag's or Terralux, I wanted something that would wow people. Since the D size batteries have more capacity than AA's why not utilize the D Mag light into something that really shines. At least that was my justification.
The problem with boosting the voltage up to around 10volts and 6oomA of current to run these 3 leds in series is that power in = power out, minus efficiency of the converter. This means around 4 to 5 amps of input current on 2 D cells. I'd expect to get 4 to 5 hours continous use on the D cells but I'm not sure about current handling capability on the stock Mag light switch. Maybe someone can enlighten me there?
I decided to use Linear Technologies LT1619 low voltage current mode pwm controller because of its ability to work down to 1.8 volts. I sized up a n-channel mosfet with a balance of low RDSon resistance and also low Vgs threshold to work at 1.8 volts. The inductor is probably a little bigger than needed but wanted to make sure it could handle a variety of current capability. Anyhow I've simulated it on Linear's switcher cad, have layed out the pcb to a 2-sided 1"x1" board. I know its not the smalest thing but its robust and there is lots of room within the cavaty of the 'D' size Mag light.
I'm curious to know if anyone would be interested in this driver board. For me to get the fab (NRE) done on the gerber files is $140 and the unpopulated pcb boards are $8 ea in quantites of 12. So if I buy 12 of them my first batch is $20/ea. All of the parts can be bought at Mouser and Digikey. I'd provide a schematic and parts list but I don't have the resources to assemble. With the schematic you'd always be able to repair if needed. I did choose parts that can be hand soldered for the most part. Resistors and caps are 0805 instead of 0603 and the mosfet and pwm converter are SO-8 size. I think it's workable by hand. I know at work I have a gal do all of my small soldering becuase I can't. There is one small sot-6 transisor which I use as a current to voltage converter to save efficiency instead of a power hungry current sense resitor.
Now I haven't built this but I have worked with DC-DC power supplies and I believe it will work fine. Let me know if anyone is interested as I'm interested not in making money but in amortizing the cost to me.
One other thought. A lot of you guys probably have that LaCross BC-900 battery charger. The required input power to it is 3Vdc with 4amp capability. The power supply adapter that comes with it plugs into 120vac. I have always wanted to make an a dc-dc converter so that I could plug into my 12v outlet on a vehicle. If I don't get much interest in the boost converter mentioned above I may actually combine this project (which is also already designed) onto the same pcb fabrication so that I share the NRE charges.
Comments, suggestions, or questions welcome.
Jeff