Hello,
I am working on a project (Small portable table lamp) that uses a LIPO battery (3.7v-4.2v)to power an LED. The LED is a Cree XPg3 and requires 2.87v to give the lumen output I require. Currently I am using an Adafruit 4920 breakout to provide 3.3v and act as the driver for the LED. I then use a 1ohm 1W resistor to give me the required 2.87v. This was calculated from the Cree XPg3 datasheet. I am sure this is probably not the best way to set up the circuit but with limited electronics experience I used what was readily available and have built several prototypes all of which work pretty much as required. I recharge the LIPO via a USB powered charge base I have designed and containing a LIPO charging board that connects to the lamp base via detachable connections. So far all is working OK.
Now however I would like to go to the next step and build my own PCB to be incorporated into the lamp base that will produce the required 2.87v constant voltage from the LIPO recognising that when the LIPO voltage will vary over its charged lifetime and when it falls below a threshold it will stop operating until the LIPO is recharged. I have looked at the schematic for the Adafruit 4920 and that uses a TPS62827 IC and did think of using that schematic reworked to my needs to produce the result I am after. However two things I need to consider. The TPS62827 is not available anywhere I can find and the delivery time from Texas Instruments is 50-70 weeks. Secondly I am sure for my basic, simple purposes there is a less universal circuit than the very lovely Adafruit circuit and that will give me the 2.87 (or3.3v) in a simpler way and maybe using an IC like the 555 that is available and may work.
So to my question. Can anyone recommend a circuit/schematic I should look at with a view to using it or adapting it to my needs. Not wedded to the 555 but it is at least still readily available and from what I have read may well do what I need but I am sure there are many other IC that will do as good or better a job.
Sadly at this stage in my amateur learning process (I was an architect in my professional life and have no training at all in electronics) I am not capable of just starting with a datasheet and getting a working circuit and also I am sure this is a problem that has been solved elegantly countless times before by many much smarter than me.
Hope someone can help and advise. Just one final comment this lamp I am designing is not for commercial sale but when finally working will be gifts to my family but I benefit greatly because it is also a very engaging, engrossing exercise with huge rewards to my learning along the way. I am very much enjoying the journey.
Les
I am working on a project (Small portable table lamp) that uses a LIPO battery (3.7v-4.2v)to power an LED. The LED is a Cree XPg3 and requires 2.87v to give the lumen output I require. Currently I am using an Adafruit 4920 breakout to provide 3.3v and act as the driver for the LED. I then use a 1ohm 1W resistor to give me the required 2.87v. This was calculated from the Cree XPg3 datasheet. I am sure this is probably not the best way to set up the circuit but with limited electronics experience I used what was readily available and have built several prototypes all of which work pretty much as required. I recharge the LIPO via a USB powered charge base I have designed and containing a LIPO charging board that connects to the lamp base via detachable connections. So far all is working OK.
Now however I would like to go to the next step and build my own PCB to be incorporated into the lamp base that will produce the required 2.87v constant voltage from the LIPO recognising that when the LIPO voltage will vary over its charged lifetime and when it falls below a threshold it will stop operating until the LIPO is recharged. I have looked at the schematic for the Adafruit 4920 and that uses a TPS62827 IC and did think of using that schematic reworked to my needs to produce the result I am after. However two things I need to consider. The TPS62827 is not available anywhere I can find and the delivery time from Texas Instruments is 50-70 weeks. Secondly I am sure for my basic, simple purposes there is a less universal circuit than the very lovely Adafruit circuit and that will give me the 2.87 (or3.3v) in a simpler way and maybe using an IC like the 555 that is available and may work.
So to my question. Can anyone recommend a circuit/schematic I should look at with a view to using it or adapting it to my needs. Not wedded to the 555 but it is at least still readily available and from what I have read may well do what I need but I am sure there are many other IC that will do as good or better a job.
Sadly at this stage in my amateur learning process (I was an architect in my professional life and have no training at all in electronics) I am not capable of just starting with a datasheet and getting a working circuit and also I am sure this is a problem that has been solved elegantly countless times before by many much smarter than me.
Hope someone can help and advise. Just one final comment this lamp I am designing is not for commercial sale but when finally working will be gifts to my family but I benefit greatly because it is also a very engaging, engrossing exercise with huge rewards to my learning along the way. I am very much enjoying the journey.
Les