Hi! I did the "getting to blinky" KiCAD tutorial and got overconfident and decided I'd like to create my first PCB. I'd like to build a switching power supply that will let me use a 3.5V lipoly battery to power a 12V 120mm computer fan.
I looked around quite a bit at different datasheets and selected the LT1308B:
http://cds.linear.com/docs/en/datasheet/1308abfb.pdfPage 20 of the datasheet has pretty much exactly the circuit I'd like to build, so I'm pretty much ripping it off, but adding a couple things to the example application circuit:
1. A switch to let me shut down the boost converter (using the SHDN pin)
2. A low-battery indicator LED
Here is the schematic I came up with:
You can also see the full KiCAD files here:
https://github.com/kevin1024/fanboostI'm looking for general advice / review, and have a couple specific questions:
1. In the example application on page 20 of the LT1308B datasheet, it says the output is 12v 300mA. I was hoping for output more around 400mA, how do they get this figure?
2. I'm using the LBO pin for the low battery detector. It's an "open collector", and I think the way I have it wired up, the LED will stay on until the battery is low. I think I'd rather have this work the opposite way (the LED lights up when the battery is low). Or maybe even have 2 LEDs, one red and one green. I think I have to use a transistor for this, does that seem right?
3. Should I just wire the battery in with a SPST switch instead of using the SHDN pin? (this just occurred to me)