Friday, May 29, 2009

Switching Mode Power Supply... my new frontier...

Ever since I started playing with electronics, I have never ventured into switching mode power supply (SMPS) arena... Linear regulators have served me fine since my projects are low power and low voltage.

For my new project, still in development, I needed to charge a large capacitor bank to 400V. More over, it needed to be portable thus ruling out the use of mains transformer. So, with it, I have to learn all the complexity of SMPS. Below is my test board... so far working but require significant fine tuning to improve efficiency and charging speed.

Tuesday, May 26, 2009

PCB UV Exposure Box DIY

Since some of you are wondering how my UV exposure box looks like, I shot the photos below for your viewing pleasure. The unit uses 2x8W UV lights obtained from Farnell. The box was fabricated from HDF board (the same board used by picture frame shop) and the exposure area was lined with aluminum foil to improve reflectivity. The tubes are about 4" apart and 4" below the frosted glass. The frosted glass is intended to diffuse the UV so that there are no UV bright spots.

I've also made a simple PIC-based timer to time the exposure. Using the Kingsten PCB, exposure is 90 seconds. I use inkjet transparencies to make the exposure film. So far, I've managed to get 0.25mm track with 0.25mm separation with no problem. PCB are developed using NaoH developer and etches using Fe2Cl3. From exposure to PCB ready to drill in less than 20 minutes. I'll never go back to iron-on method... :-)