My workbench needed a new light and the only way was to build my own. So I bought for a few bucks a 20W LED-chip in cold white and a suitable lens with ~70 degrees opening angle (which was more expensive than the LED, btw).
The forward voltage of the LED is 34V @ 750mA. Since I also wanted to dim the lamp, I need a driver. After some research I found the ZXLD1366. This is a tep-down converter for high power LEDs (up to 60V @ 1A). A schematic later, I had a small board with another step-down converter (LM2594HV) to generate 12V for two NE555 and a fan. The two NE555 are used to generate PWM for the LED driver and the fan, mounted on the heatsink.
The schematic is realy simple: