LED replacement for DCA lamps
A drop-in replacement for film projector lamps, no modifications necessary.
A drop-in replacement for film projector lamps, no modifications necessary.
In the heyday of home 8mm film projectors, the DCA lamp was a popular, economical choice. However, in modern times their availability has plummeted and "new old stock" bulbs typically cost upwards of US$60. Some people have re-fitted their old projectors to use LED lighting, but this involves irreparably altering the 8mm projector itself. Could I come up with a cheap, drop-in replacement for the DCA lamp using modern LEDs?
Modern COB (chip-on-board) LEDs are bright enough to replace the 150W DCA bulb, but the challenge lies in how to power them. DCA lamps happily took 21.5(ish) VAC, while a 10W LED module requires roughly 10 VDC to operate. This means, in addition to the LED driver circuitry, there needs to be a bridge rectifier to turn the 21.5 VAC into some usable DC voltage. This can then be fed into a standard LED driver circuit.
The physical form of the new bulb is limited by PCB manufacturing ability. Two PCBs, a "base" PCB and an "upright" PCB, contain the entire circuit when slotted into each other. The rectification stage is placed on the base. This stage is dominated by two beefy 2200 μF capacitors that smooth the rectified waveform. Sandwiched between these capacitors is the upright PCB, which holds the LED itself and the LED driver circuit. I'm quite happy with this approach, which I think cleverly utilizes the PCBs themselves to form the necessary bulb structure.
