Voltage Multiplier for Power LED Driver

Posted on Feb 5, 2014

This power supply circuit is designed around the garden variety  12VAC landscape lighting transformer. Transformer availability and selection has long been a problem for the experimenter, and has often driven them to experiment with dangerous off-line capacitor limited power supplies. However, the long neglected 12V landscape lighting transforme

Voltage Multiplier for Power LED Driver
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r is a good solution due to numerous advantages such as low cost, availability, and power variations (VA ratings). Directly rectifying the 12V transformer secondary is not a good choice because the rectified voltage is generally way high (typically 18VDC) due to peak detection of the sine wave ”in the past, this required a large, inefficient ballast resistor to drop the extra 6V. However, a voltage multiplier (quadrupler) has some very interesting properties ” not only does it increase the voltage substantially, but it offers low voltage regulation that is ideal for powering constant voltage devices such as LEDs. The combination of the 12V lighting transformer and the voltage multiplier is like a match made in heaven. The multiplier delivers 36V (loaded). To accommodate the higher output voltage, (3) 12V LED devices are connected in series to match this voltage. The voltage may be adjusted simply by varying capacitor size. Capacitors are garden variety aluminum electrolytics. The common 3 to 4W LED is bright, but a little low to be useful in general purpose lighting. Connecting (3) in series provides 9 to 12W, a much more useful level of illumination. The 12V LED unit is commonly available due to automotive and 12V battery applications. The initial circuit considered was the classic Cockcroft-Walton multiplier. While it functions, the output current tends to be too limited for this application. Note that all circuits tested...

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