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24vac Powered Isolated +5v Supply --
August 8, 2009
24vac is a very popular power supply in many industrial systems. It is often used in
systems that involve water. It is also popular with many inside and outside lighting
systems. The lower voltage means the danger of human electrocution is much less.
But, many DC powered sensors and control circuits associated with 24vac systems need to be fully
isolated from the 24vac supply. The circuit below accomplishes this feat using an off the
shelf 24v DC to 5v power module. A charge pump scheme using a series capacitor limits the
current to a safe level. A zener diode keeps the input voltage to the module at about 24v
DC. Two polarized capacitors wired in series operate as a non-polarized capacitor. A
schottky diode in parallel with witch each capacitor insures that the part is not reversed
biased. With the components selected, the +5v output is rated at about 100ma.
Click on Drawing
Below to view PDF version of Schematic
