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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. |
