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I have a 28V-0-28V, 7Amps centre tapped transformer to supply voltage to my load. Load will be a cell (plates are connected in both series and parralel) used in Chlorinator. I have a voltage regulator L7805CV. The link is below. [http://www.farnell.com/datasheets/2307057.pdf?_ga=2.224828637.639084130.1536017950-602646683.1536017950][1]

What I want is to use the same centre tapped transformer for the voltage regulator to get 5V. From the datasheet I found that Vi for regulator has to be around 10V to get Vout 5V. But the transformer is rated at 28V-0-28V. How can I drop voltage after Bridge rectifier but before feeding on to voltage regulator, Vin?

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  • \$\begingroup\$ Why did you choose the wrong transformer? Why not use a proper wall 5V supply? It is possible to use a carefully select light bulb or power resistor to drop 18 to 25Vdc depend on your cap size and load current but you Chlorinator load curve is undefined. \$\endgroup\$
    – D.A.S.
    Commented Sep 4, 2018 at 1:40

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Rectify the transformer output, and feed it into a switching regulator instead, such as one of these

https://www.pololu.com/category/131/step-down-voltage-regulators

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  • \$\begingroup\$ I have kept that for my last option. At the moment, I am trying to feed the Vin at Voltage regulator using another transformer 12V-0-12V (2A). This transformer is solely for voltage regulator only. However, another transformer is used for providing power to load and zero crossing detection. I am not getting any good sign from my test. \$\endgroup\$
    – user3560453
    Commented Sep 4, 2018 at 1:53
  • \$\begingroup\$ Vin is expecting a DC voltage, not AC. There is only 1 diode for reverse polarity protection, which is no sufficient for for AC to DC rectification, and insufficient (in my opinion) capacitance for input filtering. \$\endgroup\$
    – CrossRoads
    Commented Sep 4, 2018 at 2:10

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