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RO Water Controller - Power Supply Board <<< Previous Next >>>

Power Circuit

Image of board

The power supply can be broken down into a series of functions.

Transformer

This steps down the voltage from 240V AC to 18V AC.

Rectifier

The bridge rectifier (B1) converts AC to DC. However the output from this is varying and the voltage is dropped by 1.4V

Smoothing

The output from the rectifier is not smooth, so a high value capacitor (C1) is added to circuit. This smoothes the voltage in other words supplies voltage to the circuit when the DC voltage from the rectifier is falling. This provides a pretty clean voltage but the voltage still contains a slight ripple.

Regulator

The regulator chip (IC1) and capacitors (C2, C3) smoothes the voltage even further, eliminating the slight ripple from the smoothing. It also provides a stable, accurate, known voltage for circuits, which in this case is 12 volts. You must also use a heat sink with the regulator.

Why I have used a 18 volt transformer?

Input voltage to the regulator should be at least 2 volts higher than the output voltage. Also the bridge rectifier loses 1.4 volts.

12+2+1.4 = 15.4 volts

Using the above, the transformer should supply at least 15.4 volts. The regulator in this circuit can have a maximum input voltage of 35 volts and still provide an output of 12 volts. So with this in mind I choose an 18 volt transformer.

I created this board first and used another package other than the Eagle software. I have modified the circuit and PCB slightly when transferring into the Eagle software and wish to build the board and replace the existing board in the controller. Once I have made sure everything is Ok, I will update the website with the schematic files and PCB layouts files.

 

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