ATX regulation

Discussion in 'General Electronics Chat' started by Shagas, Jan 14, 2014.

  1. Shagas

    Thread Starter Active Member

    May 13, 2013
    802
    74
    Hello

    I have decided to make myself a power supply from a cheap (30 bucks) computer ATX power supply that I have purchased a few months ago.

    I am enclosing a diagram of the breakout board that I want to make for it.
    DSC_0137.jpg

    Basically I will be taking the outputs of the ATX power supply , feeding them into a box where I will have my circuitry and the outputs are as follows:

    - Raw outputs for high current applications:
    3.3v
    5v
    12v

    - Regulated clean output 9v and -9 for op amps using 7809 regulators + more filtering

    - Regulated variable output 0-10 volts using an LM317 or similar.

    I have a few questions that I would like some input on.
    Firstly , as seen in the diagram the raw outputs and the variable output will have current sense resistors . I have never done current sensing before but I know the principle .

    I will be using an AVR as the mcu and LCD driver for this supply so I will have 8 adc inputs which I can use.
    Can anyone advise how I can implement current sensing for my outputs using and AVR?
    I'm guessing I'll first have to use OP amps to amplify the drop across the resistor to get it up to a reasonable level but i'm slightly confused as what I should power the OP amps from and how the references are going to work since I want to monitor all 4 outputs as shown in the diagram.

    Another thing I would like input on is filtration . For my +- 9v outputs that I'm intending to use for op amp experiments I'm planning to use positive and negative voltage regulators. Seeing as the ATX is an SMPS i'm afraid that I will still get alot of noise on the outputs of the regulators. Is there anything special that I can use to achieve ultra low ripple?

    ps. I am aware that for the voltage monitoring of the variable output (0-10 volts) I will have to use a potential divider to get at least half the voltage so I can use it with a 5v powered AVR ADC

    Thanks in advance
    Tim
     
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