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Pinky

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Posts posted by Pinky

  1. I mean an electronics cad program like protel or eagle.
    Sorry i didn't mention it.I thought it was obvious.

    I am now using eagle and it is great.It has a huge component database and is generally very good,
    but it has very small pads, that's why i asked for opinions to try other programs too.

  2. Hi.
    I guess you are referring to " http://www.electronics-lab.com/projects/power/010/index.html" project

    As Mike suggested you need LM317T that can handle 1.5A.
    I have some more suggestions to make.

    Firstly, about the transformer. LM317 can handle 3V to 37V but you should go to 30-32V.
    Also, LM317 needs input to be +3V from output approximately.
    A transformer 230V/28V is not needed. 230V/24V will not give you 21V as Mike said because the 24V is the AC voltage that the secondary coil of the transformer has.
    After the bridge you will have 24*1.4 (sqrt(2)) DC voltage so you will have 33.6V which is enough to give you 30V.

    Secondly, everyone uses R1=240 without looking at LM317's specs.
    The LM317 datasheet suggests 240 but if you want to avoid the worst case scenario (load=0.Vout=1.25) since LM317 needs at least 10mA current flowing, with 1.25 Reference Voltage you must have R1<125, so many circuit makers (e.g velleman) use R1=120

    Also for better output you can put a 10uF tantalum capacitor accross the 4.7k potensiometer.
    For safety you can also put 2 protection diodes (e.g 1N4001,1N4007). One accross R1 facing towards LM317's output and one from LM317's output towards LM317's input so that when you cut off the switch the capacitors do not discharge through LM317.

    The last i want to say is that LM317 dissipates extra voltage as heat and also it gives 1.5A only
    when (Vin-Vout)<15V, so if you have 24*1.4=33V input and you want 5V as output you will not have 1.5A and LM317 will be very hot.
    An easy solution to this is to get a transformer 230V/2*12V and use a switch in order to use only 12V or 24V as input, so if you want e.g 9V you can have 12*1.4 as input which is far more good than 24*1.4

    Some of what i suggested are extreme but i believe make the circuit better.

    Thank you.

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