need advice on Linear regulator power supply.

Discussion in 'The Projects Forum' started by INS-ANI, Aug 15, 2008.

  1. INS-ANI

    Thread Starter New Member

    Aug 15, 2008
    We r given a theoritical project on Linear regulator power supply.
    I need advice from this board regarding the same.
    The input is as usual 230V,50Hz and output is -5V,1.5A

    we r supposed to use a vol regulator IC in last stage, which is be IC 7905.
    the architecture will be

    (input)-(LPF)-(Transformer)-(rectifier)-(Filter)-(Vol regulator)-(output)

    few details which i have are
    * X'mer is in centre tapped supply.
    *use 79XX series vol reg.
    *use heat sink

    what i need to know
    *What are the filters i am using at various stages and why? or why am i not using other filters?
    *what rectifier,transformer,vol reg is most suitable and why?

    the actual problem statement is
    Q) Design a LPRS with following specifications
    output -5V,1.5A
    mains -15% to 10%
    Ripple factor 10%
    Find load and line regulations
    also consider using miniature CKT breaker,MCB,Fuse,heat sink,MOV.
    F should remain constant throught the supply.
    Simulate it on multisim.
    i request you to please add if possible the following items
    *ckt diag
    *componets u r suggesting
    *cost of component(INR)
    *data sheet/features of component used.

    we have to just simulate and submit the report asap.
    i feel quite helpless as i have no experience of handling such electronics project. so i will need ur help so that i can learn the techniques and start designing myself.
    I will sincerely appreciate if you answer keeping in mind that i am trying to be self dependent.
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    You seem to be contradicting yourself. you say you are trying to be self dependent but then ask for someone to provide you with a finished project including the cost of components and datasheets. Which bit do you intend doing yourself? Have you done any research or downloaded any datasheets?
  3. Tahmid

    Active Member

    Jul 2, 2008
    I have attached the circuit.
    The transformer should be a 230v to 6v transformer. No need for center tapping. No need for LPF as this is a linear power supply. The diode used is 1N5408, 3A, 1000v. C1 and C3 are 1000uF 50v capacitors, although you can use 16v caps. C2 and C4 are 0.1uF 50v ceramic caps. The IC is a fixed negative voltage regulator: 7905 and should be mounted on adequate heatsink.
    The fuse is a 1A standard fuse connected to the input. No need to use ckt breaker or MOV as this is a linear power supply.
    You can look up the datasheets at:

    The parts I suggested are those that I have used are running successfully. Instead of 50v caps, you can use 16v caps. The diode can be 1N5401 as well.

  4. SgtWookie


    Jul 17, 2007
    This appears to be a homework assignment, with some rather specific requirements.

    It isn't a good idea to hand students a completed schematic, because then they won't have applied any effort themselves in working out the problem, so they will not learn anything.

    Your schematic does not address numerous requirements that the OP has been given, so it is not really suited for their purpose.
  5. SgtWookie


    Jul 17, 2007
    You use a low-pass filter prior to the transformer in order to filter out line transients such as may be caused by heavy motors on the same mains line switching on and off, or lightning. Without such filtering, the transformer and subsequent parts may be subjected to voltages that may damage them. A "pi filter" is one way to reduce or eliminate such transients.

    After the rectification of the AC output of the transformer, a filter is required to remove the ripple component. Often, this is simply a large capacitor to remove the low frequencies paired with a small capacitor to remove the high frequencies.