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Your opinion about a PSU from this site.

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by bchris, Nov 29, 2012.

  1. bchris

    bchris Member

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    Hello to you all.

    I came upon this schematic as I was browsing here, and it seems to fit my needs (with a little more output power perhaps) for a workbench PSU.

    I just wanted to ask you fellas if you have build it.
    Also I am somewhat concerned about that 2n3904 (on the far left) used as a temperature sensor.

    What do you say?
    Does it worth the trouble?


    PS:
    If this post is in the wrong section, please except my apologies and feel free to move it in place.
     
  2. panic mode

    panic mode Well-Known Member

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    it looks good, i admit i only glanced over it but didn't see anything raising red flag.

    Si diodes are commonly used as a temperature sensor.
    their forward voltage drop changes about 2mV/deg. here they used B-E junction of a transistor as a diode.

    what do your expectations from a bench power supply?
     
  3. bchris

    bchris Member

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    Thanks for the reply.

    As for my expectations for a workbench PSU, I am thinking of muscling this up a little, like 2x30V@10A.
    It would be digitally controlled by an MCU.

    This design got my eye for parallel feature. It is exactly was I was looking for / trying to design myself.
     
  4. dave

    Dave New Member

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  5. k7elp60

    k7elp60 Active Member

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    I have built a large number of power supplys both fixed voltage and variable. Before you start give some thought to what you plan to use the powersupplys for. On my work bench I have two adjustable power supplies. The small one is 0 to +/- 20 Volts with automatic current limiting to about 0.4A. I use it for general experimentation and testing of multiple devices. The other one is 6 to 14V current limited to 8A and also 12-28V limited to 4A.
    One thing I have learned is you do not want to use a 3 terminal regulator. The reason is they all seem to have automatic current limiting and some have input versis output differential power limiting. As a result on a adjustable powersupply, even if you have a large enought heatsink for the 3 terminal regulator they will shut down if the input/output diverential is large, even if the current supplied to the load is small.
    I use regular transistors and op-amps for the smaller power supply, and use a LM723N as a control for the high power power supply. Something else I have done that may seem different is in the big power supply I have 4 line to low voltage transformers in parallel. I have found this works fine if all the transformers are the same mfg number and from the same lot.
    Ned
     
    Last edited: Dec 1, 2012
  6. ronv

    ronv Well-Known Member Most Helpful Member

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    Probably the hardest thing about a linear supply is understanding what you really need. I've found it is easy to let the spec creep and suddenly you find out you need a heatsink and transformer the size of a truck.
     
  7. bchris

    bchris Member

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    You are both right. It is easy to get caught in the "As many amperes as possible" thing...
    However, here's my situation: I am a hobbyist with limited space. In fact, my workbench is my desk which resides in my living room...

    So I need one (a dual in this case) PSU to cover all my needs.
    My needs now, are mainly powering electronics homebrew projects for which 1 amp is more than adequate.
    Once in a while though, I need to power some electromagnet and this is where the amperes really makes a difference.

    Now like I said, my desk/workbench is pretty packed as it is, so what I awant to do is replacing my current 2 amps psu with this one.

    Thanks for your time.
     
  8. k7elp60

    k7elp60 Active Member

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    I would be happy to send you a schematic of my latest design for a dual power supply. It is limited to 400mA because of the size of the heatsinks, but the series pass transistors are good for 5A.
    It doesnot have adjustable current limiting, just a short circuit type of current limiting. I would also give you a parts list and new values to raise the current to 1A. I would be happy to send you the series pass transistors and any other parts I have for free,
    Ned
     
    Last edited: Dec 4, 2012

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