power supply for op amp experiments

Discussion in 'The Projects Forum' started by Neil Groves, May 26, 2015.

  1. Neil Groves

    Thread Starter Member

    Sep 14, 2011
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    I am about to try and teach myself some op amp stuff, but I only have a variable bench power supply, I googled split supplies and there are plenty but my question is do I need some sort of current/overload protection on both + and - rails?

    I am very safety conscious as I don't have much money and hate to destroy components so do I need output current limiting in the design or not and if so, can someone point me in the general direction of circuits that will allow me to play with op amps safely please?

    Neil.
     
  2. Brownout

    Well-Known Member

    Jan 10, 2012
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    You probably need overcurrent protection once you get into high power stuff > 1W. Most of your early work will probably be in milliwatt range. Current limiting circuits are easy to construct. I can either good them for you, or you can find a circuit and ask about it. Look for circuits that use a transistor emitter resistor as a sense element.
     
  3. Lestraveled

    Well-Known Member

    May 19, 2014
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    Most op-amps are very low current devices, less than .020 amps is normally all they draw. Current limiting the power supply will normally not protect an op-amp. The easiest way to hurt an op-amp is to do something bad to its inputs, which takes even less current. I suggest you buy inexpensive parts like the TL080 series or the LF351 series op-amps to play with.
     
  4. DickCappels

    Moderator

    Aug 21, 2008
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    I've been using adjustable power supplies based on the LM317 and LM337 since they first came out. They are internally current limited to something like an amp and I have not killed an opamp yet. Maybe I was just lucky.

    If you follow Lestraveled's advice, you will only be risking parts that cost less than half a dollar, and more often closer to a dime.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    What is your variable bench power supply, as 0~30V or 0~ ±30V?
    When we do the op amp experiments, sometimes we have to using ±V, so you can make a new one as Dick mentioned that I also had one or to do the similar as Two 4 kinds ±5~15V fixed power, another method is to make 30V to ±12V.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,023
    3,236
    An adjustable limit can be helpful when powering up a new circuit but it's not a requirement.
    I normally set the power supply voltage to the desired value and the current limit to zero (or the lowest value).
    Then I slowly increase the limit while watching the voltage.
    If the circuit voltage doesn't rise to the set value after reaching the design circuit current, then I know something is amiss with the circuit wiring.

    Edit: But, of course, you can also do a similar test without an adjustable limit.
    You just slowly raise the voltage from zero while watching the current.
     
    Last edited: May 26, 2015
  7. bance

    Member

    Aug 11, 2012
    315
    34
    I used an ICL7660 to give me a negative rail, before I got a decent bench supply. There are also designs for circuits that will produce a negative rail from 555 timers or even discrete components. You will inevitably release the magic smoke as you learn, which is why I always buy several of whatever IC's I am using. Some say one can't learn without burning a component or two.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    What type of bench supply do you presently have?
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    one could always use two sets of AA batteries(rechargables save a few $) and just use them for split supply service. No need for fancy virtual ground conversion chips and some cheaper supplies cannot be stacked to give a centered ground and +/- outputs without disabling the ground on one of the power cords(dangerous operation mode)
     
  10. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    Ok thanks guys, I am using a 0-15v bench supply so I'll just feed 12v of it into one of those op amp rail splitter circuits and use that as a 6v, 0 and minus 6v supply.
     
  11. bance

    Member

    Aug 11, 2012
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    34
    Neil, one thing to watch when using relatively low power rails with op-amp circuits is that you often need some headroom, since many op-amps can only swing to within a volt or two of the power rail, this may limit your output signal. Look for clipping!
    Have fun,

    Steve.
     
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  12. KJ6EAD

    Senior Member

    Apr 30, 2011
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    You have HSC in Santa Clara so you can probably find a surplus tabletop brick power supply very inexpensively that will have +5V/+12 or +15V/-12 or -15V outputs. You can also buy the same new from Jameco in Belmont.

    http://www.halted.com/

    http://www.jameco.com/
     
  13. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    But why buy when I can have fun building ;)
     
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  14. ScottWang

    Moderator

    Aug 23, 2012
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    The 2SC1384 and 2SA684 are 1A a pair of bjt, if you could find some similar or bigger than 1A then you could use them.
    12Vto_two6V_2SC1384_2SA684_ScottWang.gif
     
  15. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    Awesome Scott, thankyou very much! !
     
  16. KJ6EAD

    Senior Member

    Apr 30, 2011
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    No reason other than convenience. I didn't know that you intended to build a power supply, only that you needed one for op amp circuits.
     
  17. ScottWang

    Moderator

    Aug 23, 2012
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    Maybe the reason is that the DIY is fun ... :D

    I bought the power supply DIY kits to built and bought some of adapters as AC110V to 5Vdc and AC110V to 12Vdc, and I will buy some AC110V to 9V in the future, and I also designed the power supply by myself, DIY is a pleasure ... ;)
     
    Neil Groves likes this.
  18. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Let me explain a little too much.

    I'm not arguing against the joy of DIY, only accommodating the two requirements stated in the original post:
    To address the first requirement, I offered an option to save time so that the available time could be spent on op amp circuits instead of on building up required lab infrastructure. To address the second concern, I offered a local surplus source since buying a built surplus supply is usually less expensive than building one of the same capability, even from a kit.

    Now I see that a third, higher priority requirement has been added to the specifications:
    I've made my own flux before, just for fun so I understand the goal now. ;)
     
  19. ScottWang

    Moderator

    Aug 23, 2012
    4,855
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    You already done what you should do, we just offering the ideas for the TS, the choice is belongs to the TS.
     
  20. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    Ok guys......I have all the info I require, can we all calm down please?

    Thankyou to everyone that contributed.

    Neil.
     
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