+ Post New Thread
Results 1 to 11 of 11
  1. #1
    Full Member level 3
    Points: 1,359, Level: 8

    Join Date
    Jul 2016
    Posts
    183
    Helped
    2 / 2
    Points
    1,359
    Level
    8

    Current source to simulate load transients

    Hi all,

    Can someone tell me what's the best way to have a current source to perform load transient simulations? I could use idc source but that's an ideal source and that could lead to massive voltage at its terminals.

    Regards.

  2. #2
    Advanced Member level 5
    Points: 30,746, Level: 42
    BigBoss's Avatar
    Join Date
    Nov 2001
    Location
    Turkey
    Posts
    4,512
    Helped
    1359 / 1359
    Points
    30,746
    Level
    42

    Re: Current source to simulate load transients

    Why don't you use non-ideal current source ?? Use Norton equivalent ( a high valued parallel resistor )



    •   AltAdvertisement

        
       

  3. #3
    Full Member level 3
    Points: 1,359, Level: 8

    Join Date
    Jul 2016
    Posts
    183
    Helped
    2 / 2
    Points
    1,359
    Level
    8

    Re: Current source to simulate load transients

    Thanks for your kind reply. I thought about that but how big can that resistance be? I thought about using a current mirror as well - for example, but here we would be limited by it's bandwidth.

    In addition to this the current source impedance should change with the current itself as well isn't it?

    Do you implement your current sources like that?



    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 5
    Points: 40,234, Level: 49

    Join Date
    Mar 2008
    Location
    USA
    Posts
    6,494
    Helped
    1903 / 1903
    Points
    40,234
    Level
    49

    Re: Current source to simulate load transients

    I like a simple switched FET with a drain resistor to set
    the current. "Active loads" (E-load, or multi-device
    current source / sink) can add their own time- and
    frequency-domain (mis)behaviors and these can be
    hard to de-embed from the response. This of course
    pertaining to the real world / bench.

    A pulsed current source has infinite impedance. This
    is unlike almost any real load. A switch and resistor
    (or poly vccs) could be more realistic. What do you
    know about the application load-space? Maybe you
    want to "box it" with the ipulse and a switched
    resistor, these being the max and min impedances
    that a load of a given current could present.



  5. #5
    Advanced Member level 5
    Points: 19,190, Level: 33
    Achievements:
    7 years registered
    crutschow's Avatar
    Join Date
    Feb 2012
    Location
    L.A. USA Zulu -8
    Posts
    3,690
    Helped
    878 / 878
    Points
    19,190
    Level
    33

    Re: Current source to simulate load transients

    You've told us what you don't want but no details about what you do want.

    What frequency response do you need?
    What exactly are the transient test conditions you need to generate (voltage, transient duration, pulse shape, current, etc.)?

    Can't make good suggestions without knowing that information.
    Zapper
    Curmudgeon Elektroniker



    •   AltAdvertisement

        
       

  6. #6
    Full Member level 3
    Points: 1,359, Level: 8

    Join Date
    Jul 2016
    Posts
    183
    Helped
    2 / 2
    Points
    1,359
    Level
    8

    Re: Current source to simulate load transients

    Sorry about that, you are right.

    I intend to do load transients to an LDO. I want to make a load step at the output for several current value and combinations.

    What you mean by pulse shape? If it is a pulse you are I directly saying that it it a pulse, like square-wave.

    What you mean by transient duration duration? You mean the step duration? Like rise/fall time? I would say 10ns, 100ns,1us.

    In addition to this I want to do the same to an amplifier (two stage) and to class AB amplifier.



  7. #7
    Advanced Member level 5
    Points: 19,190, Level: 33
    Achievements:
    7 years registered
    crutschow's Avatar
    Join Date
    Feb 2012
    Location
    L.A. USA Zulu -8
    Posts
    3,690
    Helped
    878 / 878
    Points
    19,190
    Level
    33

    Re: Current source to simulate load transients

    Quote Originally Posted by CAMALEAO View Post
    ..............
    I intend to do load transients to an LDO. I want to make a load step at the output for several current value and combinations.

    What you mean by pulse shape? If it is a pulse you are I directly saying that it it a pulse, like square-wave.

    What you mean by transient duration duration? You mean the step duration? Like rise/fall time? I would say 10ns, 100ns,1us.

    In addition to this I want to do the same to an amplifier (two stage) and to class AB amplifier.
    By pulse duration I mean how long is the load applied?

    Do you really need variable rise and fall times?
    If this is for a voltage regulator, the rise and fall times do not have to be extremely fast, since the response time of a regulator is generally relatively slow.

    What type of amplifiers do you have that need a transient load test?
    Normally that's only done for power supplies that see varying loads.
    Zapper
    Curmudgeon Elektroniker



  8. #8
    Advanced Member level 5
    Points: 30,746, Level: 42
    BigBoss's Avatar
    Join Date
    Nov 2001
    Location
    Turkey
    Posts
    4,512
    Helped
    1359 / 1359
    Points
    30,746
    Level
    42

    Re: Current source to simulate load transients

    Quote Originally Posted by CAMALEAO View Post
    Thanks for your kind reply. I thought about that but how big can that resistance be? I thought about using a current mirror as well - for example, but here we would be limited by it's bandwidth.

    In addition to this the current source impedance should change with the current itself as well isn't it?

    Do you implement your current sources like that?
    A typical internal parallel resistor of a practical current source can be considered as 50k-100k Ohm.
    Try with these values.



  9. #9
    Advanced Member level 5
    Points: 40,234, Level: 49

    Join Date
    Mar 2008
    Location
    USA
    Posts
    6,494
    Helped
    1903 / 1903
    Points
    40,234
    Level
    49

    Re: Current source to simulate load transients

    Quote Originally Posted by crutschow View Post
    Do you really need variable rise and fall times?
    If this is for a voltage regulator, the rise and fall times do not have to be extremely fast, since the response time of a regulator is generally relatively slow.
    As a sometime designer of LDO ICs I'll disagree with this.
    An interest in just how fast load-slew a LDO can maintain
    regulation against, is common for things like FPGA I/O
    supplies and the sensitive high speed serial resources'
    supplies. Small signal analysis is not good for large signal
    load steps. You need to challenge the regulator with
    "realistic++" to see what it's capable of, but hyperabrupt
    steps will just drive you crazy trying to fix an unfixable
    "problem".



  10. #10
    Full Member level 3
    Points: 1,359, Level: 8

    Join Date
    Jul 2016
    Posts
    183
    Helped
    2 / 2
    Points
    1,359
    Level
    8

    Re: Current source to simulate load transients

    Só hat would be the best solution then? As suggested by onde person I can use a resistor in parallel. Is this tbe best approach bigboss?



    •   AltAdvertisement

        
       

  11. #11
    Advanced Member level 5
    Points: 19,190, Level: 33
    Achievements:
    7 years registered
    crutschow's Avatar
    Join Date
    Feb 2012
    Location
    L.A. USA Zulu -8
    Posts
    3,690
    Helped
    878 / 878
    Points
    19,190
    Level
    33

    Re: Current source to simulate load transients

    I'd be happy to help if you answer my questions in post #5 about the voltage and current values of the tests which, for some reason, you seem to be reluctant to state.
    Zapper
    Curmudgeon Elektroniker



--[[ ]]--