1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

LTSpice, power ESR, capacitance ESR, Charge Graph

Discussion in 'Circuit Simulation & PCB Design' started by ACharnley, Oct 25, 2017.

  1. ACharnley

    ACharnley Member

    Joined:
    Oct 25, 2015
    Messages:
    223
    Likes:
    1
    Hi,

    Just learning LTSpice.

    Here I have a 50F capacitor with circa 20mOhm ESR and a power supply of 5V with a high 12ohm ESR.

    I'm expecting a charge graph over several seconds but as you can see, the power supply ESR appears to have no effect?

    Regards,

    Andrew
     

    Attached Files:

  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,099
    Likes:
    562
    Location:
    AZ 86334
    You have a 50 FARAD capacitor, not a 50uF one....

    Your time constant will be 1000000 times longer than you expect. The dV/dt during 10s (your simulation duration) will be uV! When simulating anything, you always should do an estimate in your head. If we charge 50uF through 10Ω, wouldn't you expect the time-constant to be 500uS? So simulate for 5000us or 5ms.

    It is bad practice to give the same electrical node two different names. In your case, V+ and Vout. Pick one, or the other.

    Also, if you expect to show the charging current transient from zero Volts to 5V, then you must instruct the simulator not to "precharge" the capacitor by doing its normal DC bias solution ahead of the Transient simulation.

    Run the attached circuit with and without the "startup" in the .tran statement and see the difference on V(out). Note the "Start external DC supply voltages at 0V" check box in the "Edit Simulation Command".

    ch.png
     

    Attached Files:

    Last edited: Oct 25, 2017
    • Like Like x 1
  3. ACharnley

    ACharnley Member

    Joined:
    Oct 25, 2015
    Messages:
    223
    Likes:
    1
    Th 50F value is correct (supercapacitors). The "startup" command is what was missing, thank you!
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,099
    Likes:
    562
    Location:
    AZ 86334

    Where can you buy Super Capacitors with 12mΩ ESR?
     
  6. ACharnley

    ACharnley Member

    Joined:
    Oct 25, 2015
    Messages:
    223
    Likes:
    1
    See Nesscap eshsr-0100c0-002r7.

    It's 25mohm for the pair, max.
     

Share This Page