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Thread: Tl494 smps

  1. #1

    Post Tl494 smps

    Hi all

    I made TL494 push pull Smps for car amp(No feedback)
    my test amp is 100w.

    i tested with AWG26 wire and output Dropped from 32 to 17 volt in 60% music volume

    core information
    pri:5+5 turns(17 Layer)
    sec:13+13 turns(7 layer)
    i Calculate for 200w smps power.(Double AMP power)

    but there is a lot of voltage drop.

    i try to use AWG18(~1mm wire) or Thicker wire for core of smps to have less layer but I do not know the current of any wire.
    And how to avoid switching voltage drop

    please help me
    thanks
    Last edited by noorworkshop; 11-28-2017 at 08:50 PM.

  2. #2

    Post Smps

    This is my core for 200w smps power (100w amp power):
    photo_۲۰۱۷-۱۱-۱۷_۱۱-۲۳-&.jpg


    and this is for 4x80w Marshall Amplifier:
    photo_2017.jpg

    How is the core computation of the converter??
    (Which is the size of the wire too small (the wire thickness is higher) and its low drop)

    Circuit Frequency is 32Khz but i can change it(if needed)
    Last edited by noorworkshop; 11-28-2017 at 08:52 PM.

  3. #3
    .... Silvio's Avatar
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    @Noorworkshop.
    1) Please upload schematic so that we can see why is the large voltage drop you are experiencing.
    2) What type of material the core has? EX. Epcos N87 etc.
    3) What dimensions the core has? (inside dia, outside dia, thickness).
    4) If you changed any components such as different transistors etc please specify.

    We will try to help you the best we could to make a successful smps.

    Regards, Silvio

  4. #4
    Dear Silvio

    its my schematic(in test i use irfz44 fets).

    core name is OR38.
    inside dia:~22mm
    outside dia:~38mm
    thickness:15mm

    i just change fets from IRF3205 To IRFZ44.

    thank you for help.
    Attached Images Attached Images

  5. #5

  6. #6
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    Switching frequency 27Khz Topology push pull 32-0-32 (64v @ 3.5A) = 224 watts
    Primary turns 4+4
    Wire gauge AWG 20 0.8mm
    Number of strands for primary 4 wires
    current in primary winding around 18 amps at 200 watts load (current density @ 6 Amps per mm˛)

    Start from center tap with 8 wires in hand and wind together ( you can glue bundle of 4 wires side by side to make life easier) Distribute evenly around the core and keep symmetry as much as possible.

    secondary turns 11+11
    number of strands 1


    The voltage in the secondary can rise a little due to the car battery being charged when the vehicle is running and the input voltage can rise up to 14 volts, However with this input voltage the secondary voltage also rises a bit and can go up to 38v
    If your amp cannot take up till 38v you can lessen one or two turns on the secondary, The volts per turn is 3.25v

    Mosfets. the IRF3205 is better than IRFz44

    Winding practice. Use symmetry as much as you can during winding. You will be better off starting with the secondary first and then after taping it up (use Mylar tape two layers). For secondary start with 2 wires in your hand and that start will be the center tap, You will finish your turns together with the 2 wires, You will put the ends of these the wires to the input of the output bridge rectifier. the center tap with 2 wires will be the ground. Distribute the wires evenly around the core.

    Tip You can align the wires side by side and tighten them up, when aligned perfectly you can stick them together with some super glue, This will help out during winding.

    I hope you have a better idea what current is involved in the primary circuit, and it may be the winding not being symmetrical that you are experiencing voltage drop. It could also be the fets having larger resistance (IRFZ44) than the the ones suggested in your schematic. Be sure to use adequate wire gauge to handle the current on the primary circuit,

    Regards Silvio
    Last edited by Silvio; 12-03-2017 at 01:28 AM.

  7. #7
    .... Silvio's Avatar
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    @Noorworkshop

    Regarding the mosfets if you are using IRFZ44 then you have to parallel 2 on each side. This is due that the RDS of the IRfZ44 is higher than the IRF3025.

    RDS for IRFZ44 is 0.022 ohms while the RDS of the IRF3205 is only 0.008 ohms.

    In case you are using 2 transistors (IRFZ44) on each leg then change also the gate resistors from 10 to 22 ohms so that the equivalent resistance will be seen by the TL494.

    The reason behind all this is that there is too much voltage drop when using IRFz44 but you can overcome this problem by using transistors in parallel to overcome this problem.

    Regarding the last post you did not tell me the core material and the calculations are for PC40 ferrite. If by any chance you may know it than post back and I can make new calculations for you.

    Regards Silvio
    Last edited by Silvio; 12-03-2017 at 09:31 AM.

  8. #8
    Thanks sir for helping.
    Can you explain that how to choose awg for smps core?

    For exmple:
    I need to convert 12 to 310 volt 400w.
    with 30khz PWM generator (tl494) frequency.

    how to calculate it

  9. #9
    Does anyone have tl494 push pull smps' schematic that have feedback?

    I choose it's schematic for use:

    https://up.iranblog.com/files/1528447742.png

    but i think it need resistor between pin 2 and 3 (feedback for error amp) of tl494.
    Attached Images Attached Images
    Last edited by noorworkshop; 06-07-2018 at 12:04 PM.

  10. #10
    .... Silvio's Avatar
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    Quote Originally Posted by noorworkshop View Post
    Thanks sir for helping.
    Can you explain that how to choose awg for smps core?

    For exmple:
    I need to convert 12 to 310 volt 400w.
    with 30khz PWM generator (tl494) frequency.

    how to calculate it
    Please make it clear for me so that I give you the right answer. In push pull configuration the frequency of the chip is double the frequency arriving at the transformer.

    So if the frequency of the TL494 is 30Khz then the output frequency is 15Khz.

    What frequency are you planning to run at the transformer?

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