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Thread: 1kW smps project (based on MicrosiM design)

  1. #1341
    diysmps Member CDJKuznec's Avatar
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    Silvio, very big thank you.

  2. #1342
    hi silvio,



    my current protection not working...im using 24mm yellow toroid found in pc atx supply....

    100:1 turns ratio....without protection smps works fine ,i loaded smps with 1000 watts halogen (+ 90-0-90).....when protection connected smps does not start
    led stays on pin 3 of ne555 . i changed it with lm358 smps works ok but ocp not working i want to set it on 1kw...

    iam using 4 mur160 and 100 ohm as burden resistor before the bridge getting 6 volts across diodes when loaded with halogen... can vary vollage with preset how many volts needed on pin 6 of lm358 to trigger ne555....i have changed multiple lm393 and 358 all showing same behaviour...iaam attaching the schematic

    thanks in advance...
    Attached Images Attached Images

  3. #1343
    .... Silvio's Avatar
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    Hi Ravs, I see no detail in schematic for the current transformer however in my version I used a ratio of 22:1. I suggest you select a green core instead and the diameter of this core may also be 15mm.
    Wind the current transformer with 0.4mm ecw and change the resistor R113 to 10 ohms. You can also use 2x22R in parallel of 0.5W each instead as a burden resistor. The 1uF capacitor is to be left in circuit and changed to a non polarized low ESR one. I also suggest that the burden resistor be on the AC side before the diode. The diode will preferably be after the burden resistor.

    Please understand that there are spikes generated by the current transformer and these are triggering you overload protection. These have to be looked at by making a 2 turn coupling loop on the core and seen on an oscilloscope These spikes must be clamped with a capacitor and resistor (snubber) or capacitor across the burden resistor otherwise you get a lot of false triggering.

    It could also be the case that the cold filament of the lamp is drawing a lot of current until it heats up and overloading your smps, this current surge may be triggering your protection circuit.

    This part of overload setting your smps is important and must be conducted by inserting loads gradually until you get to the wanted tripping current. Keep in mind that with the transformer and mosfets used settle out for no more than 1200W at the output do this by calculation the V X I= W. Be informed that IRFP460 could not handle more than 13A at the halfbridge this current will give you around 1500w but you have to consider also the efficiency of about 80% and at the output the wattage will be somewhat less due to switching losses and diodes, transformer, volt drop at the input capacitors etc.

    If a mosfet is rated at 20A it does not mean you run at that current we rate for 0.25 for continuous use and maybe a little more than 0.5 for audio purpose. So at the peak watts of 1200W do not leave the load for more than 5 seconds at a time.

    One last note. See that you have adequate supply de-coupling near the op amp as these have very sensitive inputs and may false trigger. Be sure to fit the heatsink to the mosfets and output diodes, these heat up very quickly with load.

    Good luck Regards, Silvio

  4. #1344
    .... Silvio's Avatar
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    Quote Originally Posted by ravs View Post
    hi silvio,



    my current protection not working...im using 24mm yellow toroid found in pc atx supply....

    100:1 turns ratio....without protection smps works fine ,i loaded smps with 1000 watts halogen (+ 90-0-90).....when protection connected smps does not start
    led stays on pin 3 of ne555 . i changed it with lm358 smps works ok but ocp not working i want to set it on 1kw...

    iam using 4 mur160 and 100 ohm as burden resistor before the bridge getting 6 volts across diodes when loaded with halogen... can vary vollage with preset how many volts needed on pin 6 of lm358 to trigger ne555....i have changed multiple lm393 and 358 all showing same behaviour...iaam attaching the schematic

    thanks in advance...
    Regarding the threshold voltage which the over current protection triggers is around 2.5v. As you can see the rail voltage to the opamp is 5v, this is divided by 2 with R123 and R118. (22K) creating a voltage reference of 2.5v.
    To sum up all 2.5v should show up on pin 6 (LM393)at a current of around 6 to 8 amps on the output depending on how regulation holds the voltage at the output.( I am assuming you are loading both rails in series creating 180vdc)
    I also do not see an output inductor and looks very odd to me as the smps is a regulated one. You will need inductors of around 20uH on each rail.

    Regards Silvio
    Last edited by Silvio; 05-29-2020 at 10:11 AM. Reason: Forgot a few tips

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