Viewing 8 posts - 9 through 16 (of 97 total)
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  • #6758
    maredentro72
    Participant

    It lacks the value of the SCR polarization resistance.

    #6760
    Amilcare
    Keymaster

    Between 4 10k and what you have on hand

    #6762
    maredentro72
    Participant

    Just to understand, vary the frequency of the integrated work that brings benefits? Better high or low?

    #6764
    Amilcare
    Keymaster

    The higher and lower in theory are the magnetization current on the core, the advantages are the reduction of the ferrite section and lower filter capacity.
    Conversely a higher frequency is not always tolerated by the mosfet that it needs time to load / unload the gate capacitance and achieve the status of on / off. In fact it reduces the time of the PWM. For example if you have a 100kz operating frequency means you have total 10us between on and off and if the mosfet should be on for at 2US means that if you have a rise time of 1uS would conduction time halved. Imagine then with the new built-in translators who come to work at 1MHz what you may have.

    #6766
    maredentro72
    Participant

    So if I understand should keep the oscillator IC between 60-80kHz not to do wrong to none and to use mosfet with a capacity of low and see if IRF840 gate is amongst the lowest in the table.
    At this point it is also useless to have a trimmer to change the frequency, once decided that mosfet going to use you look at the chart and set the standard value of CT (for example 330pF) we vary between RT 20 e 30 Kohm.

    #6771
    maredentro72
    Participant

    I modified the schema and now is practically equal to that in the article here in EA.
    SMPS V2

    I brought the frequency to 70kHz, I hope it is not too much and I hope I have made mistakes in the diagram.

    #6778
    maredentro72
    Participant

    Two questions out of curiosity.
    What does the NTC input?
    And the transformer can be realized with a simple toroid adequately dimensioned and not core to EI or E

    Alberto

    #6780
    Amilcare
    Keymaster

    The NTC serves to limit the current at ignition with discharged capacitors. When it is cold it has a high resistance that is lowered when its temperature increases due to the jule effect. In working conditions its resistance has a negligible value in the circuit in which it is inserted.
    The core must be in two distinct sections to create resistance to the passage of magnetizing currents. The air section of about 1mm between the two semi-nuclei has the function of the limiting resistor on an LED, in its absence the current would rise to levels such as not to guarantee safe operation.
    In one case in a very old German textbook they suggested reducing the section at one point of the toroid to limit the magnetization currents. Without questioning the competence and my personal esteem for the author of this book, However, I find the solution impractical as the result is obtained empirically without a precise rule and without knowing if the result obtained is sufficient or requires further thinning of the section without a field test. If you want to try your hand at a hacksaw file in reducing the section of your toroid, go ahead, I ask you to keep me informed of the results.
    Amilcare

Viewing 8 posts - 9 through 16 (of 97 total)
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