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  1. Replies
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    [SOLVED]Closed: Re: Best topology DCDC adjustable output

    100nF on the 25k pot is a bad idea as it introduces too much delay in the volt loop.

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    why is there a diode in the opto led drive ...?

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    as you vary...
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    [SOLVED]Closed: Re: Best topology DCDC adjustable output

    your 50k res across the o/p caps need to be 10W, better to make them 220k ( 3W ) each

    just write, snubber per each fet on the fet snubber components. i.e. 15nF & 3//220R on EACH ...
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    Closed: Re: Bridge Rectifier won't Rectify

    capacitance will dominate for hi-Z loads ... and when the source is hi-Z

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    you can buy special diodes for EHV and higher currents - not that cheap - but do work ...
  4. Closed: Re: Passing radiated EMC with an SMPS involves an element of luck...how much agree?

    For plastic case you need a topology that is inherently very quiet in the first place, and heatsinks all tied to +Vcc or 0v, - this is why we design resonant converters for many of our products...
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    Closed: Re: BJT V(ce) ON in common emitter mode

    I meant when the emitter is common to the load sorry, - emitter follower - which seemed what the OP was trying to do
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    [SOLVED]Closed: Re: Best topology DCDC adjustable output

    control loop / feedback components / freq comp - should all be done on the LT4430, main control IC should be unity follower.

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    bias pin 5 to 2V5 from the 5v1 ref ( ...
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    Closed: Re: BJT V(ce) ON in common emitter mode

    you can never get Vce < Vbe in common emitter config. For max Hfe at a given Ic you need to carefully select a xtor from its data sheet, Hfe falls off for very low Ic
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    [SOLVED]Closed: Re: Best topology DCDC adjustable output

    Just a note on reading english, 10 ohm to each fet means just that, not a fet pair, similarly for fet snubbers, 15nF & 6.8 ohm across each fet, not fet pair.

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    pins 6&7...
  9. Closed: Re: Pulse transformer output measured vs. calculated?

    Air core xfmr's are notorious for very high magnetising current loading the driving voltage ( i.e. pulling it down), and not so great coupling to the sec ...
  10. [SOLVED]Closed: Re: Center tapped transformer (forward converter)

    for such mismatched loads - the proposed ckt is not such a good idea ... buck ckt off the 24V to derive the 12v would be better ...
  11. Closed: Re: LTC4020 not regulating, blowing sense resistors during debug

    you may need to have a power supply that can supply lot more current to keep the ckt working - try adding 1000uF or more, temporarily to the input wires to your board ( right at the board ) - ...
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    [SOLVED]Closed: Re: Best topology DCDC adjustable output

    Try and put at least 4u7 from the CT, centre tap, of the LV side to gnd, this wdg should be near the fets, this gives turn off current some where to go until it can reach the big electro's (...
  13. Closed: Re: LTC4020 not regulating, blowing sense resistors during debug

    Current sensing is very important - read the data sheet carefully on using caps to filter the signal ...

    reading the whole datasheet very carefully will likely reveal the causes - the chips...
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    [SOLVED]Closed: Re: magnet wire parasitic properties

    capacitance varies heavily with winding structure ...! there is no magic figure ...
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    [SOLVED]Closed: Re: Best topology DCDC adjustable output

    the choke that goes to the mid point of the o/p caps - correct ...

    Sensing Vout from the midpoint is a bad idea.

    a 10E resistor to each gate after the 33 ohm is also a good idea for fets...
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    [SOLVED]Closed: Re: Best topology DCDC adjustable output

    for your new ckt choke needed only in the neg line, you diodes will have to be 1200V at least due to rev rec spikes - 2 x 800V in series recommended- snubbers across each.

    split up you...
  17. Closed: Re: Determine the power of the ferrite ring in its dimensions

    put 5 turns on it and measure the L, from that you can work out the Ur, if it is quite high ( > 3000 ) it is likely a common mode choke material - not a power ferrite.
  18. Closed: Re: Mutual Inductance between two toroids Coils?

    if the RF current xfmrs are toroidal with complete windings all round the toroid - then there is very little external field and the CT's can be placed one width ( of the toroid ) apart.
  19. Closed: Re: Calculating switching losses of a mosfet when switching energy is not given

    typically in a circuit with an inductive load, the current must rise to full value before the volts across the device turning on can fall - so turn on losses are Vbus x 0.5 Iload x time to...
  20. Closed: Re: Single conductor inside hollow conductor

    13 Turns on a steel core will give you a much better indication @ 50Hz
  21. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    IEC61558 has been withdrawn - it is no longer an applicable standard - from my recent information received.
  22. Closed: Re: Single conductor inside hollow conductor

    50 Hz is way too low for 13 turns on an unknown core size

    for ferrite Bpk < 0.3T Bpk = Erms /( 4.44 F. N Ae ) for sine wave. Ae = ferrite core area, N = turns, F...
  23. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    They list the standards in the data sheet - it is a matter of reading same.
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    Closed: Re: Mosfet Driver Vs BJT Driver

    Put the npn on the top and the pnp on the bottom and you have an emitter follower, tie the bases together and use 100R resistor - for a 5V drive you will need a logic level fet or a level shift...
  25. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    The whole reason for the 1 second test - at the higher voltage - is speed of manufacture, over the 1 min test. The voltage is scaled up ( not linearly ) such that the 5kV ac for 1 sec is...
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