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  1. Closed: Re: Stacking diodes for high voltage rectification

    without the snubbers and sharing resistors the diode with the lowest leakage current will break down in reverse first, then the next lowest leakage current, etc ...
  2. Closed: Re: Center tapped transformer (forward converter)

    For 2W on the 12V rail - its hard to beat the MC34063A - and its pretty cheap - remember you still need the diodes to rectify the Tx wdg and a choke and a cap to form the raw voltage - ...
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    Closed: Re: Bridge Rectifier won't Rectify

    you need a small HV cap across each high value resistor, and a compensating C across the 100k, same RC time constant for each I think ...
  4. Closed: Re: Stacking diodes for high voltage rectification

    The dv/dt of a 900Vpk sine wave at 200kHz, at the zero xing ( where it is maximum) is, I think , 1.13V/ns, or 282V in 250nS, so a little slower than my estimated 900V in 250nS for an...
  5. Closed: Re: Stacking diodes for high voltage rectification

    do you know the leakage inductance of your transformer?

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    Let us assume the low figure of 18pF per diode, at 200kHz this is 44k-ohm, lets say we have 900 volt reverse and 1V...
  6. Closed: Re: Stacking diodes for high voltage rectification

    You'll find out pretty quick if you try to rectify any thing greater than 1kV at 200kHz... do you have any wiring inductance, Tx leakage inductance, diode capacitance ....
  7. Closed: Re: Stacking diodes for high voltage rectification

    This is the first time you have mentioned 200kHz or higher, unless you have significant experience in this field - I would suggest abandoning this endeavour.

    There are no commercial products...
  8. Closed: Re: Stacking diodes for high voltage rectification

    I would suggest 220pF ( 2kV ) and 4k7 ( at least 600V rated ) for the RC snubber for 50/60Hz rectification
  9. Closed: Re: Stacking diodes for high voltage rectification

    you would need an RC snubber across each diode as well as voltage sharing resistors ( 1Meg-ohm - 4.7 Meg Ohm ) across each diode so that the voltage is shared when off.
  10. Closed: Re: Center tapped transformer (forward converter)

    it is a discrete buck switcher - not a partic good one but may suffice for low power, see also NCP3064 ( i think ) for an easy buck switcher with current limit

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

    Pin 5 still needs to be biased to 3v5 from the 5v1 pin, else the pnp has no volts to pull down on.

    take the 100k off the base of the opto - discard, if you must put something on the base...
  12. Closed: Re: Pulse transformer output measured vs. calculated?

    what is the amp scale of the trace?
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    Closed: Re: BJT V(ce) ON in common emitter mode

    else you have to find a xtor that is spec'd for a min gain at amin temp that will fall into your desired range, as mentioned above - if the Ice goes up - the Vce will go up - for a given...
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    Closed: Re: BJT V(ce) ON in common emitter mode

    for power xtors, most data sheet specify Vce ON for saturated gain, usually Ic/Ib = 10 or 5

    Zetex did a range of xtors designed to give very low Vce on for quite modest base drive Ic/Ib ...
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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 ...
  18. 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...
  23. 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 ...
  24. 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 ...
  25. 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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