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Recent content by cupoftea

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    Equivalent circuit of electrolytic capacitor

    Hi, Bottom of page 10 of this gives an equivalent circuit model of an Aluminium electrolytic capacitor... https://www.mouser.co.uk/datasheet/2/447/KEM_A4049_EDH-3316662.pdf They identify "Co" and "Ce". They say Ce=0.01 x Co Page 1 of this...
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    Dual Synchronous Buck poor choice for 405W and 450kHz?

    Thanks and what is the resistance between the sw node and the bottom rail when the bottom mosfet is ON ?........approx 6milliOhms - how much time is spent in voltage transition ? ( either way )..........<100ns - what is the voltage doing in this transition time ? ( either way...
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    Half Bridge Series Resonant converter operation above resonant frequency

    ...it "should" be soft switching when above the upper resonant frequency, yes. As you know, you shoudl have protection to stop you going so low in fsw that you are in the bad capacitive mode... Though many are saying if you use SiC FETs and SiC antipllel diodes then you wont get bad rev rec...
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    Dual Synchronous Buck poor choice for 405W and 450kHz?

    Thanks, when ON?...as you know, its the rdson...some 8millOhms or so. By Vcc you mean the input voltage (27V for us)?.......not the "vcc" of the chip?... which is only some 5v. In the time old way, we wish to smash the upper fet off fast, and get minimal switch loss....thus the RCDZ snubber...
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    Dual Synchronous Buck poor choice for 405W and 450kHz?

    Thanks , snubbing on the Vin bus, could surely only mean an RC snubber?
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    Dual Synchronous Buck poor choice for 405W and 450kHz?

    Thanks, you possibly call for snubbing on the DC bus....by this you must surely mean an RCD clamp on the upper FET?, so that when it turns off, the stray inductive current that was going into it has got somewhere to flow. You would think that it would be enough to have a 1uF MLCC right by the...
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    Dual Synchronous Buck poor choice for 405W and 450kHz?

    Thanks, even though you appear to give countenance to it, you then show that it was not done with "plain vanilla" Synchronous Buck. You say that they used "resonant gate drive" and carefully designed low capacitance chokes. Also, that there was some form of snubbing on the Vin Bus. Most cheap...
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    Dual Synchronous Buck poor choice for 405W and 450kHz?

    Hi, Would you agree that the following spec is too high in power and Vin for a Dual Synchronous Buck solution at 450kHz (each Buck at 450kHz)… 27Vin 13.5Vout 30A out.(405W) No isolation needed. This is too much for a Dual Synchronous Buck with each 202W Buck stage switching at 450kHz. The...
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    Inrush module for input filter

    Its as though its been hot plugged.....ie, a sudden voltage step. (BTW, budget wont stretch to a hot swap control chip......maybe a cheap FET switched inrush resistor...but is that needed?, or do we rely on the legendary pulse withstanding capabilites of wet electrolytic dielectric?)
  10. C

    PSU company is giving poor advice.

    Also, suppose the Power supply which supplies the SMPS is a mains transformer with diode rectifier and smoothing cap.....most of the time, the diodes arent even conducting...so its just going to look like its big output capacitor.....Ie , no ideal voltage source at all......it will be virtually...
  11. C

    Inrush module for input filter

    Thanks, but no we cant use higher L...we need the cheapest and smallest. Am actually wondering whether the attached inrush pulse will be dangerous, after several years of this once per day. Ie, this inrush pulse into the 470uF, 50V capacitor EDH447M050A9SAA. (LTspice also attached) Its...
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    PSU company is giving poor advice.

    Thanks.. Also, the attached shows that the "law" that Zout of the SMPS input filter should be more than 10x lower than the SMPS Zin is not even accurate. The attached shows an SMPS with a crossover of 6700Hz. At up to 6700Hz, its Zin is -3.42 Ohms. The Zout of the shown input filter is 0.56...
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    PSU company is giving poor advice.

    Hi, The Vicorpower "DCM design guide" is giving very poor input filter advice. DCM design guide: https://www.vicorpower.com/documents/design_guides/DG-DCM-Design-Guide-VICOR.pdf On eg page 12 it is saying that the output impedance of the input filter should stay MORE than 10 times less than...
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    Skin effect in fuses.

    Thanks, we are not sure how it is known that the 2.16mm thick fuse, has a conducting element that is only some 35um thick?. Its datasheet doesnt state this. For the reason that we assume the full 2.16mm thickness is carrying the fuse current, we need to keep it with flat DC current in it.
  15. C

    SMPS input filter

    Hi Please may i add the following, on the subject of big filters being needed even for high frequency SMPS... The pointlessness of high switching frequency DCDC SMPS: We are doing a DCDC Buck SMPS, 24Vin to 12Vout at 300W. We could do it at say 500kHz switching frequency and so we only need...
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