Boost converter synchronous rectification implementation

Discussion in 'The Projects Forum' started by ahto555, May 6, 2012.

  1. ahto555

    ahto555 Thread Starter Member

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    Does anyone have good idea how to implement synchronous rectification (n-FET instead of Schottky rectifier diode) in simple single inductor boost topology?
    Circuit bases on UC3843, 250 kHz, Vin 9-14.5V, Vout 18-34V, inductor peak current 25A.
  2. SgtWookie

    SgtWookie Expert

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  3. ahto555

    ahto555 Thread Starter Member

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    Thank you for advice! I am well aware of high end boost chips with integrated synchronous rectification. I have even run LTC3703 based circuit for my application in LTSpice. But I am old scool through-hole type and not very comfortable in SMD soldering.
    I was hoping someone has tried something similar to this - http://www.radiolocman.com/shem/schematics.html?di=105520
  4. SgtWookie

    SgtWookie Expert

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    I took a look at the article you referenced, and immediately shuddered thinking of what was happening to the LM393/LM2903 that had to sink ~43mA current, when that was about 10x as much as it should have been tasked. They really should have used an LM111/LM311 instead.

    I'm pretty old-school myself, but you will quickly find that all of the good new stuff is only made in SMT/SMD packages. While you might think that leaves hobbyists in the dust, that is not necessarily the case. It's much easier to make circuit boards for, as there are no holes to drill for the ICs; and soldering really isn't too bad if you use solder paste and a toaster oven; just takes some practice.

    SMT/SMD resistors and caps are pretty challenging for me if they are smaller than 0805; I like to stick with 1206 or larger.

    Manufacturers are driving the push to the smaller SMD/SMT packaging; they take less real estate on the PCB's, which means lower costs - and the package leads being much shorter means less parasitic inductance, so they can operate at higher speeds than DIP equivalents.

    While it may seem intimidating to go SMD, try a few projects in it, and you may start to appreciate the benefits; the multitudes of newer IC offerings are certainly within your grasp.
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