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Type: Posts; User: mtwieg

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  1. Closed: Re: Which transformers can pass approvals testing rergarding isolation voltage testin

    I'm assuming the TIW insulation didn't fail, unless it was damaged during handling (as FvM suggests). Was insulating tubing used to protect the windings as they terminate to the pins?

    What was the...
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    Closed: Re: LTSpice Noise Analyis

    Just look at the datasheet. The AD8429 is based on the typical three-amp circuit, so it basically has two cascaded amp stages. When the gain of the first stage is high, its noise dominates the...
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    Closed: Re: Class D amplifier simulation

    Well if the load really is just a capacitance, then no the flywheel diodes don't matter.

    Capacitive loads have their own problems though, mainly large current spikes and switching losses. I assume...
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    Closed: Re: Class D amplifier simulation

    I wouldn't even bother using real FET models, at least to start. Just use voltage controlled switches in place of the FETs (if your load is inductive, make sure to put diodes across the switches)....
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    Closed: Re: Integrated planar transformer

    I did come across that same app note, lots of good rules of thumb, but nothing really specific :/

    I would definitely need some sort of jig to apply pressure between the two halves while...
  6. Closed: Re: Type one compensator...why is everybody giving it a phase of -90 degreees

    Often the 180 contributed by the opamp is left out during analysis. It's then accounted for by calculating phase margin relative to -180 degrees, rather than -360.

    So long as it's done...
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    Closed: Re: Integrated planar transformer

    Yeah I know if I made my own clamp, I'd have to put some sort of cushion, maybe like a soft thermal pad. But I was hoping to minimize the number of manually assembled custom parts. That's why simply...
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    Closed: Integrated planar transformer

    Anyone here done an integrated planar transformer before? By integrated, I mean that all the windings are on your main PCB, instead of having a separate PCB for windings. My PCB is already going to...
  9. Closed: Re: Reducing radiated emissions in an offline flyback SMPS transformer

    Agreed, it's most likely a conducted EMC (probably common mode) which is being radiated via long interconnects. So it needs to be treated like a conducted EMC issue. Increase common mode filtering,...
  10. Closed: Re: Offline flyback SMPS with bigger core generally has less transformer loss

    Keep in mind the number of turns will likely be different, especially if you optimize the gap. It's certainly not impossible for the smaller core to yield less losses, but that requires more info...
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    Closed: Re: Switching regulator peak current

    They can, especially with very high switching frequencies, but usually if this is the case the design hasn't been properly optimized. A good engineer will estimate both DC and AC losses for the...
  12. Closed: Re: Measuring leakage inductance of flyback transformer

    Measuring open circuit impedances will be much more susceptible to parasitic capacitances, I think.

    And accurate LCR meters aren't expensive anymore. I use this and it works fine for hundreds of...
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    Closed: Re: H-Bridge heating without load

    I think you've eliminated shoot-through as a possible cause. That really leaves the Eoss losses. This is why soft switching is important at high voltages. Depending on what your load is, getting ZVS...
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    Closed: Re: H-Bridge heating without load

    Yeah, I just realized this, see above. Also confirmed it with a simple SPICE simulation.
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    Closed: Re: H-Bridge heating without load

    Eoss is energy stored in Coss, the drain source capacitance. It is always dissipated by the FETs, unless some amount of soft switching occurs.

    - - - Updated - - -


    Interesting. Note that in...
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    Closed: Re: H-Bridge heating without load

    The device datasheet gives a plot of Eoss vs Vds, it's about 1.6uJ at 250V. So with no load and 100kHz, you should see about 0.32W per FET of dissipation. Not enough to account for what you're...
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    Closed: Re: Totem pole pfc challenges

    Yes, the peak to peak Vout_cm is not very different between the two circuits. But leakage is measured in RMS, and as you mentioned, the leakage current from the totem pole comes in sharp pulses. This...
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    Closed: Re: Synchronous Buck Converter FET selection

    Sounds like switching losses are the likely culprit. There are several components to switching loss worth considering.
    1. Cross conduction. Obviously this is the most important one to rule out...
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    Closed: Re: Totem pole pfc challenges

    That was my initial plan. I wound transformers of my own with single and double screens added, and dropped those into a PSFB dev kit. It only seemed to lower emissions by about 6dB (in the frequency...
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    Closed: Re: Totem pole pfc challenges

    Right, I didn't really state the fundamental problems. Lets use Vout_dm and Vout_cm to refer to the differential and common mode components of Vout, respectively. Cy is the capacitor connecting Vout...
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    Closed: Totem pole pfc challenges

    I've done a few boost PFC front ends, but am now looking at maybe giving the totem pole PFC a try. A brief literature search shows that it has many caveats, most of which derive from the fact that...
  22. Closed: Re: Estimating ripple current of 8 x paralel MLCC 500V 2.2nF for a resonant converter

    I typically use ceramic caps from TDK, as they provide very detailed data on each part number (ESR vs frequency, temperature vs Irms and frequency, capacitance vs DC bias, etc), and they make this...
  23. Closed: Re: electromagnetic compatibility tests question

    For emissions testing, it's unlikely that software will have any significant impact, so it's often fine to test that with prototype code. Immunity might be more software dependent (since in some...
  24. Closed: Re: Isolated Dual interleaved PFC'd Flyback controller IC

    Indeed, I'm guessing your operating mode changes throughout the mains cycle. Must use a high performance digital controller.
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    Closed: Re: iPhone charger vs Samsung charger.

    Most "samsung" chargers are bootlegs. Perhaps this is less common with apple products.
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