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  1. mrinalmani

    Lead acid battery full charge voltage

    Hello everyone What I understand is that a fully charged flooded lead acid battery measures 12.6V. But different sources mention different charging voltages, such as 13.6V or even as high as 14.6V. Especially for automobile batteries, multiple sources say that the alternator voltage should be...
  2. mrinalmani

    Optimum placement of current shunt resistor

    Hello I was wondering what will be a better placement for the current shunt resistor between the two diagrams shown below. - Gate drivers and all other analogue sub-parts are ground referenced. Thank you
  3. mrinalmani

    12V full bridge over heating

    I found out the problem. Majority of the loss is coming from high amount of ripple current circulating between the decoupling capacitors and the cable inductance of power cable connecting 12V source to the PCB. (Measured 1.5uH using LCR meter) Strategic placement of capacitors on the PCB...
  4. mrinalmani

    Current ringing in H bridge

    Hi Thanks for the replies. The resistor inductance measured on LCR meter is 500nH. I think it is a probe issue because the ringing disappears with a differential probe.
  5. mrinalmani

    Current ringing in H bridge

    Hi thanks everyone for the reply. After all the suggestions, I tried to see the effect of probing. In the protos of the previous post VDS was measured using a HV differential probe and inductor current using a normal passive probe. I made three measurements: 1. Measure current with differential...
  6. mrinalmani

    Current ringing in H bridge

    Hi I have a tied an RL load to a 12V H-Bridge operating in a usual fashion where alternate FETs are ON followed by a large dead time where all FETs are OFF and then the adjacent pair of FETs are turned ON and the cycle repeats. L = 32uH wound on gapped ferrite core. R = 0.25 Ohm To sense the...
  7. mrinalmani

    12V Full bridge waveform doubt

    Hi I am testing a 12V full bridge converter connected to a step up transformer. The output of the transformer is rectified using a SiC bridge diode. There's no inductor between the SiC output and the bulk capacitor. The transformer is being driven by simple PWM. Alternate high and low FETs are...
  8. mrinalmani

    12V full bridge over heating

    Hi, thanks for the reply. I understand that RMS is what we should be talking about instead of average, but I think the error of approx 300% to 400% is too large to depend on RMS or average especially as the duty cycle approaches 100%. - The current magnitude is different for different snapshots...
  9. mrinalmani

    12V full bridge over heating

    Hi Thanks for the reply. Here's the approximate loss calculation method I used. Rds_on at Tj = 80C = 2.5mOhm max. Rise and fall time = 25ns approx. V_ds = 13V, I_Out = 40A avg. Based on this: I^2R loss = 40x40x2.5m = 4W. But the switch is only active 50% time in full bridge so loss = 2W. For...
  10. mrinalmani

    12V full bridge over heating

    Hi I am working on a 12V phase shifted full bridge connected to a 1:38 step-up transformer. The output of the transformer is rectified using SiC diode bridge. Fsw = 80KHz. The MOSFET is PSMN2R030YLDX with 2mOhm resistance and maximum 2.5mOhm at Tj = 80C. - When driving 40A current into the...
  11. mrinalmani

    3KW PFC topology

    Hi We have to design PFC with multiple power outputs ranging from 3KW to 10KW. Input voltage range 160V to 280V and output voltage = 400V. Up till now I have only designed and tested between 200W to 800W. I especially liked CrM topology over CCM, they simply run very smooth and cool. I was...
  12. mrinalmani


    1. Add ceramic decoupling capacitors close to the bridge 2. If the FETs still overshoot, add an RC snubber across each drain-source. A reasonable value to start with would be 1 Ohm in series with 4.7nF.
  13. mrinalmani

    Input Capacitor selection For 450W Synchronous Buck

    Just to share some experience, I've never actually had the need to use electrolytic capacitors for any buck converter at such frequencies. And also, an X7R cap in 0805 package can easily handle over 3 amps of current. With a 1210 size cap, I will be expecting over 6A capability to begin with.
  14. mrinalmani

    80kHz CCM PFC followed by 80kHz Two transistor forward...beat with each other?

    I think the beat effect will be even more severe at 80KHz followed by 70KHz, beating at 10KHz. If both the stages are at 80KHz then beat will be in order of a few 100Hz considering slight mismatch. But to beat at such low frequency the system should probably have a very low damping factor. It's...
  15. mrinalmani

    Isolated feedback in flyback switcher

    Hi We are trying to make a cost effective isolated DC-DC supply using a simple switcher IC in flyback mode. I have seen several AC-DC offline switchers making use of an auxiliary winding of the transformer for feedback. An example circuit is attached below. My question is - can we do the same...
  16. mrinalmani

    Current transformer waveform severe distortion

    I figured out the solution. Thanks everyone, thanks FvM. - If the transformer was ideal then with secondary shorted out (0 burden) there would be no magnetizing current and net flux in core would be zero. - As we increase burden, it will act in parallel to the magnetizing inductance and current...
  17. mrinalmani

    Current transformer waveform severe distortion

    Thanks for the reply. But since this is a current transformer, ∫Vdt concept doesn't quite fit here. Or am I missing something? The current is already dictated by the primary current. If the core were to saturate it should rather saturate at the top of sinusoid. But the photo looks as if it...
  18. mrinalmani

    Current transformer waveform severe distortion

    Hi I've wound a simple current transformer with 1:100 turn ratio using a small toroidal nanocrystalline core. It more or less works OK, but there are two issues. 1. The current aligns to voltage at every cycle end but goes goes slightly out of phase during falling slope of the voltage. (Please...
  19. mrinalmani

    H-Bridge heating without load

    Hi everyone, thanks for the replies There is no shoot through for sure, I increased the dead-band to 400ns to make sure about this. As just pointed out by @mtwieg and then again by @FvM, the charge delivered to Coss of a MOSFET happens through a much higher voltage across the complementary pair...
  20. mrinalmani

    H-Bridge heating without load

    Thank you for the valuable replies. I do not see any cross conduction, there is also no dip in the bus voltage which would insinuate cross-conduction. I have tested with dead-band as wide as 500ns but it doesn't help. If you refer to the 1st or second photo, you will notice that the Vds voltage...

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