Charging Circuit Problem

Discussion in 'General Electronics Chat' started by AsstdBin, Feb 2, 2015.

  1. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    Was hoping someone could look at this schema and give me some suggestions on where to look. I can get the circuit to charge by jumping the Q18 drain and source Terminals. The PCB has two P-channel mosfets that appear to my, nearly blind eyes in this respect, to have two mosfets to accomplish the same task-battery charge. Also wondering what Mosfet Gates Drivers look like. If anyone has a minute to look at the circuits and give me an educated /experienced opinion on this I would certainly appreciate it.
     
  2. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    If I am reading this correctly Q17 could be bad and Q18 would complete the task independently...?

    What would the expected value (in volts) be to operate the gate in a 14.4v system?
     
  3. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    If my understanding is correct fundamentally the mosfet driver applies voltage to the gate which in turn causes voltage/electrons to pass through the drain and the source has a constant supply waiting for the gate to close the circuit....is this correct fundamentally? I am gathering the p-channels also have a body terminal...?
     
    Last edited: Feb 2, 2015
  4. #12

    Expert

    Nov 30, 2010
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    Q17 and Q18 are in series. If jumping Q18 makes this thing start, then Q18 is either not getting the message or Q18 is bad.

    P type mosfets kind of resemble PNP transistors in that you can put positive on their source (emitter), pull the gate (base) low, and current flows. In your drawing, the MCU is supposed to tell the gate driver to pull the gate of Q18 low.

    A gate driver can be in any sort of package, usually black plastic and square. This one has at least 5 pins. Two of them are connected to mosfet gates. That is where to go poking around with a voltmeter.

    What is, "low"? The drawing says it is about 1.77 volts. That is about 14 volts lower than the 16 volts arriving at Q17. For a mosfet gate, 10V is a lot.

    So, measure the gate of Q18. High or Low?
    If it's "high" you have to back up to the gate driver and see if it is getting instructions from the MCU. That's where this all falls apart because you don't have a schematic, you have a block diagram.

    There's a start on this.
     
  5. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    #12 Thanks for the reply.

    My records show voltage to the gate on Q18 was 19.97v while charging with a 22.5v input to the board. The source to this particular gate was 21.79v.

    Thanks for correcting me, I see the gate terminal is actually lowering the voltage thereby completing the circuit on the mosfet.

    Now I wait on the mosfets from china...ugh
     
  6. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    Edit: The first "Charge" line in #6 is the same information as "Batt. Only" (second line) and should be omitted.

    So it should read:............G---D----S
    Battery Only (G-D-S): 14.8, 15.5, 14.8
    Charger Connected....: 3.1, 15.8, 15.9
     
  7. #12

    Expert

    Nov 30, 2010
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    My experience tells me that gate drivers have a huge ability to deliver current, so, if the gate shorted, the driver would be fried and then become an open circuit (thus not able to pull the gate low). If the gate did NOT short, then the driver is failing to pull a perfectly good mosfet gate low.

    We are at, "Oh $h1T". The driver isn't driving. Does that mean it isn't getting the message from the MCU or is the driver bad? Try to read a part number on the driver.

    Drivers are generally stupid brutes. They usually get a "low" from the MCU and deliver a "low" at their output, but some of them are inverters and work the opposite way. The best way to corner this beast is to find the part number and measure input voltages.
     
  8. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    OK, I took some high-res images of the board. Is there any way I can get these to you? I will get the number as soon as I find it. Will do some research on drivers.
     
  9. #12

    Expert

    Nov 30, 2010
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    Download them to your writing box. Drag&drop works for me.
     
  10. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    Easy enough.... The 5 buttons form an arrow pointing upwards. Q18 mosfet, now removed, is just up and left of the left arrow. Oh, two .5ohm SMD resistors have also been removed from the top right of the arrow at R257 and R235.
     
    Last edited: Feb 6, 2015
  11. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    OKAY, I think I traced the driver back to a "34063 PJKVA" located at "U3" with eight legs.
     
    Last edited: Feb 6, 2015
  12. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    I searched for 34063 PJKVA and was not able to find any information.
     
  13. #12

    Expert

    Nov 30, 2010
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    Same here. I can post a random dual high side driver so you can better imagine what is inside one.
     
  14. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    I will try contacting a couple microelectronics suppliers to see if they can get some data on it for a potential replacement. I want to study it some more though and post some data to see how it is behaving next chance I get. Thanks for helping me with my project.
     
  15. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    I did a search for "Mosfet Driver 34063" and found a bit of information. Unfortunately, I now must figure out which one. Here is a link to a few different ones with some minor variations of the same and here is the abbreviated version.

    The watt meter shows (on a good working robot) that they charge at 33watts. It appears with this information the charge current is .275 amps at 120v.
     
    Last edited: Feb 6, 2015
  16. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    Data sheets for the "34063" show them fitting the profile of a mosfet driver. Problem is there are a few variations. One is where voltage is increased to close the S/D circuit and another which lowers to do the same. This answer is quite obvious in my case as the bot lowers to create the circuit. However, the problem is worsened as there are variations of both. :( Will probe this to gather data in hopes that you can tell me what particular version I am needing. Here is what I have determined so far-not much:

    mosfet driver.jpg
     
  17. #12

    Expert

    Nov 30, 2010
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    No, you found voltage regulators. Those are not gate drivers.
    Big problem: If we can't find its datasheet, you not only can't know what pin is which, you can't buy a replacement!

    Anybody else have a clue where the datasheet is for this one?
     
    Last edited: Feb 7, 2015
  18. AsstdBin

    Thread Starter New Member

    Jan 31, 2015
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    I had a person at element14 suggest a KA34063A by Fairchild (data sheet attached.) Emailed them...waiting for response.

    From the looks of this thing it appears that terminal 5 is the gate controller that is some amplified before getting to the gate by a few volts.

    Here are the terminal voltages:

    Mosfet Driver voltage.jpg
     
    Last edited: Feb 8, 2015
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