Charge pump

Discussion in 'The Projects Forum' started by Kingsparks, Mar 13, 2013.

  1. Kingsparks

    Thread Starter Member

    May 17, 2011
    118
    5
    Good day everyone. I'm a night hawk so this is early for me but the dogs woke me to an intruder. (Lost sole, 1, & 1/2 mile off public road up a posted drive? Sure!)

    Anyhow, I want to assemble a half bridge type drive and need a charge pump. It is only recently I have started messing around with MOSFET. (Recently being since I escaped the hospital several months ago.) I am not sure how much higher than the low side transistor the high side needs to be, or even the maximum for the charge pump.

    Also frequency for the oscillator. I think I have this one too low, if the circuit I modeled it on is correct it should be adjustable up to 2, 2.5KHz. (Higher to refresh the boot better or more often maybe?)

    Examples in applications notes use a much higher frequency and I can go higher if need I need to. The circuit will be operating at something like 36KHz, adjustable +/- 2KHZ maybe.

    I have two extra comparators in the LM339 I will be using in the main circuit so that is the reason for the comparator as an oscillator. I think I have seen two used also but if one will work I'll stick with it.

    Of course, I can build the circuit and smoke some transistors if need be, but with my shaky hands now days that is time consuming, if someone will lend their experience I would appreciate it.

    Oh yes, I will be driving 2N7002 if they ever get here. SOT23 package and won't that be a challenge with my shaky hands?

    Also another question; In the terms of service it is stated, GIF, JPEG or PGN should be used to up-load attachments. I have been using PDF but can convert quickly. Should I, or is PDF okay?

    Thanks.
    Roland
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,229
    Typically the high-side MOSFET is driven by a bootstrap charge pump. These use the PWM switching signal to generate the charge, not a separate oscillator. This gives some info on that.


    PDF, GIF, and PNG are fine for you posting. Just don't use JPEG for drawings as they tend to be fuzzy.
     
  3. Kingsparks

    Thread Starter Member

    May 17, 2011
    118
    5
    Thank you, I had noticed the fuzzy aspect of JPEG, thought it might be my system.

    The Fairchild application note is appreciated also. I was just reviewing one from Linear Technology with some useful help.

    I know the charge pump is usually derived from the PWM feature in this type application, I am trying something different, probably won't work but I learn that way.

    Thanks again for your help.

    Roland
     
    Last edited: Mar 13, 2013
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,004
    1,525
    Here's one I'm thinking of using in a circuit, pages 17 and 18.
     
  5. Kingsparks

    Thread Starter Member

    May 17, 2011
    118
    5
    Thanks shortbus.

    That's very close to what I had in mind and the information contained in the AN should answer any questions remaining. Between the one I found, the one crutschow suggested and this one, if I can't glean enough information from them then it will indicate I'm going senile. (Hmm, did I really say that?)

    Thanks again.
    Roland :cool:
     
  6. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,229
    The fuzzy lines are the result of the compression algorithm used for JPEG. It's optimized for preserving the essence of a picture using high compression factors but not for preserving sharp edges in a line drawing. The other file format compression methods preserve line edges so schematics and mechanical drawings maintain their sharpness.

    If you don't use too high a compression factor with JPEG, a drawing will look better, but it's just not a good format for those types of files.
     
    Kingsparks likes this.
  7. Kingsparks

    Thread Starter Member

    May 17, 2011
    118
    5
    Hi crutschow.

    I'll keep that in mind, I had been using JPEG in a conversion program to combine text with my CAD and back to PDF. Works okay that way as going back to PDF seems to clear up the out of focus appearance but just as a picture to say paste in a word document, no go.

    Thank for the info, I will put it to use.
    Roland :eek:
     
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