Home Forums GuitarPCB Build Support Charge Pump Confusion (answered)

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  • #4358
    Kirk
    Participant

    Hi,

    I saw this listing on the sponsor’s site:
    <h2 class=”single-post-title product_title entry-title”>Charge Pump IC for all Pump’d Up series boards 7660S Brand</h2>
    The description stated that it flipped the polarity for those projects that utilize the PNP type transistor. My understanding of a charge pump is that it would, e.g.,allow a 9V potential conveniently power a pedal requiring an 18V potential as the charge pump boosted the potential from 9V to 18V inside the pedal. What’s the scoop on this difference of function?

    #4362
    Billy
    Moderator

    A 7660S can be used as a voltage inverter for positive ground circuits meaning you can use a normal +9v adaptor and daisy chain with standard negative ground pedals rather than use an uncommon positive ground adaptor the pumped up series integrates it into the circuit if you look at the power supply section in the schematics

     

    The datasheet contains all the information and circuit examples for it’s uses

    #4374
    Kirk
    Participant

    Hi Billy,

    Thank you for clearing this up for me.

     

    #4378
    wilkie1
    Moderator

    The 7660S charge pump can also be used to double the positive voltage although that function is not used in these circuits.  The data sheet shows how to add capacitors to do this.

    #4404
    Kirk
    Participant

    Hi Wilkie and thank you for pointing out the data sheet as the place where the charge pump function and the capacitor values that are involved in boosting potential are found.

    #4406
    Billy
    Moderator

    This is an interesting read

     

    https://bogdan.nimblex.net/diy/2016/12/08/testing-charge-pump-ics.html

     

    This guy tests a few different charge pumps but initially it explains briefly how it works with the internal CMOS switching, caps charging and inverting the voltage etc

     

    Datasheets are of course great for any component usually giving circuit examples for what they can be used for but not always giving a clear explanation in laymans terms so I usually google to try to understand better for example I like to know what each pin function is

     

    On the 7660S in particular the LV pin (pin 6) took me a while to figure out, when I used a 7660S to give me -3v for a Selmer Buzztone build in conjunction with a voltage regulator

     

    It ended up oscillating with a loud squeal until I eventually figured out LV must be low voltage as soon as I grounded pin 6 the squeal disappeared of course if I hadn’t skimmed over the datasheet I’d have seen the circuit with LV going to a switch to ground but they are definitely not always 100% obvious or clear

     

    Anyway I often breadboard one or two of the datasheet circuits it does help you to understand it’s functions especially if you do what I do and change external caps etc to see how it’s affected but you can waste a lot of time messing around haha

    #4413
    Kirk
    Participant

    Billy, thank you so much for this. This is exactly what I was looking for in terms of guidance.

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