Charge Pump Confusion (answered)

[Anonymous]

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?

[Billy]

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

[Anonymous]

Hi Billy,

Thank you for clearing this up for me.

 

[Anonymous]

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.

[Anonymous]

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.

[Billy]

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

[Anonymous]

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

[Author]

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