Charge Pump

[Rohit Chatterjee]

Hello all....I am trying a build (on paper first) a system whereby a capacitor array consisting of 10 capacitors may charged to voltages of 2 V, 4 V,6 V....20 V...I may use an input voltage of 2 V, and a clock with peak-to-peak voltage of 2 V...I guess i should use a charge pump right????Can anyone suggest which what type of charge pump may be used....the literature available on the net is confusing.....Please suggest some suitable charge pump IC....

 

[4pyros]

How much power does your 2 volt supply have. Charge pumps are for mostly low power like solor cells. If your power supply has a good amount of power I would use a voltage multiplier. Andy

 

[audioguru]

An ICL7660 charge pump IC works with a supply as low as 2V but then its current is only 2mA. If it steps up the voltage to 4V then its current is only 1mA.

 

[Rohit Chatterjee]

@4pyros....
Nothing is mentioned about the power....I mean this problem is being implemented o n paper for the tym being...but its a low power application....How much power is reqd for the voltage multiplier???Can i multiply the voltage upto 20 V????

@audioguru...
I am gonna use it to charge up a capacitor array....So even if the current is low is it really that much of a concern???I mean it will take a lil more tym....but is there any other drawback????

 

[audioguru]

Two ICL7660 charge pump ICs can quadruple 2V into 8V if there is no load current. A third ICL7660 cannot be used because the max supply voltage for an ICL7660A is only 13V. You could make your own charge pump with many parts to double the 8V to 16V.
But what good is voltage without any current?

 

[Rohit Chatterjee]

But what good is voltage without any current?

True....but can i use a buffer op-amp for the 8 V...i mean if i connect the 8 V i/p to the op-amp....wont i get an 8 V o/p with reasonable current???After all it is supposed to have infinite input impedance theoretically....

 

[BrownOut]

Having rails for an output of 8V from an opamp obviates the need for a charge pump.

 

[Rohit Chatterjee]

Of course...what was I thinking....silly me
So i guess there is no IC which can multiple 2 V upto a level of 20 V and still provide sufficient current???

 

[audioguru]

But you forgot to say how much current you want at 20V.
Charge pump ICs use Cmos for very low voltage loss. But Cmos has a very low output current when its supply is only 2V.

 

[Rohit Chatterjee]

Ok...truth is i am not sure myslf....actually I mean to charge a capacitor array using these voltages.....Is current that much of an issue in that case????even if the current is a bit low, the capacitors will get charged eventually, wont they????