Charge Pump Question

[SeanMiracle]

Hey guys,

I want to build a 9v - 18v charge pump. I'm using this image:



I only need the 17v output. So, my questions is: Can I just wire in the C1 and C2, and D1 and D2, and ignore the others? Or do I have to modify it by not including the 25v and 33v outputs?

Thanks,

- Sean

[thomasha]

Hi,
I can't see your image, but if its a charge pump, every combination of 2 diodes and 2 caps adds the initial voltage, with the diodes voltage drop.
So if you only need 17v you just need 2 diodes and 2 capacitors, and the components that the IC requires to work properly in a specified frequency.
greetings!
Thomas

[SeanMiracle]

Also, GEOFX says to use 1N5817 diodes. I'm ordering from Mammoth and they only 1N5818 diodes. Can I use those?

[SeanMiracle]

Thanks Thomas.

I think I'm going to use vero board instead. I found a layout that only uses 2 diodes and 2 capacitors. I just have the question about the diodes (see above).

[thomasha]

Hi,
i think you can use the 1N5818,

after a quick look at the datasheet it seems that the main difference is the power/voltage it can handle, and 1N5818 has the higher one, so, no problem.

They both seem to have the same recovery time (500 ns).

[SeanMiracle]

Thomas, you're awesome.

Last question (I think), when using a charge pump, how does it affect the current? Does it have a limit? Or can as much pass through it as the main 9v supply can offer?

- Sean

[thomasha]

Well,
there is a limit, and it's pretty low. For a MAX1044 it's only 10mA.

I only used a charge pump for the Murder one submini amp, and what I experienced was that when I should have something like 85V I only had 60V under load, and each stage instead of adding 10.8V, was only adding something like 4 to 5V.

The problem was not with the diodes (I remember using ultra fast signal diodes 1N4148), but with the capacitors. With better capacitors the voltage increased, so I would say that for the voltage level the diodes handle (9v) the ultrafast diodes are no problem, but the forward voltage drop due to the diode material (0.6 to 0.3 V) and the capacitors make the difference.

So, if you want more information, I suggest reading this:
http://www.maximintegrated.com/app-notes/index.mvp/id/725

There are some IC's that provide a higher current, but it's still in the 80mA range. I know that a lot of pedals use the max1044 or the ICL7660 , so this probably won't be a problem for your build.

Cheers
Thomas

[SeanMiracle]

That was very helpful.

I looked at some other forums, and people recommended the LT1054 series chips. Apparently they can offer up to 100mA (though the voltage drops a bit if you draw that much).

I want to power a MXR M108 10-Band EQ from a Godlyke 9V daisy chain. The M108 draws 26mA, so I can't use a MAX1044 or an ICL7660. I ended up ordering a LT1054 CPE4. Hopefully it works!

Thanks again Thomas, you've been a great help.

- Sean