sanity check question on charge pumps

[Sensei Tim]

So i'm in the middle of doing an amp sim build for a fellow.

Normally most people have 9V DC power supplies, and i use a charge pump to run the circuits at 18V.

This guy, however, has a 12V DC power supply.

I checked the spec sheet for the LT1054 and it says it can take an input voltage up to 15V.

If i make this charge pump:



and i power it with my 9V power supply when tuning the jfets, will it still output the same voltage if he uses a 12V DC supply?  gut feeling says yes, but i want to confirm first.

[Beaker]

No I don't think it will, its a simple doubler (I think) so feed in 9V and you get 18V out. Feed in 12V and you get 24V out.

A very quick google suggests using a LTC3265 to convert 12V to 15V. I don't know what you will get out if you feed it 9V.

I'm sure someone more knowledgeable - and helpful - will chip in though!

[Beaker]

Scratch my last post as I misread yours - I thought you wanted 15V output.

I'm sure I remember someone taliking about this a while ago, but I can't find the relevant posts.

Try Mark's Simple Voltage Doubler. You might be able use this fix on the layout you posted, but it's an easier hack if you use Mark's version.

Add a extra column on the right hand side, and fit a 18V Zenner diode parallel to the cap (so between the output and ground). Actually you don't even need to add a column if you can squeeze one in the gap between the 5817 and the 100uF cap.

It will still double the input voltage, but the Zenner will limit the output to 18V, regardless of the input voltage - so you can happily use either 9V or 12V for the input. With a constant output, you can test and bias the pedal with your 9V supply, and it should work the same and need no further adjustments with his 12V supply.

I'm pretty sure this will do the job, but someone PLEASE correct me if I'm wrong!

[Silver Blues]

That sounds OK to me but I think the 7660S can take an absolute maximum of 12v, so maybe try that trick with the 1054 pump instead?

I think a resistor is also involved in using a Zener as a voltage regulator.

[Beaker]

Bugger!

You are right Silver, both tha icl7660 and the max1044 have a top supply limit of 10V. So It's not going to work.

[Travis]

If he powers it with 12V instead of 9V he will get a higher voltage, but you don't need to worry about rebiasing the JFETs because their bias is proportional to the supply voltage. Just like when you switch from 9V to 18V you don't need to rebias.

He should probably get a regular 9V supply at some point since it is the standard but as long as you mind your voltage tolerances here you shouldn't have any issues. I'd probably include some voltage regulation to protect the charge pump though

[Sensei Tim]

Travis, that's what I suspected too, but in the discussion for the ecstasy circuit there was talk about the 9/18v switch not working because of some of the 100r resistors.


See link here:

http://tagboardeffects.blogspot.ca/2014/06/goosoniqueworx-seventheaven.html?m=1

Post by Dk from December 2015 near the bottom

[Travis]

My hunch is that the voltage drop from the 100r resistors will remain proportional unless there is some issue with a reduction in current causing an increased voltage drop. If that's the case, one would think you could simply lower the value of the resistors to get more current flowing

I personally have not experienced an issue where a power supply change required rebiasing

[Sensei Tim]

So i think i found a solution to this problem.

I'm going to use an LT1054 charge pump (input max 15V) and then use an 18V regulator (input max 35V) to bring the voltage down to 18V.

Should work with any DC input from 9 to 14-ish volts.

[Beaker]

Sounds like a plan.

[induction]

If his 12 VDC adapter is unregulated, it could put out more than 15 V in some cases. So maybe protect the LT1054 with a 12V zener.

[Sensei Tim]

yeah i have a 14 v zener just in case, but it is CIOKS which i think is regulated.

On Thu, May 19, 2016 at 12:08 PM, induction [via Guitar FX Layouts] <[hidden email]> wrote:

If his 12 VDC adapter is unregulated, it could put out more than 15 V in some cases. So maybe protect the LT1054 with a 12V zener.

---

If you reply to this email, your message will be added to the discussion below:

http://guitar-fx-layouts.42897.x6.nabble.com/sanity-check-question-on-charge-pumps-tp30596p30802.html

To unsubscribe from sanity check question on charge pumps, click here.
NAML