Author Topic: Charge pumps questions  (Read 361 times)

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nonoxxx

Charge pumps questions
« on: June 26, 2017, 03:47:17 AM »
Hello,
I was looking at some charge pumps schematics and I have some questions :

Does running an opamp at 18 V (on the RC4558 documentation 18 V it's specified like an 'absolute maximum rating') can cause premature use of the OPAMP?.

And what is the best chipset? I have seen MAX1044, IC7660... it's difficult to choose.

Thanks.




« Last Edit: June 26, 2017, 03:55:55 AM by nonoxxx »

darron

Re: Charge pumps questions
« Reply #1 on: June 26, 2017, 04:12:45 AM »
if you're worried about hitting the 18V, then don't use 1N5819 diodes, use 1n400x style instead. then you'll be closer to 17V.


in my personal experience use the 7660S over the MAX1044. The 1044 is only rated to 10V from memory, so could be easily damaged by somebody with an unregulated power supply. crap, it's even close to a fresh battery. the tiniest bit over current or over voltage and they blow. they are not forgiving for a second.

to put my mind at ease over this, i put a 1W 12V zener diode in the reverse direction across the power supply, after first series protection diode. the 7660S is rated for 12V and it a tiny bit tougher. sometimes people like to try plugging effects into 18V PSU too and just assume everything will be okay. in that instance, the zener should hopefully shut the PSU down on over-current and protect the pedal.
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nonoxxx

Re: Charge pumps questions
« Reply #2 on: June 26, 2017, 04:34:50 AM »
thanks, a lot,
I will order a bunch of 7660 and  will do some experiments on stripboards. like 9v to 17, 9v to 15 regulated  , and 9v to : with a switch 15 regulated and 9 regulated  .

I will start with this layout :


antonis

Re: Charge pumps questions
« Reply #3 on: June 26, 2017, 05:17:53 AM »
Does running an opamp at 18 V (on the RC4558 documentation 18 V it's specified like an 'absolute maximum rating') can cause premature use of the OPAMP?.
As is clearly written in any Op-Amp specification data sheet:
"All voltage values, unless otherwise noted, are with respect to the midpoint between VCC+ and VCC–"

So, if you intend to power RC4558 with single supply (VCC- -> 0V) you can go up to +36V for VCC+..!!

Of course, for recommended operating conditions, a min-max supply difference between 10V & 30V is advisable..
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nonoxxx

Re: Charge pumps questions
« Reply #4 on: June 26, 2017, 05:22:13 AM »

Ok I don't understand but if there is no  problem for runing it at 18V. Thanks :)

What is the best IC tu use ( banzai music seems to have several 7660's type in stock) ?
-Maxim ICL7660 CPA
-ICL7660 ACPA
-ICL7660 SCPA
-ICL7660CPA Plus


and musik ding only one type
- ICL7660S

reddesert

Re: Charge pumps questions
« Reply #5 on: June 26, 2017, 05:36:10 AM »
Get charge pumps that have the boost feature. Here that means the "S" designator, so the ICL7660 SCPA, not CPA.  This allows boosting the pump frequency out of the audio band. Without it, you will often have a high pitched whine.  The LT1054 operates at a high frequency by default so it doesn't need a boost.

antonis

Re: Charge pumps questions
« Reply #6 on: June 26, 2017, 05:39:29 AM »
Ok I don't understand but if there is no  problem for runing it at 18V.
OK too but, IMHO, the point should be to understand it.. :icon_wink:

Probably by English suck but plz try a little bit more.. :icon_redface:

Op-Amps have no internal ground point so they totally shrung off any external circuit "zero" point..

The only thing, relative to their power supply, they care for is the voltage DIFFERENCE between their Vcc & Vee..
(none of their supply pins ought to have some specific kind of polarity with respect to ground..)

e.g. for an Op-Amp rated to (+)(-)18V, any combination between +36/0 & -36/0 should be accepted, as long as the more possitive (or less negative) supply is connected to VCC+.. :icon_wink: 
(we could easily go further to combinations like +72/+36 or so, but let it be..)

P.S.
The above stands for ANY device with maximum voltage rating..
e.g. a 35V capacitor is rated for this specific voltage difference between its "plates", so you can connect one of its legs to, +15V say, and the other one to +50V..
« Last Edit: June 26, 2017, 05:49:52 AM by antonis »
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nonoxxx

Re: Charge pumps questions
« Reply #7 on: June 26, 2017, 08:10:54 AM »
If I don't understand, it's not your fault lol and as a french guy my english is worse than your's :D , but it's my lack of electronical knowledge,
For me 9 is 9 v and 18v is 18v :)
so know I understand how it works , on pin 4 and 8 of these opamps the only thing important is the voltage difference at VCC+ and VCC- , not the voltage at vcc+.

Thanks :)

PRR

Re: Charge pumps questions
« Reply #8 on: June 26, 2017, 09:35:17 PM »
Most *older* chip op-amps are specified for maximum 36V. Many millions run for many years on 30V (+/-15V). 18V is not a problem.

There are some newer op-amp chips aimed for 3V and 5V operation. Some may be rated as low as 7V. Others are OK to 18V. I would not use a charge pump (doubler) from 9V to 18V with a 18V-max chip. That's too close to the limit. While the doubler may "only" change 9V to 17V (not quite double), not all "9V" supplies are exactly-right. If you go a little over 18V, typically the chip works for a while and then quits at a bad time.

antonis

Re: Charge pumps questions
« Reply #9 on: June 27, 2017, 07:03:02 AM »
Most *older* chip op-amps are specified for maximum 36V.
I have 3 x TL081 inside a bench-top PS working on +35/-5.6V for more than 20 years with absolutely no problem..
(maybe the're from "Blue Monday" production line..)

I recently replaced them with 3 x TLE2021 (+/- 20V) to give them dignified retirement and also check for newer Op-Amp durability..
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