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Bipolar using 7660S IC, not effective enough.
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isak



Joined: Dec 13, 2009
Posts: 704
Location: Israel
Audio files: 18

PostPosted: Thu Jul 24, 2014 7:39 am    Post subject: Bipolar using 7660S IC, not effective enough.
Subject description: please help.
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hi guys.

i build the BugCrusher using this scheme:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

i wanted to use it as an pedal effect so i used the 7660S IC to get bipolar supply and it works great! no problems what so ever.
this is how i used the 7660S:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

when building the more complex bugcrusher with cv inputs the 7660S fakes and i dont really know why, i was wandering if someone with more experience then me can explain.

this is the scheme:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

all the info i can give you is...
1 - when all ic's are connected in the (-)V rail i get (-)2.2V.
2 - when i take out all IC's i get (-)V rail as expected.
3 - all ic's have decoupling caps.
4 - i use LF398 instead AD781
5 - when using a normal bipolar (+)12V/(+)15V (-)12V/(-)15V supply it works perfect!

my goal is to power the more complex bugcrusher via 7660S.

if you have any question please ask.
i thank you in advance for helping out.
cheers,
Isak E.

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brock



Joined: May 26, 2011
Posts: 94
Location: Canada

PostPosted: Thu Jul 24, 2014 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Isak,

You are seeing the effect of the high output impedance of the charge pump when you draw significant current. At 5V input the output impedance is approximately 120R. Take a look at figure 7 in the datasheet http://www.intersil.com/content/dam/Intersil/documents/icl7/icl7660s-a.pdf and you can see what is going on.

You have a few options to make this work better.
    You could parallel 2 or more 7660s. You just need one output cap for all paralleled devices.
    You could run the charge pump from 9V and regulate the output at -5V to make it more stable, you may find you still need more than one device to get the current you require.
    You could try a higher output current part such as an LT1054
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isak



Joined: Dec 13, 2009
Posts: 704
Location: Israel
Audio files: 18

PostPosted: Thu Jul 24, 2014 11:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi brock.

thank you for replying and for explaining.
have another Q, i dont know if its related but ill try anyway..
i have to sets of decoupling caps.
2 X 100nF from (+) and (-) to ground.
2 X 10uF from (-) and (+) to ground.
it seems that i forgot to connect the (+) side.
take a look on the next photo...


no connection.png
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no connection.png



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brock



Joined: May 26, 2011
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PostPosted: Thu Jul 24, 2014 12:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm not exactly sure what the question is you're asking. If it is "will not having the caps connected to the regulator output cause a problem?", I would guess that it could. Your regulator might be oscillating so you aren't even getting the 5V in to the charge pump that you expect. Did it make a difference when you connected it?
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isak



Joined: Dec 13, 2009
Posts: 704
Location: Israel
Audio files: 18

PostPosted: Thu Jul 24, 2014 12:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Did it make a difference when you connected it?

i didnt try yet cause i'm not home ATM.
later on i'll try and post the results.

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isak



Joined: Dec 13, 2009
Posts: 704
Location: Israel
Audio files: 18

PostPosted: Thu Jul 24, 2014 4:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, that didnt helped but i tried another bipolar using 555 chip Smile
http://www.circuitstoday.com/positive-voltage-to-negative-voltage-converter
that works perfect!

i thank you for your help!

cheers,
Isak.

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