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'[EE]: -ve supply rail.....creation (charge pump-is'
2000\11\28@144411 by D Lloyd

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Hi,

I am currently using the configuration shown to obtain a -ve supply in the
region of -2.5V, for an LCD. Is there a more optimal solution?
The clock is driven straight from a buffer, at 4MHz.

                                1n4148                 100n       3K3
                           -------|<--------------------|
|---------R-------------CLK (3V Drive)
                           |                             |
+3        +3       GND                     _|_
  |           |                                         ^   1n4148
--- C1   Z 6V8                                |
---          |                                          |
  |_____|__________________|__________TO LCD ( ~ -2.5V)

Apologies for the very bad ASCII.

C1=100nF, Z=Zener diode, 6V8, cathode to +3V rail (got a bit squashed up at
that side!),

Anyone help, please? I know it's nasty, but it only needs to control the
contrast.

Regards,

Dan

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2000\11\29@044216 by Vasile Surducan

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On Tue, 28 Nov 2000, D Lloyd wrote:

> Hi,
>
> I am currently using the configuration shown to obtain a -ve supply in the
> region of -2.5V, for an LCD. Is there a more optimal solution?
 if -2.5 it's enough it's ok, you don't need zenner
 if you need more, use a npn, in colector a resistor to + ( greater than
5v is better) a doubler bridge ( 2capacitors 2 diodes) conected for -V at
output.
vasile

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2000\11\29@060425 by D Lloyd

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part 1 2149 bytes content-type:text/plain; charset=us-ascii
Hi,

The supply rail is 3.3V and I only require ~-2.5V, so there is no need to
modify?

When you say "bridge", do you mean this arrangement?

VCC
|
D1
                                                                     c1
|
                                                  --------------|
|------------------D2>----------------> 2*VCC
                     vcc                      |
|
                        |                         |
----C2
SQW GENERATOR--------|
----
                                                  |
|gnd
                                                  |
                                                  --------------|
|-----------------<D4-----------------> -1*VCC
                                                                     c3
|                           |
|                        ----- c4
D3                     -----
|gnd                   |gnd

Sorry about the ascii, again. The diagram shows both legs but the positive
side is not required.

D1 anode to VCC and is Schottky
D2 (zener) cathode to C2
D3 cathode to gnd, and is Schottky
D4 cathode to C3

Dan




(Embedded     Vasile Surducan <spam_OUTvasileTakeThisOuTspamL30.ITIM-CJ.RO>TakeThisOuTspamMITVMA.MIT.EDU>> image moved   29/11/2000 09:28
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pic16367.pcx)





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Subject:  Re: [EE]: -ve supply rail.....creation (charge pump-ish)

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On Tue, 28 Nov 2000, D Lloyd wrote:

> Hi,
>
> I am currently using the configuration shown to obtain a -ve supply in
the
> region of -2.5V, for an LCD. Is there a more optimal solution?
 if -2.5 it's enough it's ok, you don't need zenner
 if you need more, use a npn, in colector a resistor to + ( greater than
5v is better) a doubler bridge ( 2capacitors 2 diodes) conected for -V at
output.
vasile

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part 2 165 bytes content-type:application/octet-stream; (decode)

part 3 144 bytes
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2000\11\29@171115 by Edson Brusque

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As we're already on the subject...

   There's some way to create +12V and -12V from just +5V? Without the use
of a DC-DC converter?

   Thanks,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2685  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
-----------------------------------

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2000\11\30@024008 by Vasile Surducan

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You'll find the doubler bridge schematics at
http://www.geocities.com/vsurducan/c520.htm
PS: Your ascii schematics are really mess...
vasile

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'[EE]: -ve supply rail.....creation (charge pump-is'
2000\12\01@032722 by D Lloyd
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part 1 849 bytes content-type:text/plain; charset=us-ascii
Hi,

Cheers for the link. I know the ascii art is bad. I could have posted a gif
with the file but....well....

Regards,

Dan




(Embedded     Vasile Surducan <EraseMEvasilespam_OUTspamTakeThisOuTL30.ITIM-CJ.RO>spam_OUTspamTakeThisOuTMITVMA.MIT.EDU>> image moved   30/11/2000 07:39
to file:
pic27005.pcx)





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Subject:  Re: [EE]: -ve supply rail.....creation (charge pump-ish)

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You'll find the doubler bridge schematics at
http://www.geocities.com/vsurducan/c520.htm
PS: Your ascii schematics are really mess...
vasile

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part 2 165 bytes content-type:application/octet-stream; (decode)

part 3 136 bytes
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2000\12\01@042118 by Peter L. Peres

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>some way

MAX232 ? Other higher power charge pumps (usually discrete, can have PIC
control). Usually charge pumps become bad choices as the required power
increases.

Peter

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