Positive To Negative Voltage DC-DC Converter?

• Mar 17, 2006

• #1

U

ulaska

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dc positive to negative converter

Hello,

i need to build a DC-DC converter.

input (+12V) --> output (-5V) min 1.5A

i found some switching Regulators, ie. LM2576. but i cannot see a true regulated -5 V Voltage, there was some peaks -7V, also output current is low.

can you please suggest me a solution with minimum parts

thank you.

 

• Mar 17, 2006

• #2

I

IanP

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positive to negative voltage

To build a dc-dc converter that can generate stabile negative output voltages you will have to use a transformer ..
Take a look at the attached circuit.
Although it was designed to convert +V to +V, by changing the polarity of assorted components at the secondary site you will be able to generate required negative voltage ie. +V to -V ..
The LM385 looks like an obsolete part, but it can be easily replaced by the LM431 shunt regulator ..

Regards,
IanP

 

• Mar 17, 2006

• #3

Davood Amerion

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dc to negative dc converter

Hi ulaska;
do you see this circuit in LM2576 datasheet?

it is 0.7A at -12V but i think for -5V current reach to 1.5A
you can check it.
(use LM2576-5 inseted of LM2576-12)

regards,
Davood.

 

• Mar 18, 2006

• #4

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ulaska

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negative dc dc converter

i have made this circuit in the attechment.

when i looked the output signal with an oscilloscope , but there was spikes on the output signal , +/-1V.

how can i smooth the output negative signal.?

thank you.

 

• Mar 18, 2006

• #5

Davood Amerion

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positive negative converter

Hi ulaska
Use good electrolitc capacitor (low ESR) and use extra capacitors 0.1uF
(DISK or multilayer) parallel with output capacitor.
Or yo could use LC filter circuit in output,
with L=100-150uH and same capacitor.

Regards,
Davood.

 

• Mar 19, 2006

• #6

R

rextor

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negative voltage dc dc

if this material could help u building ur DC-DC converter design

 

• Mar 19, 2006

• #7

R

rextor

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dc negative converter

try this reference as wel....

 

• Mar 19, 2006

• #8

R

rextor

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positive to negative converter

some more ref. for ur project....

 

• Mar 25, 2006

• #9

U

ulaska

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positive to negative voltage converter

Hello, and thanks all.

We modified it , according to Davoods' circuit.

also placed the Diode and L1 (and C2) near to IC.

also output LC , L=20uH, c= 100uF.

now the -5V volt is very smooth. i suggest this circuit. it needs a few component.

thanks all.

 

• Feb 15, 2007

• #10

saeed_pk

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negative dc-dc converter

There is another method for smoothing -5 volt use 7905 regulator with a 10 µF Cap .

 

• Feb 17, 2007

• #11

asas

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dc-dc converter, negative output

The most practial away is to use a 7905 regulator, llike saeed_pk said!!

This may help:

 

• Mar 1, 2007

• #12

A

ashad

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lm2576 negative converter

i also used the ICL7660 but the output current is only 45mAmp

 

• Jun 27, 2009

• #13

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y_bother

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convert dc positive to dc negative

HI ALL
i need to get a -12 V from the car battary with at leaat 1.5 A
any ideas?

thanx in advance

 

• May 29, 2010

• #14

B

bcjrstan

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I use Davoods' circuit. but i get only -1.23v output , other than -5v .
any help or suggestion.
thanks

 

• Jun 30, 2010

• #15

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taiatran

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Re: dc to negative dc converter

Hi Davood,

Your suggested circuit is almost the one I am looking for a Positive to negative -12V, but need a little more current output to at least -1.2A.

- Is it possible that I can double the output current from -0.7A to -1.4A by connecting two output of Lm2576-12 together in this circuit?

-Or use other similar IC with higher current LM2677-12 with 5A step-down voltage regulator?.

I need to dc-dc convert and regulate from a 19.5V 3.34A ac to dc laptop adapter and need dual Pos & Neg +12V 1.2A, and -12V 1.2A Max supply for my power opamp opa564 circuit.

Thanks & regards,

Tai
taiatran@yahoo.com