### Author Topic: Negative voltage in circuit  (Read 1399 times)

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#### Vindhyachal.takniki

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##### Negative voltage in circuit
« on: February 12, 2015, 09:11:48 pm »
I need negative voltage in my circuit with common ground wrt positive voltage

1. One option is to generate negative supply by placing a full- bridhe & then using 7905.
It includes lots of extra components to be used.
2. Another option is to use TC7660. Simple to use & works good. Only problem is its output voltage falls with current. For a load current of -10 mA and a supply voltage of +5V, the output voltage would be -4.3V.

3.I need to generate regulated -5V,-2.5V&-1.8V

4.Any other way to do that?

#### kg4arn

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##### Re: Negative voltage in circuit
« Reply #1 on: February 12, 2015, 09:31:51 pm »
What is the current demand for each negative supply?

#### Vindhyachal.takniki

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##### Re: Negative voltage in circuit
« Reply #2 on: February 12, 2015, 10:02:31 pm »
50mA max.

#### electr_peter

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##### Re: Negative voltage in circuit
« Reply #3 on: February 13, 2015, 03:11:53 am »
How do you power your circuit? If you have spare transformer tap, use that.
Other option would be inverting DC/DC voltage inverter. There are also isolated DC/DC 5V in/5V out converters (at a higher cost of course).

#### IanB

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##### Re: Negative voltage in circuit
« Reply #4 on: February 13, 2015, 04:25:11 am »
If you are powering your circuit with low voltage AC from a transformer then can't you just rig up a voltage inverting leg off the AC source? (I think it only needs a couple of diodes and a couple of capacitors. Both are cheap jelly-bean components.)
I'm not an EE--what am I doing here?

#### mariush

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##### Re: Negative voltage in circuit
« Reply #5 on: February 13, 2015, 04:42:46 am »
If you don't want to complicate your life with multiple taps on transformer, you could also resort to using a cheap mc34063 switching regulator in inverting mode :  http://www.intusoft.com/onsemipdfs/AN920-D.pdf

There's a software on Sourceforge which makes the math super easy: http://sourceforge.net/projects/mc34063uc/

Smf