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-5V PSU out of +5V or +9V

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neazoi

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Hello,
I am trying to find a schematic for a -5V PSU that can be derived from +5V or +9V input voltage. Current consumption is about 300-500mA. My transformer has not gor a center tap. I would like to use a +9v from a jack wall

I am going to use this to feed some opamps
The simplest the better, I would prever the use of linear regulators.

Thank you
 
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kapilp

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You can use MAX660 by National Semi. Works good. Check the datasheet for details. Are you sure your op-amps will consume 300-500mA? Try to verify that with a table top dc power supply.
 
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neazoi

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I am trying to make a circuit to replace this one. I would make this one if I could find the details of the coil used.

I avoid MAX chips because maxim stops the production of specific types afrer some years.
 

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kapilp

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the series that i gave you is easily replaceable by other manufacturers like Maxim/National/Linear/Intersil, with varying performance for same pinout ... you should have no issues in finding a replacement. In any case the manufacturer is National and the part is very popular
 
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neazoi

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is there a military ceramic package version of it?
 

kapilp

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i dont think so .... check the datasheets and websites of manufacturers quoted above ... you should be able to find something of interest
 
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The easiest method would be to use a 9Vdc wall adapter just for the -5V regulator. They're cheap too.
 
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saikat36

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Easiest way to get -5V from +9V is to use Voltage regulator 7905.
 
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betwixt

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Ignore Saikat36's last reply, it's nonsense!

The 7660 and it's clones has been available for years and will be around for a long time yet. The schematic you show is to generate +12V as well as -5V so it is more complicated than necessary. Your current requirement is quite high so the schematic wouldn't manage to cope anyway. I suggest you look at DC-DC converters which you buy as small plastic packages and have isolated outputs. Either you could get one with "+5 0v -5V" which has the advantage that the + and - outputs track each other, this might help to keep op-amp center rails at 0V, or you can get a single +5V output and reverse the output pins so it gives you -5 out. The outputs are isolated from the input supply so it's quite safe to do that.

Brian.
 
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kapilp

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The DC-DC converters mentioned by Brian usually are described as being 'awesome'/'great' depending on manufacturer. You will get them for all sorts of specifications for +/-5V output. But they also tend to cost a little more than other options.
I still recommend that you try out the circuit with a lab power supply (opamps using 800mA current seems a little too much), get the optimum current requirement and then evaluate the options given in this forum.
 
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neazoi

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Easiest way to get -5V from +9V is to use Voltage regulator 7905.
You cannot. the 7905 requires a negative input voltage.

---------- Post added at 13:16 ---------- Previous post was at 13:15 ----------

Thanks a lot guys
 

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Sorry for unintentionally giving wrong information.
 
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BradtheRad

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Here's a clever method to obtain a negative supply from positive pulses.

www.edaboard.com/attachments/8893d1115569736-555_179.gif

Also:

newelectronicdesings2011.blogspot.com/2009/11/negative-supply-from-single-positive.html

Provides low power only. If you want more than a few mA...

Then you'll send the oscillator pulses to drive a mosfet. It will chop the pure + supply DC. Then you send that through the conversion stage. Use higher value capacitors depending.
 
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saikat36

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Your procedure is too messy to implement mate.
Can anybody suggest atleast simpler process than that?
 
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neazoi

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Here's a clever method to obtain a negative supply from positive pulses.

www.edaboard.com/attachments/8893d1115569736-555_179.gif

Also:

newelectronicdesings2011.blogspot.com/2009/11/negative-supply-from-single-positive.html

Provides low power only. If you want more than a few mA...

Then you'll send the oscillator pulses to drive a mosfet. It will chop the pure + supply DC. Then you send that through the conversion stage. Use higher value capacitors depending.

I have seen that before. It works, but only for low current. I do not believe it can provide 300-500mA of current as it is.
I am interested to see the final though
 

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I have seen that before. It works, but only for low current. I do not believe it can provide 300-500mA of current as it is.
I am interested to see the final though
Now that I refresh my memory using the circuit simulator...

To get more power it won't work to simply chop the supply with a mosfet.

The device that provides pulses has to both source and sink current.

More like a hi power op amp. It must have very low ON resistance at the output pin.
 
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memarian

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neazoi

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These integrated solutions all work I am pretty sure and thank you.

Has anyone seen a way todo it using discrete components and avoiding the tapped coil?
 

betwixt

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Look up the 8 pin IC called MC34063A, they are very inexpensive and can be wired to provide a regulated step-up, step-down or voltage inversion with a negative output in excess of 100mA. The data sheet shows how to do it and you only need one single coil inductor which you can buy or wind yourself.

Brian.
 

memarian

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These integrated solutions all work I am pretty sure and thank you.

Has anyone seen a way todo it using discrete components and avoiding the tapped coil?
Hi,

For Discrete implementation , take a look at Buck-Boost topology. All of these integrated circuits use this.Take a look at these :

Wikipedia Buck-Boost Converter
http://pdfserv.maxim-ic.com/en/an/AN660.pdf
http://www.fairchildsemi.com/onlineseminars/regularTopologies_implementations.pdf
http://www.ceet.niu.edu/faculty/zinger/research/thesis/chandran/13.pdf
 

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