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Old 1st Aug 2020, 1:34 pm   #21
merlinmaxwell
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Default Re: Device to simulate a dual rail power supply from a single DC source

Now I must do something that uses the op amp power rail trick for fun, I wonder how using the power pins has a different frequency/phase relationship with a "normal" output pin. Probably not much if a sufficient current is taken.
At work I am (using a current and horrible term) "mentoring" a young, knowledgeable, thinking electronics engineer, I must tell him about this.

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Old 1st Aug 2020, 1:51 pm   #22
Mooly
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Default Re: Device to simulate a dual rail power supply from a single DC source

I added a simple 'virtual ground' option thus giving a split supply to one of my old Farnell PSU's. These had three terminals on the front (one is never used and for constant current as I recall).

I used an opamp (741 I think) and pair of small complementary output transistors with simple current limiting for each. So the virtual ground gives a split rail to whatever the main supply is set at and with a 100ma limit per rail.

It has proved invaluable over the years.
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Old 1st Aug 2020, 3:10 pm   #23
Refugee
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Default Re: Device to simulate a dual rail power supply from a single DC source

You can get dual rail bench power supplies.
I have got one.
It is a real pain if the output terminals get loose though.
https://www.vintage-radio.net/forum/...ad.php?t=89688
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Old 16th Aug 2020, 5:31 pm   #24
bikerhifinut
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Default Re: Device to simulate a dual rail power supply from a single DC source

I spotted this and it looks promising for a low current opamp job, I think it would work as well with an LM386? because I have a few looking for a job to do.

Does the potentiometer have to be 1 meg?

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Old 16th Aug 2020, 5:43 pm   #25
merlinmaxwell
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Default Re: Device to simulate a dual rail power supply from a single DC source

I don't think the opamp would be very happy driving all that capacitance, electrolytics may have enough series resistance to make it work.
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Old 16th Aug 2020, 6:26 pm   #26
bikerhifinut
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Default Re: Device to simulate a dual rail power supply from a single DC source

Quote:
Originally Posted by merlinmaxwell View Post
I don't think the opamp would be very happy driving all that capacitance, electrolytics may have enough series resistance to make it work.
Its an LM386 small power amp chip Merlin, however going back through the thread it has been noted by Mark hennesy that I would be limited to +/- 6V which aint enough so I think its down to using another circuit.

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Old 16th Aug 2020, 8:09 pm   #27
AdrianH
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Default Re: Device to simulate a dual rail power supply from a single DC source

Back to I think the original enquiry, not sure if anyone has already suggested the device but I have used a couple of NMA1215SC units in the past, single 12 Volt in that particular part provides plus and minus 15 Volts at 100mA, there were other outputs as well such as the NMA1212SC for 12 Volts etc.

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Old 16th Aug 2020, 9:08 pm   #28
radioman
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Default Re: Device to simulate a dual rail power supply from a single DC source

A few years ago, a power op-amp like the L165 could be used for this application.
Here's the example from the datasheet :-

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Old 16th Aug 2020, 11:07 pm   #29
bikerhifinut
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Default Re: Device to simulate a dual rail power supply from a single DC source

That looks more like it.
Is the L165 still a current device?
If not what is a suitable currently available option?
The circuits a bit more sophisticated than the one I spotted but looks much more like what I need and shouldn't take up too much space.


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Old 18th Aug 2020, 11:06 am   #30
bikerhifinut
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Default Re: Device to simulate a dual rail power supply from a single DC source

I've ordered 5 x L165 from eBay, it seems nobody over here supplies them any more.
I hope they are genuine, they were only 9.50 all in though so its basically 2 pints and a bag of crisps that currently I am not enjoying regularly.
When they arrive I shall report back with results as I feel sure there are others in my situation.

A.
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