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Old 8th September 2013, 11:51 AM   #1
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Default 12 volt power supply

I need to invert +12 volt to - 12 volt dc so that I can use both for op-amps. How please?
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Old 8th September 2013, 03:47 PM   #2
Minion is offline Minion  Canada
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Maybe explain in more detail what you want to do . Like why do you need -12v ??
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Old 8th September 2013, 04:11 PM   #3
John8 is offline John8  United Kingdom
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If it is just for a couple of op-amps have you looked at the ICL7660A voltage multiplier chip run in the inverting mode. This will generate -12V from +12V.
Alternatively use a +6V supply as a virtual ground for the op-amps if you don't need a large voltage swing.
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Old 8th September 2013, 04:17 PM   #4
gootee is offline gootee  United States
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Is it for a bench supply, or an automotive application, or a portable (batteries)?

If it's just for use where there are wall outlets, or for "lab" use, you can use two 12v wall warts and connect the negative of one to the positive of the other and call it ground.
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Old 8th September 2013, 05:24 PM   #5
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Quote:
Originally Posted by Minion View Post
Maybe explain in more detail what you want to do . Like why do you need -12v ??
Most op amps, e.g. TL071 run on "dual rail" (e.g. + 12 and -12 volts) I have +12. Need - 12 for TL071

Last edited by stoppage; 8th September 2013 at 05:28 PM. Reason: forgot something
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Old 8th September 2013, 05:51 PM   #6
gootee is offline gootee  United States
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How much current or power is available from your existing 12-Volt supply? What type of supply is it?

Also, there are several other possible (and possibly better) ways to obtain or build a bi-polar bench supply. Are you looking for the cheapest way, or the easiest way, or would a better way be something that you would want to consider?
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Old 8th September 2013, 08:58 PM   #7
dangus is offline dangus  Canada
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I might be tempted to buy a DC-DC converter module. For maximum quality, I'd use one with +/-15V outputs and regulate down to +/- 12V with linear regulators.

MC34063 switching regulators are found in nearly every car cellphone and USB charger. The application note clearly shows how to hook one up for negative output, and board layouts are provided, if you can't easily alter the charger layout.
http://www.onsemi.com/pub_link/Colla...MC34063A-D.PDF
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Old 8th September 2013, 09:02 PM   #8
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Most opamps are very happy with + and - 15 volt supplies. No need to regulate them down to + and - 12 volts.
We really need more information from stoppage so that we can understand why he can't just use a bipolar supply.
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Old 8th September 2013, 09:49 PM   #9
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Quote:
Originally Posted by gootee View Post
How much current or power is available from your existing 12-Volt supply? What type of supply is it?

Also, there are several other possible (and possibly better) ways to obtain or build a bi-polar bench supply. Are you looking for the cheapest way, or the easiest way, or would a better way be something that you would want to consider?
P { margin-bottom: 0.08in; } „S-60-15 - 60W 15V 4A Enclosed Switching Power Supply“
S-60-15 - 60W 15V 4A Enclosed Switching Power Supply
Its a 15 volt adjusted down. I just need a reasonable-quality - (minus)12/-15 volt supply for opamps so that I don't have to bother with "virtual earth" etc
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Old 8th September 2013, 10:08 PM   #10
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An inverter IC is likely your best bet. Even the 555 will do the job, and there are many others, for instance the ICL7660 and MC34063 already mentioned. Maxim, On Semi, TI, etc. probably all have a few varieties.
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