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how can get -5V from +5 or +12?

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EEHobby

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I have to use a amplifier, it requires -5 supply. The power I have is +12V. How can get a -5V from a +5V or +12V. Thanks.
 

GlamZ

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Use a switch mode regulator to generate it, I seem to remember the MAX774 being a -5V generator. Depending on what you are planning on doing it may be advisable to follow the output with a 7905 linear regulator

If it simply an op-amp then simply a virtual ground!
 

IanP

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Have a look at DC/DC charge pumps converters ..
Pretty common configuration is Vout= - Vin ..
For example,
LM2662/3 will deliver -5V @ 200mA when supplied of +5V ..
MAX660 --> -5V @ 100mA
ICL7660(MAX660) --> -5V @ 20mA .. and so on ..

You can also consider generating -5V from +9 to +12V with 555 timer (see picture below, both diodes 1N4148, or similar)

Regards,
IanP
 

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throwaway18

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Read the forum. There is another active thread about this problem

(as johnsmith101 says the poeple suggesting it can be done with just an opamp are wrong)
 

GlamZ

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Throwaway. Please read my reply again.

I DID not say it could be done with an op-amp. I said if it was FOR an op amp you could use a negative earth.

ie. From the 12v supply available you could easily set-up an op-amp from a +6 / -6 supply using a virtual earth.

Since the original question made no reference to power requirements, or to why a -5V supply was needed it was just a guess at what might be being made.

Sorry, may have been my fault, the original may not have read too clearly but without what the full requirements are the replies can end up being massive as you try to second guess them.

regards.
 

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