negative supply

t.man said:

how can one make a negative voltage supply? would interchanging the wires of, say a 12V adapater, suffice?

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ericgibbs said:

hi t,

Buy a mains 12V dc plug adaptor and you can use it either has a +12V or -12V supply, connect the +V lead to your circuit 0V/common and the other lead is the -V12.

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t.man said:

i dont know if i get you. are u saying i should connect ,what i normally use as +12V lead, to 0V/GND . because when i use multimeter i can see when i interchange leads i measure negative voltage.

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ericgibbs said:

If you use separate 12Vdc psu adaptor, connect the +12V lead to 0V ground and the other lead is -12V.

Think of it like a 12V battery, you can connect those either way around to give a +V or -V with respect to 0V.

OK.?

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t.man said:

I can not use the same psu adapter to provide both +V and -V?

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Exactly what are you trying to do with these supplies.?

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t.man said:

it is for this amplifier circuit. it uses LF442-CN. so i can see it'll require +15V and -15V. am i right?

if yes, how can i supply these voltages?

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ericgibbs said:

hi,

Are you amplifying ac or dc signals, and ver what range of input/output voltages.?

Do you have a circuit diagram.?

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t.man said:

i think its dc. im not sure of input signals but output runs from 0 to about 2.5V or something like that

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ericgibbs said:

hi t,
The input pin3 is grounded, but you have a 10K going to 15V on pin3.? also a 10uF.?

You could consider using a 7660 -Voltage generator ic, running from the +V rail to give a negative voltage.
There are more modern/better devices than the 7660, but it will give you an idea.

If an output voltage of close to 0V to say +2.5Vdc is OK, it would be possible to use a OPA that will work from a single supply.

EDIT:
You could build one of these 555's

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t.man said:

use this as -V supply?

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ericgibbs said:

hi t,
The input pin3 is grounded, but you have a 10K going to 15V on pin3.? also a 10uF.?

You could consider using a 7660 -Voltage generator ic, running from the +V rail to give a negative voltage.
There are more modern/better devices than the 7660, but it will give you an idea.

If an output voltage of close to 0V to say +2.5Vdc is OK, it would be possible to use a OPA that will work from a single supply.

EDIT:
You could build one of these 555's

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t.man said:

which 555? LM or NE?

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ericgibbs said:

hi t,
I would use a TTL version, IIRC they can output about 200mA.

EDIT: added a data extract.

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t.man said:

so i only use my +12V supply as input to VCC and ground and i get -VCC as output to supply my circuit?

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ericgibbs said:

hi,
Thats the way its usually done.

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t.man said:

hi, i want to check the items at the store, what values are the caps? i.e is it 220uF and 0.05uF?

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