SparkFun Forums

[mattltm]

Hi all,

I have an item of equipment that I need to run from a 12v DC supply. The item is a headphone amp that currently runs from a 9V AC wall wart.

Inside, the 9V AC is converted down to +9v DC, Ground and -9v DC. This supply then goes into an array of V4580L Op Amps.

I have found a point where I can inject +9v DC, ground and -9v DC and figured that the easiest way to get it running from 12v DC would be to build a dual rail power supply using a TS7809 and a TS7909 regulator.

The TS7809 is easy but i'm a bit confused about the TS7909. I've never built a -ve supply before and i'm not sure in my head how it works! Does the regulator go on the -12v line and the +12v become the ground? Where does the common ground come from? The -12v?

I have found a few examples online showing how to build a dual rail supply using the ts78xx and ts79xx but they all show a 120/240v input and i'm not sure how to modify the circuit for a 12v DC input.

Can anyone help me out here as my head is starting to hurt!

[n1ist]

That technique won't work as the 7909 needs a negative supply for it to regulate. Probably the easiest would be to use a DC-DC converter module (either a 12VDC in to +/-9VDC out or an isolated 12VDC in to 9VDC out one for -9V and a 7809 for +9V)

Depending on the circuit, you may be able to modify it to run on +/-6V and create a virtual ground with a resistor divider and buffer.
/mike

[mattltm]

Thanks. Thats why I was getting confused!

I have an ICL7660 in the junk draw so I guess I could use that to get a 12V + and - supply then feed into the 2 regulators. Or I could use the 7809 to put 9v into the 7660 and get the + and - 9v that way.

I think I may try the virtual ground first and see if it operates with +/- 6v.

Whats the best option?

[viskr]

As you've got an ICL7660, I'd go with that to generate the -12V. The V4580L will operate up to +/-15V supplies. Just make sure your 12V supply really is 12V and not a lot more (which it might be if it is just a cheap linear walwort).

In any case you will have to filter the switching noise from the supply, but that might be as easy as a small R and a big C.

A virtual ground may work as well, but 6V may not be enough for the headphones. If you have a scope a quick check of voltage levels going into the headphones would tell you (no most meters are too slow to measure that).