±5V from up to +12v

Further complications...

The spice models for 7805's are less than robust... they're capable of sinking current, which no real 7805 can do. ...Jim Thompson

Grin, Hey, the TCA0372's are burning a hole in my parts bin :^) (maybe the OP only needs ~100mA) I must admit when you (or someone else?) pointed out these 1 amp IC's in a dip8 package I was a bit 'concerned'. (I'd really like a nice to-220 style metal tab.. or a surface mount with 'power pads' on the bottom.)

George H.

Just how strict is the need for +/- 5V? With a 7905 you could make a "strict" 5V supply, with the ground to negative voltage being whatever is left over. The diagram shows what you'd get with your 12V supply, assuming that it's actually 12V in practice:

V+ o------------o------------o +5V | .-----. .--| |---------o GND | '-----' | LM7905 V- o------o------------------o -7V

As with other circuits using the LM7x05, you need to make sure that the current is flowing the correct direction at the "out" pin -- in this case the ground current would need to have a net flow from the +5V rail, or the chip would fall out of regulation.

They're amazingly useful if you think of them as a 100-200 mA part with a lot of overload capacity and a very nice low Zout.

I recently used them to make a single-ended high-Z front end amplifier whose input could be biased +-5V from ground. I used voltage regulators to make the +-5, referenced to the "adjustable ground" at the output of a TCA0372. Worked great, and for half a buck, they're unbeatable. I agree, it would be great if they came in a power pad package. Of course there's always the LM675 for that, but it isn't half a buck!

Cheers

Phil Hobbs

Here you go....

...Jim Thompson

If you only need a watt or two, there are cheap SIP dc/dc converters that will do this.

Daniel Pitts wrote in news:hbRdu.262470$ snipped-for-privacy@fx29.iad:

The other replies have covered in some detail the disadvantages of starting with +12V DC in.

Do you have any adapters with AC output between 8V and 12V (RMS)?

If so, a much better approach would be to half-wave rectify the AC with a diode and electrolytic reservoir capacitor for each supply to get positive and negative unregulated supplies with a common 0V, then using

A 8 or 9V AC supply is ideal for +/-5V output, but higer voltages can be used although the regulators will run hotter. Component choices depend on input voltage, load current on each output and mains supply frequency, so tell us what AC output supplies you have available (nominal voltage and current + measured output voltage unloaded) and the required output currents so we can help you pick the best one.

If you dont have any AC output adapters, the use of a DC-DC converter module to get a negative rail has already been mentioned. There are a few issues with ripple on the output, and potentially with power supply sequencing so you had better tell us which volume control chip you intend to use.

Is there a program to interpret that script? Hopefully one that runs on Mac, DOSBOX, or the web?

Thanks, Daniel.

LTspice IV download from

petrus bitbyter

Thanks! I'll see if this is in my capability to understand and build, but it looks nice at first glance.

Thanks for all the suggestions everyone. I see how my original thoughts were flawed.

I also realized I should probably get a better idea of what my amperage will be. I'm guessing

I think the TL431 is still readily available. Back when I did more discrete designs it was my favorite reference device... AND it can act like an OpAmp (as in your case). ...Jim Thompson

Looks like I can get some.

Idea:

• Use a 5V (unregulated) adapter. Regulate to 5V with a 7805.

• Use a charge pump IC to generate a -5V rail from the regulated +5V rail.

You can get a center-tapped transformer for a couple of dollars, or rip it out of something. You can build your own dual-voltage AC adapter easily with a center tapped transformer and bridge rectifier or discrete diodes. Your device then just has to provide the reservoir capacitors and regulators.

Why not find some discarded old device (e.g. piece of audio gear) which has a dual supply in it already and re-use its power entry and perhaps more. Throw out the circuit board and build your own device in its place.

You can also use two identical AC adapters to get the equivalent of a center-tapped transformer, if you can live with the clunkiness.

I just scabbed an old DC drive that had a lots of pulse transformers for the SCR's, nice ones too. Also, I got the dual SCR's and full heat sink which like 10x15 inches..

I save parts like this for bench concept theories and home projects, anything else, like at work, we buy new stuff. But saving parts from these large units gives lots of parts you can hang together with jumper wires (fuses) as some one I know referred to them, and experiment.

Jamie