Power switch for Op-amp w/dual P/S

[Alan0354]

If you do dual supply, you have to be careful in what IC you use. They can latch up if the power sequence is not correct. I think opamp is usually safe to lost one rail, but many other IC will hung if the power up sequence is not right. I actually went to Linear Technologies to show them one of their ADC latched up with our power supply and they were red faced. That's the reason I did not go with single supply. If it is just opamps, it is very easy, definitely simpler than to have to extra transistors to turn voltages on.

Attached is a typical schematic that use single supply. Opamp is on +9V and ground. Input is biased a 4.5V. It is easy as they are all AC coupled. There is no power up or input being grounded problem.

[guitician]

It worked on my first tests. I'm trying a OPA1641 and it says that the absolute max PS is +/- 20, but the data section shows +/- 18 as the Max?
I added 1k2 series resistors to both rails during the tests to be safe, but they added hiss noise. I want to try it without them, but my new 9v batts are +/- 19.3 Vdc in pairs. Under 20, but over 18. I guess I could drop some volts across some diodes.

No caps at all in this circuit, due to the dual voltages. I may add an output cap because of what it may be plugged into.

[g1]

Are 9V rechargeables 9V, or less?

[guitician]

I bought 2 for a $1 9V carbon/zinc for testing, but will use alkaline when finished.

[PeanutNore]

Another way to do dual supply is to use a charge pump IC. You could use 2 batteries, or an 18v dc wall wart, to supply the +18v and the charge pump IC uses a flying capacitor to create a -18v supply from it as well. Then you can switch off the +18v which will cut the power to the charge pump, eliminating the -18v supply as well. You just need to select a charge pump with a switching frequency well over audio frequency.

[arcanek]

Are 9V rechargeables 9V, or less?

The most common ones are 8.4V. You can find some 9.6V ones, though. The best 9V are the ultralife ones if you can find them on sale. They're not rechargeable, though. Nowadays, you can find a wide array of LiPo batteries of just about any size.

[g1]

That's what I was hoping, the 8.4V ones would give him about +/-17 instead of 19. And they're rechargeable .

[guitician]

Yeah, I may look for those and use rechargeable batteries. I've had it connected for two days now and they all measure 8.5V with a light load. That's with leaving the Neg. supply connected and lifting just the Pos. supplies ground connection via the input jack when it's unplugged. Sounds real nice with no noise or oscillation. We'll see if it stays that way as they drain over the next few months.