Voltage Inverter Coming Out Uneven

[Box_Stuffer]

I built this 555 voltage Inverter.





My One Spot power supply produces 9.5 volts, but only 8.5 volts is coming out of the inverter. I have it plugged into a breadboard op-amp circuit and it is working. But, that means that the op-amp is getting 9.5v at the positive pin and -8.5v at the ground pin. Will I get any negative effects running it this way? What can I do to get closer to 9 volts?

[drdn0]

I built this 555 voltage Inverter.





My One Spot power supply produces 9.5 volts, but only 8.5 volts is coming out of the inverter. I have it plugged into a breadboard op-amp circuit and it is working. But, that means that the op-amp is getting 9.5v at the positive pin and -8.5v at the ground pin. Will I get any negative effects running it this way? What can I do to get closer to 9 volts?

Some slight asymmetricality in output headroom, but probably not noticeable whatsoever. There are going to be voltage losses across the diodes, and if you're using rectifier diodes like 1N4007's it's going to be 0.7v per diode. 


Ps. just use something like a LT1054 in the future. Less parts, much less complexity, you're not ending up with something that's functioning close to the audio band (a quick Google suggests this is operating at only 20khz; I haven't done the math though) and the costs are utterly trivial. It might have made sense when 1054's were $15 or more, but given they're currently under $5AUD from Mouser there's zero reason to use a 555.

[R.G.]

drdn0 is right on all counts.
Each diode takes a bite off the resulting negative voltage. The defined-purpose inverters like the LT1054 do better, but even these will have some losses; fortunately, this won't matter much to most pedal-oriented uses. And the 555 has problems in pedal use, not lelast because the non-CMOS versions (which have to be used for power inverters making current) have bad problems making noise. They pull a few hundred milliamperes of current on power and ground for a short time on every output transition. The pulses are hard to keep out of your audio.