He wants two outputs. The "regular" output and a mirror (or inverse or -180) of it.

Is that correct?

 

He wants two outputs. The "regular" output and a mirror (or inverse or -180) of it.

Is that correct?

Yes that's exactly correct.
Unfortunately, and though the results do appear to work out with square waves, I was not been able to accomplish this while changing wave types with the suggested configurations.

 

Ok, I got that, but I am still confused. Are you trying to mirror a square wave with a triangle wave, or sine wave?

It can be done, but it wouldn't be "bi-phasic".

 

Hi

The LM358 is lower maximum voltage than 741. http://www.ti.com.cn/cn/lit/ds/symlink/lm358.pdf

 

Here's a circuit that boosts the voltage output capability of an op amp.
It bootstraps the ±power so that it's always about a diode-drop below the 1N965 15V zener voltage.
Actually, lower voltage zeners could be used to reduce power dissipation in the op amp since you just need the minimum operating voltage across the amp.
The supply voltages can be lower, of course, to whatever is needed to get the desired peak output voltage plus the op amp supply voltage.

 

And so my guess is that the resistors used in the feedback loops which are clearly wrong

No, they aren't. You copied #12's schematic incorrectly. The left side of R1 does not go to GND. It connects to pin 2 of the opamp, forming an attenuator with R2. This sets the gain of the circuit.

However, that gain is incorrect. While the inverting output from U2 is the same amplitude as the input, the non-inverting output from U1 is at a gain of 2 even though it uses the same feedback resistor values. This is a consequence of the math of negative feedback circuits.

If you want unity gain through both circuits, the solution is to connect the left side of R1 to U1 pin 2 as mentioned, and eliminate R2 so that the non-inverting circuit is a voltage follower. If you want a gain of 2 in both circuits, leave R2 in the non-inverting circuit and double the value of R4 in the inverting circuit.

Besides the term "bi-phasic", other things are confusing. All of your scope images with two waveforms show then offset from each other by a DC voltage. Do you really want the two outputs to be at different average DC values, or did you offset them in the display for clarity?

ak

 

Ok, I got that, but I am still confused. Are you trying to mirror a square wave with a triangle wave, or sine wave?

It can be done, but it wouldn't be "bi-phasic".

What I'm looking for, is to mirror whatever input signal going into the amplifier. ie, if we send a sine wave into the inputs, then I'm looking for a bi-phasic(180°) sine wave on the outputs. same for a square, see-saw, inverted saw-tooth, and so-on and so-forth. That said, I want to use a dual op-amp to produce a 58v peak to peak signal between both signals

 

Hi

The LM358 is lower maximum voltage than 741. http://www.ti.com.cn/cn/lit/ds/symlink/lm358.pdf

I only need 28v p/channel

 

No, they aren't. You copied #12's schematic incorrectly. The left side of R1 does not go to GND. It connects to pin 2 of the opamp, forming an attenuator with R2. This sets the gain of the circuit.

However, that gain is incorrect. While the inverting output from U2 is the same amplitude as the input, the non-inverting output from U1 is at a gain of 2 even though it uses the same feedback resistor values. This is a consequence of the math of negative feedback circuits.

If you want unity gain through both circuits, the solution is to connect the left side of R1 to U1 pin 2 as mentioned, and eliminate R2 so that the non-inverting circuit is a voltage follower. If you want a gain of 2 in both circuits, leave R2 in the non-inverting circuit and double the value of R4 in the inverting circuit.

Besides the term "bi-phasic", other things are confusing. All of your scope images with two waveforms show then offset from each other by a DC voltage. Do you really want the two outputs to be at different average DC values, or did you offset them in the display for clarity?

ak

Hi AnalogKid and thanks so much for the correction.
I tried your first recommendation and low and behold it worked like a charm(see here);

However, when I then tried to replicate this same configuration with the LM358P *which are the packages that I have on hand, and found that it would not behave the same way in terms of output;

That said, would you have any ideas as to what might cause the discrepancy between both configurations and packages?

PS. You are correct on the dual channel scope analysis of the signal in that I wanted to show both sides of the waveform. Though under normal circumstances, I'd display the signal on a single channel to show the entire waveform(symmetrically).

 

Here's a circuit that boosts the voltage output capability of an op amp.
It bootstraps the ±power so that it's always about a diode-drop below the 1N965 15V zener voltage.
Actually, lower voltage zeners could be used to reduce power dissipation in the op amp since you just need the minimum operating voltage across the amp.
The supply voltages can be lower, of course, to whatever is needed to get the desired peak output voltage plus the op amp supply voltage.

Great crutschow,
That looks like a very handy circuit to use.
Thanks so much for sharing.

 

I would like to apologize for not finishing this out. You can see I was posting from 3 am to 6 am. That's because I was unable to sleep due to muscle spasms in my upper back. My first response was to list op-amps which can handle this voltage without external boosters. All in all, I missed the copy mistake of JBee and did not have the patience to persuade him to use the right amplifier chip.

I got a Chiropractor to pop a few things back into place today and expect to be recovering for a couple more days.
Don't worry. Pulled muscles and such are a normal part of my life. It just takes a few days to heal.

 

That said, I want to use a dual op-amp to produce a 58v peak to peak signal between both signals

Peak to peak is a value defined wrt specific points of one signal. The sentence above makes no sense to me.

 

Peak to peak is a value defined wrt specific points of one signal. The sentence above makes no sense to me.

I meant to say between both outputs (same signal)

 

I tried your first recommendation and low and behold it worked like a charm(see here);
However, when I then tried to replicate this same configuration with the LM358P *which are the packages that I have on hand, and found that it would not behave the same way in terms of output;That said, would you have any ideas as to what might cause the discrepancy between both configurations and packages.

Same answer as before - look at your own schematics. The 747 is powered from +27 V and -27 V. The 358 is powered from +27 V and GND. That other -27 V of headroom is important. The output of an opamp can *not* exceed either of its power supply rails.

After 33 posts, I think I know what you want to do - take a single-ended signal in and produce two outputs 180 degrees out of phase but with the same ground reference so a differential load will see twice the source voltage. In the audio power amp world this is called a BTL circuit - Bridge-Tied Load.

EDIT: Removed incorrect paragraph.

ak

 

"The packages you have on hand" can *not* do this. "Normal" opamps rarely have operating voltages greater than +/-22 V and do not have rail-to-rail outputs, so the most you can expect from your circuit is about +/-40 V; a 58 V differential output is not possible with these parts. The circuit in post #25 is one of several ways to increase the operating voltage range or output current range of an opamp, but it needs a lot of headroom and does not work with quad or dual opamps like the 358. Reconsider high voltage opamps as a less complex overall solution.

Please see this working sketch of lm358 used to produce 57v(peak to peak) bi-phasic output. The problem with this particular configuration however, is that I am not able to reconfigure it for signal generator input rather than with the capacitor and resistor oscillator configuration.

 

After 33 posts, I think I know what you want to do - take a single-ended signal in and produce two outputs 180 degrees out of phase but with the same ground reference so a differential load will see twice the source voltage.

I can confirm the first portion(single input, double output(out of phase). Though I must admit that the remainder of the post is outside my knowledge and capacity.

That said, my hope was that I could simply reconfigure the sketch shown above to accept a signal generator input to get the job done. Though it's beginning to look as though this may not be possible.

 

I removed an incorrect paragraph from my previous response. oops.

The circuit in post #35 is a classic opamp multivibrator (hysteretic oscillator) followed by a comparator acting as an inverter. Neither opamp is operating in a linear manner, but you are correct that the basic configuration is what you want (The second schematic in post #29 will do what you want when fixed, as will #12's posts #13 or #14).

After way too long, I've hit upon your problem - and it is not your fault. The data sheet for the LM358 has the negative voltage power input pin labeled as GND instead of Vee. THIS IS WRONG, and has been wrong since 1971. That pin can be connected the same as the negative power pin of any normal opamp. The LM358 was unique in its day because the part could interact with digital logic circuits if the V- pin were connected to GND, but this was not a requirement for just about anything else. The part is rated for 32 V between Vcc and Vee (GND). If you simulate it with +/-16 V, you should get the correct outputs.

BUT - the post #29 schematic still has different gains for the two output signals. I recommend using #12's schematic in post #13. This one has two advantages. First, the first gain stage affects both output phases equally, making the circuit much easier to adapt to various input signal amplitudes. Second, the inverting stage is driven by the non-inverting stage output, so if there is any distortion there caused by its load, that distortion is mirrored in the inverted output. This is a better approximation of a true balanced output.

ak

 

BUT - the post #29 schematic still has different gains for the two output signals. I recommend using #12's schematic in post #13. This one has two advantages. First, the first gain stage affects both output phases equally, making the circuit much easier to adapt to various input signal amplitudes. Second, the inverting stage is driven by the non-inverting stage output, so if there is any distortion there caused by its load, that distortion is mirrored in the inverted output. This is a better approximation of a true balanced output.

Hello again AnalogKid, and thanks so much for your ongoing help with this.
That said, I tried running one of the configurations you mentioned at an earlier time but couldn't get the output to display properly. And so I wanted to ask if you could take a look and hopefully identify what it is I did wrong?

 

I recommend using #12...

PS. I based the sketch on the following schematic;

 

The COM pin of the signal generator is tied to GND, which is the negative power connection for the opamp. This means that the opamp output is trying to swing below GND because that's where part of the input signal is. There are several ways to fix this. First, to test what is happening, change the LM358 pin 8 connection to +15V, and change the pin 4 connection to -15V.

ak