How Can I Adjust Vcc to Correct a 10V Output on my Amp Power Supply?

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Discussion Overview

The discussion revolves around adjusting the supply voltage (Vcc) to achieve a desired output voltage from an operational amplifier in a bi-state multivibrator circuit. Participants explore the relationship between Vcc and output saturation, as well as potential circuit configurations to improve performance.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant notes that when setting Vcc to 10V, the maximum output is approximately 9.18V, questioning if there is a factor in the datasheet that accounts for this discrepancy.
  • Another participant provides the equation Vout = A(Vp - Vn), suggesting that increasing Vcc could change the output range, while also noting the theoretical saturation limits of the op-amp.
  • A participant emphasizes that practical saturation occurs at a lower voltage than Vcc, proposing that to achieve a 10V output, Vcc should be increased to around 10.66V.
  • One participant suggests using a voltage comparator with specific configurations to potentially solve the saturation issue, while another inquires about the specific circuit being used.
  • Another participant mentions being limited to using resistors, op-amps, and capacitors, describing their circuit as a waveform generator and expressing concerns about saturation at lower Vcc values.
  • A suggestion is made to use a rail-to-rail-output op-amp, specifically the Linear LTC1152, to achieve the desired output without saturation.
  • One participant refers to the TL08x series datasheet, indicating that to achieve ±10V output, at least ±11.2V supplies are necessary, and suggests testing with ±12V supplies.
  • Another participant shares their experience with a 15V Vcc on a 741 op-amp, noting that the maximum output is about 13V and indicating a plan to adjust the amplitude to reach the desired output.

Areas of Agreement / Disagreement

Participants express various approaches to addressing the output saturation issue, with no consensus on a single solution. Multiple competing views on circuit design and voltage requirements remain present throughout the discussion.

Contextual Notes

Participants reference specific op-amp models and their datasheets, indicating that performance may vary based on the chosen components and configurations. There is mention of the need for empirical testing to establish output characteristics under different conditions.

Who May Find This Useful

Individuals interested in operational amplifier design, circuit optimization, and those facing similar issues with output saturation in electronic circuits may find this discussion relevant.

unknown_2
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Hi, I'm trying to understand how to correct when you put Vcc as 10V your max output is like 9.18V. Is there a factor on the data sheet or what? I'm trying to build a bi-state multivibrator to generate a 10V peak value but it's being saturated.


thanks.
 
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Vout = A(Vp-Vn)

A = open loop gain specified by op amp (usually around x10^5)
Vp = non-inverting input
Vn = inverting input

Vcc is normally around tens of volts. Have you tried increasing it to change the range?

Based on the eq above, in the linear range:

-Vcc< Vout < -Vcc
 
Last edited:
What is your output circuit?

Bob S
 
well open loop gain is so big that it'll, ideally saturate at Vcc and -Vcc. but practically it'll saturate at a lower value ( 10V saturate to 9.11V). i want to increase Vcc and -Vcc such that i can compensate for this decrease in output voltage. so in order to saturate at say 10V I need to increase Vcc and -Vcc to a higher number like 10.66V to compensate.
 
looking for a way to calculate it so i can apply it to different Vcc voltages
 
Why don't you use a voltage comparator with an npn open collector output with a resistor pullup, or a pnp collector output with the emitter tied to Vcc? What circuit are you using?

Bob S
 
i'm limited to resistors, opamps and capacitors. My full circuit it a waveform generator. the bi-state multivibrator output is acting as a square wave generator. and i want a 8vp-p value. but if i put 4V and -4V for Vcc and -Vcc it'll def be saturated and inaccurate.
 
unknown_2 said:
Hi, I'm trying to understand how to correct when you put Vcc as 10V your max output is like 9.18V. Is there a factor on the data sheet or what? I'm trying to build a bi-state multivibrator to generate a 10V peak value but it's being saturated.thanks.
I don't know if all datasheets follow the same convention, but for the TL08x series, TI uses VOM for the maximum output voltage. Look at Figure 10 on p. 10 at

http://focus.ti.com/lit/ds/symlink/tl081a.pdf

It is a graph of max. peak output voltage vs. supply voltage, under 10 kΩ load. So for that type of op-amp, you'd need at least ±11.2V supplies to get ±10V out.

Also, the specs on p. 7 mention VOM, the max. peak output voltage swing, is at least ±12V and typically ±13.5V for a load of 10 kΩ and ±15V inputs.

That being said, could you just try supplying ±12V to your op-amp and see what happens?

unknown_2 said:
looking for a way to calculate it so i can apply it to different Vcc voltages
The graph I referred to above shows a pretty linear response. If your op-amp's datasheet doesn't have such a curve, then you could measure max. output for a few different supply voltages, with whatever load resistance you use in practice, and make your own graph.
 
Last edited:
  • #10
what I've done is put 15V Vcc and the max out on the 741 is about 13V. so that 13V output i'll just shrink the amplitude to get my desired value.
 

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