Op-amp (ua741) with only positive supply voltage

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Discussion Overview

The discussion revolves around the operation of the ua741 operational amplifier when powered by a single positive supply voltage and ground, rather than the conventional dual supply voltage configuration. Participants explore the implications of this setup on functionality, reference voltages, and circuit design considerations.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that the ua741 can function with only a positive supply voltage, suggesting that a pseudo ground must be created, typically using a voltage divider.
  • There is a proposal that one of the inputs should serve as a voltage reference, with some arguing it can be set anywhere between +V and ground, while others question if it must be half of the total supply voltage.
  • Concerns are raised regarding the role of a capacitor connected to the pseudo ground, with some stating it provides a low impedance path, while others inquire about its necessity in amplifying unchanging DC voltages.
  • Participants discuss the power consumption implications of using a voltage divider to create a pseudo ground, with some noting that it could draw substantial power from the supply.
  • There are suggestions that a high resistance divider and an op amp buffer could be alternatives to achieve a low impedance DC pseudo ground without excessive power draw.
  • One participant mentions the concept of a virtual Earth input as another potential solution.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and configuration of the pseudo ground, the role of capacitors, and the implications of power consumption. No consensus is reached on these points.

Contextual Notes

Participants highlight the need for careful consideration of impedance and power consumption when designing circuits with a single supply voltage. The discussion reflects various assumptions about the operational characteristics of the ua741 in this configuration.

weitao
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Normally the connection of supply voltage is +-V but now is +V and ground.
What happen if Op-amp (ua741) with only positive supply voltage? The op-amp still function?
 
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Yes it can still function. The +V remains +V, the ground becomes -V and you need to create a pseudo ground in place of the ground. This is usually done with a voltage divider to create a voltage halfway between +V and ground. A relatively large capacitor is usually connected between the junction of the voltage divider resistors and ground, or +V or both.
 
Is it necessary that one of the input (role as voltage reference) must be half of the total of the supply voltage?
 
No. It can be anywhere between +V and ground.
 
skeptic2 said:
Yes it can still function. The +V remains +V, the ground becomes -V and you need to create a pseudo ground in place of the ground. This is usually done with a voltage divider to create a voltage halfway between +V and ground. A relatively large capacitor is usually connected between the junction of the voltage divider resistors and ground, or +V or both.

What would the capacitor do in the circuit? also, if voltage divider is used, wouldn't that consume power from the power supply?
 
If all you want to do is amplify an unchanging DC voltage then you may not need the capacitor. The purpose of the capacitor is to provide a low impedance path to the pseudo-ground. It should do that even at the lowest frequency the op amp will handle. How low of an impedance is for you to decide. If it is not low enough, the pseudo-ground will develop a voltage which may cause positive or negative feedback.
 
Abstr7ct said:
also, if voltage divider is used, wouldn't that consume power from the power supply?

Yes it will, and if you want a low impedance DC pseudo-ground, it will draw substantial power from the power supply. If you get into that situation you may be able to accomplish the same effect with a high resistance divider and an op amp buffer.
 
skeptic2 said:
Yes it will, and if you want a low impedance DC pseudo-ground, it will draw substantial power from the power supply. If you get into that situation you may be able to accomplish the same effect with a high resistance divider and an op amp buffer.

Or use a virtual Earth input?
 
weitao said:
Normally the connection of supply voltage is +-V but now is +V and ground.
What happen if Op-amp (ua741) with only positive supply voltage? The op-amp still function?
A google search will turn up plenty of information, e.g., http://www.eng.yale.edu/ee-labs/morse/compo/sloa058.pdf[/color]
 
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