What is the Circuit for a Diode OR Gate with a 12V Battery Backup?

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Discussion Overview

The discussion revolves around the electrical circuit design for a diode OR gate that incorporates a 12V battery backup. Participants explore the behavior of the circuit under different power supply conditions and seek clarification on the circuit's configuration and functionality.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant references a source that describes how the 12V battery activates only during a power failure, prompting questions about the circuit loops involved.
  • Another participant notes that in one proposed loop configuration, the orientation of the diode prevents current flow, while in a different configuration, the diode orientation allows current to flow, raising questions about what prevents current in the latter case.
  • A participant explains the behavior of the diodes under different power supply conditions, detailing how the second diode becomes reverse biased when the 15V supply is active and how it conducts when the supply is turned off, affecting the first diode's state.
  • Another participant expresses a desire to modify the circuit design to include a resistor representing Earth resistance and asks for feedback on the proposed changes.

Areas of Agreement / Disagreement

Participants are exploring different configurations and behaviors of the circuit, with some agreement on the functioning of the diodes under varying conditions, but no consensus on the proposed circuit modifications or the implications of the resistor inclusion.

Contextual Notes

Participants have not fully resolved the implications of the diode orientations and the role of the resistor in the circuit. There are also assumptions regarding the behavior of the circuit under different power supply conditions that remain unexamined.

Who May Find This Useful

This discussion may be useful for individuals interested in electrical engineering, circuit design, and the behavior of diodes in power supply systems.

dobry_den
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Hi! http://www.phys.uAlberta.ca/~gingrich/phys395/notes/node71.html" 's an electrical network for a diode OR gate. It says there that "[t]he 12 V battery does nothing until the power fails; then it takes over without interruption."

I just wonder what electrical circuits (closed loops) are there. I attached an image of how I think the loop looks when the 15V power supply works. But what about the battery loop in this case?
 

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In Loop1 (see the attached images), the orientation of the diode makes it impossible for the current to flow. But in the Loop2, the orientation of the same diode is fine for the current to flow - so what stops it from flowing?
 

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When the 15V supply is on, the 2nd diode is reverse biased (with about 14.3V on its cathode, and 12V on its anode). When the 15V supply is turned off, then the second diode conducts with 12V on its anode and about 11.3V on its cathode. This puts the first diode into reverse bias (off), with 11.3V on its cathode and 0V on its anode. Make sense?
 
Yep, it makes in a way..thanks. But still, I have another question. Could the electric circuit be redrawn in the way I did it in the attached image? The resistor is there to incorporate the resistance of the Earth. Or would you propose any changes?

Any help is appreciated, thanks in advance.
 

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