Dramatic voltage drop at voltage regulator output

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Discussion Overview

The discussion revolves around a voltage drop issue encountered in a power supply block for a senior project, specifically at the output of a 6V voltage regulator when a servo motor is connected. Participants explore potential causes and solutions related to circuit design, component specifications, and thermal management.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes a significant voltage drop at the output of the 6V regulator when a servo motor is connected, suggesting the regulator may be shutting down due to overheating.
  • Another participant proposes that the 6V regulator could be overheating because the servo motor draws a substantial current (half an amp), and questions whether a heat sink has been installed.
  • Concerns are raised about the need for ceramic capacitors in the circuit, as their absence could lead to oscillation issues, referencing the datasheets for the voltage regulators.
  • Participants suggest testing the health of the 12V battery under load, as a drop in voltage could explain the observed behavior.
  • One participant mentions that the servo motor works fine when powered independently, indicating that the issue may lie within the regulator circuit.
  • Another participant discusses the possibility of the servo circuit drawing too much current and suggests using a resistive load to verify the 6V output's current capacity.
  • There is a mention of thermal data from the regulator's datasheet, indicating that the power dissipation could lead to excessive heating and shutdown.
  • Participants discuss various troubleshooting steps, including using a lab power supply with current limiting to monitor the regulator's output voltage as current is increased.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the cause of the voltage drop and potential solutions. There is no consensus on the exact issue, as various hypotheses about current draw, thermal management, and circuit design are presented.

Contextual Notes

Some participants note the importance of thermal management and the need for capacitors, while others question the necessity of certain components based on their understanding of the circuit. The discussion highlights the complexity of diagnosing the problem without definitive measurements or tests.

  • #31
jim380 said:
okay. I think I found the problem. When the regulator is loaded with a 12 ohms resistor, the battery voltage drops from 12V to 3.4V . I've tried a couple new batteries, still the same problem.
Well done.
What type of 12 volt battery are you using, make, model, chemical technology and capacity?
 
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  • #33
Data shows discharge Rate = 480µA
It is doing very well to produce 150 mA.
 
  • #34
Baluncore said:
Data shows discharge Rate = 480µA
It is doing very well to produce 150 mA.

Yes. I figured. I also tried powering the 6v regulator using a power generator in my lab. Everything works fine when loaded with the same resistor. I'm literally running out of ideas.
 
  • #35
If you have a lab supply that works, how come you are running out of ideas?
You need to get either an 8V to 12V power supply rated at 1 amp output that runs from the AC mains,
or a 12V gel cell with sufficient capacity to produce 1 amp.
 

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