Is the STMicroelectronics L7912CV Voltage Regulator Suitable for a +12V Output?

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Discussion Overview

The discussion centers around the suitability of the STMicroelectronics L7912CV voltage regulator for achieving a +12V output. Participants explore the wiring, input voltage, and expected output, while addressing potential issues related to the regulator's operation.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes their setup with the L7912CV, noting that they expect a 12V output but are receiving the same voltage as the input (15.5V).
  • Another participant inquires about the connection of the red lead to the negative terminal of the LiPo battery, seeking clarification on the output reading.
  • A participant mentions the importance of capacitor values as specified in the datasheet, suggesting that the output may behave differently under no load or lightly loaded conditions.
  • Concerns are raised about the correct wiring of a negative voltage regulator, with one participant suggesting that the battery may have been connected backwards, potentially damaging the regulator.
  • There is a clarification that the 7812 series is intended for +12V outputs, contrasting with the L7912CV, which is a negative voltage regulator.

Areas of Agreement / Disagreement

Participants express differing views on the wiring and functionality of the voltage regulator, with no consensus reached regarding the cause of the output issue or the correct setup.

Contextual Notes

Participants reference specific capacitor values and loading conditions that may affect the regulator's performance, but these factors remain unresolved in the context of the discussion.

c d
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[mod note: thread moved from homework forum]

I have this Mouser voltage regulator

https://www.mouser.com/ProductDetail/STMicroelectronics/L7912CV/?qs=sGAEpiMZZMug9GoBKXZ75xbXFDWiKqpmvrbz5I0HaKg%3D

Wired according to datasheet https://www.mouser.com/ds/2/389/l79-974159.pdf see insert photo.

https://plus.google.com/photos/phot...0/6526650605024626690?authkey=CPTx7ezW74_OiAE

Would expect to see 12 V output. Input is 15.5 V Wired this a couple of times, get same output as input.

Before I go a lot further, am I on the right track? Your thoughts?
 
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cd, do you have the red lead going to the negative terminal of the LiPo?

Interpreting your meter reading, is the O/P positive or negative with respect to ground?
 
Red goes to positive of lipo and "input" terminal (middle of three wires) of voltage regulator, thanks for asking. btw, "input" is 15.5 V [positive] with respect to ground. Reading the "output" terminal with respect to ground and getting the same...
 
Spec sheet calls for a C1 value of 2.2 uF for tantalum, but 10x or more when an electrolytic is used. Probably want to add a back diode across the output, too, but I don't think that's the problem. Negative regulators (more so than positive regulators) have a tendency to exhibit this symptom when under no load or lightly loaded (under 5 mA) conditions.
 
Why do you have the input positive with respect to ground on a negative voltage regulator?
 
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c d said:
Red goes to positive of lipo and "input" terminal (middle of three wires) of voltage regulator, thanks for asking. btw, "input" is 15.5 V [positive] with respect to ground. Reading the "output" terminal with respect to ground and getting the same...
79XX series are negative regulators. From what you say i'd guess you hooked the battery backwards. Likely it's shot now.

edit - average supernova and i crossed in the mail..
 
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The 7812 series are for +12V.