Proteus Professional, messing with my mind.

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SUMMARY

The discussion centers on a user's experience with circuit simulations while working with a simple LED series circuit powered by a 19.5V supply. The user is attempting to drop 4.1V at 4.2A using a 2.7 Ohm resistor instead of the required 1 Ohm resistor. The simulation results show an unexpected 0.23 amp reading, leading to confusion regarding the circuit's behavior. Participants highlight that the simulation software may not accurately handle negative voltages, which could misrepresent real-world outcomes, such as excessive current leading to potential LED damage.

PREREQUISITES
  • Basic understanding of LED forward voltage and current ratings
  • Knowledge of Ohm's Law for calculating resistance and voltage drops
  • Familiarity with circuit simulation software
  • Experience with series circuits and power supply configurations
NEXT STEPS
  • Research the limitations of circuit simulation software, particularly regarding negative voltage handling
  • Learn about LED thermal management and safe operating currents
  • Explore the practical implications of using incorrect resistor values in LED circuits
  • Investigate alternative circuit simulation tools that provide more accurate results
USEFUL FOR

Electronics enthusiasts, hobbyists experimenting with LED circuits, and individuals interested in circuit simulation accuracy and safety precautions.

SleepyFace-_-
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Hi Guys, fresh meat here.

I have a simple LED series circuit I'm currently playing with. 700ma forward voltage leds at 3.3v (blue) and 2.2v (red).

Its working fine, I have it rigged to a 19.5V power supply and a 2.7 Ohm, 25 W resistor.

I need 15.4 out of the 19.5, meaning I have to drop 4.1v @ 4.2 A. I should be using a 1 ohm resistor, but all I had even close in the wattage dept. was the 2.7.

In my effort to increase my exp points while I wait for more components, I decided to start messing with circuit simulations so I create the same circuit, with no resistor, and start getting readings...The results seriously messed with the thin layer of understanding I though I had:

ledseries.png


The leds are set to the correct voltages and draws, yet I'm seeing a .23 amp reading on the ammeter.

I have a feeling I am missing something here...I tried using both a DC voltage source and a battery to the same effect...Can anyone shed some light on this?

Thanks for your help!
 
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Look at the voltages at the LED's. Some of them are negative; your simulation program can't handle this case.

(In real life current would be very large and the diodes would catch fire)
 
Last edited:

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