Search results

Search Forums New Posts
  1. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Meanwhile, speaking of communication, I'm happy to have learned something new. It's completely pointless to talk about design equations, as I tried to do in my very first post to this thread, when the topic is a flawed simulation result. The fellow using a simulator simply doesn't think about...
  2. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Thanks for the new result. Since in my calc's I fecklessly neglected such refined details as the ~5mV saturation voltage of the pin 7 discharge transistor, "close enough for gov't work" is about the best I could have expected, and fully believe your simulation is now more realistic than my...
  3. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Just to mention: If you look back over all my posts to this thread, I think you'll see that I never even once criticized your chosen (nor any other) simulator. I questioned only the accuracy of the simulation, which we now know was compromised by the model being used. I wish I'd noticed the...
  4. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Sorry, but I have no idea what a "silicone" diode is or what its forward voltage drop might be. Silicon diodes, by contrast, I'm fairly familiar with, and how their forward voltage drop varies with current density, temperature, etc. I made considerable use of that familiarity here, for...
  5. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Well, Martin, perhaps you came late to this discussion and so missed some useful context. The original subject of this thread is an article I wrote and was recently published in EDN Design Ideas. Opinions were offered here that seemed relevant to some points in my article, so I replied to...
  6. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Well, don't look now, but I just did. I used it as an example of a component with a parameter (trigger voltage) that's independent of the tolerances of external components. :cool:
  7. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    The 555 trigger voltage (as a fixed fraction of the supply voltage when the CV pin is unloaded) is a parameter of the 555, independent of the tolerances any external components. I figured that's what you didn't understand. I see I was right.
  8. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Thanks for (now) using a more accurate model. Please now, just for fun, apply it with its more accurate trigger points, to the circuit in your first post to this thread, and see what happens to the respective duty cycle predictions for both your and my values for R3.
  9. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Please see Martin's post, to which those comments were addressed. Happy to help.
  10. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    "The data sheet states max, typ and min for many specs." But not for the trigger voltage, which, please recall, was the subject of my comments. If you don't understand the meaning and significance to this discussion of the 555 trigger voltage, you might follow your own kind advice to me, and...
  11. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    "1% to 20%"? I humbly suggest you take a closer look at that LM555 datasheet linked to above. If you do, you'll notice that there are no specified min/max limits on threshold and trigger voltages. Therefore, when attempting to predict the performance of a 555 application circuit, you're left...
  12. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Hi, Martin What you say is of course true. I do wonder, however, what, in this context, the rationale for deliberately using an arbitrary and atypical Vtrig might be, especially without bothering to say so? Hence, maybe it's more plausible to simply conclude it's that simulation that's...
  13. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    "I trust the simulation..." Well, that makes one of us.:) In other news, did you know that every 555 datasheet on the planet says the Trigger voltage is 1/3V+, therefore 1.667V when V+ = 5V, not ~1.85V as shown by your "accurate" simulation?
  14. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Actually, it should (if your simulation works accurately) make (pretty close) to a 50% duty cycle. Wouldn't that be fun? See figure 14: https://datasheet.octopart.com/LM555CM-NOPB-Texas-Instruments-datasheet-7283993.pdf
  15. CircutScoper

    Voltage regulator or not?

    Sez here 12ga cu wire is only 1.588 ohms per 1000'. So 2x75' should impose only 0.24 ohms = less than 1V drop at 4A.
  16. CircutScoper

    Voltage regulator or not?

    I'd guess your pump motor is brushed/commutated and that's making so much electrical noise (a.k.a. arcs and sparks) when running as to discombobulate (EE technical term) the power supply. I'd try a large electrolytic capacitor (say 1000uF @ 16V) across the supply output terminals to suppress...
  17. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Thanks for satisfying my curiosity. Just for fun, you might want to try R3 = 22k, no other change.
  18. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    "Do you mean R2 or R3?" R2. The resistor that connects to C2, THRS, and TRIG. Make it zero ohms and see if what your simulation then predicts for the "high" and "low" times look realistic.
  19. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Okay. Please try this experiment. What output waveform does your simulation predict if R2 = 0, all other values left unchanged?
  20. CircutScoper

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Your simulation would be more realistic if it took into account that the effective discharge (output low) timeconstant isn't just R2C2 but is in fact (R2+R1R3/(R1+R3))C2. So, as shown in my EDN article, to get a 50:50 duty cycle, R3 should = 0.225R1 = 11.2k. Not 13.7k.
View older results
Top