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I want to use a 555 timer to generate a ramp to my soft starter. The problem is, I want it to be continuous after reaching it's value. Unlike this shown below,

enter image description here

Instead of discharging I want it to remain on. How can I adjust this basic 555 ramp generator circuit to do this?

m.Alin
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Maraldz
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  • Why is using a 555 a design requirement? – jippie Dec 16 '12 at 18:19
  • It's not necessarily a requirement, I figured it would be the easiest to work with. However I'm open to suggestions. – Maraldz Dec 16 '12 at 18:21
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    Did you think about a non inverting integrator? You will need a rail to rail single supply op amp, a couple of resistors and a capacitor. Is the ramp duration time-critical? What are the initial and final voltages? How much current do you need? – Vladimir Cravero Dec 16 '12 at 18:49
  • My voltage and current specs aren't really finalized yet. I want my ramp duration to be about 2 seconds but to have the ability to be adjusted up to 5 seconds using a pot. – Maraldz Dec 16 '12 at 19:09
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    Tell us what you really want to accomplish, not how you think it should be done. A 555 timer for this seems both inappropriate and silly in the first place, but without knowing what you actually want, it is not possible to suggest a alternative. – Olin Lathrop Dec 16 '12 at 19:32
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    Then a non inverting integrator should do the trick. You can adjust the timing with a potentiometer too. – Vladimir Cravero Dec 16 '12 at 19:36
  • @OlinLathrop If it's not possible to suggest an alternative, how come Vladimir did? You can't just say that what I think is inappropriate and silly and not back it up. Post something productive or don't comment at all.

    Vladimir thank-you I will turn my focus onto the non-inverting integrator rather than the 555 timer.

     – Maraldz Dec 16 '12 at 20:18
  • Vladimir is guessing. It's incredible that you spent the effort arguing instead of fixing the problem. Since you won't coorperate, this is a non-question and needs to be closed. – Olin Lathrop Dec 16 '12 at 22:08

1 Answers1

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Disconnect pin 6 (threshold) from the output and pull it to ground with a resistor. You can still pull it to supply voltage to manually reset the output.

Note that the output will go to the full supply voltage instead of 2/3 of it as in the given circuit.

starblue
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