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Q&A Is it possible to calculate the rise/fall time of an operational amplifier ?

I am planning to use the LM318 operational amplifier to generate a PWM signal and I need to know how to calculate the rise/fall time. LM318/LM218/LM118 datasheet -The slew rate is 70 V/µs maximum...

1 answer  ·  posted 2y ago by deleted user  ·  edited 1y ago by Lorenzo Donati‭

Question opamp rise-time fall-time
#6: Post edited by user avatar Lorenzo Donati‭ · 2023-08-03T13:41:20Z (over 1 year ago)
rise-time fall-time
#5: Post edited by user avatar Peter Mortensen‭ · 2023-01-07T16:06:16Z (almost 2 years ago)
Copy edited (e.g. ref. <https://en.wikipedia.org/wiki/Pulse-width_modulation> and <https://en.wikipedia.org/wiki/Volt>). 
Is it possible to calculate the rise/fall time of an operational amplifier ?
  • Hi guys so i am planning to use LM318 operational amplifier to generate a pwm signal and i need to know how to calculate the rise/fall time thank you.
  • [LM318/LM218/LM118 datasheet](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ti.com/lit/gpn/LM318-N&ved=2ahUKEwjN7LqX6L77AhUYVaQEHYrCCPQQFnoECA0QAQ&usg=AOvVaw2teDo15HVgRulQWeLnMu54)
  • **Edit:**
  • -The slew rate is 70v/ųs max.
  • -Slew rate can reach 150v/ųs
  • But with a condition of"feedforward compensation will boost the slew rate to over
  • 150V/μs and almost double the bandwidth."
  • **Edit2:**
  • As suggested from Mr. Olin here my calculation:
  • the LM318 offer 70v/ųs and the output voltage that i need is 18v so:
  • (18 V) / (70V/µs) = 0.257143 ųs = 257.143 ns.
  • And then i did this:
  • (257.143/5)×4 = 205.714 ns.
  • Because rise/fall time start at 10% and end at 90%.
  • And in case of 150v/ųs this gonna be:
  • (18 V) / (150 V/µs) = 0.12 µs = 120 ns
  • (120/5)×4 = 96ns.
  • Is my calculation correct? Thank you.
  • I am planning to use the LM318 operational amplifier to generate a PWM signal and I need to know how to calculate the rise/fall time.
  • [LM318/LM218/LM118 datasheet](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ti.com/lit/gpn/LM318-N&ved=2ahUKEwjN7LqX6L77AhUYVaQEHYrCCPQQFnoECA0QAQ&usg=AOvVaw2teDo15HVgRulQWeLnMu54)
  • -The slew rate is 70 V/µs maximum
  • -Slew rate can reach 150 V/µs
  • But with a condition of "feedforward compensation will boost the slew rate to over
  • 150 V/μs and almost double the bandwidth."
  • As suggested from Mr. Olin, here is my calculation:
  • the LM318 offers 70 V/µs and the output voltage that I need is 18 V so:
  • (18 V) / (70 V/µs) = 0.257143 µs = 257.143 ns.
  • And then I did this:
  • (257.143/5)×4 = 205.714 ns.
  • Because the rise/fall time start at 10% and end at 90%.
  • And in case of 150 V/µs this is going to be:
  • (18 V) / (150 V/µs) = 0.12 µs = 120 ns
  • (120/5)×4 = 96 ns.
  • Is my calculation correct?
#4: Post edited by (deleted user) · 2022-11-21T13:37:27Z (almost 2 years ago)
  • Hi guys so i am planning to use LM318 operational amplifier to generate a pwm signal and i need to know how to calculate the rise/fall time thank you.
  • [LM318/LM218/LM118 datasheet](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ti.com/lit/gpn/LM318-N&ved=2ahUKEwjN7LqX6L77AhUYVaQEHYrCCPQQFnoECA0QAQ&usg=AOvVaw2teDo15HVgRulQWeLnMu54)
  • **Edit:**
  • -The slew rate is 70v/ųs max.
  • -Slew rate can reach 150v/ųs
  • But with a condition of"feedforward compensation will boost the slew rate to over
  • 150V/μs and almost double the bandwidth."
  • **Edit2:**
  • As suggested from Mr. Olin here my calculation:
  • the LM318 offer 70v/ųs and the output voltage that i need is 18v so:
  • (18 V) / (70V/µs) = 0.2571428571 ųs = 257.143 ns.
  • And then i did this:
  • (257.143/5)×4 = 205.714 ns.
  • Because rise/fall time start at 10% and end at 90%.
  • And in case of 150v/ųs this gonna be:
  • (18 V) / (150 V/µs) = 0.12 µs = 120 ns
  • (120/5)×4 = 96ns.
  • Is my calculation correct? Thank you.
  • Hi guys so i am planning to use LM318 operational amplifier to generate a pwm signal and i need to know how to calculate the rise/fall time thank you.
  • [LM318/LM218/LM118 datasheet](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ti.com/lit/gpn/LM318-N&ved=2ahUKEwjN7LqX6L77AhUYVaQEHYrCCPQQFnoECA0QAQ&usg=AOvVaw2teDo15HVgRulQWeLnMu54)
  • **Edit:**
  • -The slew rate is 70v/ųs max.
  • -Slew rate can reach 150v/ųs
  • But with a condition of"feedforward compensation will boost the slew rate to over
  • 150V/μs and almost double the bandwidth."
  • **Edit2:**
  • As suggested from Mr. Olin here my calculation:
  • the LM318 offer 70v/ųs and the output voltage that i need is 18v so:
  • (18 V) / (70V/µs) = 0.257143 ųs = 257.143 ns.
  • And then i did this:
  • (257.143/5)×4 = 205.714 ns.
  • Because rise/fall time start at 10% and end at 90%.
  • And in case of 150v/ųs this gonna be:
  • (18 V) / (150 V/µs) = 0.12 µs = 120 ns
  • (120/5)×4 = 96ns.
  • Is my calculation correct? Thank you.
#3: Post edited by (deleted user) · 2022-11-21T13:33:49Z (almost 2 years ago)
  • Hi guys so i am planning to use LM318 operational amplifier to generate a pwm signal and i need to know how to calculate the rise/fall time thank you.
  • [LM318/LM218/LM118 datasheet](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ti.com/lit/gpn/LM318-N&ved=2ahUKEwjN7LqX6L77AhUYVaQEHYrCCPQQFnoECA0QAQ&usg=AOvVaw2teDo15HVgRulQWeLnMu54)
  • **Edit:**
  • -The slew rate is 70v/ųs max.
  • -Slew rate can reach 150v/ųs
  • But with a condition of"feedforward compensation will boost the slew rate to over
  • 150V/μs and almost double the bandwidth."
  • Hi guys so i am planning to use LM318 operational amplifier to generate a pwm signal and i need to know how to calculate the rise/fall time thank you.
  • [LM318/LM218/LM118 datasheet](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ti.com/lit/gpn/LM318-N&ved=2ahUKEwjN7LqX6L77AhUYVaQEHYrCCPQQFnoECA0QAQ&usg=AOvVaw2teDo15HVgRulQWeLnMu54)
  • **Edit:**
  • -The slew rate is 70v/ųs max.
  • -Slew rate can reach 150v/ųs
  • But with a condition of"feedforward compensation will boost the slew rate to over
  • 150V/μs and almost double the bandwidth."
  • **Edit2:**
  • As suggested from Mr. Olin here my calculation:
  • the LM318 offer 70v/ųs and the output voltage that i need is 18v so:
  • (18 V) / (70V/µs) = 0.2571428571 ųs = 257.143 ns.
  • And then i did this:
  • (257.143/5)×4 = 205.714 ns.
  • Because rise/fall time start at 10% and end at 90%.
  • And in case of 150v/ųs this gonna be:
  • (18 V) / (150 V/µs) = 0.12 µs = 120 ns
  • (120/5)×4 = 96ns.
  • Is my calculation correct? Thank you.
#2: Post edited by (deleted user) · 2022-11-21T08:15:42Z (almost 2 years ago)
  • Hi guys so i am planning to use LM318 operational amplifier to generate a pwm signal and i need to know how to calculate the rise/fall time thank you.
  • Hi guys so i am planning to use LM318 operational amplifier to generate a pwm signal and i need to know how to calculate the rise/fall time thank you.
  • [LM318/LM218/LM118 datasheet](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ti.com/lit/gpn/LM318-N&ved=2ahUKEwjN7LqX6L77AhUYVaQEHYrCCPQQFnoECA0QAQ&usg=AOvVaw2teDo15HVgRulQWeLnMu54)
  • **Edit:**
  • -The slew rate is 70v/ųs max.
  • -Slew rate can reach 150v/ųs
  • But with a condition of"feedforward compensation will boost the slew rate to over
  • 150V/μs and almost double the bandwidth."
#1: Initial revision by (deleted user) · 2022-11-20T19:45:08Z (almost 2 years ago) 
Is it possible to calculate the rise/fall time of an operational amplifier ?
Hi guys so i am planning to use LM318 operational amplifier to generate a pwm signal and i need to know how to calculate the rise/fall time thank you.