# Ideal op-amp used as a digital buffer: rise time

Vo = Vin, so the rise time for both should be the same, but the capacitor takes some time charging.

How can I find the charging time without any other information here?

• The charging time is proportional to R*C. What is the R of an ideal opamp output? Jul 18 at 5:31
• All the information is in the word "ideal". What is the dv/dt of an ideal op-amp? Jul 18 at 5:32
• Since the input rise time is not zero, you don't have a paradox. You can calculate the required output current from your ideal op-amp. Jul 18 at 5:47
• For ideal opamp rise time is 0, so as soon as the input changes output will change. That means answer should be 0. Is that correct? Jul 18 at 6:09
• @sheetal No. The rise time is not zero for the ideal op amp, but the max. slew rate is infinite. This means that the ideal opamp follower always will satisfy Vo = Vin as you correctly write. Jul 18 at 6:16