# Questions about uA741 op amp

Discussion in 'General Electronics Chat' started by worldHello, Dec 1, 2014.

1. ### worldHello Thread Starter New Member

Oct 15, 2014
23
0
I use uA741 to build a Wien bridge oscillator. If you don't know what that is, it is a circuit that can convert DC into AC.

I am able to get a 60 Hz 5 V sine wave, and this is with a load (R: 2 ohms, C: 100nF). The current should be approximately Irms = 5/2 = 2.5 A since the capacitance is so small.

However, according to the datasheet uA741 does not output very much current (something like 5mA, I can't remember). Given that, how do I reason it ? Why can the op amp provide > 2 A ?

2. ### atferrari AAC Fanatic!

Jan 6, 2004
2,648
764
A nice and simple trick is to show the schematics.

Believe me. It works marvels.

Oct 15, 2014
23
0
4. ### MrChips Moderator

Oct 2, 2009
12,447
3,363
The last time I checked the data sheet of uA741 the max output current was 25mA.

5. ### GopherT AAC Fanatic!

Nov 23, 2012
6,061
3,823
It looks like you can use ohms law but have not figured out how to calculate reactive capacitance.
Google what that is at 60Hz for a 100nF capacitor (reactive capacitance calculator). You will see that 2A is not possible and a fuller view of Ohm's law really works.

6. ### worldHello Thread Starter New Member

Oct 15, 2014
23
0
Yes. Something like that, but how come I could get 2A?

7. ### worldHello Thread Starter New Member

Oct 15, 2014
23
0
Well, the impedance Xc is really big (Since C is so small )which makes Vrms/Xc really small. So one can just ignore it because it is so small.

8. ### MrChips Moderator

Oct 2, 2009
12,447
3,363
Simple. You are seeing 60Hz AC noise pickup.

Nov 23, 2012
6,061
3,823

Jan 6, 2004
2,648
764