Questions about uA741 op amp

Thread Starter

worldHello

Joined Oct 15, 2014
23
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 ?
 

GopherT

Joined Nov 23, 2012
8,009
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 ?
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.
 

Thread Starter

worldHello

Joined Oct 15, 2014
23
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. You will see that 2A is not possible and a fuller view of Ohm's law really works.
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.
 

#12

Joined Nov 30, 2010
18,224
Yes. Something like that, but how come I could get 2A?
You can't. Not from that chip. You couldn't possibly be talking about how you measured 2 amps coming through the output pin. You would have mentioned the smoke if that was true. You must be talking about theory, and that leaves us to help with your mistake in either math or understanding. Only a drawing of your circuit can help us now.
 
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