-1

I have been reading about load resistance, checking even some video online and even ended up to one post in Here.

Unfortunately, I couldn’t find any source that would help me with that I’m having trouble and that is finding the load resistance of OP-Amps.

The first picture asks which load resistance is connected to U2 ?

enter image description here

The second one asks which load resistance is connected to U1?

This is my attempt to find the load resistance for U1 (second op amp picture) enter image description here

I1+I2= IA

By no means this is homework, I would just appreciate some help.

E199504
  • 227
  • 1
  • 7
  • Load resistance is what is hooked up to the OUTPUT of your amplifier circuit. In your figures, there is nothing hooked up, so load resistance is infinite (i.e., open circuit) – Scott Seidman Jan 03 '20 at 15:44
  • similar to this one here https://electronics.stackexchange.com/questions/414081/which-load-resistance-is-connected-to-generator-u2 – E199504 Jan 03 '20 at 15:57

1 Answers1

0

Since these are all dc sources, you simply need to analyze the circuit and determine how much current flows from each of the sources. Given that value of current and the known value of voltage, use Ohm's Law to find the effective load resistance on each supply.

If the supply voltages are not given then you will need to find an expression for the supply current as a function of the supply voltage(s).

One assumption that you can probably make is that that if the circuit has negative feedback, as both of your examples do, then the voltages at the inverting and non-inverting inputs will be the same. If you are assuming that the op amp is ideal you can also assume that no current flows into or out of the inverting and non-inverting inputs.

Elliot Alderson
  • 31,192
  • 5
  • 29
  • 67
  • The op amps are ideal. Obove I added an attempt to find the load resistance for the second op amp picture. I'm not sure if it right – E199504 Jan 03 '20 at 18:22
  • You must label the direction of the currents in your schematic and use consistent labels in equations. Your attempt refers to "U" but which U is it? – Elliot Alderson Jan 03 '20 at 21:06
  • Elliot Alderson, I was using U1 – E199504 Jan 03 '20 at 21:10
  • Again, you must label the direction of currents in your schematic and use consistent labels in equations. Fix the equations. Label the schematic. As it stands, your "attempt" is just an algebraic manipulation of Ohm's Law...it has no meaning in the context of your circuit. – Elliot Alderson Jan 03 '20 at 22:53
  • I updated the seond photo with the current for U1 . i dont really know where do go from there onsidering i dont understand the question of finding the load resistance – E199504 Jan 03 '20 at 23:57
  • If this is not homework, then where did the problem come from? Give us more context for the question. Also, tell us what you know about analyzing circuits...do you know KVL and KCL? Superposition? Node-voltage method? – Elliot Alderson Jan 04 '20 at 00:23
  • Yes I do know KVL and KCL. As first part it asked what is the effect of these signals at the output terminal of the circuit and find this using superposition. I did so for both of the circuits above . The next part was which load resistance is connected to Generator U2(for first circuit ), U1( for the second circuit on the question above) – E199504 Jan 04 '20 at 13:26