opamps

[Vergil]

Hi Guys,
  Please, I need help understanding the basics of Microlinear amplifiers (especially Negative feed back). I've gone online to search, read textbooks, but still no avail. I want to be able to solve questions relating to it.
  Is there anyway you all can help? any secret I aught to know? either to show me a site that is very good, or recomend a book...or simply write a few lines about it, I will be very greatful.
  Basically, grant me some wisdom regarding this area, point me in the right direction.

Thanks.

[audioguru]

Just think of an opamp asd having infinite voltage gain. The two resistors for the negative feedback make the voltages at both inputs the same. Then simply use Ohms Law to determine the voltage at the output and the amount of closed loop gain.

[indulis]

Just apply the following to get the "general idea" of how they work

1) the inputs to the opamp have infinte impedance... this means no current will flow into of out of an input.

2) the output has zero impedance... this basically means it could supply infinte current

3) the output will do whatever it has too to make both inputs the same (voltage)

4) then as guru said, apply ohms law.

For example

take a opamp with a 1K input resistor to the negative input and a 10K resistor from the negative input to the output (feedback).  The 1K is connected to a 10V source and the positve input is connected to ground.

Since the positive input is a ground (0V) the negative input wants to be a 0V and the output will do what ever it can to make that happen. So, if the negative input has to be at 0V, that means that the 1K has 10V across it and 10mA is flowing from the source towards the opamp. Since no current can flow into, or out of the input, all of it must flow through the feedback resistor. With 10mA flowing through 10K, that 100V, so if the negative input end of the resostor is at 0V and there is 100V across the feedback resistor, then the output must be at -100V.

If you apply this thought process, you can solve any DC opamp circuit. If you add "C's & L's" it's a bit more complicated.