Hi AAC -

I have been making my way through AN-72, "The LM3900: A New Current-Differencing Quad of Plus or Minus Input Amplifiers." (http://www.ti.com/lit/an/snoa653/snoa653.pdf). I'm breadboarding different circuits to learn about the chip. It's still a little mysterious to me, though an I can't get some of the circuits to work at all.

Most importantly to me, though, is Figure 42 - "the Squarewave Generator." It doesn't seem to be easily tunable. I'm not sure I understand why. Can anyone shed some light on this particular subject?

 

In what way do you find it difficult to tune? The output frequency will be proportional to 1/R1C1.

 

Regards, Dana.

 

Well, I'm at a loss. I know it looks like a pretty standard oscillator circuit, but I'm wondering if there's anything particular about this operation, since it's a current-differencing amplifier, as opposed to the more familiar variety of op-amp.
I've built the schematic several times, replaced the chip, and adjusted the R1 value : no oscillation.
The only variation from the datasheet is that I'm using 12v, instead of 15v. Is that enough to cause this problem? Does anyone have any suggestions?

 

Set part up in a proto board as a basic amplifier, try both
inverting and non inverting configurations, see if part is
working correctly.

12V vs 15V should not affect basic circuit operation.


Regards, Dana.

 

Well, I'm at a loss. I know it looks like a pretty standard oscillator circuit, but I'm wondering if there's anything particular about this operation, since it's a current-differencing amplifier, as opposed to the more familiar variety of op-amp.
I've built the schematic several times, replaced the chip, and adjusted the R1 value : no oscillation.
The only variation from the datasheet is that I'm using 12v, instead of 15v. Is that enough to cause this problem? Does anyone have any suggestions?

suggestion : Re check the connection on breadboard..Might be surprised you missed something