Tuning LM3900-based oscillators

Thread Starter

BarryBozeman

Joined Apr 1, 2016
41
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?
 

Thread Starter

BarryBozeman

Joined Apr 1, 2016
41
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?
 

danadak

Joined Mar 10, 2018
4,057
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.
 

Zeeus

Joined Apr 17, 2019
615
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
 
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