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NE 566

I understand the working of the circuit, a Voltage Control Oscillator, except the part where the inverted square wave from the Schmitt Trigger gets fed to the Constant current source/sink. Pins 5 and 6 are maintained at the same voltage so when the modulation i/p voltage is increased, the pin 6 voltage also increases => Constant current decreases => Decreasing charging current for capacitor => A longer charging time => Wider pulses.

I'd appreciate it if anyone could hazard a guess about the Schmitt trigger feedback to the Current source/sink.

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  • \$\begingroup\$ It switches the current direction. \$\endgroup\$
    – user76844
    May 31, 2016 at 6:05
  • \$\begingroup\$ The feedback from the Schmitt trigger output is essential to make the circuit oscillate. Without it the circuit would get stuck in a certain state C1 charged or C1 discharged. The feedback makes it oscillate between those states. \$\endgroup\$ May 31, 2016 at 6:42

1 Answer 1

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The current source can be switched to operate either as a current source or a current sink.

When it sources a current the capacitor C1 gets charged, when it sinks a current C1 gets discharged.

Having a constant current results in a constant slope and produces the triangular waveform. To get a rising and falling edge the current needs to change direction.

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  • \$\begingroup\$ Thank you. That makes sense... I didn't think about the source/sink needing a signal to switch between the two. \$\endgroup\$ Jun 1, 2016 at 18:50

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