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Project Notes

#543 PLL Ramp Generator

A simple CD4046 ramp generator circuit from a design by M.S. Nagaraj published in Elektor 7/1994.



The VCO in the DC4046 normally produces a triangular signal, but this circuit arrangement generates a saw. The original circuit was by M.S. Nagaraj and published in Elektor Magazine 7/1994.

The saw tooth is achieved by significantly off-setting the rise and fall times of the VCO by using C1a capacitor value much greater than the C1b capacitor. The capacitor(s) on C1a and C1b set the VCO frequency.

So - not a perfect saw tooth, but very close.

In the circuit I test here, C1a = 1nF, and C1b = 10pF, so a resulting frequency difference of 100:1.






With VR1 adjusted for minimum freuqency of ~3.5kHz:


With VR1 adjusted for maximum freuqency of ~128.9kHz:


Credits and References

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This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.