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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.

Build

Notes

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.

Constructionlished

Breadboard

Schematic

RampGenerator_bb_build

Performance

With VR1 adjusted for minimum freuqency of ~3.5kHz:

scope_min

With VR1 adjusted for maximum freuqency of ~128.9kHz:

scope_max

Credits and References

About LEAP#543 CD4046Oscillators
Project Source on GitHub Project Gallery Return to the LEAP Catalog

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

LEAP is my personal collection of electronics projects, 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 (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.