Resonance: CD4046BE Phase Locked Loop Resonance Demo

The CD4046BE Phase Locked Loop (PLL) is a versatile chip that does neat stuff. It contains a Voltage Controlled Oscillator (VCO) that can be used on its own to produce a nice square wave output, or it can be used as a full PLL to “lock in” to the resonant frequency of a coil, for example, using feedback from the RF that the coil emits when resonating at its natural frequency, driven by the VCO in the chip.

This property makes it popular with Tesla Coil builders, as it automagically compensates for the shifts in resonance caused by corona discharge or environment. It will track the change in resonant frequency and respond by varying its VCO output to keep the coil resonating and producing that delicious RF feedback.

I’m working on developing a “PLL Exciter”, sort of a step up from the ordinary Slayer Exciter pseudoSolidState Tesla Coil. If I can work up a bipolar transistor or mosfet driver stage, put a primary on the coil shown here, and keep the PLL part working properly, maybe it will even turn into an actual miniSSTC and make corona or psarks.

The schematic is a slightly modified version of the standard PLL schematic found in the Data Sheet for the CD4046BE, or also in many SSTC builder’s sites. The tiny C1 capacitor and the resistors set the upper and lower frequency bounds of the VCO; there is the usual 0.1 uF decoupling cap across the power input leads, and a 10k potentiometer is used to vary the input voltage to the VCO. Since I made this video I’ve changed the antenna to a single loop about 5 inches across, placed horizontally under the bottom of the coil, and it works much better.

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