Making a FET Phase Light -- The Learning Circuit 32

In case it's of any interest, the circuit has its roots in this phase-shift oscillator:

https://en.wikipedia.org/wiki/Phase-shift_oscillator

That has three RC networks and just a single transistor to give enough gain to make up for the losses through the passive

components. The transistor gives 180 degrees of phase shift (an inversion) and the three RC networks contribute the other 180

(ideally they'd each contibute 60 degrees, but for the BJT case it doesn't divide that neatly because of the way that the

transistor loads the last stage).

In Karen's circuit, each RC network is followed by its own gain stage. The two additional stages invert twice, leaving

things as they were. Each gain stage can then drive an LED as its load.

Here it is in a simulator.

I've made the first capacitor a slightly different value (2.15uF) to the other two to encourage the simulation in getting the

oscillation started - in a real circuit they'd never be identical (and the gate thresholds and resistors would be different

too). The real circuit probably starts quicker than the simulation. [I've also used a voltage generator rather than a voltage

source for the power. That just enables me to have the power applied after the simulation start time (at time = 1s).]

First plot is all the waveforms on top of each other which shows how it gets going with one stage getting a slight edge over

the others and then forcing the others into the sequence. The second one is with the waveforms separated and shows more

clearly how the resulting phases drive the three LEDs.

That's great additional information. Thanks, Jon!

That's great additional information. Thanks, Jon!