Electric OU: Supplement: MOSFETs… How do they WORK?? Part 5a
(Please watch the previous videos in this series to see the development and explanation of the circuit and its purpose. Not able to go on our field trip due to rainfall, we went ahead and started without you, on completing the invention of the oscillator. I think we should call it a “relaxation oscillator” since it relaxes me to hear it clicking in the background. If you’ve been following along, everything should be perfectly clear. No schematics are necessary I hope !! The MOSFET is still controlling the light (and now the relay coil too). But the mosfet is being controlled by the relay, which is being controlled by the mosfet !! It’s a feedback loop. When the relay and light are OFF, the relay is relaxed and the wire that allows the gate and tantalum cap to charge is connected, so they charge quickly. As soon as the gate is charged, the mosfet conducts drain-to-source and the light comes on… and the relay is pulled in, disconnecting the gate capacitance from the charging resistor from the positive rail, and simultaneously connecting the gate to the discharging resistor/holding cap combo which discharges at a rate set by the trimpot. When the charge on the tantalum cap is below that required to keep the mosfet gate charged, the mosfet turns off, the relay relaxes, the charging resistor is connected to the gate capacitances…. lather rinse repeat. By adjusting the trimpot to greater resistances we slow the rate of discharge so the light stays on longer. Now… if we …
