Electric OU: REVISED MOSFET Triangle Drive Offset Demo
IMPORTANT NOTICE: This video fixes a problem with the Scope Probe in the last mosfet video that caused an inaccurate display of the Drain Trace waveform.
The previous video concerning the effect of Offset on the behaviour of a mosfet being driven by a Triangle Ramp waveform showed a scope trace from the Mosfet Drain that was inaccurate, due to a problem with the internal circuitry of the probe. The main point of that video was not affected, as the probe showed the mosfet switching well enough, but the discerning Scoposcopist would have noticed that the waveform didn’t quite look as it should have.
I’ve repaired the probe (I hope) and re-shot the scene, and now you can see that the drain trace waveforms are looking as they should look.
With the circuit arranged as shown, the load is on the high side of the mosfet, and the voltage at the mosfet Drain is at the battery voltage when the mosfet is OFF. When the mosfet turns on — becoming a low resistance channel — the voltage across it drops.
So when the offset is cranked all the way to the positive maximum, the triangle waveform is all sufficiently positive enough to turn the mosfet on, so it stays on for 100 percent of the time.