Electric OU: Supplement: MOSFETs… HOW Do They Work? Part 5
Please watch the other parts from Parts 2&3 (one video) and Part 4 first, as I am building up the circuit in stages. (Part 1 is from a long time ago and isn’t necessary to understand these segments, but these present ones should be viewed in order.) In the last video I demonstrated how the magnitude of the gate charge is what keeps a mosfet turned on and to what degree. The charge must be removed or allowed to bleed off the gate for the mosfet to turn off. Adding a 33 microFarad tantalum capacitor in parallel with the mosfet’s gate-source capacitance adds greatly to the total charge at the gate, of which only a tiny portion is needed to keep the gate itself charged and open. This charge can then be bled off at any desired rate by using a variable resistor. I’ve here illustrated a basic RC timer circuit, using a variable resistor to control the rate of the decay of the mosfet’s gate charge and thus to control the timing of the shutoff of the load. Now all we need is a repetitive way to re-charge the gate every time it discharges fully, and we will have invented the oscillator. Parts used so far: IRF530N mosfet (almost any n-ch mosfet will work but the time performance will vary) 470R resistor 100R resistor 1M potentiometer 10M ten-turn trimpot 33 microFarad tantalum capacitor “2-cell” flashlight bulb 4 volt DC power source “ElCheepo” DMMs
