Astable Multivibrator


If you have been keeping up with my videos, you would have seen the Dual Driver in the high voltage section, here is the diagram again to save you searching


but lets just concentrate on the basic oscillator and driver mosfet


This is a very versatile circuit, and is in fact the first working transistor circuit I built at around the age of 15, and I still prefer it instead of the ubiquitous NE555.
Not only is it an oscillator, but it has 2 opposing outputs which can be used to drive a multitude of things, in the dual driver page I show several ways to drive transformers as inverters to generate high voltages.

With a bit of rewiring of the variable resistor, this can easily be made into a PWM driver as in this diagram below



Notice the use of one output, this circuit can be used to drive a DC motor as a speed controller, and in fact that is what I have done for my coil winder, using a cordless drill motor and gearbox.

If you feel that you want the best of both worlds, how about another slight change to the variable resistor and adding another, now you can control the mark space ratio (pwm) and the frequency



As I suggested above, this is very versatile and robust, and is open for experimentation, if you change the values of the capacitors to something bigger in value, you will get a longer delay between switching, you could use it as a timer.
Because it is an oscillator, you could use it for a tone generator, i'm sure some of you may want to try adding a resistor network instead of the variable resistor, and make a musical keyboard, others may wat to flash some lights, speaking of lights, this circuit can have more stages added, and can sequence the outputs like this



When used to drive a transistor on the output, remember that the transistor you are driving it from musy be in the turned off state for the driven transistor to be turned on via the resistor connected to the positive rail
The basic circuit can be driven from one supply voltage (say 6 - 12 volts), while powering the output transistors and load from a much higher voltage, providing the negative rail is common to both supplies.



The oscillator could use PNP transistors while the drivers use NPN on mosfets, in which case the oscillator transistors will turn the driven transistors on (inverse to the normal circuit)

Have fun with this circuit, change values and transistors, also search for other "Astable Multivibrator" for more ideas.







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