High power alarm Oscillator
This project is a power oscillator that will surprise you of the power that can make a circuit with a single transistor.
The circuit is simple. 10K resistor supplies current to the base of the transistor to turn completely on when the key is first closed. The initial source of the base current is the 12 volt supply and the voltage induced in the lower half portion of the winding center-tapped transformer.
After a lapse of time, the transformer core becomes saturated magnetic flux and the induced voltage falls to zero. When this happens, the transistor base current is reduced sufficiently to allow the transistor to start out of the full working order.
When the transistor begins to emerge from the condition, the collector current of the transistor down decreases the magnetic field of the transformer. This decrease in flux induces a reverse bias voltage to try to stop further transistor.
This action is regenerative because a change in the collector current causes the polarity of the base voltage induced increasing the change (decrease) in the collector current. This change of state of full StART to fully Stop happens very quickly.
After a time, the collapsing magnetic field begins to slow down as it approaches its minimum alimentation. The bias voltage caused by the magnetic flux change is exceeded by the voltage supplied by the batteries, and the transistor is turned back on again to restart the cycle.
No capacitor is used in this circuit, the saturation characteristics of the transformer alone provide the switching characteristics of this circuit. Oscillators of this type are used for DC converters and AC inverters for DC to DC, but usually with two transistors in a type of operation in two alternations.
This project uses about 100 mA battery, so if you use this circuit, the batteries need to be replaced often. Note that the 12 volt power is equal to the voltage of the automobile batteries. Then, you could therefore use such as burglar alarm oscillator without changes in a car.