Reverse Bias Oscillators

Description: Several NPN transistors can oscillate within the audio frequency range when reverse biased. The minimum supply voltage required is 7V for low-power transistors like the BC109, BC238, and 2N2222A; it increases to 12V for medium-power transistors such as the BD139, and reaches 16V for power transistors like the BUX22 and 2N6543. The current drain is 4mA at 9V, with an oscillation frequency of 550Hz. The base terminal is typically left open.

The described circuit utilizes multiple NPN transistors configured in a manner that allows for audio frequency oscillation. When reverse biased, these transistors can enter a state of oscillation, which is commonly exploited in audio applications. The choice of transistors is crucial, as each type has specific voltage and current requirements that influence the overall performance of the circuit.

For low-power applications, transistors such as the BC109, BC238, and 2N2222A operate effectively with a minimum supply voltage of 7V. These devices are suitable for low-current applications and can generate oscillations at a frequency of approximately 550Hz when supplied with 9V and a current drain of 4mA.

Medium-power transistors like the BD139 require a higher minimum supply voltage of 12V, making them more suitable for applications that demand slightly higher power levels.

For high-power applications, transistors such as the BUX22 and 2N6543 are utilized, necessitating a minimum supply voltage of 16V. These transistors are capable of handling larger currents and can sustain the oscillation without significant distortion or loss of amplitude.

The base terminal of the transistors is typically left open, which allows for a self-oscillating condition to be established. This configuration can lead to a robust oscillation mechanism, as the transistors can amplify the feedback signal generated by the circuit itself.

In summary, the circuit design leverages the characteristics of various NPN transistors to achieve audio frequency oscillation, with careful consideration given to supply voltage and current ratings based on the specific transistor type employed. This versatility allows for a wide range of applications in audio signal generation and processing.There are a number of npn transistors that will oscillate in the audio range when reverse biased. Minimum supply voltage is 7V for low power transistors such as BC109, BC238 and 2N2222A, it becomes 12V for medium power transistors such as BD139 and is 16V for power transistors as BUX22 and 2N6543. Current drain is 4mA at 9V and frequency of oscill ation is 550Hz. The base is normally left open.