Triode tube breakdown

Crystal Oscillator

Mobile Phone Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 7.5PF 10PPM 20PPM 30PPM

Single Chip Microcontroller STM32L151CCU6

When the base of a transistor is open, and the voltage between the collector and emitter increases to a certain level, a breakdown phenomenon occurs as shown in Figure 1. The current (IC) rises rapidly, and once it reaches point A, the voltage drop across the transistor suddenly decreases, causing a sharp increase in current. The segment from A to B is referred to as secondary breakdown, and its transition time is on the order of milliseconds. At this stage, the transistor exhibits a negative resistance characteristic, which can be utilized to create a relaxation oscillator.

As illustrated in Figure 2, a stable DC power supply is obtained by first stepping down the 220V AC using resistor Rl, then rectifying it with diode D, and filtering it with capacitor Cl. This DC power charges capacitor C2 through resistor R2. As the voltage at the C2 terminal increases, it eventually reaches the breakdown voltage of the transistor V. When V breaks down, the resistance between its collector and emitter becomes very low, allowing C2 to discharge quickly through the speaker and the transistor. After discharging, V turns off, and the power supply begins recharging C2 through R2. Due to the short conduction time of V, the power consumption remains within acceptable limits, preventing damage to the transistor. Once C2 is fully charged again, V turns on once more, initiating an oscillation that drives the speaker to produce sound.

The circuit in Figure 3 is similar to that in Figure 2 but differs in the way the transistor is connected. The transistor used in this case is a 3DG12. According to the configuration in Figure 2, the breakdown voltage is 30V, while in Figure 3, it is only 7V. Therefore, when the resistor and capacitor values are the same, the oscillation frequency in Figure 3 is higher than that in Figure 2. When the power plug is removed, the charge stored in C1 continues to provide DC power to the oscillator. As the charge in C1 diminishes, the oscillation frequency gradually decreases. This makes the circuit suitable for use as a hypnosis device. It is recommended to plug in the power before use and then unplug it for operation to ensure safety. By selecting appropriate values for R2 and C2, the speaker can emit a sound resembling rain that starts dense and gradually fades, creating a hypnotic effect. The capacity of C1 determines the working time of the device, and increasing the time can be achieved by connecting multiple capacitors in parallel. With a 22μF C1, the device can operate for up to eight minutes.

Component selection includes: R1 = 2.2kΩ, R2 = 1MΩ, D = 1N4007, C1 = 22μF / 400V, C2 = 0.33μF / 160V, V = 3DG12, and the speaker impedance is 8Ω. The withstand voltage of C2 needs to be greater than the breakdown voltage of V. The transistor V can be selected from small-power transistors such as 9013, 9014, 9018, or the 3DG series. However, the breakdown voltage may vary slightly depending on the specific transistor used.

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