This circuit resembles a "capacitor three-point" oscillator, where alternating current flows through the collector of a transistor. When metal is brought near, the coil generates a magnetic field that can detect the presence of metal. The circuit uses an LC sine wave oscillator (capacitor three-point type) capable of producing frequencies in the tens of megahertz range. The oscillation frequency is determined by the values of inductor L and capacitors C2, C3, and C4. Capacitor C1 acts as an AC ground, allowing the circuit to resonate with the inductor.
Only the detection portion of the metal detection circuit is shown here, without the full detection circuit. When the inductor (L) comes close to a metal object, the high-frequency voltage induced by the sensing coil is picked up by the high-frequency oscillator and sent to the amplification stage. Finally, the signal is output through a speaker, indicating the presence of metal.
The formula for the oscillation frequency is F = 1/(2π√(LC)). In analyzing the transistor circuit, an AC equivalent method is commonly used. To achieve oscillation, the three terminals of the transistor are typically connected to capacitors in a ring configuration. Different capacitors charge and discharge, satisfying the basic conditions for oscillation. If the phase shift in the feedback loop exceeds 135 degrees, sustained oscillation can occur.
At power-up, capacitors C1, C2, and C3 begin charging. Since C1 has a larger capacitance, it establishes a voltage quickly. Once this voltage reaches a certain threshold, the transistor turns on, causing the voltage across C3 to drop and the voltage across C4 to rise. This causes the transistor to turn off, allowing C1 to recharge. During this process, current flows through the induction coil, and C3 is recharged. Meanwhile, the voltage on C4 discharges through parallel resistors, gradually lowering the voltage at the emitter. As the voltage on the transistor becomes forward-biased again and the voltage on C1 increases, the transistor turns on once more, completing the cycle.
This continuous charging and discharging creates a stable oscillating signal, which is essential for the metal detection function.
Usb To Usb-C Cables,Fast Charging Usb C Data Cable,Customizable Type-C Data Cable,Premium Type-C Data Cable
Dongguan Pinji Electronic Technology Limited , https://www.iquaxusb4cable.com