SU557825A1 - Ultrasonic generator with automatic frequency control - Google Patents

Description

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The invention relates to the field of acoustic engineering and can be used in technological processes, for example, in the chemical, medical, watch and jewelry industries, where a certain value of the amplitude of the transducer working element is required.

Ultrasonic oscillators with automatic frequency control are known, containing a transducer, a sensor, an amplifier, an anti-parasitic filter, a phase shifter, a power amplifier, a limiter, and a voltage regulator.

Known generators have a complex circuit and the associated high labor intensity in the manufacture and configuration, low maintainability and high cost.

The closest technical solution to the present invention is a generator containing an amplifying cascade on two transistors connected by a transformer coupling to an oscillating circuit of a piezo emitter.

With the obvious simplicity of the scheme, it does not provide highly efficient operation of the piezo emitter, since it does not ensure the operation of the piezoelectric elements at the frequency of their mechanical resonance. The transistors are excited by a signal proportional to the total current of the piezo emitter, which does not coincide in phase with the voltage across it due to the presence of an uncompensated piezo plate capacitance. Therefore, the piezo emitter operates at the frequency of electrical resonance, not mechanical. In addition, this generator is less reliable in operation, since the transistors are not protected against overvoltage in the emitter-base circuit, which can occur during load fluctuations.

The aim of the invention is to increase the efficiency and availability of the generator.

This is achieved in the proposed generator by driving the input to the transistors.

the amplifying stage from the secondary winding of a differential transformer through a phase-shifting capacitor and two diodes shunting the input of each transistor when a blocking voltage is applied to them. The selected amplitude of the excitation signal ensures the operation of transistors in an economical key mode.

The feature of the circuit is a soft self-excitation of the oscillator, the possibility of using one differential transformer winding to drive two transistors, while due to the shunt effect of the diode, the possibility of breakdown of the locked transistor along the emitter-base circuit is excluded.

The drawing shows a schematic diagram of the proposed generator.

The installation contains an amplifier cascade 1 on two transistors 2 and 3 with an output transformer 4, an output circuit 5 with a capacitor 6 compensating for the capacitive current of the piezo-emitter 7 and feedback, including a differential transformer 8, a phase-shifting capacitor 9 and two diodes 10, And included in the emitter-base sections of each transistor of the amplifier cascade.

The amplifier stage operates in the auto-oscillator mode at the frequency of the mechanical resonance of the piezo-emitter. A signal proportional to the current of the mechanical branch of the piezo emitter is distinguished by the use of a differential transformer 8, in the magnetic flux of which the components of the capacitive currents of the piezoelectric sender 7 and the specially selected capacitor 6 are mutually destroyed. The capacitor 9 corrects the phase of the excitation signal applied to the input of the transistors, with one transistor opening in each half-period of the excitation voltage, and its excitation current flows through a diode shunting the locked transistor. This allows the use of a differential transformer 8 without a midpoint on the secondary winding, which simplifies the circuit. The same measure provides protection of the locked transistor against overvoltage across the output terminals, since the input terminals are shorted by a conducting diode. In addition, the inclusion of diodes at the input of a push-pull auto-oscillator allows for a more gentle self-excitation than in conventional push-pull circuits with A / C-chains in the base circuits of transistors.

Claims (1)

Invention Formula An auto-tuning ultrasonic generator containing an amplifying cascade on two transistors connected by a transformer coupling to an oscillating circuit of a piezoelectric transducer, characterized in that, in order to increase the efficiency and increase the reliability of the generator, the frequency-tuning block is made of a differential transformer circuit connected with an oscillating circuit of a piezo emitter, and the outputs of its secondary winding are connected, respectively: the first to the base of the first transistor, the second to the b se of the second transistor, the phase-shifting the capacitor of the circuit is connected between the first output of the secondary winding and the base of the first transistor, and the amplifier cascade contains two diodes connected by negative leads to the base of the corresponding transistor, and positive leads between each other and the emitters of the transistors.