DE2535807A1 - Ultrasonic oscillator circuit for liquid spray - has coupling transformer between pulse circuit and piezoelectric oscillator - Google Patents

Abstract

A liquid spray device has a piezoelectric spray unit inductively coupled to the sociallator portion of the circuit by a transformer (2). The oscillator has a transistor (5) which has the primary (21) of th transformer between its collector and base. A resistor (6) in series with the primary has the supply connection (100) at their junction. A return coupling transformer (3) is positioned in the base emitter circuit with a capacitor (4) between the secondary (31) and the primary (32) of this transformer at a further contact (101) is located at the junction between this capacitor (4) and the secondary.

Description

Excitation circuit for piezoelectric oscillating system The invention relates to excitation electronics for a piezoelectric oscillating system for liquid atomization.

In the German Offenlegungsschrift 2 308 584 (YPA 73/7020) is a such a piezoelectric oscillating system described. A piezoelectric transducer is excited by an alternating voltage to form ultrasonic vibrations. The converter is arranged on the base of a regular, massive sound transmitter, there is an atomizer plate at the tip of the sound transducer. Through the piezoelectric transducers are generated in the sound transmitter, which are transferred to the atomizer plate with increased amplitude.

The object of the invention is to provide an extremely simple structure Specify excitation electronics for such a vibration system, the excitation electronics only need an operating voltage between 6 to 12 V direct current, and where Shifts in the resonance frequency of the oscillating system do not lead to any interference target.

This task is solved by an electronic excitation system, which accordingly the characterizing part of claim 1 is formed.

The invention is explained below with reference to the figure.

The figure shows a circuit diagram of the excitation electronics. For the atomizer 1 its equivalent circuit diagram is used.

Electrically, the atomizer behaves like a capacity 10, to of a further capacitance 11 and an inductance 12 and an ohinscher contact 13 are connected in parallel. The capacity 10 depends essentially on the electrical The capacity of the piezoceramic of the atomizer decreases and becomes "electrical" accordingly Called capacity. The capacitance 11, the inductance 12 and the resistor 13 become by the mechanical properties of the atomizer, in particular by its mechanical properties Inertia, definitely, accordingly one speaks of "mechanical capacity" and "mechanical inductance".

The actual excitation electronics consists of only five circuit elements, a coupling transformer 2, a feedback transformer 3, a capacitor 4, a transistor 5 and a resistor 6.

The circuit is constructed in the following manner; Between the terminals 100, 101 are the resistor 6, the secondary coil 31 of the transformer 3 and the capacitor 4.

The primary coil 32 of the transformer 3, the Transistor 5 and the primary coil 21 of the transmission transformer 2. It is the emitter of the transistor is connected to the coil 32, the collector to the coil 21, the base of the transistor is connected between the resistor 6 and the coil 31.

This circuit can be operated with DC voltages between 6 V and 12 V. depending on which transmission ratio for the coupling transformer 2 is selected.

The excitation frequency for the nebulizer is essentially through the series resonant circuit consisting of the coil 31 and the capacitor 4 is specified.

Since the ultrasonic transducer via the coupling transformer 2 only is inductively coupled to the excitation circuit, all safety regulations are advantageous for contact protection well met.

The current feedback achieved by the transformer 3 leads to a high level of stabilization of the atomizer operation, with all fluctuations in the Resonance frequency of the atomizer, for example due to heating, production-related Scattering and under the damping influence of the liquid to be atomized the atomizer can be compensated.

The atomizer has two resonance frequencies, a so-called series resonance where f11,12 is the frequency, and where CII is capacitance 11 and where L12 is inductance 12. Furthermore, the oscillator has what is known as parallel resonance at the frequency where C10 is the capacitance 10.

Because the impedance of the atomizer in the case of series resonance is a minimum reached, so that a high power is consumed at a given voltage on the transducer is intended to operate the excitation electronics at this frequency and to be interpreted accordingly.

The circuit elements of the excitation electronics are to be dimensioned in such a way that the following applies: C each denotes a capacitance and L an inductance, the indices denote the respective positions in the figure.

The ratio of the number of turns N of the secondary and primary coil N31 / N32 of the transformer 3 is approximately equal to the current gain factor of transistor 5.

If the atomizer is loaded or heated, this oscillating system becomes slightly out of tune as the mechanical inductance and capacitance change: The second quotient in the above conditional equation becomes smaller. Through this will the impedance between the collector and the terminal 100 is greater.

At the same time, the impedance of the primary coil 31 and the Capacitor 4 existing series resonant circuit lower. So that becomes the potential at the base of the transistor despite lower collector or emitter currents little changed. The decreasing frequency of the nebulizer therefore causes an active one Feedback mechanism.

In addition, it must be achieved that at the intended operating frequency for the atomizer there is as little phase shift as possible between current maxima and voltage maxima at the atomizer. As already stated at the beginning, the intended operating frequency is: If no phase shifts are to occur at this frequency, the condition must at least approximately be fulfilled: C10L22 = L12C11.

This ensures that the atomizer also has sufficient power can record if the resonance frequency of the transducer, as described above, something is changed.

With the excitation electronics according to the invention, an atomizer unit built by disturbances such as warming or irregular fluid supply to the transducer, its function is not affected, because the resonance frequency Supportive current feedback ensures that the atomizer is also attenuated Operation. Since the excitation electronics only consist of a small number of components, can achieve a very small construction volume and an extremely low price will. The excitation electronics work with low voltage.

2 claims 1 figure

Claims (2)

Claims t1.) Excitation electronics for an ultrasonic transducer, in which the vibrations are generated with piezoceramic means, thereby g I do not know that the ultrasonic transducer has a coupling transformer (2) is inductively coupled to the excitation electronics that the excitation electronics one The transistor (5) has the primary coil in the collector-base circuit of this transistor (21) of the coupling transformer (2) and a resistor (6) is between the primary coil and the resistor have a connection (100) for supplying the operating voltage and that in the base-emiter circuit of this transistor there is a feedback transformer (3) lies, with this between the secondary coil (31) and the primary coil (32) Transformer is a capacitor (4), and between this capacitor (4) and the secondary coil another connection (111) for supplying the operating voltage is arranged, and that the elements of the activation circuit are dimensioned so that the following applies: (C4L31) -1/2 <(C11L12) -1/2 <(C10L22) -1/2 and C10L22 # capacity L12C11 where with C4 the capacitance of the capacitor (4), with L31 the inductance of the secondary coil (D ') of the feedback transformer (3) and with L22 the inductance of the secondary coil (22) of the coupling transformer (2), and where C10 is the electrical Capacitance, C11 the mechanical capacitance and L12 the mechanical inductance of the Ultrasonic vibrators (1) are. 2. excitation electronics according to claim 1, characterized g e k e n n z e i c h -n e t that a DC voltage between 6 and 12 V is provided as the operating voltage is. Blank page