JPS63290005A - Overload preventing device for power amplifier - Google Patents

Abstract

PURPOSE:To suppress the output current of a power amplifier below a saturation area, and to enable a frequency sweep in a wide band without any control by providing a compensation circuit, which has a contrary characteristic against the frequency characteristic of a load current, in the input side of the power amplifier. CONSTITUTION:The compensation circuit 11 and the power amplifier 12 are connected in series to the output side of an oscillator 10 to oscillate at a prescribed frequency, and in addition, a load 13, consisting of a capacitive element such as a piezo-electric vibrator, etc., or an inductive element such as a magnetostrictive vibrator, etc., is connected at the output side of the said power amplifier 12. The compensation circuit 11 has the frequency characteristic, which is contrary to the frequency characteristic of the load current, supplied from the power amplifier 12 to the load 13, and it is the circuit to increase or decrease and compensate the output voltage of the oscillator 10. Since the output load current (i) of the power amplifier 12 is maintained to be constant by the compensation circuit 11, it the output voltage of the oscillator 10 is set previously in one frequency in the sweep frequency range and within a range, in which the load current (i) of the power amplifier 12 is not saturated, the frequency sweep in the wide band can be executed without any control.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an overload prevention device for a power amplifier that supplies power to a load.

(Prior Art) Conventionally, as a technology in this field, there has been a technology as shown in FIG. 2, for example. The configuration will be explained below.

FIG. 2 is a block diagram showing an example of the configuration of a load driving device using a conventional power amplifier.

This device converts the signal generated by an oscillator 1 into a power amplifier 2.
This is used to amplify the signal and drive the load 3.

Here, if negative vJ3 is a capacitive element (C) such as a piezoelectric vibrator in an ultrasonic generator, or a dielectric element (L) such as a magnetostrictive vibrator, the load impedance is It changes by 1/ωC or ω[ with respect to f (=ω/2π, ω: angular frequency). Therefore, when driving the load 3 at an arbitrary frequency f, the load current increases at the frequency f where the load impedance is low, and the output of the power amplifier 2 may become overloaded.

Therefore, conventionally, overload conditions have been prevented in the following manner, for example.

(2) Set the voltage applied to the power amplifier 2 so that the load current does not exceed the output current limit of the power amplifier 2 at the sweep upper limit or lower limit frequency. For this purpose, the power amplifier 2
The output voltage of the oscillator 1, which is input to the oscillator 1, was adjusted.

■ The frequency was divided into multiple sections within the sweep frequency range, and the voltage applied to power amplifier 2 was set in stages so that it did not exceed the output current limit of that power amplifier within that section. .

(Problems to be Solved by the Invention) However, the apparatus having the above configuration has the following problems.

In the above prevention measure (2), the voltage applied to the power amplifier 2 is determined by the load impedance of the upper limit station wave number, so even though there is a margin in the voltage that can be applied in the low frequency range f, the voltage applied to the power amplifier 2 is There was a problem in that the output current of the motor was limited, and the driving ability for the load 3 was reduced.

In addition, in the above-mentioned preventive measure (2), the input of the power amplifier 2 must be adjusted every time the number of routed waves is increased by 1 (v1) in an interval, which makes the operation complicated.

The present invention provides an overload prevention device for a power amplifier that solves the problems of the prior art, such as reduced drive capacity and complicated operation.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a device for supplying power from a power amplifier to a capacitive or dielectric load by frequency sweeping. A compensation circuit having opposite characteristics to the power amplifier is provided on the input side of the power amplifier.

(Function) According to the present invention, since the overload prevention device for the power amplifier is configured as described above, even if the load impedance determined by the sweep frequency changes, the compensation circuit adjusts the input power of the power amplifier accordingly. It works to increase or decrease the voltage and keep the load current output from the power amplifier constant. This prevents the power amplifier from being overloaded. Therefore, the above-mentioned problem can be eliminated.

(Embodiment) FIG. 1 is a block diagram of a configuration of an overload prevention device for a power amplifier showing an embodiment of the present invention.

In FIG. 1, a compensation circuit 11 and a power amplifier 12 are connected in cascade to the output side of an oscillator 10 that excavates at a predetermined frequency, and a capacitor such as a soup-electric type vibrator is connected to the output side of the power amplifier 12. A load 13 consisting of a dielectric element such as a magnetic element or a magnetostrictive vibrator is connected.

The compensation circuit 11 has a frequency characteristic opposite to the frequency characteristic of the load current supplied from the power amplifier 12 to the load 13, and is a circuit that adjusts and compensates for the output voltage of the oscillator 10.

FIGS. 3(1) and 3(2) are circuit diagrams showing an example of the configuration of the compensation circuit 11. The compensation circuit 11 in FIG. 3(1) is composed of a low-pass filter (hereinafter referred to as LP) consisting of an inductor 20 and a capacitor 21 branch-connected to the inductor 20. Also, the compensation circuit 11 in FIG. 11 is composed of a bypass filter (hereinafter referred to as IIPF) consisting of a capacitor 22 and an inductor 23 branch-connected to the capacitor 22.The LPF and HPF combine the positive and negative actance characteristics of the inductor and capacitor to obtain a predetermined frequency characteristic. This is the circuit that obtains the following.

The operation of the power amplifier overload prevention device configured as described above will be explained.

When a voltage of a predetermined frequency is output from the oscillator 10, this output voltage is amplified by a power amplifier 12 through a compensation circuit 11, and then supplied to a load 13.

When the load 13 is a capacitive element (C), its impedance is 1/ωC, and when the load 13 is a dielectric element (C), its impedance is 1/ωC.
In the case of , the impedance becomes ωL.

When the load applied voltage ■ is constant, the load current i supplied from the power amplifier 12 to the load 13 has a frequency f
(=ω/2π), the capacitive element increases proportionally with i=v·ωC, and the inductive element decreases proportionally with i=v·1/ω[. The slope of these load currents i with respect to the frequency f is
Capacitive element (3CIB10Ct, dielectric element -6d)
It becomes B10Ct. Therefore, if the load 13 is a capacitive element, the slope is -6d in the opposite direction to the slope of 5dB10ct.
When the compensation circuit 11 is configured with the LPF shown in FIG. 3 (1) having a B10ct characteristic, and the load 13 is an inductive element, the slope is -66 [5dB10 in the opposite direction to 310ct.
If the compensation circuit 11 is configured with the HPF shown in FIG. 3 (2) having a
The current i supplied from the power amplifier 12 is maintained at a constant value.

In this way, since the output J load current i of the power amplifier 12 is held constant by the compensation circuit 11, the output voltage of the oscillator 10 can be adjusted in advance at one frequency within the sweep frequency range.
If the load current i of the power amplifier 12 is set within a range that does not saturate, a wide band frequency sweep can be performed without adjustment.

Note that the present invention is not limited to the illustrated embodiment; for example, the compensation circuit 11 may be configured with other filters such as an RC filter other than the LC filter shown in FIG. It is also possible to do so. Also, the first
The circuit described above may be added to the device shown in the figure.

(Effects of the Invention) As explained in detail above, according to the present invention, a compensation circuit having an inverse characteristic to the frequency characteristic of the load current is provided on the input side of the power amplifier. Even if the load impedance changes, the output current of the power amplifier is suppressed below the saturation range, making it possible to sweep a wide frequency band without adjustment.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a power amplifier overload prevention device according to a practical example of the present invention, FIG. 2 is a block diagram of a conventional device, and FIGS. FIG. 3 is a circuit diagram showing a configuration example of the compensation circuit shown in the figure. 10... Oscillator, 11... Compensation circuit,
12...Power amplifier, 13...Load.

Claims (1)

[Claims] In a device that supplies power from a power amplifier to a capacitive or dielectric load by frequency sweep, a compensation circuit having characteristics opposite to the frequency characteristics of the load current is provided on the input side of the power amplifier. Features: Overload prevention device for power amplifiers.