JPS62124477A - Vibrator driving circuit for ultrasonic sound wave transmitter - Google Patents

Abstract

PURPOSE:To prevent a power transistor (TR) from breaking down by applying the terminal voltage of the capacitor of an RC time constant circuit to the base of a switching TR connected between the base of the power TR and the ground. CONSTITUTION:The switching Tr2 is connected between the base of the power Tr1 and the ground. Then, the time constant circuit composed of a resistance R3 and capacitor C1 is connected to the output line of a pulse oscillator A and the ground and the terminal voltage Vc of the capacitor C1 is applied to the base of the Tr2. If abnormality occurs at a point t1 of time and a DC voltage Vd is developed at the output terminal (a) of the oscillator A, the capacitor C1 is charged through the resistance R3 and the voltage of the capacitor C1 is applied to the base of the Tr2. When the voltage Vc exceeds a threshold value Vt a certain time tau later, the Tr2 turns on to lower the base potential of the Tr1 to zero, thereby turning off the Tr1 forcibly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a vibrator drive circuit for an ultrasonic transmitter used in an ultrasonic object detector.

[Background Art] Generally, in an ultrasonic transmitter, as shown in Fig. 3,
The output of the high frequency power transistor Tr is boosted by a pulse transformer T and applied to the ultrasonic transducer S. A transmission signal consisting of a high-frequency pulse as shown in Figure $4 is applied to the base of this power transistor Tr, and when there is no transmission signal, the voltage at the input ia becomes L level and the power transistor Tr is turned off. Although it is supposed to be
If a DC voltage is applied to the input i due to a circuit failure or malfunction due to power supply noise, the resistance of the pulse transformer T is small, so the expensive high-frequency power transistor Tr+ may be overloaded. There is a problem in that current flows and the power transistor Tr is destroyed.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and when an abnormal voltage is applied to the input of a power transistor for driving a resonator, the negative abnormal input is immediately cut off and the power transistor is activated. It is an object of the present invention to provide a vibrator drive circuit for an ultrasonic transmitter that can prevent destruction.

[Disclosure of the Invention] The ultrasonic transmitter vibrator drive circuit according to the present invention applies the output of the pulse oscillator to the base of the power transistor via the base resistor, and connects the collector of the power transistor to the primary of the pulse transformer. In a resonator drive circuit that is connected to a DC power supply via a coil and also applies the secondary voltage of a pulse transformer to the resonator, a pulse is applied to the base of a switching transistor connected between the base of the power transistor and ground. It is characterized by applying the terminal voltage of the capacitor of the RC time constant circuit connected between the output m of the oscillator and the ground, and when a DC voltage appears at the input of the power transistor for some reason, the time A voltage is applied to the base of the switching transistor through a constant circuit, the switching transistor becomes conductive, and the power transistor is forcibly turned off.

FIG. 1 shows an embodiment of the circuit of the present invention. In the same figure, a pulse oscillator A outputs a transmission signal consisting of the high-frequency pulse shown in FIG.
, is applied to the base of. Further, the collector of the power transistor Tr is connected to a DC power supply vb via the primary coil of the pulse transformer T, and the secondary voltage of the pulse transformer T is applied to the vibrator S. The configuration up to this point is the same as the conventional example shown in FIG. 3, but in the present invention, a switching transistor Tr2 is further connected between the base of the power transistor Tr and the ground, and
A time constant circuit consisting of a resistor R1 and a capacitor C5 is connected between the output terminal of the pulse oscillator A and the ground, and the terminal voltage Vc of this capacitor C1 is connected to the switching transistor T.
One base of r2 is applied.

FIG. 2 shows the operation of the circuit of the present invention.

b and c show the waveforms of point a, point b, and point 0 in Figure 1, respectively. 6 During normal operation, a high-frequency pulse signal is output to point a, and this is amplified and a high-frequency pulse signal is also output to point 0. However, the terminal voltage Vc of the capacitor C1 of the time constant circuit hardly increases, and therefore the switching transistor Tr2 is in an off state.

If some abnormality occurs at time t1 in Fig. 2 and a DC voltage Vd appears at the output terminal a of the pulse oscillator A, the capacitor C3 is charged through the resistor R3 of the time constant circuit.
The terminal voltage Vc of this capacitor C1 is applied to the base of the switching transistor Tr2. When this voltage Vc exceeds the threshold value Vt after a certain period of time τ, the switching transistor Tr2 becomes conductive and the power transistor Tr2 becomes conductive.
, the base potential of the power transistor Trl is set to zero, and the power transistor Trl
force off. Therefore, as in the conventional example shown in Figure 3, a DC voltage is applied to the base of the power transistor, and an excessive current flows into the power transistor through the pulse transformer with low DC impedance, causing a mismatch that destroys the expensive power transistor. This can be prevented.

[Effects of the Invention] As described above, the advantage of the present invention is that the high frequency power transistor used in the vibrator drive circuit of the ultrasonic transmitter can be protected by adding the C± and am same sides. Therefore, there is an advantage that the reliability against 7ji source noise X and the like can be improved.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of various parts showing the same operation as above, and Fig. 3 is a circuit diagram of a conventional example.
The IS4 diagram is the same waveform diagram as above. A is a pulse oscillator, S is a vibrator, T is a pulse transformer,
Trl is a power transistor, Tr2 is a switching transistor, and R1-R3 are resistances %R,,c. is a time constant circuit. Agent Patent Attorney Ishi 1) Chief 7 Figure 1 Figure 4

Claims (1)

[Claims] (1) The output of the pulse oscillator is applied to the base of the power transistor via the base resistor, the collector of the power transistor is connected to the DC power supply via the primary coil of the pulse transformer, and the secondary voltage of the pulse transformer is In a resonator drive circuit configured to apply voltage to the resonator, the base of the switching transistor connected between the base of the power transistor and the ground is connected to the terminal of the capacitor of the RC time constant circuit connected between the output terminal of the pulse oscillator and the ground. A vibrator drive circuit for an ultrasonic transmitter, characterized in that it is formed by applying a voltage.