JP2015192985A - Ultrasonic vibrator drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a transistor oscillation circuit from an excessive current with a simple circuit configuration.SOLUTION: An ultrasonic vibrator drive circuit comprises: a transistor oscillation circuit 20 which drives an ultrasonic vibrator TD; and a protection circuit 30 which protects the oscillation circuit. The protection circuit 30 comprises: an FET Q2 for cutting off a power supply line to the oscillation circuit 20; a current detection resistor R3 which generates the voltage drop in proportion to the supply current to the oscillation circuit 20; and an SCR which turns on when the voltage drop is equal to or greater than a predetermined value and holds the on-state afterward by itself. The FET Q2 is controlled by the SCR so as to be in a conduction state in an off-state of the SCR, and be in a cut-off state in an on-state of the SCR to cut off the power supply to the oscillation circuit 20.

Description

  The present invention relates to an ultrasonic transducer driving circuit that drives an ultrasonic transducer (piezoelectric transducer) for generating ultrasonic waves to atomize a liquid.

  An ultrasonic atomizer that generates ultrasonic waves to atomize a liquid is widely used. In such an ultrasonic atomizer, if an event occurs in which the ultrasonic transducer itself or both ends of the ultrasonic transducer are short-circuited, the transistor of the ultrasonic transducer drive circuit may be damaged. is there. In addition, it is known that leakage current is generated due to deterioration of the ultrasonic vibrator, and it is necessary to take a protection measure against an ultrasonic atomizer malfunction due to the leakage current.

  FIG. 2 shows a basic circuit configuration of a conventional ultrasonic transducer driving circuit. In this figure, the ultrasonic transducer drive circuit is an ultrasonic vibration connected between the collector and base of the transistor Q1 via the oscillation transistor Q1, capacitors C1 to C4, coils L1 and L2, and bias resistors R1 and R2. A Colpitts oscillation circuit having a child TD, and a DC power supply 10 is connected between the positive and negative power supply lines.

  In the circuit configuration of FIG. 2, when both ends of the ultrasonic transducer TD are short-circuited, the collector-base of the oscillation transistor Q1 is short-circuited, an excessive current flows, and the transistor Q1 is damaged.

  FIG. 3 shows another circuit configuration of a conventional ultrasonic transducer drive circuit. In addition to the circuit configuration of FIG. 2, a DC cut capacitor C6 is inserted in series with the ultrasonic transducer TD. In this case, the DC component current can be cut by the capacitor C6, and damage to the oscillation transistor Q1 caused by short-circuiting both ends of the ultrasonic transducer TD can be avoided, but a bias current is always applied to the base of the transistor Q1. Since it is necessary to supply via the resistors R1 and R2, it is basically difficult to prevent the base current from flowing when the bias current supply side is short-circuited.

  Japanese Patent Application Laid-Open No. H10-228707 adds an overcurrent protection function to a spray device using a piezoelectric vibrator.

In Japanese Patent Laid-Open No. 2003-79728, an analog / digital conversion circuit for providing a current-voltage conversion circuit and a full-wave rectification circuit between a drive circuit and a vibrator and binarizing the output thereof, an overcurrent A logic operation mechanism is required to measure these events. If a processing circuit such as a microcomputer is used, advanced processing is possible, but there is a cost for the power supply for the microcomputer and the microcomputer itself. The current consumption also increases somewhat.

  As another countermeasure against excessive current, a configuration has been proposed in which a resistor fuse is inserted in the drive circuit, and when the excessive current flows, the fuse is blown to disconnect the circuit connection. However, with this measure, the user cannot easily replace the resistance fuse even when the drive circuit components are almost usable, so it is not possible to use the drive circuit for operation, and it is necessary to return the equipment to the seller for repair. To do.

  The present invention has been made in view of such a situation, and an object thereof is to provide an ultrasonic transducer driving circuit capable of protecting a transistor oscillation circuit from an excessive current with a simple circuit configuration.

  Another object of the present invention is to provide an ultrasonic transducer driving circuit capable of improving safety by detecting an excessive current or leakage current of a transistor oscillation circuit and stopping operation with a simple circuit configuration. There is.

The first aspect of the present invention is an ultrasonic transducer drive circuit. The ultrasonic transducer driving circuit includes a transistor oscillation circuit that drives the ultrasonic transducer, and a protection circuit that protects the oscillation circuit.
The protection circuit includes a first semiconductor switch element for cutting off a power supply line to the oscillation circuit, a current detection resistor that generates a voltage drop proportional to a supply current to the oscillation circuit, and the voltage drop is predetermined. A second semiconductor switch element that turns on at a value or higher and then self-holds the on state;
The first semiconductor switch element is controlled by the second semiconductor switch element, and when the second semiconductor switch element is in an OFF state, the first semiconductor switch element is in a conductive state, and the second semiconductor switch element In the on state, the first semiconductor switch element is cut off, and power supply to the oscillation circuit is cut off.

  In the first aspect, a voltage due to the voltage drop may be applied to a gate of the second semiconductor switch element through a time constant circuit.

  In the first aspect, the switch for turning on / off the driving of the ultrasonic transducer by the oscillation circuit may be provided so as not to release the self-holding of the second semiconductor switch element.

  In the first aspect, the second semiconductor switch element may be a thyristor or a triac.

  It should be noted that any combination of the above-described constituent elements, and those obtained by converting the expression of the present invention between methods and systems are also effective as aspects of the present invention.

  According to the ultrasonic transducer driving circuit of the present invention, the transistor oscillation circuit can be protected from an excessive current by a protection circuit having a simple circuit configuration. Further, safety can be improved by detecting an excessive current or leakage current of the transistor oscillation circuit and stopping the operation.

1 is a circuit diagram showing a first embodiment of an ultrasonic transducer driving circuit according to the present invention. The circuit diagram of the conventional basic ultrasonic transducer drive circuit. The circuit diagram of another conventional ultrasonic transducer drive circuit. The circuit diagram which shows 2nd Embodiment of the ultrasonic transducer | vibrator drive circuit which concerns on this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent component, member, process, etc. which are shown by each drawing, and the overlapping description is abbreviate | omitted suitably. In addition, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

  FIG. 1 shows a first embodiment of an ultrasonic transducer driving circuit according to the present invention, in which a protection circuit 30 is added to a transistor oscillation circuit (Colpitts oscillation circuit) 20 similar to FIG. The transistor oscillation circuit 20 and the protection circuit 30 are mounted on the drive substrate, and the ultrasonic transducer TD is connected between the collector and base of the transistor Q1 mounted on the drive substrate, as in the case of FIG.

  The protection circuit 30 includes an N type MOSFET Q2 of enhancement type as a current detection resistor R3 and a first semiconductor switch element inserted in series in a negative power line connecting the transistor oscillation circuit 20 and the DC power source 10. And a resistor R4 connected between the positive power supply line and the negative power supply line, a thyristor (SCR: Q3) as a second semiconductor switch element, and a voltage drop of the current detection resistor R3 at the gate of the thyristor Q3. CR time constant circuit (capacitor C5 and resistor R5) for applying a voltage.

  In the transistor oscillation circuit 20, a switch SW1 for turning on / off the driving of the ultrasonic transducer TD is inserted between the bias resistors R1 and R2 and the base of the transistor Q1, and the resistor R6 is a current detector for detecting the base of the transistor Q1. The resistor R3 is connected between one end of the resistor R3. The resistor R6 ensures that the transistor Q1 is turned off by setting the base of the transistor Q1 to the potential of the negative line when the switch SW1 is turned off.

  In the protection circuit 30, the current detection resistor R3 generates a voltage drop proportional to the current supplied to the oscillation circuit 20, and the voltage across the resistor R3 passes through a time constant circuit composed of a capacitor C5 and a resistor R5, and the thyristor Q3. (When the N-type MOSFET Q2 is conductive, the voltage drop substantially becomes the voltage between the gate and the cathode of the thyristor Q3). The thyristor Q3 is turned on when the gate voltage with respect to the cathode becomes a predetermined value (for example, 1 V) or more. The predetermined value is a voltage value corresponding to a voltage drop of the current detection resistor R3 when an excessive current flows from the DC power supply 10 into the transistor oscillation circuit 20. When the thyristor Q3 is turned on, the gate of the N-type MOSFET Q2 has the same potential as the negative power supply line, and the N-type MOSFET Q2 is turned off.

  The time constant of the time constant circuit composed of the capacitor C5 and the resistor R5 is set so that the protection function of the protection circuit 30 works immediately after the N-type MOSFET Q2 becomes conductive when the power supply voltage is turned on. That is, when the internal resistance of the N-type MOSFET Q2 immediately after power-on is not negligible, the voltage drop due to the series resistance value of the current detection resistor R3 and the N-type MOSFET Q2 that is the voltage between the gate and the cathode of the thyristor Q3 increases. Although the gate voltage of thyristor Q3 becomes excessive and may be erroneously recognized as being in an overcurrent state, it may turn on, but the time constant of the time constant circuit (for example, several tens of ms) gradually increases the gate voltage and turns on the power. The malfunction of the thyristor Q3 immediately after is avoided. The time constant circuit also prevents abrupt gate voltage fluctuation caused by external noise or the like.

  In the configuration of FIG. 1, after connecting the ultrasonic vibrator TD between the collector and base of the oscillation transistor Q1 of the transistor oscillation circuit 20, the DC power supply 10 is connected between the positive power supply line and the negative power supply line. When the switch SW1 inserted in the base bias circuit of the transistor Q1 is turned on, the transistor oscillation circuit, which is a Colpitts oscillation circuit, oscillates and generates ultrasonic vibrations in the ultrasonic transducer TD. Perform liquid atomization. Under normal conditions, the voltage drop of the current detection resistor R3 of the protection circuit 30 is a voltage value lower than a predetermined value at which the thyristor Q3 is turned on. For this reason, the voltage of the positive power supply line is applied to the gate of the N-type MOSFET Q2 via the resistor R4, and the N-type MOSFET Q2 is kept on. When the switch SW1 is turned off, the oscillation of the transistor oscillation circuit 20 is stopped and the ultrasonic vibration of the ultrasonic transducer TD is also stopped.

  On the other hand, when an excessive current flows through the oscillation transistor Q1 due to a short circuit state of the ultrasonic transducer TD itself, the voltage drop of the current detection resistor R3 of the protection circuit 30 becomes equal to or higher than a predetermined value at which the thyristor Q3 is turned on. A voltage value is applied to the gate of the thyristor Q3 through a time constant circuit composed of a capacitor C5 and a resistor R5 with a slight time delay (at this time, the N-type MOSFET Q2 is conducting, and the voltage drop is applied to the gate of the thyristor Q3 and the cathode). Voltage). Therefore, the thyristor Q3 is turned on, and the gate potential of the N-type MOSFET Q2 becomes the potential of the negative power supply line (the gate-source is substantially short-circuited), and the N-type MOSFET Q2 is turned off (to the transistor oscillation circuit 20). Shut off the power supply line. Once the thyristor Q3 is turned on, a current flows through the resistor R4 to hold the turn-on state. For this reason, the N-type MOSFET Q2 also maintains the OFF state, and the energization stop to the transistor oscillation circuit 20 is continued.

  When the switch SW1 is turned on / off, the turned-on thyristor Q3 cannot be returned to the off state. The thyristor Q3 can be returned to the OFF state by disconnecting the DC power supply 10 from the drive circuit and connecting the DC power supply 10 thereafter.

  According to the present embodiment, the following effects can be achieved.

(1) An N-type MOSFET Q2 for cutting off the power supply line to the transistor oscillation circuit 20, a current detection resistor R3 that generates a voltage drop proportional to the supply current to the oscillation circuit 20, and the voltage drop is a predetermined value or more. The transistor oscillating circuit 20 can be protected from an excessive current by the protection circuit 30 having a simple circuit configuration including the thyristor Q3 that is turned on and then maintains the on state.

(2) The thyristor Q3 in the protection circuit 30 self-holds its state once turned on. For this reason, even if the cause of the excessive current is removed, the inconvenience that the transistor oscillation circuit 20 is energized again can be eliminated.

(3) The gate voltage of the thyristor Q3 is supplied through a time constant circuit composed of the capacitor C5 and the resistor R5, and the operation of the stable protection circuit 30 which is not affected by noise by appropriately setting the value of the capacitor C5. Can be realized.

(4) The thyristor Q3 of the protection circuit 30 is off in the normal operation state, does not consume standby current, and only consumes current for self-holding through the resistor R4 even after detection of excessive current. Since a processing circuit such as a microcomputer is not used, software development is unnecessary and the circuit can be easily configured.

  FIG. 4 shows a second embodiment of the present invention. In the second embodiment, a protection circuit 40 is added to a transistor oscillation circuit (Colpitts oscillation circuit) 20 similar to that shown in FIG. The transistor oscillation circuit 20 and the protection circuit 40 are mounted on the drive substrate, and the ultrasonic transducer TD is connected between the collector and base of the transistor Q1 as in the case of FIG.

  The protection circuit 40 detects a DC current component of the ultrasonic transducer TD (in other words, a leakage current flowing through the ultrasonic transducer TD itself), and when the leakage current exceeds a predetermined threshold, the transistor The power supply line to the oscillation circuit 20 is cut off to stop its operation.

  The protection circuit 40 is an N-type MOSFET Q2 as a first semiconductor switching element for cutting off the power supply line to the transistor oscillation circuit 20, and is turned on when the gate voltage is a predetermined value or more, and thereafter the on-state is self-held. Thyristor Q3 as a semiconductor switching element, a light emitting diode D2 as a stop display connected in series to the thyristor Q3, a source follower as an amplifier circuit having an N-type MOSFET Q4, capacitors C7 and C8, resistors R4, R8 to R14.

  In the transistor oscillation circuit 20, in order to detect the direct current component of the ultrasonic transducer TD, a series connection of a DC blocking capacitor C9 and a resistor R7 is provided between one end of the ultrasonic transducer TD and the base of the oscillation transistor Q1. The resistors R8 and R9 in the protection circuit 40 are connected in series with the ultrasonic transducer TD while being inserted. That is, a series circuit of an ultrasonic transducer TD and resistors R8 and R9 is connected between the positive and negative power lines of the DC power supply 10, and the resistor R9 generates a detection voltage proportional to the DC current component of the ultrasonic transducer TD. It becomes a current detection resistor to be generated.

  In the protection circuit 40, a capacitor C7 for removing an AC component is connected in parallel with the resistor R9. At both ends of the capacitor C7, the AC component becomes “zero” when the positive-side current component and the negative-side current component are summed (integrated), so that only the DC component that is a leakage current can be detected.

  The source follower as an amplifier circuit that amplifies a detection voltage proportional to the direct current component of the ultrasonic transducer TD includes an N-type MOSFET Q4, and a voltage divided by resistors R8 and R9 is applied to its gate. It is like that. Since the supply voltage of the DC power supply 10 is as high as 48V, for example, the base voltage is lowered to 5V or less which is easy to handle with a general FET. The input side of the source follower has a high impedance, and the resistors R8 and R9 can have a sufficiently high resistance value so that the transistor oscillation circuit 20 is not affected. The output side of the source follower has a low impedance, and the thyristor Q3 can be reliably turned on. The output voltage of the source follower is supplied to the gate of the thyristor Q3 through a CR time constant circuit including a capacitor C8 and a resistor R12. By setting the value of the capacitor C8 appropriately, a stable operation that is not affected by noise can be realized.

  The coil L3 and the capacitor C10 inserted in the base bias circuit of the oscillation transistor Q1 of the transistor oscillation circuit 20 are provided to prevent the AC component from flowing out of the transistor oscillation circuit 20, and the resistor R15 is the base of the transistor Q1. In order to stabilize the current, it is inserted between the coil L3 and the base of the transistor Q1. The constant voltage diode D1 and the resistor R7 are provided for protecting the transistor Q1.

  In the second embodiment of FIG. 4, when the leakage current of the ultrasonic transducer TD exceeds a predetermined threshold value, the voltage across the resistor R9 proportional to the leakage current becomes a predetermined value or more, and the source of the N-type MOSFET Q4 The voltage is equal to or higher than a predetermined value at which the thyristor Q3 is turned on, and this voltage value is applied to the gate of the thyristor Q3 through a CR time constant circuit including a capacitor C8 and a resistor R12. Therefore, the thyristor Q3 is turned on, and the gate potential of the N-type MOSFET Q2 becomes the potential of the negative power supply line (the gate-source is substantially short-circuited), and the N-type MOSFET Q2 is turned off (to the transistor oscillation circuit 20). Shut off the power supply line. Once the thyristor Q3 is turned on, a current flows through the resistor R4 to hold the turn-on state. For this reason, the N-type MOSFET Q2 also maintains the OFF state, and the energization stop to the transistor oscillation circuit 20 is continued. When the thyristor Q3 is turned on, the light emitting diode D2 serving as the stop display unit is turned on during the operation stop period of the transistor oscillating circuit 20 to notify the abnormality.

  According to the second embodiment, the following effects can be obtained.

(1) The N-type MOSFET Q2 for cutting off the power supply line to the transistor oscillation circuit 20 and the direct current component of the ultrasonic transducer TD (leakage current flowing in the ultrasonic transducer TD itself and parallel to the ultrasonic transducer TD) A leakage current is detected by a protection circuit 40 having a current detection resistor R9 that generates a voltage proportional to the leakage current flowing through the thyristor Q3, and a thyristor Q3 that turns on when the voltage proportional to the leakage current exceeds a predetermined value and then self-holds the ON state. When the current reaches a predetermined threshold value, the operation of the transistor oscillation circuit 20 is stopped and disabled, thereby preventing a problem caused by the leakage current. Therefore, safety can be improved with a simple circuit configuration.

(2) The thyristor Q3 in the protection circuit 40 self-holds its state once turned on. For this reason, it is possible to eliminate the inconvenience of reusing before the cause of the operation stop of the transistor oscillation circuit 20 is removed. Further, the operation stop can be notified to the operator by turning on the light emitting diode D2.

(3) The gate voltage of the thyristor Q3 is supplied through a time constant circuit composed of the capacitor C8 and the resistor R12, and the operation of the stable protection circuit 40 which is not affected by noise by setting the value of the capacitor C8 appropriately. Can be realized.

(4) The thyristor Q3 of the protection circuit 40 is off in the normal operation state, does not consume standby current, and only consumes current for self-holding through the resistor R4 even after detection of leakage current abnormality. Since a processing circuit such as a microcomputer is not used, software development is unnecessary and the circuit can be easily configured.

  The present invention has been described above by taking the embodiment as an example. However, it is understood by those skilled in the art that various modifications can be made to each component and each processing process of the embodiment within the scope of the claims. By the way. Hereinafter, modifications will be described.

  In each embodiment, the Colpitts oscillation circuit is exemplified as the transistor oscillation circuit. However, a Hartley oscillation circuit and other transistor oscillation circuits may be used.

  In each embodiment, the N-type MOSFET is used as the first semiconductor switch element. However, other semiconductor switch elements can be used. For example, a circuit configuration using a bipolar transistor is also possible.

  Although the thyristor is exemplified as the second semiconductor switch element, a triac or the like may be used. It is also possible to use a flip-flop as the second semiconductor switch element.

  In the second embodiment, the leakage current detection voltage amplification circuit includes a source follower having an FET Q4, but an operational amplifier may also be used.

DESCRIPTION OF SYMBOLS 10 DC power supply 20 Transistor oscillation circuit 30,40 Protection circuit C1-C9 Capacitor D1 Constant voltage diode D2 Light emitting diode L1, L2, L3 Coil Q1 Oscillation transistor Q2, Q4 Enhancement type N type MOSFET
Q3 Thyristor R1-R15 Resistance SW1 Switch TD Ultrasonic vibrator

Claims (4)

A transistor oscillation circuit for driving the ultrasonic vibrator, and a protection circuit for protecting the oscillation circuit;
The protection circuit includes a first semiconductor switch element for cutting off a power supply line to the oscillation circuit;
A current detection resistor that produces a voltage drop proportional to the supply current to the oscillator circuit;
A second semiconductor switch element that turns on when the voltage drop is equal to or greater than a predetermined value, and then self-holds the on state;
The first semiconductor switch element is controlled by the second semiconductor switch element, and when the second semiconductor switch element is in an OFF state, the first semiconductor switch element is in a conductive state, and the second semiconductor switch element The ultrasonic transducer drive circuit, wherein in the on state, the first semiconductor switch element is in a cut-off state to cut off power supply to the oscillation circuit.   2. The ultrasonic transducer driving circuit according to claim 1, wherein a voltage due to the voltage drop is applied to a gate of the second semiconductor switch element through a time constant circuit.   The switch for turning on and off the driving of the ultrasonic transducer by the oscillation circuit is provided so as not to release the self-holding of the second semiconductor switch element. Ultrasonic transducer drive circuit.   4. The ultrasonic transducer driving circuit according to claim 1, wherein the second semiconductor switch element is a thyristor or a triac. 5.

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