Buzzer driving device

DETAILED DESCRIPTION According to the invention, the hysteresis circuit operates until the output voltage rises to or above the operation threshold value after the start of the charging of the charging/discharging circuit and thereafter remains inoperative unless the output voltage falls to or below the stop threshold value which is smaller than the operation threshold value, due to the discharging of the charging/discharging circuit.
The buzzer operates in response to the drive signal from the driving circuit while the hysteresis circuit operates.
Accordingly, the buzzer will not operate even if the source voltage falls for a certain reason, unless the output voltage of the charging/discharging circuit returns to its original level after falling to or below the stop threshold value.
Thus, unlike the prior art buzzer driving circuits, there can be prevented an erroneous operation of the buzzer in which the buzzer operates when it should not.
According to an alternative embodiment, the charging/discharging circuit may be constituted by an integrating circuit or the like.
The charging/discharging circuit may comprise a series circuit may comprise a charging/discharging resistor and a capacitor.
The hysteresis circuit may comprise a first inverter having an input terminal connected with a contact of the charging/discharging resistor and the capacitor via a voltage dividing resistor and an output terminal connected with an input terminal of the driving circuit.
The hysteresis circuit may further comprise a second inverter having a source terminal connected with the direct-current source via the switch, an input terminal connected with the output terminal of the first inverter, and an output terminal connected with the input terminal of the first inverter via another voltage dividing resistor.
There can be provided a buzzer driving device free from erroneous operations by constituting the charging/discharging circuit by the series circuit including the resistor and the capacitor and by constituting the hysteresis circuit by the first and second inverters such as CMOS inverters and the two voltage dividing resistors