Patent ID: 6137270
Filing Date: 2000-10-24
Classification: G10K

Abstract:
A device connectable with a direct current source for driving a buzzer, comprising:switch means for coupling said direct current source to said buzzer;a charging/discharging circuit connected with the direct-current source via said switch means and which performs charging and discharging at a predetermined time constant (CR) when the switch means is turned on and off, respectively, and produces an output voltage in accordance therewith, said charging/discharging circuit comprising a series circuit having a charging/discharging resistor having a contact and a capacitor connected to said contact;a hysteresis circuit to which said output voltage of the charging/discharging circuit is input and which operates while the output voltage rises to or above an operation threshold value (V.sub.T) after the start of the charging of the charging/discharging circuit and thereafter becomes inoperative and remains inoperative unless the output voltage falls to or below a stop threshold value (V.sub.S) which is smaller than the operation threshold value (V.sub.T) due to the discharging of the charging/discharging circuit, the hysteresis circuit comprising a first inverter having an input terminal contact connected with said contact of the charging/discharging resistor and the capacitor via a first voltage dividing resistor and an output terminal contact connected with an input terminal of the driving circuit, and a second inverter having a source terminal contact connected with the direct-current source via the switch means, an input terminal connected with the output terminal contact of the first inverter, and an output terminal contact connected with the input terminal contact of the first inverter via a second voltage dividing resistor; anda driving circuit, connected between said hysteresis circuit and said buzzer for outputting a drive signal for said buzzer in response to the operation of the hysteresis circuit.