Abstract:
A protective circuit for a supersonic humidifier includes a compare circuit to obtain working voltage at two terminals of an ultrasonic vibrating member to decide whether the humidifier is to be continued to operate or stopped so as to protect it from burning up. The protective circuit does not utilize a vibration needle, a float, a magnetic switch and a HALL IC used in conventional humidifiers.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a protective circuit for a supersonic humidifier, particularly to one utilizing a compare circuit to obtain working voltage at two terminals of an ultrasonic vibrating member for deciding to turn off or continue to let a switch on so that the humidifier may be timely stopped in case of no water left in a water tank, without possibility of burning up. 
   Nowadays, conventional supersonic humidifiers all use a detective element in a water tank to detect if there is water in the water tank or not so that an ultrasonic vibrating member should continue to operate or not with the power switch being on. In this way the humidifier may operate normally, protected from burning up in case of no water in the water tank. 
   However, the detective element such as a vibrating needle, a magnetic switch, a HALL IC in cooperation of a float occupies large dimensions, hardly applicable to a comparatively small humidifier. Besides, in case that water in the water tank is used up, or the float is placed upside down, the detecting element may detect erroneously to let the humidifier continue to operate, resulting in burning up. 
   SUMMARY OF THE INVENTION 
   This invention has been devised to offer a protective circuit for a supersonic humidifier, which can produce compared signals for deciding whether the humidifier should continue to operate or to stop. 
   The feature of the invention is a drive circuit containing a compare circuit to obtain working current, working voltage at two terminals of an ultrasonic vibrating member to decide to continue or stop operation of the humidifier so as to protect it from burning up. 

   
     BRIEF DESCRIPTION OF A DRAWING 
     This invention will be better understood by referring to the accompanying drawing, wherein: 
       FIG. 1  is a diagram of a protective circuit for a supersonic humidifier in the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A preferred embodiment of a protective circuit for a supersonic humidifier in the present invention, as shown in  FIG. 1 , includes an input terminal of DCV power source, a voltage stabilizing circuit A connected to the input terminal, a drive circuit B having a terminal P 2  of an inductance L 1 , an ultrasonic vibrating member Y 1 , a capacitor C 3  and a resistor R 6 , and continually connected to the voltage stabilizing circuit A, an indicator L 1 , an ultrasonic vibrating member Y 1 , a capacitor C 3 , and a resistor R 6 . Then input signal is fed at the terminal P 2  to a voltage dividing circuit composed of a resistor  13 , a diode D 3  and a capacitor C 5 , and then to a compare circuit C composed of resistor R 12 , and a minus input terminal or a second pin of an OP amplifier U 2 A, functioning as a signal input. Another terminal P 1  of the ultrasonic vibrating member Y 1  is connected to one terminal of a resistor R 9 . supplying a signal input (or input voltage), which is divided by the resister R 9  and the R 10 , and the terminal P 11  may produce a divided voltage to be sent as an input to the third pin of the OP amplifier U 2 A, that is, the signal input coming from P 2  is sent to the second pin  2  of the OP amplifier U 2 A, and the signal input coming from the terminal P 1  is sent to a third pin  3  of the OP amplifier U 2 A. As the input at the P 1  is sent to the compare circuit, the voltage sent from the P 1  to the P 11  of the compare circuit (C) is stable and constant because the voltage at the P 1  is equal to that at the input terminal of the DCV source. For example, if the voltage at the input terminal of the DCV source is 24 v, that at the P 1  is also 24 v. If the value of the resistor R 9  and R 10  of the compare circuit C are the same, the voltage at the P 11  is 11 v, after divided. So the input voltage at the third pin of the OP amplifier U 2 A is also 11 v. Nevertheless, P 2  is affected by the signal alteration by the water level in the water tank of the humidifier by detection of the ultrasonic vibrating member Y 1 , the voltage (signal) at the P 2  sent to the P 12  may alter depending on the water quantity in the store tank of the ultrasonic vibrating member Y 1 . 
   In operation of the protective circuits, the ultrasonic vibrating member Y 1  operates normally in case the water level in the water tank of the humidifier is normal, so the working current, the working voltage received by the terminal P 2  is normal. In other words, the two values of the signal sources at the terminals p 1  and P 2  transmitted to the second and the third pin of the OP amplifier U 2 A are substantially stable, so the signal sent from the first pin  1  of the OP amplifier U 2 A to an integrated circuit IC 1  is relatively stable. Then input voltage sent to the third pin  3  of the U 2 A, is larger than that sent to the second pin  2 , keeping the U 2 A ON. Then output voltage from the output pin  1  of the U 2 A is equal to that at the P 11  to let the ICI operate normal. Therefore, transistors Q 1  and Q 2  in the driving circuit B of the ultrasonic vibrating member Y 1  is normally ON, with the ultrasonic vibrating member Y 1  kept stable under operation. But provided that the water in the water tank is used up and dry, the working current, the working voltage of the ultrasonic vibrating member Y 1  may change (given each value changing larger or smaller than the normal value, resting on the material and manufacturing methods of makers of ultrasonic vibrating members.) In this invention, the working current, the working voltage and the supersonic frequency are enhanced, as the ultrasonic vibrating member produces high temperature, the working current is also upgraded, with the working voltage elevated at the same time and with the voltage at the P 2  increased accordingly. P 11 , so the input voltage of at the second pin  2  of the OP amplifier U 2 A is higher than that at the third pin  3 , forcing the first pin  1  of the OP amplifier U 2 A not to transmit a signal output to the IC 1 , turning the OP amplifier U 2 A OFF, and subsequently the transistors Q 1  and Q 2  also turned Off, stopping the ultrasonic vibrating member Y 1  so as to protect the humidifier. 
   While the preferred embodiment of the protective circuit for a supersonic humidifier has been described above, it will be recognized and understood that various modifications may be made therein and the appended claims are intended to cover all such modifications that may fall within the spirit and scope of the invention.