Patent Publication Number: US-8995680-B2

Title: Power-saving monitoring circuit applied to an electrostatic earphone having a thin film and a plurality of electrode plates

Description:
FIELD OF THE INVENTION 
     The present invention relates to a power-saving monitoring circuit, in particular to the power-saving monitoring circuit applied in an electrostatic earphone that is driven by a high voltage. 
     BACKGROUND OF THE INVENTION 
     In general, an electrostatic earphone has excellent frequency response and provides a very broad range of playing an audio frequency signal. 
     However, the operation of the electrostatic earphone is driven by boosting a low voltage (such as several volts) to a high voltage (such as several hundreds of volts). In general, a conventional electrostatic earphone uses utility power as the low-voltage power source. If the power source is changed to a primary battery or a secondary battery, then the efficiency of converting the low voltage to the high voltage will be affected significantly, or the primary or secondary battery may be even damaged during the conversion which will affect the service life of the battery adversely. 
     In addition, the power source of the conventional electrostatic earphone is maintained at a power supplying state, no matter whether the electrostatic earphone has received an input of the audio frequency signal. Therefore, the power supply method intangibly causes a waste of energy and the using time of the primary or secondary battery. Obviously, the conventional electrostatic earphone requires an improved circuit to overcome the aforementioned problem. 
     SUMMARY OF THE INVENTION 
     It is a primary objective of the present invention to provide a power-saving monitoring circuit, wherein a switch unit is trigger by an audio frequency signal automatically, so that a driving module converts a first voltage into a second voltage (which is a high voltage) to drive an electrostatic earphone, so as to achieve the power saving effect. 
     Another objective of the present invention is based on the aforementioned power-saving monitoring circuit, wherein the magnitude of a reference voltage is selected to determine the voltage sensitivity of the audio frequency signal used for triggering a control signal of the switch unit. 
     A further objective of the present invention is based on the aforementioned power-saving monitoring circuit, wherein a latch circuit is provided for maintaining, setting or resetting the control signal for triggering the control unit. 
     Another objective of the present invention is based on the aforementioned power-saving monitoring circuit, wherein a delay circuit is provided for compensating the electric power switching loss caused by a quick switch executed by the driving module, since a portion of the continuous audio frequency signals lower than the voltage sensitivity cannot be detected. 
     Another objective of the present invention is based on the aforementioned power-saving monitoring circuit, wherein a trigger unit is provided for triggering the control unit directly, so that the driving module can drive the electrostatic earphone no matter whether the audio frequency signal is detected. 
     To achieve the aforementioned and other objectives, the present invention provides a power-saving monitoring circuit applied to an electrostatic earphone having a thin film and a plurality of electrode plates. The power-saving monitoring circuit comprises a power supply unit, an input unit, a detection unit, a switch unit, a driving module and an output unit. Wherein, the power supply unit is provided for generating a first voltage; the input unit is provided for receiving an audio frequency signal; the detection unit is coupled to the input unit for detecting the audio frequency signal received by the input unit and selectively generating a control signal corresponding to the audio frequency signal according to the voltage amplitude of the audio frequency signal; the switch unit has a control terminal, an input terminal and an output terminal. Wherein, the switch unit is coupled to the power supply unit through the input terminal, and the switch unit receives a control signal through the control terminal, and the switch unit controls a conducting state between the input terminal and the output terminal according to the control signal for selectively transmitting the first voltage from the input terminal to the output terminal; the driving module is coupled to the switch unit for selectively converting the first voltage into a second voltage according to the conducting state to drive the thin film; and the output unit is coupled to the input unit for outputting the audio frequency signal to the electrode plates. 
     Compared with the prior art, the power-saving monitoring circuit of the present invention detects whether an audio frequency signal is inputted, in order to automatically generate a second voltage (which is a high voltage) required for driving an electrostatic earphone and reduce power consumption to achieve the power saving effect. Since the voltage of the audio frequency signal is still too low among the continuous audio frequency signals and cannot be detected, a delay circuit provides a time constant for extending the trigger time required for stopping the output of the second voltage. In addition, the present invention also provides a trigger control which is not affected by the audio frequency signal, so that the second voltage can drive the electrostatic earphone directly with or without having the audio frequency signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of a power-saving monitoring circuit in accordance with a first preferred embodiment of the present invention; 
         FIG. 2  is a schematic block diagram of a power-saving monitoring circuit in accordance with a second preferred embodiment of the present invention; 
         FIG. 3  is a schematic view of the connection of a pre-amplification unit, an input unit and a detection unit as depicted in  FIG. 1 ; 
         FIG. 4  is a schematic block diagram of a power-saving monitoring circuit in accordance with a third preferred embodiment of the present invention; 
         FIG. 5  is a schematic view of the circuit of a latch unit as depicted in  FIG. 4 ; 
         FIG. 6  is a schematic block diagram of a power-saving monitoring circuit in accordance with a fourth preferred embodiment of the present invention; and 
         FIG. 7  is a schematic view of the circuit of a latch unit as depicted in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The objects, characteristics and effects of the present invention will become apparent with the detailed description of the preferred embodiments and the illustration of related drawings as follows. 
     With reference to  FIG. 1  for a schematic block diagram of a power-saving monitoring circuit in accordance with the first preferred embodiment of the present invention, the power-saving monitoring circuit  10  is applied to an electrostatic earphone  2 . Wherein, the electrostatic earphone  2  comprises a thin film  22  and a plurality of electrode plates  24 , and the thin film  22  is disposed between the electrode plates  24 . In the electrostatic earphone  2 , the thin film  22  is driven by a high voltage (approximately equal to 500 volts), and an audio frequency signal AFS is transmitted to the electrode plates  24  for producing sound to the electrostatic earphone  2 . Wherein, the audio frequency signal AFS is defined as a signal of a sound wave with a frequency falling within a range from 5 Hz to 50 KHz. 
     Wherein, the power-saving monitoring circuit  10  comprises a power supply unit  12 , an input unit  14 , a detection unit  16 , a switch unit  18 , a driving module  20  and an output unit  26 . 
     The power supply unit  12  is provided for generating a first voltage FV. For example, the power supply unit  12  can be utility power converted into DC, a primary battery, a secondary battery, or any combination of the above. For example, the power supply unit  12  is a lithium-ion battery (Li-ion), and the lithium-ion battery can be resupplied by converting utility power into DC. In addition, the lithium-ion battery supplies the first voltage FV equal to 3.7 volts. 
     The input unit  14  receives the audio frequency signal AFS which is outputted to the electrode plates  24  directly through the output unit  26 . 
     The detection unit  16  is coupled to the input unit  14  for detecting the audio frequency signal AFS of the input unit  14 . If the input unit  14  has received an inputted audio frequency signal AFS, the input unit  14  will have a change of voltage amplitude, and the detection unit  16  will generate a control signal CS corresponding to the audio frequency signal AFS according to the voltage amplitude of the audio frequency signal AFS. 
     The switch unit  18  has a control terminal  182 , an input terminal  184  and an output terminal  186 . For example, the switch unit  18  can be a three-terminal component such as a transistor (BJT) or a metal oxide semiconductor field effect transistor (MOSFET). For example, the switch unit  18  of this embodiment is the metal oxide semiconductor field effect transistor, wherein the control terminal  182  is corresponsive to a gate, and the input terminal  184  is corresponsive to a source, and the output terminal  186  is corresponsive to a drain. 
     In addition, the switch unit  18  is coupled to the power supply unit  12  through the input terminal  184  to receive the first voltage FV, and the switch unit  18  receives the control signal CS through the control terminal  182 . In addition, the switch unit  18  controls a conducting state between the input terminal and the output terminal according to the control signal CS for transmitting the first voltage FV from the input terminal to the output terminal  186 . Wherein, the conducting state is defined as a connection or a disconnection between the input terminal  184  and the output terminal  186 . 
     The driving module  20  is coupled to the switch unit  18 , and the driving module  20  selectively converts the first voltage FV into a second voltage to drive the thin film  22  according to the conducting state. Wherein, the second voltage has a voltage value greater than the voltage value of the first voltage. In another preferred embodiment, the driving module  20  comprises a rectifier unit and a transformer unit (not shown in the figure), wherein the rectifier unit and the transformer unit convert the first voltage into the second voltage. 
     Therefore, the power-saving monitoring circuit  10  can selectively generate the control signal CS according to the situation whether or not the audio frequency signal AFS is detected by the detection unit  16 , and the control signal can trigger the switch unit  18  whether or not to supply the first voltage FV to the driving module  20  to convert to the second voltage SV (which is a high voltage) required for driving the electrostatic earphone  2 . In other words, if the audio frequency signal AFS has not been inputted or cannot be detected by the detection unit  16 , then the first voltage FV cannot be supplied to the driving module  20 , so that the driving module  20  will not have the power consumption issue. 
     With reference to  FIG. 2  for a schematic block diagram of a power-saving monitoring circuit in accordance with the second preferred embodiment of the present invention, the power-saving monitoring circuit  10 ′ further comprises a reference unit  28  and a pre-amplification unit  30  in addition to the power supply unit  12 , the input unit  14 , the detection unit  16 , the switch unit  18 , the driving module  20  and the output unit  26  as described in the first preferred embodiment. 
     Wherein, the reference unit  28  is coupled to the detection unit  16 . The reference unit  28  generates a reference voltage RV, and the detection unit  16  can use the reference voltage as a determination basis to determine whether or not the voltage amplitude is sufficient to generate the control signal CS corresponding to the audio frequency signal AFS. In other words, the reference voltage RV can be adjusted to determine the voltage sensitivity detected by the detection unit  16  and use it as the basis for determining whether the audio frequency signal AFS can be detected. 
     The pre-amplification unit  30  is coupled to the input unit  14  and the detection unit  16 . Wherein, the pre-amplification unit  30  is provided for amplifying the voltage amplitude of the audio frequency signal AFS and outputting the voltage amplitude to the detection unit  16 . The pre-amplification unit  30  amplifies the voltage amplitude of the audio frequency signal AFS in compliance with the electric properties of the detection unit  16 . 
     With reference to  FIG. 3  for a schematic view of the connection of the pre-amplification unit  30 , the input unit  14  and the detection unit  16  in details, the pre-amplification unit  30  is comprised of an operational amplifier OPA and a plurality of resistors R 1 , R 2 , R 3 , and the times of voltage amplification of the pre-amplification unit  30  is determined by the resistance ratio of R 1  to R 2 . 
     With reference to  FIG. 4  for a schematic block diagram of a power-saving monitoring circuit in accordance with the third preferred embodiment of the present invention, the power-saving monitoring circuit  10 ″ further comprises a delay unit  32  and a latch unit  34  in addition to the power supply unit  12 , the input unit  14 , the detection unit  16 , the switch unit  18 , the driving module  20  and the output unit  26  as described in the first preferred embodiment. 
     The delay unit  32  is coupled to the detection unit  16 , and the delay unit  32  delays a time constant t of the control signal CS to form a delay signal DS. For example, the delay unit  32  is comprised of a resistor and at least one selected from a capacitor or an inductor. In other words, the delay unit  32  must charge the capacitor or the inductor before the control signal CS reaches the switch unit  18  or the latch unit  34 , and the original voltage level of the control signal CS can be resumed till the time constant t is reached. For example, the delay unit  32  of this emboidment is comprised of a resistor R and a capacitor C, and the time constant t is calculated by the following mathematical equation:
 
t=RC
 
     The latch unit  34  is coupled to the detection unit  16 , the delay unit  32  and the switch unit  18 . After the latch unit  34  receives the control signal CS and the delay signal DS, the latch unit  34  generates other control signal CS′ for controlling the switch unit  18 . In addition, a voltage level of the other control signal CS′ is maintained, set, or reset by the latch unit  34  according to the control signal CS. 
     With reference to  FIG. 5  for the circuit connection of the latch unit  34  in accordance with the third preferred embodiment of the present invention, the latch unit  34  is a D-latch in this embodiment, and it is noteworthy that the latch unit  34  can also be of another type such as a RS latch or a JK latch. 
     In  FIG. 5 , the D-latch has a first input terminal  342  (for receiving the control signal CS), a second input terminal  344  (for receiving the delay signal DS), a first output terminal  346  and a second output terminal  348 , In additon, the first output terminal  346  and the second output terminal  348  ouput opposite logic potentials respectively, and the switch unit  18  selects a voltage level outputted from the first output terminal  346  or the second output terminal  348  as the control signal CS′. Wherein, the D-latch is comprised of four NAND gates and one NOT gate, and Table 1 shows a truth table of the D-latch. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 First 
                 Second 
                 First 
                 Second 
                   
               
               
                 input 
                 input 
                 output 
                 output 
               
               
                 terminal 
                 terminal 
                 terminal 
                 terminal 
                 Action 
               
               
                   
               
             
            
               
                 0 
                 0 
                 Maintain 
                 Maintain 
                 Maintain 
               
               
                 1 
                 0 
                 0 
                 1 
                 Control and turn on the 
               
               
                   
                   
                   
                   
                 switch unit, so that a 
               
               
                   
                   
                   
                   
                 conducting state between 
               
               
                   
                   
                   
                   
                 the power supply unit and 
               
               
                   
                   
                   
                   
                 the driving module occurs 
               
               
                   
                   
                   
                   
                 to let the driving module 
               
               
                   
                   
                   
                   
                 obtain the first voltage. 
               
               
                 0 
                 1 
                 1 
                 0 
                 Control and turn off the 
               
               
                   
                   
                   
                   
                 switch unit, so that a dis- 
               
               
                   
                   
                   
                   
                 connection state between 
               
               
                   
                   
                   
                   
                 the power supply unit and 
               
               
                   
                   
                   
                   
                 the driving module occurs 
               
               
                   
                   
                   
                   
                 to stop the driving module 
               
               
                   
                   
                   
                   
                 from obtaining the first 
               
               
                   
                   
                   
                   
                 voltage. 
               
               
                 1 
                 1 
                 Maintain 
                 Maintain 
                 Maintain 
               
               
                   
               
            
           
         
       
     
     From the truth table, if the voltage of the second input terminal  344  is at the state if logic 0 (representing a voltage equal to 0 volt), then the logic state of the first output terminal  346  is maintained at the original voltage level which is logic 0 or logic 1 (such as a voltage equal to 5 volts) regardless of the input condition of the first input terminal  342 ; and if the voltage level of the second input terminal  344  is at the state of logic 1, then the first output terminal  346  is set to the state of logic 1, or the voltage level of the first output terminal  346  is reset to logic 0 according to the voltage level of the first output terminal  346 . 
     In the truth table, the control terminal  182  of the switch unit  18  can be triggered to change or maintain the conducting state between the input terminal  184  and the output terminal  186 . 
     With reference to  FIG. 6  for a schematic block diagram of a power-saving monitoring circuit in accordance with the fourth preferred embodiment of the present invention, the power-saving monitoring circuit  10 ′″ further comprises a trigger unit  36  and a logic gate unit  38  in addition to the power supply unit  12 , the input unit  14 , the detection unit  16 , the switch unit  18 , the driving module  20 , the output unit  26 , the delay unit  32  and the latch unit  34  as described in the third preferred embodiment. 
     The trigger unit  36  generates a trigger signal TS. For example, the trigger unit  36  is a press key. 
     The logic gate unit  38  is coupled to the trigger unit  36  and the detection unit  16 , and after the logic gate unit  38  receives the trigger signal TS and the control signal CS, a logic signal LS is generated and transmitted to the latch unit  34 . In  FIG. 7 , the logic gate unit  38  of this embodiment is an OR gate. When the D-latch is used, the truth table of the D-latch is as shown in Table 2. Wherein, the logic signal LS of the first input terminal  342  is generated by the trigger signal TS and the control signal CS through the OR gate. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 First 
                   
                   
                   
                   
               
               
                   
                   
                 input 
                 Second 
                 First 
                 Second 
               
               
                   
                   
                 terminal 
                 input 
                 output 
                 output 
               
               
                 CS 
                 TS 
                 (LS) 
                 terminal 
                 terminal 
                 terminal 
                 Action 
               
               
                   
               
             
            
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 Maintain 
               
               
                 0 
                 1 
                 1 
                 0 
                 1 
                 0 
                 Determined by TS 
               
               
                   
                   
                   
                   
                   
                   
                 to turn on the switch unit 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 Determined by CS 
               
               
                   
                   
                   
                   
                   
                   
                 to turn on the switch unit 
               
               
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 Jointly determined by 
               
               
                   
                   
                   
                   
                   
                   
                 TS, CS to turn on the 
               
               
                   
                   
                   
                   
                   
                   
                 switch unit 
               
               
                   
               
            
           
         
       
     
     The power-saving monitoring circuit of the present invention detects whether an audio frequency signal is inputted to automatically generate a second voltage which is a high voltage required for driving the electrostatic earphone, so as to reduce the power consumption and achieve the power saving effect. In addition, the voltage of the audio frequency signal is still too low among the continuous audio frequency signals and cannot be detected, so that the delay circuit can provide a time constant for extending the trigger time required for stopping the output of the second voltage. In addition, the present invention also provides a trigger control that will not be affected by the audio frequency signal, and the second voltage can drive the electrostatic earphone directly with or without having the audio frequency signal. 
     While the invention has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.