TWI661445B - Power-supply device of induction type power supply system and rf magnetic card identification method of the same - Google Patents

Abstract

A power supply device applied to an inductive power supply system includes a power supply coil, an auxiliary coil, a power supply drive module, an auxiliary drive module, a resonance frequency measurement module, a voltage measurement module, and a processing module. The power supply driving module drives the power supply coil. The auxiliary drive module drives the auxiliary coil. The resonance frequency measurement module judges the resonance frequency of the power supply coil according to the capacitive sensing parameter measurement related to the power supply coil. The voltage measurement module tracks and locks the maximum oscillating voltage of the auxiliary coil. When the processing module judges that the resonance frequency is stable and the oscillating voltage drops more than a certain percentage, the power supply driving module is placed in an inoperative state.

Description

   Power supply device of inductive power supply system and radio frequency magnetic card identification method thereof   

The invention relates to an inductive power supply technology, and in particular to a power supply device applied to an inductive power supply system and a radio frequency magnetic card identification method thereof.

In the inductive power supply system, the power supply device drives the power supply coil to generate resonance after sending the electromagnetic energy, and then receives the electromagnetic energy generated by the power supply coil through resonance through the coil of the power receiving device to convert the energy into direct current. Power transmission.

In daily life, smart cards implemented by means of radio frequency magnetic cards can communicate using technologies such as near field communication (NFC). However, most RF magnetic cards require only a small amount of electromagnetic energy to drive them. When the RF magnetic card receives too much electromagnetic energy, the chip will be damaged. If a user accidentally inserts a radio frequency magnetic card into a power supply coil of a power supply device of an inductive power supply system, and the power supply device is not provided with a detection mechanism, the radio frequency magnetic card chip will be easily destroyed when transmitting a power signal.

Therefore, how to design a new power supply device applied to an inductive power supply system and a radio frequency magnetic card identification method to solve the above-mentioned shortcomings is an urgent problem in the industry.

An object of the present invention is to provide a power supply device applied to an inductive power supply system, including: a power supply coil, an auxiliary coil, a power supply drive module, an auxiliary drive module, a resonance frequency measurement module, a voltage measurement module, and a process. Module. The power supply driving module is electrically coupled to the power supply coil and configured to drive the power supply coil. The auxiliary driving module is electrically coupled to the auxiliary coil, and is configured to drive the auxiliary coil when the power supply driving module is in an inoperative state. The resonance frequency measurement module is electrically coupled to the power supply coil, and is configured to measure the resonance frequency of the power supply coil according to the capacitive sensing parameter related to the power supply coil. The voltage measurement module is electrically coupled to the auxiliary coil, and is configured to track and lock the maximum oscillation voltage of the auxiliary coil. When the processing module judges that the resonance frequency is stable and the oscillating voltage drops more than a certain percentage, the power supply driving module is placed in an inoperative state.

Another object of the present invention is to provide a radio frequency magnetic card identification method applied to a power supply device of an inductive power supply system, including: driving a power supply coil of the power supply device by a power supply driving module electrically coupled to the power supply coil; The resonance frequency measurement module electrically coupled to the power supply coil measures the resonance frequency of the power supply coil according to the capacitive sensing parameter related to the power supply coil; when the auxiliary coil of the power supply device is in an inoperative state, the An auxiliary drive module that is coupled to the auxiliary coil is driven; a voltage measurement module electrically coupled to the auxiliary coil is tracked and locked to the maximum oscillation voltage of the auxiliary coil; and the processing module is stable in determining the resonance frequency and the oscillation voltage When the drop exceeds a specific ratio, the power supply drive module is in a non-operation state.

The advantage of applying the present invention is that the power supply device detects the resonance frequency of the power supply coil and tracks and locks the largest oscillation voltage among the oscillation voltages of the auxiliary coils, so as to determine the radio frequency magnetism when the resonance frequency is judged to be stable and the oscillation voltage has fallen more than a specific ratio. The existence of the card further makes the power supply driving module inoperative, and prevents the RF magnetic card from being damaged by the power supply coil transmitting power.

1‧‧‧ Inductive power supply system

100‧‧‧ Power supply device

102‧‧‧Power supply coil

104‧‧‧Auxiliary coil

106‧‧‧Power Drive Module

108‧‧‧ auxiliary drive module

110‧‧‧Resonant Frequency Measurement Module

112‧‧‧Voltage measurement module

113A, 113B‧‧‧ Power Switching Elements

114A, 114B‧‧‧Power supply resonance capacitor

115‧‧‧Processing Module

116A-116C‧‧‧Detect resonance capacitor

118A, 118B‧‧‧ resistance

120‧‧‧ Digital Analog Converter

122‧‧‧ Comparator

124‧‧‧Divided Voltage Module

130‧‧‧Microcontroller

140‧‧‧Power Supply

150‧‧‧ Power receiving device

152‧‧‧Power receiving coil

154‧‧‧Load Module

160‧‧‧RF Magnetic Card

162‧‧‧coil

164‧‧‧Chip Module

170‧‧‧tip module

PS‧‧‧ Coil Signal

Vd‧‧‧Oscillation voltage

Vr‧‧‧ comparison result

Vref‧‧‧Reference voltage

200‧‧‧RF magnetic card identification method

201-212‧‧‧step

FIG. 1 is a block diagram of an inductive power supply system according to an embodiment of the present invention; and FIG. 2 is a flowchart of a radio frequency magnetic card identification method according to an embodiment of the present invention.

Please refer to Figure 1. FIG. 1 is a block diagram of an inductive power supply system 1 according to an embodiment of the present invention. The inductive power supply system 1 includes a power supply device 100 and a power receiving device 150. Wherein, the power supply device 100 is configured to generate power, and transmits the power to the power receiving device 150 in a wireless manner to supply power to the power receiving device 150.

The power supply device 100 includes a power supply coil 102, an auxiliary coil 104, a power supply driving module 106, an auxiliary driving module 108, a resonance frequency measurement module 110, a voltage measurement module 112, and a processing module 115.

In one embodiment, the power supply driving module 106, the auxiliary driving module 108, the resonance frequency measurement module 110, the voltage measurement module 112, and the processing module 115 can be integrated into a single microcontroller 130, and the microcontrol The device 130 can be electrically coupled to the power supply 140 to receive power from the power supply 140 and enable the modules contained therein to operate. However, the present invention is not limited to this.

The power supply driving module 106 is electrically coupled to the power supply coil 102 and is configured to drive the power supply coil 102. In one embodiment, the power supply driving module 106 is a pulse width modulator, and outputs different oscillation frequencies of different levels under the control of the processing module 115 to drive the power supply coil 102.

In one embodiment, the power supply device 100 further includes power supply resonance capacitors 114A and 114B and power switching elements 113A and 113B, which are electrically coupled to one of the two ends of the power supply coil 102 and the power supply drive module 106, respectively.

When the power supply driving module 106 is in the working state, the power supply coil 102 is driven to supply power to the power receiving device 150. In one embodiment, the power receiving device 150 includes a power receiving coil 152 and a load module 154. The power receiving coil 152 is configured to receive power from the power supply coil 102 and is converted by the load module 154.

When the power supply driving module 106 is in an inoperative state, the power supply coil 102 is stopped from being driven to further stop power supply to the power receiving device 150.

The auxiliary driving module 108 is electrically coupled to the auxiliary coil 104 and is configured to drive the auxiliary coil 104 when the power supply driving module 106 is in an inoperative state. In one embodiment, the auxiliary driving module 108 is a wave width modulation unit and outputs different oscillation frequencies of different levels under the control of the processing module 115 to drive the auxiliary coil 104.

In one embodiment, the power supply device 100 further includes detecting resonance capacitors 116A-116C. Among them, the detection resonance capacitors 116A and 116B are electrically coupled between one of the two ends of the auxiliary coil 104 and the auxiliary drive module 108, and the detection resonance capacitor 116C is electrically coupled between the detection resonance capacitors 116A and 116B. . The detection resonance capacitors 116A-116C are configured to resonate with the auxiliary coil 104 when the auxiliary driving module 108 is driving.

In an embodiment, the power supply device 100 may optionally include a resistor 118A and a resistor 118B, which are connected in series with one of the two ends of the auxiliary coil 104 and the auxiliary driving module in series with the detection resonant capacitor 116A and the detection resonant capacitor 116B, respectively. 108, configured to limit the drive current of the 108 port of the auxiliary drive module to provide protection.

In one embodiment, the power supply coil 102 operates at approximately 100 kHz, and the auxiliary coil 104 operates at approximately 13.56 MHz or 6.78 MHz. Therefore, the operating frequency band of the auxiliary coil 104 is higher than the operating frequency band of the power supply coil 102.

The resonance frequency measurement module 110 is electrically coupled to the power supply coil 102 and is configured to determine the resonance frequency of the power supply coil 102 according to the capacitive sensing parameter measurement related to the power supply coil 102.

In one embodiment, the capacitive sensing parameters related to the power supply coil 102 include a combination of the inductance of the power supply coil 102 and the capacitance of the power supply resonant capacitors 114A and 114B.

The voltage measurement module 112 is electrically coupled to the auxiliary coil 104 and is configured to track and lock the maximum oscillating voltage Vd of the auxiliary coil 104. In one embodiment, the voltage measurement module 112 includes a digital analog converter 120 and a comparator 122.

The digital-to-analog converter 120 is configured to generate a reference voltage Vref. The comparator is electrically coupled to the digital analog converter 120 and the auxiliary coil 104, and is configured to receive the reference voltage Vref and the oscillation voltage Vd of the auxiliary coil 104, so as to track and lock the maximum value by comparing the reference voltage Vref and the oscillation voltage Vd. The oscillation voltage Vd.

In an embodiment, the power supply device 100 may optionally include a voltage dividing module 124 electrically coupled between the auxiliary coil 104 and the comparator 122. The oscillating voltage Vd received by the comparator 122 is a divided voltage of the voltage of the auxiliary coil 104. However, it should be noted that if the components of the voltage measurement module 112 have sufficient withstand voltage, they can also directly receive the voltage of the auxiliary coil 104 without going through the voltage dividing module 124 to compare with the reference voltage Vref.

The processing module 115 determines whether the resonance frequency is stable and whether the oscillating voltage Vd has fallen more than a specific ratio, so as to determine whether there is, for example, but not limited to, the RF magnetic card 160 shown in FIG. 1 in the power supply range of the power supply coil 102. It should be noted that although the RF magnetic card 160 is shown together with other components in the inductive power supply system 1 in FIG. 1, the RF magnetic card 160 is not actually part of the inductive power supply system 1.

In one embodiment, the radio frequency magnetic card 160 may be, for example, but not limited to, a smart card module that communicates through near field communication technology. In one embodiment, the RF magnetic card 160 may include a coil 162 and a chip module 164. Among them, when the auxiliary driving module 108 drives the auxiliary coil 104, the signal of the auxiliary coil 104 will be received by the coil 162, and the RF magnetic card 160 will provide a small amount of power to drive the chip module 164 in the RF magnetic card 160 to generate a modulated signal. The signal reaches the coil 162 and is reflected on the auxiliary coil 104 through the coil 162.

The determination mechanism of the processing module 115 will be described in more detail below.

First, the processing module 115 determines whether the resonance frequency is equal to a frequency lock value by using the resonance frequency detected by the resonance frequency measurement module 110. In one embodiment, the frequency lock value is a record lock value of the resonance frequency of the power supply coil 102.

In more detail, when the resonance frequency is not equal to the frequency lock value, the processing module 115 will determine that different objects of the power supply coil 102 are approaching, causing the resonance frequency to change and become unstable, and further update the frequency lock value to the measured value. The latest resonant frequency. When the resonance frequency is equal to the frequency lock value, the processing module 115 determines that the resonance frequency is stable.

It should be noted that the above-mentioned "equality" does not have to be 100% equal. There can be a reasonable range of error between the resonance frequency and the frequency lock value. When the resonance frequency is very close to the frequency lock value, that is, the difference is less than a specific range, it can be judged that the resonance frequency and the frequency lock value are "equal."

Further, at the same resonance frequency, the processing module 115 uses the oscillation voltage Vd detected by the voltage measurement module 112 to determine whether the oscillation voltage Vd is greater than a voltage lock value.

In one embodiment, the voltage lock value is the maximum oscillating voltage Vd captured when the power supply coil 102 is located at the same resonance frequency. Therefore, with respect to the oscillation voltage Vd currently measured, the voltage lock value is equivalent to the oscillation voltage Vd previously measured.

In more detail, when the oscillation voltage Vd is greater than the voltage lock value (that is, the oscillation voltage Vd measured this time is greater than the oscillation voltage Vd measured last time), the processing module 115 determines that the oscillation voltage Vd has not decreased. If it exceeds a specific ratio, the voltage lock value is further updated to the latest measured oscillation voltage Vd.

When the oscillating voltage Vd is not greater than the voltage lock value (that is, the oscillating voltage Vd measured this time is not greater than the oscillating voltage Vd measured last time), the processing module 115 will capture a specific ratio (for example, but not (Limited to 75%) to set a critical value.

The processing module 115 further determines that the oscillating voltage Vd has fallen more than a specific ratio when the oscillating voltage Vd is less than a critical value, and determines that the oscillating voltage Vd has not fallen more than the specific ratio when the oscillating voltage Vd is not less than the critical value.

Therefore, when the processing module 115 determines that the resonance frequency is stable and the oscillating voltage Vd drops by more than a specific percentage, it is determined that a radio frequency magnetic card 160 exists in the power supply range of the power supply coil 102. At this time, the processing module 115 will keep the power supply driving module 106 in a non-working state, so as to avoid the power generated by the power supply driving module 106 driving the power supply coil 102 from damaging the radio frequency magnetic card 160.

In one embodiment, the power supply device 100 may optionally include a prompt module 170. The processing module 115 may control the prompting module 170 to prompt the user to display the radio frequency magnetic card by, for example, but not limited to, displaying a signal, a buzzer, a speaker, a screen display, or a combination thereof when determining that the radio frequency magnetic card 160 is detected. The card 160 is removed.

In one embodiment, the magnetic carrier of the RF magnetic card 160 will absorb the high-frequency oscillation energy on the auxiliary coil 104, but it will not affect the resonance frequency of the power supply coil 102. When there are other metal objects, it will affect the resonance frequency of the power supply coil 102 and absorb the high-frequency oscillation energy on the auxiliary coil 104 at the same time. Therefore, the above-mentioned measurement and judgment method can first determine that the resonance frequency of the power supply coil 102 has not changed, so as to exclude the possibility of other metal objects, and further determine whether there is an RF magnetic card 160 according to the oscillation voltage Vd of the auxiliary coil 104. Judge.

The power supply device 100 of the present invention detects the resonance frequency of the power supply coil 110 and tracks and locks the maximum oscillating voltage Vd of the auxiliary coil 112 to determine the radio frequency magnetic card 160 when the resonance frequency is determined to be stable and the oscillating voltage Vd has fallen beyond a specific ratio. The existence of the power supply further disables the power supply driving module 106 and prevents the RF magnetic card 160 from being damaged by the power transmitted by the power supply coil 102.

Please refer to Figure 2. FIG. 2 is a flowchart of a radio frequency magnetic card identification method 200 according to an embodiment of the present invention. The radio frequency magnetic card identification method 200 can be applied to the power supply device 100 of the inductive power supply system 1 shown in FIG. 1. The radio frequency magnetic card identification method 200 includes the following steps (it should be understood that the steps mentioned in this embodiment can be adjusted according to actual needs, except for the order in which they are specifically described, or even simultaneously or partially simultaneously carried out).

At step 201, detection is started.

In step 202, the power supply coil 102 is driven by the power supply driving module 106, so that the resonance frequency measurement module 110 measures the resonance frequency of the power supply coil 102 according to the capacitive sensing parameter related to the power supply coil 102.

In one embodiment, the capacitive sensing parameters related to the power supply coil 102 include a combination of the inductance of the power supply coil 102 and the capacitance of the power supply resonant capacitors 114A and 114B.

In step 203, the auxiliary coil 104 is driven by the auxiliary driving module 108 when the power supply driving module 106 is in an inoperative state, so that the voltage measurement module 112 tracks and locks the maximum oscillating voltage Vd of the auxiliary coil 104.

In step 204, the processing module 115 determines whether the resonance frequency is equal to the frequency lock value. In one embodiment, the frequency lock value is a record lock value of the resonance frequency of the power supply coil 102.

When the resonance frequency is not equal to the frequency lock value, in step 205, the processing module 115 will determine that there are different objects approaching the power supply coil 102, causing the resonance frequency to change and become unstable, and further update the frequency lock value to the latest measured Resonance frequency.

Then, the processing module 115 will end the detection. In an embodiment, after step 205, the flow returns to step 201 to achieve the purpose of continuous detection in a polling manner.

When the resonance frequency is equal to the frequency lock value, the processing module 115 determines that the resonance frequency is stable. It should be noted that the above-mentioned "equality" does not have to be 100% equal. There can be a reasonable range of error between the resonance frequency and the frequency lock value. When the resonance frequency and the frequency lock value are very close, that is, the difference is less than a specific range, the resonance frequency and the frequency lock value can be judged to be "equal." Therefore, when the processing module 115 determines that the resonance frequency is equal to the frequency lock value, it is further determined in step 207 whether the maximum oscillation voltage Vd of the auxiliary coil 104 is greater than the voltage lock value.

In one embodiment, the voltage lock value is the maximum oscillating voltage Vd captured when the power supply coil 102 is located at the same resonance frequency. Therefore, with respect to the oscillation voltage Vd currently measured, the voltage lock value is equivalent to the oscillation voltage Vd previously measured.

When the oscillating voltage Vd is greater than the voltage lock value (that is, the oscillating voltage Vd measured this time is greater than the previous measurement of the oscillating voltage Vd), in step 208, the processing module 115 updates the voltage lock value to the amount The latest oscillation voltage Vd was measured.

Then, the processing module 115 will end the detection. In an embodiment, after step 205, the flow returns to step 201 to achieve the purpose of continuous detection in a polling manner.

When the oscillating voltage Vd is not greater than the voltage lock value (that is, the oscillating voltage Vd measured this time is not greater than the oscillating voltage Vd measured last time), in step 209, the processing module 115 will capture a specific ratio ( For example, but not limited to, a voltage lock value of 75%) is set as a critical value.

In step 210, the processing module 115 determines whether the oscillating voltage Vd is not less than a critical value.

When the processing module 115 judges that the oscillating voltage Vd is not less than a critical value, it will judge that the oscillating voltage Vd has not fallen more than a specific percentage, and determine that there is no radio frequency magnetic card 160 within the power supply range of the power supply coil 102 at step 206 to end this time. Detect. In an embodiment, after step 206, the flow returns to step 201 to achieve the purpose of continuous detection by polling.

When the processing module 115 determines that the oscillating voltage Vd is less than a critical value, it determines that the oscillating voltage Vd has dropped by more than a certain percentage. Therefore, it is determined in step 211 that a radio frequency magnetic card 160 exists in the power supply range of the power supply coil 102, and the power supply driving module 106 is located at In a non-working state, to avoid damage to the RF magnetic card 160 caused by the power generated by the power supply driving module 106 driving the power supply coil 102.

In step 212, the processing module 115 controls the prompt module 170 to prompt the user to remove the RF magnetic card 160.

In an embodiment, after step 212 ends, the process may return to step 201 to perform detection again, and achieve the purpose of continuous detection by polling.

The above descriptions are merely preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, and improvement made within the principles of the present invention shall fall within the protection scope of the present invention.

Claims (16)

A power supply device applied to an inductive power supply system includes: a power supply coil; an auxiliary coil; a power supply drive module electrically coupled to the power supply coil and configured to drive the power supply coil; an auxiliary drive module, Electrically coupled to the auxiliary coil and configured to drive the auxiliary coil when the power supply drive module is in a non-working state; a resonance frequency measurement module is electrically coupled to the power supply coil and configured to communicate with A capacitive sensing parameter related to the power supply coil measures a resonance frequency of the power supply coil; a voltage measurement module electrically coupled to the auxiliary coil and configured to track and lock one of the maximum oscillating voltages of the auxiliary coil; and A processing module, when determining that the resonance frequency is stable and the oscillating voltage drops by more than a specific ratio, causes the power supply driving module to be in the inoperative state. The power supply device according to claim 1, wherein when the processing module determines that the resonance frequency is stable and the oscillating voltage drops by more than a specific percentage, it determines that a radio frequency magnetic card is stored in a power supply range of the power supply coil. The power supply device according to claim 1, wherein the voltage measurement module includes: a digital analog converter configured to generate a reference voltage; and a comparator electrically coupled to the digital analog converter and the auxiliary device. A coil configured to receive the reference voltage and the oscillating voltage to track and lock the oscillating voltage. The power supply device according to claim 3, wherein the comparator is configured to control the digital analog converter with a feedback mechanism to track and lock the oscillating voltage with the reference voltage according to a comparison result of the oscillating voltage and the reference voltage. . The power supply device according to claim 4, further comprising a voltage dividing module, which is electrically coupled between the auxiliary coil and the comparator, and the oscillating voltage received by the comparator is a fraction of a voltage of the auxiliary coil. Pressure. The power supply device according to claim 1, wherein when the processing module determines that the resonance frequency is unstable or that the oscillating voltage does not fall below the specific ratio, the power supply driving module is placed in a working state to drive the power supply coil. Send a power signal. The power supply device according to claim 1, wherein the processing module determines whether the resonance frequency is equal to a frequency lock value, and determines that the resonance frequency is stable when the resonance frequency is equal to the frequency lock value; the processing module further When the resonance frequency is not equal to the frequency lock value, it is determined that the resonance frequency is unstable, and the frequency lock value is further updated to the latest measured resonance frequency. The power supply device according to claim 1, wherein the processing module determines whether the oscillating voltage is greater than a voltage lock value, and when the oscillating voltage is not greater than the voltage lock value, extracts the voltage lock value of the specific ratio to It is set to a critical value, and further, when the oscillating voltage is less than the critical value, it is judged that the oscillating voltage has fallen more than the specific ratio, and when the oscillating voltage is not less than the critical value, it is judged that the oscillating voltage has not fallen more than the specific ratio ; The processing module further judges that the oscillating voltage has not fallen more than the specific ratio when the oscillating voltage is greater than the voltage lock value, and further updates the voltage lock value to the latest measured oscillating voltage. A radio frequency magnetic card identification method applied to a power supply device of an inductive power supply system includes: driving a power supply coil of one of the power supply devices by a power supply driving module electrically coupled to one of the power supply coils; A resonance frequency measurement module coupled to the power supply coil measures a resonance frequency of the power supply coil according to a capacitive sensing parameter related to the power supply coil; so that an auxiliary coil of the power supply device is located in the power supply drive module. When in a non-working state, it is driven by an auxiliary driving module electrically coupled to the auxiliary coil; a voltage measurement module electrically coupled to the auxiliary coil is tracked and locked to one of the largest oscillation voltages of the auxiliary coil And when a processing module is judged to determine that the resonance frequency is stable and the oscillating voltage drops more than a specific ratio, the power supply driving module is placed in an inoperative state. The radio frequency magnetic card identification method according to claim 9, further comprising: when the processing module judges that the resonance frequency is stable and the oscillating voltage drops by more than a specific ratio, judges that a power supply range of the power supply coil has a radio frequency in it Magnetic card. The radio frequency magnetic card identification method according to claim 9, further comprising: causing a digital analog converter of the voltage measurement module to generate a reference voltage; and causing a comparator of the voltage measurement module to receive the reference voltage. And an oscillating voltage related to one of the auxiliary coils to track and lock the oscillating voltage. The radio frequency magnetic card identification method according to claim 11, further comprising: enabling the comparator to control the digital analog converter to track and reference the reference voltage with a feedback mechanism according to a comparison result of the oscillation voltage and the reference voltage. This oscillation voltage is locked. The radio frequency magnetic card identification method according to claim 12, further comprising: causing the comparator to receive a divided voltage of a voltage of the auxiliary coil as the oscillating voltage. The radio frequency magnetic card identification method according to claim 9, further comprising: enabling the processing module to place the power supply driving module in a working state when determining that the resonance frequency is unstable or the oscillating voltage does not exceed the specific ratio. To drive the power supply coil to transmit a power signal. The radio frequency magnetic card identification method according to claim 9, further comprising: causing the processing module to determine whether the resonance frequency is equal to a frequency lock value, and determining that the resonance frequency is stable when the resonance frequency is equal to the frequency lock value; And making the processing module judge that the resonance frequency is unstable when the resonance frequency is not equal to the frequency lock value, and further updating the frequency lock value to the latest measured resonance frequency. The radio frequency magnetic card identification method according to claim 9, further comprising: causing the processing module to determine whether the oscillating voltage is greater than a voltage lock value, and capturing the specific ratio when the oscillating voltage is not greater than the voltage lock value. The voltage lock value is set to a critical value, and further, when the oscillating voltage is less than the critical value, it is judged that the oscillating voltage drops more than the specific ratio, and when the oscillating voltage is not less than the critical value, the oscillating voltage is judged and Did not fall below the specific ratio; and made the processing module judge that the oscillating voltage did not fall beyond the specific ratio when the oscillating voltage was greater than the voltage lock value, and further updated the voltage lock value to the latest measured Oscillating voltage.