TWI492605B - Device for preventing embezzlement of telephone line - Google Patents

Description

Telephone line anti-theft device

The present invention relates to a telephone system, and more particularly to a telephone line antitheft device.

With the development of the telecommunications industry, the telephone has not only become one of the important means of communication, but also a variety of tools for activities such as telephone entertainment, chat, and television hotlines. However, the cost of these activities is higher. As shown in FIG. 1, the general telephone line is a terminal that directly connects the user's telephone terminal to the telephone line. In this way, when the telephone line is led indoors, if the person privately connects the other telephone terminal to the user's telephone line and sms, the user will not notice. Therefore, the phenomenon of stealing telephone lines sometimes occurs, thereby causing users to suffer economic losses.

In view of this, it is necessary to provide a telephone line anti-theft device.

A telephone line anti-theft device includes a rectifier circuit, a first control circuit, a second control circuit, a switch circuit, and a multi-resonant circuit. The rectifier circuit is configured to receive an AC voltage of the external line and rectify the AC voltage to output a DC voltage. The first control circuit is coupled to the output of the rectifier circuit for receiving a DC voltage and generating a first control signal based on the DC voltage. The second control circuit is coupled to the first control circuit for monitoring a state of use of the user telephone terminal connected to the telephone line to generate a second control signal. The switching circuit is connected to the first control circuit and the second control circuit, and is rooted The multi-resonant circuit is turned on or off according to the first control signal and the second control signal.

The above-mentioned telephone line anti-theft device, through the first control and the second control circuit, opens a multi-resonant circuit when someone steals a telephone line at the middle of other phones, which not only prevents the telephone line from being stolen. When the user's telephone terminal is working, the multi-resonant circuit is turned off, which does not affect the normal use of the telephone terminal by the user.

200‧‧‧ telephone line anti-theft device

10‧‧‧Rectifier circuit

20‧‧‧First control circuit

30‧‧‧Second control circuit

32‧‧‧First gating circuit

34‧‧‧Second gate circuit

40‧‧‧Switch circuit

50‧‧‧Multiple resonant circuits

Figure 1 is a schematic diagram of an existing telephone line system.

2 is a schematic diagram of a telephone line anti-theft system according to a preferred embodiment.

3 is a block diagram showing the structure of a telephone line anti-theft device according to a preferred embodiment.

4 is a detailed circuit diagram of a telephone line anti-theft device according to a preferred embodiment.

Referring to FIG. 2, during the process of introducing the telephone line from the outdoor into the room, someone may privately connect other user telephone terminals to the telephone line and steal the user's telephone line. The invention provides a telephone line anti-theft device 200, which is installed indoors and connected to an outer line first access line A, an outer line second access line B, a telephone first access line C, and a telephone second access line D. Used to prevent theft of telephone lines. Wherein, the outer line first access line A and the outer line second access line B are connected to the outer line, the first access line C of the telephone and the second access line D of the telephone are connected to the user telephone terminal, and in general, the outer line The voltage of the external circuit is about 50V, and in the present embodiment, the voltage of the external line is 50V.

Please refer to FIG. 3 , which is a structural block diagram of a telephone line anti-theft device 200 according to a preferred embodiment. The telephone line anti-theft device 200 includes a rectifying circuit 10, a first control circuit 20, a second control circuit 30, a switching circuit 40, and a multi-resonant circuit 50. Among them, rectification The circuit 10 is connected between the first line A of the outer line and the second line B of the outer line, and is connected to the first control circuit 20. The first control circuit 20 is connected to the second control circuit 30 and connected to the multi-resonant circuit 50 through the switch circuit 40.

The rectifier circuit 10 is configured to receive the AC voltage V of the external line and rectify the AC voltage V to output a DC voltage V ₀ . Wherein, when the telephone line is not in use, the AC voltage V is at a high level; and when the telephone line is used, that is, the subsequent circuit is connected to the load, the AC voltage V will be pulled low to a low level. In the present embodiment, the AC voltage V is 50V AC when the telephone line is not in use, and the AC voltage V is reduced to about 9V when the telephone line is used. Corresponding to the AC voltage V, the DC voltage V _{0 is} also at a high level when the telephone line is not in use, and the DC voltage V _{0 is} also at a low level when the telephone line is used.

The first control circuit 20 is configured to receive the DC voltage V ₀ and generate a first control signal. Corresponding to the change of the DC voltage V ₀ , the first control signal also has two forms. When the DC voltage V ₀ is at a high level, the first control signal is at a low level; when the DC voltage V ₀ is at a low level, the first control signal is at a high level.

The second control circuit 30 is configured to monitor the operating state of the user's telephone terminal to generate a second control signal. Wherein, the second control signal has only a low level. When the user's telephone terminal is operating, the second control circuit 30 operates to output a second control signal of a low level; when the user's telephone terminal is not operating, the second control circuit 30 also ceases to operate.

The switch circuit 40 is configured to receive the first control signal and the second control signal, and is turned on or off under the control of the first control signal and the second control signal.

The multi-resonant circuit 50 starts to oscillate when the switch circuit 40 is turned on, and stops when the switch circuit 40 is turned off.

The working principle of the switch circuit 40 is analyzed below to analyze the working principle of the entire telephone line anti-theft device 200: when no one uses the telephone line, on the one hand, the AC voltage V is at a high level, so the DC voltage V ₀ is at a high level. The first control signal is at a low level; on the other hand, the second control circuit 30 is stopped. Therefore, the switching circuit 40 receives only the first control signal at a low level. At this time, the switch circuit 40 is turned off, and the multi-resonant circuit 50 is stopped.

When someone steals the telephone line with another telephone terminal, on the one hand, the AC voltage V is at a low level, so the DC voltage V ₀ is at a low level, and the first control signal is at a high level; It does not work, so the second control circuit 30 stops working. Therefore, the switching circuit 40 receives only the first control signal at a high level. At this time, the switch circuit 40 is turned on, and the multi-resonant circuit 50 is oscillated, thereby increasing the load on the telephone line, and further lowering the level of the AC voltage V. Since the AC voltage V, which is itself at a low level, is further pulled low, other telephone terminals used to steal the telephone line will not function properly due to the operating voltage being too low.

When the user's telephone terminal is working normally, on the one hand, the AC voltage V is at a low level, so the DC voltage V ₀ is at a low level, and the first control signal is at a high level; on the other hand, the second control circuit 30 generates a low battery. Flat second control signal. Therefore, the switch circuit 40 simultaneously receives the first control signal of the high level and the second control signal of the low level, and the second control signal pulls the high level of the first control signal low, so the switch circuit 40 is turned off. The multi-resonant circuit 50 stops vibrating.

Please refer to FIG. 4, which is a specific circuit diagram of a telephone line anti-theft device 200 according to a preferred embodiment. The rectifier circuit 10 is a bridge rectifier circuit composed of four diodes D1 to D4 connected between the first line A of the outer line and the second line B of the outer line. The rectifier circuit 10 is configured to receive the AC voltage V of the external line introduced by the external line first access line A and the external line second access line B, and rectify the AC voltage V, and output from the output end of the rectifier circuit 10 H outputs a DC voltage V ₀ . Wherein, when the telephone line is not in use, the DC voltage V ₀ is at a high level, and its voltage value is 50V; and when the telephone line is used, the DC voltage V ₀ is at a low level, and its voltage value is 9V.

The first control circuit 20 includes a voltage comparator U1, a sampling circuit 22, and a reference circuit 24. The inverting input terminal of the voltage comparator U1 is connected to the sampling circuit 22, the non-inverting input terminal thereof is connected to the reference circuit 24, and the output terminal thereof is connected to the second control circuit 30 and the switching circuit 40.

The sampling circuit 22 is for receiving the DC voltage V ₀ from the rectifier circuit 10 and outputting a sampling voltage V _{T to} the inverting input terminal of the voltage comparator U1. The reference circuit 24 is for receiving the DC voltage V ₀ from the rectifier circuit 10 and outputting a reference voltage V _{R to the non-} inverting input terminal of the voltage comparator U1. The voltage comparator U1 compares the sampling voltage V _T with the reference voltage V _R to output a first control signal.

Specifically, the sampling circuit 22 includes a first voltage stabilizing diode DZ1, a first voltage dividing resistor R1, and a second voltage dividing resistor R2. The cathode of the first voltage stabilizing diode DZ1 is connected to the output terminal H of the rectifier circuit 10, and the anode of the first voltage stabilizing diode DZ1, the first voltage dividing resistor R1 and the second voltage dividing resistor R2 are sequentially electrically connected. Ground.

When the DC voltage V ₀ outputted by the rectifier circuit 10 is higher than the voltage regulator voltage of the first voltage regulator diode DZ1, the first voltage regulator diode DZ1 is broken down, and is applied to the first voltage divider resistor R1 and the second component. The total voltage V1 on the voltage resistor R2 is equal to the DC voltage V ₀ output from the rectifier circuit 10. When the DC voltage V ₀ outputted by the rectifier circuit 10 is lower than the voltage regulator voltage of the first voltage regulator diode DZ1, the first voltage regulator diode DZ1 is not broken down, and is applied to the first voltage dividing resistor R1 and the second The total voltage V ₁ across the voltage dividing resistor R2 is zero. Wherein, in order to change the total voltage V ₁ of the first voltage dividing resistor R1 and the second voltage dividing resistor R2 with the change of the DC voltage V ₀ , the voltage regulator voltage of the first voltage stabilizing diode DZ1 should be between DC Between the high level of voltage V ₀ and its low level. In this example, the regulated voltage of the first Zener diode DZ1 is 12V.

A first reference circuit 24 comprises a current limiting resistor R5, a second zener diode DZ2, a filter capacitor C1, the third voltage-dividing resistor R3, a fourth resistor R4 and the voltage dividing node J _0. One end of the first current limiting resistor R5 is connected to the output terminal H of the rectifier circuit 10, and the other end of the first current limiting resistor R5, the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 are electrically connected in series and grounded. The anode of the second voltage stabilizing diode DZ2 is grounded, and the cathode of the second voltage stabilizing diode DZ2 is electrically connected to the filter capacitor C1 through the node J ₀ between the resistor R5 and the third voltage dividing resistor R3, and is grounded. The first current limiting resistor R5, the second voltage stabilizing diode DZ2 and the filter capacitor C1 form a voltage stabilizing circuit for regulating and filtering the voltage V ₀ outputted by the rectifier circuit 10 to the third voltage dividing resistor. R3 and the fourth voltage dividing resistor R4 provide a constant voltage V ₂ . In order to make the second voltage regulator diode DZ2 play a voltage regulation role, it should be ensured that the voltage regulator voltage of the second voltage regulator diode DZ2 is lower than the DC voltage V ₀ . In this embodiment, the regulated voltage of the second Zener diode DZ2 is 5V.

The inverting input terminal of the voltage comparator U1 is electrically connected between the first voltage dividing resistor R1 and the second voltage dividing resistor R2 of the sampling circuit 22, so that the voltages of the first voltage dividing resistor R1 and the second voltage dividing resistor R2 After V ₁ is divided, the output sampling voltage V _{T ,} that is, the divided voltage of the second voltage dividing resistor R2 is supplied to the inverting input terminal of the voltage comparator U1.

The non-inverting input terminal of the voltage comparator U1 is electrically connected between the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 of the reference circuit 24, so that the voltage of the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 is V. ₂ After being divided by the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4, the output reference voltage VR, that is, the voltage divider on the fourth voltage dividing resistor R4 is divided to the non-inverting input terminal of the voltage comparator U1. Among them, since the voltage V ₁ is variable, the sampling voltage V _T is also variable. The stable voltage V ₂ is constant, so the reference voltage V _R is also constant.

The voltage comparator U1 compares the sampling voltage V _T received by the inverting input terminal with the reference voltage V _R received by the non-inverting input terminal. If the sampling voltage V _{T is} higher than the reference voltage V _R , the voltage comparator U1 outputs a low voltage. If the sampling voltage V _{T is} higher than the reference voltage V _R , the voltage comparator U1 outputs a high level. In order to enable the voltage comparator U1 to output two forms of high and low levels, that is, two forms of the first control signal, the sampling voltage VT and the reference voltage V _R must satisfy certain conditions, that is, the sampling voltage VT is high. At or below the reference voltage V _R two forms. Therefore, in this embodiment, the first voltage dividing resistor R1 uses a resistance value of 200 M ohms, the second voltage dividing resistor uses a resistance value of 100 K ohms, the third voltage dividing resistor uses a resistance value of 100 K ohms, and the fourth voltage dividing resistor A resistance value of 50K ohms is used.

The second control circuit 30 includes a first gating circuit 32 and a second gating circuit 34. Both the first gating circuit 32 and the second gating circuit 34 are connected to the output of the voltage comparator U1 via a second current limiting resistor R6.

The first gating circuit 32 includes a first biasing resistor R11, a second transistor Q4, and a first diode D5. The first bias resistor R11 is connected in parallel to the emitter and the base of the second transistor Q4. The emitter and the base of the second transistor Q4 are also electrically connected to the outer line first access line A and the first line of the telephone line C, respectively. The collector of the second transistor Q4 is electrically connected to the cathode of the first diode D5. The anode of the first diode D5 is electrically connected to the output of the voltage comparator U1 via a resistor R6.

The second gating circuit 34 includes a second bias resistor R12, a third transistor Q5, and a second diode D6. The second bias resistor R12 is connected in parallel to the emitter and the base of the third transistor Q5, and the emitter and the base of the third transistor Q5 are also connected to the external line respectively. The incoming line B and the second access line D of the telephone are electrically connected. The collector of the third transistor Q5 is electrically connected to the cathode of the second diode D6. The anode of the second diode D6 is electrically connected to the output end of the voltage comparator U1 through the second current limiting resistor R6.

When the telephone is used, the external line access lines A, B and the telephone access lines C, D form a loop. If the first line A of the outer line outputs a positive voltage, and the second line B of the outer line outputs a negative voltage. The base of the third transistor Q5 obtains a current, and the third transistor Q5 is turned on; if the first line A of the external line outputs a negative voltage, and the second line of the external line B outputs a positive voltage, the second line The base of the crystal Q4 obtains a current, and the second transistor Q4 is turned on. That is, when the telephone is used, one of the first gating circuit 32 and the second gating circuit 34 must be turned on. Therefore, the collector of the second transistor Q4 or the third transistor Q5 outputs a second control signal, that is, a low level, and the first output of the voltage comparator U1 is output through the first diode D5 or the second diode D6. The control signal is pulled low.

The switching circuit 40 includes a first transistor Q1 and a light emitting diode LED. The base of the first transistor Q1 is connected to the output terminal of the voltage comparator U1 through the second current limiting resistor R6, the emitter thereof is grounded, the collector is connected to the cathode of the LED, and the anode of the LED is LED It is connected to the output H of the rectifier circuit 10.

When the first control signal output by the voltage comparator U1 is at a high level, the first transistor Q1 is turned on, and the light emitting diode LED emits light. When the first control signal output by the voltage comparator U1 is at a low level, the first transistor Q1 is turned off, and the light emitting diode LED does not emit light. The collector of the first transistor Q1 is also connected to the multi-resonant circuit 50.

The multi-resonant circuit 50 includes a first capacitor C2, a second capacitor C3, a resistor R8, a first resistor R9, a second resistor R10, a PNP-type transistor Q2, an NPN-type transistor Q3, and a speaker DY. The base of the PNP type transistor Q2 is connected to the collector of the first transistor Q1 through R8, the emitter thereof is connected to the output terminal H of the rectifier circuit 10, and the collector thereof passes through the resistor R10. Ground.

The base of the NPN type transistor Q3 is connected between the collector of the PNP type transistor Q2 and the second resistor R10, and its collector is connected to the output terminal H of the rectifier circuit 10 through the speaker DY, and its emitter is grounded.

The first capacitor C2 is connected in series with the first resistor R9 and is connected between the base of the PNP-type transistor Q2 and the collector of the NPN-type transistor Q3, and the first capacitor C2 is connected to the base of the PNP-type transistor Q2 and Between the resistors R8 and the first resistor R9 is connected between the collector of the NPN-type transistor Q3 and the speaker DY.

The second capacitor C3 is connected between the base and the collector of the PNP type transistor Q2, and one end of the first capacitor C3 is connected between the base of the PNP type transistor Q2 and the resistor R8, and the other end is connected to the PNP type. Between the collector of crystal Q2 and the second resistor R10.

The first transistor Q1 of the above embodiment is used as a switch, which can be replaced by other transistors having a switching function, such as a MOS tube, etc., and the LED of the LED is used as a prompting function, and can be replaced by other light emitting devices. . If other components are used, the peripheral circuits may be adjusted according to the characteristics of the components, and details are not described herein.

The working state of the telephone line anti-theft device 200 and the corresponding working principle will be described below.

When no telephone line is used, the outer line first access line A and the outer line second access line B introduce an alternating voltage V of the outer line, and the alternating voltage V is 50V. The rectifier circuit 10 rectifies the AC voltage V and outputs a DC voltage V _{0 of} 50V.

At this time, the voltage of the cathode of the first stabilizing diode DZ1 is 50V. Because the voltage regulator voltage of the first Zener diode DZ1 is 12V, which is smaller than the voltage V ₀ on the cathode of the diode DZ1, the first Zener diode DZ1 is broken down, thereby being applied to the first voltage dividing resistor R1 and The total voltage V ₁ on the second voltage dividing resistor R2 is 50V. The resistance values of the first voltage dividing resistor R1 and the second voltage dividing resistor R2 are 2M ohms and 100K ohms, respectively, and V ₁ is divided by the first voltage dividing resistor R1 and the second voltage dividing resistor R2, and the second voltage dividing resistor R2 The divided voltage is approximately 2.5V and is output to the inverting input of voltage comparator U1.

The voltage stabilizing circuit composed of the first current limiting resistor R5, the second voltage stabilizing diode DZ2 having a regulated voltage value of 5V, and the filter capacitor C1 also receives the DC voltage V ₀ from the rectifying circuit 10, and is subjected to voltage stabilization and filtering. Thereafter, the total voltage V ₂ applied to the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 is 5V. The resistance values of the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 are 100K ohms and 50K ohms, respectively, and V ₂ is divided by the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4, and the fourth voltage dividing resistor R4 The divided voltage value is approximately 1.67V and is applied to the non-inverting input of voltage comparator U1.

Therefore, the voltage of the inverting input terminal of the voltage comparator U1 is 2.5V, and the voltage of the non-inverting input terminal of the comparator U1 is 1.67, and the voltage of the inverting input terminal of the voltage comparator U1 is higher than the voltage of the non-inverting input terminal of the voltage comparator U1. The comparator U1 outputs a low level such that the first transistor Q1 is turned off, causing the light emitting diode LED to not emit light, and the oscillating circuit 50 does not operate.

When someone steals the telephone line with another telephone terminal, the AC voltage V introduced into the external line by the first line A of the outer line and the second line B of the outer line is reduced from the original 50V to 9V, and is rectified by the rectifier circuit 10 and output. 9V DC voltage V ₀ .

At this time, the voltage on the cathode of the first stabilizing diode DZ1 is about 9V. Because the voltage of the first voltage regulator diode DZ1 is 12V, which is greater than the voltage on the cathode of the first voltage regulator diode DZ1, the first voltage regulator diode DZ1 is not broken down, and is added to the first voltage divider. The voltage on the resistor R1 and the second voltage dividing resistor R2 is 0, and is applied to the inverting input terminal of the voltage comparator U1 to be 0V.

The voltage stabilizing circuit composed of the first current limiting resistor R5, the second voltage stabilizing diode DZ2 having a regulated voltage value of 5V, and the filter capacitor C1 also receives the DC voltage V ₀ from the rectifying circuit 10, and is subjected to voltage stabilization and filtering. Thereafter, the total voltage V ₂ applied to the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 is 5V. The resistance values of the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 are 100K ohms and 50K ohms, respectively, and the voltage division of the fourth voltage dividing resistor R4 after V ₂ is divided by the third voltage dividing resistor R3 and the fourth R4 voltage. The value is approximately 1.67V and is applied to the non-inverting input of voltage comparator U1.

Therefore, the voltage of the inverting input terminal of the voltage comparator U1 is 0V, and the voltage of the non-inverting input terminal of the voltage comparator U1 is 1.67V, and the voltage of the inverting input terminal of the voltage comparator U1 is lower than the voltage of the non-inverting input terminal of the voltage comparator U1. The voltage comparator U1 outputs a high level, and the first transistor Q1 is turned on, so that the light emitting diode LED emits light, and the multi-resonant circuit 50 operates and causes the speaker DY to output a sound, thereby increasing the load on the telephone line. The voltage on the telephone line is reduced, making other telephone terminals inoperable.

When the user's telephone terminal works normally, the AC voltage V introduced into the external line by the first line A of the outer line and the second line B of the outer line is reduced from the original 50V to 9V, and is rectified by the rectifier circuit 10 to output a DC of 9V. Voltage V ₀ .

At this time, the voltage on the cathode of the first stabilizing diode DZ1 is about 9V. Because the voltage of the first voltage regulator diode DZ1 is 12V, which is greater than the voltage on the cathode of the first voltage regulator diode DZ1, the first voltage regulator diode DZ1 is not broken down, and is added to the first voltage divider. The voltage across the resistor R1 and the second voltage dividing resistor R2 is zero, so that the voltage applied to the inverting input terminal of the voltage comparator U1 is 0V.

The voltage stabilizing circuit composed of the first current limiting resistor R5, the second voltage stabilizing diode DZ2 having a regulated voltage value of 5V, and the filter capacitor C1 also receives the DC voltage V ₀ from the rectifying circuit 10, and is subjected to voltage stabilization and filtering. Thereafter, the total voltage V ₂ applied to the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 is 5V. The resistance values of the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4 are 100K ohms and 50K ohms, respectively, and V ₂ is divided by the third voltage dividing resistor R3 and the fourth voltage dividing resistor R4, and the fourth voltage dividing resistor R4 The divided voltage value is approximately 1.67V and is applied to the non-inverting input of voltage comparator U1.

Therefore, the voltage 0V of the inverting input terminal of the voltage comparator U1 is lower than the voltage 1.67 of the non-inverting input terminal of the voltage comparator U1, and the voltage comparator U1 outputs a high level. At this time, the user uses the telephone, the external line access lines A, B and the telephone access lines C, D form a loop, and one of the second transistor Q4 and the third transistor Q5 must be turned on, so that the second transistor Q4 or the first The collector of the three transistor Q5 outputs a low level, and the high level of the output of the voltage comparator U1 is pulled low to the low level via the first diode D5 or the second diode D6, the first transistor Q1 When the LED is off, the LEDs do not emit light, and the multi-resonant circuit 50 does not work, thereby not affecting the normal operation of the user's telephone terminal.

In other implementations, the multi-resonant circuit 50 may be composed of other components, and the resistance values of the first voltage dividing resistor R1, the second voltage dividing resistor R2, the third voltage dividing resistor R3, and the fourth voltage dividing resistor R4, and the first The voltage regulation voltage of the voltage regulator diode DZ1 and the second voltage regulator diode DZ2 can be changed according to the needs of the circuit design, and the same effect can be achieved, which will not be described here.

The telephone line anti-theft device 200 passes through the first control circuit 20 and the second control circuit 30, and when the telephone line is stolen, the switch circuit 40 is controlled to be turned on, so that the LED of the LED and the multi-resonant circuit 50 start to vibrate to drive the speaker DY. Work not only allows the user to know that the telephone line has been stolen, but also reduces the voltage of the telephone line, prevents the telephone line from being stolen, and has no effect on the telephone line and the user's telephone terminal. In addition, the circuit of the embodiment has a simple structure and is completed by using common basic components, which greatly reduces Low manufacturing costs.

In summary, the present invention complies with the requirements of the invention patent and submits a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and equivalent modifications or variations made by those skilled in the art of the present invention should be included in the following claims.

200‧‧‧ telephone line anti-theft device

10‧‧‧Rectifier circuit

20‧‧‧First control circuit

30‧‧‧Second control circuit

32‧‧‧First gating circuit

34‧‧‧Second gate circuit

40‧‧‧Switch circuit

50‧‧‧Multiple resonant circuits

Claims (14)

A telephone line anti-theft device is improved in that the telephone line anti-theft device comprises a rectifying circuit, a first control circuit, a second control circuit, a switching circuit and a multi-resonant circuit for receiving an AC voltage of an external line, and Recharging the AC voltage to output a DC voltage; the first control circuit is coupled to the output of the rectifier circuit for receiving the DC voltage and generating a first control signal according to the DC voltage; the second control circuit and the first a control circuit is connected for monitoring a usage state of the user telephone terminal connected to the telephone line to generate a second control signal; the switch circuit is connected to the first control circuit and the second control circuit, and according to the first control signal and The second control signal turns on or off the multi-resonant circuit, the first control circuit includes a voltage comparator, a sampling circuit and a reference circuit, and the inverting input end of the voltage comparator is connected to the sampling circuit, and the non-inverting input terminal and the reference circuit Connected, the output end of which is connected to the second control circuit and the switch circuit; the sampling circuit is used for Receiving the DC voltage to output a sampling voltage to the inverting input terminal; the reference circuit is configured to receive the DC voltage to output a reference voltage; the voltage comparator compares the sampling voltage with the reference voltage, and according to the comparison result The first control signal is generated. The telephone line anti-theft device according to claim 1, wherein the second control circuit detects that the user telephone terminal is in use, the second control circuit outputs the second control signal, and the second control signal is located Low level; the second control circuit detects that the second control circuit has no output when the user's telephone terminal is in the standby state. The telephone line anti-theft device according to claim 1, wherein the first control signal comprises two forms of high and low levels, and when the direct current voltage is at a high level, the first control signal is at a low level; When the DC voltage is at a low level, the first control signal is at a high level. The telephone line anti-theft device according to claim 3, wherein the switch circuit receives only the first control signal when the user's telephone terminal is in a standby state, and the switch circuit when the first control signal is at a high level. The multi-resonant circuit is turned on; when the first control signal is at a low level, the switch circuit turns off the multi-resonant circuit. The telephone line anti-theft device according to claim 2, wherein the switch circuit receives the first control signal and the second control signal when the user's telephone terminal is in use, and the second control signal is pulled. The level of the first control signal is low, and the switching circuit turns off the multi-resonant circuit. The telephone line anti-theft device according to claim 1, wherein the sampling circuit comprises a first voltage stabilizing diode, a first voltage dividing resistor and a second voltage dividing resistor, the rectifier circuit output end, the first voltage regulator The cathode of the diode is connected to the output end of the rectifier circuit, and the anode of the first voltage stabilizing diode, the first voltage dividing resistor and the second voltage dividing resistor are electrically connected in sequence and grounded. The telephone line anti-theft device according to claim 6, wherein the reference circuit comprises a voltage stabilizing circuit, a third voltage dividing resistor and a fourth voltage dividing resistor, and the voltage stabilizing circuit, the third voltage dividing resistor and the fourth point The voltage resistors are grounded in series and then grounded. The voltage stabilizing circuit receives the DC voltage and provides a stable voltage to the third voltage dividing resistor and the fourth voltage dividing resistor. The telephone line anti-theft device according to claim 7, wherein the voltage stabilizing circuit comprises a first current limiting resistor and a second voltage stabilizing diode, and one end of the first current limiting resistor is connected to an output end of the rectifying circuit The other end of the first current limiting resistor is electrically connected to the third voltage dividing resistor; the anode of the second voltage stabilizing diode is grounded, and the cathode of the second voltage stabilizing diode is connected to the first current limiting resistor and Between the third voltage divider resistors. The telephone line antitheft device according to claim 6 or 7, wherein the inverting input terminal of the voltage comparator is electrically connected between the first voltage dividing resistor and the second voltage dividing resistor; the voltage comparator is The non-inverting input is electrically connected between the third voltage dividing resistor and the fourth voltage dividing resistor. The telephone line anti-theft device according to claim 9, wherein the second control circuit package a first gating circuit and a second gating circuit, the first gating circuit comprising a first biasing resistor, a second transistor and a first diode, the first biasing resistor being coupled to the second transistor Between the emitter and the base, the emitter and the base of the second transistor are electrically connected to the first line of the outer line and the first access line of the telephone, and the collector of the second transistor The cathode of the first diode is electrically connected, and the anode of the first diode is electrically connected to the output of the voltage comparator; the second gate circuit includes a second bias resistor, a third transistor, and a a diode, the second bias resistor is connected in parallel between the emitter and the base of the third transistor, and the emitter and the base of the third transistor are electrically connected to the second line of the external circuit respectively a line and a second telephone access line, the collector of the third transistor is electrically connected to the cathode of the second diode, and the anode of the second diode is electrically connected to the output of the voltage comparator . The telephone line anti-theft device according to claim 10, wherein the switch circuit comprises a first transistor, a base of the first transistor is connected to an output end of the voltage comparator, and the first transistor is emitted. The pole is grounded, and the collector of the first transistor is connected to the output end of the rectifier circuit and the multi-resonant circuit. The telephone line anti-theft device according to claim 11, wherein the multi-resonant circuit comprises a first capacitor, a second capacitor, a first resistor, a second resistor, a PNP-type transistor, an NPN-type transistor, and a speaker. The base of the PNP type transistor is electrically connected to the collector of the first transistor, and the emitter thereof is electrically connected to the output end of the rectifier circuit, and the collector is respectively connected to the base of the second resistor and the NPN type transistor. Electrically connected; the emitter of the NPN-type transistor is grounded, and the collector is connected to the output end of the rectifier circuit through a speaker; the first capacitor and the second resistor are connected in series and connected to the base of the PNP-type transistor and Between the collectors of the NPN type transistors, and the first capacitor is connected to the base of the PNP type transistor, and the second resistor is connected to the collector of the NPN type transistor; the second capacitor is connected to the PNP type transistor Between the base and the collector. The telephone line antitheft device according to claim 10, wherein the telephone line antitheft device further comprises a light emitting element connected to the collector and the rectifying current of the first transistor. Between the outputs of the road. The illuminating device is a light emitting diode, and the cathode of the illuminating diode is electrically connected to the collector of the first transistor, and the illuminating diode is The anode is electrically connected to an output end of the rectifier circuit.