CN217984569U

CN217984569U - Hard turn-off battery charging circuit for evidence obtaining camera

Info

Publication number: CN217984569U
Application number: CN202221163631.1U
Authority: CN
Inventors: 寇一波; 梁虎; 杨小辉
Original assignee: Bixing Iot Technology Shenzhen Co ltd
Current assignee: Bixing Iot Technology Shenzhen Co ltd
Priority date: 2022-05-16
Filing date: 2022-05-16
Publication date: 2022-12-06
Anticipated expiration: 2032-05-16

Abstract

The utility model discloses a hard turn-off battery charging circuit that camera was used of collecting evidence, this circuit is including charging current detection module, comparator module, switch module triplex, and charging current detection module connects in the input that charges, detects charging current, and charging current detection module has connect the comparator module, and the comparator module connects switch module. When the external adapter is connected, and the battery starts to charge, the charging current detection module can always detect the charging current and compare the charging current with an internal set value, when the charging current is reduced to a certain value, the system considers that the battery is full of, the comparator module can send a signal to the switch module, and the switch module can be closed, so that the function of disconnecting the charger is realized. The utility model discloses can monitor battery charging current constantly, when the charging current that the system detected, when being less than the default, think that the battery has been full of, cut off hardware charging circuit, have with low costs, characteristics that the reliability is high.

Description

Hard turn-off battery charging circuit for evidence obtaining camera

Technical Field

The utility model belongs to the technical field of charge, concretely relates to turn-off battery charging circuit firmly that camera of collecting evidence was used.

Background

The portable evidence obtaining camera equipment is specially used for investigation and evidence obtaining of public security criminal investigation sites, the equipment is in a portable type, a built-in lithium battery is used for supplying power, and a charging circuit part is specially designed for preventing safety accidents such as long-term charging and overcharging of the battery caused by long-term unplugging of a charger during charging.

The evidence obtaining camera is powered by an internal lithium battery, and the traditional charging method is that an external charger charges the battery, and the battery supplies power to the system.

Fig. 1 is a block diagram of battery charging inside a conventional camera product. The adapter charges the battery pack directly through the charging module, and the structure has the defects that:

1. after the charger fully charges the battery, because the charger is not pulled out, although the charging current is very small or close to zero, the battery is not disconnected with the battery, and the battery is always in a floating charging state;

2. the long-term float-charging battery can shorten the service life of the battery, and the accident of battery spontaneous combustion can also occur with a certain probability.

In conclusion: the existing charging circuit only meets the charging requirement of the battery, but neglects the harm of long-term floating charge, the long-term floating charge firstly shortens the service life of the battery, and secondly increases the probability of spontaneous combustion.

SUMMERY OF THE UTILITY MODEL

In order to solve the above problem, the first-line object of the present invention is to provide a hard turn-off battery charging circuit for a camera for evidence collection, which can constantly monitor the charging current of the battery, and when the charging current detected by the system is smaller than a preset value, the battery is considered to be full, the hardware charging circuit is cut off, and the charging safety and reliability are ensured.

In order to achieve the above object, the technical solution of the present invention is as follows.

The circuit comprises a charging current detection module, a comparator module and a switch module, wherein the charging current detection module is connected to a charging input end to detect charging current, the charging current detection module is connected with the comparator module, and the comparator module is connected with the switch module. The voltage reference chip U1, the comparator U2 and the peripheral resistor form a comparator module, the detected charging current is compared with a built-in threshold value, and finally a high-level or low-level signal is output; r9, LED1, BJT1, Q1A, Q1B and R10 form a switch module, wherein Q1A and Q1B are P-type MOS tubes; r9 is connected with the input end of the LED1, the output end of the LED1 is connected with the base electrode of the BJT1, two P-type MOS tubes are connected with Q1A and Q1B in series and connected with the collector electrode of the BJT1, when high level is input at the left end of R9, the LED1 is conducted, the BJT1 is conducted, the Q1A and Q1B are conducted, and the module is started; when a low level is input at the left end of R9, the LED1 is not conducted, the BJT1 is not conducted, the two P-type MOS tubes Q1A and Q1B are closed, and the module is turned off.

When the external adapter is connected, and the battery starts to charge, the charging current detection module can always detect the charging current and compare the charging current with an internal set value, when the charging current is reduced to a certain value, the system considers that the battery is full of, the comparator module can send a signal to the switch module, and the switch module can be closed, so that the function of disconnecting the charger is realized.

Furthermore, the power input end is also provided with an anti-surge circuit which is arranged in front of the charging current detection module and used for carrying out anti-surge protection on the input end.

Furthermore, D1 is a TVS diode, C1 is an electrolytic capacitor, and D1 and C1 are connected in parallel to form an anti-surge circuit.

Furthermore, the anti-surge circuit is connected with a constant current module, and a resistor R4 forms a charging current detection module which is connected behind the constant current module and used for detecting the magnitude of the charging current.

Further, the peripheral resistor includes R1, R2, R3, R5, R6, R7, and R8, which are respectively disposed at the input and output ends of the comparator U2.

Furthermore, the U1 is a constant current type voltage reference chip, and the function of the U1 is to dynamically keep the voltage at the point B (input ends of the resistors R1 and R2) to be lower by 2.48V than the voltage at the point A (input end of the resistor R4).

Furthermore, the resistor R6 is a positive feedback resistor, and the resistor R6 is arranged at the input end of the comparator U2, so that the characteristic of Schmitt trigger is realized.

Furthermore, the constant current module is M1, the M1 module is a universal DC/DC voltage reduction charging module, the output voltage is 12.6V, and the current constant current value is 2A.

Further, the LED1 also serves as a charging indicator, and when the LED1 is turned on, charging is indicated, and when the LED1 is turned off, charging is terminated.

Further, a capacitor C2 is arranged between the U2 and an emitter (i.e., a power supply cathode) of the BJT1, and the C2 capacitor has an effect of sending a signal of forced conduction when the system is powered on and started up, so as to turn on the MOS switch module. Because the circuit has a self-locking function, when the system is powered on, no trigger signal exists, and the MOS tube is kept in a cut-off state.

The utility model discloses the circuit that realizes is located inside the camera product, between external charger interface and the built-in battery that charges, can monitor battery charging current constantly. When the battery is fully charged, the charging current of the battery is reduced until the battery is fully charged, and the current is close to zero. When the charging current detected by the system is smaller than the preset value, the battery is considered to be fully charged, and the hardware charging circuit is cut off.

The utility model discloses the circuit that realizes has sufficient safety guarantee through pure hardware realization, has improved the safety guarantee that the camera charges, has with low costs, characteristics that the reliability is high. At present, some intelligent evidence obtaining camera products may have functions of software detection and software instruction cut-off charging, but the situations that a software system does not crash and a program does not run away cannot be guaranteed. In contrast, the pure hardware cut-off circuit is used as the last pass of safety guarantee, and as long as the reliability of the components is high, the consistency of the components is good, and the reliability of the whole circuit is higher.

Drawings

Fig. 1 is a battery charging block diagram of a conventional camera.

Fig. 2 is a block diagram of a system implemented by the present invention.

Fig. 3 is a circuit diagram implemented by the present invention.

Fig. 4 is a block diagram of each module in the circuit implemented by the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Fig. 2 shows, the utility model discloses the hard turn-off battery charging circuit that the camera that realizes was used turns off, this circuit including charging current detection module, comparator module, switch module triplex, charging current detection module connects in the input that charges, detects charging current, and charging current detection module has connect the comparator module, and the comparator module connects the switch module. When the external adapter is connected, and the battery starts to be charged, the charging current detection module can always detect the charging current and compare the charging current with an internal set value, when the charging current is reduced to a certain value, the system considers that the battery is fully charged, the comparator module can send a signal to the switch module, and the switch module can be closed, so that the function of disconnecting the charger is realized.

As shown in fig. 3 and 4, the adapter 19V is input into the system, and the component D1 is a TVS diode for preventing static electricity and surge. And C1 is an electrolytic capacitor for storing energy and preventing surge voltage. D1 and C1 constitute an input anti-surge circuit. The M1 module is a constant current module converting 19V to 12.6V, the M1 module is a universal DC/DC voltage reduction charging module, the output voltage is 12.6V, and the current constant current value is 2A. The current detection and comparator module is composed of U1, R2, R3, R4, R5, R6, R7, R8 and U2 components and is used for detecting the magnitude of charging current, comparing the magnitude of the charging current with a preset threshold value and finally outputting a high level or low level signal, the magnitude of the R4 resistor is used for setting the threshold value of the comparator, and the R6 resistor is a positive feedback resistor, so that the characteristic of Schmidt trigger is realized. The electronic switch module is composed of the devices of R9, LED1, BJT1, Q1A, Q1B and R10. When high level is input at the left end of R9, the LED1 is conducted, the BJT1 is conducted, the two P-type MOS tubes Q1A and Q1B are conducted, and the module is started. When a low level is input at the left end of R9, the LED1 is not conducted, the BJT1 is not conducted, the two P-type MOS tubes Q1A and Q1B are closed, and the module is turned off. The LED1 also serves as a charging indicator lamp, when the LED1 is on, the charging is indicated, and when the LED1 is off, the charging is ended. The C2 capacitor has the function of enabling the system to send out a signal of forced conduction when the system is just powered on and started up, and the signal is used for starting the MOS tube switch module. Because the circuit has a self-locking function, when the system is powered on, no trigger signal exists, and the MOS tube is kept in a cut-off state.

The comparator module consists of the components of U1, R2, R3, R4, R5, R6, R7, R8 and U2, has low cost and high reliability, and utilizes the constant current characteristic of the voltage stabilizing chip U1 to make a constant voltage subtraction circuit.

The electronic switch module is composed of the R9, the LED1, the BJT1, the Q1A, the Q1B and the R10, has the characteristics of low cost and high reliability, utilizes the fixed voltage drop characteristic of the LED, raises the threshold value of a high-level signal of the system, and effectively solves the interference of burr interference voltage on the system.

Meanwhile, the switch module formed by connecting the two back-to-back P-type MOS tubes in series effectively prevents reverse voltage and current from flowing backwards.

The working principle of the circuit. When the charging current flows through the R4 resistor, a voltage drop is generated across the resistor, and the voltage drop is equal to the current value multiplied by the R4 resistance value, i.e. 0.22 × i, i.e. the voltage at point D is equal to the voltage at point a, i.e. 12.6 minus 0.22 × i.

D＝12.6-0.22*I

U1 is a constant current type voltage reference chip, the function of U1 is to dynamically keep the voltage at the point B lower than the voltage at the point A by 2.48V, and 2.48V is set in the U1 chip. The R2 and R3 resistors have the function of dividing the voltage at the point A and the voltage at the point B to generate a new voltage C. The voltage at the point a is 12.6v, the voltage at the point b is 12.6V-2.48v =10.12v, the divided voltage at the point C is related to the values of the resistors R1 and R2, and when R1=220 ohm and R2=10K (10000) ohm, the voltage at the point C is calculated according to the following equation of the principle of consistent current of the series circuit:

(12.6-C)/220＝(C-10.12)/10000

solving the above equation can result in C =12.5466, i.e. the voltage at point C is 12.5466V.

Voltage at point D =12.6-0.22 × I, when I =0.2427, D =12.5466, and corresponds to the voltage at point C.

Therefore, the current 0.2427 (a) is a boundary, when the charging current is less than 0.2427A, the U2 comparator outputs low level, the LED1 is not turned on, and the MOS switch circuit is turned off. When the charging current is larger than 0.2427A, the U2 comparator outputs high level, the BJT1 is conducted, and the MOS tube is started.

The following table shows different resistance values of R4, corresponding to the turn-off threshold.

Table 1 turn-off threshold comparison table corresponding to different R4 resistance values

The U1 voltage stabilization chip is TL431, and CJ431 and KA431 chips with the same functions can be used.

The U2 voltage comparator is an LM339 chip, and LM393 and LM2903 chips having the same function may be used.

The two MOS transistors Q1A and Q1B are P-type MOS transistor FDS4935, and other types of P-type MOS transistors such as AO4409, AO4407, IRF5210 and IRF4905 can also be used.

The BJT1 is an MMBT3904 triode, and other types of triodes can be used, such as 2N3904, S8050, 9018 and 9014.

The LED1 light emitting diode is a red LED, and a yellow LED, a green LED, a blue LED, or a white LED may be used.

In a word, the utility model discloses the circuit that realizes is located inside the camera product, between external charger interface and the built-in battery that charges, can monitor battery charging current constantly. When the battery is fully charged, the charging current of the battery is reduced until the battery is fully charged, and the current is close to zero. When the charging current detected by the system is smaller than the preset value, the battery is considered to be fully charged, and the hardware charging circuit is cut off.

And, the utility model discloses a pure hardware realizes, and the security is high.

The above description is only exemplary of the present invention and should not be construed as limiting the present invention, and any modifications, equivalents and improvements made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.

Claims

1. A hard turn-off battery charging circuit for a camera for obtaining evidence comprises a charging current detection module, a comparator module and a switch module, wherein the charging current detection module is connected with a charging input end and detects charging current; the voltage reference chip U1, the comparator U2 and the peripheral resistor form a comparator module, the detected charging current is compared with a built-in threshold value, and finally a high-level or low-level signal is output; r9, LED1, BJT1, Q1A, Q1B and R10 form a switch module, wherein Q1A and Q1B are P-type MOS tubes; r9 is connected with the input end of the LED1, the output end of the LED1 is connected with the base electrode of the BJT1, two P-type MOS tubes are connected in series, Q1A and Q1B are connected with the collector electrode of the BJT1, when high level input is carried out at the left end of R9, the LED1 is conducted, the BJT1 is conducted, the Q1A and Q1B are conducted, and the module is started; when the low level at the left end of R9 is input, the LED1 is not conducted, the BJT1 is not conducted, the two P-type MOS tubes Q1A and Q1B are closed, and the module is turned off.

2. The hard-off battery charging circuit for a forensic camera as claimed in claim 1 wherein the power input is further provided with an anti-surge circuit, the anti-surge circuit being provided in front of the charging current detection module for anti-surge protection of the input.

3. The hard-turn-off battery charging circuit for a forensic camera as claimed in claim 2 wherein D1 is a TVS diode, C1 is an electrolytic capacitor and D1 and C1 are connected in parallel to form an anti-surge circuit.

4. The hard-off battery charging circuit for a forensic camera as in claim 2 wherein the anti-surge circuit is connected to the constant current module, and the resistor R4 forms a charging current detection module connected to the rear of the constant current module.

5. The hard-off battery charging circuit for a forensic camera as claimed in claim 1 wherein the peripheral resistor comprises R1, R2, R3, R5, R6, R7, R8 provided at the input and output of comparator U2 respectively.

6. The hard turn-off battery charging circuit for a forensic camera as in claim 4 wherein U1 is a constant current type voltage reference chip.

7. The hard turn-off battery charging circuit for a forensic camera as in claim 5 wherein the R6 resistor is a positive feedback resistor and R6 is provided at the input of comparator U2.

8. The hard-off battery charging circuit for a forensic camera as in claim 1 wherein the LED1 also serves as a charge indicator, with LED1 on indicating charging and LED1 off indicating end of charging.

9. A hard turn-off battery charging circuit for a forensic camera as claimed in claim 8 in which a capacitor C2 is provided between U2 and the emitter of the BJT 1.