Portable car refrigerator battery charging selection and protection circuit and charging method

Abstract

The application provides a portable vehicle-mounted refrigerator battery charging selection and protection circuit and a charging method, which comprises a main input end, a secondary input end, an input selection circuit, a protection circuit and a voltage detection circuit, one end of the input selection circuit is connected with the protection circuit, the other end of the input selection circuit is connected with the main input end and the secondary input end respectively, and the protection circuit is electrically connected with the voltage detection circuit; the input selection circuit comprises a main input circuit and a secondary input circuit, the main input circuit is connected with the main input end, and the secondary input circuit is connected with the secondary input end. The portable vehicle-mounted refrigerator battery charging selection and protection circuit has the advantages of convenient charging, good circuit protection effect, long service life and wide application range.

Description

Technical Field

[0001] This invention relates to the field of protection circuit technology, and in particular to a portable vehicle refrigerator battery charging selection and protection circuit and charging method. Background Technology

[0002] With the rapid development of the automotive industry, to meet people's needs, refrigerators have merged with cars, resulting in miniaturized and intelligent car refrigerators. Portable car refrigerators are increasingly favored by consumers. They have built-in batteries and can be powered by the car battery or by solar energy. During charging, both the car battery and the car refrigerator battery need to be protected simultaneously. Solar charging is more economical than directly using the car battery. When using the car battery to charge the car refrigerator battery, the car battery must be protected to prevent it from being completely depleted. Other drawbacks include poor charging performance, inadequate circuit protection, and short battery life. Summary of the Invention

[0003] To address the shortcomings of the aforementioned related technologies, this invention proposes a portable vehicle refrigerator battery charging selection and protection circuit and charging method that features convenient charging, good circuit protection, and increased service life.

[0004] To solve the above-mentioned technical problems, in a first aspect, embodiments of the present invention provide a portable vehicle refrigerator battery charging selection and protection circuit, including: a main input terminal, a secondary input terminal, an input selection circuit, a protection circuit, and a voltage detection circuit. One end of the input selection circuit is connected to the protection circuit, and the other end of the input selection circuit is connected to the main input terminal and the secondary input terminal respectively. The protection circuit is electrically connected to the voltage detection circuit.

[0005] The input selection circuit includes a main input circuit and a secondary input circuit. The main input circuit is connected to the main input terminal, and the secondary input circuit is connected to the secondary input terminal.

[0006] Preferably, the protection circuit includes a main input protection circuit and a secondary input protection circuit, wherein the main input protection circuit is connected to the main input circuit, and the secondary input protection circuit is connected to the secondary input circuit.

[0007] Preferably, the main input circuit includes: a first bidirectional Zener diode and a first transistor, the first end of the first bidirectional Zener diode is connected to the main input terminal and the base of the first transistor respectively, the second end of the first bidirectional Zener diode is grounded, the collector of the first transistor is connected to the main input protection circuit, and the emitter of the first transistor is grounded.

[0008] Preferably, the main input protection circuit includes: a first resistor, a second resistor, a third resistor, a first Zener diode, a first MOSFET, and a second MOSFET. The first terminal of the first resistor and the first Zener diode connected in parallel is connected to the main input terminal. The source of the first MOSFET is connected to the main input terminal. The gate of the first MOSFET is connected to the first terminal of the second resistor. The second terminal of the second resistor is connected to the collector of the first Zener diode. The drain of the second MOSFET is connected to the drain of the first MOSFET. The gate of the second MOSFET is connected in series with the first terminal of the third resistor. The second terminal of the third resistor is grounded. The source of the second MOSFET is connected to the secondary input protection circuit. The gate of the first MOSFET is connected to the voltage detection circuit. The gate of the second MOSFET is connected to the secondary input terminal.

[0009] Preferably, the secondary input protection circuit includes: a third MOSFET, a fourth resistor, and a fifth resistor. The two ends of the fourth resistor are respectively connected to the source of the second MOSFET and the source of the third MOSFET. The gate of the third MOSFET is connected in series with the fifth resistor and grounded. The drain of the third MOSFET is connected to the secondary input protection circuit, and the gate of the third MOSFET is connected to the main input terminal.

[0010] Preferably, the voltage detection circuit includes a main control chip, which has PA1 pin, PA2 pin and PA3 pin. PA1 pin is connected to the gate of the first MOS transistor, and PA3 pin is used to output a battery charging enable signal.

[0011] Preferably, the secondary input protection circuit further includes: a fourth MOSFET, a sixth resistor, a seventh resistor, and a second Zener diode. The first end of the parallel connection between the sixth resistor and the second Zener diode is connected to the secondary input terminal. The second end of the parallel connection between the sixth resistor and the second Zener diode is connected in series with the first end of the seventh resistor. The second end of the seventh resistor is connected to the secondary input circuit. The gate of the fourth MOSFET is connected in series with the first end of the seventh resistor. The source of the fourth MOSFET is connected to the secondary input terminal. The drain of the fourth MOSFET is connected to the drain of the third MOSFET. The gate of the fourth MOSFET is connected to the PA2 pin.

[0012] Preferably, the secondary input circuit includes a second bidirectional Zener diode, an eighth resistor, and a second transistor. The first terminal of the second bidirectional Zener diode is connected to the secondary input terminal, and the second terminal of the second bidirectional Zener diode is grounded. The first terminal of the eighth resistor is connected to the secondary input terminal, and the second terminal of the eighth resistor is connected to the base of the second transistor and the secondary input circuit. The collector of the second transistor is connected in series with the second terminal of the seventh resistor, and the emitter of the second transistor is grounded.

[0013] Preferably, the secondary input circuit further includes a third transistor, the base of which is connected to the main input terminal, the collector of which is connected to the eighth resistor and the base of the second transistor, and the emitter of which is grounded.

[0014] Secondly, embodiments of the present invention provide a charging method for a portable vehicle refrigerator battery charging selection and protection circuit, the charging method comprising the following steps:

[0015] S1. Collect the first node and the second node of the main control chip respectively to obtain the voltage of the first node and the voltage of the second node;

[0016] S2. Determine if there is voltage. If yes, proceed to step S3; otherwise, return to step S1.

[0017] S3. Perform multiple samplings, where the average of N samplings is taken as one group, and N groups of samplings are performed. The average of the N samples is then taken as one valid data point.

[0018] S4. Preset range is maintained for a preset time;

[0019] S5. When only the main input exists, output the charging enable signal;

[0020] S6. When both the main input and the secondary input exist, determine if the voltage drop of the car battery with the secondary input exceeds the threshold. If yes, stop outputting the charging enable signal and return to step S1. If no, output the charging enable signal.

[0021] Compared with related technologies, this invention connects one end of the input selection circuit to the protection circuit, and the other end of the input selection circuit to both the main input terminal and the secondary input terminal. The protection circuit is electrically connected to the voltage detection circuit. The input selection circuit includes a main input circuit and a secondary input circuit. The main input circuit is electrically connected to the voltage detection circuit, and the secondary input circuit is connected to the secondary input circuit and then to the voltage detection circuit. The main input circuit is connected to the main input terminal, and the secondary input circuit is connected to the secondary input terminal. This effectively improves the charging efficiency of portable car refrigerator batteries, efficiently utilizes renewable energy, protects car refrigerator and car batteries, provides good battery protection, and increases battery life. Attached Figure Description

[0022] The present invention will now be described in detail with reference to the accompanying drawings. The above and other aspects of the present invention will become clearer and more readily understood through the detailed description following the accompanying drawings. In the drawings:

[0023] Figure 1The circuit diagram of the portable vehicle refrigerator battery charging selection and protection circuit of the present invention;

[0024] Figure 2 for Figure 1 A partial enlarged view of the first input main circuit;

[0025] Figure 3 for Figure 1 A partial enlarged view of the secondary input main circuit;

[0026] Figure 4 The circuit diagram is the equivalent circuit of the input selection circuit of this invention;

[0027] Figure 5 This is a flowchart of the charging method for the portable vehicle refrigerator battery charging selection and protection circuit of the present invention.

[0028] In the diagram, 1 is the main input terminal, 2 is the main input protection circuit, 3 is the secondary input terminal, 4 is the input selection circuit, 5 is the protection circuit, 6 is the voltage detection circuit, 7 is the main input circuit, 8 is the secondary input protection circuit, and 9 is the secondary input circuit. Detailed Implementation

[0029] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0030] The specific embodiments / examples described herein are specific implementations of the present invention, used to illustrate the concept of the invention, and are illustrative and exemplary, and should not be construed as limiting the implementation methods or scope of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein, all of which are within the protection scope of the present invention.

[0031] Example 1

[0032] Please refer to Figures 1-4 As shown, where, Figure 1 The circuit diagram of the portable vehicle refrigerator battery charging selection and protection circuit of the present invention; Figure 2 for Figure 1 A partial enlarged view of the first input main circuit; Figure 3 for Figure 1 A partial enlarged view of the secondary input main circuit; Figure 4 The circuit diagram is for the equivalent circuit of the input selection circuit of this invention.

[0033] This invention provides a portable car refrigerator battery charging selection and protection circuit 5, comprising: a main input terminal 1, a secondary input terminal 3, an input selection circuit 4, a protection circuit 5, and a voltage detection circuit 6. One end of the input selection circuit 4 is connected to the protection circuit 5, and the other end of the input selection circuit 4 is connected to both the main input terminal 1 and the secondary input terminal 3. The protection circuit 5 is electrically connected to the voltage detection circuit 6. The input selection circuit 4 includes a main input circuit 7 and a secondary input circuit 9. The main input circuit 7 is electrically connected to the voltage detection circuit 6, and the secondary input circuit 9 is connected to the voltage detection circuit 6. The main input circuit 7 is connected to the main input terminal 1, and the secondary input circuit 9 is connected to the secondary input terminal 3. The voltage detection circuit 6 detects and outputs signals to the main input circuit 7 and the secondary input circuit 9. This improves the charging efficiency of the portable car refrigerator battery, efficiently utilizes renewable energy, protects the car refrigerator battery and the car battery, provides good battery protection, and increases battery life.

[0034] In this embodiment, the protection circuit 5 includes a main input protection circuit 2 and a secondary input protection circuit 8. The main input protection circuit 2 is connected to the main input circuit 7, and the secondary input protection circuit 8 is connected to the secondary input circuit 9. The main input protection circuit 2 protects the main input circuit 7, and the secondary input protection circuit 8 protects the secondary input circuit 9, resulting in good protection and high safety of the circuit.

[0035] In this embodiment, the main input circuit 7 includes a first bidirectional Zener diode D1 and a first transistor Q3. The first terminal of the first bidirectional Zener diode D1 is connected to the main input terminal 1 and the base of the first transistor Q3, respectively. The second terminal of the first bidirectional Zener diode D1 is grounded. The collector of the first transistor Q3 is connected to the main input protection circuit 2, and the emitter of the first transistor Q3 is grounded. When the main input voltage is normal, the first transistor Q3 is turned on, thereby turning on the main input protection circuit 2. The voltage output by the main input protection circuit 2 provides a protection effect, stabilizing battery charging.

[0036] In this embodiment, the main input protection circuit 2 includes: a first resistor R1, a second resistor R2, a third resistor R3, a first Zener diode D2, a first MOSFET Q1, and a second MOSFET Q2. The first end of the parallel connection between the first resistor R1 and the first Zener diode D2 is connected to the main input terminal 1. The source of the first MOSFET Q1 is connected to the main input terminal 1. The gate of the first MOSFET Q1 is connected to the first end of the second resistor R2. The second end of the second resistor R2 is connected to the collector of the first transistor Q3. The drain of the second MOSFET Q2 is connected to the drain of the first MOSFET Q1. The gate of the second MOSFET Q2 is connected in series with the first end of the third resistor R3. The second end of the third resistor R3 is grounded. The source of the second MOSFET Q2 is connected to the secondary input protection circuit 8. The gate of the first MOSFET Q1 is connected to the voltage detection circuit 6. The gate of the second MOSFET Q2 is connected to the secondary input terminal 3.

[0037] In this embodiment, the secondary input protection circuit 8 includes a third MOSFET Q4, a fourth resistor R4, and a fifth resistor R5. The two ends of the fourth resistor R4 are connected to the source of the second MOSFET Q2 and the source of the third MOSFET Q4, respectively. The gate of the third MOSFET Q4 is connected in series with the fifth resistor R5 and grounded. The drain of the third MOSFET Q4 is connected to the secondary input protection circuit 8, and the gate of the third MOSFET Q4 is connected to the main input terminal 1. By connecting the base of the first transistor Q3, the first resistor R1, and the two ends of the first Zener diode D2 to the source and gate of the first MOSFET Q1, respectively, and connecting the second resistor R2 to the collector of the first transistor Q3, when the main input voltage is normal, the first transistor Q3 is turned on, driving the first MOSFET Q1 to turn on. Current flows into the battery terminal through the parasitic diode of the second MOSFET Q2. If a secondary input exists, the second MOSFET Q2 is turned off, forming a dual input protection circuit with the third MOSFET Q4. The first MOSFET Q1 and the second MOSFET Q2 have low internal resistance and low on-state voltage drop characteristics. By disconnecting the third MOSFET Q4, the source and drain voltages of the third MOSFET Q4 are turned off, and the circuit selects the main input, realizing the selection of the vehicle refrigerator battery charging circuit.

[0038] The first resistor R1 and the second resistor R2 are high-precision resistors, serving as gate and source protection resistors for the first MOSFET Q1. The second resistor R2 limits the current when the first transistor Q3 is turned on, acting as a current-limiting voltage divider resistor. The McAd_Sun point detection voltage is led out at the connection between the second resistor R2 and the first MOSFET Q1, saving the voltage sampling circuit while also protecting and driving the MOSFET.

[0039] In this embodiment, the voltage detection circuit 6 is the main control chip U1. The main control chip U1 has PA1, PA2, and PA3 pins. The PA1 pin is connected to the gate of the first MOS transistor Q1, and the PA3 pin is used to output a battery charging enable signal. The main control chip is used to detect the voltage of the main input circuit 7 and the secondary input circuit 9 and to output signals.

[0040] Optionally, the voltage detection circuit 6 is mainly used for undervoltage protection of car batteries and time-delay protection of car refrigerator batteries. It generally uses an MCU to detect the voltage and uses the detected voltage to achieve the effect of protecting the circuit.

[0041] Specifically, after powering on the main control chip U1, the circuit uses the chip's built-in ADC conversion module to obtain the digital values ​​of the level conversion between the second resistor R2 and the seventh resistor R7, and performs multiple acquisitions. The voltage stabilization time is calculated by the timer in the main control chip. After the voltage stabilizes for a period of time, the enable signal for charging the refrigerator battery is output at pin PA3 of the main control chip U1. This can prevent the refrigerator battery from being damaged by undervoltage, voltage instability, or frequent plugging and unplugging during charging caused by the car battery charging the refrigerator battery. The above method effectively extends the service life of the portable car refrigerator battery.

[0042] In this embodiment, the secondary input protection circuit 8 further includes: a fourth MOSFET Q5, a sixth resistor R6, a seventh resistor R7, and a second Zener diode D4. The first end of the parallel connection between the sixth resistor R6 and the second Zener diode D4 is connected to the secondary input terminal 3. The second end of the parallel connection between the sixth resistor R6 and the second Zener diode D4 is connected in series with the first end of the seventh resistor R7. The second end of the seventh resistor R7 is connected to the secondary input circuit 9. The gate of the fourth MOSFET Q5 is connected in series with the first end of the seventh resistor R7. The source of the fourth MOSFET Q5 is connected to the secondary input terminal 3. The drain of the fourth MOSFET Q5 is connected to the drain of the third MOSFET Q4. The gate of the fourth MOSFET Q5 is connected to the PA2 pin.

[0043] In this embodiment, the secondary input circuit 9 includes a second bidirectional Zener diode D3, an eighth resistor R8, and a second transistor Q6. The first terminal of the second bidirectional Zener diode D3 is connected to the secondary input terminal 3, and the second terminal of the second bidirectional Zener diode D3 is grounded. The first terminal of the eighth resistor R8 is connected to the secondary input terminal 3, and the second terminal of the eighth resistor R8 is connected to both the base of the second transistor Q6 and the secondary input circuit 9. The collector of the second transistor Q6 is connected in series with the second terminal of the seventh resistor R7, and the emitter of the second transistor Q6 is grounded. This design saves on the need for a voltage sampling circuit while also protecting and driving the MOSFET.

[0044] In this embodiment, the secondary input circuit 9 further includes a third transistor Q7. The base of the third transistor Q7 is connected to the main input terminal 2, the collector of the third transistor Q7 is connected to the eighth resistor R8 and the base of the second transistor Q6, and the emitter of the third transistor Q7 is grounded.

[0045] In this embodiment, the equivalent circuit schematic of the input selection circuit is as follows: Figure 2 As shown, the circuit is in Figure 1 Based on this, diodes D3 and D4 were added. The positive terminal of diode D3 is connected to the main input terminal, and the positive terminal of diode D4 is connected to the secondary input terminal. The negative terminals of diodes D3 and D4 are connected together and then connected to the output terminal (Output).

[0046] In specific implementation, the main input terminal 1 is connected to the first terminal of the first bidirectional Zener diode D1, and the second terminal of the first bidirectional Zener diode D1 is connected to ground. The base of the first transistor Q3, the first resistor R1, and the two ends of the first Zener diode D2 are connected to the source and gate of the first MOSFET Q1, respectively. The second resistor E2 is connected to the collector of the first transistor Q3. When the main input voltage is normal, the first transistor Q3 conducts, driving the first MOSFET Q1 to conduct, and the circuit flows to the battery terminal through the parasitic diode of the second MOSFET Q2. If a secondary input exists, the second MOSFET Q2 is cut off, providing dual protection for the main input circuit along with the third MOSFET Q4. The secondary input terminal CarBattery is connected to one end of the second bidirectional Zener diode D3, and the other end of the second bidirectional Zener diode D3 is connected to ground. The sixth resistor R6 and the two ends of the second Zener diode D4 are connected to the source and gate of the first MOSFET Q1, respectively. The two ends of the eighth resistor R8 are connected to the sixth resistor R6, the collector of the third transistor Q7, and the base of the second transistor Q6, respectively. The seventh resistor R7 is connected to the collector of the second transistor Q6. The emitters of the second transistor Q6 and the third transistor Q7 are connected to ground. The base of the third transistor Q7 is connected to the main input terminal SunEnergy. The VCC pin of the main control chip U1 is connected to the power supply VCC. The GND pin of the main control chip U1 is connected to the power supply GND. The PA1 pin of the main control chip U1 is connected to the gate of the first MOSFET Q1. The PA2 pin of the main control chip U1 is connected to the gate of the fourth MOSFET Q5. PA3 outputs the battery charging enable signal for the car refrigerator.

[0047] The first resistor R1 and the second resistor R2 are high-precision resistors. To protect the first MOSFET Q1 and the first transistor Q3, a point McuAd_Sun is led out at the connection between the second resistor R2 and the first MOSFET Q1 to detect a relatively accurate voltage. The sixth resistor R6 and the seventh resistor R7 are also high-precision resistors. For the fourth MOSFET Q5 and the second transistor Q6, a point McuAd_Car is led out at the connection between the seventh resistor R7 and the fourth MOSFET Q5 to detect the voltage. This saves on the voltage sampling circuit while protecting and driving the MOSFETs. When both primary and secondary inputs are present, the collector of the third transistor Q7 is at a high level, and Q7 is turned on. The collector of the second transistor Q6 is at a low level, and the base and emitter of the second transistor Q6 are at the same potential, so Q6 is turned off. At this time, the fourth MOSFET Q5 is turned off, thus performing the first function of cutting off the secondary input power supply. The third MOSFET Q4 is used to achieve the second function of cutting off the secondary input power supply. This simple dual protection provides more reliable protection for the refrigerator battery and the input circuit.

[0048] The PA1 pin of the main control chip U1 is connected to the gate of the first MOSFET Q1, and the PA2 pin of the main control chip U1 is connected to the gate of the fourth MOSFET Q5. PA3 outputs the vehicle refrigerator battery charging enable signal Chg_En, which detects the voltage of the main input and secondary input, determines whether the voltage is safe and reliable, and then outputs the charging enable signal. At the same time, it detects the secondary input voltage and its voltage drop, stops the vehicle refrigerator charging, and protects the car battery.

[0049] Example 2

[0050] like Figure 5 As shown, Figure 5 This is a flowchart illustrating the charging method of the portable vehicle refrigerator battery charging selection and protection circuit of the present invention. An embodiment of the present invention provides a charging method for the portable vehicle refrigerator battery charging selection and protection circuit, the charging method comprising the following steps:

[0051] S1. Acquire the voltages of the first and second nodes of the main control chip respectively. Acquire the node voltages V1 and V2 of nodes McuAd_Car and McuAd_Sun respectively through acquisition channels ADC1 and ADC2.

[0052] S2. Determine if there is voltage. If yes, proceed to step S3; otherwise, return to step S1.

[0053] S3. Perform multiple samplings, where N samples are averaged together and N samples are taken as a group, then the average of these N samples is taken as one valid data point. Optionally, perform multiple samplings, where 8 samples are averaged together and 8 samples are taken as a group, then the average of these 8 samples is taken as one valid data point. Of course, multiple samplings are not limited to 8 times; they can also be 9, 10, 11 times, etc. Furthermore, it can be 8N times, where N≥1.

[0054] S4. Preset range to remain for a preset time. The preset time can be 20s, 30s, etc.

[0055] S5. When only the main input exists, output the charging enable signal;

[0056] S6. When both the main input and the secondary input exist, determine if the voltage drop of the car battery with the secondary input exceeds the threshold. If yes, stop outputting the charging enable signal and return to step S1. If no, output the charging enable signal.

[0057] Specifically, the node voltages V1 and V2 of node McuAd_Car and node McuAd_Sun are acquired through the first channel ADC1 and the second channel ADC2, respectively. At this time, the voltage value V1 acquired by channel ADC1 is:

[0058] V1 = (Vs×R7) / (R6+R7) - Vce1 where Vf is the solar input voltage and Vce1 is the on-state voltage drop of transistor Q3.

[0059] At this time, the voltage value V2 obtained by channel ADC2 is:

[0060] V2 = (Vf×R2) / (R1+R2) - Vce2, where Vs is the input voltage of the car battery and Vce2 is the on-state voltage drop of transistor Q6.

[0061] When the main input is present, the ADC2 pin of the main control chip U1 detects the voltage at the connection point between the gate of the first MOSFET Q1 and the second resistor R2. When this voltage is within the normal range and remains for a certain period of time, the main control chip U1 outputs a charging enable signal Chg_En. When the secondary input is present, the ADC1 pin of the main control chip detects the voltage at the connection point between the gate of the MOSFET Q5 and the seventh resistor R7. When this voltage is within the normal range, remains for a certain period of time, and there is only the secondary input, the main control chip outputs a charging enable signal Chg_En. When there is only the secondary input, while detecting the stable voltage signal, it is necessary to determine the voltage drop of the car battery. When the voltage drop exceeds the set threshold, the charging enable signal is stopped.

[0062] After the main control chip U1 is powered on, the circuit uses the chip's built-in ADC conversion module to obtain the digital values ​​of the level conversion between the second resistor R2 and the seventh resistor R7, and performs multiple acquisitions. The voltage stabilization time is calculated by the timer in the main control chip. After the voltage stabilizes for a period of time, the enable signal for charging the refrigerator battery is output at pin PA3 of the main control chip U1. This can prevent the refrigerator battery from being damaged by undervoltage, voltage instability, or high-frequency plugging and unplugging when the car battery charges the refrigerator battery. The above method effectively extends the service life of the portable car refrigerator battery.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any alterations, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A portable vehicle refrigerator battery charging selection and protection circuit, characterized in that, include: The system includes a main input terminal, a secondary input terminal, an input selection circuit, a protection circuit, and a voltage detection circuit. One end of the input selection circuit is connected to the protection circuit, and the other end of the input selection circuit is connected to both the main input terminal and the secondary input terminal. The protection circuit is electrically connected to the voltage detection circuit. The input selection circuit includes a main input circuit and a secondary input circuit. The main input circuit is connected to the main input terminal, and the secondary input circuit is connected to the secondary input terminal. The protection circuit includes a main input protection circuit and a secondary input protection circuit, wherein the main input protection circuit is connected to the main input circuit and the secondary input protection circuit is connected to the secondary input circuit; The main input circuit includes: a first bidirectional Zener diode and a first transistor. The first end of the first bidirectional Zener diode is connected to the main input terminal and the base of the first transistor, respectively. The second end of the first bidirectional Zener diode is grounded. The collector of the first transistor is connected to the main input protection circuit. The emitter of the first transistor is grounded. The main input protection circuit includes: a first resistor, a second resistor, a third resistor, a first Zener diode, a first MOSFET, and a second MOSFET. The first end of the first resistor and the first Zener diode connected in parallel is connected to the main input terminal. The source of the first MOSFET is connected to the main input terminal. The gate of the first MOSFET is connected to the first end of the second resistor. The second end of the second resistor is connected to the collector of the first Zener diode. The drain of the second MOSFET is connected to the drain of the first MOSFET. The gate of the second MOSFET is connected in series with the first end of the third resistor. The second end of the third resistor is grounded. The source of the second MOSFET is connected to the secondary input protection circuit. The gate of the first MOSFET is connected to the voltage detection circuit. The gate of the second MOSFET is connected to the secondary input terminal. The secondary input protection circuit includes a third MOSFET, a fourth resistor, and a fifth resistor. The two ends of the fourth resistor are respectively connected to the source of the second MOSFET and the source of the third MOSFET. The gate of the third MOSFET is connected in series with the fifth resistor and grounded. The drain of the third MOSFET is connected to the secondary input protection circuit. The gate of the third MOSFET is connected to the main input terminal. The voltage detection circuit includes a main control chip, which has PA1 pin, PA2 pin and PA3 pin. PA1 pin is connected to the gate of the first MOS transistor, and PA3 pin is used to output a battery charging enable signal. The secondary input protection circuit further includes: a fourth MOSFET, a sixth resistor, a seventh resistor, and a second Zener diode. The first end of the parallel connection between the sixth resistor and the second Zener diode is connected to the secondary input terminal. The second end of the parallel connection between the sixth resistor and the second Zener diode is connected in series with the first end of the seventh resistor. The second end of the seventh resistor is connected to the secondary input circuit. The gate of the fourth MOSFET is connected in series with the first end of the seventh resistor. The source of the fourth MOSFET is connected to the secondary input terminal. The drain of the fourth MOSFET is connected to the drain of the third MOSFET. The gate of the fourth MOSFET is connected to the PA2 pin. The secondary input circuit includes a second bidirectional Zener diode, an eighth resistor, and a second transistor. The first terminal of the second bidirectional Zener diode is connected to the secondary input terminal, and the second terminal of the second bidirectional Zener diode is grounded. The first terminal of the eighth resistor is connected to the secondary input terminal, and the second terminal of the eighth resistor is connected to the base of the second transistor and the secondary input circuit. The collector of the second transistor is connected in series with the second terminal of the seventh resistor, and the emitter of the second transistor is grounded.

2. The portable vehicle refrigerator battery charging selection and protection circuit as described in claim 1, characterized in that, The secondary input circuit also includes a third transistor, the base of which is connected to the main input terminal, the collector of which is connected to the eighth resistor and the base of the second transistor, and the emitter of which is grounded.

3. A charging method for the portable vehicle refrigerator battery charging selection and protection circuit as described in any one of claims 1-2, characterized in that, The charging method includes the following steps: S1. Collect the first node and the second node of the main control chip respectively to obtain the voltage of the first node and the voltage of the second node; S2. Determine if there is voltage. If yes, proceed to step S3; otherwise, return to step S1. S3. Perform multiple samplings, where the average of N samplings is taken as one group, and N groups of samplings are performed. The average of the N samples is then taken as one valid data point. S4. Preset range is maintained for a preset time; S5. When only the main input exists, output the charging enable signal; S6. When both the main input and the secondary input exist, determine if the voltage drop of the car battery with the secondary input exceeds the threshold. If yes, stop outputting the charging enable signal and return to step S1. If no, output the charging enable signal.

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