Dual-power-supply automatic switching protection circuit

Abstract

The invention relates to a dual-power-supply automatic switching protection circuit which comprises an automobile power supply input end, an original automobile USB power supply input end, a cigarette lighter power supply output end, an external equipment power supply output end, a comparator, a first switch unit and a second switch unit. The input end of the comparator is connected with the original vehicle USB power supply input end and the cigarette lighter power supply output end, the output end of the comparator is connected with the first switch unit and the second switch unit, when the original vehicle USB power supply voltage is larger than the voltage of the cigarette lighter power supply output end, the output end of the comparator outputs low level, and when the original vehicle USB power supply voltage is smaller than the voltage of the cigarette lighter power supply output end, the output end of the comparator outputs low level. The output end of the comparator outputs a high level; the first switch unit is used for controlling the cigarette lighter power supply to output to the external equipment power supply, and the second switch unit is used for controlling the original vehicle USB power supply voltage to output to the external equipment power supply. The circuit not only can overcome the defect that double power supplies cannot be inserted simultaneously, but also can well protect equipment of an original vehicle from the risk of voltage backflow.

Description

Technical Field

[0001] The invention relates to the technical field of power supply, and in particular to a dual power supply automatic switching protection circuit. Background Art

[0002] The design circuit plug-in devices currently on the market are as follows Figure 1 As shown. BATT is the car input, usually 12V. Then the LED_5V above is the output of the cigarette lighter, connected to the power supply of the external device, and USB+5V is the output voltage of the original car USB. Figure 1 As shown, due to the damage of the cigarette lighter, BATT will directly flow back into the USB+5V of the original car, so the resistor R1 on the market is chosen to be disconnected, and the DM and DP of the original car will be connected to the external device, which will cause some devices that must use USB+5V to not be able to use normally. This defect is very large. This circuit can only have a large defect. This greatly affects the car owner's experience when using external devices. Moreover, the USB+5V of the original car cannot be installed at will, so the USB+5V of the device cable cannot be installed at will. However, many original car devices have an output of 500MA, which leads to the need for large current when using external devices. When switching to use the external cigarette lighter, it is necessary to supply more power than the device.

[0003] The original car USB power supply cannot be plugged in and out at will because of the difficulty of installation, while the cigarette lighter can be plugged in and out at will. Many existing things can only use the cigarette lighter to replace the original car USB power supply, but when you want to use the original car USB, you can no longer use it. At present, many devices on the market can only use the original car USB. Once the original car USB power supply is not plugged in, but only the data cable, the 5V of the external cigarette lighter will not work properly, causing compatibility problems with the device. If you plug them in at the same time and install them incorrectly, it will cause the cigarette lighter to pass directly, unable to reduce the voltage and damage the external device, or high voltage will flow back into low voltage, damaging the power supply. Summary of the invention

[0004] Based on this, it is necessary to provide a dual power supply automatic switching protection circuit to address the above technical problems. It can switch the power supply at will, and at the same time, it can insert the cigarette lighter without damage when installing USB+5V and cigarette lighter. It can not only solve the defect of not being able to insert dual power supplies at the same time, but also protect the original car's equipment well to avoid the risk of backflow voltage, greatly improving the owner's experience.

[0005] A dual power automatic switching protection circuit comprises a power module, a comparison module and a power switching control module; the power module comprises a car power input terminal, an original car USB power input terminal, a cigarette lighter power output terminal and an external device power output terminal, and the car power input terminal is connected to the cigarette lighter power output terminal; the comparison module comprises a comparator, and the power switching control module comprises a first switch unit and a second switch unit, the first switch unit comprises a first switch tube and a second switch tube, and the second switch unit comprises a third switch tube, a fourth switch tube and a fifth switch tube; the first input terminal of the comparator is connected to the original car USB power input terminal, the second input terminal of the comparator is connected to the cigarette lighter power output terminal, and the output terminal of the comparator is respectively connected to the control terminal of the first switch tube and the control terminal of the third switch tube, when the original car USB power voltage is greater than the voltage of the cigarette lighter power output terminal, the output terminal of the comparator outputs a low level, and when the original car USB When the power supply voltage is less than the voltage at the cigarette lighter power output end, the output end of the comparator outputs a high level; the input end of the first switch tube is respectively connected to the original vehicle USB power input end and the cigarette lighter power output end, the output end of the first switch tube is grounded, and the input end of the first switch tube is also connected to the control end of the second switch tube; the input end of the second switch tube is used to be connected to the cigarette lighter power output end, and the output end of the second switch tube is connected to the external device power output end; the input end of the third switch tube is respectively connected to the original vehicle USB power input end and the control end of the fourth switch tube, the output end of the third switch tube is grounded, and the output end of the fourth switch tube is grounded; the input end of the fourth switch tube is respectively connected to the control end of the fifth switch tube, the original vehicle USB power input end, and the cigarette lighter power output end, the input end of the fifth switch tube is used to be connected to the original vehicle USB power input end, and the output end of the fifth switch tube is connected to the external device power output end.

[0006] Preferably, the first switch unit further includes a sixth switch tube, the control end of the sixth switch tube is connected to the input end of the first switch tube, the input end of the sixth switch tube is connected to the cigarette lighter power output end, and the output end of the sixth switch tube is connected to the input end of the second switch tube.

[0007] Preferably, the second switch unit also includes a seventh switch tube, the input end of the seventh switch tube is connected to the USB power input end of the original vehicle, the output end of the seventh switch tube is connected to the input end of the fifth switch tube, and the control end of the seventh switch tube is connected to the input end of the fourth switch tube.

[0008] Preferably, the comparison module also includes a first resistor, a second resistor, a third resistor and a fourth resistor; one end of the first resistor is connected to the USB power input terminal of the original vehicle, the other end of the first resistor is connected to one end of the second resistor, and the other end of the second resistor is grounded, wherein the connection end of the first resistor and the second resistor is connected to the first input terminal of the comparator; one end of the third resistor is connected to the cigarette lighter power output terminal, the other end of the third resistor is connected to one end of the fourth resistor, and the other end of the fourth resistor is grounded, wherein the connection end of the third resistor and the fourth resistor is connected to the second input terminal of the comparator.

[0009] Preferably, the comparison module further includes a first capacitor and a second capacitor; the first capacitor is connected in parallel with the second resistor, and the second capacitor is connected in parallel with the fourth resistor.

[0010] Preferably, the dual power automatic switching protection circuit also includes a first diode and a second diode; the positive terminal of the first diode is connected to the original vehicle USB power input terminal, the negative terminal of the first diode is connected to the input terminal of the first switch tube, and the negative terminal of the first diode is also connected to the input terminal of the fourth switch tube; the positive terminal of the second diode is connected to the cigarette lighter power output terminal, and the negative terminal of the second diode is connected to the input terminal of the first switch tube.

[0011] Preferably, the first switching unit also includes a fifth resistor and a sixth resistor; one end of the fifth resistor is connected to the output end of the comparator, the other end of the fifth resistor is connected to one end of the sixth resistor, and the other end of the sixth resistor is grounded, wherein the connection end of the fifth resistor and the sixth resistor is connected to the control end of the first switching tube.

[0012] Preferably, the second switching unit also includes a seventh resistor and an eighth resistor; one end of the seventh resistor is connected to the output end of the comparator, the other end of the seventh resistor is connected to one end of the eighth resistor, and the other end of the eighth resistor is grounded, wherein the connection end of the seventh resistor and the eighth resistor is connected to the control end of the third switching tube.

[0013] Preferably, the dual power automatic switching protection circuit further includes a power management chip; the vehicle power input terminal is connected to the input terminal of the power management chip, and the output terminal of the power management chip is connected to the cigarette lighter power output terminal.

[0014] Preferably, the dual power automatic switching protection circuit also includes a ninth resistor; the original vehicle USB power input terminal is connected to one end of the ninth resistor, and the other end of the ninth resistor is connected to the cigarette lighter power output terminal.

[0015] The above-mentioned dual power automatic switching protection circuit comprises a power module, a comparison module and a power switching control module; the power module comprises a car power input terminal, an original car USB power input terminal, a cigarette lighter power output terminal and an external device power output terminal, and the car power input terminal is connected to the cigarette lighter power output terminal; the comparison module comprises a comparator, and the power switching control module comprises a first switch unit and a second switch unit, the first switch unit comprises a first switch tube and a second switch tube, and the second switch unit comprises a third switch tube, a fourth switch tube and a fifth switch tube; the first input terminal of the comparator is connected to the original car USB power input terminal, the second input terminal of the comparator is connected to the cigarette lighter power output terminal, and the output terminal of the comparator is respectively connected to the control terminal of the first switch tube and the control terminal of the third switch tube. When the voltage of the original car USB power supply is greater than the voltage of the cigarette lighter power output terminal, the output terminal of the comparator outputs a low level, and when ... When the power supply voltage is less than the voltage at the cigarette lighter power output end, the output end of the comparator outputs a high level; the input end of the first switch tube is respectively connected to the original vehicle USB power input end and the cigarette lighter power output end, the output end of the first switch tube is grounded, and the input end of the first switch tube is also connected to the control end of the second switch tube; the input end of the second switch tube is used to be connected to the cigarette lighter power output end, and the output end of the second switch tube is connected to the external device power output end; the input end of the third switch tube is respectively connected to the original vehicle USB power input end and the control end of the fourth switch tube, the output end of the third switch tube is grounded, and the output end of the fourth switch tube is grounded; the input end of the fourth switch tube is respectively connected to the control end of the fifth switch tube, the original vehicle USB power input end, and the cigarette lighter power output end, the input end of the fifth switch tube is used to be connected to the original vehicle USB power input end, and the output end of the fifth switch tube is connected to the external device power output end. Therefore, it is possible to switch power sources at will, and insert the cigarette lighter without damage when installing USB+5V and the cigarette lighter. It can not only solve the defect of not being able to insert dual power supplies at the same time, but also protect the original car's equipment from the risk of backflow voltage, greatly improving the owner's experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A circuit diagram of an external device for a dual power automatic switching protection circuit in one embodiment; Figure 2 A circuit diagram of a comparator block in a dual power automatic switching protection circuit in one embodiment; Figure 3 The figure is a circuit diagram of a power switching control module in a dual power automatic switching protection circuit in an embodiment. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] The present invention provides a dual power supply automatic switching protection circuit. Among them, a specific design circuit of the dual power supply automatic switching protection circuit is combined with the following Figure 1 , Figure 2 and Figure 3 Specifically, Figure 1 On the basis of increase Figure 2 and Figure 3 The circuit is used to realize the dual power supply automatic switching protection circuit of the present invention.

[0019] In one embodiment, a dual power automatic switching protection circuit includes a power module, a comparison module, and a power switching control module; the power module includes a car power input terminal, an original car USB power input terminal, a cigarette lighter power output terminal, and an external device power output terminal, and the car power input terminal is connected to the cigarette lighter power output terminal. Specifically, Figure 1 As shown, BATT is the car power input terminal, which generally inputs 12V voltage. LED_5V is the cigarette lighter power output terminal, which is used to connect to the power output terminal of the external device. USB_+5V is the power output terminal of the external device.

[0020] The comparison module includes a comparator, and the power switching control module includes a first switch unit and a second switch unit. The first switch unit includes a first switch tube and a second switch tube, and the second switch unit includes a third switch tube, a fourth switch tube and a fifth switch tube; the first input end of the comparator is connected to the original car USB power input end, the second input end of the comparator is connected to the cigarette lighter power output end, and the output end of the comparator is respectively connected to the control end of the first switch tube and the control end of the third switch tube. When the original car USB power supply voltage is greater than the voltage of the cigarette lighter power supply output end, the output end of the comparator outputs a low level, and when the original car USB power supply voltage is less than the voltage of the cigarette lighter power supply output end, the output end of the comparator outputs a high level; the input ends of the first switch tube are respectively connected to the original car USB The power input end and the cigarette lighter power output end are connected, the output end of the first switch tube is grounded, and the input end of the first switch tube is also connected to the control end of the second switch tube; the input end of the second switch tube is used to connect to the cigarette lighter power output end, and the output end of the second switch tube is connected to the power output end of the external device; the input end of the third switch tube is respectively connected to the original vehicle USB power input end and the control end of the fourth switch tube, the output end of the third switch tube is grounded, and the output end of the fourth switch tube is grounded; the input end of the fourth switch tube is respectively connected to the control end of the fifth switch tube, the original vehicle USB power input end, and the cigarette lighter power output end, the input end of the fifth switch tube is used to connect to the original vehicle USB power input end, and the output end of the fifth switch tube is connected to the power output end of the external device. In one example, the first switch unit also includes a sixth switch tube, the control end of the sixth switch tube is connected to the input end of the first switch tube, the input end of the sixth switch tube is connected to the cigarette lighter power output end, and the output end of the sixth switch tube is connected to the input end of the second switch tube. In one example, the second switch unit also includes a seventh switch tube, the input end of the seventh switch tube is connected to the USB power input end of the original vehicle, the output end of the seventh switch tube is connected to the input end of the fifth switch tube, and the control end of the seventh switch tube is connected to the input end of the fourth switch tube.

[0021] in, Figure 2 For the specific circuit diagram of the comparison module, the comparator uses a TL331IDBVR chip. Figure 3 FIG. 2 is a specific circuit diagram of the power switching control module. Figure 3 As shown, the first switch tube is the transistor Q0006, the second switch tube is the switch tube Q5, the sixth switch tube is the switch tube Q4. The third switch tube is the transistor Q0001, the fourth switch tube is the transistor Q0002, the fifth switch tube is the switch tube Q3, and the seventh switch tube is the switch tube Q1. Specifically, Figure 2 As shown, the first input terminal of the comparator is connected to USB+5V, and the second input terminal of the comparator is connected to LED_5V. The first input terminal is IN+, and the second input terminal is IN-. The output terminal of the comparator is LOW_VOLTAGE2_DET[1], which is connected to Figure 3 As shown in [1], LOW_VOLTAGE2_DET is connected. Figure 3 As shown, they are connected to the control end of transistor Q0001 and the control end of transistor Q0006 respectively. Figure 2 As shown in the figure, when the voltage of USB+5V is greater than that of LED_5V, the output of the comparator outputs a low level, and when the voltage of USB+5V is less than that of LED_5V, the output of the comparator outputs a high level. Specifically, when the original car USB_+5V is installed but the cigarette lighter is not plugged in, the voltage of LED_5V is equivalent to 0V. At this time, the pins 1 and 3 of the comparator perform a voltage comparison, and a low voltage appears on pin 4, and LOW_VOLTAGE2_DET[1] outputs a low voltage. In addition, as Figure 3 As shown, USB_+5V will start transistor Q0002 to work, causing switch tube Q1 to turn on, and then the current of USB_+5V is connected to the power output end of the external device through the diode in switch tube Q3, thereby realizing the output of the original car USB+5V to the power output end of the external device. Figure 3 As shown, since [1] LOW_VOLTAGE2_DET is a low voltage, the control end of transistor Q0006 and the control end of transistor Q0001 are both low voltages, and both transistors are not conducting.

[0022] In one example, the comparison module also includes a first resistor, a second resistor, a third resistor, and a fourth resistor; one end of the first resistor is connected to the USB power input terminal of the original vehicle, the other end of the first resistor is connected to one end of the second resistor, and the other end of the second resistor is grounded, wherein the connection end of the first resistor and the second resistor is connected to the first input terminal of the comparator; one end of the third resistor is connected to the cigarette lighter power output terminal, the other end of the third resistor is connected to one end of the fourth resistor, and the other end of the fourth resistor is grounded, wherein the connection end of the third resistor and the fourth resistor is connected to the second input terminal of the comparator.

[0023] The comparison module further includes a first capacitor and a second capacitor; the first capacitor is connected in parallel with the second resistor, and the second capacitor is connected in parallel with the fourth resistor.

[0024] Specifically, Figure 2 As shown, the first resistor is resistor R0017, the second resistor is resistor R0016, the third resistor is resistor R0014, and the fourth resistor is resistor R0015. The first capacitor is capacitor C0008, and the second capacitor is capacitor C0007.

[0025] When the device is plugged into the cigarette lighter, Figure 2As shown, the pin 1 and pin 3 of the comparator P_U1 perform a voltage comparison. The resistors R0016 and R0017 of pin 1, and the resistors R0014 and R0015 of pin 3, both of which are set to divide the voltage, are used to compare and judge the inserted cigarette lighter LED_5V, indicating that the voltage of the cigarette lighter is required. Therefore, a high voltage appears at pin 4 of the comparator P_U1 at this time. Figure 2 LOW_VOLTAGE2_DET[1] outputs a high voltage. Figure 3 The transistor Q0006 shown is working, while the transistor Q0002 is not working, which causes the switch tube Q1 to be cut off and the switch tube Q4 to work. Then the diode in the switch tube Q5 is turned on, and the current of LED_5V is connected to the power output end of the external device through the diode in the switch tube Q5, thereby realizing the output of LED_5V to the power output end of the external device.

[0026] In one example, the dual power automatic switching protection circuit also includes a first diode and a second diode; the positive terminal of the first diode is connected to the original vehicle USB power input terminal, the negative terminal of the first diode is connected to the input terminal of the first switch tube, and the negative terminal of the first diode is also connected to the input terminal of the fourth switch tube; the positive terminal of the second diode is connected to the cigarette lighter power output terminal, and the negative terminal of the second diode is connected to the input terminal of the first switch tube.

[0027] Specifically, Figure 3 As shown, the first diode is a diode D1, and the second diode is a diode D2. The diode D1 and the diode D2 can protect the original vehicle USB power supply and the cigarette lighter power supply.

[0028] In one embodiment, the first switching unit also includes a fifth resistor and a sixth resistor; one end of the fifth resistor is connected to the output end of the comparator, the other end of the fifth resistor is connected to one end of the sixth resistor, and the other end of the sixth resistor is grounded, wherein the connection end of the fifth resistor and the sixth resistor is connected to the control end of the first switching tube.

[0029] Specifically, Figure 3 As shown, the fifth resistor is resistor R0009, and the sixth resistor is resistor R0008. The connection end of resistor R0009 and resistor R0008 is connected to the control end of transistor Q0006, so that the control end of transistor Q0006 can be provided with a divided voltage to prevent the output voltage of the comparator from being too large and damaging transistor Q0006.

[0030] In one embodiment, the second switching unit also includes a seventh resistor and an eighth resistor; one end of the seventh resistor is connected to the output end of the comparator, the other end of the seventh resistor is connected to one end of the eighth resistor, and the other end of the eighth resistor is grounded, wherein the connection end of the seventh resistor and the eighth resistor is connected to the control end of the third switching tube.

[0031] Specifically, Figure 3 As shown, the seventh resistor is resistor R0005, and the eighth resistor is resistor R0004. The connection end of resistor R0005 and resistor R0004 is connected to the control end of transistor Q0001, so that the control end of transistor Q0001 can be provided with a divided voltage to prevent the output voltage of the comparator from being too large and damaging transistor Q0001.

[0032] In one embodiment, the dual power automatic switching protection circuit further includes a power management chip; the vehicle power input terminal is connected to the input terminal of the power management chip, and the output terminal of the power management chip is connected to the cigarette lighter power output terminal.

[0033] In one example, the dual power automatic switching protection circuit also includes a ninth resistor; the original vehicle USB power input terminal is connected to one end of the ninth resistor, and the other end of the ninth resistor is connected to the cigarette lighter power output terminal.

[0034] Specifically, Figure 1 As shown, the power management chip is a chip of the MP2315GJ model, namely, chip U19. The input terminal VIN of chip U19 is connected to the car power input terminal BATT, and is used to manage the input of the car power. In addition, its output terminal is connected to the cigarette lighter power output terminal LED_5V, so that it can provide voltage to the cigarette lighter. And, as Figure 1 As shown, the ninth resistor is resistor R1. Resistor R1 is connected to the original vehicle USB power input terminal USB_5V and the cigarette lighter power output terminal LED_5V respectively.

[0035] In summary, the dual power automatic switching protection circuit of the present invention is combined with Figure 1 , Figure 2 and Figure 3 As shown, the voltage can be switched freely between the cigarette lighter and the USB+5V of the original car, thus solving the compatibility defect problem in the market. In addition, when the cigarette lighter is damaged, the 12V that comes in at this time, in the comparator state, still goes through the switch tubes Q4 and Q5. At this time, the switch tube Q4 works, and the diode of the switch tube Q5 conducts the interface. At this time, the switch tube Q3 is in the cut-off state, and the output 12V voltage will not be fed back to the USB+5V to directly damage the original car's machine, thereby realizing the risk of damaging the original car's power supply by the dual power supply, and realizing the function of automatic switching to protect the power supply.

[0036] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A dual power supply automatic switching protection circuit, characterized in that: It includes a power supply module, a comparison module, and a power supply switching control module; The power module includes a car power input terminal, an original car USB power input terminal, a cigarette lighter power output terminal and an external device power output terminal, and the car power input terminal is connected to the cigarette lighter power output terminal; The comparison module includes a comparator, the power switching control module includes a first switch unit and a second switch unit, the first switch unit includes a first switch tube and a second switch tube, and the second switch unit includes a third switch tube, a fourth switch tube and a fifth switch tube; The first input end of the comparator is connected to the original car USB power input end, the second input end of the comparator is connected to the cigarette lighter power output end, and the output end of the comparator is respectively connected to the control end of the first switch tube and the control end of the third switch tube. When the voltage of the original car USB power supply is greater than the voltage of the cigarette lighter power output end, the output end of the comparator outputs a low level, and when the voltage of the original car USB power supply is less than the voltage of the cigarette lighter power output end, the output end of the comparator outputs a high level. The input end of the first switch tube is respectively connected to the USB power input end of the original car and the cigarette lighter power output end, the output end of the first switch tube is grounded, and the input end of the first switch tube is also connected to the control end of the second switch tube; The input end of the second switch tube is used to be connected to the power output end of the cigarette lighter, and the output end of the second switch tube is connected to the power output end of the external device; The input end of the third switch tube is respectively connected to the USB power input end of the original vehicle and the control end of the fourth switch tube, the output end of the third switch tube is grounded, and the output end of the fourth switch tube is grounded; The input end of the fourth switch tube is respectively connected to the control end of the fifth switch tube, the original vehicle USB power input end and the cigarette lighter power output end; the input end of the fifth switch tube is used to connect to the original vehicle USB power input end; the output end of the fifth switch tube is connected to the power output end of the external device.

2. The dual power supply automatic switching protection circuit according to claim 1 is characterized in that: The first switch unit also includes a sixth switch tube, the control end of the sixth switch tube is connected to the input end of the first switch tube, the input end of the sixth switch tube is connected to the cigarette lighter power output end, and the output end of the sixth switch tube is connected to the input end of the second switch tube.

3. The dual power automatic switching protection circuit according to claim 1 is characterized in that: The second switch unit also includes a seventh switch tube, the input end of the seventh switch tube is connected to the USB power input end of the original vehicle, the output end of the seventh switch tube is connected to the input end of the fifth switch tube, and the control end of the seventh switch tube is connected to the input end of the fourth switch tube.

4. The dual power automatic switching protection circuit according to claim 1 is characterized in that: The comparison module also includes a first resistor, a second resistor, a third resistor, and a fourth resistor; One end of the first resistor is connected to the USB power input terminal of the original car, the other end of the first resistor is connected to one end of the second resistor, the other end of the second resistor is grounded, wherein the connection end of the first resistor and the second resistor is connected to the first input terminal of the comparator; One end of the third resistor is connected to the cigarette lighter power supply output end, the other end of the third resistor is connected to one end of the fourth resistor, the other end of the fourth resistor is grounded, wherein the connection end of the third resistor and the fourth resistor is connected to the second input end of the comparator.

5. The dual power automatic switching protection circuit according to claim 4 is characterized in that: The comparison module also includes a first capacitor and a second capacitor; The first capacitor is connected in parallel with the second resistor, and the second capacitor is connected in parallel with the fourth resistor.

6. The dual power supply automatic switching protection circuit according to claim 1, characterized in that: The dual power supply automatic switching protection circuit also includes a first diode and a second diode; The positive terminal of the first diode is connected to the USB power input terminal of the original vehicle, the negative terminal of the first diode is connected to the input terminal of the first switch tube, and the negative terminal of the first diode is also connected to the input terminal of the fourth switch tube; The positive terminal of the second diode is connected to the output terminal of the cigarette lighter power supply, and the negative terminal of the second diode is connected to the input terminal of the first switch tube.

7. The dual power automatic switching protection circuit according to claim 1, characterized in that: The first switch unit further includes a fifth resistor and a sixth resistor; One end of the fifth resistor is connected to the output end of the comparator, the other end of the fifth resistor is connected to one end of the sixth resistor, the other end of the sixth resistor is grounded, and the connection end of the fifth resistor and the sixth resistor is connected to the control end of the first switch tube.

8. The dual power automatic switching protection circuit according to claim 1, characterized in that: The second switch unit further includes a seventh resistor and an eighth resistor; One end of the seventh resistor is connected to the output end of the comparator, the other end of the seventh resistor is connected to one end of the eighth resistor, the other end of the eighth resistor is grounded, and the connection end of the seventh resistor and the eighth resistor is connected to the control end of the third switch tube.

9. The dual power automatic switching protection circuit according to claim 1, characterized in that: The dual power automatic switching protection circuit also includes a power management chip; The car power input terminal is connected to the input terminal of the power management chip, and the output terminal of the power management chip is connected to the cigarette lighter power output terminal.

10. The dual power supply automatic switching protection circuit according to claim 1, characterized in that: The dual power automatic switching protection circuit also includes a ninth resistor; The original car USB power input terminal is connected to one end of the ninth resistor, and the other end of the ninth resistor is connected to the cigarette lighter power output terminal.

Images