An over-temperature and over-voltage protection circuit

Abstract

The present invention provides an over-temperature and over-voltage protection circuit, comprising a power input terminal, a control switch (1), a control switch (2), a voltage detection device, a temperature detection device, and a power output terminal; the power input terminal inputs positive and negative power inputs of a direct current power supply; the control switch (1) turns on or off by judging the high or low input voltage through the voltage detection device; the control switch (2) controls the opening and closing of the negative electrode of the power supply; the voltage detection device detects whether the input voltage exceeds a maximum threshold; the temperature detection device detects whether the temperature of a PCB board circuit exceeds a maximum temperature; and the power output device outputs positive and negative power of the direct current power supply.

Description

Technical Field

[0001] The present invention relates to the field of electronic circuits, and in particular to an over-temperature and over-voltage protection circuit. Background Art

[0002] At present, most of the mobile power supplies used in the market are charged with 5V. However, with the popularization of fast charging technology, many users will use fast charging chargers to charge 5V power supplies. Fast charging chargers are generally 9V / 12V / 20V and other different voltages. Fast charging detects the voltage combination on D+ and D- and outputs different voltages. When using these unqualified fast charging chargers, or using a 9V voltage charger to charge a 5V power supply, the mobile power supply PCBA will be burned. Due to different burnout failure phenomena, it may not be able to continue charging or working; however, there is a certain current, which causes the temperature to rise, burns the shell, and some settings catch fire, posing a great safety hazard to users. For fast charging of other devices, there are also safety hazards caused by fast charging.

[0003] The common over-temperature and over-voltage protection circuit is realized by voltage sampling and single-chip microcomputer. This implementation method is high in cost and low in reliability because the temperature range of the single-chip microcomputer is much narrower under the same production process. Summary of the invention

[0004] In order to solve the problem that there is no low-cost, high-reliability protection circuit when the input voltage is too high and the internal temperature of the device is too high, the present invention provides an over-temperature and over-voltage protection circuit.

[0005] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] An over-temperature and over-voltage protection circuit comprises a power input terminal, a control switch (1), a control switch (2), a voltage detection device, a temperature detection device, and a power output terminal;

[0007] The power input terminal inputs positive and negative power inputs of a DC power supply;

[0008] The control switch (1) is turned on or off by the voltage detection device judging the input voltage;

[0009] The control switch (2) is used to control the opening and closing of the negative electrode of the power supply;

[0010] The voltage detection device detects whether the input voltage exceeds the maximum threshold;

[0011] The temperature detection device detects whether the temperature of the PCB circuit exceeds the maximum temperature;

[0012] The power output device outputs positive and negative power of a DC power source.

[0013] Preferably, the voltage detection device comprises two series resistors (R1) and (R3), and the resistor (R3) is connected in parallel with the control switch (1); the temperature detection device comprises a positive temperature coefficient thermistor (RT1) and a resistor (R2), and the voltage detection device and the temperature detection device are connected in parallel; the control switch (1) and the control switch (2) are field effect transistors (Q1) and field effect transistors (Q2), respectively.

[0014] Preferably, the voltage across the field effect tube (Q1) is higher than the conduction voltage, i.e., it becomes the conduction state, thereby reducing the G pole voltage of the field effect tube (Q2), so that (Q2) turns to the off state, thereby shutting down the power output; the voltage across the field effect tube (Q1) is lower than the conduction voltage, i.e., it is the stop state, the field effect tube (Q2) is turned on, and the power output is normal.

[0015] Preferably, as the temperature rises, the resistance of the positive temperature coefficient thermistor (RT1) increases, thereby reducing the G-pole voltage of the field effect tube (Q2), causing (Q2) to turn off, thereby turning off the power output.

[0016] Preferably, the resistance values ​​of the resistor (R1) and the resistor (R3), the input voltage and the on-voltage of the field effect tube (Q1) satisfy the following relationship: when [R3 / (R1+R3)]*input voltage < on-voltage of the field effect tube (Q1), the on-voltage of the field effect tube (Q1) is in an absolute state; when the input voltage is ≥ the maximum threshold value, the field effect tube (Q1) is turned on.

[0017] Preferably, when the maximum temperature is reached, the resistance value of the resistor (RT1) and the resistor (R2), the input voltage, and the on-voltage of the field effect tube (Q2) satisfy the following relationship: [R2 / (RT1+R2)]*input voltage=off-voltage of the field effect tube (Q2).

[0018] Preferably, the S pole of the field effect tube (Q2) is connected to the input end of the negative electrode of the power supply, and the D pole is connected to the output of the negative electrode of the power supply.

[0019] Preferably, the G-pole voltage or the gate voltage of the field effect transistor (Q1) and the field effect transistor (Q2) is adjusted according to the maximum threshold and the maximum temperature.

[0020] Preferably, the control switch (1) and / or the control switch (2) is a switching transistor or a MOS transistor.

[0021] Preferably, the control switch (1) and / or the control switch (2) is a PMOS tube, and the PMOS tube controls the positive pole of the power supply; or the control switch (1) and / or the control switch (2) is an NMOS tube, and the NMOS tube controls the negative pole of the power supply.

[0022] The beneficial effects of the present invention are: providing an over-temperature and over-voltage protection circuit, which has no software and single-chip microcomputer in the circuit, relies on a temperature detection device and a voltage detection device to control the closing of the circuit switch, and the overall cost is lower than that of a common over-temperature and over-voltage protection circuit; because there is no software, the reliability is also high. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a circuit implementation block diagram of an embodiment of the present invention.

[0024] Figure 2 1 is a schematic diagram of a circuit implementation of an embodiment of the present invention.

[0025] Figure 3 It is another circuit implementation principle diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The present invention is described in detail below through specific embodiments in conjunction with the accompanying drawings to provide a better understanding of the present invention, but the following embodiments do not limit the scope of the present invention. In addition, it should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the drawings only show components related to the present invention rather than the number, shape and size of components in actual implementation. The shape, quantity and proportion of each component in actual implementation may be changed at will, and the component layout may also be more complicated.

[0027] Example 1

[0028] like Figure 1 As shown, an over-temperature and over-voltage protection circuit includes a power input terminal, a control switch 1, a control switch 2, a voltage detection device, a temperature detection device, and a power output terminal;

[0029] The power input terminal inputs positive and negative power inputs of a DC power supply;

[0030] The control switch 1 is turned on or off by the voltage detection device judging the input voltage;

[0031] The control switch 2 is used to control the opening and closing of the negative electrode of the power supply;

[0032] The voltage detection device detects whether the input voltage exceeds the maximum threshold;

[0033] The temperature detection device detects whether the temperature of the PCB circuit exceeds the maximum temperature;

[0034] The power output device outputs positive and negative power of a DC power source.

[0035] The maximum temperature and the maximum threshold can be adjusted as needed.

[0036] The G-pole voltage or the gate voltage of the field effect tube (Q1) and the field effect tube (Q2) is adjusted according to the maximum threshold value and the maximum temperature.

[0037] like Figure 2 As shown, the power input end is a USB socket, the voltage detection device includes two series resistors R1 and R3, and the resistor R3 is connected in parallel with the control switch 1; the temperature detection device includes positive temperature coefficient thermistors RT1 and R2, and the voltage detection device and the temperature detection device are connected in parallel; the control switch 1 and the control switch 2 are field effect transistors Q1 and Q2 respectively.

[0038] When the normal voltage is input and the voltage is within the set range, the field effect transistor Q2 is turned on and the power is directly passed from the input to the output device.

[0039] The principle of overvoltage protection: When the voltage is too high, the switch tube of the field effect tube Q1 changes from the off state to the on state, thereby pulling the G pole voltage of the field effect tube Q2 to within 0.1V. Because at this time the switch-off voltage of the Q2 field effect tube is greater than 0.7V (the on-state voltage of different field effect tubes is different and can be adjusted as needed), Q2 changes from the on state to the off state, thereby shutting down the power output and achieving the effect of overvoltage protection.

[0040] Principle of over-temperature protection: RT1 is a positive temperature coefficient thermistor, a positive temperature system thermistor. The higher the temperature, the greater the resistance value. Therefore, when the temperature rises, the G pole voltage of the field effect tube Q2 decreases. When the temperature rises to make the G pole voltage of the field effect tube Q2 lower than 0.7V (different field effect tubes have different cut-off voltages), Q2 is cut off, thereby shutting down the power output to achieve the effect of over-temperature protection. The conduction threshold of the field effect tube is used to realize the opening and cut-off of the circuit. Because the field effect tube generally has a built-in diode to protect the gate, the connection method of Q2 can only be to connect the S pole to the negative input terminal of the power supply and the D pole to the negative output of the power supply. If it is reversed, this circuit is invalid.

[0041] Selection method of resistors R1 and R3: If the on-voltage of Q1 is 1.2V, and it is required to play a protective role when the input voltage is higher than 6.0V, then the selection method of R1 and R3 can satisfy the following formula: [R3 / (R1+R3)]*6.0=1.2. Simplifying this formula, we can get R1=4*R3; if R3=10 kilo-ohms, then R1=40 kilo-ohms; substitute the above values ​​into the formula: [10 / (10+40)]*5=1.0V, which is lower than the on-voltage of Q1. Usually Q1 is in the off state and the power supply outputs normally.

[0042] Selection method for thermistors RT1 and R2: If the normal input voltage is 5V, the on-voltage of Q2 is 1.2V, and the off-voltage is 1.0V, RT1 and R2 must meet the following formula: [R2 / (RT1+R2)]*5.0=1.0; hence RT1=4*R2. If: R2=20 kilo-ohms; if we set the over-temperature protection temperature to 90 degrees, then we should select a thermistor with a positive temperature coefficient of 80 kilo-ohms at 90 degrees. If the thermistor value at room temperature of 25°C is: 40 kilo-ohms, then [20 / (40+20)]*5=1.67V, which is greater than 1.2V, Q2 is on, and there is power output; when the temperature is 90 degrees, then [20 / (80+20)]*5=1V, Q2 is off, and there is no power output, thus achieving the over-temperature protection effect.

[0043] The advantage of the over-temperature and over-voltage protection circuit of this embodiment is that it is low in cost. Common over-voltage protection uses a self-recovery fuse plus a voltage-stabilizing diode, which costs 0.25+0.05=0.30 yuan. The protection circuit of this embodiment only needs two resistors plus a transistor = 0.002*2+0.03=0.034 yuan.

[0044] Another advantage of the over-temperature and over-voltage protection circuit of this embodiment is that the over-voltage protection does not generate heat. In the prior art, a PTC thermistor and a voltage-stabilizing diode control circuit are used. When the current is too large or the temperature is too high, the current is reduced by the PTC thermistor. When the voltage is too high, the voltage-stabilizing diode absorbs the excess voltage. At the same time, the current increases, the temperature rises, and the resistance of the PTC thermistor increases, achieving a voltage stabilization effect. However, when the voltage is too high, the voltage-stabilizing diode will generate heat. The higher the voltage, the more serious the heat, which poses a safety hazard.

[0045] The temperature protection threshold of the over-temperature and over-voltage protection circuit in this embodiment can be set to different temperature protection ranges according to different product usage scenarios, which is low-cost and easy to use.

[0046] The over-temperature and over-voltage protection circuit of this embodiment has no software and single-chip microcomputer, and the overall cost is lower than that of the common over-temperature and over-voltage protection circuit. Because there is no software, the reliability is also high.

[0047] like Figure 3 As shown, in a variant embodiment of the present embodiment, the control switch 1 and / or the control switch 2 is a PMOS tube, and the PMOS tube is used to control the positive pole of the power supply. At this time, the temperature detection device includes a negative temperature coefficient thermistor RT2.

[0048] In other alternative embodiments of this embodiment, the control switch 1 and / or the control switch 2 is a switch transistor or an NMOS transistor. It should be noted that when a transistor is used as a switch control transistor, the transistor has an amplification area and it is not easy to achieve constant temperature control; the NMOS transistor controls the negative pole of the power supply.

[0049] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art of the present invention, several equivalent substitutions or obvious variations can be made without departing from the concept of the present invention, and the performance or use is the same, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. An over-temperature and over-voltage protection circuit, characterized in that: It includes a power input terminal, a first field effect transistor (Q1), a second field effect transistor (Q2), a voltage detection device, a temperature detection device, and a power output terminal; The power input terminal inputs positive and negative power inputs of a DC power supply; The first field effect transistor (Q1) is turned on or off by the voltage detection device judging the input voltage; The second field effect transistor (Q2) is used to control the opening and closing of the negative electrode of the power supply; The voltage detection device detects whether the input voltage exceeds the maximum threshold, and the voltage detection device is composed of two first resistors (R1) and a third resistor (R3) connected in series, and the third resistor (R3) is connected in parallel with the first field effect tube (Q1); The temperature detection device detects whether the temperature of the PCB circuit exceeds the maximum temperature, the temperature detection device is composed of a positive temperature coefficient thermistor (RT1) and a second resistor (R2), and the voltage detection device and the temperature detection device are connected in parallel; The power output device outputs positive and negative power of a DC power supply; when the voltage across the first field effect tube (Q1) is higher than the conduction voltage, it becomes a conduction state, thereby reducing the G pole voltage of the second field effect tube (Q2), so that the second field effect tube (Q2) is turned off, thereby shutting down the power output; when the voltage across the first field effect tube (Q1) is lower than the conduction voltage, it is an absolute state, the second field effect tube (Q2) is turned on, and the power output is normal; As the temperature rises, the resistance of the positive temperature coefficient thermistor (RT1) increases, thereby reducing the G-pole voltage of the second field effect transistor (Q2), causing the second field effect transistor (Q2) to turn off, thereby turning off the power output; The resistance values ​​of the first resistor (R1), the third resistor (R3), the input voltage and the on-voltage of the first field effect tube (Q1) satisfy the following relationship: when [R3 / (R1+R3)]*input voltage < the on-voltage of the first field effect tube (Q1), the on-voltage of the first field effect tube (Q1) is in an absolute state; when the input voltage is ≥ the maximum threshold value, the on-voltage of the first field effect tube (Q1) is turned on; When the maximum temperature is reached, the resistance of the positive temperature coefficient thermistor (RT1) and the second resistor (R2), the input voltage, and the on-voltage of the second field effect transistor (Q2) satisfy the following relationship: [R2 / (RT1+R2)]*input voltage=off-voltage of the second field effect transistor (Q2).

2. The over-temperature and over-voltage protection circuit according to claim 1, characterized in that: The S pole of the second field effect transistor (Q2) is connected to the input end of the negative electrode of the power supply, and the D pole is connected to the output of the negative electrode of the power supply.

3. The over-temperature and over-voltage protection circuit according to claim 1, characterized in that: The G-pole voltage or the gate voltage of the first field effect transistor (Q1) and the second field effect transistor (Q2) is adjusted according to the maximum threshold and the maximum temperature.

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