A hot air gun and its control method

Abstract

The present invention discloses a hot air gun and a hot air gun control method. The hot air gun comprises a temperature detection element (14) and a comparison element (21), wherein one end of the temperature detection element (14) is connected to a DC power supply, and the other end is connected in series with a capacitor (22) and a fixed resistor (23) connected in parallel; the comparison element (21) is provided with a first input port (4), a second input port (5) and an output port (6), wherein the first input port (4) detects the voltage value from the capacitor (22) to the ground, and the second input port (5) detects the voltage value from the fixed resistor (23) to the ground; the comparison element (21) compares the voltage value of the first input port with the voltage value of the second input port, obtains a comparison signal and outputs it to the control circuit (3); when the voltage value of the first input port is greater than the voltage value of the second input port, the control circuit (3) controls the heating wire (13) to work. The present invention can protect the hot air gun to prevent high temperature from damaging the fan and the circuit board, and has a high safety factor.

Description

Technical Field

[0001] The present invention relates to the technical field of electric tools, and in particular to a hot air gun and a control method thereof. Background Art

[0002] When a traditional hot air gun is in use, the heating core and the fan work at the same time when the switch is closed. When the hot air gun is started hot, a certain temperature will exist in the gun body. After operation, the heating wire will heat up immediately. Since it takes some time for the fan to rotate, the air supply is not timely, causing the temperature of the gun body to suddenly rise. Or, during use, the air outlet is blocked due to improper operation. Since the heating wire continues to heat up and the heat cannot be dissipated, the high temperature at this time may impact the fan blades or circuit boards and other parts that are not resistant to high temperatures, thereby reducing the tool life or causing damage.

[0003] Please refer to the utility model patent No. CN209731584U announced on December 3, 2019, which discloses an over-temperature protection circuit. When the temperature suddenly rises, the temperature fuse is disconnected first, the main heating wire stops heating, and the auxiliary heating wire and the fan motor continue to work. At this time, there is very little heat, and it works normally after waiting for the temperature fuse to recover. The use of a fuse in this circuit will result in a long waiting time and cannot promptly suppress the impact of high temperature on the circuit board or fan.

[0004] Therefore, it is necessary to design a heat gun that can suppress the influence of high temperature on the circuit board to solve the above problems. Summary of the invention

[0005] In view of the deficiencies in the prior art, an object of the present invention is to provide a low-cost, high-sensitivity hot air gun and a control method thereof.

[0006] The present invention solves the problems of the prior art by adopting the following technical scheme: comprising: a power supply, a shell, a switch installed on the shell, a fan installed in the shell, and a motor driving the fan, wherein a heating wire and a switch tube connected in series with each other and then in parallel with the motor are connected between the positive and negative poles of the power supply; the switch tube is electrically connected to a control circuit, and the on-off is controlled by the control circuit; the control circuit is electrically connected to a temperature protection circuit, and the temperature protection circuit is provided with a temperature detection element and a comparison element, wherein one end of the temperature detection element is connected to a DC power supply, and the other end is connected in series with a capacitor and a fixed resistor connected in parallel; the comparison element is provided with a first input port, a second input port, and an output port; the capacitor is connected to the temperature detection element One end of the capacitor is connected to the first input port, the other end of the capacitor is grounded, and the first input port detects the voltage value from the capacitor to the ground; the end of the fixed resistor connected to the temperature detection element is connected to the second input port, the other end of the fixed resistor is grounded, and the second input port detects the voltage value from the fixed resistor to the ground; the output port is electrically connected to the control circuit, the comparison element compares the voltage value of the first input port with the voltage value of the second input port to obtain a comparison signal, and the comparison signal is output to the control circuit through the output port; when the voltage value of the first input port is greater than the voltage value of the second input port, the control circuit controls the switch tube to be turned on, and the heating wire works.

[0007] A further improvement is: when the heating wire is working, if the voltage value of the first input port is less than the voltage value of the second input port, the control circuit controls the switch tube to disconnect, the heating wire does not work, and the motor drives the fan to rotate for cold blowing.

[0008] A further improved solution is: the comparison signal is a high level signal or a low level signal.

[0009] A further improvement is that the temperature detection element is an NTC resistor, which is used to detect the temperature near the fan.

[0010] A further improvement is that a diode is connected in series between the temperature detection element and the capacitor.

[0011] A further improvement is that a diode is connected in series between the temperature detection element and the fixed resistor.

[0012] A further improvement is that the comparison element is an operational amplifier.

[0013] The present invention can also adopt the following technical solutions to solve the problems of the prior art: a hot air gun control method, providing a temperature protection circuit and a control circuit electrically connected to the temperature protection circuit, the temperature protection circuit is provided with a temperature detection element and a comparison element, one end of the temperature detection element is connected to a DC power supply, and the other end is connected in series with a capacitor and a fixed resistor connected in parallel; the comparison element is provided with a first input port, a second input port and an output port; one end of the capacitor connected to the temperature detection element is connected to the first input port, the other end of the capacitor is grounded, and the first input port detects the voltage value from the capacitor to the ground; one end of the fixed resistor connected to the temperature detection element is connected to the second input port, the other end of the fixed resistor is grounded, and the second input port detects the voltage value from the fixed resistor to the ground, wherein the hot air gun control method has the following steps:

[0014] Start the switch, the motor drives the fan to rotate, and at the same time the voltage value of the first input port rises, the first input port of the comparison element detects the voltage value of the capacitor to ground, and the second input port detects the voltage value of the fixed resistor to ground; if the voltage value of the first input port rises and is greater than the voltage value of the second input port, the comparison element outputs a comparison signal to the control circuit, the control circuit controls the switch tube to turn on, the heating wire starts working, and the hot air gun heats up.

[0015] A further improvement scheme is: when the heating wire is in a continuous working state, if the temperature of the heating wire rises sharply, the resistance value of the temperature detection element decreases, the voltage value of the second input port increases, and when the voltage value of the first input port is less than the voltage value of the second input port, the comparison element outputs a comparison signal to the control circuit, the control circuit controls the switch tube to disconnect, the heating wire does not work, and the motor drives the fan to rotate for cold blowing; when the temperature drops, the voltage value of the first input port is greater than the voltage value of the second input port, and the heating wire continues to work.

[0016] A further improved solution is: the comparison signal is a high level signal or a low level signal.

[0017] Compared with the prior art, the present invention has the following beneficial effects: a temperature protection circuit is provided, and the temperature protection circuit compares the voltage values ​​of two input ports through a comparison element. The first input port detects the voltage from the capacitor to the ground, and the second input port detects the voltage from the fixed resistor to the ground. The capacitor and the fixed resistor are connected in parallel and then in series with the temperature detection element. When the voltage of the first input port is less than the voltage value of the second input port, the hot air gun performs cold blowing; when the voltage of the first input port is greater than the voltage value of the second input port, the hot air gun performs heating. By detecting the voltage values ​​of the two input ports, the hot air gun can be protected to prevent high temperature from damaging the fan and the circuit board, and the safety factor is relatively high. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings:

[0019] Figure 1 is a schematic diagram of a hot air gun of the present invention;

[0020] Figure 2 The invention discloses a heat gun control circuit diagram.

[0021] Meaning of the reference numerals in the figures:

[0022] 100, hot air gun 1, housing 11, fan 12, motor 13, heating wire 14, temperature detection element 15, circuit board 16, switch 17, switch tube 2, temperature protection circuit 21, comparison element 22, capacitor 23, fixed resistor 3, control circuit 4, first input port 5, second input port 6, output port DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with the accompanying drawings and implementation modes.

[0024] See also Figure 1 As shown, a hot air gun 100 and a control method thereof involved in an embodiment of the present invention are shown. The hot air gun 100 includes a shell 1, a fan 11 installed in the shell, a motor 12 driving the fan 11, a heating wire 13, a temperature detection element 14 and a circuit board 15. The temperature detection element 14 is installed on a heating wire 13 bracket close to one side of the fan 11, and is used to detect the temperature around the fan 11. The temperature detection element 14 is connected to the circuit board 15. The hot air gun 100 also includes a switch 16 installed on the shell 1, and the switch 16 is connected to the circuit board 15.

[0025] See also Figure 2 As shown, an implementation scheme of the hot air gun control circuit diagram of the present invention is shown, the circuit board 15 includes a temperature protection circuit 2 and a control circuit 3, the heating wire 13 and a switch tube 17 are connected in series between the positive pole and the negative pole of the power supply, the motor 12 and the resistor R1 are connected between the positive pole and the negative pole of the power supply, and are connected in parallel with the series heating wire 13 and the switch tube 17, the switch tube 17 is electrically connected to the control circuit 3, the control circuit 3 is electrically connected to the temperature protection circuit 2, and the control circuit 3 controls the heating wire 13 to work according to the temperature around the fan 11.

[0026] The temperature protection circuit 2 includes a temperature detection element 14 and a comparison element 21. One end of the temperature detection element 14 is connected to a DC power supply, and the other end is connected in series with a capacitor 22 and a fixed resistor 23 connected in parallel. The comparison element 21 is provided with a first input port 4, a second input port 5 and an output port 6. The end of the capacitor 22 connected to the temperature detection element 14 is connected to the first input port 4, and the other end of the capacitor 22 is grounded. The first input port 4 detects the voltage value from the capacitor 22 to the ground; the end of the fixed resistor 23 connected to the temperature detection element 14 is connected to the second input port 5, and the other end of the fixed resistor 23 is grounded. The second input port 5 detects the voltage value from the fixed resistor 23 to the ground; in this embodiment, a comparison element 21 is connected in series with the capacitor 22 and the temperature detection element 14 to detect the voltage value from the fixed resistor 23 to the ground. The first input port 4 is connected to the connection point between the capacitor 22 and the diode D1 through the resistor R4, and detects the voltage value from the capacitor 22 to the ground (i.e., the voltage value from point c to the ground). The first input port 4 is connected to the other end of the diode D1 through the resistor R3, and the resistors R3 and R4 charge the capacitor 22; a diode D6 is connected in series between the fixed resistor 23 and the temperature detection element 14, and the second input port 5 detects the voltage value from the fixed resistor 23 to the ground (i.e., the voltage value from point b to the ground). The comparison element 21 compares the voltage value of the first input port with the voltage value of the second input port to obtain a comparison signal, which is output to the control circuit 3 through the output port 6. The control circuit 3 controls the on and off of the switch tube 17, thereby controlling whether the heating wire 13 is heated. In this embodiment, the comparison element 21 is an operational comparator, and the comparison signal is a high level signal or a low level signal. When the comparison element 21 outputs a low level signal, the control circuit 3 controls the conduction of the switch tube 17, thereby controlling the heating wire 13 to heat up; when the comparison element 21 outputs a high level signal, the control circuit 3 controls the disconnection of the switch tube 17, thereby controlling the heating wire 13 not to heat up. In this embodiment, the temperature detection element 14 is an NTC resistor, and its resistance is 200K at normal room temperature, and its resistance decreases with the increase of temperature. The resistance value of the fixed resistor 23 is 22K, the voltage of the DC power supply is 5V, and the diode D6 is a silicon diode.

[0027] Working principle of the heating wire in this embodiment:

[0028] When the switch 16 is closed, since the fan 11 is connected to the power supply, the fan 11 starts to rotate. When the diode D1 is turned on, the capacitor 22 is charged through the resistor R6, and the voltage of the capacitor 22 (the voltage value from point c to ground) gradually increases, and the voltage value of the first input port 4 gradually increases; when the diode D6 is turned on, the voltage value from point b to ground is the voltage divided by the fixed resistor 23, the temperature detection element 14 and the diode D6 on the DC power supply. When the voltage value from point c to ground is less than the voltage value from point b to ground, that is, the voltage value of the first input port 4 is less than the voltage value of the second input port 5, the comparison element 21 outputs a high-level signal to the control circuit 3, and the control circuit 3 controls the switch tube 17 to be disconnected, the heating wire 13 does not heat up, and the motor 12 drives the fan 11 to rotate for cold blowing. In this embodiment, when the switch 16 is closed, the temperature around the fan 11 detected by the temperature detection element 14 is the room temperature of 25°C, the resistance value of the temperature detection element 14 is 200K, the voltage value of the second input port 5 is 0.43V, and the time for the voltage of the first input port 4 to rise to be equal to the voltage of the second input port 5 is 4 seconds. Therefore, the cold blowing time of the hot air gun is 4 seconds.

[0029] Working principle of hot air gun heating: the capacitor 22 is gradually charged, that is, the voltage value from point c to ground gradually increases. When the voltage value from point c to ground rises to a value greater than the voltage value from point b to ground, that is, the voltage value of the first input port 4 is greater than the voltage value of the second input port 5, the comparison element 21 outputs a low-level signal to the control circuit 3, and the control circuit 3 controls the switch 16 to turn on, that is, the heating wire 13 works, and at this time, the hot air gun 100 is heated. That is, after the fan 11 performs cold blowing for 4 seconds, the hot air gun is heated.

[0030] Protection principle of hot air gun: When the hot air gun works normally, the resistors R3 and R4 further charge the capacitor 22, so that the voltage of the capacitor 22 is maintained the same as the voltage of the diode D6 to the ground (that is, the voltage value from point a to the ground is the same as the voltage value from point c to the ground). Since the voltage value of the diode D6 to the ground is higher than the voltage value from the fixed resistor 23 to the ground (that is, the voltage value from point a to the ground is higher than the voltage value from point b to the ground), at this time, the voltage value of the first input port 4 is always higher than the voltage value of the second input port 5, and the temperature detection element 14 is installed near the fan 11, so the temperature detection element 14 is basically maintained at room temperature. When the muzzle of the hot air gun is blocked or other reasons cause the high temperature of the cavity to rush back to the fan 1 or the circuit board 15, the resistance value of the temperature detection element 14 drops sharply, and the voltage of the fixed resistor 23 to the ground increases, that is, the control circuit 3 controls the heating wire 13 to stop working for protection. For example, when the temperature around the fan 13 suddenly rises by 28°C, the resistance value of the temperature detection element 14 drops to 58.402K, and the voltage value of the second input port 5 is 1.18V. Since the voltage across the capacitor 22 cannot change suddenly, at this time, the voltage value from point c to ground is less than the voltage value from point b to ground, that is, the voltage value of the second input port 5 is higher than the voltage value of the first input port 4. The comparison element 21 outputs a high-level signal to the control circuit 3, and the control circuit 3 controls the switch tube 17 to disconnect for protection, the heating wire 13 does not work, and the motor 12 drives the fan 11 to rotate for cold blowing. When the temperature drops, the voltage value of the first input port 4 is greater than the voltage value of the second input port 5, the heating wire 13 works, and the hot air gun heats.

[0031] The hot air gun of the present invention is provided with a temperature protection circuit 2, and the temperature protection circuit 2 compares the voltage values ​​of two input ports through a comparison element 21. The first input port 4 detects the voltage from the capacitor 22 to the ground, and the second input port 5 detects the voltage from the fixed resistor 23 to the ground. The capacitor and the fixed resistor are connected in parallel and then in series with the temperature detection element. When the voltage of the first input port 4 is less than the voltage value of the second input port 5, the hot air gun performs cold blowing; when the voltage of the first input port 4 is greater than the voltage value of the second input port 5, the hot air gun performs heating. By detecting the voltage values ​​of the two input ports, the hot air gun can be protected to prevent high temperature from damaging the fan 11 and the circuit board, and the safety factor is relatively high.

[0032] The present invention is not limited to the above specific embodiments. A person skilled in the art can easily understand that there are many other alternatives to the hot air gun and the hot air gun control method of the present invention without departing from the principle and scope of the present invention. The protection scope of the present invention shall be subject to the content of the claims.

Claims

1. A hot air gun, comprising: A power supply, a housing (1), a switch (16) mounted on the housing (1), a fan (11) mounted in the housing (1), and a motor (12) driving the fan (11); a heating wire (13) and a switch tube (17) connected in series with each other and then in parallel with the motor (12) are connected between the positive and negative poles of the power supply; the switch tube (17) is electrically connected to a control circuit (3) and is controlled to be on and off by the control circuit (3); the control circuit (3) is electrically connected to a temperature protection circuit (2); the temperature protection circuit (2) is provided with a temperature detection element (14) and a comparison element (21); one end of the temperature detection element (14) is connected to a DC power supply, and the other end is connected in series with a capacitor (22) and a fixed resistor (23) connected in parallel; the comparison element (21) is provided with a first input port (4), a second input port (5) and an output port (6); the capacitor (22) and the temperature detection element (14) are connected to each other in series. One end of the element (14) connected to the first input port (4) is connected to the first input port (4), the other end of the capacitor (22) is grounded, and the first input port (4) detects the voltage value from the capacitor (22) to the ground; one end of the fixed resistor (23) connected to the temperature detection element (14) is connected to the second input port (5), the other end of the fixed resistor (23) is grounded, and the second input port (5) detects the voltage value from the fixed resistor (23) to the ground; the output port (6) is electrically connected to the control circuit (3), the comparison element (21) compares the voltage value of the first input port with the voltage value of the second input port to obtain a comparison signal, and the comparison signal is output to the control circuit (3) through the output port (6); when the voltage value of the first input port is greater than the voltage value of the second input port, the control circuit (3) controls the switch tube (17) to be turned on, and the heating wire (13) works.

2. The hot air gun according to claim 1, characterized in that: When the heating wire (13) is working, if the voltage value of the first input port is less than the voltage value of the second input port, the control circuit (3) controls the switch tube (17) to be disconnected, the heating wire (13) does not work, and the motor (12) drives the fan (11) to rotate for cold blowing.

3. The hot air gun according to claim 1, characterized in that: The comparison signal is a high level signal or a low level signal.

4. The hot air gun according to claim 1, characterized in that: The temperature detection element (14) is an NTC resistor and is used to detect the temperature near the fan (11).

5. The hot air gun according to claim 1, characterized in that: A diode is connected in series between the temperature detection element (14) and the capacitor (22).

6. The hot air gun according to claim 1, characterized in that: A diode is connected in series between the temperature detection element (14) and the fixed resistor (23).

7. The hot air gun according to claim 1, characterized in that: The comparison element (21) is an operational amplifier.

8. A method for controlling a hot air gun, for controlling a hot air gun as claimed in any one of claims 1 to 7, comprising a temperature protection circuit (2) and a control circuit (3) electrically connected to the temperature protection circuit (2), wherein the temperature protection circuit (2) is provided with a temperature detection element (14) and a comparison element (21), wherein one end of the temperature detection element (14) is connected to a DC power supply, and the other end is connected in series with a capacitor (22) and a fixed resistor (23) connected in parallel; the comparison element (21) is provided with a first input port (4), a second input port (5) and an output port (6). port (6); one end of the capacitor (22) connected to the temperature detection element (14) is connected to the first input port (4), the other end of the capacitor (22) is grounded, and the first input port (4) detects the voltage value from the capacitor (22) to the ground; one end of the fixed resistor (23) connected to the temperature detection element (14) is connected to the second input port (5), the other end of the fixed resistor (23) is grounded, and the second input port (5) detects the voltage value from the fixed resistor (23) to the ground, wherein the hot air gun control method comprises the following steps: The switch is started, the motor (12) drives the fan (11) to rotate, and at the same time, the voltage value of the first input port (4) increases, the first input port (4) of the comparison element (21) detects the voltage value of the capacitor (22) to the ground, and the second input port (5) detects the voltage value of the fixed resistor (23) to the ground; if the voltage value of the first input port increases and is greater than the voltage value of the second input port, the comparison element (21) outputs a comparison signal to the control circuit (3), and the control circuit (3) controls the switch tube (17) to turn on, the heating wire (13) starts to work, and the hot air gun (100) starts heating.

9. The hot air gun control method according to claim 8, characterized in that: When the hot air gun (100) is in a continuous working state, if the temperature of the heating wire (13) rises sharply, the resistance value of the temperature detection element (14) decreases, the voltage value of the second input port increases, and when the voltage value of the first input port is less than the voltage value of the second input port, the comparison element (21) outputs a comparison signal to the control circuit (3), and the control circuit (3) controls the switch tube (17) to disconnect, the heating wire (13) does not work, and the motor (12) drives the fan (11) to rotate for cold blowing; when the temperature drops, the voltage value of the first input port is greater than the voltage value of the second input port, and the heating wire (13) continues to work.

10. The hot air gun control method according to claim 9, characterized in that: The comparison signal is a high level signal or a low level signal.

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