A hot bed load switching circuit and 3D printing apparatus

Abstract

The present disclosure provides a hot bed load switching circuit and a 3D printing device, and relates to the technical field of 3D printing. The circuit comprises a flicker suppression module and a hot bed master control unit, which are electrically connected and connected to a switching switch module, and are used for controlling the working mode of the switching switch module according to the level state of a on-off control signal; the switching switch module receives a voltage identification control signal of a hot bed power supply, and the output end is connected to a first hot bed load resistor and a second hot bed load resistor; when the on-off control signal is a first level, the flicker suppression module makes the switching switch module in a voltage identification mode, and controls the connection mode of the first hot bed load resistor and the second hot bed load resistor according to the high and low voltage corresponding to the voltage identification control signal; when the on-off control signal is a second level, the flicker suppression module makes the switching switch module in a flicker suppression mode, and forcibly connects the first hot bed load resistor and the second hot bed load resistor in series. The present disclosure guarantees the safety of electricity use and reduces test flicker.

Description

Technical Field

[0001] This disclosure relates to the field of 3D printing technology, and more specifically, to a heated bed load switching circuit and a 3D printing device. Background Technology

[0002] Different countries / regions have different mains voltages, such as low-voltage / high-voltage AC power zones. The heated bed is a key component of 3D printing equipment, primarily used to prevent warping of printed parts and improve adhesion through heating, playing a crucial role in 3D printing. Current technologies for switching loads on AC heated beds under different voltages are mainly focused on the 3D printing field. Their core objective is to maintain stable heating power for the heated bed under different input voltages by switching load resistance or adjusting voltage output.

[0003] In related technologies, a switching module is used to control the connection relationship of the heating resistors and change the total resistance value to adapt to different voltages. However, during the operation of the AC heating bed, the power supply current is large in some cases, which may cause electromagnetic compatibility (EMC) flicker problems. Utility Model Content

[0004] The purpose of this disclosure is to provide a heated bed load switching circuit and a 3D printing device, which aims to solve the problem that when multiple switching modules are used to control the series or parallel connection of heating resistors to change the total resistance value to adapt to different voltages in the related technology, the power supply current is large when the heating resistors are connected in parallel during the operation of the AC heated bed, which may cause flickering during electromagnetic compatibility testing.

[0005] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure.

[0006] According to a first aspect of this disclosure, a heated bed load switching circuit is provided, comprising: a flicker suppression module, a switching module, a first heated bed load resistor, and a second heated bed load resistor; the input terminal of the flicker suppression module is electrically connected to a heated bed main control unit, and the output terminal of the flicker suppression module is connected to the first input terminal of the switching module; the flicker suppression module is used to receive an on / off control signal issued by the heated bed main control unit, and to control the operating mode of the switching module according to the level state of the on / off control signal; the second input terminal of the switching module is electrically connected to a heated bed power supply unit, and is used to receive a voltage identification control signal issued by the heated bed power supply unit; the two output terminals of the switching module are respectively connected to the first heated bed load resistor and the second heated bed load resistor, wherein, when the on / off control signal is at a first level, the flicker suppression module is used to put the switching module in a voltage identification mode, and the switching module is used to control the connection mode of the first heated bed load resistor and the second heated bed load resistor according to the high and low voltages corresponding to the voltage identification control signal; when the on / off control signal is at a second level, the flicker suppression module is used to put the switching module in a flicker suppression mode, and the switching module is used to force the first heated bed load resistor and the second heated bed load resistor to be connected in series.

[0007] In the above implementation, when the on / off control signal is at the first level, the flicker suppression module is used to put the switching module in voltage recognition mode. The switching module is used to control the connection mode of the first and second heated bed load resistors according to the high or low voltage corresponding to the voltage recognition control signal. When the on / off control signal is at the second level, the flicker suppression module is used to put the switching module in flicker suppression mode. The switching module is used to force the first and second heated bed load resistors to be connected in series. When the first and second heated bed load resistors are connected in parallel, the supply current may be too large. When the on / off control signal is at the second level, the flicker suppression module is turned on, forcibly switching the first and second heated bed load resistors from parallel mode to series mode to reduce the supply current, thereby suppressing the flickering problem in electromagnetic compatibility testing, reducing safety risks, and improving the overall circuit safety.

[0008] In one exemplary embodiment of this disclosure, the switching module is in voltage identification mode, wherein when the voltage identification control signal corresponds to a low voltage, the switching module connects the first hot bed load resistor and the second hot bed load resistor in parallel; when the voltage identification control signal corresponds to a high voltage, the switching module connects the first hot bed load resistor and the second hot bed load resistor in series.

[0009] Through the above implementation method, when the switching module receives the voltage identification control signal, if the voltage identification control signal corresponds to a low voltage, the first hot bed load resistor is connected in parallel; if the voltage identification control signal corresponds to a high voltage, the first hot bed load resistor is connected in series, thereby realizing automatic control of the series and parallel connection of the first hot bed load resistor and the second hot bed load resistor.

[0010] In one exemplary embodiment of this disclosure, the switching module is a dual-channel relay, which includes: a first contact group and a second contact group. The first contact group includes a first contact, a second contact, and a third contact. The first contact is connected to a first end of a first heated bed load resistor; the second contact is connected to an intermediate tap between the first heated bed load resistor and the second heated bed load resistor; and the third contact is connected to a power input terminal. The second contact group includes a fourth contact, a fifth contact, and a sixth contact. The fourth contact is connected to a first end of the second heated bed load resistor; the fifth contact is connected to the intermediate tap; and the sixth contact is connected to a power input terminal. When the first contact and the second contact are connected, and the fourth contact and the fifth contact are connected, the first heated bed load resistor and the second heated bed load resistor are connected in series. When the second contact and the third contact are connected, and the fifth contact and the sixth contact are connected, the first heated bed load resistor and the second heated bed load resistor are connected in parallel.

[0011] Through the above implementation method, the switching module is a dual-channel relay, which includes two contact groups. The knife switch switches between the two contact groups to achieve contact conduction in the first and second contact groups. For example, when the first contact is connected to the second contact and the fourth contact is connected to the fifth contact, the first and second hot bed load resistors are connected in series. When the second contact is connected to the third contact and the fifth contact is connected to the sixth contact, the first and second hot bed load resistors are connected in parallel. Only a dual-channel switching switch is needed to achieve the series and parallel control of the first and second hot bed load resistors, reducing the use of relay switches and reducing some control signals. This makes the hot bed heating control less susceptible to interference and avoids safety risks caused by interference.

[0012] In an exemplary embodiment of this disclosure, when in the voltage identification mode, the on / off control signal is at a first level and the flicker suppression module is not turned on; when in the flicker suppression mode, the on / off control signal is at a second level and the flicker suppression module is turned on, so as to switch the conduction relationship of the switching module.

[0013] Through the above implementation method, the flicker suppression module is turned on or off according to the level signal provided by the relay according to different control stages, so as to adjust the conduction relationship of the switching module accordingly. For example, when in voltage recognition mode, the on / off control signal is a low level signal, the flicker suppression module is not turned on and will not trigger the forced switching of the switching module; if in flicker suppression mode, due to the large supply current, it is necessary to switch the connection mode of the first hot bed load resistor and the second hot bed load resistor to series connection, the on / off control signal is a high level signal, the flicker suppression module is turned on, so as to switch the conduction relationship of the switching module and force the first hot bed load resistor and the second hot bed load resistor to be connected in series.

[0014] In one exemplary embodiment of this disclosure, the on / off control signal remains at the first level; when the voltage identification control signal corresponds to a low voltage and enters the proportional-integral-derivative control stage, the on / off control signal is pulled high to the second level, the flicker suppression module is turned on, so as to switch the conduction relationship of the switching module and force the first hot bed load resistor and the second hot bed load resistor to be connected in series.

[0015] In one exemplary embodiment of this disclosure, the flicker suppression module includes: a first transistor whose base receives an on / off control signal, whose collector is connected to a first input terminal of a switching module, and whose emitter is grounded; wherein, the first transistor is configured such that: when the on / off control signal is low, the first transistor is cut off, the flicker suppression module does not interfere with the working state of the switching module, and the switching module maintains a voltage recognition mode; when the on / off control signal is high, the first transistor is turned on, and outputs a control signal to the switching module through its collector, forcing it to switch to the flicker suppression mode and maintaining the first heated bed load resistor and the second heated bed load resistor connected in series.

[0016] In one exemplary embodiment of this disclosure, the flicker suppression module further includes: a first filtering unit composed of a first resistor and a first capacitor connected in parallel; one end of the first resistor is connected to the base of a first transistor, and the other end of the first resistor is grounded, the first resistor being used to stabilize the static level of the base; the first capacitor is connected in parallel across the two ends of the first resistor, the first capacitor being used to filter out high-frequency interference of the on / off control signal; the base of the first transistor receives the on / off control signal through the first filtering unit, and after filtering and level stabilization, controls the on and off states of the first transistor.

[0017] Through the above implementation method, the signal entering the flicker suppression module can be filtered, high-frequency interference signals can be filtered out, while low-frequency signals are allowed to pass through.

[0018] In one exemplary embodiment of this disclosure, the heated bed load switching circuit further includes: a second transistor, the base of which receives a voltage identification control signal, the collector of which is connected to the second input terminal of the switching module, and the emitter of which is grounded; the second transistor is used to convert the voltage identification control signal into a control signal adapted to the voltage identification mode of the switching module, so as to control the series-parallel switching of the first heated bed load resistor and the second heated bed load resistor.

[0019] In one exemplary embodiment of this disclosure, the heated bed load switching circuit further includes a second filter unit consisting of a second resistor and a second capacitor connected in parallel; one end of the second resistor is connected to the base of the second transistor, and the other end of the second resistor is grounded, and the second resistor is used to stabilize the static level of the base; the second capacitor is connected in parallel across the two ends of the second resistor as a filter capacitor to filter out high-frequency noise of the voltage identification control signal; the voltage identification control signal is filtered by the second filter unit in sequence and the level is stabilized before being input to the base of the second transistor to control the conduction and cutoff states of the second transistor.

[0020] In the above implementation, the second filtering unit is mainly used to filter out high-frequency interference signals in the voltage identification control signal input to the switching module, while allowing low-frequency signals to pass through. This is mainly achieved through the bypassing effect of the capacitor on high-frequency signals and the path control of the resistor on low-frequency signals to achieve frequency selective attenuation. For example, the second filtering unit can be an RC parallel filter circuit.

[0021] In one exemplary embodiment of this disclosure, the system further includes: an AC switch module connected to the second input terminal of the switching switch module, for receiving a heated bed heating control signal, controlling the switching switch module to open or close according to the heated bed heating control signal, and connecting when the power supply voltage of the AC switch module crosses zero.

[0022] In one exemplary embodiment of this disclosure, the AC switching module includes: a zero-crossing optocoupler and a bidirectional thyristor. The zero-crossing optocoupler is used to detect the zero-crossing of the heated bed heating control signal through a current-limiting resistor, and controls the connection of the bidirectional thyristor when the power supply voltage of the zero-crossing optocoupler crosses zero, thereby supplying power to the switching module to control the on / off state of the switching module.

[0023] Through the above implementation method, the zero-crossing trigger signal of the bidirectional thyristor is provided to the zero-crossing moment through the zero-crossing optocoupler, thereby realizing the switching control of the switching module.

[0024] In one exemplary embodiment of this disclosure, the heated bed load switching circuit further includes a constant current source, which includes a third transistor and a third resistor. The base of the third transistor is connected to the input terminal of the heated bed heating control signal, the collector of the third transistor is connected to a zero-crossing optocoupler, and the emitter of the third transistor is grounded through the third resistor. The constant current source is used to eliminate current fluctuations in the drive current of the zero-crossing optocoupler.

[0025] Through the above implementation method, setting a constant current source circuit to drive the zero-crossing optocoupler can ensure that the driving current fluctuation of the zero-crossing optocoupler is small and will not be falsely triggered to conduct through the zero-crossing optocoupler.

[0026] In one exemplary embodiment of this disclosure, the heated bed load switching circuit further includes a low-pass filter module, one end of which is connected to the input terminal of the heated bed heating control signal, and the other end is connected to a constant current source. The heated bed heating control signal is filtered by the low-pass filter module and then input to the constant current source.

[0027] Through the above implementation method, the low-pass filter module can filter out invalid pulse signals when the 3D printing equipment starts up, which can prevent the 3D printing equipment from shaking.

[0028] In one exemplary embodiment of this disclosure, the heated bed load switching circuit further includes a pull-down resistor, the first end of which is connected to a low-pass filter module, and the second end of which is grounded. The pull-down resistor is used to limit the instantaneous current at the input terminal of the heated bed heating control signal.

[0029] By adding a pull-down resistor through the above implementation method, the instantaneous current at the input terminal of the heated bed heating control signal can be limited, so that the heated bed heating control signal is pulled down by default through the pull-down resistor, thus preventing the heated bed heating function from starting immediately upon power-up of the entire circuit.

[0030] According to a second aspect of this disclosure, a 3D printing apparatus is provided, comprising: a printing heated bed; and a heated bed load switching circuit as described in any embodiment of the first aspect above.

[0031] In the heated bed load switching circuit of this 3D printing equipment, a switching module receives voltage identification control signals and on / off control signals. Based on these signals, it switches the series-parallel connection mode of the first and second heated bed load resistors to control their connection. Specifically, when the on / off control signal is at the first level, the switching module is in voltage identification mode, controlling the connection method of the first and second heated bed load resistors according to the high or low voltage corresponding to the signal. When the on / off control signal is at the second level, the switching module is in flicker suppression mode, forcibly connecting the first and second heated bed load resistors in series. When the first and second heated bed load resistors are connected in parallel, the supply current may be too high. When the on / off control signal is at the second level, the flicker suppression module is activated, forcibly switching the first and second heated bed load resistors from parallel mode to series mode to reduce the supply current, thereby suppressing flickering issues during electromagnetic compatibility testing, reducing safety risks, and improving the overall circuit safety.

[0032] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0033] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0034] Figure 1 This is a schematic diagram of the structure of an example heated bed load switching circuit disclosed herein;

[0035] Figure 2 This is a schematic diagram of the structure of another example of the heated bed load switching circuit disclosed herein;

[0036] Figure 3 This is a schematic diagram of the structure of another example of the heated bed load switching circuit disclosed herein;

[0037] Figure 4 This is a schematic diagram of the structure of an example switching circuit of this disclosure;

[0038] Figure 5 This is a schematic diagram of the structure of another example of the heated bed load switching circuit disclosed herein;

[0039] Figure 6 This is a schematic diagram of the structure of another example of the heated bed load switching circuit disclosed herein;

[0040] Figure 7 This is a schematic diagram of the structure of another example of the heated bed load switching circuit disclosed herein;

[0041] Figure 8 This is a schematic diagram of the circuit structure of an example heated bed load switching circuit disclosed herein. Detailed Implementation

[0042] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore detailed descriptions of them will be omitted. Furthermore, the drawings are merely illustrative of this disclosure and are not necessarily drawn to scale.

[0043] Although relative terms such as "upper" and "lower" are used in this specification to describe the relative relationship of one component of an icon to another, these terms are used only for convenience, such as according to the orientation of the examples in the accompanying drawings. It is understood that if the device of the icon is flipped so that it is upside down, the component described as "upper" will become the component described as "lower." When a structure is "upper" of another structure, it may mean that the structure is integrally formed on the other structure, or that the structure is "directly" mounted on the other structure, or that the structure is "indirectly" mounted on the other structure through another structure.

[0044] The terms “a,” “one,” “the,” and “at least one” are used to indicate the existence of one or more elements / components / etc.; the terms “including” and “having” are used to indicate an open-ended inclusion and to mean that there may be other elements / components / etc. in addition to the listed elements / components / etc.; the terms “first” and “second” are used only as markers and are not a limitation on the number of objects.

[0045] In the field of 3D printing, the heated bed is a key component, primarily used to prevent warping of printed parts and improve adhesion through heating, playing a crucial role in the 3D printing process. Switching the load for an AC heated bed under different voltages is typically achieved by changing the load resistance or adjusting the voltage output, ensuring the heated bed maintains stable heating power under varying input voltages.

[0046] Currently, a common approach is to control the series or parallel connection of the heating resistor using two sets of switching modules (such as relays or solid-state relays) to change the total resistance and adapt to different voltages. This can be achieved by combining a dual-channel switching transistor (such as a MOSFET) with the heating resistor and switching the circuit topology via a control signal. For example, at 110V, it can switch to parallel (low resistance) and at 220V, it can switch to series (high resistance) to maintain constant power.

[0047] In addition, some systems use voltage detection circuits (such as voltage divider networks and rectifier filter modules) to identify the input voltage, and then use control circuits (such as microcontrollers) to adjust the PWM signal to drive the switching transistor, dynamically adjusting the voltage across the heated bed. Voltage detection and closed-loop control are achieved through step-down capacitors, optocouplers, and analog comparators.

[0048] However, the above two implementation schemes have the following problems:

[0049] (1) In the scheme of controlling the heating resistor in series or parallel by two sets of switching modules (such as relays or solid-state relays), if the mains voltage in the low-voltage area is used for heating the hot bed, the supply current is large and the switching is frequent, which may pose a risk of flickering in the electromagnetic compatibility (EMC) test. In addition, using two relay switches to switch the load resistor results in more control signals, and there is also a risk that the heating control of the hot bed is easily interfered with.

[0050] (2) Insufficient anti-interference capability: Electromagnetic interference (EMI) and power grid harmonics (such as the 3rd and 5th harmonics) may cause the voltage detection circuit to misjudge and lead to switching errors. For example, when THD > 5%, the voltage identification control signal error based on FFT can reach ±2%; or long-distance wiring (such as inside a 3D printer) may introduce ground potential difference, causing the differential sampling circuit to malfunction.

[0051] (3) Switching component lifespan issues: Relay / SSR contacts wear out, and frequent switching (such as once per printing task) can cause mechanical contacts to oxidize or stick together. The typical lifespan is about 100,000 cycles, and it needs to be replaced after long-term use. In high-temperature environments (such as heated bed surface temperature > 100°C), the on-resistance (RDS) of the MOSFET may increase by more than 30%, causing thermal runaway. For example, the WSR180N08 transistor's continuous current capability drops to 28A at 100°C, which may lead to overload.

[0052] Therefore, how to provide a hot bed load switching circuit with a long lifespan of switching elements, strong anti-interference ability, fewer control signals, and no risk of EMC test flickering is a technical problem that urgently needs to be solved by those skilled in the art.

[0053] The technical solutions provided in this disclosure can be applied to various fields such as power management, motor control, heating, testing and measurement, and industrial automation. They are particularly suitable for applications requiring dynamic adaptation to operating conditions (such as voltage, current, power, and frequency), such as heated bed control in consumer-grade 3D printing equipment. In these scenarios, during heated bed heating, when the heated bed load resistors are connected in parallel, the supply current is large and may switch frequently, easily causing EMC test flickering. This disclosure addresses this issue by using a flicker suppression module to control a switching module, forcibly switching the first and second heated bed load resistors from parallel to series mode to reduce the supply current, thereby suppressing electromagnetic compatibility test flickering and improving the overall circuit safety.

[0054] First, this disclosure provides a heated bed load switching circuit 100, such as... Figure 1 As shown, the heated bed load switching circuit 100 may include a switching module 200, a flicker suppression module 300, a first heated bed load resistor 400, and a second heated bed load resistor 500. Specifically:

[0055] The input terminal of the flicker suppression module 300 is electrically connected to the heated bed main control unit, and the output terminal of the flicker suppression module 300 is connected to the first input terminal of the switching module 200. The flicker suppression module 300 is used to receive the on / off control signal sent by the heated bed main control unit and control the working mode of the switching module 200 according to the level state of the on / off control signal. The second input terminal of the switching module 200 is electrically connected to the heated bed power supply unit and is used to receive the voltage identification control signal sent by the heated bed power supply unit. The two output terminals of the switching module 200 are respectively connected to the first heated bed load resistor 400 and the second heated bed load resistor 500. When the on / off control signal is at the first level, the flicker suppression module 300 is used to put the switching module 200 into the voltage recognition mode. The switching module 200 is used to control the connection mode of the first hot bed load resistor 400 and the second hot bed load resistor 500 according to the high and low voltages corresponding to the voltage recognition control signal. When the on / off control signal is at the second level, the flicker suppression module 300 is used to put the switching module 200 into the flicker suppression mode. The switching module 200 is used to force the first hot bed load resistor 400 and the second hot bed load resistor 500 to be connected in series.

[0056] The voltage identification control signal is a high / low level signal used to characterize the range of the input voltage of the heated bed power supply. It corresponds to the high / low voltage of the input voltage. In this embodiment, the voltage identification control signal can be issued by the heated bed power supply unit. For example, the heated bed power supply unit may include a heated bed power supply and a voltage detection circuit. The voltage detection circuit can output corresponding high / low level signals according to the range of the input voltage provided by the heated bed power supply. For instance, when the power supply of the heated bed load switching circuit 100 is AC mains power, it typically has a high-voltage zone (200-230V) AC signal and a low-voltage zone (100-130V) AC signal. The voltage identification control signal output by the voltage detection circuit can output high / low level signals according to the high-voltage zone AC signal and the low-voltage zone AC signal. For example, it can be low level when the high-voltage zone AC signal is input and high level when the low-voltage zone AC signal is input. In this embodiment, the first input terminal of the switching module 200 refers to the pin of its electromagnetic coil. The flicker suppression module adjusts the conduction relationship of the switching module 200 by controlling the electromagnetic coil of the switching module 200. The on / off control signal is a control signal used to control the on / off state of the flicker suppression module. When the on / off control signal is at the first level, the flicker suppression module is not conducting; when the on / off control signal is at the second level, the flicker suppression module is conducting, thereby forcibly switching the conduction relationship of the switching module. In this embodiment, the on / off control signal can be issued by the main control unit of the heated bed of the 3D printing equipment (e.g., the control board of the 3D printer, microcontroller, etc.) corresponding to the heated bed load switching circuit.

[0057] The switching module 200 can switch the series-parallel connection of the first heated bed load resistor 400 and the second heated bed load resistor 500 according to the voltage identification control signal. For example, under the condition of a low-voltage (100-130V) AC signal, the voltage identification control signal is high, and the switching module 200 switches the first heated bed load resistor 400 and the second heated bed load resistor 500 to be connected in parallel; under the condition of a high-voltage (200-230V) AC signal, the voltage identification control signal is low, and the switching module 200 switches the first heated bed load resistor 400 and the second heated bed load resistor 500 to be connected in series.

[0058] Because the resistance of the heated bed load resistors in parallel is smaller than that in series, the heating power of the heated bed is close to that of the heated bed load resistors in the high-pressure zone (200-230V) when they are in series. By switching the module to receive the voltage identification control signal, if the voltage identification control signal corresponding to the low-pressure zone (100-130V) AC signal is high, the first heated bed load resistor is connected in parallel; if the voltage identification control signal corresponding to the high-pressure zone (200-230V) AC signal is low, the first heated bed load resistor is connected in series, thus achieving automatic control of the series and parallel connection of the first and second heated bed load resistors.

[0059] In this embodiment, when the on / off control signal is low, the switching module 200 is in voltage recognition mode. The switching module 200 controls the connection mode of the first hot bed load resistor 400 and the second hot bed load resistor 500 according to the high or low voltage corresponding to the voltage recognition control signal. Specifically, when the mains power is a low-voltage AC signal (100-130V), the voltage recognition control signal is high, and the switching module 200 switches the first hot bed load resistor 400 and the second hot bed load resistor 500 to be connected in parallel; when the mains power is a high-voltage AC signal (200-230V), the voltage recognition control signal is low, and the switching module 200 switches the first hot bed load resistor 400 and the second hot bed load resistor 500 to be connected in series.

[0060] When the on / off control signal is high, the switching module 200 is in flicker suppression mode, forcibly switching the first hot bed load resistor 400 and the second hot bed load resistor 500 into a series connection. That is, when the switching module 200 is in flicker suppression mode, if the voltage identification control signal corresponds to a low-voltage zone (100-130V) AC signal, the switching module 200 forcibly switches the first hot bed load resistor 400 and the second hot bed load resistor 500 into a series connection; if the voltage identification control signal corresponds to a high-voltage zone (200-230V) AC signal, the switching module 200 does not perform any processing.

[0061] In some alternative embodiments of this disclosure, such as Figure 4As shown, the switching module 200 can be a dual-channel relay. The dual-channel relay, by expanding the control channel, achieves a flexible one-to-two control design, significantly simplifying circuit layout in fields such as smart homes and industrial control. It can prioritize matching core parameters such as coil voltage and contact capacity based on load power, control method (synchronous / independent), and environmental conditions, while also paying attention to electrical safety and lifespan optimization. For example, the dual-channel relay can be a double-pole double-throw switch, which includes a first contact group and a second contact group. The first contact group includes a first contact 1, a second contact 2, and a third contact 3. The first contact 1 is connected to the first end of the first heated bed load resistor 400, the second contact 2 is connected to the intermediate tap between the first heated bed load resistor 400 and the second heated bed load resistor 500, and the third contact 3 is connected to the power input terminal. The second contact group includes a fourth contact 4, a fifth contact 5, and a sixth contact 6. The fourth contact 4 is connected to the first end of the second heated bed load resistor 500, the fifth contact 5 is connected to the intermediate tap, and the sixth contact 6 is connected to the power input terminal. Specifically, when the first contact 1 and the second contact 2 are connected, and the fourth contact 4 and the fifth contact 5 are connected, the first heated bed load resistor 400 and the second heated bed load resistor 500 are connected in series. The input signal of the mains live wire AC_L is input to terminal A of the heated bed load resistor through the first contact 1 and the second contact 2. The heated bed load resistors AC and CB are connected in series, and the input signal is transmitted from terminal B of the heated bed load resistor to the mains neutral wire AC_N. When the second contact 2 and the third contact 3 are connected, and the fifth contact 5 and the sixth contact 6 are connected... When the circuit is on, the first heated bed load resistor 400 and the second heated bed load resistor 500 are connected in parallel. The input signal from the mains live wire AC_L is input to the intermediate tap C through the sixth contact 6 and the fifth contact 5. In one branch, the input signal passes through the heated bed load resistor CB and is transmitted from the heated bed load resistor's terminal B to the mains neutral wire AC_N. In the other branch, the input signal passes through the heated bed load resistor CA and is output from the heated bed load resistor's terminal A, then is transmitted to the mains neutral wire AC_N through the second contact 2 and the third contact 3. In this embodiment, only a dual-channel switching switch is needed to realize the series-parallel control of the first and second heated bed load resistors, reducing the use of relay switches and reducing some control signals. This makes the heated bed heating control less susceptible to interference and avoids safety risks caused by interference.

[0062] The flicker suppression module 300 receives the on / off control signal. When the on / off control signal is at the first level, the switching module 200 is in voltage recognition mode, controlling the connection method of the first heated bed load resistor 400 and the second heated bed load resistor 500 according to the high or low voltage corresponding to the voltage recognition control signal. When the on / off control signal is at the second level, the switching module 200 is in flicker suppression mode, the flicker suppression module 300 is turned on, and the first heated bed load resistor 400 and the second heated bed load resistor 500 are forcibly switched to a series connection to reduce the supply current and reduce the risk of flickering during EMC testing. The levels of the first and second levels are set according to the conduction level of the first transistor 3002. For example, the first transistor 3002 can be an NPN transistor, in which case the first level is low and the second level is high.

[0063] In practical applications, when the voltage identification control signal of the first heated bed load resistor 400 and the second heated bed load resistor 500 are at a high level (i.e., the input voltage is a low-voltage (100-130V) AC signal) and the on / off control signal is at a high level, the flicker suppression module 300 is turned on, switching the parallel state of the first heated bed load resistor 400 and the second heated bed load resistor 500 to a series state.

[0064] In some optional embodiments of this disclosure, the heated bed load switching circuit 100 can be applied to the heated bed of a 3D printing device. During the operation of the heated bed, the temperature can be precisely controlled by proportional integral derivative control (PID). The main purpose of the PID control stage is to eliminate temperature fluctuations, smooth the transition (avoid temperature overshoot or undershoot), and reduce current surges. In this embodiment, PID control is mainly used for temperature stabilization during the constant temperature stage, and it will also intervene in advance in the later stage of the heating stage (when approaching the target temperature) to ensure a smooth temperature transition. Specifically, in the proportional-integral-derivative (PID) control stage, proportional control adjusts the power based on the current temperature difference, integral control eliminates steady-state errors, and derivative control predicts temperature change trends. The non-PID stage is the initial stage of heated bed heating. This stage operates from the start of heating until it approaches the target temperature (typically reaching 90-95% of the target temperature). Heating is performed using full power or fixed power output to achieve rapid temperature rise and shorten preheating time. In this stage, the system does not use PID algorithms for fine-tuning; the connection of the two heated bed load resistors is controlled by a voltage recognition control signal. This stage is suitable for when the heated bed is first started and needs to be rapidly heated from room temperature to the operating temperature. The PID stage is the precise temperature control stage for the heated bed. This stage operates from when the heated bed temperature approaches the target temperature (typically with a temperature difference within 5-10℃) until it is maintained at a constant temperature. PID algorithms are used for dynamic adjustment to achieve precise temperature control and eliminate temperature fluctuations. In this embodiment of the disclosure, during the non-proportional-integral-derivative control stage, the switching module 200 is in voltage recognition mode, and during the proportional-integral-derivative control stage, the switching module 200 is in flicker suppression mode.

[0065] In this embodiment, when the heated bed load switching circuit 100 is in voltage identification mode, the switching module 200 controls the first heated bed load resistor 400 and the second heated bed load resistor 500 in series and parallel according to the voltage identification control signal. For example, when the voltage identification control signal corresponding to the AC signal in the low voltage zone (100-130V) is high, the switching module 200 connects the first heated bed load resistor 400 and the second heated bed load resistor 500 in parallel; when the voltage identification control signal corresponding to the AC signal in the high voltage zone (200-230V) is low, the switching module 200 connects the first heated bed load resistor 400 and the second heated bed load resistor 500 in series.

[0066] In practical applications, the on / off control signal can be adjusted by a corresponding controller (e.g., a microcontroller). Correspondingly, when the on / off control signal is at the second level, the switching module 200 is in flicker suppression mode, and the flicker suppression module 300 is turned on. This switches the conduction relationship of the switching module 200, thereby switching the parallel connection of the first hot bed load resistor 400 and the second hot bed load resistor 500 to a series connection, reducing their operating current and thus lowering the risk of excessive flicker during EMC testing. Specifically, when in voltage recognition mode, the on / off control signal is a low-level signal, and the controller does not intervene to adjust it; the on / off control signal remains low, and the flicker suppression module 300 is not turned on. When in flicker suppression mode, the controller intervenes to adjust the on / off control signal, pulling it high to switch it to a high-level signal, turning on the flicker suppression module 300, thus switching the conduction relationship of the switching module 200 and forcing the first hot bed load resistor 400 and the second hot bed load resistor 500 into series connection.

[0067] In this embodiment, the voltage identification control signal can be a hardware control signal, and the on / off control signal can be a software control signal. The hardware control signal has a higher priority than the software control signal. The hardware control signal can switch between series and parallel connections, but the software control signal only allows the heated bed load resistors to be changed from a parallel state to a series state. This is because, under normal circumstances, the aforementioned switching module switches the heated bed load resistors to a series state when the input voltage is 220V (high-voltage AC voltage) and to a parallel state when the input voltage is 110V (low-voltage AC voltage). However, during the software control phase, the overall circuit may encounter software malfunctions (e.g., software freezes, control logic problems, etc.), which could lead to situations where the two heated bed load resistors are switched to a parallel state when the input voltage is 220V (high-voltage AC voltage) and switched to a series state when the input voltage is 110V (low-voltage AC voltage). When the input voltage is 220V (AC voltage in the high-voltage zone), switching the two heated bed load resistors to parallel connection can lead to a decrease in overall resistance, potentially increasing the heated bed power by more than four times. This results in a significant increase in heat generation from the heated bed equipment, causing instability in the overall heated bed system. Therefore, to prevent this, this embodiment uses a switching module to switch the series-parallel connection of the heated bed load resistors based on hardware control signals. This prioritizes the use of hardware control signals for control, resulting in higher reliability.

[0068] In some optional embodiments of this disclosure, the first hot bed load resistor 400 and the second hot bed load resistor 500 can be two wire-wound resistors. A middle tap of the wire-wound resistor is led out from the connection point between the two wire-wound resistors. With the middle tap of the wire-wound resistor as the dividing point, the wire-wound resistors on both sides can respectively form the first hot bed load resistor 400 and the second hot bed load resistor 500. At the same time, the size, length, material and other parameters of the wire-wound resistors can be changed according to actual needs to adjust the resistance values ​​of the first hot bed load resistor 400 and the second hot bed load resistor 500.

[0069] In some alternative embodiments of this disclosure, such as Figure 2 As shown, the flicker suppression module 300 includes a first transistor 3002. The on / off control signal is input to the switching module 200 through the first transistor 3002. The first transistor 3002 is used to convert the input voltage at the input terminal of the on / off control signal. Specifically, the base of the first transistor 3002 receives the on / off control signal, its collector is connected to the first input terminal of the switching module 200, and its emitter is grounded. The first transistor is configured such that: when the on / off control signal is low, the first transistor 3002 is off, and the flicker suppression module 300 does not interfere with the operation of the switching module 200, allowing the switching module 200 to maintain a voltage recognition mode; when the on / off control signal is high, the first transistor 3002 is on, outputting a control signal to the switching module 200 through its collector, forcing it to switch to the flicker suppression mode and maintaining the series connection between the first heated bed load resistor 400 and the second heated bed load resistor 500.

[0070] The flicker suppression module 300 also includes a first filtering unit 3001, which consists of a first resistor and a first capacitor connected in parallel. One end of the first resistor is connected to the base of the first transistor 3002, and the other end is grounded. The first resistor is used to stabilize the static level of the base. The first capacitor is connected in parallel across the first resistor and is used to filter out high-frequency interference from the on / off control signal. The base of the first transistor 3002 receives the on / off control signal through the first filtering unit 3001, and after filtering and level stabilization, controls the conduction and cutoff states of the first transistor 3002. The first filtering unit 3001 is mainly used to filter out high-frequency interference signals while allowing low-frequency signals to pass through. It mainly achieves frequency selective attenuation by using the capacitor to bypass high-frequency signals and the resistor to control the path of low-frequency signals. The first resistor stabilizes the cutoff state of the first transistor 3002, and the first capacitor filters out high-frequency noise. Together, they ensure the stability and reliability of the "on / off control signal (Relay_Change)," avoiding abnormal switching of the hot bed power supply due to signal interference or malfunction, thereby suppressing load flicker.

[0071] In some alternative embodiments of this disclosure, such as Figure 3As shown, the heated bed load switching circuit 100 also includes a second transistor 700. The base of the second transistor 700 receives the voltage identification control signal, its collector is connected to the first input terminal of the switching module 200, and its emitter is grounded. The second transistor 700 is used to convert the level of the voltage identification control signal into a control signal adapted to the voltage identification mode of the switching module 200, so as to control the series-parallel switching of the first heated bed load resistor 400 and the second heated bed load resistor 500. The voltage identification control signal is input to the switching module 200 through the second transistor 700. The second transistor 700 is used to perform voltage conversion on the input voltage of the voltage identification control signal input terminal so that the input voltage of the overall circuit, after conversion, can meet the start-up voltage of the switching module 200.

[0072] In the low-voltage region (100-130V), the voltage identification control signal corresponding to the AC signal is high level. The high level is greater than the conduction voltage of the second transistor 700, so the second transistor 700 is turned on, and the control switching module 200 connects the first heated bed load resistor 400 and the second heated bed load resistor 500 in parallel. In the high-voltage region (200-230V), the voltage identification control signal corresponding to the AC signal is low level. The low level is less than the conduction voltage of the second transistor 700, so the second transistor 700 is turned off, and the control switching module 200 connects the first heated bed load resistor 400 and the second heated bed load resistor 500 in series.

[0073] Furthermore, the second transistor 700 may include a second filter unit 600, which consists of a second resistor and a second capacitor connected in parallel. One end of the second resistor is connected to the base of the second transistor 700, and the other end is grounded. The second resistor acts as a pull-down resistor to stabilize the static level of the base. The second capacitor is connected in parallel across the second resistor, acting as a filter capacitor to remove high-frequency noise from the voltage identification control signal. After the voltage identification control signal is filtered and stabilized by the second filter unit 600, it is input to the base of the second transistor 700 to control the conduction and cutoff states of the second transistor 700. The second filter unit 600 is mainly used to filter out high-frequency interference signals in the voltage identification control signal input to the switching module 200, while allowing low-frequency signals to pass through. This frequency-selective attenuation is mainly achieved through the bypassing effect of the capacitor on high-frequency signals and the path control of the resistor on low-frequency signals.

[0074] Specifically, the second transistor 700 can convert the input voltage identification control signal (such as the high-voltage / low-voltage zone detection signal) into the drive level required by the switching module 200 (such as 3.3V→24V). It can also perform signal isolation to prevent high-voltage side noise from interfering with the low-voltage control circuit. At the same time, it can enhance the drive capability and provide sufficient current to drive the relay or solid-state switch. The second filter unit 600 can filter out high-frequency noise, suppress switching noise and EMI interference (such as noise from the input power supply) in the voltage identification control signal. It can also smooth the signal to prevent malfunctions caused by voltage fluctuations (such as misjudgment when the mains voltage drops instantaneously). At the same time, it can enhance robustness and ensure reliable operation in harsh electrical environments.

[0075] In some alternative embodiments of this disclosure, such as Figure 5 As shown, the heated bed load switching circuit 100 also includes an AC switch module 1000, which is connected to the second input terminal of the switching module 200. The AC switch module 1000 receives the heated bed heating control signal and controls the switching module 200's on / off state according to the signal. It connects when the AC switch module 1000's power supply voltage crosses zero. Triggering the signal at the AC voltage zero-crossing point reduces inrush current and electromagnetic interference. In practical applications, the heated bed heating function can be controlled by the heated bed heating control signal. If the circuit is energized, the heated bed will be in a continuous heating state, making it impossible to adjust according to actual needs. Therefore, in this embodiment, controlling the heated bed's on / off state through the AC switch module 1000, and further controlling the on / off state of the double-pole double-throw relay K1, effectively regulates the heating function of the heated bed. It can turn the heated bed on or off according to the characteristics of the heated bed heating control signal and actual application requirements, thereby achieving regulation. In this embodiment, the second input terminal of the switching module 200 refers to the pin of its switching switch (i.e., the first contact group and the second contact group mentioned above).

[0076] Specifically, such as Figure 6As shown, the AC switch module 1000 includes a zero-crossing optocoupler 10001 and a bidirectional thyristor 10002. The bidirectional thyristor 10002 is connected to the second input terminal of the switching module 200. The zero-crossing optocoupler 10001 is used to detect the zero-crossing of the heated bed heating control signal through a current-limiting resistor. When the power supply voltage of the zero-crossing optocoupler 10001 crosses zero, it controls the connection of the bidirectional thyristor 10002, supplying power to the switching module 200 to control its on / off state. The zero-crossing optocoupler 10001 provides a trigger signal for the bidirectional thyristor 10002 at the zero-crossing moment, thereby realizing the switching control of the switching module 200. The zero-crossing optocoupler 10001 is an optocoupler with a built-in zero-crossing detection circuit, used to trigger a signal when the AC voltage crosses zero (Zreo-Crossing), which can reduce inrush current and electromagnetic interference. When the AC voltage approaches 0V, the zero-crossing detection circuit in the zero-crossing optocoupler 10001 triggers the optocoupler output signal, enabling zero-crossing detection and achieving electrical isolation between the low-voltage control terminal (such as an MCU) and the high-voltage AC terminal. This avoids switching capacitive / inductive loads at non-zero-crossing points, reducing current surges and thus reducing switching losses. Switching the load at the AC zero-crossing point protects the equipment and reduces EMI (Electromagnetic Interference, unwanted electromagnetic signals generated or received by electronic equipment during operation that may interfere with the normal operation of other equipment or cause performance degradation).

[0077] Specifically, a triode for alternating current (TRIAC) is a semiconductor switching device that can conduct alternating current in both directions. It can control high voltage and large current with low voltage and small current, and can be triggered to conduct in both the positive and negative half-cycles of the alternating current.

[0078] In some optional embodiments of this disclosure, a fourth resistor 10003 and a fifth resistor 10004 are connected in series between the output terminal of the zero-crossing optocoupler 10001 and the gate of the bidirectional thyristor 10002. The fourth resistor 10003 is used to limit the output current of the zero-crossing optocoupler 10001, which can precisely control the output current of the zero-crossing optocoupler 10001 and limit the output current of the zero-crossing optocoupler 10001 to the safe range of 5-50mA required for triggering the bidirectional thyristor. The resistance value can be 100-500Ω. At the same time, it can also prevent overcurrent damage to the internal phototransistor of the optocoupler and extend the device life. The fifth resistor 10004 is used to suppress the high-frequency oscillation of the gate of the bidirectional thyristor 10002, which can eliminate the gate parasitic oscillation. It forms an RC damping network with the gate capacitance of the bidirectional thyristor to suppress MHz-level high-frequency oscillation, thereby reducing EMI electromagnetic interference. It can reduce radiated noise by 15-20dB (30-100MHz band) and can also provide anti-trigger protection to prevent false triggering and improve anti-interference capability.

[0079] Furthermore, a buffer absorption module 10005 can be provided between the input and output terminals of the bidirectional thyristor 10002 to absorb voltage spikes from the thyristor 10002. For example, the buffer absorption module 10005 can be an RC series filter circuit, which is a passive filter circuit composed of a resistor R and a capacitor C connected in series. By utilizing the low impedance characteristic of the capacitor for high-frequency signals and the high impedance characteristic of the resistor for low-frequency signals, frequency-selective attenuation of the input signal is achieved. Its core principle is series voltage division: signals of different frequencies generate different voltage distributions in the RC series network, thereby filtering out signals within a specific frequency range. The resistor in the RC series filter circuit is typically 51-100Ω (to suppress surge current), and the capacitor is typically 0.1-0.47μF (to absorb energy). Connecting the resistor and capacitor in series can absorb the 500-1000V / μs voltage surge generated during turn-off and limit the voltage change rate across the bidirectional thyristor to a safe range of less than 50V / μs.

[0080] In some alternative embodiments of this disclosure, such as Figure 7 As shown, the heated bed load switching circuit 100 also includes a constant current source 900, which includes a third transistor 9001 and a third resistor 9002. The base of the third transistor 9001 is connected to the input terminal of the heated bed heating control signal, the collector of the third transistor 9001 is connected to a zero-crossing optocoupler 10001, and the emitter of the third transistor 9001 is grounded through the third resistor 9002. By setting the constant current source 900 circuit to drive the zero-crossing optocoupler 10001, it can be ensured that the driving current fluctuation of the zero-crossing optocoupler 10001 is small, and the zero-crossing optocoupler 10001 will not be falsely triggered. For example, the third transistor 9001 can be an NPN transistor. The constant current source 900 can provide a stable output current, unaffected by changes in load resistance or power supply voltage fluctuations, and can provide a stable current to the zero-crossing optocoupler 10001. The constant current source 900 provided in this disclosure includes at least one NPN transistor, utilizing the current amplification characteristics of the transistor and resistive feedback to achieve constant current output. The constant current source 900 circuit based on the NPN transistor is simple, low-cost, and does not require operational amplifiers or application-specific integrated circuits (ICs).

[0081] In some optional embodiments of this disclosure, in order to improve the stability of the heated bed heating control signal, a low-pass filter module 800 is provided between the base of the third transistor 9001 of the constant current source 900 and the input terminal of the heated bed heating control signal. One end of the low-pass filter module 800 is connected to the input terminal of the heated bed heating control signal, and the other end is connected to the base of the third transistor 9001 of the constant current source 900. The heated bed heating control signal is input to the constant current source 900 after being filtered by the low-pass filter module 800. The low-pass filter module 800 can filter out invalid pulse signals when the 3D printing equipment starts up, which can prevent the 3D printing equipment from shaking.

[0082] Furthermore, the constant current source 900 may also include a fourth transistor, the base of which is grounded through a third resistor 9002, the collector is connected between the base of the third transistor 9001 and the input terminal of the heated bed control signal, and the emitter is grounded.

[0083] Low-pass filtering is a signal processing technique used to allow low-frequency signals to pass through while attenuating or filtering out high-frequency signals. The core of the low-pass filter module 800 is the cutoff frequency; signals below the cutoff frequency pass through with minimal attenuation, while signals above the cutoff frequency are significantly attenuated. Low-pass filters based on circuit elements include RC filters, LC filters, and active filters. RC filters consist of resistors and capacitors, LC filters consist of inductors and capacitors (suitable for high-frequency applications), and active filters utilize operational amplifiers to provide gain and steeper roll-off characteristics (such as Butterworth and Chebyshev filters). This disclosure preferably uses an RC filter composed of resistors and capacitors.

[0084] Furthermore, such as Figure 7 As shown, the low-pass filter module 800 is grounded through the pull-down resistor 8001. The first end of the pull-down resistor 8001 is connected to the low-pass filter module 800, and the second end of the pull-down resistor 8001 is grounded. By adding the pull-down resistor 8001, the instantaneous current at the input end of the heated bed heating control signal can be limited, so that the heated bed heating control signal is pulled down by default through the pull-down resistor 8001, thus preventing the heated bed heating function from starting immediately upon power-up of the entire circuit.

[0085] Specifically, the pull-down resistor 8001 ensures the stable state of the circuit node by providing a defined reference potential. When there is no valid control signal input, the pull-down resistor 8001 pulls the signal line potential to a low level, forming a defined initial state. At the moment the circuit is powered on, it effectively absorbs any transient interference pulses that may occur, preventing accidental activation of the heating function due to misinterpretation as a valid signal. In practical applications, adding a pull-down resistor can significantly reduce the false trigger rate; through the current-limiting effect of the resistor (e.g., a resistance value of 5-10kΩ can be selected), the transient current at the input terminal is limited to a safe range (usually less than 1mA), protecting the upstream control circuit; and it provides a clear reference ground for the control signal.

[0086] By fixing the potential at 0V when the signal line is floating, random noise introduced by the floating signal line is avoided. In 3D printing equipment, the pull-down resistor 8001 can prevent power-on jitter, eliminate malfunctions that may occur due to sudden current changes after the equipment is powered on, and achieve EMI protection. It provides a low-impedance discharge path for high-frequency interference and reduces radiated noise. In conjunction with a low-pass filter, it can achieve high-frequency filtering and DC stabilization, with the pull-down resistor 8001 ensuring a stable quiescent potential.

[0087] To enhance understanding, this disclosure also provides a specific implementation scheme in conjunction with a concrete application example, please refer to the example provided. Figure 8 The circuit structure diagram shown is shown.

[0088] The low-pass filter module 800 includes a resistor R8 and a capacitor C54. The first terminal of capacitor C54 is connected to the first terminal of resistor R8, and the second terminal of capacitor C54 is grounded. The second terminal of resistor R8 is connected to the input terminal of the heated bed heating PWM control signal. The first terminal of pull-down resistor R57 is connected to the second terminal of resistor R8, and the second terminal of pull-down resistor R57 is grounded. The heated bed heating PWM control signal is input to the second terminal of resistor R8. The pull-down resistor R57 limits the instantaneous current at the input terminal of the heated bed heating PWM control signal, ensuring that the PWM control signal is pulled down by default through the pull-down resistor R57, preventing false triggering of the heated bed heating function upon power-up.

[0089] In this embodiment, the heated bed heating PWM (Pulse Width Modulation) control signal precisely controls the heating power by adjusting the duty cycle (the ratio of conduction time to period) of the pulse signal, thereby achieving stable temperature control. Heated beds (such as 3D printer heated beds and industrial heating platforms) typically require stable temperature control (error ±1~2℃) and have relatively high power (tens to hundreds of watts). PWM control ensures that the heating element consumes power only when it is on (almost no power consumption when it is off), avoiding the energy waste caused by continuous heating of the element in linear control. High-frequency switching (tens to hundreds of Hz) allows for rapid response to temperature changes, and dynamic balance can be achieved in conjunction with PID control. Furthermore, the heated bed heating PWM control signal can be a digital signal (high and low levels), making it less susceptible to analog noise and resulting in more stable control accuracy. In practical applications, the heated bed heating PWM control signal can be a PWM signal generated by a microcontroller (MCU) and input to the heated bed load switching circuit through its input terminal.

[0090] Furthermore, the first end of resistor R8 is connected to the base of NPN transistor Q1 in the constant current source 900, and the collector of NPN transistor Q1 is connected to pin 2 of zero-crossing optocoupler U2; the emitter of NPN transistor Q1 is grounded through resistor R9. Optionally, the constant current source 900 also includes NPN transistor Q2, the base of which is connected to the emitter of NPN transistor Q1, the collector of which is connected to the constant current source 900, and the emitter of which is grounded. The constant current source 900 can provide a stable output current, unaffected by changes in load resistance or power supply voltage fluctuations, and can provide a stable current to the zero-crossing optocoupler U2.

[0091] A capacitor C7 is connected to pin 1 of the zero-crossing optocoupler U2, pin 4 is connected to the bidirectional thyristor U3, and pin 6 is connected to the bidirectional thyristor U3 through current-limiting resistors R6, R64, and R54. The current-limiting resistors R6, R64, and R54 are connected in series and primarily serve as the current-limiting resistor for the output of the zero-crossing optocoupler U2, and also as the current-limiting resistor for the gate input of the bidirectional thyristor U3. In this embodiment, setting the current-limiting resistors in a series configuration reduces the risk of overheating due to excessively high resistance values ​​in a single resistor.

[0092] Resistors R52 and R53 are connected in parallel between pin 4 of the zero-crossing optocoupler U2 and the bidirectional thyristor U3. The function of resistors R52 and R53 is to prevent the bidirectional thyristor U3 from being falsely triggered.

[0093] A resistor R7 and a capacitor C3 are connected in series between the input and output terminals of the bidirectional thyristor U3. One end of the resistor R7 is connected to the resistor R54, and one end of the capacitor C3 is connected to the switching module 200. The resistor R7 and the capacitor C3 are the aforementioned buffer absorption module 10005, which is used to absorb voltage spikes of the bidirectional thyristor U3.

[0094] The heated bed heating PWM control signal is filtered by a low-pass filter module 800 (R8+C54) to remove invalid pulse signals during 3D printer startup. Then, it is controlled by a constant current source 900 (Q2+Q1+R9) to switch the zero-crossing detection optocoupler U2. The zero-crossing optocoupler U2 then controls the on / off state of the bidirectional thyristor U3. In practical applications, the heating function of the heated bed can be controlled solely by the heated bed heating PWM control signal. If only the constant current source 900 is used to control the power supply, the heated bed will be in a continuous heating state, making it impossible to adjust according to actual needs. Therefore, in this embodiment, a zero-crossing optocoupler U2 and a bidirectional thyristor U3 are added. The zero-crossing optocoupler U2 controls the on / off state of the bidirectional thyristor U3, further controlling the on / off state of the double-pole double-throw relay K1. This effectively regulates the on / off state of the heated bed heating function, allowing the heated bed to be turned on or off based on the characteristics of the heated bed heating PWM control signal and actual application requirements, thereby achieving regulation.

[0095] The six contacts in the double-pole double-throw relay K1 are PIN3, 4, 5, 6, 7, and 8. Among them, PIN4 is connected to the mains live wire through the bidirectional thyristor U3 module, PIN5 is connected to the mains live wire through the bidirectional thyristor U3, PIN6 is connected to pin 1 of the heated bed winding resistor, PIN7 is connected to pins 3 and 4 of the heated bed winding resistor, and PIN8 is connected to the mains neutral wire.

[0096] In this embodiment, the double-pole double-throw relay K1 is controlled by a voltage identification control signal AC_SIG. This voltage identification control signal AC_SIG can detect and analyze the voltage characteristics (such as RMS value, peak value, frequency, phase, etc.) of the AC mains through a front-end voltage identification circuit, and convert it into a processable electrical signal (such as digital quantity, analog quantity, or specific protocol data).

[0097] In this embodiment, the voltage identification control signal AC_SIG can be a specific digital signal. For example, the voltage identification control signal AC_SIG is low when AC input is in the high-voltage zone (200-230V) and high when AC input is in the low-voltage zone (100-130V). According to the characteristics of the selected double-pole double-throw relay K1, when the mains voltage is in the high-voltage zone (200-230V), PIN4-6 and PIN3-7 of the double-pole double-throw relay K1 are turned on respectively. At this time, the input voltage of the mains live wire is input from PIN4 through PIN6 to pin 1 of the heated bed winding resistor and output from the mains neutral wire. The heated bed winding resistors on both sides of the middle tap of the heated bed resistor are in series. When the mains voltage is in the low-voltage zone (100-130V), the double-pole double-throw relay... PIN6-8 and PIN5-7 of K1 are turned on. At this time, the input voltage of the mains live wire is input from PIN5 through PIN7 to pins 3 and 4 of the heated bed winding resistor. The input signal of pin 3 is input to PIN6 through the heated bed winding resistor above the middle tap of the heated bed resistor and pin 1, and output to the mains neutral wire through PIN6 and PIN8. The input signal of pin 4 of the heated bed winding resistor is output to the mains neutral wire through the heated bed winding resistor below the middle tap of the heated bed resistor and pin 2. At this time, the heated bed winding resistors on both sides of the middle tap of the heated bed resistor are in parallel. Because the resistance of the heated bed windings in parallel is smaller than that in series, the heating power of the heated bed is close to the power of the series state of the heated bed winding resistor circuit in the high voltage zone (200-230V).

[0098] Additionally, the Relay_Change on / off control signal only takes effect when the AC_SIG signal is high (i.e., when the input is in the low-voltage zone). After the heated bed has completed full-power heating and entered PID control, the microcontroller can pull the Relay_Change signal high. At this time, the conduction relationship of the double-pole double-throw relay K1 is switched, so that PIN4-6 and PIN3-7 of the double-pole double-throw relay K1 are turned on respectively, thereby switching the heated bed winding resistor to a series state, reducing its operating current, and thus reducing the risk of excessive EMC test flicker. At other times, the Relay_Change signal is pulled low.

[0099] The second transistor 700 includes a third NPN transistor Q9. The second filter unit 600 includes a capacitor C56 and a resistor R56. The capacitor C56 and the resistor R56 are connected in parallel between the resistor R55 and the base of the third NPN transistor Q9. The collector of the third NPN transistor Q9 is connected to the switching module 200, and the emitter of the third NPN transistor Q9 is grounded. The low-pass filter module 800 composed of the resistor R55, the resistor R56, and the capacitor C56 plays a filtering role.

[0100] The flicker suppression module 300 includes a fourth NPN transistor Q10, and the first filter unit 3001 includes a capacitor C57 and a resistor R67. The capacitor C57 and the resistor R67 are connected in parallel between the base of the fourth NPN transistor Q10 and ground. The collector of the fourth NPN transistor Q10 is connected to the output terminal of the resistor R55, and the emitter of the fourth NPN transistor is grounded.

[0101] The flicker suppression module 300 receives the on / off control signal and conducts when the on / off control signal is high, switching the conduction relationship of the switching switch module 200 to change the parallel state of the first hot bed load resistor 400 and the second hot bed load resistor 500 to a series state, thereby reducing the supply current and the risk of flickering during EMC testing. In practical applications, when the voltage identification control signal is high (i.e., when the input voltage is a low-voltage (100-130V) AC signal), the flicker suppression module 300 conducts, controlling the double-pole double-throw relay K1 to switch the parallel state of the first hot bed load resistor 400 and the second hot bed load resistor 500 to a series state.

[0102] In this embodiment, the voltage identification control signal AC_SIG can be a hardware control signal, and the on / off control signal Relay_Change can be a software control signal. The hardware control signal has a higher priority than the software control signal. The hardware control signal can be used to switch the series and parallel relationship of the hot bed winding resistors AC and CB, but the software control signal only allows the hot bed load resistors to be changed from parallel to series.

[0103] This disclosure also provides a 3D printing device, which mainly includes a heated bed and a heated bed load switching circuit 100. The heated bed is one of the most important components in a 3D printer, mainly used to maintain the temperature stability of the printing platform (build plate) during the printing process. It solves problems such as model warping and detachment caused by uneven material cooling by heating uniformly, significantly improving printing success rate and quality. The heated bed load switching circuit 100 is mainly used to switch the series and parallel connection relationship of the load resistors of the heated bed. In practical applications, the heated bed load switching circuit 100 described in any of the above embodiments can be used.

[0104] In some optional embodiments of this disclosure, the heated bed load switching circuit 100 may include a switching module 200, a first heated bed load resistor 400, and a second heated bed load resistor 500. The switching module 200 switches the conduction relationship of the first heated bed load resistor 400 and the second heated bed load resistor 500 according to the input voltage identification control signal, thereby switching the series or parallel connection relationship of the first heated bed load resistor 400 and the second heated bed load resistor 500. For example, when the voltage identification control signal is high, the switching module 200 switches the first heated bed load resistor 400 and the second heated bed load resistor 500 to parallel connection; when the voltage identification control signal is low, the switching module 200 switches the first heated bed load resistor 400 and the second heated bed load resistor 500 to series connection. Because the resistance value of the heated bed load resistors in parallel is smaller than that in series connection, the heating power of the heated bed is close to the power in the high-pressure zone (200-230V) when the heated bed load resistors are in series connection. When the switching module receives the voltage identification control signal, if the voltage identification control signal is high, the first hot bed load resistor is connected in parallel; if the voltage identification control signal is low, the first hot bed load resistor is connected in series, thereby realizing automatic control of the series and parallel connection of the first and second hot bed load resistors.

[0105] Furthermore, when the on / off control signal is at the first level, the switching module 200 is in voltage recognition mode, controlling the connection method of the first hot bed load resistor and the second hot bed load resistor according to the high and low voltage corresponding to the voltage recognition control signal; when the on / off control signal is at the second level, the switching module 200 is in flicker suppression mode, forcibly connecting the first hot bed load resistor and the second hot bed load resistor in series, reducing their operating current, thereby reducing the risk of excessive flicker in EMC testing.

[0106] In the above implementation, when the on / off control signal is at the first level, the switching module is in voltage recognition mode, controlling the connection method of the first and second heated bed load resistors according to the high or low voltage corresponding to the voltage recognition control signal. When the on / off control signal is at the second level, the switching module is in flicker suppression mode, forcibly connecting the first and second heated bed load resistors in series. When the first and second heated bed load resistors are connected in parallel, the supply current may be too large. When the on / off control signal is at the second level, the flicker suppression module is turned on, forcibly switching the first and second heated bed load resistors from parallel mode to series mode to reduce the supply current, thereby suppressing flickering problems in electromagnetic compatibility testing, reducing safety risks, and improving the overall circuit safety.

[0107] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments thereof. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not claimed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

Claims

1. A hot bed load switching circuit, characterized by, include: Flicker suppression module, switching module, first heated bed load resistor and second heated bed load resistor; The input terminal of the flicker suppression module is electrically connected to the heated bed main control unit, and the output terminal of the flicker suppression module is connected to the first input terminal of the switching module. The flicker suppression module is used to receive the on / off control signal sent by the heated bed main control unit and control the working mode of the switching module according to the level state of the on / off control signal. The second input terminal of the switching module is electrically connected to the heated bed power supply unit and is used to receive the voltage identification control signal issued by the heated bed power supply unit. The two output terminals of the switching module are respectively connected to the first heated bed load resistor and the second heated bed load resistor. When the on / off control signal is at the first level, the flicker suppression module is used to put the switching module in voltage recognition mode, and the switching module is used to control the connection mode of the first hot bed load resistor and the second hot bed load resistor according to the high and low voltage corresponding to the voltage recognition control signal. When the on / off control signal is at the second level, the flicker suppression module is used to put the switching module in flicker suppression mode, and the switching module is used to force the first hot bed load resistor and the second hot bed load resistor to be connected in series.

2. The hot bed load switch circuit of claim 1, wherein, The switching module is in voltage recognition mode, wherein, The voltage identification control signal corresponds to a low voltage, and the switching module connects the first heated bed load resistor and the second heated bed load resistor in parallel; or, The voltage identification control signal corresponds to a high voltage, and the switching module connects the first heated bed load resistor and the second heated bed load resistor in series.

3. The hot bed load switch circuit of claim 1, wherein, The switching module is a dual-channel relay, which includes a first contact group and a second contact group. The first contact group includes a first contact, a second contact, and a third contact. The first contact is connected to the first end of the first heated bed load resistor; the second contact is connected to the center tap between the first heated bed load resistor and the second heated bed load resistor; and the third contact is connected to the power input terminal. The second contact group includes a fourth contact, a fifth contact, and a sixth contact. The fourth contact is connected to the first end of the second heated bed load resistor; the fifth contact is connected to the intermediate tap; and the sixth contact is connected to the power input terminal. When the first contact is connected to the second contact and the fourth contact is connected to the fifth contact, the first heated bed load resistor and the second heated bed load resistor are connected in series; when the second contact is connected to the third contact and the fifth contact is connected to the sixth contact, the first heated bed load resistor and the second heated bed load resistor are connected in parallel.

4. The hot bed load switch circuit of claim 1, wherein, When in the voltage recognition mode, the on / off control signal is at the first level, and the flicker suppression module is not turned on; When in the flicker suppression mode, the on / off control signal is at the second level, and the flicker suppression module is turned on to switch the conduction relationship of the switching module.

5. The hot bed load switching circuit of claim 4, wherein, The on / off control signal remains at the first level; when the voltage identification control signal corresponds to a low voltage and enters the proportional-integral-derivative control stage, the on / off control signal is pulled high to the second level, the flicker suppression module is turned on, so as to switch the conduction relationship of the switching module and force the first hot bed load resistor and the second hot bed load resistor to be connected in series.

6. The heated bed load switching circuit according to claim 1, characterized in that, The flicker suppression module includes: a first transistor, whose base receives an on / off control signal, whose collector is connected to the first input terminal of the switching module, and whose emitter is grounded; the first transistor is configured as follows: When the on / off control signal is low, the first transistor is cut off, and the flicker suppression module does not interfere with the working state of the switching module, so that the switching module maintains the voltage recognition mode. When the on / off control signal is high, the first transistor is turned on, and the control signal is output to the switching module through the collector, forcing it to switch to the flicker suppression mode and keeping the first heated bed load resistor and the second heated bed load resistor connected in series.

7. The hot bed load switching circuit of claim 6, wherein, The flicker suppression module further includes: a first filter unit composed of a first resistor and a first capacitor connected in parallel; One end of the first resistor is connected to the base of the first transistor, and the other end of the first resistor is grounded. The first resistor is used to stabilize the static level of the base. The first capacitor is connected in parallel across the two ends of the first resistor, and the first capacitor is used to filter out high-frequency interference from the on / off control signal; wherein, The base of the first transistor receives the on / off control signal through the first filter unit, and after filtering and level stabilization, controls the on / off state of the first transistor.

8. The heated bed load switching circuit according to claim 6, characterized in that, Also includes: Second transistor, The base of the second transistor receives the voltage identification control signal, the collector of the second transistor is connected to the second input terminal of the switching module, and the emitter of the second transistor is grounded. The second transistor is used to convert the voltage identification control signal into a control signal adapted to the voltage identification mode of the switching module, so as to control the series-parallel switching of the first heated bed load resistor and the second heated bed load resistor.

9. The hot bed load switch circuit of claim 8, wherein, The system also includes a second filter unit consisting of a second resistor and a second capacitor connected in parallel. One end of the second resistor is connected to the base of the second transistor, and the other end of the second resistor is grounded. The second resistor is used to stabilize the static level of the base. The second capacitor is connected in parallel across the two ends of the second resistor as a filter capacitor to filter out high-frequency noise in the voltage identification control signal; The voltage identification control signal is filtered and stabilized by the second filtering unit in sequence, and then input to the base of the second transistor to control the conduction and cutoff states of the second transistor.

10. The hot bed load switch circuit of claim 1, wherein, Also includes: An AC switch module, connected to the second input terminal of the switching switch module, is used to receive the heated bed heating control signal, control the switching switch module to open or close according to the heated bed heating control signal, and connect when the power supply voltage of the AC switch module crosses zero.

11. The hot bed load switch circuit of claim 10, wherein, The AC switching module includes: a zero-crossing optocoupler and a bidirectional thyristor. The zero-crossing optocoupler is used to detect the zero-crossing of the heated bed heating control signal through a current-limiting resistor. When the power supply voltage of the zero-crossing optocoupler crosses zero, it controls the connection of the bidirectional thyristor to supply power to the switching module and control the switching of the switching module.

12. The hot bed load switch circuit of claim 11, wherein, Also includes: A constant current source is provided, comprising a third transistor and a third resistor. The base of the third transistor is connected to the input terminal of the heated bed heating control signal, the collector of the third transistor is connected to the zero-crossing optocoupler, and the emitter of the third transistor is grounded through the third resistor. The constant current source is used to eliminate current fluctuations in the drive current of the zero-crossing optocoupler.

13. The hot bed load switch circuit of claim 12, wherein, Also includes: A low-pass filter module is provided, with one end connected to the input terminal of the heated bed heating control signal and the other end connected to the constant current source. The heated bed heating control signal is filtered by the low-pass filter module and then input to the constant current source.

14. The heated bed load switching circuit according to claim 13, characterized in that, Also includes: A pull-down resistor is provided, with its first end connected to the low-pass filter module and its second end grounded. The pull-down resistor is used to limit the instantaneous current at the input of the heated bed control signal.

15. A 3D printing device, characterized by include: Printing heated bed; as well as The heated bed load switching circuit according to any one of claims 1-14.

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