Power supply regulator circuit for laser printer heater and regulating method

Abstract

The application discloses a power regulator circuit and a regulating method for a laser printer heater, and comprises a rectifier module, an AC input end of the rectifier module is connected with an AC power supply, a DC output end of the rectifier module is connected with a heater, an inductor, a drain and a source of a MOSFET and a first resistor in sequence to form a closed first loop, one end of the inductor is connected with a first end of the heater, the other end of the inductor is connected with the drain of the MOSFET and an anode of a first diode respectively, a cathode of the first diode is connected with a second end of the heater, a gate of the MOSFET is connected with a control circuit, the control circuit collects voltages output by the rectifier module and voltages between the first resistor, compares the voltages after processing, selects a higher voltage, and uses the voltage to generate a driving pulse signal for driving the MOSFET to open and close, and the application adjusts a duty ratio of a conduction time of the MOSFET, automatically adjusts a current in the heater and voltages between the heater, and adjusts an electric power input into the heater.

Description

Technical Field

[0001] This invention relates to the field of power supply circuit technology, and in particular to a power regulator circuit and regulation method for a laser printer heater. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] The final step in a laser printer's printing process is "fixing," which involves heating the paper to fuse the toner, text, or image onto the paper. Early printers often used tungsten filament lamps as heaters, while newer printers mostly use PTC (positive temperature coefficient) ceramic heaters to achieve higher printing speeds and efficiency.

[0004] PTC heaters have very low resistance at room temperature, but their resistance increases rapidly once the temperature reaches a certain value. They offer advantages such as rapid heating and automatic temperature limiting when heating at a fixed voltage. Because printers operate over a wide voltage range, PTC heaters must also be adaptable to different operating voltages.

[0005] Currently, PTC heaters perform well at a nominal voltage of 115V, but when operating at a nominal voltage of 230V, they suffer from problems such as excessive inrush current, rapid temperature rise, and frequent triggering of over-temperature protection, which seriously affects printing speed. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes a power regulator circuit and adjustment method for a laser printer heater, which can automatically adjust the operating voltage and heating power of the PTC heater according to the mains voltage level, enabling the PTC heater to operate well even under higher mains voltages (e.g., 264V).

[0007] In some implementations, the following technical solutions are adopted:

[0008] A power regulator circuit for a laser printer heater includes: a rectifier module, the AC input terminal of which is connected to an AC power source, and the DC output terminal of which is connected in series with a heater, an inductor, the drain and source of a MOSFET, and a first resistor to form a closed first circuit; one end of the inductor is connected to the first end of the heater, and the other end of the inductor is connected to the drain of the MOSFET and the anode of a first diode, respectively, and the cathode of the first diode is connected to the second end of the heater;

[0009] MOSFET gate connection control circuit;

[0010] The control circuit collects the voltage output from the rectifier module and the voltage across the first resistor, processes and compares them, and selects the higher voltage to generate a drive pulse signal to drive the MOSFET to turn on and off. By adjusting the duty cycle of the MOSFET's conduction time, the current in the heater and the voltage across the heater are automatically adjusted, thereby regulating the electrical power supplied to the heater.

[0011] When the MOSFET is turned on, the first circuit is connected, and AC power is supplied to the heater and inductor. Part of the energy is consumed by the heater, and the other part is stored in the inductor.

[0012] When the MOSFET is turned off, the AC power supply is cut off, and the energy stored in the inductor is sent to the heater through the first diode.

[0013] The control circuit includes: a voltage sampling unit, a proportional amplifier unit, and a voltage selection unit connected in sequence; a current sampling unit connected to an integral amplifier unit and then connected to the voltage selection unit; the output of the voltage selection unit connected in sequence to a PWM modulation unit and a driving unit; and the output of the driving unit connected to a MOSFET.

[0014] The voltage sampling unit is connected to the DC output terminal of the rectifier module and is used to collect the pulsating DC voltage output by the rectifier module, convert it into a DC voltage proportional to its peak or average value, and then adjust the converted DC voltage to a DC voltage suitable for the control circuit.

[0015] The voltage sampling unit includes:

[0016] The first input terminal of the voltage sampling unit is connected in sequence to the second diode, the fourth resistor, the first capacitor, and the second input terminal of the voltage sampling unit; one end of the fifth resistor is connected between the fourth resistor and the first capacitor, and the other end is connected to the cathode of the Zener diode. The anode of the Zener diode is connected to the output terminal of the voltage sampling unit. A sixth resistor is connected between the second input terminal and the output terminal of the voltage sampling unit.

[0017] The current sampling unit is connected across the first resistor and is used to collect the voltage across the first resistor. The voltage is a high-frequency pulse voltage that is proportional to the first loop current. The integrating amplification unit is used to integrate and amplify the difference between the high-frequency pulse voltage and the reference voltage to obtain an integrated DC voltage that is related to the average value of the first loop current.

[0018] The voltage selection unit includes:

[0019] The first input terminal of the voltage selection unit is connected to the anode of the third diode, the second input terminal of the voltage selection unit is connected to the anode of the fourth diode, and the cathodes of both the third and fourth diodes are connected to the output terminal of the voltage selection unit; one end of the seventh resistor is connected to the output terminal of the voltage selection unit, and the other end is connected to the zero potential reference point.

[0020] In another implementation, the control circuit includes a PWM power management chip, a voltage sampling unit, and a drive unit;

[0021] The voltage sampling unit is connected to the DC output terminal of the rectifier module and is used to collect the pulsating DC voltage output by the rectifier module, convert it into a DC voltage proportional to its peak or average value, and then adjust the converted DC voltage to a DC voltage suitable for the control circuit.

[0022] The output of the voltage sampling unit is connected to the PWM power management chip. The PWM power management chip receives the voltage output by the voltage sampling unit and simultaneously acquires the voltage across the first resistor. After comparing the two voltages, the higher voltage is selected to generate the drive pulse signal for driving the MOSFET to turn on and off.

[0023] The output of the PWM power management chip is connected to the drive unit, and the output of the drive unit is connected to the MOSFET.

[0024] In other embodiments, the following technical solutions are adopted:

[0025] A method for regulating a power regulator circuit for a laser printer heater, comprising:

[0026] The input AC power is converted into a pulsating DC voltage; the peak or average value of the pulsating DC voltage is collected, and it is filtered and divided into a DC control voltage suitable for the control circuit and capable of reflecting the level of the pulsating DC voltage; the DC control voltage is proportionally amplified to obtain the first voltage;

[0027] A high-frequency pulse voltage that is proportional to the high-frequency pulse current in the first circuit is collected on the first resistor. The difference between the high-frequency pulse voltage and the reference voltage is integrated and amplified to obtain a second voltage that reflects the average value of the high-frequency pulse voltage.

[0028] The magnitudes of the first voltage and the second voltage are compared, and the higher one is selected for PWM modulation to obtain a drive pulse with a duty cycle related to the input power supply and high-frequency pulse current, which drives the MOSFET to turn on and off. By adjusting the duty cycle of the MOSFET's on-time, the current in the heater and the voltage across the heater are automatically adjusted, thereby regulating the electrical power supplied to the heater.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] (1) The power regulator circuit for laser printer heater of the present invention collects the voltage output by the rectifier module and the voltage across the first resistor, processes them, selects the higher voltage for PWM modulation, and can automatically adjust the working voltage and heating power of the PTC heater according to the power supply voltage, so that the PTC heater can work well even under mains voltage up to 264V.

[0031] (2) The present invention obtains the current information in the PTC heater by detecting the voltage across the first resistor. The control circuit adjusts the duty cycle of the MOSFET according to the detection result. If the current is too large, the duty cycle is reduced. This can effectively limit the starting current of the PTC heater and prevent EMC (electromagnetic compatibility) problems, device damage, and reduced service life caused by excessive starting surge current.

[0032] (3) The circuit structure of the present invention is simple, easy to implement, low in cost and small in size. It is not only suitable for new printers, but also for upgrading and transforming existing printers. It is stable and reliable in operation, with low power consumption and high efficiency.

[0033] (4) The present invention enables the PTC heater to work well in the full voltage range of 90V-264V. Moreover, under steady state, the duty cycle of the MOSFET in each mains cycle is basically constant. Thus, after filtering out high frequency ripple, the input current is a sine wave in phase with the mains voltage, and the input power factor is greater than 0.99, which will not cause harmonic interference to the mains.

[0034] Other features and advantages of the invention 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 the invention. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the power regulator circuit for the laser printer heater in Embodiment 1 of the present invention;

[0036] Figure 2 This is a schematic diagram of the voltage sampling unit structure in Embodiment 1 of the present invention;

[0037] Figure 3 This is a schematic diagram of the voltage selection unit structure in Embodiment 1 of the present invention;

[0038] Figure 4 This is a schematic diagram of the power regulator circuit for the laser printer heater in Embodiment 2 of the present invention.

[0039] The components include: 1. Rectifier module, 2. Heater, 3. Inductor, 4. First diode, 5. MOSFET, 6. First resistor, 7. Second resistor, 8. Third resistor, 9. Operating power supply, 10. Voltage sampling unit, 11. Proportional amplifier unit, 12. Current sampling unit, 13. Reference voltage unit, 14. Integral amplifier unit, 15. Voltage selection unit, 16. PWM modulation unit, and 17. Drive unit.

[0040] 101. Second diode; 102. Fourth resistor; 103. First capacitor; 104. Fifth resistor; 105. Zener diode; 106. Sixth resistor; 151. Third diode; 152. Fourth diode; 153. Seventh resistor;

[0041] 18. TL494 chip, 19. Second capacitor, 20. Eighth resistor, 21. Ninth resistor, 22. Tenth resistor, 23. Eleventh resistor, 24. Third capacitor, 25. Twelfth resistor. Detailed Implementation

[0042] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0043] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0044] Example 1

[0045] In one or more embodiments, a power regulator circuit for a laser printer heater is disclosed, combined with Figure 1 Specifically, it includes: rectifier module 1, heater 2, inductor 3, first diode 4, MOSFET (insulated gate field effect transistor) 5, first resistor 6, second resistor 7, third resistor 8, and control circuit.

[0046] The rectifier module 1 is a rectifier bridge. Its two AC input terminals are connected to an AC power source (e.g., mains power). The DC (DC+) output terminal of the rectifier bridge is connected to the second terminal of heater 2. The first terminal of heater 2 is connected to the first terminal of inductor 3. The second terminal of inductor 3 is connected to the drain of MOSFET 5 and to the anode of the first diode 4. The cathode of the first diode 4 is connected to the second terminal of heater 2. The source of MOSFET 5 is connected to the first terminal of the first resistor 6. The second terminal of the first resistor 6 is connected to the DC- terminal of the rectifier bridge and to the zero-potential reference point GND. The gate of MOSFET 5 is connected to the first terminal of the second resistor 7, which is connected to the control circuit. A third resistor 8 is connected between the gate and source of MOSFET 5. The second resistor, generally called the drive resistor, regulates the drive speed and suppresses parasitic high-frequency oscillations in the drive circuit. The third resistor prevents the MOSFET gate from being floating and maintains the MOSFET gate's electrostatic grounding.

[0047] The power regulator circuit for the laser printer heater in this embodiment includes three main circuits:

[0048] (1) An input circuit consisting of AC mains power and the AC input terminal of a rectifier bridge;

[0049] (2) A first circuit is formed by connecting the DC output terminal of the rectifier, the two ends of the heater, the inductor, the drain and source of the MOSFET, and the first resistor in series and closing the circuit.

[0050] (3) A freewheeling circuit consisting of a first diode, an inductor and a heater connected in series and closed.

[0051] The first circuit is a controlled circuit. When the MOSFET is turned on, the first circuit is connected, and the power energy is sent to the heater and the inductor. Part of the energy is consumed by the heater, and the other part is stored in the inductor, causing the inductor current to rise. When the MOSFET is turned off, the power energy is cut off, and the energy stored in the inductor is sent to the heater through the first diode, causing the inductor current to drop. By adjusting the duty cycle of the MOSFET's on-time, the current in the heater and the voltage across the heater can be adjusted, so that the power supplied to the heater can be controlled.

[0052] The switching on and off of a MOSFET is controlled by a control circuit; combined with Figure 1 The control circuit structure of this embodiment specifically includes: a working power supply 9, a voltage sampling unit 10, a proportional amplifier unit 11, a current sampling unit 12, a reference voltage unit 13, an integral amplifier unit 14, a voltage selection unit 15, a PWM modulation unit 16, and a drive unit 17.

[0053] The operating power supply 9 supplies power to each functional unit; the first input terminal of the voltage sampling unit 10 is connected to the DC+ output terminal of the rectifier bridge, the second input terminal of the voltage sampling unit 10 is connected to the DC- output terminal of the rectifier bridge, the output terminal of the voltage sampling unit 10 is connected to the input terminal of the proportional amplifier unit 11, and the output terminal of the proportional amplifier unit 11 is connected to the first input terminal of the voltage selection unit 15; the two input terminals of the current sampling unit 12 are respectively connected to the two ends of the first resistor 6, the output terminal of the current sampling unit 12 is connected to the input terminal of the integrating amplifier unit 14, the integrating amplifier unit 14 is also connected to the reference voltage unit 13, and the output terminal of the integrating amplifier unit 14 is connected to the second input terminal of the voltage selection unit 15; the output terminal of the voltage selection unit 15 is connected to the input terminal of the PWM modulation unit 16, the output terminal of the PWM modulation unit 16 is connected to the input terminal of the drive unit 17, and the output terminal of the drive unit 17 is connected to the second end of the second resistor 7.

[0054] The voltage sampling unit 10 converts the pulsating DC voltage output by the rectifier bridge into a DC voltage proportional to its peak or average value, and obtains a low-voltage DC voltage suitable for the control circuit through voltage division; the proportional amplifier unit further adjusts the DC voltage sent by the voltage sampling unit and makes it have sufficient driving capability to meet the requirements of subsequent circuits.

[0055] The current sampling unit 12 collects the high-frequency pulse voltage across the first resistor, which is proportional to the chopper circuit current, and sends it to the integration amplification unit 14. The integration amplification unit 14 integrates and amplifies the difference between the high-frequency pulse voltage and the reference voltage to obtain an integrated DC voltage related to the average value of the first circuit current, and sends it to the voltage selection unit 15.

[0056] The voltage selection unit 15 compares the voltages at its two input terminals and selects the higher voltage to be sent to the PWM modulation unit 16 through its output terminal. The PWM modulation unit 16 has a triangular wave (or sawtooth wave) generator. The PWM modulation unit 16 compares the DC voltage at its input terminal with the triangular wave voltage. When the triangular wave voltage is higher than the input DC voltage, it outputs a high level, and vice versa. Thus, the DC voltage is modulated by the PWM modulation unit and converted into a drive pulse with a duty cycle that varies with the DC voltage. The lower the DC voltage, the larger the duty cycle of the drive pulse, and vice versa. The PWM modulation unit sends the drive pulse to the drive unit 17, which amplifies it and drives the MOSFET.

[0057] In this embodiment, the two voltages collected by the current sampling unit 12 and the voltage selection unit 15 reflect the high and low mains voltage and the current flowing through the PTC heater, respectively. Through processing, the DC voltages related to the two are obtained. The control circuit adjusts the duty cycle of the MOSFET conduction time based on the DC voltage to ensure that the PTC heater obtains appropriate heating power.

[0058] Combination Figure 2 The voltage sampling unit 10 includes a second diode 101, a fourth resistor 102, a first capacitor 103, a fifth resistor 104, a Zener diode 105, and a sixth resistor 106. The anode of the second diode 101 is connected to the first input terminal of the voltage sampling unit. The cathode of the second diode 101 is connected in series with the fourth resistor 102 and then to the first terminal of the first capacitor 103, and is also connected to the first terminal of the fifth resistor 104. The second terminal of the fifth resistor 104 is connected to the cathode of the Zener diode 105. The anode of the Zener diode 105 is connected to the first terminal of the sixth resistor 106 and is also connected to the output terminal of the voltage sampling unit. The other end of the first capacitor 103 is connected to the second terminal of the sixth resistor 106 and is also connected to the second input terminal of the voltage sampling unit.

[0059] In a specific implementation, the fourth resistor has a resistance of tens of ohms, while the fifth resistor has a resistance of hundreds of kilohms. When the rectifier output pulsating DC reaches its peak, the first capacitor is rapidly charged to the peak value of the DC pulsating voltage and drops very little before the next voltage peak arrives. The voltage of the first capacitor is output from the output terminal of the voltage sampling unit after being divided by the fifth resistor, the Zener diode, and the sixth resistor. This output voltage is a low-voltage DC voltage suitable for the control circuit requirements.

[0060] Combination Figure 3 The voltage selection unit 15 includes a third diode 151, a fourth diode 152, and a seventh resistor 153. The anodes of the two diodes 151 and 152 are respectively connected to the two input terminals of the voltage selection unit. The cathodes of the two diodes 151 and 152 are both connected to the first terminal of the seventh resistor 153 and to the output terminal of the voltage selection unit. The second terminal of the seventh resistor 153 is connected to the zero potential reference point GND.

[0061] Due to the unidirectional conductivity of diodes, the diode connected to the higher voltage input terminal is forward-biased and the diode connected to the lower input terminal is reverse-biased and cut off. Therefore, if the forward voltage drop of the diode is ignored, the output voltage of the voltage selection unit is always equal to the voltage at the higher voltage input terminal.

[0062] In this embodiment, the functional units such as the working power supply 9, the proportional amplifier unit 11, the current sampling unit 12, the reference voltage unit 13, the integral amplifier unit 14, the PWM modulation unit 16, and the drive unit 17 are all implemented using known technologies.

[0063] Example 2

[0064] In one or more embodiments, a power regulator circuit for a laser printer heater is disclosed, combined with Figure 4 Specifically, it includes: rectifier module 1, heater 2, inductor 3, first diode 4, MOSFET (insulated gate field effect transistor) 5, first resistor 6, second resistor 7, third resistor 8, and control circuit.

[0065] The difference between this embodiment and Embodiment 1 is that the control circuit of this embodiment includes a working power supply 9, a voltage sampling unit 10, a driving unit 17, a PWM power management chip, a second capacitor 19, an eighth resistor 20, a ninth resistor 21, a tenth resistor 22, an eleventh resistor 23, a third capacitor 24, and a twelfth resistor 25.

[0066] The structure and function of the voltage sampling unit and the driving unit can be the same as in Embodiment 1.

[0067] The PWM power management chip selected is the TL494 chip 18; the two error amplifiers in the TL494 chip constitute the proportional amplifier unit and the integral amplifier unit respectively, the two diodes in the chip and a constant current source constitute the voltage selection unit, the PWM modulation circuit in the chip constitutes the PWM modulation unit in the technical solution, and the reference voltage circuit in the chip constitutes the reference voltage unit in this technical solution, thereby simplifying the control circuit.

[0068] Specifically, the output terminal of the voltage sampling unit 10 is connected to pin (1) of the TL494 chip 18, pins (2) and (3) of the TL494 chip 18 are connected together, pin (4) of the chip is connected to GND, pin (5) of the chip is connected to the first end of the second capacitor 19, the second end of the second capacitor 19 is connected to GND, pin (6) of the chip is connected to the first end of the eighth resistor 20, the second end of the eighth resistor 20 is connected to GND; the second capacitor 19 is the timing capacitor of the sawtooth wave oscillator in the PWM power management chip, and the eighth resistor 20 is the timing resistor of the oscillator. The two determine the oscillation frequency of the sawtooth wave.

[0069] Pin (7) of the chip is connected to GND, pin (8) of the chip is connected to the working power supply VCC, pins (9) and (10) of the chip are connected together and connected to the input terminal of the drive unit 17, pins (11) and (12) of the chip are both connected to VCC, pin (13) of the chip is connected to GND, pin (14) of the chip is the reference voltage output terminal, connected to the first end of the ninth resistor 21, the second end of the ninth resistor 21 is connected to pin (15) of the chip and connected to the first end of the tenth resistor 22, the second end of the tenth resistor 22 is connected to GND, pin (16) of the chip is connected to the first end of the eleventh resistor 23, the second end of the eleventh resistor 23 is connected to the first end of the first resistor 6, and the third capacitor 24 and the twelfth resistor 25 are connected in parallel and then connected across pins (3) and (15) of the chip.

[0070] The ninth resistor 21 and the tenth resistor 22 form a reference voltage divider circuit, and at the same time, together with the operational amplifiers corresponding to pins (15), (16) and (3) in the chip, they form an integrating amplifier. The third capacitor 24 is an integrating capacitor, the twelfth resistor 25 is a DC operating point stabilizing resistor, and the eleventh resistor 23 forms the simplest current detection unit.

[0071] The driving unit 17 includes an NPN transistor, a PNP transistor, and two resistors, which are connected in a typical complementary push-pull driving circuit.

[0072] The circuit structure of this embodiment is simple, easy to implement, low in cost, and small in size. It is suitable not only for new printers but also for upgrading and retrofitting existing mass-produced printers.

[0073] Example 3

[0074] In one or more embodiments, a control method for a power regulator circuit for a laser printer heater is disclosed, specifically including the following process:

[0075] (1) According to Figures 1 to 3 Connecting circuits or according to Figure 4 Connect the circuits to form a power regulator system;

[0076] (2) The input AC power is rectified into a pulsating DC voltage by the rectifier bridge;

[0077] (3) The peak or average value of the pulsating DC voltage is collected by the voltage sampling unit, and then filtered and divided into a low-voltage DC control voltage that is suitable for the control circuit and can reflect the high or low level of the pulsating DC voltage.

[0078] (4) The DC control voltage output by the voltage sampling unit is further adjusted by the proportional amplifier unit and given sufficient driving capability;

[0079] (5) The high-frequency pulse voltage on the first resistor, which is proportional to the high-frequency pulse current in the high-frequency chopper circuit, is detected by the current detection unit and sent to the integration and amplification unit.

[0080] (6) A reference voltage is generated by the reference voltage unit and sent to the integrating amplifier unit;

[0081] (7) The difference between the high-frequency pulse voltage and the reference voltage is integrated and amplified by the integrating amplifier unit to obtain a DC voltage output that reflects the average value of the high-frequency pulse voltage. When the average value of the high-frequency pulse voltage is greater than the reference voltage, the DC voltage output by the integrating amplifier rises. Conversely, when the average value of the high-frequency pulse voltage is less than the reference voltage, the DC voltage output by the integrating amplifier falls. The output voltage of the integrating amplifier is sent to the voltage selection unit through its output terminal.

[0082] (8) The voltage selection unit compares the DC voltage at its two input terminals and selects the higher one to send to the PWM modulation unit through the output terminal;

[0083] (9) The input DC voltage is modulated by the PWM modulation unit to obtain a drive pulse whose duty cycle is related to the mains voltage and the high-frequency pulse current of the high-frequency chopper circuit. The modulation direction is: the higher the input DC voltage, the smaller the duty cycle of the drive pulse.

[0084] (10) The drive pulse output by the PWM modulation unit is sent to the drive unit for amplification and then drives the MOSFET to turn on and off. When the input mains voltage increases or the high-frequency pulse current sent to the heater is too large, the MOSFET’s duty cycle is automatically reduced, thereby realizing automatic adjustment of the input power of the heater.

[0085] Using the technical solution disclosed in this embodiment, when the mains voltage is high, the MOSFET drive pulse is narrower and the MOSFET conduction time is shorter; conversely, when the mains voltage is low, the drive pulse is wider and the MOSFET conduction time is longer. With appropriate parameter matching, the electric power obtained by the heater can be basically unaffected by changes in the mains voltage. On the other hand, the heater resistor has PTC (positive temperature coefficient) characteristics. Its resistance is very small when cold, resulting in a large starting current. When the current detection unit detects an excessive current, it will cause the output voltage of the integrating amplifier to rise rapidly. When the current exceeds the limit value, the output voltage of the integrating amplifier will be higher than the output voltage of the proportional amplifier, thereby the voltage selection unit outputs a higher voltage, the duty cycle of the drive pulse decreases, and the heater current is limited.

[0086] The method in this embodiment can automatically adjust the operating voltage and heating power of the PTC heater according to the mains voltage, so that the PTC heater can work well even under mains voltages as high as 264V.

[0087] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A power regulator circuit for a laser printer heater, characterized in that, include: The rectifier module has its AC input terminal connected to an AC power source, and its DC output terminal connected in series with a heater, an inductor, the drain and source of a MOSFET, and a first resistor to form a closed first loop. One end of the inductor is connected to the first end of the heater, and the other end of the inductor is connected to the drain of the MOSFET and the anode of a first diode. The cathode of the first diode is connected to the second end of the heater. The gate of the MOSFET is connected to a control circuit. The control circuit collects the voltage output from the rectifier module and the voltage across the first resistor, processes and compares them, and selects the one with the higher voltage to generate the drive pulse signal to drive the MOSFET to turn on and off. By adjusting the duty cycle of the MOSFET's on-time, the current in the heater and the voltage across the heater are automatically adjusted, thereby regulating the electrical power supplied to the heater. The control circuit includes: a voltage sampling unit, a proportional amplifier unit, and a voltage selection unit connected in sequence; a current sampling unit connected to an integral amplifier unit and then connected to the voltage selection unit; the output of the voltage selection unit connected in sequence to a PWM modulation unit and a driving unit; and the output of the driving unit connected to a MOSFET. The current sampling unit is connected across the first resistor to collect the voltage across the first resistor. The voltage is a high-frequency pulse voltage that is proportional to the first loop current. The integrating amplification unit is used to integrate and amplify the difference between the high-frequency pulse voltage and the reference voltage to obtain an integrated DC voltage related to the average value of the first loop current. The first input terminal of the voltage selection unit is connected to the anode of the third diode, the second input terminal of the voltage selection unit is connected to the anode of the fourth diode, and the cathodes of both the third and fourth diodes are connected to the output terminal of the voltage selection unit; one end of the seventh resistor is connected to the output terminal of the voltage selection unit, and the other end is connected to the zero potential reference point.

2. The power regulator circuit for a laser printer heater as described in claim 1, characterized in that, When the MOSFET is turned on, the first circuit is connected, and AC power is sent to the heater and inductor. Part of the energy is consumed by the heater, and the other part is stored in the inductor. When the MOSFET is turned off, the AC power supply is cut off, and the energy stored in the inductor is sent to the heater through the first diode.

3. The power regulator circuit for a laser printer heater as described in claim 1, characterized in that, The gate of the MOSFET is connected to the control circuit via a second resistor in series, and a third resistor is connected between the gate and source of the MOSFET.

4. The power regulator circuit for a laser printer heater as described in claim 1, characterized in that, The voltage sampling unit is connected to the DC output terminal of the rectifier module and is used to collect the pulsating DC voltage output by the rectifier module, convert it into a DC voltage proportional to its peak or average value, and then adjust the converted DC voltage to a DC voltage suitable for the control circuit.

5. A power regulator circuit for a laser printer heater as described in claim 1 or 4, characterized in that, The voltage sampling unit includes: The first input terminal of the voltage sampling unit is connected in sequence to the second diode, the fourth resistor, the first capacitor, and the second input terminal of the voltage sampling unit; one end of the fifth resistor is connected between the fourth resistor and the first capacitor, and the other end is connected to the cathode of the Zener diode. The anode of the Zener diode is connected to the output terminal of the voltage sampling unit. A sixth resistor is connected between the second input terminal and the output terminal of the voltage sampling unit.

6. The power regulator circuit for a laser printer heater as described in claim 1, characterized in that, The control circuit includes a PWM power management chip, a voltage sampling unit, and a drive unit; The voltage sampling unit is connected to the DC output terminal of the rectifier module and is used to collect the pulsating DC voltage output by the rectifier module, convert it into a DC voltage proportional to its peak or average value, and then adjust the converted DC voltage to a DC voltage suitable for the control circuit. The output of the voltage sampling unit is connected to the PWM power management chip. The PWM power management chip receives the voltage output by the voltage sampling unit and simultaneously acquires the voltage across the first resistor. After comparing the two voltages, the higher voltage is selected to generate the drive pulse signal for driving the MOSFET to turn on and off. The output of the PWM power management chip is connected to the drive unit, and the output of the drive unit is connected to the MOSFET.

7. A method for adjusting the power regulator circuit for a laser printer heater as described in any one of claims 1-6, characterized in that, include: The input AC power is converted into a pulsating DC voltage; the peak or average value of the pulsating DC voltage is collected, and it is filtered and divided into a DC control voltage suitable for the control circuit and capable of reflecting the level of the pulsating DC voltage; the DC control voltage is proportionally amplified to obtain the first voltage; A high-frequency pulse voltage that is proportional to the high-frequency pulse current in the first circuit is collected on the first resistor. The difference between the high-frequency pulse voltage and the reference voltage is integrated and amplified to obtain a second voltage that reflects the average value of the high-frequency pulse voltage. The magnitudes of the first voltage and the second voltage are compared, and the higher one is selected for PWM modulation to obtain a drive pulse with a duty cycle related to the input power supply and high-frequency pulse current, so as to drive the MOSFET to turn on and off. By adjusting the duty cycle of the MOSFET's on-time, the current in the heater and the voltage across the heater are automatically adjusted, thereby regulating the electrical power supplied to the heater. The control circuit includes: a voltage sampling unit, a proportional amplifier unit, and a voltage selection unit connected in sequence; a current sampling unit connected to an integral amplifier unit and then connected to the voltage selection unit; the output of the voltage selection unit connected in sequence to a PWM modulation unit and a driving unit; and the output of the driving unit connected to a MOSFET. The current sampling unit is connected across the first resistor to collect the voltage across the first resistor. The voltage is a high-frequency pulse voltage that is proportional to the first loop current. The integrating amplification unit is used to integrate and amplify the difference between the high-frequency pulse voltage and the reference voltage to obtain an integrated DC voltage related to the average value of the first loop current. The first input terminal of the voltage selection unit is connected to the anode of the third diode, the second input terminal of the voltage selection unit is connected to the anode of the fourth diode, and the cathodes of both the third and fourth diodes are connected to the output terminal of the voltage selection unit; one end of the seventh resistor is connected to the output terminal of the voltage selection unit, and the other end is connected to the zero potential reference point.

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