JP2016046831A - Power supply, fixation device, and image forming apparatus with the fixation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a malfunction or a failure of a semiconductor switching element by reducing variations in a voltage to be applied to a gate terminal of the semiconductor switching element.SOLUTION: A power supply generates a voltage by alternately turning on first and second switching elements which are connected in series. In the power supply, the first and second switching elements are driven in such a manner that the first switching element is turned on by applying a positive voltage to the first switching element, after the positive voltage is applied, a negative voltage is applied to the first switching element for a predetermined period and a reference voltage is then applied to first switching means, thereby turning off the first switching element, and during the predetermined period in which the negative voltage is applied, a positive voltage is applied to the second switching element, thereby turning on the second switching element.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power supply device including a drive unit that alternately drives two switching elements, and a fixing device including the power supply device.

  As a half-bridge driving circuit in a conventional power supply device, a driving circuit that applies a positive voltage and a negative voltage to a gate terminal of a voltage-driven semiconductor switching element is known. (See Patent Document 1.) Also, a plurality of systems are known as drive circuits in which semiconductor switching elements are arranged one above the other. An example is shown in FIG. 10. FIG. 10A is a half-bridge full-wave rectification type drive circuit, FIG. 10B is a half-bridge half-wave rectification type drive circuit, and FIG. Drive circuit. FIG. 10D shows a voltage resonance circuit. In the circuit of FIG. 10, Q1 is a high-side switching element, and Q2 is a low-side switching element.

JP-A-4-265661

  In the driving circuit in which the semiconductor switching elements as described above are arranged above and below, it is necessary to adjust the semiconductor switching elements so that they do not conduct alternately and overlap each other. For example, two semiconductor switches are controlled so as not to be turned on twice, for example, a semiconductor switch to be turned on may be erroneously turned on due to a variation in the voltage (gate voltage) of the gate terminal of the conductive semiconductor switch element. Measures are needed.

  A power supply device of the present invention for solving the above-described problems includes a first switching element connected in series and disposed on a high potential side, a second switching element disposed on a low potential side, and the first switching element In the power supply device that generates a voltage by alternately turning on the second switching element and applying the positive voltage to the first switching element, the first switching element is turned on and the positive voltage is applied. Then, a negative voltage is applied to the first switching element for a predetermined period, and then a reference voltage is applied to the first switching means to turn off the first switching element, so that the negative voltage is applied. In the predetermined period, the first and second switching elements are turned on by applying a positive voltage to the second switching element. And drives the switching element.

  Further, the heating device of the present invention is a fixing device for fixing a toner image transferred to a recording medium to the recording medium, and includes a heating element, an excitation coil for generating heat from the heating element, and a resonance capacitor. A power source for driving the circuit and the resonant circuit, the power source being connected in series, the first switching element disposed on the high potential side and the second switching disposed on the low potential side A power source that alternately turns on the first switching element and the second switching element to generate a voltage, and turns on the first switching element by applying a positive voltage to the first switching element. Then, after applying the positive voltage, a negative voltage is applied to the first switching element for a predetermined period, and then a reference voltage is applied to the first switching means to thereby apply the first switch. The first and second switching elements are turned on by applying a positive voltage to the second switching element during the predetermined period when the negative voltage is applied to the chucking element. The second switching element is driven.

  As described above, according to the present invention, fluctuations in the voltage applied to the gate terminal of the semiconductor switching element can be reduced, and malfunctions and failures of the semiconductor switching element can be reduced.

1 is a circuit diagram of a power supply device according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating a method for driving the power supply device according to the first embodiment. FIG. 3 is a diagram illustrating a voltage state of each element during driving of the power supply device according to the first embodiment. FIG. 6 is a diagram illustrating an image forming apparatus according to a second embodiment. FIG. 6 is a diagram illustrating a fixing device according to a second embodiment. FIG. 6 is a diagram illustrating a power supply device according to a second embodiment. FIG. 10 is an explanatory diagram illustrating operation waveforms according to the second embodiment. It is a figure explaining the modification of a power supply device. It is a figure explaining the heating apparatus which can apply the power supply device of a modification. It is a figure which shows the example of the drive circuit of a power supply device.

(Example 1)
A first embodiment will be described with reference to FIGS. FIG. 1 is a circuit diagram of the power supply device of this embodiment. FIG. 2 is a diagram for explaining a driving method of the circuit diagram of FIG. 1, and FIG.

  FIG. 1 shows an example of a half-bridge circuit for connecting two semiconductor switching elements up and down and alternately turning them on. The circuit of the present embodiment is a drive circuit that generates power to be supplied to a motor as an example of a power supply target (load). In FIG. 1, Q1 and Q2 are voltage-driven first and second semiconductor switching elements, the semiconductor switching Q1 is a high potential side (high side) switching element, and Q2 is a low potential side (low side). Switching element. These semiconductor switching elements Q1, Q2 are alternately turned on / off. 3, 4, 7, 8, 15, and 16 are resistance elements, and 5, 6, 11, 13, 14, and 19 are diodes. Further, 9, 17 are electromagnetic transformers, and 10, 18 are FETs (Field Effect Transistors / field effect transistors) as third and fourth switching elements. Reference numerals 12 and 20 denote DC power supplies, and reference numeral 22 denotes a load. Here, MOSFETs or IGBTs can be used as the voltage-driven semiconductor switching elements Q1 and Q2. Q1 and Q2 may be voltage-driven semiconductor switching elements other than these elements. The control circuit 40 is a circuit that controls on / off of the switching elements 10 and 18.

  Next, a method for driving the circuit of FIG. 1 will be described with reference to FIG. In FIG. 2, a pulse control signal (SigH signal) is input from the control circuit 40 between the gate and source of the switching element 10. Similarly, a pulse control signal (SigL signal) is input from the control circuit 40 between the gate and source of the switching element 18. When the SigH signal is input to the switching element 10, an induced voltage is generated on the output side of the transformer 9, and a positive voltage Vp pulse corresponding to the ON state of the SigH signal is generated. Further, when the SigH signal changes from on to off during the off period of the SigL signal, a negative voltage Vm pulse is generated for a predetermined period shorter than the off state of the SigH signal. Thereafter, during the remaining off period, a gate drive voltage signal (VgsH signal) that returns to the reference potential (0 V) is input between the gate and source of the switching element Q1. Here, the ratio between the positive voltage Vp and the negative voltage Vm is determined by the ratio of the resistance values of the resistance element 7 and the resistance element 8. Further, the resistance elements 7 and 8 also have a function of a damping resistance for the induced voltage of the transformer 9. Similarly, a gate drive signal VgsL that changes to a positive voltage Vp, a negative voltage Vm, and a reference voltage (0 V) according to the SigL signal is input between the gate and source of the switching element Q2. Further, the gate drive signal VgsH and the gate drive signal VgsL have a timing relationship in which VgsL changes to the positive voltage Vp while VgsH is a negative voltage and VgsH changes to the positive voltage Vp while VgsL is a negative voltage.

  Further, the operation of this embodiment will be described in detail with reference to FIG. FIG. 3 is a diagram for explaining a voltage state of circuit elements related to driving when the half-bridge circuit of FIG. 1 is driven. Here, FIG. 3A shows the voltage state of the circuit element of this embodiment, and FIG. 3B shows the voltage state of the circuit element in the conventional drive circuit.

  First, the state of the conventional drive circuit will be described with reference to FIG. In FIG. 3B, a positive voltage is applied to the semiconductor switching element Q1 for a period corresponding to the SigH signal to turn it on. Thereafter, the negative voltage Vm is applied for a predetermined period, and the semiconductor switching element Q1 is turned off. When the gate-source voltage VgsH of the voltage-driven semiconductor switching element Q1 changes suddenly from the negative voltage Vm to the positive voltage Vp, the drain-source voltage VdsL changes from 0V to Vin. As a result, the gate-source capacitance Cgs is charged through the gate-drain capacitance Cgd of the voltage-driven semiconductor switching element Q2, and the potential of the gate drive signal VgsL increases. As a result, the potential of the gate drive signal VgsL exceeds the threshold voltage Vth of the semiconductor switching element Q2. In this case, the semiconductor switching element Q2 that is originally turned off is turned on, and there is a possibility that the circuit may break down due to malfunction or when both Q1 and Q2 overlap and become conductive (or There was a case where the margin to reach was small.)

  On the other hand, in the drive circuit of this embodiment as shown in FIG. 3A, the gate drive signal VgsH changes from the reference potential (0 V) to the positive voltage Vp as the pulse control signal (SigH signal) is turned on. . Therefore, the voltage increase is smaller than the conventional change from Vm to Vp. That is, the increase in potential of the gate drive voltage VgsL is also reduced, and it is possible to prevent the threshold voltage Vth from being exceeded. The feature of this embodiment is that the increase in the voltage between the gate and the source of the semiconductor switching element Q1 is reduced as compared with the conventional one.

  As described above, according to the first embodiment, when the switching element Q1 of the half-bridge circuit is turned on, the gate-source capacitance of the switching element Q2 is prevented from suddenly increasing to prevent Q2 from being turned on. be able to. Accordingly, it is possible to increase the margin for malfunction or failure of the switching element Q2, and the reliability can be improved.

(Example 2)
Next, Example 2 will be described with reference to FIGS. 4, 5, 6, and 7. In this embodiment, the half-bridge circuit of the first embodiment is applied to an image forming apparatus. First, an electrophotographic laser beam printer as an image forming apparatus according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 4, the image forming apparatus of this embodiment has a photosensitive drum 101 as an image carrier in the apparatus main body. A charger 102, a developing device 104, a transfer roller 108, a cleaning device 109, and the like are provided around the photosensitive drum 101. The photosensitive drum 101 is rotationally driven in the direction of the arrow in the figure at a predetermined peripheral speed, that is, an image forming speed. To do.

  The laser beam scanner 103 outputs a laser beam L that is modulated based on image information input from a host device such as a computer or an image reading device (not shown), and an image is formed on the surface of the uniformly charged photosensitive drum 101. An electrostatic latent image corresponding to the information is formed. The electrostatic latent image is developed into a toner image by the developing device 104 using a developer.

  On the other hand, sheets P as recording media stacked on the paper feed tray 105 are sent out one by one by the supply roller 106. The conveyance of the sheet P is adjusted by the roller 107 so as to be synchronized with the toner image formed on the photosensitive drum 101, and the sheet P is introduced into the transfer nip T formed by the photosensitive drum 101 and the transfer roller 108. In the transfer nip T, a high voltage (also referred to as transfer bias) is applied to the transfer roller 108, so that the toner image formed on the photosensitive drum 101 is transferred to the sheet P.

  After the toner image is transferred to the sheet P, the toner remaining on the photosensitive drum 101 is removed by the cleaning device 109, and then the operation proceeds to the next toner image forming operation. Further, the sheet P on which the toner image is transferred is conveyed to the fixing device 110. In the fixing device 110, heat and pressure are applied to the sheet P on which the toner image is transferred to fix the toner image on the sheet P, and the sheet P is discharged to the paper discharge tray 111. The fixing device 110 is connected to the power supply device 120 and is supplied with power necessary for the fixing operation.

  Next, the fixing device 110 will be described. The fixing device 110 in this embodiment is an induction heating type fixing device using a magnetic induction heat generating film (metal film). First, the overall configuration of the fixing device 110 will be described with reference to FIG.

  In FIG. 5, the fixing device 110 includes a heating element 110 </ b> A and a pressure roller 110 </ b> B that forms a fixing nip portion N in pressure contact with the heating body 110 </ b> A. The heating element 110A has a film inner surface guide stay 119 having a semicircular arc shape (a bowl shape) facing upward in a transverse section. Inside the guide star 119, an exciting coil as a wire ring, that is, a heating coil 112, and a core material 113 as an exciting core are disposed. Further, a cylindrical (endless) magnetic induction heat generating film 114 is slidably fitted on the outside of the guide stay 119. Further, a cover plate 115 is put on the opening on the upper surface of the guide stay 119, and a pressurizing stay 116 is further provided thereon.

  The pressure roller 110B is composed of a core metal 117a and an elastic layer 117b made of silicone rubber or fluorine rubber coated on the periphery thereof, and is pressed against the lower surface of the guide stay 119 with a predetermined pressing force across the film 114. Has been. The pressure roller 110B is rotated in the direction of the arrow in the figure by a motor M as driving means. Due to the frictional force between the pressure roller 110B and the outer surface of the film 114 by this rotational driving, the film 114 slides in close contact with the lower surface of the guide stay 119, and rotates around the guide stay 119.

  Further, a thermistor 118 as a temperature detection member is disposed in a portion corresponding to the fixing nip portion N on the lower surface of the guide stay 119 on the inner surface of the film 115. Further, a power supply device 120 for applying a high frequency current to the exciting coil 112 is connected. When a high frequency current is applied to the exciting coil 112 by the power supply device 120, heat is generated by magnetic induction heating in the region of the fixing nip N of the film 114. The temperature of the fixing nip portion N is detected by the thermistor 118, and the detected temperature information is input to the control circuit of the power supply device 120 so that the temperature of the fixing nip portion N becomes a predetermined fixing temperature. To control the high frequency current applied to the exciting coil 112.

  Next, the power supply device 120 which is a characteristic part of the present invention will be described. The power supply device 120 is a voltage resonance type converter as shown in FIG. A line filter 32, a bridge diode 33, a filter capacitor 21, a switching element 1, a main switching element 2, a first resonance capacitor 24, a second resonance capacitor 25, and a gate drive circuit 26 are provided. Further, the fixing device 110 includes an exciting coil 23 (consisting of the exciting coil 23 because it is the same as the heating coil 112 and is a component of the resonance circuit), a magnetic induction exothermic film 114, a thermistor 118, and the like. . The fixing device 110 includes connectors 29, 30, and 31, a temperature detection circuit 37 connected to the thermistor 118 in the fixing device 110, and a switching control circuit 34. The first resonance capacitor 24, the second resonance capacitor 25, and the exciting coil 23 in the fixing device 110 constitute a voltage resonance circuit.

  Next, the operation of each part will be described with reference to FIGS. FIG. 7 is an explanatory diagram showing operation waveforms in the circuit configuration of FIG. S1 is a gate voltage waveform of the switching element Q1, and S2 is a gate voltage waveform of the main switching element Q2. S3 is a current waveform of the main switching element Q2, and S4 is a voltage waveform of the main switching element Q2. S5 is the current waveform of the first resonant capacitor 24, S6 is the current waveform of the second resonant capacitor 25, S7 is the current waveform of the switching element 1, S8 is the current waveform of the body diode of the switching element 1, and S9 is excitation. It is an exciting current waveform of the coil 23. Note that the AC voltage input from the commercial AC power supply (AC line) is full-wave rectified by the bridge diode 33 via the line filter 32 and applied to the first and second switch elements Q1 and Q2.

  First, when the switching element Q2 is switched on, an induced current flows from the diode bridge 33 to the exciting coil 23. Simultaneously with switching off (point A), the exciting coil 23 generates a flyback voltage in a direction to maintain the current. Since a difference in residual charge between the first resonance capacitor 24 and the second resonance capacitor 25 occurs, immediately after the switching element Q2 is turned off, the resonance period ω = √ (L × C) determined by the second resonance capacitor 25 and the excitation coil 23 Draw an arc determined by). Here, it is assumed that the second resonant capacitor 25 is set to have a capacity of about 1/10 with respect to the first resonant capacitor 24. Accordingly, the voltage immediately after turning off generates a flyback voltage with a high period (period AB).

  The vibration of the flyback voltage turns on the body diode of the switching element Q1 at a point (point B) when the flyback voltage rises to the initial charge voltage of the first resonance capacitor 24. The voltage is increased by switching to a gentle sine wave by the combined capacitance of the first resonant capacitor 24 and the second resonant capacitor 25. The current waveform of the first resonant capacitor 24 at this time is shown in S5, and the current waveform of the body diode of the switching element Q1 is shown in S8. The current waveform of the second resonance capacitor 25 is shown in S6.

  The voltage rises with time and reaches the maximum value (point C) when ω / 4 (a period of ¼ of the resonance period) has elapsed. On the other hand, since the current waveform of the first resonance capacitor 24 is a cosine wave current corresponding to the differential waveform of the voltage waveform, the maximum voltage value (point C) is the minimum current value (zero cross waveform). Since the body diode of the switching element Q1 is turned off after the zero cross point, the gate of the switching element Q1 is turned on to regenerate current (CD period). When the switching element Q1 is turned off (point D), the first resonant capacitor 24 is disconnected, and the second resonant capacitor 25 having a small capacity is resonated to draw a high-cycle arc (DE period). The gate drive circuit 26 for turning on and off the first and second switch elements Q1 and Q2 is the same as the circuit configuration described in the first embodiment.

  The temperature detection circuit 37 is connected to the thermistor 118 and the switching control circuit 34, and the switching control circuit 34 controls the operation of the switching elements 10 and 18 based on a signal from the temperature detection circuit 37. Specifically, the frequency is controlled by a frequency modulation circuit 35 provided in the switching control circuit 34. Alternatively, the off time (also referred to as duty width) is controlled by the duty control circuit 36. This frequency control and off-time control may be selected from either one or in combination, and are used for control to appropriately control the voltage induced in the heating coil 23. Is done.

  The gate driving method of this embodiment is the same as that of the first embodiment. However, in this embodiment, the excitation coil 23 constituting the voltage resonance circuit can be removed together with the fixing device 110 from the laser beam printer main body. When the connectors 29 and 30 are connected with high resistance, or when the power supply is operated with the connectors 29 and 30 removed, the load of the half bridge circuit constituted by the switching elements Q1 and Q2 becomes capacitive. Thereby, the voltage fluctuation of the gate drive voltage signal VgsL resulting from the gate drive voltage signal VgsH is increased. Therefore, if the gate driving method of the present embodiment is implemented, as in the first embodiment, malfunctions and failures of the lower (low potential side) voltage-driven semiconductor switching element due to the voltage change of the gate drive waveform are eliminated. The margin can be increased and reliability can be secured.

  In the present embodiment, an example of application as a power source of an electromagnetic induction heating type fixing device is shown. However, the present invention can be applied to a general switching power supply if the temperature detection circuit 37 is configured to detect the output voltage.

<Modification of power supply device>
Next, a modification of the power supply device 120 described in the second embodiment will be described with reference to FIG. The configuration of FIG. 8 differs in the configuration of the resonance circuit in the power supply device 120 of the second embodiment. The characteristic part of a modification is demonstrated below.

  The power supply device 120 of FIG. 8 is a current resonance type converter, and the current resonance circuit has a switching element Q1, a switching element Q2, a resonance capacitor 24, a gate drive circuit 26, an excitation coil 23, a magnetic induction heat, as shown in FIG. It is comprised with the property film 114.

  When the switching element Q1 is turned on, a current starts to flow through the series resonance circuit constituted by the exciting coil 23 and the resonance capacitor 24, and when Q1 continues to be on, a peak determined by the resistance of the series resonance circuit and a circuit (not shown). After becoming current, the current decreases. Next, when the switching element Q1 is turned off and then the switching element Q2 is turned on, a current due to the coil current and the electric charge stored in the resonance capacitor 24 flows to the neutral side through the second switching element 2. This current also increases with time, and after reaching a peak value determined by a circuit constant, the current decreases. At this time, the current flowing through the series resonance circuit constituted by the excitation coil 23 and the resonance capacitor 24 becomes a sine wave.

  The modified gate driving method is the same as that of the second embodiment, and the same effect can be obtained. Moreover, the drive circuit of a modification is applicable to the structure shown in FIG. 9 as a heating apparatus, for example. The configuration of FIG. 9 includes an exciting coil 112, a closed magnetic core 121, a conductive film 122, and a pressure roller 117. When a high frequency current is applied to the exciting coil 112 by the power supply device 120, an electromotive force is generated in the circumferential direction of the conductive film 122, and Joule heat is generated according to the resistance value of the conductive film 122. The entire conductive film 122 is heated. The pressure roller 117 is pressed against the lower surface of a guide stay (not shown) with a predetermined pressing force with the conductive film 122 interposed therebetween. The pressure roller 117 is rotated by a motor M as driving means. The rotating force of the pressure roller 117 and the outer surface of the conductive film 122 causes the film 122 to rotate while closely contacting the lower surface of the guide stay (not shown). In addition, in FIG. 8, although it is the structure using a closed magnetic core, the heating apparatus using a closed magnetic core is applicable similarly.

Q1, Q2 Switching element 3, 4, 7, 8, 15, 16 Resistance element 5, 6, 11, 13, 14, 19 Diode 10, 18 FET
12, 20 DC power supply 22 Load

Claims (12)

A first switching element connected in series and disposed on the high potential side, a second switching element disposed on the low potential side, and the first and second switching elements are alternately turned on to voltage In the power supply that generates
The first switching element is turned on by applying a positive voltage to the first switching element, and after applying the positive voltage, a negative voltage is applied to the first switching element for a predetermined period, and then the first switching element is turned on. The first switching element is turned off by applying a reference voltage to the switching means, and the positive voltage is applied to the second switching element in the predetermined period when the negative voltage is applied. A power supply apparatus that drives the first and second switching elements to turn on two switching elements. A first transformer for driving the first switching element;
A second transformer for driving the second switching element;
A third switching element for driving the first transformer;
A fourth switching element for driving the second transformer;
The power supply apparatus according to claim 1, wherein the third and fourth switching elements are alternately turned on.   3. The power supply apparatus according to claim 2, further comprising a control unit for driving the third and fourth switching elements.   The power supply apparatus according to any one of claims 1 to 3, wherein the first and second switching elements are MOSFETs or IGBTs. In a fixing device for fixing a toner image transferred to a recording medium to the recording medium,
A heating element;
A resonance circuit including an excitation coil and a resonance capacitor for generating heat from the heating element;
A power supply for driving the resonant circuit;
The power supply is
A first switching element connected in series and disposed on the high potential side, a second switching element disposed on the low potential side, and the first and second switching elements are alternately turned on to voltage A power supply that generates
The first switching element is turned on by applying a positive voltage to the first switching element, and after applying the positive voltage, a negative voltage is applied to the first switching element for a predetermined period, and then the first switching element is turned on. The first switching element is turned off by applying a reference voltage to the switching means, and the positive voltage is applied to the second switching element in the predetermined period when the negative voltage is applied. A fixing device that drives the first and second switching elements to turn on two switching elements. A first transformer for driving the first switching element;
A second transformer for driving the second switching element;
A third switching element for driving the first transformer;
A fourth switching element for driving the second transformer;
The fixing device according to claim 5, wherein the third switching element and the fourth switching element are alternately turned on.   The fixing device according to claim 6, further comprising a control unit for driving the third and fourth switching elements.   The fixing device according to claim 5, wherein the first and second switching elements are MOSFETs or IGBTs. Furthermore, temperature detecting means for detecting the temperature of the heating element;
The fixing device according to claim 5, further comprising a control unit that controls the power source in order to control a temperature of the heating element.   The fixing device according to claim 5, wherein the resonance circuit is a current resonance circuit or a voltage resonance circuit.   The fixing device according to claim 5, wherein the resonance circuit is configured such that the excitation coil can be removed from the resonance circuit. Image forming means for forming a toner image on a recording medium;
A fixing device according to any one of claims 5 to 11,
An image forming apparatus, wherein the toner image is fixed on the recording medium by the fixing device.

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