JP2017073006A - Heater drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically replace a heater control switching element with another switching element immediately when a heater control switching element fails, so that heater control can be continued. A triac TRA2 is connected in parallel to a triac TRA1 as a spare switching element, and a light receiving side circuit of a photocoupler PC2 outputs a control signal for controlling on / off of one of the triac TRA1 and the triac TRA2. . A Zener diode ZD is provided between the control terminal of the triac TRA2 and the light receiving side circuit of the photocoupler PC2. The current output circuit 31 outputs a current to the Zener diode ZD when the triac TRA1 fails. To short-circuit the Zener diode. [Selection] Figure 1

Description

  The present invention relates to a heater driving circuit.

  An image forming apparatus that performs printing by an electrophotographic method heats and pressurizes a toner image transferred onto a recording sheet and fixes the toner image onto the recording sheet. Such a fixing device has a fixing heater for heating. In addition, such an image forming apparatus controls a fixing temperature of a fixing device by controlling a switching element such as a triac that performs on / off control of a fixing heater.

  FIG. 2 is a circuit diagram illustrating an example of a heater driving circuit.

  In the heater driving circuit shown in FIG. 2, when the triac TRA1 is in the on state, AC power obtained from the commercial power source is supplied to the fixing heater 101, and when the triac TRA1 is in the off state, the AC power obtained from the commercial power source is Not supplied to the fixing heater 101. The triac TRA1 is turned on or off according to the voltage applied to the gate. A voltage corresponding to the amount of light emitted by the light emitting side circuit of the photocoupler PC2 is applied to the gate of the triac TRA1 by the resistors R3 and R4 and the light receiving side circuit of the photocoupler PC2.

  On the other hand, the switching power supply circuit 102 generates DC power from a commercial power source and supplies it to a CPU (Central Processing Unit) 201, and the CPU 201 operates with the DC power. Then, the CPU 201 controls the conduction current of the light emission side circuit of the photocoupler PC2 according to the control program, switches between the on state and the off state of the triac TRA1, and performs the on / off control of the fixing heater 101.

  On the other hand, when a defect occurs in a PLL (Phase Locked Loop) circuit due to wafer level burn-in or the like in the semiconductor chip manufacturing process, the fuse element is cut and the defective PLL circuit is replaced with a spare PLL circuit ( For example, see Patent Document 1).

JP 2002-94372 A

  However, due to voltage abnormality in the commercial power supply, lightning surge, etc., the switching element for controlling on / off of the fixing heater may fail. In that case, the fixing heater will not operate due to the failure of the switching element, and printing may be performed. It becomes impossible.

  It is also possible to blow the fuse manually and replace the failed switching element with a spare switching element. Even in such a case, the fuse is blown manually from the occurrence of the switching element failure. Cannot print during the period up to.

  The present invention has been made in view of the above problems. When a heater control switching element fails, the heater control switching element is automatically replaced with another switching element and the heater control is continued. It is an object of the present invention to obtain a heater drive circuit that can be performed.

  The heater drive circuit according to the present invention includes a switching element connected in series to the heater, a spare switching element connected in parallel to the switching element, and one of the switching element and the spare switching element being turned on / off A control circuit that outputs a control signal to be controlled; a Zener diode provided between a control terminal of the auxiliary switching element and the control circuit; and a current output to the Zener diode when the switching element fails. And a first current output circuit for short-circuiting the Zener diode.

  According to the present invention, when the heater control switching element fails, the heater drive circuit that automatically replaces the heater control switching element with another switching element and allows the heater control to continue can be performed. Get it.

  These and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a heater driving circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram illustrating an example of a heater driving circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a heater driving circuit according to an embodiment of the present invention. The heater driving circuit shown in FIG. 1 drives the fixing heater 1 with AC power from a commercial power source. The fixing heater 1 is a heater in a fixing device of an electrophotographic image forming apparatus (multifunction machine, printer, etc.). The heater driving circuit shown in FIG. 1 includes a switching power supply circuit 2. The switching power supply circuit 2 generates DC power from the AC power of the commercial power supply and supplies power to a control system (such as the CPU 3) that controls the fixing heater 1.

  In FIG. 1, a triac TRA1 is a switching element connected in series to the fixing heater 1. The triac TRA2 is a spare switching element connected in parallel to the triac TRA1. The triac TRA1 and the triac TRA2 supply AC power from a commercial power source to the fixing heater 1 when in the on state.

  In this embodiment, since AC power is supplied to the fixing heater 1, a triac capable of conducting current in both directions is used for these switching elements.

  The photocoupler PC2 includes a light emitting side circuit and a light receiving side circuit, and the two are coupled with light to be electrically insulated. The light-receiving side circuit of the photocoupler PC2 is a control circuit that outputs a control signal for controlling on / off of one of the triac TRA1 and the triac TRA2. Specifically, the CPU 3 outputs a control signal from the light receiving side circuit of the photocoupler PC2 to one of the triac TRA1 and the triac TRA2 via the resistor R2 and the photocoupler PC2. Since the light receiving side circuit of the photocoupler PC2 needs to conduct current in both directions, for example, a zero cross type triac coupler is used as the photocoupler PC2.

  The T1 terminal of the triac TRA1 is connected to a commercial power source, and a resistor R4 is disposed between the gate terminal and the T1 terminal of the triac TRA1. Further, a fuse FS3, a light receiving side circuit of the photocoupler PC2, and a resistor R3 are arranged in series between the gate terminal and the T2 terminal of the triac TRA1. When the fuse FS3 is not cut and the light-receiving side circuit of the photocoupler PC2 is in a conductive state, a current flows through the resistors R3 and R4, and a gate voltage is applied to the triac TRA1 due to a voltage drop at the resistors R3 and R4. Applied.

  The T1 terminal of the triac TRA2 is connected to a commercial power supply, the anode terminal of the Zener diode ZD is connected to the gate terminal of the triac TRA2, and the cathode terminal of the Zener diode ZD and the T1 terminal of the triac TRA2 are connected. A resistor R5 is disposed on the board. Further, between the cathode terminal of the Zener diode ZD and the T2 terminal of the triac TRA2, the light receiving side circuit of the photocoupler PC2 and the resistor R3 are arranged in series.

  Thus, the Zener diode ZD is provided between the gate terminal of the triac TRA2 and the light receiving side circuit of the photocoupler PC2. In a state where the Zener diode ZD is not short-circuited, the gate voltage of the triac TRA2 is always at a low level due to the reverse bias of the Zener diode ZD, and the triac TRA2 is turned off. When the Zener diode ZD is short-circuited, the reverse bias of the Zener diode ZD disappears, and when the light receiving side circuit of the photocoupler PC2 is in a conductive state, a current flows through the resistors R3 and R5, and the resistors R3 and R5 caused by this current As a result of the voltage drop, a gate voltage is applied to the triac TRA2, and the triac TRA2 is turned on.

  The current output circuit 31 is connected in parallel to the Zener diode ZD, and outputs a current to the Zener diode ZD to short-circuit the Zener diode ZD when the triac TRA1 fails. That is, the current output circuit 31 destroys the PN junction of the Zener diode ZD (partially) with a predetermined power, and short-circuits the anode and the cathode of the Zener diode ZD. At this time, the current output circuit 31 conducts the current to the Zener diode ZD so that the Zener diode ZD is not completely destroyed and the power is such that the PN junction can be partially destroyed. Note that after the Zener diode ZD is short-circuited, the current output circuit 31 immediately ends the conduction of the current to the Zener diode ZD.

  Further, a fuse FS3 is provided between the gate terminal of the triac TRA1 and the light receiving side circuit of the photocoupler PC2, and the current output circuit 32 is connected in parallel to the fuse FS3. At the time of failure, a current is output to the fuse FS3 to cut the fuse FS3. Note that after the fuse FS3 is disconnected, the current output circuit 32 immediately ends the conduction of the current to the fuse FS3.

  Further, the detection circuit 33 detects the applied voltage (or conduction current) of the fixing heater 1.

  The CPU 3 is a control unit that operates using the DC power generated by the switching power supply circuit 2 as a power source and operates according to a control program.

  In the switching power supply circuit 2, AC power obtained from a commercial power supply is rectified by the diode bridge DB, and the rectified DC power is stepped down to a rated voltage by a DC / DC converter and output. A fuse FS1 is provided in front of the diode bridge DB, a capacitor C1 is provided as a differential mode noise filter, an inductor L1 and capacitors C2 and C3 are provided as common mode noise filters, and A surge absorber ZNR is provided. Further, a smoothing capacitor C4 is provided after the diode bridge DB.

  The switching power supply circuit 2 includes a converter switching element Q1 and a standby converter switching element Q2, a control circuit 11, a rectifier circuit 12, and a selector 13 in the DC / DC converter portion.

  Converter switching element Q1 is connected to the first winding of transformer TR and performs a switching operation in accordance with a control signal.

  The spare converter switching element Q2 is connected in parallel to the converter switching element Q1 in the DC / DC converter portion. Here, converter switching element Q1 and standby converter switching element Q2 are field effect transistors (FETs).

  The control circuit 11 outputs a control signal for controlling on / off of one of the converter switching element Q1 and the standby converter switching element Q2. The rectifier circuit 12 supplies the control circuit 11 with DC power obtained by rectifying AC power induced in the third winding of the transformer TR as a power source.

  The selector 13 switches the output destination of the control signal from the control circuit 11 from the converter switching element Q1 to the standby converter switching element Q2 when the converter switching element Q1 fails.

  Further, in the switching power supply circuit 2, the rectifier circuit 21 rectifies secondary AC power induced in the second winding of the transformer TR, and the light emission side circuit of the resistor R 1 and the photocoupler PC 1 is output from the rectifier circuit 21. The DC voltage is detected and notified to the control unit 11. The control unit 11 adjusts the duty of the control signal so that the rectified DC voltage becomes constant. Further, the detection circuit 22 detects the output DC voltage of the rectifier circuit 21 and notifies the CPU 3 of it.

  The CPU 3 controls the current output circuits 31 and 32 and the selector 13 according to the control program.

  Specifically, the CPU 3 receives the detection signal from the detection circuit 33 via the insulation circuit 41, and based on the detection signal from the detection circuit 33 (that is, the applied voltage or conduction current value of the fixing heater 1). When a failure of TRA1 is detected and a failure of TRIAC TRA1 is detected (for example, when the applied voltage of fixing heater 1 is 70% or less of the rated voltage during the period when the control signal for turning on is supplied to TRIAC TRA1), immediately Then, a control signal is output to the current output circuits 31 and 32 through the insulating circuits 42 and 43, and the zener diode ZD is short-circuited and the fuse FS3 is cut off.

  The CPU 3 outputs a control signal to the current output circuits 31 and 32 during a period in which both ends of the light receiving side circuit of the photocoupler PC2 are open via the resistor R2 and the light emitting side circuit of the photocoupler PC2. The short circuit of the Zener diode ZD and the cutting of the fuse FS3 may be performed.

  The CPU 3 detects a failure of the converter switching element Q1 based on a detection signal from the detection circuit 22 (that is, a value of the output DC voltage of the rectifier circuit 21), and detects a failure of the converter switching element Q1 ( (For example, when the output DC voltage of the rectifier circuit 21 is 70% or less of the rated voltage), a selection signal is immediately output to the selector 13 via the insulation circuit 51, and the output destination of the control signal of the control unit 11 is switched to the preliminary converter. Switch to element Q2. As a result, power supply to the CPU 3 is not supplied due to the failure of the converter switching element Q1, and the CPU 3 may not be able to detect the failure of the triac TRA1, short-circuit the Zener diode ZD, and disconnect the fuse FS3. Lower.

  The insulating circuits 41, 42, 43, 51 are, for example, photocouplers, and electrically isolate the input side and the output side from the output side according to the electric signal input to the input side. Output.

  Next, the operation of the heater driving circuit will be described.

  In the heater driving circuit shown in FIG. 1, when the triac TRA1 is in an on state in a normal state (that is, a state where the triac TRA1 has not failed), AC power obtained from a commercial power source is supplied to the fixing heater 1, When the TRA 1 is in the off state, AC power obtained from the commercial power source is not supplied to the fixing heater 1.

  Therefore, the CPU 3 controls on / off of the triac TRA1 in the normal state by controlling the light receiving side circuit of the photocoupler PC2 via the light emitting side circuit of the photocoupler PC2.

  Specifically, in a normal state, a gate voltage corresponding to the light emission amount by the light emission side circuit of the photocoupler PC2 is applied to the gate terminal of the triac TRA1 by the resistors R3 and R4 and the light reception side circuit of the photocoupler PC2. The triac TRA1 is turned on or off according to its gate voltage.

  In the normal state, the triac TRA2 is continuously turned off without being turned on by the reverse bias of the Zener diode ZD.

  When the triac TRA1 fails, the triac TRA1 is continuously turned off regardless of the gate voltage applied, and the applied voltage (or conduction current) of the fixing heater 1 decreases. When the value of the applied voltage (or conduction current) of the fixing heater 1 notified by the detection circuit 33 becomes equal to or less than a predetermined threshold, the CPU 3 determines that the triac TRA1 has failed and controls the current output circuits 31 and 32. A signal is output, and the current output circuits 31 and 32 are caused to short-circuit the Zener diode ZD and cut the fuse FS3.

  After the fuse FS3 is cut by the current output circuit 32 and the zener diode ZD is short-circuited by the current output circuit 31, the CPU 3 receives the light receiving side of the photocoupler PC2 through the light emitting side circuit of the photocoupler PC2. By controlling the circuit, on / off control of the triac TRA2 is performed.

  Specifically, in this state, the Zener diode ZD is short-circuited and the reverse bias is substantially zero. Therefore, the gate terminals of the triac TRA2 include resistors R3 and R5 and a light receiving side circuit of the photocoupler PC2. Thus, a gate voltage corresponding to the light emission amount by the light emission side circuit of the photocoupler PC2 is applied, and the triac TRA2 is turned on or off according to the gate voltage.

  In this state, since the fuse FS3 is cut, no gate voltage is applied to the triac TRA1, and the triac TRA1 is turned off without being turned on.

  Thus, even when the triac TRA1 fails, the fixing heater 1 can be controlled by using the triac TRA2 instead of the triac TRA1.

  As described above, according to the above embodiment, the triac TRA2 is connected in parallel to the triac TRA1 as a spare switching element, and the light receiving side circuit of the photocoupler PC2 is one of the triac TRA1 and the triac TRA2. A control signal for controlling on / off is output. A Zener diode ZD is provided between the triac TRA2 and the light receiving side circuit of the photocoupler PC2, and the current output circuit 31 outputs a current to the Zener diode ZD when the triac TRA1 fails. Is short-circuited.

  Thereby, when the heater control triac TRA1 breaks down, the heater control triac TRA1 is automatically replaced with the triac TRA2 and the heater control of the fixing heater 1 can be continued.

  Various changes and modifications to the above-described embodiment will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. That is, such changes and modifications are intended to be included within the scope of the claims.

  For example, the heater driving circuit according to the above embodiment controls the fixing heater 1 in the fixing device, but may control other heaters.

  In the above embodiment, a fuse that is not connected in series to the triac TRA2 but connected in series to the triac TRA1 may be separately provided. In that case, the fuse that blows out in a shorter time than the fuse FS2 is used.

  In the above embodiment, when the image forming apparatus incorporating the heater driving circuit includes a notification unit (display unit), the triac TRA1 (or the converter switching element Q1) fails and the spare triac TRA2 (or spare) It is also possible to notify the user or service person that the converter switching element Q2) has been replaced by using a notification unit (display unit).

  The present invention is applicable to, for example, an electrophotographic image forming apparatus.

2 Switching power supply circuit 3 CPU (an example of a control unit)
11 Control circuit (example of converter control circuit)
13 selector 31 current output circuit (an example of a first current output circuit)
32 Current output circuit (an example of a second current output circuit)
33 detection circuit FS3 fuse PC2 photocoupler (an example of a control circuit)
Q1 Converter switching element Q2 Reserve converter switching element TRA1 Triac (an example of switching element)
TRA2 triac (an example of a spare switching element)
ZD Zener diode

Claims (5)

A switching element connected in series to the heater;
A preliminary switching element connected in parallel to the switching element;
A control circuit that outputs a control signal for controlling on / off of one of the switching element and the auxiliary switching element;
A Zener diode provided between the control terminal of the auxiliary switching element and the control circuit;
A first current output circuit that outputs a current to the Zener diode to short-circuit the Zener diode when the switching element fails;
A heater drive circuit comprising: A fuse provided between a control terminal of the switching element and the control circuit;
A second current output circuit that outputs a current to the fuse and cuts the fuse when the switching element fails;
The heater driving circuit according to claim 1, further comprising: A detection circuit for detecting an applied voltage or conduction current of the heater;
A control unit for controlling the first current output circuit;
The control unit detects a failure of the switching element based on the applied voltage or conduction current of the heater detected by the detection circuit, and immediately detects the failure of the switching element, the first current output circuit Controlling the short circuit of the Zener diode,
The heater drive circuit according to claim 1. A switching power supply circuit for generating DC power from AC power of the commercial power supply;
When the switching element and the auxiliary switching element are in an ON state, supply AC power of a commercial power source to the heater,
The control unit operates with the DC power generated by the switching power supply,
The switching power supply circuit outputs a spare converter switching element connected in parallel to the converter switching element of the DC / DC converter portion, and a control signal for controlling on / off of one of the converter switching element and the spare converter switching element. A converter control circuit that performs the operation, and a selector that switches the output destination of the control signal from the converter control circuit from the converter switching element to the standby converter switching element when the converter switching element fails.
The heater drive circuit according to claim 1.   The heater driving circuit according to any one of claims 1 to 4, wherein the heater is a fixing heater in a fixing device.

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