JP5164474B2 - Power supply - Google Patents

Description

  The present invention includes a first DC stabilized power supply circuit that supplies power to a control unit having a CPU having a reset circuit that outputs a reset signal when the power supply voltage drops below a predetermined threshold voltage, and is driven by the control unit. A second DC stabilized power supply circuit that supplies power to the load group and supplies an output voltage that is higher than an output voltage of the first DC stabilized power supply circuit, and a load from the second DC stabilized power supply circuit to the load group. The present invention relates to a power supply device including a safety switch for switching a power supply state.

  Two or more devices are provided with a load group such as a motor and a heater that are driven by receiving a high voltage power supply and a control unit such as a microcomputer that controls the load group by receiving a low voltage power supply. In many cases, a multi-output power supply device that outputs a voltage of 1 is provided.

  Further, since the operation of the controller becomes unstable when the supplied voltage becomes unstable, the controller generally outputs a reset signal when the supplied voltage falls below a predetermined threshold voltage. A reset circuit for causing the control unit to perform a reset operation is provided.

  In the multi-output power supply device, when power supply is resumed to a load group that has stopped power supply, cross regulation deteriorates, that is, an inrush current to the load group that receives power supply from the high voltage side occurs, resulting in a voltage on the low voltage side. May decrease. The deterioration of the cross regulation is caused by the fact that the voltage on the low voltage side grounded in common with the high voltage side fluctuates due to the fluctuation of the ground voltage level due to the return current of the inrush current.

  The deterioration of the cross regulation that occurs when the power supply from the high voltage side to the load group is resumed is assumed in advance, and the control unit is naturally configured so that the operation does not become unstable due to the deterioration of the cross regulation. Is done. However, when the cross regulation deteriorates, if the voltage supplied from the low voltage side falls below the threshold voltage of the reset circuit, the reset circuit does not require the reset operation of the control unit, but the reset signal is sent to the control unit. Will be output.

In order to prevent the deterioration of the cross regulation and prevent the control unit from performing an unnecessary reset operation, the inrush current may be reduced. Patent Document 1 includes an FET element on the primary side of the switching regulator, and the primary side of the transformer. A power supply device has been proposed in which a reset voltage generated in a winding is divided by a voltage dividing resistor and input to the gate of the FET element to reduce an inrush current.
Japanese Utility Model Publication No. 5-21988

  However, the power supply device proposed in Patent Document 1 reduces the inrush current by changing the resistance value on the primary side by using the FET element installed on the primary side, and has two different types with the primary side in common. It is difficult to apply the technology to a multi-output power supply device that outputs a voltage.

  In addition, the deterioration of cross regulation can be prevented by reducing the return current of the generated inrush current with a coil connected in series to the load group, but in this case, a large space is required for installing the coil. In addition, there are problems of cost increase and weight increase due to an increase in parts.

  In view of the above-described problems, an object of the present invention is to provide a power supply device that does not cause the CPU to execute an unnecessary reset operation even if cross regulation deteriorates due to the occurrence of an inrush current.

In order to achieve the above-mentioned object, the first characteristic configuration of the power supply device according to the present invention is the reset signal when the power supply voltage falls below a predetermined threshold voltage as described in claim 1 of the claims. The first DC stabilized power supply circuit that feeds power to a control unit having a CPU having a reset circuit that outputs the power and the load group driven by the control unit, and the output of the first DC stabilized power supply circuit A power supply device configured to include a second DC stabilized power supply circuit that supplies power at an output voltage higher than the voltage, and a safety switch that switches a power supply state from the second DC stabilized power supply circuit to the load group, A resistance voltage dividing circuit connected between the output voltage of the first DC stabilized power supply circuit and the ground, and the threshold voltage is defined, a resistance between the voltage dividing terminal of the resistance voltage dividing circuit and the ground Capacitor parallel circuit and A series circuit of a Tokappura in parallel, the safety switch said photocoupler is actuated and is closed, a predetermined required from the partial voltage terminal for charging the capacitor with the energization of the parallel circuit time A voltage adjusting unit that lowers the threshold voltage only, and stops the photocoupler when the safety switch is opened, and discharges the capacitor through the resistor of the parallel circuit while maintaining the threshold voltage. It is in the point to have.

The power supply device has a first DC stabilized power supply circuit and a second DC stabilized power supply circuit, and when the power supply from the second DC stabilized power supply circuit is stopped by the safety switch, the safety switch is closed. When the power supply from the second DC stabilized power supply circuit is started, the cross regulation deteriorates due to the generation of an inrush current to the load group, and the output voltage of the first DC stabilized power supply circuit decreases temporarily. However, according to the above-described configuration, the threshold voltage of the reset circuit can be lowered for a predetermined time after which the capacitor is charged after the safety switch is closed. Therefore, an unnecessary reset operation of the CPU due to the deterioration of the cross regulation. Can be prevented. Even if a separate switch circuit for discharging is not provided, the capacitor is quickly discharged when the safety switch is opened, so that the same operation can be appropriately repeated after the safety switch is closed next time. it can.

According to the second feature configuration, in addition to the first feature configuration described above, the predetermined time required for charging the capacitor is the first feature when the safety switch is closed. The time constant of the parallel circuit is set so that the time is longer than the time when the output voltage of the DC stabilized power supply circuit is lowered .

According to the above-described configuration, an unnecessary reset operation of the CPU is surely prevented during the time when the output voltage of the first DC stabilized power supply circuit is lowered due to the inrush current generated when the safety switch is closed. be able to.

  As described above, according to the present invention, it is possible to provide a power supply device that does not cause the CPU to execute an unnecessary reset operation even if cross regulation deteriorates due to an inrush current. .

  The power supply apparatus of the present invention will be described using a copying machine which is an example of an image forming apparatus equipped with the power supply apparatus.

  As shown in FIG. 2, the copying machine 1 adopting the electrophotographic system includes an operation unit 10 on which a display unit including a liquid crystal screen, a start key for starting a copying operation, and the like are arranged, and a document feeding table 11. An image reading unit 12 that sequentially feeds the placed document and photoelectrically converts the document image to read it as image data; an image processing unit 13 that converts the image data read by the image reading unit 12 into output image data; The image forming unit 14 forms a toner image based on the output image data and transfers the toner image to a sheet, the heat fixing unit 15 heats and fixes the toner image transferred on the sheet, and the image forming unit 14 uses the toner. A sheet storage unit 16 that stores a sheet onto which an image is transferred, a transport mechanism 17 that transports the sheet, a sheet discharge unit 18 that discharges the sheet, and a functional block that controls the function of the copying machine 1. To execute the process A control unit 19 of a power supply apparatus of the present invention, and a power supply unit 2 for supplying power to each unit.

  The power supply unit 2 is a multi-output power supply device that uses a commercial power supply as an input source. As shown in FIG. 1, the first DC stabilized power supply circuit 20 that supplies power to the control unit 19 and the first DC stabilized power supply The second DC stabilized power circuit 21 that feeds a load group such as a lamp, a clutch, and a motor with an output voltage V2 that is higher than the output voltage V1 of the circuit 20, and the power feeding state of the second DC stabilized power circuit 21 to the load group And a safety switch 22 for switching.

  As shown in FIG. 3, the first DC stabilized power supply circuit 20 and the second DC stabilized power supply circuit 21 step down the AC voltage fed from the commercial power supply by the transformer T, respectively. Rectifying and smoothing circuits 200 and 210 that rectify by a diode and smooth by a capacitor and switching regulators 201 and 211 are configured to output predetermined DC voltages V1 and V2.

  The safety switch 22 is configured by an interlock switch using a micro switch or the like that is installed on the front surface or the side surface of the copying machine 1 and whose contacts are opened and closed by opening and closing the main body cover. The contact state of the interlock switch is input to the power supply unit 2 via the signal line, and the operating state of the second DC stabilized power circuit 21, that is, the power supply state from the second DC stabilized power circuit 21 to the load group. Configured to switch between. When the main body cover is opened, the safety switch 22 is opened, and power supply from the second DC stabilized power supply circuit 21 to the load group is stopped. When the main body cover is closed, the safety switch 22 is closed and power is supplied from the second DC stabilized power supply circuit 21 to the load group.

  As shown in FIG. 1, the control unit 19 includes a CPU 191, a ROM that stores an operation program of the CPU 191, a RAM that serves as a work area, an input port that receives signals from sensors and the like installed in each unit, An output port for outputting a control signal to the load group and a reset circuit 190 for outputting a reset signal to the CPU 191 are provided. Here, the CPU 191 is configured to execute a reset operation when a low-level reset signal output from the reset circuit 190 is input.

  As shown in FIG. 4A, the reset circuit 190 includes a comparator CMP, a transistor Q1 that receives a signal output from the comparator CMP, a capacitor C1 that is connected to the collector of the transistor Q1, and a capacitor C1. A Schmitt trigger circuit ST to which a voltage of 1 is input, a transistor Q2 to which a signal output from the Schmitt trigger circuit ST is input as a base, and the like are provided.

  By the way, in the power supply unit 2, when the body cover that has been opened is closed and the safety switch 22 is closed, and the output voltage V2 is supplied from the second DC stabilized power supply circuit 21 to the load group, the load group Due to the inrush current, a short-time voltage drop occurs in the output voltage V1 of the first DC stabilized power supply circuit 20.

As shown in FIG. 4B, when the output voltage V1 drops below a predetermined threshold voltage Vs due to the voltage drop, the reset circuit 190 outputs a high level signal, and the subsequent transistor Q1 is turned on. Since the voltage Vb at the node B decreases, the Schmitt trigger circuit ST continues until the voltage drop recovers and the voltage Vb becomes the threshold voltage Vst at which the Schmitt trigger circuit ST outputs a high level signal. A low level signal is output from the trigger circuit ST, and the subsequent transistor Q2 is turned off, and a low level reset signal is output to the CPU 191. The CPU 191 that has received the reset signal executes the reset operation even though the reset operation is not originally required. Here, the threshold voltage Vs is calculated from the voltage dividing ratio of the resistors R1 and R2, and is represented by [Equation 1].
[Equation 1]
Vs = Vref · (R1 + R2) / R2

  Therefore, in order to prevent an unnecessary reset operation of the CPU 191, the power supply unit 2 includes a voltage adjustment unit 23 that reduces the threshold voltage Vs for a predetermined time when the safety switch 22 is closed. The CPU 191 is configured to prevent unnecessary reset operation of the CPU 191 due to voltage drop.

  As shown in FIG. 5A, the voltage adjusting unit 23 is connected in series with the photocoupler PhC connected to the node A to which the resistors R1 and R2 of the reset circuit 190 are connected, and the photocoupler PhC. The resistor R6 and the capacitor C2 are connected in parallel. The photocoupler PhC includes a light emitting diode and a phototransistor.

  In the voltage adjusting unit 23, when the safety switch 22 is closed and the output voltage V2 is supplied from the second DC stabilized power supply circuit 21, the light emitting diode emits light, the phototransistor is turned on, and the resistor R6 and the capacitor C2 is connected in parallel with the resistor R2 of the reset circuit 190. Therefore, the threshold voltage Vs is determined by the voltage dividing ratio of the resistors R1, R2, R6 and the capacitor C2. That is, the resistors R1, R2, R6 and the capacitor C2 constitute the resistor voltage dividing circuit of the present invention.

  The parallel resistance R′2 and the threshold voltage Vs due to the resistance R2, the resistance R6, and the capacitor C2 change as shown in FIG. 5B according to the change of the output voltage V2. Here, the value of the parallel resistor R′2 is the value of only the resistor R2 when the safety switch 22 is opened, and the charging of the capacitor C2 is completed after the safety switch 22 is closed, and the resistor R2 and the resistor R6 are connected in parallel. The time until the resistance value is stabilized is determined by the time constant τ between the resistor and the capacitor C2.

  The time constant τ can be adjusted by appropriately setting the resistance value and the capacitance of the capacitor C2. The resistance value and the capacitance of the capacitor C2 can be adjusted by the inrush current generated when the safety switch 22 is closed. The time constant τ is adjusted to be longer than the time Tdrp at which the voltage drop occurs. Further, the resistance values of the resistors R1, R2, and R6 and the capacitance of the capacitor C2 are adjusted so that the output voltage V1 does not become smaller than the threshold voltage Vs at least during the voltage drop occurrence time Tdrp after the safety switch 22 is closed. Is done.

  That is, the photocoupler PhC changes and sets the voltage dividing ratio of the resistance voltage dividing circuit for a predetermined time τ when the safety switch 22 is closed and the output voltage V2 of the second DC stabilized power supply circuit 21 is applied. The voltage adjusting unit 23 reduces the threshold voltage Vs for a predetermined time τ longer than at least the voltage drop occurrence time Tdrp after the safety switch 22 is closed. Therefore, even if the safety switch 22 is closed and an inrush current to the load group is generated, the CPU 191 does not execute an unnecessary reset operation.

  When the predetermined time τ elapses after the safety switch 22 is closed, the lowered threshold voltage Vs returns to the normal value, so that the reset circuit 190 has the output voltage V1 from the threshold voltage Vs that has returned to the normal value. When the voltage drops for some reason, a low level reset signal is output to cause the CPU 191 to execute the reset operation.

  Below, the change operation | movement of the threshold voltage Vs by the voltage adjustment part 23 is demonstrated using the flowchart shown in FIG.

  When the main body cover is opened and the safety switch 22 is opened (S1), the power supply from the second DC stabilized power supply circuit 21 is stopped and the photocoupler PhC is turned off (S2), so that the threshold voltage Vs. As shown in [Equation 1], the value is determined by the voltage dividing ratio of the resistors R1 and R2 (S3). In addition, when the photocoupler PhC is turned off, the electric charge stored in the capacitor C2 is discharged through the resistor R6.

When the safety switch 22 is closed (S4), the photocoupler PhC is turned on by receiving power from the second DC stabilized power supply circuit 21 (S5), so the threshold voltage Vs is expressed by [Equation 2]. As shown, the value is determined by the voltage division ratio between the parallel resistor R′2 and the resistor R1 including the resistors R2 and R6 and the capacitor C2 (S6), and charging of the capacitor C2 is started (S7). ).
[Equation 2]
Vs = Vref · (R1 + R′2) / R′2

When a predetermined time τ elapses after the safety switch 22 is closed (S8), the charging of the capacitor C2 is completed, so that the threshold voltage Vs is composed of resistors R2 and R6 as shown in [Equation 3]. The value determined by the voltage division ratio between the parallel resistor and the resistor R1 (S9).
[Equation 3]
Vs = Vref · (R1 + R2 // R6) / (R2 // R6)
However, R2 // R6 = R2 / R6 / (R2 + R6)

  Another embodiment will be described below.

  In the above-described embodiment, the copying machine in which the power supply device of the present invention is mounted has been described. However, the power supply device is not mounted only in the copying machine, but other image forming apparatuses such as a multifunction peripheral and a printer, or Alternatively, it may be mounted on equipment other than the image forming apparatus.

  In the above-described embodiment, the power supply adjustment unit 23 is configured to include the photocoupler PhC. However, instead of the photocoupler PhC, for example, the output voltage V2 from the second DC stabilized power supply circuit 21 is the base. May be provided, and the voltage dividing ratio of the resistance voltage dividing circuit may be adjusted by the transistor. In this case, it goes without saying that the output voltage V2 input to the base of the transistor should be stepped down in accordance with the specifications of the base by inserting a resistor or the like.

  Each of the above-described embodiments is merely an example of the present invention, and the scope of the present invention is not limited by the description. The specific configuration of each part is appropriately selected within the scope of the effects of the present invention. It goes without saying that changes can be designed.

Illustration of power supply and control unit External view of copier Explanatory drawing of 1st direct current stabilization power supply circuit and 2nd direct current stabilization power supply circuit (A) is explanatory drawing of a reset circuit, (b) is explanatory drawing of the reset signal output by a reset circuit. (A) is explanatory drawing of a reset circuit and a voltage adjustment part, (b) is explanatory drawing of the threshold voltage change of the output voltage of the 1st direct current | flow stabilization power supply circuit before and after closing of a safety switch. Flowchart for explaining threshold voltage changing operation of output voltage of first DC stabilized power supply circuit by voltage adjustment unit

2: Power supply (power supply unit)
19: Control unit 20: First DC stabilized power circuit 21: Second DC stabilized power circuit 22: Safety switch (interlock switch)
23: Voltage adjustment unit 190: Reset circuit 191: CPU

Claims (2)

A first DC stabilized power supply circuit that supplies power to a control unit having a CPU having a reset circuit that outputs a reset signal when the power supply voltage falls below a predetermined threshold voltage, and a load group driven by the control unit A power supply is switched between a second DC stabilized power supply circuit that supplies power at an output voltage higher than an output voltage of the first DC stabilized power supply circuit, and a power supply state from the second DC stabilized power supply circuit to the load group. A power supply device configured with a safety switch,
A resistance voltage dividing circuit connected between the output voltage of the first DC stabilized power supply circuit and the ground, and the threshold voltage is defined, a resistance between the voltage dividing terminal of the resistance voltage dividing circuit and the ground A parallel circuit of a capacitor and a series circuit of a photocoupler are connected in parallel, and when the safety switch is closed, the photocoupler is activated, and the capacitor is energized from the voltage dividing terminal to the parallel circuit. The threshold voltage is lowered only for a predetermined time required for charging, and when the safety switch is opened, the photocoupler is stopped, and the capacitor is connected via the resistor of the parallel circuit while maintaining the threshold voltage. A power supply device including a voltage adjusting unit for discharging . The time constant of the parallel circuit is set so that the predetermined time required for charging the capacitor is longer than the time when the output voltage of the first DC stabilized power supply circuit is lowered when the safety switch is closed. It has been has claim 1 power supply device according.

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