JP6043130B2 - Switching power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to a technology for stabilizing a switching power supply device.

  When the switching power supply device is unloaded or when the load is extremely small, a phenomenon of repeated starting and stopping may occur. For this reason, Patent Document 1 discloses a configuration in which a bleeder resistor is provided in a switching power supply device and power necessary for stable operation of the switching power supply device is consumed. FIG. 5 shows a schematic configuration of a switching power supply apparatus 300 having such a bleeder resistance. The AC voltage input via the AC plug 1 is applied to the switching power supply unit 4 via the power line filter 3. The switching power supply unit 4 generates a DC voltage VCC from the input AC voltage and applies the DC voltage to the load 6. In FIG. 5, reference numeral 7 is a bleeder resistor for stably operating the switching power supply unit 4, and reference numeral 8 is for connecting the bleeder resistor 7 to the switching power supply unit 4 or disconnecting it from the switching power supply unit 4. It is a transistor. Further, reference numeral 10 denotes a current detection resistor, reference numeral 12 denotes an operational amplifier, and reference numerals 9, 11, 13, 14, and 15 denote resistors that determine the amplification gain of the operational amplifier 12.

  First, the reason why the switching power supply device 300 repeats starting and stopping when there is no bleeder resistor 7 and no load is connected to the switching power supply device 300 or when the connected load is extremely small is described. To do. FIG. 6 is a schematic configuration diagram of the switching power supply unit 4. The insulating transformer 5 of the switching power supply unit 4 has three windings of a primary winding 5a, a secondary winding 5c, and an auxiliary winding 5b. The AC voltage input via the power line filter 3 is converted into a DC voltage by a rectifier circuit including a diode bridge 71 and a capacitor 72. The power supply control IC 23 switches the current flowing in the primary winding 5 a by turning on and off the FET 22, and thereby the voltage generated in the secondary winding 5 c is a rectifier circuit composed of a diode 73 and a capacitor 74. Convert to DC voltage and output. The output of the auxiliary winding 5b is rectified by the diode 20 and the capacitor 21 and used as the power supply voltage of the power supply control IC 23. Here, the power supply control IC 23 performs control to stabilize the output voltage regardless of fluctuations in the current flowing through the load of the switching power supply device 300 by changing the drive duty of the FET 22 or the like. Since the power supply voltage of the power supply control IC 23 is generated from the output of the auxiliary winding 5b, it drops as the current flowing through the secondary winding 5c decreases. Here, when the switching power supply device 300 has no load or an extremely small load, the voltage obtained from the auxiliary winding 5b may be lower than the minimum operating voltage necessary for operating the power supply control IC 23. When the voltage from the auxiliary winding 5b falls below the minimum operating voltage, the power supply control IC 23 stops, but since the AC voltage is continuously input to the switching power supply unit 4 from the AC plug 1 side, the power supply control IC 23 is activated again. In the same manner, the operation of stopping is repeated.

  Therefore, as shown in FIG. 5, by connecting the bleeder resistor 7 in parallel with the load on the load side of the switching power supply unit 4, the voltage obtained from the auxiliary winding 5b becomes equal to or higher than the minimum operating voltage of the power supply control IC 23. In addition, the output current of the secondary winding 5c is increased. However, if the voltage from the auxiliary winding 5b becomes equal to or higher than the minimum operating voltage of the power supply control IC 23 due to the current flowing through the load 6, the power consumed by the bleeder resistor 7 is unnecessary power consumption. Therefore, the bleeder resistor 7 is switched so as to be connected to or disconnected from the switching power supply unit 4 according to the current flowing through the load 6. Specifically, as shown in FIG. 5, a current value flowing through the load 6 is detected by a circuit including an operational amplifier 12 from the voltage across the current detection resistor 10. Then, the switching power supply device 300 and the bleeder resistor 7 are connected or disconnected by turning on or off the transistor 8 based on the detection result.

JP-A-7-337007

  In the configuration shown in FIG. 5, if the voltage drop in the current detection resistor 10 is large, that is, if the resistance value of the current detection resistor 10 is large, the voltage drop in the current detection resistor 10 when the power consumption in the load 6 increases. The accuracy of the power supply voltage VCC applied to the load 6 is affected. Therefore, the resistance value of the current detection resistor 10 needs to be reduced. On the other hand, if the resistance value of the current detection resistor 10 is small and the potential difference between both ends of the current detection resistor 10 is small, the influence of the input offset voltage of the operational amplifier 12 cannot be ignored and the detection accuracy of the current value flowing through the load 6 is affected. . That is, the configuration shown in FIG. 5 requires a complicated current detection circuit that satisfies the conflicting conditions.

  The present invention provides a switching power supply device that operates stably with an inexpensive configuration, and an image forming apparatus including the switching power supply device.

According to one aspect of the present invention, switching power supply means for converting an alternating voltage into a direct current voltage, a direct current voltage from the switching power supply means in an on state is applied to a resistor, and a direct current voltage from the switching power supply means in an off state is applied. A first switch means not applied to the resistor; and a DC voltage from the switching power supply means is applied to the load in an on state, and a DC voltage from the switching power supply means is not applied to the load in an off state; A switching power supply comprising: a switching element that is turned on in response to turning on a power switch of the switching power supply; and In response to the second switch means being turned on, the first switch means is turned off, and Said first switching means in response to the second switching means is turned off is Ri Do the on state, due to the power switch to the on state, the side connected to the switching power supply unit of the power supply switch The second switch means is turned on by the fluctuation of the potential on the opposite side .

  The switching power supply device can be stably operated with an inexpensive configuration.

The schematic block diagram of the switching power supply device by one Embodiment. Explanatory drawing of the operation | movement in the switching power supply device by one Embodiment. The schematic block diagram of the switching power supply device by one Embodiment. Explanatory drawing of the operation | movement in the switching power supply device by one Embodiment. The schematic block diagram of the switching power supply device by background art. The schematic block diagram of a switching power supply part. The figure which shows the example characteristic at the time of the light load of a switching power supply device.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First embodiment>
FIG. 1 is a schematic configuration diagram of a switching power supply apparatus 100 according to the present embodiment. In FIG. 1, an alternating voltage input via the AC plug 1 is applied to the switching power supply unit 4 via the power line filter 3. The switching power supply unit 4 converts the input AC voltage to generate a DC voltage. For example, when the switching power supply device 100 is a power supply device used in an image forming apparatus, the load 6 controls, for example, a brushless motor for conveying a recording material, a laser scanner motor, a laser drive circuit, and the like. It becomes a control board or the like.

  FIG. 6 is a schematic configuration diagram of the switching power supply unit 4 according to the present embodiment, as already described. As described above, the power supply control IC 23 restarts and repeats the same operation of stopping, so the switching power supply device 100 does not operate stably.

  Therefore, in FIG. 1, a bleeder resistor 7 for stably operating the switching power supply device 100 is inserted in parallel with the load 6 on the load 6 side of the switching power supply unit 4. The resistance value of the bleeder resistor 7 is determined so that a current equal to or greater than the minimum current value necessary for stably operating the switching power supply unit 4 flows through the switching power supply unit 4. Further, when a sufficient current flows through the load 6 and the switching power supply device 100 operates stably without providing the bleeder resistor 7, the bleeder resistor 7, the switching power supply unit 4, A P-channel FET 113 is provided between the two. The resistors 111 and 112 are resistors for driving the FET 113 (first switch unit). When the FET 113 is in an on state (hereinafter simply referred to as “on”), a DC voltage output from the switching power supply unit 4 is applied to the bleeder resistor 7, and the switching power supply unit 4 operates stably in the switching power supply unit 4. The necessary current flows. On the other hand, when the FET 113 is in the off state (hereinafter simply referred to as “off”), the DC voltage output from the switching power supply unit 4 is not applied to the bleeder resistor 7. Further, in the present embodiment, the power switch 110 (second switch unit) of the switching power supply device is provided between the FET 113 connected in parallel and the load 6. Hereinafter, the potential on the switching power supply unit 4 side of the power switch 110 is referred to as VCC1, and the potential on the load 6 side is referred to as VCC2. As shown in FIG. 1, the gate of the FET 113 is connected to VCC2 via a resistor 111.

  When an AC voltage is applied to the AC plug 1 with the power switch 110 turned off, the switching power supply unit 4 applies a DC voltage to the load side. At this time, since the power switch 110 is OFF, no DC voltage is applied to the load 6. Since the resistor 112 is grounded, the gate voltage of VCC2 and the FET 113 is 0V, and thus the FET 113 is turned on. Therefore, the switching power supply unit 4 and the bleeder resistor 7 are connected, and the voltage VCC1 is applied to the bleeder resistor 7. As a result, a current flows from the switching power supply unit 4 to the bleeder resistor 7, so that the switching power supply device 100 operates stably.

  Next, when the user turns on the power switch 110, a DC voltage is supplied to the load 6, and the gate voltage of the FET 113 rises via the resistor 111, so that the FET 113 is turned off. As a result, the bleeder resistor 7 is disconnected from the switching power supply unit 4. Thereafter, when the user turns off the power switch 110, VCC2 becomes 0V, so that the FET 113 is turned on and a current flows through the bleeder resistor 7. Thus, in the present embodiment, the state of the FET 113 is changed in conjunction with the change in the line connecting the power switch 110 and the load 6 due to the change in the state of the power switch 110. FIG. 2 shows the relationship between the on / off state of the power switch 110 and the current flowing through the VCC 2 and the bleeder resistor 7. In FIG. 2, VCC2 is on indicates that VCC2 is a predetermined potential supplied to the load, and VCC2 is off indicates that the potential of VCC2 is 0V. Further, when the bleeder resistance current is on, it indicates that a current is flowing through the bleeder resistance 7, and when the bleeder resistance current is off, it indicates that no current is flowing through the bleeder resistance 7.

  The bleeder resistor 7 is a resistor for allowing a minute current necessary to stably operate the switching power supply unit 4. For example, if VCC1 is + 3.3V and the current necessary for stable operation of the switching power supply unit 4 is 10 mA, the resistance value of the bleeder resistor 7 is 330Ω. While the power switch 110 is on, a current flowing from the switching power supply unit 4 to the ground via the resistors 111 and 112 is generated. However, the resistors 111 and 112 are resistors for driving the FET 113 with a voltage, and a large resistance value such as 33 kΩ can be used for the resistors 111 and 112, for example. In this case, the current flowing through the resistors 111 and 112 is 0.05 mA. The current flowing through the bleeder resistor 7, for example, 10 mA, or the current flowing through the load 6, for example, 3 A, is very small. The power consumption at can be ignored.

  In this way, the power switch 110 is arranged on the secondary output side of the switching power supply unit 4, that is, the load 6 side, the bleeder resistor 7 is provided on the upstream side (VCC1 side) of the power switch 110, and the control signal for driving the FET 113 Is taken from the downstream side (VCC2 side) of the power switch 110. With this configuration, the switching power supply device 100 can be stably operated with an inexpensive configuration without using a current detection resistor for detecting a current flowing through the load 6.

  As an example, it is assumed that the switching power supply unit 4 has light load characteristics shown in FIG. It is assumed that VCC1 is 3.3V and the resistance value of the bleeder resistor 7 is 330Ω. Since the current flowing through the bleeder resistor 7 is 10 mA when the power switch 110 is off, the power consumption in the switching power supply is 0.29 W when the bleeder resistor 7 is not connected, but the bleeder resistor 7 Is improved to 0.15W. That is, as a result of stabilizing the operation with the bleeder resistor 7, the power consumption can be reduced by 0.14W.

<Second embodiment>
Next, a second embodiment will be described with reference to FIGS. For example, a power supply device used in a device including a hard disk drive (HDD) does not immediately cut off the power supply voltage even if the power switch is turned off, until the access to the HDD ends and the head returns to the home position. Needs to supply power to the HDD. As described above, the switching power supply apparatus 200 according to the present embodiment is configured not to immediately stop power supply by an operation of turning off the power switch but to stop power supply after a predetermined delay time. Such a power switch configuration is called a soft switch.

  FIG. 3 is a schematic configuration diagram of the switching power supply apparatus 200 in the present embodiment. In the present embodiment, an FET 220 that is a switching element is provided at the position of the power switch 110 of the first embodiment. Note that the resistors 221 and 222 and the transistors 223 and 224 in FIG. 3 are provided to control the FET 220. In the present embodiment, the power switch 210 is provided between the base of the transistor 223 and the output of the switching power supply unit 4. More specifically, the base of the transistor 223 is connected to the side opposite to the side connected to the switching power supply unit 4 of the power switch 210.

  Only the base current of the transistor 223 flows through the power switch 210 in FIG. 3, and a switch having a lower current rating than the power switch 110 in FIG. 1 can be used. The base of the transistor 224 is connected to a latch signal that is a control signal output from the load 6, and the output of the power switch 210 is connected to the input portion of the power-on detection signal of the load 6. Note that when no power is supplied to the load 6, the output level of the latch signal is low.

  When an AC voltage is input from the AC plug 1 while the power switch 210 is off, the switching power supply unit 4 outputs a DC voltage. However, since the power switch 210 is off, the transistor 223 is also off, and since the output level of the latch signal is also low, the transistor 224 is also off. Therefore, the FET 220 is also turned off and no voltage is applied to the load 6. When the power switch 210 is turned on, the base potential of the transistor 223 varies and the transistor 223 is turned on. Therefore, current flows through the resistors 221 and 222 and the transistor 223, the gate voltage of the FET 220 is lowered, the FET 220 is also turned on, and the DC voltage output from the switching power supply unit 4 is applied to the load 6. When the load 6 is activated upon receiving power supply, the load 6 sets the latch signal to high. The timing when the latch signal is set to “high” is determined by the reset release time or the like in the load 6, and in the timing chart of FIG. Further, when the latch signal becomes high, the transistor 224 is turned on. Note that the operation of connecting and disconnecting the bleeder resistor 7 for stably operating the switching power supply device 200 to the switching power supply unit 4 is the same as that of the first embodiment, and thus further description thereof is omitted.

  Subsequently, when the power switch 210 is turned off, the power on detection signal changes from high to low, so that the load 6 detects that the power switch 210 is turned off. When the load 6 detects that the power switch 210 is turned off, the load 6 starts an off process sequence as shown in FIG. As shown in FIG. 4, the load 6 keeps the latch signal high until the end of the off process sequence. Therefore, even if the power switch 210 is turned off and the transistor 223 is also turned off, the transistor 224 is on, so that the FET 220 remains on. In the off processing sequence, the load 6 performs processing necessary for stopping the power supply, such as stopping access to the HDD 30, and changes the latch signal from high to low after the off processing sequence is completed. As a result, the transistor 224 is turned off, and thus the FET 220 is turned off and the power supply to the load 6 is stopped. As shown in the timing chart of FIG. 4, when the power switch 210 is turned off as a reference, the off process sequence ends after t2 seconds, and the load 6 changes the latch signal from high to low after t3 seconds later than t2 seconds. To change.

  As described above, the connection / disconnection of the bleeder resistor 7 can be controlled even with the soft switch configuration. When the power switch 210 is turned on, as in the first embodiment, current flows through the resistors 111 and 112 and power is consumed. This is a very small value, and the power consumption at the resistors 111 and 112 is as follows. It can be ignored.

  The specific values such as the resistance value of the bleeder resistance shown in the above embodiments are merely examples, and the present invention is not limited to the above values, and these allow the switching power supply device to operate stably. Therefore, it is set according to the current value necessary for this. Moreover, although FET was used as a switching element in the said embodiment, this invention is not limited to FET, Switching elements, such as another kind of transistor and a relay, can be used.

Claims (7)

Switching power supply means for converting AC voltage into DC voltage;
A first switch means for applying a DC voltage from the switching power supply means to the resistor in an ON state and not applying a DC voltage from the switching power supply means to the resistor in an OFF state;
A second switch means for applying a DC voltage from the switching power supply means to the load in an on state and not applying a DC voltage from the switching power supply means to the load in an off state;
A switching power supply device comprising:
The second switch means is a switching element that is turned on in response to turning on a power switch of the switching power supply device,
The first switch means is turned off in response to the second switch means being turned on, and the first switch means is turned on in response to the second switch means being turned off. Ri Do not the state,
The switching power supply characterized in that the second switch means is turned on due to a change in potential on the opposite side of the power switch connected to the switching power supply means by turning on the power switch. apparatus. Switching power supply means for converting AC voltage into DC voltage;
A first switch means for applying a DC voltage from the switching power supply means to the resistor in an ON state and not applying a DC voltage from the switching power supply means to the resistor in an OFF state;
A second switch means for applying a DC voltage from the switching power supply means to the load in an on state and not applying a DC voltage from the switching power supply means to the load in an off state;
A switching power supply device comprising:
The second switch means is a switching element that is turned on in response to turning on a power switch of the switching power supply device,
The first switch means is turned off in response to the second switch means being turned on, and the first switch means is turned on in response to the second switch means being turned off. State
The state of the second switch means is controlled by a signal output from the load in addition to the power switch. Switching power supply means for converting AC voltage into DC voltage;
A first switch means for applying a DC voltage from the switching power supply means to the resistor in an ON state and not applying a DC voltage from the switching power supply means to the resistor in an OFF state;
A second switch means for applying a DC voltage from the switching power supply means to the load in an on state and not applying a DC voltage from the switching power supply means to the load in an off state;
A switching power supply device comprising:
The second switch means is a switching element that is turned on in response to turning on a power switch of the switching power supply device,
The first switch means is turned off in response to the second switch means being turned on, and the first switch means is turned on in response to the second switch means being turned off. State
The second switch means is turned off when the power switch is turned off and the load outputs a signal for turning the second switch means off, and the power switch is turned on. Alternatively, the switching power supply device is turned on when the load outputs a signal for turning on the second switch means. The state of the first switch means changes due to a change in the potential of the line between the second switch means and the load due to the change of the state of the second switch means. The switching power supply device according to any one of claims 1 to 3 . The resistor, when the first switch means is on, any one of claims 1 to 4, characterized in that provided for supplying a current of predetermined value to the switching power supply unit The switching power supply device described in 1. 6. The switching power supply device according to claim 5 , wherein the predetermined value is a current value necessary for stably operating the switching power supply means. An image forming apparatus characterized in that it comprises a switching power supply device according to any one of claims 1 to 6.

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