JP2015163040A - Power source device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize smaller size and lower cost of a device by decreasing fluctuation width of an output voltage.SOLUTION: A power source device includes a transformer T701 including a primary winding Np and a plurality of secondary windings Ns1, Ns2, a main switching element Q701 for switching a current flowing the primary winding Np of the transformer T701, an operational amplifier IC 703 which feeds back a return current corresponding to a detection voltage according to an output voltage of the secondary winding of the transformer T701 to a primary side of the transformer T701, and a power source IC701 which controls output voltages of the secondary windings Ns1, Ns2 of the transformer T701 by controlling operation of the main switching element Q701 according to the return current. The operational amplifier IC 703 feeds back a current according to the detection voltage corresponding to the output voltages of the plurality of secondary windings Ns1, Ns2 at the time of equipment operation, and at the time of equipment standby, feeds back a current according to the detection voltage corresponding to the output voltage of the secondary winding Ns2.

Description

  The present invention relates to a power supply device that outputs a plurality of DC voltages, and an image forming apparatus including the power supply device.

  In general, in a power supply device provided for operating a device, an alternating voltage generated in a secondary winding of a transformer is rectified and smoothed by a rectifying and smoothing circuit, and a DC output voltage is generated. Then, the generated output voltage of the rectifying / smoothing circuit (for example, DC (direct current) 24V) is supplied to a unit using DC24V such as a motor. In addition, in order to supply the optimum DC output voltage (for example, DC 3.3 V or DC 5 V) to each unit arranged in the apparatus, a step-down converter circuit is arranged at the subsequent stage of the rectifying and smoothing circuit according to the DC output voltage. There is also a structure (for example, refer to patent documents 1). Furthermore, there is also a power supply apparatus that employs a system that directly generates a plurality of DC output voltages required by a device from a transformer by rectifying and smoothing alternating voltages generated in a plurality of secondary windings of the transformer.

  Further, in the operation state of the device, when the state in which the device is on standby is compared with the state in which the device is in operation, the power consumption of a DC output voltage such as DC 3.3V or DC 5V is relatively high in the standby state. Is generally less. In addition, the DC output voltage such as DC 24V consumes very little power because the drive source such as the motor is not operating during the standby state of the device.

Japanese Patent No. 4289904

  In the conventional power supply apparatus proposed in Patent Document 1 described above, as shown in FIG. 6A, the alternating voltage generated in the secondary winding of the transformer is rectified and smoothed, and a DC output voltage of DC24V is obtained. Generate. Then, a step-down converter circuit is arranged at the subsequent stage of the generated DC 24V DC output voltage, and for example, a DC 3.3V DC output voltage that is used relatively frequently in equipment is generated. A power supply device shown in FIG. 6B is an example of a power supply device that reduces the size and costs of the power supply device shown in FIG. That is, in the power supply device of FIG. 6B, a plurality of secondary windings are provided in the transformer, and the alternating voltage generated in each secondary winding is rectified and smoothed, so that DC 3.3V and DC 24V required by the device are obtained. Each DC output voltage is directly generated from a transformer to achieve downsizing and cost reduction.

  In the circuit diagram shown in FIG. 6B, the insulation transformer T701 is provided with two secondary windings Ns1 and Ns2, and an output voltage Vout1 of 24V DC is generated on the secondary winding Ns1 side. An output voltage Vout2 of DC 3.3V is generated on the side of the next winding Ns2. The output voltages Vout1 and Vout2 are input to the non-inverting input terminal (+) of the operational amplifier IC703 and compared with the reference voltage. Based on the comparison result, the power supply IC701 adjusts the duty of the main switching element Q701. To control the output voltage. The circuit configuration and operation of FIGS. 6A and 6B will be described later.

  There are two states of the device that receives power supply from the power supply device: an operation state and a standby state. For example, when the device is in an operating state, the electric power required for the output voltages of DC 24V and DC 3.3V is large, and the load current is on the order of, for example, several A (amperes). On the other hand, when the device is in a standby state, a drive source such as a motor is not operating, so the load current of DC 24V is very small. Furthermore, the power required for DC 3.3V is also reduced, and the load current is in the order of, for example, several tens to several hundred mA (milliamperes), which is a current value necessary for the microcontroller to maintain a standby state. . In this way, when the fluctuation range of the load current is very large due to the large power difference between the device operation time and the device standby time, the output voltage of DC 3.3V and DC 24V can be maintained within a desired voltage range. There is a problem that it is difficult.

  The present invention has been made under such circumstances, and it is an object of the present invention to reduce the fluctuation range of the output voltage and to realize downsizing and cost reduction of the apparatus.

  In order to solve the above-described problems, the present invention is configured as follows.

  (1) A transformer having a primary winding and a plurality of secondary windings, switching means for switching a current flowing through the primary winding of the transformer, and detection according to the output voltage of the secondary winding of the transformer Feedback means for feeding back a current corresponding to the voltage to the primary side of the transformer, and by controlling the operation of the switching means according to the current from the feedback means, the output voltage of the secondary winding of the transformer A first mode for supplying a large amount of power from the secondary winding to the load, and a second mode for supplying less power from the secondary winding to the load than in the first mode. In the first mode, the feedback means outputs the current corresponding to the detection voltage corresponding to the output voltage of the plurality of secondary windings. And fed back, the power supply apparatus characterized by feeding back the current according to the output voltage of a predetermined secondary winding of the plurality of secondary windings in the case of the second mode.

  (2) An image forming apparatus comprising: an image forming unit for forming an image on a recording material; and the power supply device according to (1).

  According to the present invention, it is possible to reduce the fluctuation range of the output voltage and to reduce the size and cost of the device.

1 is a circuit diagram showing a configuration of a power supply device according to Embodiment 1 Circuit diagram showing the configuration of the power supply device of Examples 2 and 3 A circuit diagram showing composition of a power unit of Example 4. A circuit diagram showing composition of a power unit of Example 5. Schematic diagram of the image forming apparatus of Example 6 Circuit diagram showing configuration of conventional power supply device

  Embodiments of the present invention will be described below in detail with reference to the drawings.

[Outline of power supply]
First, for comparison with an embodiment to be described later, the circuit configuration and operation of a conventional general power supply apparatus will be described with reference to FIG. In the conventional power supply device, an output voltage of DC (direct current) 24V is generated by rectifying and smoothing the alternating voltage generated in the secondary winding of the insulating transformer by the rectifying and smoothing circuit. Further, a step-down converter circuit is arranged at the subsequent stage of the rectifying / smoothing circuit that generates a DC 24 V output voltage, and a DC output voltage (for example, DC 3.3 V, DC 5 V, etc.) that is optimal for each unit having various functions is generated. The Here, as an example of a step-down converter, a description will be given using a step-down converter that generates an output voltage of DC 3.3 V, which is relatively used in a control circuit.

[Circuit configuration of power supply unit]
FIG. 6A is a circuit diagram of a conventional power supply device. The circuit system of the power supply apparatus is not limited to a specific system, and here, a switching power supply apparatus using a flyback system that is frequently used in general equipment will be described as an example. In FIG. 6A, the AC voltage input from the AC voltage source AC is rectified by a bridge diode DA701 and smoothed by an aluminum electrolytic capacitor C701 having a large capacitance (hereinafter referred to as capacitor C701). A DC input voltage Vin is generated. The insulating transformer T701 includes an input-side primary winding Np, an output-side secondary winding Ns, and a primary-side feedback winding Nb. An input voltage Vin, which is a voltage between terminals of the capacitor C701, is applied between one end (start of winding) of the primary winding Np and a current outflow terminal of the main switching element Q701. That is, the high potential side (also referred to as the (+) side of the input voltage Vin) of the capacitor C701 is one end of the primary winding Np, and the low potential side of the capacitor C701 (also referred to as the (−) side of the input voltage Vin) is the main switching. It is connected to the current outflow terminal of element Q701. The other end (end of winding) of the primary winding Np is connected to the current inflow terminal of the main switching element Q701.

  The feedback winding Nb is connected to the same polarity as the primary winding Np, and the secondary winding Ns is connected to a different polarity from the primary winding Np. The feedback winding Nb is provided with a rectifying / smoothing circuit including a rectifier diode D701 and a capacitor C702, and operates as a power input terminal of a power control IC 701 (hereinafter referred to as a power IC 701) that controls the main switching element Q701. Supply voltage. Furthermore, the other end of the starting resistor R701 having one end connected to the (+) side of the input voltage Vin is connected to the power supply input terminal of the power supply IC701. The operating voltage necessary for the operation of the power supply IC 701 is supplied from the input voltage Vin via the starting resistor R701 until the output voltage of the rectifying / smoothing circuit including the rectifying diode D701 and the capacitor C702 rises to a predetermined voltage. The The control terminal of the main switching element Q701 is connected to the drive terminal of the power supply IC 701 via the resistor R702. One end of the resistor R703 is connected to the control terminal of the switching element Q701, and the other end is connected to the (−) side of the input voltage Vin. Thereby, when the main switching element Q701 is in the off state, the potential of the control terminal of the main switching element Q701 is held at the off-state potential when not operating.

  Further, the current output terminal of the light receiving element (phototransistor) of the photocoupler IC 702 is connected to the feedback terminal of the power supply IC 701, and the current input terminal of the light receiving element is connected to the power input terminal of the power supply IC 701 via the resistor R704. ing. For example, when the current flowing into the feedback terminal decreases, the power supply IC 701 reduces the on-duty (OnDuty) (time ratio of the on state) of the main switching element Q701 so that the current flows through the primary winding Np of the isolation transformer T701. shorten. Thus, control is performed to lower the voltage of the output voltage Vout1. On the other hand, when the current flowing into the feedback terminal increases, the power supply IC 701 increases the on-duty of the main switching element Q701 and lengthens the time during which the current flows through the primary winding Np of the insulating transformer T701. Thus, control for increasing the voltage of the output voltage Vout1 is performed. In this way, the power supply IC 701 performs control so that the output voltage Vout1 (here, DC24V) becomes a constant voltage.

  The secondary winding Ns of the insulating transformer T701 is provided with a rectifying / smoothing circuit (first rectifying / smoothing means) including a rectifying diode D702 and an aluminum electrolytic capacitor C703 (hereinafter referred to as a capacitor C703). Then, the alternating voltage rectified by the rectifier diode D702 is smoothed. The anode side of the rectifying diode D702 is connected to the side opposite to the primary winding of the secondary winding Ns of the isolation transformer T701, and the other end of the capacitor C703 having one end grounded to the cathode side of the diode D702. Is connected. The DC output voltage Vout1 smoothed by the capacitor C703 is divided by resistors R705 and R706, and the divided voltage (also referred to as a detection voltage) is a non-inverting input terminal ((+) terminal in the figure) of the operational amplifier IC703. ). On the other hand, the reference voltage is input to the inverting input terminal ((−) terminal in the figure) of the operational amplifier IC 703 and is compared with the detection voltage that is the divided voltage input to the non-inverting input terminal. The operational amplifier IC 703 increases or decreases the current flowing through the light emitting element (LED) of the photocoupler IC 702 via the resistor R707 by outputting an output voltage from the output terminal based on the comparison result. By increasing or decreasing the current flowing through the light emitting element (LED) of the photocoupler IC 702, the current flowing through the light receiving element (phototransistor) also increases or decreases. As a result, a current corresponding to the output voltage Vout1 is input to the feedback terminal of the power supply IC 701. Will be. A resistor R708 and a capacitor C705 connected in series between the output terminal and the non-inverting input terminal of the operational amplifier IC703 are provided for performing phase correction.

[Step-down converter circuit]
Next, the circuit configuration and operation of a step-down converter circuit that generates a lower voltage (for example, DC 3.3 V) from the DC output voltage Vout1 will be described. The step-down converter circuit shown in FIG. 6A includes a switching element Q702, an inductor L701, a comparator IC 704, a diode D703, an aluminum electrolytic capacitor C704, and resistors R709 to R712. Switching element Q702 has a current inflow terminal connected to a high potential side terminal of capacitor C703, which is the (+) side of output voltage Vout1, and a current outflow terminal connected to one end of inductor L701. The other end of the inductor L701 is connected to an aluminum electrolytic capacitor C704 (hereinafter referred to as a capacitor C704) that generates a DC output voltage Vout2. Further, the cathode terminal of the diode D703 is connected to the current outflow terminal of the switching element Q702, and the anode terminal of the diode D703 is connected to the low potential side (GND (ground) side) of the output voltage Vout1. The resistor R709 is connected between the current inflow terminal of the switching element Q702 and the control terminal, and prevents the potential of the control terminal of the switching element Q702 from becoming unstable.

  The output terminal of the comparator IC 704 is connected to one end of the resistor R710, and the other end of the resistor R710 is connected to the control terminal of the switching element Q702. The reference voltage is input to the inverting input terminal ((−) terminal in the figure) of the comparator IC 704, and the output voltage Vout2 is applied to the non-inverting input terminal ((+) terminal in the figure) by resistors R711 and R712. The divided voltage is input. The comparator IC 704 outputs a low level signal from the output terminal when the divided voltage input to the non-inverting input terminal is lower than the reference voltage input to the inverting input terminal. As a result, switching element Q702 becomes conductive, and an exciting current flows through inductor L701, whereby a charging current flows through capacitor C704 and output voltage Vout2 rises. On the other hand, when the output voltage Vout2 rises, the comparator IC 704 switches the output terminal to a high impedance state when the divided voltage input to the non-inverting input terminal is higher than the reference voltage input to the inverting input terminal, and the switching is performed. Element Q702 is turned off. As a result, the excited inductor L701 is regenerated through the diode D703, and a regenerative current flows from the diode D703, whereby a charging current is supplied to the capacitor C704. When the output voltage Vout2 is higher than the predetermined potential, the output terminal of the comparator IC 704 continues the high impedance state, thereby continuing the non-conduction state of the switching element Q702. Through the series of operations described above, the output voltage Vout1 (DC24V) and the output voltage Vout2 (DC3.3V) are respectively controlled at a constant voltage.

  By the way, microcontrollers used in device control circuits have become increasingly multifunctional in recent years, and more functions are provided. On the other hand, with the increase in functionality of microcontrollers, the power required by microcontrollers also tends to increase. In order to enable the power supply required by the microcontroller, it is necessary to supply a large amount of power from, for example, a DC 3.3V step-down converter. For this reason, the circuit becomes more complicated or a high-performance element needs to be used, leading to an increase in size and cost of the power supply device.

[Circuit configuration of other power supply units]
On the other hand, as another power supply device, each output voltage of DC 3.3V and DC 24V required by the device is directly obtained by rectifying and smoothing alternating voltages generated in a plurality of secondary windings provided in the insulation transformer. There is also a type of power supply device that generates from an insulating transformer. Below, the power supply device which produces | generates two DC output voltages from an insulation transformer is demonstrated. FIG. 6B is a circuit diagram of a power supply device that generates two DC output voltages from an insulating transformer. Note that the same reference numerals are given to circuits having the same configuration as that of the power supply device described in FIG. There are two differences in the circuit configuration of the power supply device of FIG. 6B and the power supply device of FIG. The first point is that the secondary winding Ns2 is newly provided on the output side of the insulating transformer T701 in the power supply device of FIG. 6B compared to FIG. 6A. The secondary winding Ns1 that is the first secondary winding is provided to generate an output voltage of DC 24V that is the first output voltage, and the secondary winding that is the second secondary winding. Ns2 is provided to generate an output voltage of DC 3.3V, which is the second output voltage. Furthermore, a rectifying / smoothing circuit (second rectifying / smoothing means) including a rectifying diode D801 and an aluminum electrolytic capacitor C801 (hereinafter referred to as capacitor C801) is provided in the secondary winding Ns2 newly provided in the insulating transformer T701. It has been added.

  The second point is that the output voltage input to the non-inverting input terminal of the operational amplifier IC703 for comparison with the reference voltage is not only DC24V but also DC3.3V is input via the feedback resistor R801. . With such a configuration, the operational amplifier IC 703 compares the detection voltage and the reference voltage based on the two output voltages of DC 3.3V that is the output voltage Vout2 and DC24V that is the output voltage Vout1. . Then, feedback control in which the power supply IC 701 controls the output voltage based on the comparison result is possible. In FIG. 6B, the structure of the isolation transformer is complicated because the number of secondary windings increases, but the step-down converter circuit for generating DC 3.3V described in FIG. This is effective for reducing the size and cost of the power supply device.

  By the way, there are two states, an operating state and a standby state, for a device that receives power supply from a power supply device. For example, when the device is in an operating state, the electric power required for the output voltages of DC 24V and DC 3.3V is large, and the load current is on the order of, for example, several A (amperes). On the other hand, when the device is in a standby state, a drive source such as a motor is not operating, so the load current of DC 24V is very small. Furthermore, the power required for DC 3.3V is also reduced, and the load current is in the order of, for example, several tens to several hundred mA (milliamperes), which is a current value necessary for the microcontroller to maintain a standby state. . Therefore, when the device is on standby, the power consumption is often much lower than when the device is operating.

  Table 1 is a table showing simulation results when the load currents of the output voltages of DC 3.3V and DC 24V are changed in the circuit shown in FIG. 6B. In Table 1, state 1 corresponds to a device operating state, state 2, state 3 and state 4 correspond to a device standby state. When the device is on standby, the load current changes greatly due to image processing by the device controller, access to the memory, and the like, so the states are described in three parts. Further, Vout2 (load current) and Vout1 (load current) indicate current values flowing through loads supplied with DC 3.3V and DC 24V, respectively. Further, Vout2 (output voltage) and Vout1 (output voltage) indicate voltage values generated at both ends of the capacitors C801 and C703, respectively.

  As shown in Table 1, as described in the state 2, the state 3, and the state 4, when the device is on standby, the load current fluctuation range of the output voltage Vout2 (DC 3.3V) is 2 A (ampere) (state 2 ) To 0.0165A (state 4). As the load current fluctuation range increases, as shown in Table 1, the fluctuation range of the output voltage Vout2 (DC 3.3 V) also increases from 3.256 V (state 2) to 3.344 V (state 4). . As described above, in one operating state (for example, when the apparatus is on standby), if the fluctuation range of the DC output voltage Vout2 (DC 3.3V) is large, fluctuation occurs in the voltage supplied to the controller that controls the apparatus. . It is not preferable from the viewpoint of stable operation of the controller that the voltage used as a reference for operating the controller varies.

  Moreover, as shown in Table 1, the following problems arise due to a large power difference due to a difference in load current between the device operation time and the device standby time. In other words, the load current during device operation is, for example, several volts A for DC 24 V and DC 3.3 V. On the other hand, when the apparatus is on standby, the load current of DC 24V is very small and the load current of DC 3.3V is several tens to several hundreds mA. In the circuit configuration shown in FIG. 6B, the voltage corresponding to the output voltage (load current) of 24V DC and 3.3V is always applied to the non-inverting input terminal of the operational amplifier IC 703 during the operation of the device and the standby state of the device. Have been entered. For this reason, even when the load current of 24V DC is small, for example, when the device is on standby, a voltage corresponding to the output voltage of 24V DC is input to the non-inverting input terminal of the operational amplifier IC703. Since the fluctuation range of the load current of DC 3.3V is large when the apparatus is on standby, the voltage corresponding to the output voltage of DC 3.3V input to the non-inverting input terminal of the operational amplifier IC 703 also varies. As a result, since a voltage corresponding to DC24V is superimposed on a voltage corresponding to the output voltage of DC3.3V, the fluctuation range of the output voltage of DC3.3V which is the output voltage Vout2 is increased. In this way, voltages corresponding to two DC voltages having different voltages are input to the non-inverting input terminal of the operational amplifier IC703. Therefore, when the fluctuation range of the load current is very large, there is a problem that it is difficult to maintain the DC output voltage of DC 3.3V and DC 24V within a desired voltage range.

  In the first embodiment, a description will be given of a power supply apparatus having a circuit configuration that can suppress fluctuations in the output voltage of DC 3.3 V, which is the output voltage Vout2, when a device to which power is supplied is in a standby state.

[Circuit configuration of power supply unit]
FIG. 1 is a circuit diagram showing the configuration of the power supply device of this embodiment. In addition, the same code | symbol is attached | subjected about the circuit of the same structure as the power supply device demonstrated in FIG.6 (b), and description is abbreviate | omitted. In the circuit diagram shown in FIG. 1, compared to the circuit diagram of FIG. 6B, a circuit composed of switching elements Q101 and Q102 and resistors R101, R102 and R103 and a control signal corresponding to the state of the device are input. Mode terminal (Mode in the figure) is added. Thus, the present embodiment is characterized in that it can be configured to block the input of the output voltage Vout1 to the non-inverting input terminal of the operational amplifier IC703 via the feedback resistor R705 in accordance with the input from the mode terminal.

  In FIG. 1, one end of a feedback resistor R705 (first resistor) is connected to a current inflow terminal of a switching element Q101 (first switching element), and the other end is connected to one end of a capacitor C703 and a resistor R101. The other end of the resistor R101 is connected to the control terminal of the switching element Q101. This is provided to keep the switching element Q101 in a non-conductive state even when the switching element Q101 is not driven. The current outflow terminal of the switching element Q101 is connected to one end of the voltage dividing resistor R706. The control terminal of the switching element Q101 is connected to the current inflow terminal of the switching element Q102, and the current outflow terminal of the switching element Q102 is connected to the low potential side (GND side) of the output voltages Vout1 and Vout2. The other end of the resistor R102 whose one end is connected to the low potential side (GND side) of the output voltages Vout1 and Vout2 and one end of the resistor R103 are connected to the control terminal of the switching element Q102. Furthermore, the other end of the resistor R103 is connected to the mode terminal. From the mode terminal, a high level signal is output when the device is in an operating state, and a low level when the device is in a standby state, depending on the operating state of the device supplied with power from the power supply device. Signal is input. The signal input from the mode terminal is the same in the following embodiments.

[Circuit operation of power supply unit]
Next, circuit operation will be described. When the signal from the mode terminal is a high level signal (the device is in an operating state), a high level voltage is applied to the control terminal of the switching element Q102, so that a current flows into the control terminal and the conduction state ( ON state). When the switching element Q102 becomes conductive, a current flows through the resistor R101 and a current also flows through the control terminal of the switching element Q101, so that the switching element Q101 becomes conductive. When switching element Q101 becomes conductive, the load current of output voltage Vout1 flows through feedback resistor R705, and the load current of output voltage Vout2 flows through feedback resistor R801. As a result, detection voltages corresponding to the output voltages of DC 24 V and DC 3.3 V that are input to the non-inverting input terminal are input to the non-inverting input terminal of the operational amplifier IC 703. The operational amplifier IC703 compares the detection voltage corresponding to the output voltages of DC24V and DC3.3V with the reference voltage input to the inverting input terminal, and outputs a voltage based on the comparison result from the output terminal. A feedback current (feedback current) corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 through the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 according to the feedback current input to the feedback terminal, and performs constant voltage control of the output voltages Vout1 and Vout2 generated on the secondary side of the insulating transformer T701.

  On the other hand, when the signal from the mode terminal is a low level signal (the device is in a standby state), a low level voltage is applied to the control terminal of the switching element Q102, so that the switching element Q102 is in a non-conduction state (off). State). When switching element Q102 is turned off, no current flows through resistor R101, and no current flows through the control terminal of switching element Q101, so switching element Q101 is also turned off. As a result, only the output voltage Vout2 is input to the non-inverting input terminal of the operational amplifier IC703 via the feedback resistor R801. The operational amplifier IC703 compares the detection voltage corresponding to the output voltage of DC 3.3V with the reference voltage, and outputs a voltage based on the comparison result from the output terminal. Then, a current corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 via the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 in accordance with the feedback current input to the feedback terminal, and constant voltage control of the output voltage Vout2 generated on the secondary side of the isolation transformer T701 is performed. That is, when the device is operating in the first mode, constant voltage control is performed so that the output voltage of both DC 3.3V and DC 24V is monitored to be within the range of the output voltage necessary for the device. On the other hand, by monitoring only the DC 3.3V DC output voltage during device standby in the second mode, constant voltage control is performed so as to be within the range of output voltage required during device standby.

  Table 2 shows simulation results when the load currents of the output voltages of DC 3.3V and DC 24V are changed in the circuit shown in FIG. 1 of the present embodiment. The items indicated by the vertical states 1 to 4 and the horizontal Vout2 (load current), Vout1 (load current), Vout2 (output voltage), and Vout1 (output voltage) in Table 2 are the same as in Table 1. Is omitted. The output voltage Vout2 in the state 2, the state 3 and the state 4 which are the standby states shown in Table 1 are 3.256V, 3.322V and 3.344V, respectively, and the fluctuation range is 0.088V. (= 3.344V-3.256V). On the other hand, the output voltage Vout2 in the state 2, state 3, and state 4 shown in Table 2 of the present embodiment is 3.452V, 3.48V, and 3.494V, respectively, and the fluctuation range is 0.042V (= 3 .494V-3.452V). In the power supply device of this embodiment, the circuit configuration shown in FIG. 1 makes it possible to suppress the fluctuation of the output voltage Vout2 (DC3.3V) during standby of the device, which was a problem, and stabilizes the controller during standby of the device. It becomes possible to operate. Furthermore, the circuit configuration of the power supply device of the present embodiment is reduced compared to the circuit configuration of the conventional power supply device shown in FIG. Yes. As described above, according to the present embodiment, it is possible to reduce the fluctuation range of the output voltage, and to realize downsizing and cost reduction of the device.

  In the first embodiment, the power supply apparatus having the circuit configuration capable of suppressing the fluctuation range of the output voltage Vout2 when the apparatus is on standby has been described. In the second embodiment, a description will be given of a power supply device that can suppress the fluctuation range of the output voltage Vout2 depending on the operation state of the device.

[Circuit configuration of power supply unit]
FIG. 2A is a circuit diagram illustrating a circuit configuration of the power supply device according to the present embodiment. In addition, the same code | symbol is attached | subjected about the circuit of the same structure as the power supply device demonstrated in FIG.6 (b) and FIG. 1, and description is abbreviate | omitted. In the circuit diagram shown in FIG. 2A, a circuit including a switching element Q201 and resistors R201 and R202 is added as compared with the circuit diagram of FIG. As a result, compared with the circuit configuration of the power supply device shown in FIG. 1 of the first embodiment, the feedback amount of the output voltage Vout2 to the operational amplifier IC 703 is made variable according to the operating state of the device to which power is supplied. This is a feature of the embodiment.

  In FIG. 2A, one end of a resistor R201 (second resistor) is connected to a feedback resistor R801 and a current outflow terminal of the switching element Q201. The other end of the resistor R201 is connected to the current inflow terminal of the switching element Q201, the high potential side of the output voltage Vout2, and one end of the resistor R202. That is, the resistor R201 is connected in parallel with the switching element Q201. The other end of the resistor R202 is connected to the control terminal and mode terminal of the switching element Q201.

[Circuit operation of power supply unit]
Next, circuit operation will be described. When the signal from the mode terminal is a high level signal (the device is in an operating state), a high level voltage is applied to the control terminal of the switching element Q102, and the switching element Q102 becomes conductive (ON state), and switching Element Q101 is also turned on. On the other hand, since the signal from the mode terminal is at a high level, no current flows through the resistor R202, and the switching element Q201 is not in a conductive state. As a result, the load current of the output voltage Vout1 flows through the feedback resistor R705, the load current of the output voltage Vout2 flows through the resistor R201 and the feedback resistor R801 (third resistor), and the detection voltage is the non-inverting input terminal of the operational amplifier IC703. Is input. The operational amplifier IC703 compares the detection voltage corresponding to the output voltage of DC24V and DC3.3V input to the non-inverting input terminal and the reference voltage input to the inverting input terminal, and outputs a voltage based on the comparison result. Output from the terminal. A feedback current (feedback current) corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 through the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 according to the feedback current input to the feedback terminal, and performs constant voltage control of the output voltages Vout1 and Vout2 generated on the secondary side of the insulating transformer T701.

  On the other hand, when the signal from the mode terminal is a low level signal (the device is in a standby state), a low level voltage is applied to the control terminal of the switching element Q102, so that the switching element Q102 is in a non-conduction state (off). State). When switching element Q102 is turned off, switching element Q101 is also turned off. On the other hand, since the signal from the mode terminal is at a low level, a current flows through the resistor R202, and a current flows through the control terminal of the switching element Q201, so that the switching element Q201 becomes conductive. As a result, only the output voltage Vout2 is input to the non-inverting input terminal of the operational amplifier IC703 via only the feedback resistor R801, not the resistor R201. The operational amplifier IC703 compares the detection voltage corresponding to the output voltage of DC 3.3V with the reference voltage, and outputs a voltage based on the comparison result from the output terminal. Then, a current corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 via the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 in accordance with the feedback current input to the feedback terminal, and constant voltage control of the output voltage Vout2 generated on the secondary side of the isolation transformer T701 is performed. That is, when the device is operating (the mode terminal is at the high level), the output voltage of both DC 3.3V and DC 24V is monitored, and constant voltage control is performed so as to be within the range of the output voltage necessary for the device. On the other hand, by monitoring only the DC output voltage of DC 3.3V at the time of device standby, constant voltage control is performed so as to be within the range of output voltage required at the time of device standby. In particular, with respect to DC 3.3V of the output voltage Vout2, the resistance value of the feedback resistor is changed between when the device is operating and when the device is on standby. That is, when the device is on standby, the detection voltage via the feedback resistor R801 is input to the non-inverting input terminal of the operational amplifier IC 703, thereby suppressing the fluctuation range of DC 3.3V during device standby as in the first embodiment. be able to. In addition, when the device is in operation, the feedback current value is reduced by causing the load current to flow through the resistor R201 that suppresses the fluctuation range of DC 3.3V between the device operation and the device standby time and considers the balance with the output voltage of DC 24V. change.

  Table 3 shows the simulation results when the load currents of the output voltages of DC 3.3V and DC 24V are changed in the circuit shown in FIG. The items indicated by the vertical states 1 to 4 and Vout2 (load current), Vout1 (load current), Vout2 (output voltage), and Vout1 (output voltage) in Table 3 are the same as those in Tables 1 and 2. The description is omitted. As described above, in Example 1, the fluctuation range of the output voltage Vout2 (DC 3.3V) when the device was in the standby state was 0.042V. The output voltages when the device is in operation (state 1) and standby (state 4) are 3.119V and 3.494V, respectively, from Table 2, and the fluctuation range is 0.375V (= 3.494V-3). 119V). By the way, in Table 1 for FIG. 6B, the output voltages when the device is in operation (state 1) and standby (state 4) are 3.119V and 3.344V, respectively, and the fluctuation range is 0.225V. (= 3.344V-3.119V), and the fluctuation range was larger in Example 1.

  On the other hand, the output voltage Vout2 in the state 2, the state 3 and the state 4 at the time of device standby shown in Table 3 of the present embodiment is 3.153V, 3.178V, and 3.191V, respectively. And the fluctuation range is 0.038V (= 3.191V-3.153v), and the fluctuation range of DC3.3V at the time of apparatus standby is smaller than the case of the first embodiment. Furthermore, the output voltages when the device is in operation (state 1) and in standby (state 4) are 3.119V and 3.191V, respectively, from Table 3, and the fluctuation range is 0.072V (= 3.191V-3). 119V), which is about 1/5 or less of the 0.375V in the first embodiment. In the present embodiment, the circuit configuration shown in FIG. 2A makes it possible to change the output voltage Vout2 (DC 3.3V) during device standby, which is a problem, and the output voltage Vout2 during device operation and device standby. It became possible to suppress the fluctuation of (DC 3.3V). This makes it possible to stably operate the controller during device operation and during standby. Furthermore, the circuit configuration of the power supply device of the present embodiment is reduced compared to the circuit configuration of the conventional power supply device shown in FIG. Yes. As described above, according to the present embodiment, it is possible to reduce the fluctuation range of the output voltage, and to realize downsizing and cost reduction of the device.

  In the first and second embodiments, the circuit configuration for suppressing the fluctuation range of the output voltage Vout2 (DC3.3V) has been described. In the third embodiment, the circuit configuration for suppressing the fluctuation range of the output voltage Vout1 (DC24V) will be described.

[Circuit configuration of power supply unit]
FIG. 2B is a circuit diagram illustrating a circuit configuration of the power supply device according to the present embodiment. In addition, the same code | symbol is attached | subjected about the circuit of the same structure as the power supply device demonstrated in Fig.2 (a) of Example 2, and description is abbreviate | omitted. In FIG. 2B, the circuit on the primary side of the isolation transformer T701 shown in FIG. 2A of the second embodiment is described with the circuit excluding the primary winding Np and the feedback winding Nb. Omitted. The difference between the circuit configuration of the power supply device of the present embodiment and the circuit configuration shown in FIG. 2A of the second embodiment is as follows. That is, in the circuit diagram shown in FIG. 2A of the second embodiment, the voltage on the low potential side, which is the reference of the potential of the secondary winding Ns1 for the output voltage Vout1 (DC 24V), is at the GND level. On the other hand, in FIG. 2B of the present embodiment, the low potential side, which is the reference of the potential of the secondary winding Ns1 for the output voltage Vout1, is the secondary winding Ns2 for the output voltage Vout2 (DC3.3V). Is connected to the subsequent stage of the rectifying / smoothing circuit provided in FIG. As a result, the low potential that is the reference of the potential of the output voltage Vout1 (DC 24V) is raised from the GND level to DC 3.3V, which is a feature of this embodiment. The other circuit configuration of FIG. 2B is the same as the circuit configuration of FIG. 2A of the second embodiment.

  By adopting such a configuration, the width of the output voltage can be reduced as compared with the case of the second embodiment, so that the number of turns (number of windings) of the secondary winding Ns1 of the insulating transformer T701 can be reduced. Can do. As a result, it is possible to reduce the influence of the voltage fluctuation in the output voltage Vout1 corresponding to the secondary winding Ns1 with respect to the primary side excitation of the insulating transformer T701. Furthermore, the circuit configuration of the power supply device of the present embodiment also has a reduced step-down converter circuit compared to the circuit configuration of the conventional power supply device shown in FIG. Yes. As described above, according to the present embodiment, it is possible to reduce the fluctuation range of the output voltage, and to realize downsizing and cost reduction of the device.

  In the fourth embodiment, a circuit that selects an output voltage to be subjected to feedback control in accordance with an operating state of a device that is supplied with power from a power supply device and a circuit that controls supply / cutoff of the output voltage to the device are combined. Thus, a circuit configuration in which the number of parts is reduced will be described.

[Circuit configuration of power supply unit]
FIG. 3A is a circuit diagram illustrating a circuit configuration of the power supply device according to the present embodiment. In addition, the same code | symbol is attached | subjected about the circuit of the same structure as the power supply device demonstrated in FIG. 1, and description is abbreviate | omitted. In FIG. 3A, as in the third embodiment, the primary winding Np and the feedback winding Nb of the primary side circuit of the insulation transformer T701 shown in FIG. Description of the circuit except for is omitted. The circuit configuration of the power supply apparatus according to the present embodiment illustrated in FIG. 3A is different from the circuit configuration illustrated in FIG. That is, in FIG. 3A, compared to the circuit configuration of FIG. 2A of the second embodiment, a circuit constituted by the switching element Q401, the feedback resistor R401, the load resistor R402, the resistor R403, and the resistor R404 is output voltage. It is added to the Vout1 (DC24V) side. In FIG. 3A, the switching element Q101, the resistor R101, and the feedback resistor R705 described in FIG. 2A of the second embodiment are omitted.

  In FIG. 3A, the current inflow terminal of the switching element Q401 (first switching element) is connected to the high potential side of the output voltage Vout1. The current outflow terminal of the switching element Q401 is connected to the other end of the load resistor R402 whose one end is grounded and one end of the feedback resistor R401 (first resistor). The other end of the feedback resistor R401 is connected to a connection point between the feedback resistor R801 and the resistor R706. Further, a resistor R403 is connected between the control terminal of the switching element Q401 and the current inflow terminal to prevent the switching element Q401 from being in a conductive state when not driven. Furthermore, the other end of the resistor R404 whose one end is connected to the control terminal of the switching element Q401 is connected to the current inflow terminal of the switching element Q102. Thereby, compared with the circuit configuration of the power supply apparatus shown in FIG. 2A of the second embodiment, the feedback resistor R401 of the output voltage Vout1 is connected to the subsequent stage of the switching element Q401 for interrupting the load connected to the output voltage Vout1. The point is a feature of this embodiment.

  The output voltage Vout1 (DC24V) is provided with a load resistor R402. In this case, the switching element Q401 is arranged at the output voltage Vout1, and the reactive power is reduced when the device is in a standby state or the like by supplying / cutting off power to the load resistor R402 according to the state of the load device. Many methods are used. Therefore, a circuit composed of the switching element Q401, the load resistor R402, the resistor R403, and the resistor R404 is added to the circuit of FIG. Therefore, in this embodiment, taking advantage of such a circuit configuration, the feedback resistor R401 of the output voltage Vout1 is arranged at the subsequent stage of the switching element Q401. As a result, when the device is operating, the switching element Q401 becomes conductive, a current flows through the load resistor R402, and a load current of the output voltage Vout1 flows through the feedback resistor R401 to the non-inverting input terminal of the operational amplifier IC703. On the other hand, since the switching element Q401 is in a non-conducting state when the device is on standby, the reactive power in the load resistor R402 is reduced and the load current of the output voltage Vout1 does not flow to the non-inverting input terminal of the operational amplifier IC703. Compared with the second embodiment, this circuit configuration eliminates the switching element Q101, the resistor R101, and the feedback resistor R705, thereby reducing the number of components and reducing the cost. It is a feature.

[Circuit operation of power supply unit]
Next, circuit operation will be described. When the signal from the mode terminal is a high level signal (the device is in an operating state), a high level voltage is applied to the control terminal of the switching element Q102. As a result, a current flows into the control terminal of the switching element Q102, and a conductive state (ON state) is established. When switching element Q102 is turned on, a current flows through resistors R403 and R404, and a potential difference is generated between the current inflow terminal of switching element Q401 and the control terminal, so that switching element Q401 is turned on. On the other hand, since the signal from the mode terminal is at a high level, no current flows through the resistor R202, and the switching element Q201 is not in a conductive state. As a result, the load current of the output voltage Vout1 flows through the feedback resistor R401, and the load current of the output voltage Vout2 flows through the resistor R201 and the feedback resistor R801, so that the detection voltage is input to the non-inverting input terminal of the operational amplifier IC703. The The operational amplifier IC 703 outputs from the output terminal a voltage based on the comparison result between the detection voltage corresponding to the output voltage of DC 24 V and DC 3.3 V input to the non-inverting input terminal and the reference voltage input to the inverting input terminal. To do. A feedback current (feedback current) corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 through the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 according to the feedback current input to the feedback terminal, and performs constant voltage control of the output voltages Vout1 and Vout2 generated on the secondary side of the insulating transformer T701.

  On the other hand, when the signal from the mode terminal is a low level signal (the device is in a standby state), a low level voltage is applied to the control terminal of the switching element Q102, so that the switching element Q102 is in a non-conduction state (off). State). When switching element Q102 is turned off, no current flows through resistors R403 and R404, and switching element Q401 is turned off. On the other hand, since the signal from the mode terminal is at a low level, a current flows through the resistor R202, and a current flows through the control terminal of the switching element Q201, so that the switching element Q201 becomes conductive. As a result, only the output voltage Vout2 is input to the non-inverting input terminal of the operational amplifier IC703 via only the feedback resistor R801, not the resistor R201. The operational amplifier IC703 compares the detection voltage corresponding to the output voltage of DC 3.3V with the reference voltage, and outputs a voltage based on the comparison result from the output terminal. Then, a current corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 via the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 in accordance with the feedback current input to the feedback terminal, and constant voltage control of the output voltage Vout2 generated on the secondary side of the isolation transformer T701 is performed. That is, when the device is operating (the mode terminal is at the high level), the output voltage of both DC 3.3V and DC 24V is monitored, and constant voltage control is performed so as to be within the range of the output voltage necessary for the device. On the other hand, by monitoring only the DC output voltage of DC 3.3V at the time of device standby, constant voltage control is performed so as to be within the range of output voltage required at the time of device standby.

[Circuit configuration of power supply unit]
FIG. 3B is a circuit diagram showing a circuit configuration having three DC output voltages on the output (secondary winding) side of the isolation transformer T701. In FIG. 3B, a secondary winding Ns3 (third secondary winding) is added as compared with FIG. The secondary winding Ns3 is provided with a rectifying / smoothing circuit (third rectifying / smoothing means) including a rectifying diode D501 and an aluminum electrolytic capacitor C501, and a DC output voltage Vout3 (third output voltage) is output. The Further, in FIG. 3B, a circuit including a switching element Q501 (third switching element), a load resistor R501, resistors R502 and R503, and a feedback resistor R504 (fourth resistor) is added. That is, the current inflow terminal of the switching element Q501 is connected to the high potential side of the output voltage Vout3, and the current outflow terminal is connected to the other end of the load resistor R501 whose one end is grounded and one end of the feedback resistor R504. The other end of the feedback resistor R504 is connected to one end of the feedback resistor R401. Further, a resistor R502 is connected between the control terminal of the switching element Q501 and the current inflow terminal to prevent the switching element Q501 from being in a conductive state when not driven. Furthermore, the other end of the resistor R503 having one end connected to the control terminal of the switching element Q501 is connected to the current inflow terminal of the switching element Q102.

[Circuit operation of power supply unit]
Next, circuit operation will be described. When the signal from the mode terminal is a high level signal (the device is in an operating state), a high level voltage is applied to the control terminal of the switching element Q102. As a result, a current flows into the control terminal of the switching element Q102, and a conductive state (ON state) is established. When the switching element Q102 becomes conductive, a current flows through the resistors R403 and R404 and the resistors R502 and R503, and a potential difference is generated between the current inflow terminal and the control terminal of the switching elements Q401 and Q501. The switching elements Q401 and Q501 are in the conductive state. Become. On the other hand, since the signal from the mode terminal is at a high level, no current flows through the resistor R202, and the switching element Q201 is not in a conductive state. As a result, the load current of the output voltage Vout1 flows through the feedback resistor R401, the load current of the output voltage Vout3 flows through the feedback resistor R504, and the load current of the output voltage Vout2 flows through the resistor R201 and the feedback resistor R801. As a result, the detection voltage is input to the non-inverting input terminal of the operational amplifier IC703. The operational amplifier IC 703 outputs a voltage based on the comparison result between the detection voltage corresponding to the output voltages Vout1, Vout2, and Vout3 input to the non-inverting input terminal and the reference voltage input to the inverting input terminal. Output from. A feedback current (feedback current) corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 through the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 according to the feedback current input to the feedback terminal, and performs constant voltage control of the output voltages Vout1, Vout2, and Vout3 generated on the secondary side of the insulating transformer T701.

  On the other hand, when the signal from the mode terminal is a low level signal (the device is in a standby state), a low level voltage is applied to the control terminal of the switching element Q102, so that the switching element Q102 is in a non-conduction state (off). State). When switching element Q102 is turned off, current stops flowing through resistors R403 and R404 and resistors R502 and R503, and switching elements Q401 and Q501 are turned off. On the other hand, since the signal from the mode terminal is at a low level, a current flows through the resistor R202, and a current flows through the control terminal of the switching element Q201, so that the switching element Q201 becomes conductive. As a result, only the output voltage Vout2 is input to the non-inverting input terminal of the operational amplifier IC703 via only the feedback resistor R801, not the resistor R201, and the output voltages Vout1 and Vout3 are not input. The operational amplifier IC703 compares the detection voltage corresponding to the output voltage of DC 3.3V with the reference voltage, and outputs a voltage based on the comparison result from the output terminal. Then, a current corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 via the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 in accordance with the feedback current input to the feedback terminal, and constant voltage control of the output voltage Vout2 generated on the secondary side of the isolation transformer T701 is performed. That is, when the device is in operation (the mode terminal is at a high level), the output voltage of the DC output voltage Vout2 (DC3.3V), Vout1 (DC24V), and Vout3 is monitored, so that the output voltage range required for the device is reached. Constant voltage control is performed to turn on. On the other hand, by monitoring only the DC output voltage of the output voltage Vout2 (DC3.3V) at the time of device standby, constant voltage control is performed so as to be within the range of output voltage required at the time of device standby. 3A and 3B, the switching element Q101, the resistor R101, and the feedback resistor R705 are eliminated compared to the second embodiment, so that the number of components is reduced and the power supply device Miniaturization and cost reduction can be realized. As described above, according to the present embodiment, it is possible to reduce the fluctuation range of the output voltage, and to realize downsizing and cost reduction of the device.

  In the fifth embodiment, even when the load currents of the two output voltages Vout1 and Vout2 greatly fluctuate during device operation, the circuit configuration capable of reducing the range of voltage fluctuation of the output voltages Vout1 and Vout2 can be further reduced. Will be described.

[Circuit configuration of power supply unit]
FIG. 4 is a circuit diagram showing a circuit configuration of the power supply device of this embodiment. In addition, the same code | symbol is attached | subjected about the circuit of the same structure as the power supply device demonstrated in FIG. 1, and description is abbreviate | omitted. In FIG. 4, as in the third embodiment, the primary side circuit of the insulating transformer T701 shown in FIG. 2A of the second embodiment is a circuit excluding the primary winding Np and the feedback winding Nb. Is omitted. The circuit configuration shown in FIG. 4 is different from the circuit configuration of the second embodiment shown in FIG. That is, in FIG. 4, compared to FIG. 2A of the second embodiment, a circuit composed of the switching element Q601, the feedback resistor R601, the resistors R602, and R603 is added to the output voltage Vout1 (DC24V) side. Further, in FIG. 4, the switching element Q101, the resistor R101, and the feedback resistor R705 described in FIG.

  In FIG. 4, the current inflow terminal of the switching element Q601 (first switching element) is connected to the high potential side of the output voltage Vout1, and the current outflow terminal is connected to one end of the resistor R601 (first resistor). Yes. The other end of the resistor R601 is connected to a high potential side of the output voltage Vout2, that is, a terminal opposite to the terminal of the resistor R201 (second resistor) connected to the feedback resistor R801 (third resistor). ing. The control terminal of the switching element Q601 is connected to the other end of the resistor R602 whose one end is connected to the current inflow terminal of the switching element Q102. Further, a resistor R603 is connected between the current inflow terminal of the switching element Q601 and the control terminal. As described above, the circuit configuration in which the resistor R601 provided between the output voltage Vout1 (DC24V) and the output voltage Vout2 (DC3.3V) is connected / disconnected by the switching element Q601 according to the device state is described in this embodiment. It is the feature. As a result, even when each load current fluctuates greatly during device operation, the range of voltage fluctuations of the two output voltages Vout1 and Vout2 can be further reduced.

[Circuit operation of power supply unit]
Next, circuit operation will be described. When the signal from the mode terminal is a high level signal (the device is in an operating state), a high level voltage is applied to the control terminal of the switching element Q102. As a result, a current flows into the control terminal of the switching element Q102, and a conductive state (ON state) is established. When switching element Q102 becomes conductive, current flows through resistors R603 and R602, so that switching element Q601 becomes conductive. On the other hand, since the signal from the mode terminal is at a high level, no current flows through the resistor R202, and the switching element Q201 is not in a conductive state. As a result, the load current of the output voltage Vout1 flows through the feedback resistor R601, the resistor R201, and the feedback resistor R801, and the load current of the output voltage Vout2 flows through the resistor R201 and the feedback resistor R801. Then, detection voltages corresponding to the output voltages of DC24V and DC3.3V, which are the output voltages Vout1 and Vout2, are input to the non-inverting input terminal of the operational amplifier IC703. The operational amplifier IC 703 outputs from the output terminal a voltage based on the comparison result between the detection voltage corresponding to the output voltage of DC 24 V and DC 3.3 V input to the non-inverting input terminal and the reference voltage input to the inverting input terminal. To do. A feedback current (feedback current) corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 through the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 according to the feedback current input to the feedback terminal, and performs constant voltage control of the output voltages Vout1 and Vout2 generated on the secondary side of the insulating transformer T701.

  On the other hand, when the signal from the mode terminal is a low level signal (the device is in a standby state), a low level voltage is applied to the control terminal of the switching element Q102, so that the switching element Q102 is in a non-conduction state (off). State). When switching element Q102 is turned off, no current flows to the control terminal of switching element Q601, so switching element Q601 is also turned off. On the other hand, since the signal from the mode terminal is at a low level, a current flows through the resistor R202, and a current flows through the control terminal of the switching element Q201, so that the switching element Q201 becomes conductive. As a result, only the output voltage Vout2 is input to the non-inverting input terminal of the operational amplifier IC703 via only the feedback resistor R801, not the resistor R201. The operational amplifier IC703 compares the detection voltage corresponding to the output voltage of DC 3.3V with the reference voltage, and outputs a voltage based on the comparison result from the output terminal. Then, a current corresponding to the voltage output from the operational amplifier IC 703 is input to the feedback terminal of the power supply IC 701 via the photocoupler IC 702. The power supply IC 701 controls the main switching element Q701 in accordance with the feedback current input to the feedback terminal, and constant voltage control of the output voltage Vout2 generated on the secondary side of the isolation transformer T701 is performed. That is, when the device is operating (the mode terminal is at the high level), the output voltage of both DC 3.3V and DC 24V is monitored, and constant voltage control is performed so as to be within the range of the output voltage necessary for the device. On the other hand, by monitoring only the DC output voltage of DC 3.3V at the time of device standby, constant voltage control is performed so as to be within the range of output voltage required at the time of device standby. As described above, according to the present embodiment, it is possible to reduce the fluctuation range of the output voltage, and to realize downsizing and cost reduction of the device.

  The power supply apparatus described in the first to fifth embodiments can be applied as, for example, a low-voltage power supply for an image forming apparatus, that is, a power supply that supplies power to a drive unit such as a controller (control unit) or a motor. Hereinafter, the configuration of the image forming apparatus to which the power supply devices of Embodiments 1 to 5 are applied will be described.

[Configuration of Image Forming Apparatus]
A laser beam printer will be described as an example of the image forming apparatus. FIG. 5 shows a schematic configuration of a laser beam printer which is an example of an electrophotographic printer. The laser beam printer 300 includes a photosensitive drum 311 as an image carrier on which an electrostatic latent image is formed, a charging unit 317 (charging unit) that uniformly charges the photosensitive drum 311, and an electrostatic latent image formed on the photosensitive drum 311. A developing unit 312 (developing unit) that develops an image with toner is provided. The toner image developed on the photosensitive drum 311 is transferred to a sheet (not shown) as a recording material supplied from the cassette 316 by a transfer unit 318 (transfer means), and the toner image transferred to the sheet is fixed to the fixing device 314. Then, the toner is fixed and discharged onto the tray 315. The photosensitive drum 311, the charging unit 317, the developing unit 312, and the transfer unit 318 are image forming units. The laser beam printer 300 includes the power supply device 400 described in the first to fifth embodiments. The image forming apparatus to which the power supply apparatus 400 according to the first to fifth embodiments can be applied is not limited to the one illustrated in FIG. 5, and may be an image forming apparatus including a plurality of image forming units, for example. Further, the image forming apparatus may include a primary transfer unit that transfers the toner image on the photosensitive drum 311 to the intermediate transfer belt and a secondary transfer unit that transfers the toner image on the intermediate transfer belt to the sheet.

  The laser beam printer 300 includes a controller 320 that controls an image forming operation by the image forming unit and a sheet conveying operation. The power supply device 400 according to the first to fifth embodiments includes, for example, an output voltage Vout2 ( DC 3.3V) is supplied. In addition, the power supply device 400 described in the first to fifth embodiments uses power of the output voltage Vout1 (DC 24V) to a driving unit such as a motor for rotating the photosensitive drum 311 or driving various rollers for conveying the sheet. Supply. Further, the controller 320 gives a high-level control signal indicating the operation state to the mode terminals of the first to fifth embodiments according to the operation state of the apparatus, for example, during the image forming operation, and low indicating the standby state during the standby state. A level control signal is output. As described above, according to the present embodiment, it is possible to reduce the fluctuation range of the output voltage, and to realize downsizing and cost reduction of the device.

IC701 Power supply control IC
IC703 Operational amplifier Np Primary winding Ns1, Ns2 Secondary winding Q701 Main switching element T701 Isolation transformer

Claims (13)

A transformer having a primary winding and a plurality of secondary windings;
Switching means for switching the current flowing through the primary winding of the transformer;
Feedback means for feeding back a current corresponding to a detection voltage corresponding to an output voltage of a secondary winding of the transformer to a primary side of the transformer;
Control means for controlling the output voltage of the secondary winding of the transformer by controlling the operation of the switching means according to the current from the feedback means;
With
A first mode for supplying a large amount of power from the secondary winding to the load, and a second mode for supplying less power from the secondary winding to the load than the first mode,
The feedback means feeds back the current according to the detection voltage according to the output voltage of the plurality of secondary windings in the first mode, and the plurality of the currents in the second mode. A power supply apparatus that feeds back a current corresponding to an output voltage of a predetermined secondary winding of the secondary windings. In the case of the first mode, the feedback means feeds back a current corresponding to a comparison result of a detection voltage and a reference voltage corresponding to the output voltages of the plurality of secondary windings, 2. The power supply device according to claim 1, wherein a current according to a comparison result between the output voltage of the predetermined secondary winding and the reference voltage is fed back. The plurality of secondary windings are a first secondary winding that generates a first output voltage, and a second secondary winding that generates a second output voltage,
The power supply device according to claim 1, wherein the predetermined secondary winding is the second secondary winding. The first secondary winding has first rectifying and smoothing means for rectifying and smoothing the first output voltage,
4. The power supply device according to claim 3, wherein the second secondary winding includes second rectifying / smoothing means for rectifying and smoothing the second output voltage. A first resistor and a first switching element connected in series are connected between the first rectifying and smoothing means and the feedback means,
5. The power supply device according to claim 4, wherein the first switching element is in a conductive state in the first mode and is in a non-conductive state in the second mode. A second resistor and a third resistor connected in series are connected between the second rectifying and smoothing means and the feedback means,
A second switching element is connected in parallel to the second resistor,
6. The power supply device according to claim 5, wherein the second switching element is in a non-conducting state in the first mode and is in a conducting state in the second mode. The first output voltage is higher than the second output voltage,
The power supply device according to claim 6, wherein a low potential side of the first secondary winding is connected to a subsequent stage of the second rectifying / smoothing means. A first switching element and a first resistor connected in series are connected between the first rectifying and smoothing means and the feedback means,
The first switching element is a switching element for cutting off power supply to the load,
The first resistor is connected between an output terminal of the first switching element and the feedback means;
A second resistor and a third resistor connected in series are connected between the second rectifying and smoothing means and the feedback means,
A second switching element is connected in parallel to the second resistor,
The first switching element is in a conductive state in the first mode, and in a non-conductive state in the second mode,
5. The power supply device according to claim 4, wherein the second switching element is in a non-conductive state in the first mode and is in a conductive state in the second mode. The transformer has a third secondary winding for generating a third output voltage;
The third secondary winding has third rectifying and smoothing means for rectifying and smoothing the third output voltage,
A third switching element and a fourth resistor connected in series are connected between the third rectifying / smoothing means and the feedback means,
The third switching element is a switching element for cutting off power supply to the load,
The fourth resistor is connected between the output terminal of the third switching element and the feedback means,
The power supply device according to claim 8, wherein the third switching element is in a conductive state in the first mode and is in a non-conductive state in the second mode. A first switching element and a first resistor connected in series are connected to the subsequent stage of the first rectifying and smoothing means,
A second resistor and a third resistor connected in series are connected between the second rectifying and smoothing means and the feedback means,
A second switching element is connected in parallel to the second resistor,
One end of the first resistor is connected to the output terminal of the first switching element, and the other end of the first resistor is opposite to the terminal of the second resistor connected to the third resistor. Connected to the terminal of the second resistor of
The first switching element is in a conductive state in the first mode, and in a non-conductive state in the second mode,
5. The power supply device according to claim 4, wherein the second switching element is in a non-conductive state in the first mode and is in a conductive state in the second mode.   The power supply device according to claim 10, wherein the first output voltage is higher than the second output voltage. An image forming means for forming an image on a recording material;
The power supply device according to any one of claims 1 to 11, wherein a voltage is applied to the image forming unit;
An image forming apparatus comprising: A controller for controlling the image forming means and forming an image on a recording material;
The image forming apparatus according to claim 12, wherein the controller outputs a control signal of the first mode or the second mode to the power supply device.

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