JP6053840B2 - Power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to obtaining a stabilized DC voltage from a commercial AC power source suitable for a power source of a device having a normal operation mode and an energy saving standby mode.

FIG. 13 shows a configuration of a power supply apparatus for obtaining a conventionally known stabilized DC power supply.
Devices equipped with this power supply device are, for example, a control that has a low DC voltage required for operation of a CPU, ASIC, etc., and a first DC voltage to a drive system including a motor, a solenoid, etc., which requires a relatively high voltage required for operation. It is the structure which supplies the voltage of two systems of the 2nd DC voltage to a system.

  Further, since the drive system is not operated in the standby mode in which the apparatus is in the energy saving state, no voltage is supplied to the load of the drive system. For this reason, in the standby mode, the voltage supply to the load of the drive system is cut off by a load switch (not shown) or the like. In FIG. 13, A is a first DCDC converter that supplies a drive system power supply voltage, and B is a second DCDC converter that supplies a control system power supply voltage.

Next, detailed description of FIG. 13 will be given. The configuration of each part in FIG. 13 is as follows.
700 is a commercial AC power supply, 702 is a rectifier, 703 is a smoothing capacitor, 705 is a starting resistor, 707 is a switching element, 710 is a power supply control IC, 711 is a transformer, 712 is a diode, and 713 is a capacitor. 720 is a secondary rectifier diode, 721 is a secondary smoothing capacitor, 722, 723, and 724 are resistors, and 750 is a shunt regulator. Reference numeral 714-b denotes an LED side of the photocoupler, reference numeral 728 denotes a capacitor, and reference numeral 732 denotes an FET serving as switching means of a DCDC converter that generates a second DC voltage from the first DC voltage. 734 is a gate resistor, 733 and 735 are FET driving transistors, 738 is a control IC for controlling the second DCDC converter, 739 is an inductor, 740 is a diode, 741 is a capacitor, and 742 and 743 are resistors. Reference numeral 731 denotes a first DC voltage load (drive system), and reference numeral 746 denotes a CPU (control system) as a second DC voltage load.

First, the operation of the first DCDC converter device will be described.
When an AC voltage (AC voltage) is applied from the commercial AC power supply 700, the capacitor 703 is charged with the voltage rectified by the rectifier 702. The rectifier 702 and the capacitor 703 function as a rectifying / smoothing circuit that rectifies and smoothes the AC voltage from the AC power supply. When the voltage of the capacitor 703 rises, power is supplied to the power control IC 710 via the starting resistor 705, and the power control IC 710 turns on the FET 707. When the FET 707 is turned on, a current flows through the primary winding Np of the transformer 711, and a voltage appears in each of the Ns and Nb windings by the voltage applied to the Np winding of the transformer 711. The voltage appearing in the Nb winding is blocked by the diode 712 so that no current flows, and the voltage in the Ns winding is also prevented from flowing by the diode 720. The FET 707 is turned off after a predetermined time determined by the internal circuit of the power supply control IC 710 has elapsed. Then, the voltage on the drain side of the FET 707 of the Np winding rises. Further, a current flows through the Ns winding in the direction of charging the capacitor 721 through the diode 720, the capacitor 721 is charged, and the voltage of the capacitor 721 increases. After a predetermined time determined by the internal circuit of the power supply control IC 710 has elapsed, the FET 707 is turned on and current is supplied from the capacitor 703 to the transformer 711 again. When the FET 707 is turned off after a predetermined time has elapsed by the power supply control IC 710, the capacitor 721 is charged through the diode 720 again by the Ns winding voltage. The voltage of the capacitor 721 is divided by resistors 723 and 724, and the voltage of the resistor 724 is applied to the control terminal of the shunt regulator 750. The cathode current of the shunt regulator 750 is transmitted to the power supply control IC 710 via the photocoupler 714.

  The reference voltage inside the shunt regulator 750 and the voltage of the resistor 724 divided by the resistors 723 and 724 are compared. If the voltage of the resistor 724 is higher than the reference voltage, the ON width or the ON duty of the FET 707 is decreased. Operates to lower the output voltage. When the voltage of the resistor 724 is lower than the reference voltage of the shunt regulator 750, a feedback operation is performed to increase the output voltage by increasing the on-time or on-duty of the FET 707.

Next, the operation of the second DCDC converter device will be described.
The second DCDC converter generates a second DC voltage from the output voltage of the first DCDC converter. In the normal mode, the second DCDC converter control IC 738 intermittently drives the FET 732 via the transistors 733 and 735 and the resistor 734. The resistors 742 and 743 divide the output voltage of the second DCDC converter, and the voltage of the resistor 743 is input to the second DCDC converter control IC 738. The second DCDC converter control IC 738 has a reference voltage Vref2 inside, and generates a stable second DC voltage by controlling the on-duty of the FET 732 so that Vref2 and the voltage of the resistor 743 are equal. . In this configuration, a load switch is provided on the output side that outputs the power supply voltage of the drive system in order to reduce the power in the standby mode, and the load switch is set in the standby mode by a control circuit such as a CPU or ASIC that is operated by the control system power supply. It is configured to turn off.

  However, in the configuration of FIG. 13, a reduction in efficiency of the DCDC converter due to load reduction cannot be avoided. As an example of solving such a decrease in efficiency, Patent Document 1 discloses that an output voltage is dropped in a standby mode (light load) in a RCC switching power supply device, and a desired value is obtained by a subsequent DCDC converter. A configuration for supplying a boosted output voltage to a load is disclosed. In the configuration of Patent Document 1, by reducing the output voltage in the RCC converter device, the ringing voltage of the auxiliary winding during the period when the switch element is off is set to be equal to or lower than the threshold value of the switch element. As a result, the turn-on of the switch element due to the flyback voltage is prevented, the off of the main switching element is extended, and the oscillation frequency is lowered. As a result, switching loss is reduced and circuit efficiency is improved.

JP 2000-278946 A

  However, the load current of the control system is also reduced during the period when the device is in the standby mode. Therefore, the efficiency of the second DCDC converter described above is also reduced when the device is on standby. In the configuration of Patent Document 1, measures are taken to improve the decrease in efficiency of the first DCDC converter due to a reduction in load current, but measures are not taken to improve the decrease in efficiency of the second DCDC converter.

  SUMMARY An advantage of some aspects of the invention is that it provides a power supply apparatus and an image forming apparatus that have improved efficiency in a standby mode in an energy saving state.

To solve the above problems, the present onset Ming, Ru includes the following configuration.

(1) The input DC voltage is converted into the first DC voltage by switching the input DC voltage with the first switching means, and the converted first DC voltage is applied to the first load. The first converter to be output and the first DC voltage output from the first converter are input, and the input first DC voltage is switched by the second switching means, thereby A first converter that converts the second DC voltage lower than the first DC voltage and outputs the converted second DC voltage to a second load. Reduces the switching frequency of the first switching means to a switching frequency lower than the switching frequency when the first DC voltage is output, Outputs a third DC voltage lower than the second DC voltage, said second converter is a power supply device and outputs an input the third DC voltage before Symbol second load.
(2) An image forming unit for forming an image, and an input DC voltage is switched by a first switching unit to form an image by the image forming unit. converting the first DC voltage, a first converter for outputting the converted the first DC voltage to a first load, the first DC voltage output from the first converter is inputted, By switching the input first DC voltage by the second switching means, the first DC voltage is converted into a second DC voltage lower than the first DC voltage, and the converted second DC voltage is converted into the second DC voltage. A power source having a second converter that outputs to a load of the first converter, wherein the first converter has a switching frequency of the first switching means, Serial is lowered to a lower switching frequency than the switching frequency when outputs the first DC voltage, and outputs a third DC voltage lower than said second DC voltage, the second converter, the second by controlling the operation of the switching means, an image forming apparatus and outputs the inputted third DC voltage before Symbol second load.

  According to the present invention, it is possible to improve the power supply efficiency in the standby mode, which is an energy saving state in which the efficiency is low in the conventional configuration.

1 is a circuit diagram showing a configuration of a power supply device according to a first embodiment. The circuit diagram which shows the structure of the power supply device of Example 2. The figure which compared the efficiency of the power supply of Example 1 and a prior art example The figure which shows the waveform of each part at the time of transfer to normal mode from the standby mode of the power supply device of Example 1. The figure which shows the waveform of each part at the time of transfer to standby mode from the normal mode of the power supply device of Example 1. The circuit diagram which shows the structure of the 2nd DCDC converter in Example 3. FIG. A circuit diagram showing other composition of the 2nd DCDC converter in Example 3. The circuit diagram which shows the structure of the 1st DCDC converter in the power supply device of Example 4. FIG. A circuit diagram showing composition of a power unit in Example 5. The figure which shows the connection structure from the control part of the laser printer in Example 5 to a power supply device. The flowchart which shows the operation | movement at the time of energy saving mode transfer in Example 5 The flowchart which shows the operation | movement at the time of the return from energy saving mode in Example 5. Circuit diagram showing configuration of conventional example

  Hereinafter, the best mode for carrying out the present invention will be described in detail by way of embodiments of a power supply device and an image forming apparatus.

A “power supply device” that is Embodiment 1 will be described.
The power supply apparatus according to the present embodiment is used for control and control in the first DCDC converter, in which the switching frequency is lowered particularly in a standby mode (light load), such as a driving method such as burst mode or off-time control. A configuration using an IC is assumed.

FIG. 1 is a circuit diagram of the power supply device of the present embodiment. In FIG. 1, the same parts as those in the configuration of the conventional example described above are denoted by the same reference numerals. Similar to the conventional example, the operation of the rectifying / smoothing circuit that rectifies and smoothes the AC voltage from the AC power supply, the operation of converting the voltage by the first DCDC converter, the second DCDC converter, etc. Description is omitted. A is a first DCDC converter that supplies a drive system power supply voltage, and B is a second DCDC converter that supplies a control system power supply voltage. C is a load switch.
In FIG. 1, 125 and 126 are resistors, and 127 is a transistor. This power supply includes the two states of the normal and standby modes according to the state of the device to be mounted, it is possible e replacement cut the two states.

  The CPU 746, which is the load of the second DCDC converter, controls the state of the device and also controls the operation mode of the power supply apparatus, that is, the operation in each mode of the normal mode and the standby mode. The CPU 746 turns on the transistor 127 when the power supply apparatus is set in the normal mode, and turns off the transistor 127 when the power supply apparatus is set in the standby mode. The normal mode is a state in which a DC voltage is supplied to the drive system load 731, and the standby mode is a state in which a DC voltage is not supplied to the drive system load 731.

(1) Description of operation when the power supply device is in the normal mode In the normal mode, when the CPU 746 turns on the transistor 127, the resistor 724 and the resistor 125 are connected in parallel between the control terminal and the anode of the shunt regulator 750. The shunt regulator 750 allows the current between the cathode and the anode to flow so that the voltage between the control terminal and the anode becomes a predetermined reference voltage value. For this reason, the FET 707 is controlled so that the output voltage Vout of the first DCDC converter becomes a voltage at which the result of dividing by the resistance between the resistor 723 and the resistance between the control terminal and the anode becomes the reference voltage value Vref. The output voltage Vout is expressed by the following equation.
Vout = [(resistance 723 + R) / R] × Vref
Here, R is a resistance value obtained by parallel connection of the resistor 724 and the resistor 125, and is represented by the following equation.
R = resistance 724 × resistance 125 / (resistance 724 + resistance 125)

(2) Description of operation when power supply apparatus is in standby mode When the power supply device is in the standby mode, which is an energy saving state, the CPU 746 turns off the transistor 127. When the transistor 127 is turned off, the resistance between the control terminal and the anode of the shunt regulator 750 is only the resistor 724. As described above, since the shunt regulator 750 operates so that the voltage between the control terminal and the anode is set to a predetermined reference voltage value, the output voltage Vout3 is Vout3 = [(resistor 723 + resistor 724) / resistor 724] × Vref.
It works like that. Since the resistance between the control terminal and the anode of the shunt regulator becomes higher than that in the normal mode, the output voltage decreases.

As described above, the second DC / DC converter generates the second DC voltage from the output voltage of the first DC / DC converter. When the output voltage of the first DC / DC converter decreases due to the standby operation, the ON time of the FET 732 is lengthened (on duty is increased), and the output voltage is kept constant at the second DC voltage. When the output voltage of the first DCDC converter is equal to or less than the second power supply voltage, a second DCDC converter FET 7 32 becomes locked in the on state (ON duty 100% state). Furthermore, the first DC / DC converter voltage decreases to a third DC voltage. That is, the second DCDC converter is in a continuous conduction state, and the output voltage of the first DCDC converter becomes a lower DC voltage (third DC voltage).

When the third DC voltage is Vout3 and the second DC voltage is Vout2,
Vout2> Vout3
It becomes the relationship.
Therefore, the relationship between the resistors 742, 743, and Vref2 and the resistors 723, 724, and Vref is expressed by the following relational expression.
[(Resistor 742 + resistor 743) / resistor 743] × Vref2> [(resistor 723 + resistor 724) / resistor 724] × Vref

  FIG. 3 shows a comparison between the efficiency of the power supply configured as described above and the efficiency of the conventional configuration (FIG. 13). In FIG. 3, the horizontal axis represents the load current and the vertical axis represents the efficiency, and the efficiency with respect to the load current of this embodiment and the conventional configuration is shown. In the conventional configuration, the efficiency of the second DCDC converter as well as the first DCDC converter is lowered, so the efficiency is not good. According to the present embodiment, the loss in the second DCDC converter is only the on-resistance of the FET 732, so that the efficiency of the power supply is improved.

  Further, when the shunt regulator is insufficient in the control by the shunt regulator, the control circuit may be configured by an operational amplifier (error amplifier) using the shunt regulator as a reference voltage source. Further, although the voltage in the shunt regulator is used as the reference voltage, the reference voltage may be constituted by a Zener diode.

(3) Description of operation during mode transition Next, state transition from the standby mode to the normal mode and from the normal mode to the standby mode will be described.

FIG. 4 shows the voltages of the respective parts at the time of transition from the standby mode to the normal mode. As shown in FIG. 4, at the time of transition from the standby mode to the normal mode, the voltage across the C (capacitor) 741, that is, the output voltage from the second DCDC converter changes from the third DC voltage to the second DC voltage. The transition is smooth. This is because the second DCDC converter operates to control the output voltage when the output voltage of the first DCDC converter becomes larger than the second DC voltage during the transition from the standby mode to the normal mode. As shown in the figure, the voltage across the capacitor 741 shifts from the third DC voltage to the second DC voltage, and the FET 707 and the FET 732 operate, so that the voltage across the capacitor 728 smoothly changes to the first DC voltage. Migrate to

Next, FIG. 5 shows a state in the case of shifting from the normal mode to the standby mode.
In the figure, the first DCDC converter output voltage, the FET 707 in the first DCDC converter, the gate voltage of the FET 732 in the second DCDC converter, and the output voltage of the second DCDC converter when shifting from the normal mode to the standby mode are shown. Show.

  When the output voltage of the first DCDC converter decreases, the GS voltage of the FET 707 is turned off and the FET 707 stops. Since the load current flows out even though the FET 707 of the first DCDC converter is stopped, the output voltage of the first DCDC converter decreases. That is, since the input voltage of the second DCDC converter decreases, the second DCDC converter makes the output voltage of the second DCDC converter constant while increasing the ON width (ON duty) of the gate of the FET 732. Control. When the input voltage of the second DCDC converter becomes equal to or lower than the second DC voltage, the FET 732 of the second DCDC converter remains on (voltage between the FETs 732 GS in the figure).

  When the output voltage of the first DCDC converter becomes the third DC voltage, the output voltage of the second DCDC converter is controlled by the third DC voltage in order for the FET 707 of the first DCDC converter to perform on / off operation. (State indicated by dotted line B in the figure).

  As described above, in this embodiment, the second DCDC converter output voltage is configured not to generate a steep voltage change at the time of transition (switching) between the standby mode and the normal mode.

  Thus, according to the present embodiment, the efficiency of the first and second DCDC converters in the standby mode can be improved. Further, since it is possible to prevent a sudden voltage change of the output voltage even when switching from the standby mode to the normal mode and from the normal mode to the standby mode, it is possible to suppress the occurrence of malfunction of the circuit.

A “power supply device” that is Embodiment 2 will be described.
In the first DCDC converter, the power supply device according to the present embodiment uses a control IC that increases the switching frequency in the standby mode (light load), such as the RCC method and the frequency control method. The configuration is assumed. The RCC (Ringing Choke Converter) system is a type of flyback converter, which is a converter that performs a switching operation by self-excited oscillation.

  FIG. 2 is a circuit diagram of the power supply device of this embodiment. In the present embodiment, the same parts as those in the conventional example are denoted by the same reference numerals, and the description thereof is omitted. A is a first DCDC converter that supplies a drive system power supply voltage, and B is a second DCDC converter that supplies a control system power supply voltage.

2, 742, 2 43, 2 47,248,237,251,252 resistors, 250 a comparator, 249 is the shunt regulator, the 253 and 254 is a transistor.

  In the normal mode, the CPU 746 turns on the transistor 253. Since the transistor 254 is turned off when the transistor 253 is turned on, the first DCDC converter outputs the first DC voltage by the operation of the shunt regulator 750 regardless of the operation of the comparator 250. The second DCDC converter outputs the second DC voltage by driving the FET 732 intermittently by the second DCDC converter control IC 738.

  When the CPU 746 turns off the transistor 253 in the standby mode, the transistor 254 operates according to the output of the comparator 250. The output of the comparator 250 is connected to the first DCDC converter control IC 210 via the transistor 254 and the photocoupler 714. The output of the first DCDC converter is the output voltage of the second DCDC converter is the third DC. Control to be voltage.

  The output voltage of the second DCDC converter is determined to be the second DC voltage in the normal mode, and the third DC voltage is set to a voltage lower than the second DC voltage. The output voltage of the DCDC converter decreases from the first DC voltage to the third DC voltage.

  The second DC / DC converter continues to operate while increasing the on-duty of the FET 732 in order to keep the output at the second DC voltage even when the input voltage decreases, and turns on when the input voltage becomes the second DC voltage. The duty is 100% and the FET 732 remains on. Further, the comparator 250 operates only when the output voltage of the first DCDC converter is lowered to the third DC voltage, and the FET 707 is switched. As a result, the first DCDC converter output voltage becomes the third DC voltage.

  According to the present embodiment, the efficiency of the first and second DCDC converters in the standby mode can be improved as in the first embodiment.

The “power supply device” according to the third embodiment will be described.
In the first and second embodiments, it is assumed that an IC capable of setting the on-duty to 100% is used as the control IC for the second DCDC converter. In this embodiment, it is assumed that the second DCDC converter control IC uses an IC that cannot set the on-duty to 100%, and the second DCDC converter FET is turned on. An external circuit is provided.

  As a protection function of the control IC used for the control of the second DCDC converter, there is a case where it has a duty guard function or a lower limit frequency of the oscillator (when the on-duty cannot be set to 100%). Therefore, even if the input voltage of the second DCDC converter is lowered, the FET of the second DCDC converter cannot be kept on. For this reason, the fluctuation of the output voltage increases or the output voltage decreases, and the operations as in the first and second embodiments cannot be performed. In such a case, a standby mode is provided by detecting an output voltage of the first DCDC converter and providing an external circuit for turning on the FET of the second DCDC converter when the detected voltage becomes a predetermined voltage. Sometimes the FET of the second DCDC converter can be turned on.

  A circuit of this specific example is shown in FIG. The present embodiment is a power supply apparatus having a configuration in which the second DCDC converter shown in FIG. 6 is connected to the first DCDC converter in the first embodiment.

Note that the circuit for driving the FET 501 of the second DCDC converter B in FIG. 6 includes a transistor 558, resistors 555, 556, 557, 559, 560, etc. In addition, capacitors 551, 572, 530, resistors 536, 549, a diode 529, and an inductor 528. Since the basic operation of this circuit is substantially the same as that described in the configuration of the conventional example, the description thereof is omitted, and only the configuration and operation of the external circuit D1 of this embodiment will be described.

  The external circuit D1 in this embodiment is a circuit that turns on the FET 501 of the second DCDC converter B in the standby mode. Reference numeral 600 denotes a control IC for the second DCDC converter. REF is a terminal for inputting a voltage to be controlled, C is a collector, E is an emitter, and the FET 501 is driven by connecting the gate terminal of the FET 501 to the end of the C terminal. GND is a GND terminal of the control IC.

  The external circuit D1 is a circuit including resistors 601, 604, 608, 609, and 611, transistors 602, 603, 606, and 610, and diodes 605 and 607.

  In the normal mode, the output voltage of the first DCDC converter is the first DC voltage, which is higher than the output voltage (second DC voltage) of the second DCDC converter. Therefore, the transistor 606 is turned on, a current flows from the diode 607 through the resistor 609, and the diode 605 is reverse-biased, so that the transistor 602 does not operate. Since both the transistor 603 and the transistor 610 are turned off, the control output of the IC 600 is applied to the FET 501 as it is. Therefore, the second DCDC converter continues the DCDC converter operation under the control of the IC 600.

  When the standby mode is set, a device (not shown) as a load sets the terminal 174 to Low and decreases the output voltage of the first DCDC converter. When the terminal 174 becomes Low and the output voltage of the first DCDC converter becomes lower than the second DC voltage, the transistors 602 and 603 are turned on. As a result, the transistor 610 is turned on, and the FET 501 is kept on to keep the gate of the FET 501 low.

  When returning to the normal mode, a device (not shown) that is a load causes the first DCDC converter to be in a normal mode output and makes the terminal 174 high or high impedance. Then, since the transistor 603 is turned off, the transistor 610 is also turned off, so that the IC 600 can drive the FET 501 again. At the same time, since the output voltage of the first DCDC converter starts to rise, the IC 600 starts to drive the FET 501 on time gradually shorter. The voltage fluctuation during this time is a range that is sufficiently acceptable for the load device because there is only fluctuation due to the maximum duty range of the IC 600 and the voltage increase of the first DCDC converter immediately after switching from the standby mode to the normal mode. As described above, switching with small voltage fluctuation at the time of control switching can be performed.

  FIG. 6 shows an example using discrete parts. However, if a comparator is used, a circuit can be configured more easily. Such a circuit is shown in FIG.

  FIG. 7 is different from FIG. 6 in the configuration of the external circuit. In the external circuit D2 in FIG. 7, in the normal mode, the apparatus sets the terminal 174 to High. Since the minus terminal of the comparator 1405 becomes Low, the comparator output terminal becomes OPEN, and the FET 501 is not affected. When the standby mode is entered, the device reduces the output voltage of the power supply device and sets the terminal 174 to Low. When the input voltage decreases and the negative input terminal voltage of the comparator 1405 becomes higher than the positive input terminal voltage, the comparator output becomes Low, turning on the FET 501 of the second DCDC converter.

  6 and 7, the terminals 172, 173, and 174 are connected to the CPU 746 as the control system load described in the first and second embodiments.

  According to the present embodiment, the efficiency of the first and second DCDC converters in the standby mode can be improved even when the 100% on-duty operation cannot be performed as the control IC for the second DCDC converter.

  The “power supply device” according to the fourth embodiment will be described.

  This embodiment shows an example in which the first DCDC converter is configured by an RCC circuit. In the present embodiment, the second DCDC converter is assumed to be the same DCDC converter except for the control part of the transistor 127 by the CPU 746 in the second DCDC converter B part shown in FIG. Therefore, about the 2nd DCDC converter, explanation of Example 1 is used and explanation here is omitted.

  The operation of the first DCDC converter in this embodiment will be described below with reference to FIG. In FIG. 8, 800 is a commercial AC power source, 801 is a filter circuit, 802 is a diode bridge, 803 is a capacitor, and 804 is a switching transformer. Reference numeral 805 denotes a starting resistor, 806-a denotes a phototransistor that is one end of the first photocoupler, 807 denotes a switching element, 808, 809, 811, 813, 816, and 817 denote resistors, and 810 denotes a transistor. 812 and 818 are capacitors, 814-a is a phototransistor which is one end of the second photocoupler, and 815 and 819 are diodes.

  820 is a secondary rectifier diode, 821 is an electrolytic capacitor, 822, 824 and 825 are resistors, and 823 is a shunt regulator. Further, reference numerals 835, 836, and 839 denote resistors, 833 denotes a comparator, 806-b denotes a photocoupler LED, 834 denotes a resistor, 833 denotes a comparator, and 876 denotes a transistor. Reference numeral 838 denotes a Zener diode that generates a reference voltage.

  When AC power is applied from the commercial AC power supply 800 to the diode bridge 802 via the filter circuit 801, both-wave rectification is performed by the bridge diode 802, the capacitor 803 is charged, and a DC voltage is generated across the capacitor 803. To do.

  The operation in the normal mode when the power is turned on will be described. In the normal mode, a high signal is input to the terminal 874. Therefore, the transistor 876 is turned on, and the photocoupler LED 806-b is not lit. Since the photocoupler transistor 806-a is in a high impedance state, a current from the resistor 851 flows between the base and emitter of the transistor 850, and the transistor 850 is turned on. As a result, a voltage is applied between the gate and source of the switching element 807 by voltage division of the resistor 808 connected between the starting resistor 805 and the gate source, and the switching element 807 is turned on. When the switching element 807 is turned on, a current starts to flow through the primary winding Np of the transformer 804. Then, a voltage is generated in the auxiliary winding Nb of the transformer 104 in a direction to further increase the gate voltage of the switching element 807. This voltage charges the capacitor 818 through the resistor 817. Since the voltage between both ends of the capacitor 818 is also applied between the base and emitter of the transistor 810, a sufficient base voltage is generated in the transistor 810 when charging is started and a certain time elapses, so that the base current flows and the transistor 810 is turned on. Turn on.

When the transistor 810 is turned on, the switching element 807 is turned off, and the drain-source voltage of the switching element 807 starts to rise. As a result, the voltage on the cathode side of the diode 815 of the auxiliary winding Nb drops and a voltage is generated in the reverse direction.
A current flows in the secondary winding Ns in the direction in which the diode 820 is conducted, and the capacitor 821 is charged when the voltage becomes equal to or higher than the sum of the voltage of the capacitor 821 and the forward voltage of the diode 820. At the same time, the voltage appearing in the auxiliary winding Nb discharges the capacitor 818. The diode 819 is connected for protection so that no voltage is applied beyond the reverse breakdown voltage between the base and emitter of the transistor 810. The resistor 816 and the diode 815 are connected to cause a current to flow in the direction in which the capacitor 818 is discharged and to discharge at a higher speed than the discharge by the resistor 817. In this case, the transistor 810 is turned off, so that the gate voltage of the switching element 807 is changed by the current supplied from the starting resistor 805 and the current flowing into the auxiliary winding Nb supplied through the resistor 811 and the capacitor 812. It will be decided. A resistor 841 and a diode 842 are connected to increase the speed of turning off of the switching element 807.

  Since the energy stored in the transformer 804 moves to the capacitor 821 while the switching element 807 is off, the voltage of the Ns winding decreases with time. Since the Ns winding voltage is also reflected in the output voltage of the auxiliary winding Nb, the voltage on the diode 819 anode terminal side of the Nb winding also decreases. The gate voltage of the switching element 807 is increased by being biased by the current flowing from the starting resistor 805.

  When the gate voltage of the switching element 807 becomes higher than the threshold value, the switching element 807 is turned on, and a current flows from the capacitor 803 through the transformer 804 to the Np winding through the switching element 807 toward the negative terminal of the capacitor 803. Further, since a current flows in the Nb winding from the Nb winding in the direction of the capacitor 812, the resistor 811, the resistor 808, and the Nb winding, the gate voltage of the switching element 807 further increases. As described above, the capacitor 818 is charged by the voltage of the Nb winding and the resistor 817, and the switching element 807 is turned off by turning on the transistor 810.

  The series of oscillation operations as described above is continued, and the energy stored in the transformer 804 during the ON period of the switching element 807 is stored in the capacitor 821 during the OFF period of the switching element 807, and the voltage across the capacitor 821 increases. Go.

The voltage of the capacitor 821 is divided by resistors 824 and 825. When the voltage across the resistor 825 becomes higher than the reference voltage of the shunt regulator 823, the shunt regulator 823 starts to flow current between the cathode and the anode, and the photodiode of the photocoupler 814-b emits light.
The light receiving side transistor 814-a of the photocoupler is connected to the resistor 813 and the base of the transistor 810. When the LED of the photocoupler 814 emits light, the impedance of the phototransistor 814-a decreases. Therefore, the transistor 810 is turned on and the switching element 807 is turned off. In this way, the voltage across the capacitor 821 is controlled so that the voltage across the resistor 825 becomes the reference voltage of the shunt regulator 823.

In the standby mode, the terminal 874 is set to Low. When the terminal 874 is set to Low transistors 87 6 is turned off. Then it becomes possible to control the lighting of the photodiode 8 06-b of the photocoupler by the output signal of the comparator 833.
The comparator 833 inputs the output voltage divided by the resistors 835 and 834 to the negative input terminal. Further, the reference voltage of the Zener diode 838 biased by the resistor 836 is input to the + input terminal. The comparator 833 compares the input voltage with the reference voltage, and sets the output terminal to Low when the voltage of the resistor 834 is higher than the voltage of the Zener diode 838. When the output terminal of the comparator 833 becomes Low, the photocoupler photodiode 806-b is turned on. Then, the impedance of the photocoupler transistor 806-a is lowered and the transistor 850 is turned off. Since the resistor 851 is higher than the starting resistor 805, the gate voltage at the time of starting decreases, and the switching element 807 cannot be turned on. Since the resistor 851 has a high resistance, at least two or more resistors are connected in series. The same applies to the starting resistor 805. In this state, the switching element 807 may be turned on by the voltage of the Nb winding. For this purpose, the photocoupler LED 814-b is also turned on by the output of the comparator 833, the impedance of the photocoupler transistor 814-a is lowered, and the switch element 807 is surely turned off.

  When the switching element 807 is turned off, the output voltage of the first DCDC converter, which is the voltage between the terminals 872 and 873, decreases. When the value obtained by dividing the output voltage of the first DCDC converter by the resistors 835 and 834 becomes lower than the voltage of the Zener diode 838, the comparator 833 is turned off and the LEDs 806-b and 814-b of the photocouplers are not turned on. . (Note that the output voltage at this time is the third DC voltage described in the first embodiment.) As a result, the impedance of the transistor 850 is lowered and the starting current starts to flow. Further, the impedance of the transistor 810 is increased, and the gate terminal voltage of the switching element 807 can be increased.

  Since the output voltage of the first DCDC converter is lowered between the cathode and the anode of the voltage feedback shunt regulator 823 that functions in the normal mode, the first DCDC converter has a high impedance. For this reason, the LED 814-b of the photocoupler does not light up.

Accordingly, the switching element 807 is driven with the maximum on-time as in the case of starting the power supply.
In the first embodiment, the voltage dividing ratio of the resistance input to the shunt regulator is switched in the standby / normal mode. However, if configured similarly in the RCC system, the frequency in the standby mode becomes a much higher frequency. As a result, the switching loss increases, and the efficiency is reduced.

  When the first DCDC converter is configured by an RCC circuit, the transistor 850 connected to the starting resistor is switched at the time of low voltage output in the standby mode by performing as in this embodiment, so that the loss due to the starting resistor is caused. Can also be reduced. Therefore, it is possible to further improve the efficiency of the power supply device.

  A “laser beam printer” which is Embodiment 5 will be described. In this embodiment, a case where the RCC power supply apparatus described in the fourth embodiment is applied to a laser beam printer will be described. Portions common to the fourth embodiment are denoted by the same reference numerals, description thereof is omitted, and only characteristic portions of the present embodiment are described.

The operation of the first DCDC converter in this embodiment will be described.
FIG. 9 is a circuit diagram showing the configuration of the first DCDC converter and the second DCDC converter in the laser beam printer of this embodiment. In FIG. 9, the left side of the FET 927 is a first DCDC converter portion, and the right side including the FET 927 is a second DCDC converter portion.
In FIG. 9, 927 is a main switching FET of the second DCDC converter, 928 is an inductor, 929 is a regenerative diode, 930 is a capacitor, 926 and 934 to 937 are resistors, and 938 is a Zener diode. 939 is a resistor, and 932 and 933 are comparators.

First, normal operation will be described. The comparator 932 compares the voltage of the Zener diode 938 with the voltage divided by the resistors 934 and 939 using the reference voltage as a reference voltage. When the voltage of the resistor 939 becomes lower than the voltage of the Zener diode 938, the output of the comparator 932 becomes Low, so that the gate voltage of the FET 927 decreases and the FET 927 is turned on. For this reason, a current flows through the inductor 928 to charge the capacitor 930 and the voltage across the capacitor rises. Next, when the voltage rises and the voltage of the resistor 939 becomes higher than the voltage of the Zener diode 938, the output of the comparator 932 becomes High so that the gate voltage of the FET 927 becomes high and the FET 927 is turned off. Since the inductor 928 tries to continue the current flow, the diode 929 is turned on to charge the capacitor 930 with the energy stored in the inductor 928. At this time, the diode 980 is turned on, and the comparator 932 performs an inverting operation to turn on the FET 927 in order to lower the voltage at the + input terminal of the comparator 932. By repeating the series of operations as described above, the illustrated second DCDC converter continues to oscillate.

  FIG. 10 is a connection diagram of the energy saving mode signal line from the control unit of the laser printer to the power supply device. In FIG. 10, reference numeral 188 denotes an output transistor of the control circuit, and 190 denotes a control circuit composed of a CPU or ASIC. Reference numerals 185 to 187, 271 and 272 denote resistors. The output of the drive system (+ 24V) is turned on and off by a load switch using the FET 270. The drain of the FET 270 is connected to the D end of FIG. With this configuration, when the output of the control circuit 190 is High, the output transistor 188 becomes low impedance, and the FET 270 that is a load switch is turned on. Further, when the output of the control circuit 190 becomes Low, the output transistor 188 enters a high impedance state, and the FET 270 that is a load switch is turned off.

  The operation when entering the energy saving mode will be described based on the flowchart of FIG. In the energy saving mode, the signal from the control circuit 190 is output from the resistor 272 with the output transistor 188 turned off in step 11 (abbreviated as S11 in the figure, the same applies hereinafter) to stop the supply of the first DC voltage. The gate terminal is set to a high or high impedance state. In this case, since the load switch FET 270 is turned off, the first DCDC converter does not output the first DC voltage from the terminal 171 to the outside of the power source.

  Thereafter, when the terminal 184 goes low in step 12 and the energy saving mode signal is input from the terminal 174 to the power supply device shown in FIG. 9, the transistor 175 is turned off and a current flows through the LED 906-b of the photocoupler. The operation of the power supply comparator 933 becomes effective. The comparator 933 is configured to compare the divided voltage of the resistors 935 and 937 with the voltage of the Zener diode 938. The comparator 933 is turned on when the voltage of the resistor 937 is higher than the voltage of the Zener diode 938, and a current is supplied to the LED of the photocoupler 906-b to cause the LED to emit light. The light receiving side transistor 906-a of the photocoupler 906 is connected between the base and emitter of the transistor 850, and the transistor 850 is turned off by the LED emission of the photocoupler 906, and the transistor 850 is turned on by turning off the LED. In this way, the starting resistor 805 and the switching element 807 of the first DCDC converter are turned on / off so that the output voltage of the second DCDC converter becomes the third DC voltage. By doing so, the feedback circuit of the second DCDC converter operates so as to keep the FET 927 kept on because the output voltage is always equal to or lower than the target value. In this way, the FET 927 of the second DCDC converter is fixed on and no switching loss occurs, and the loss in the second DCDC converter is only the loss due to the resistance of the FET 927 and the inductor 928. At the same time, the first DC / DC converter has a pause in a long cycle according to the increase / decrease of 3.3V, so that the switching loss is reduced and the power supply efficiency is dramatically increased.

Next, the return from the energy saving mode will be described with reference to FIG. By turning the terminal 184 High in Step 21, the transistor 175 is turned on, the control of the starting resistor 805 and the FET 907 by the comparator 933 is stopped, and the first DCDC converter output voltage goes to the first DC voltage (+ 24V). And start rising. After waiting for several ms until the output voltage of the first DCDC converter reaches the first DC voltage in step 22, the output transistor 188 is turned on in step 23. Then, the load switch FET 270 is turned on, and the first DC voltage is supplied from the terminal 171 to the load of the drive system. If there is no element that malfunctions when a halfway voltage is applied to the load of the driving system, the FET 270 that is a load switch may be eliminated so that the first DC voltage is not turned on or off.

  As described above, according to the present embodiment, the efficiency of the power supply device in the standby mode can be improved in the configuration in which the power supply device according to the present invention is applied to the laser beam printer.

702 Rectifier diode 703 Primary smoothing capacitor 711 Switching transformer 720 Secondary rectifier diode 728 Secondary smoothing capacitor 732 Switching element 746 CPU

Claims (13)

By switching the input DC voltage by the first switching means, the input DC voltage is converted to the first DC voltage, and the converted first DC voltage is output to the first load. One converter,
The first DC voltage output from the first converter is input, and the input first DC voltage is lower than the first DC voltage by switching by the second switching means. In a power supply device comprising: a second converter for converting to a second DC voltage and outputting the converted second DC voltage to a second load;
The first converter lowers the switching frequency of the first switching means to a switching frequency lower than the switching frequency when the first DC voltage is being output, and from the second DC voltage Output a low third DC voltage,
The second converter, the power supply apparatus and outputs the third DC voltage input before Symbol second load. Control means for controlling the switching frequency of the first switching means of the first converter;
The control unit switches the switching frequency of the first switching unit from the first frequency to a second frequency lower than the first frequency, thereby changing the DC voltage output from the first converter to the first frequency. The power supply device according to claim 1, wherein the DC voltage is switched from one DC voltage to the third DC voltage. The second converter, when the first converter is outputting said third DC voltage, prior Symbol the second switching means is turned on and the third said second DC voltage The power supply apparatus according to claim 1, wherein the power supply apparatus outputs the power to a load. A switch for supplying or stopping the first DC voltage from the first converter to the first load;
After the switch is turned off and the supply of the first DC voltage to the first load is stopped, the voltage output from the first converter is changed from the first DC voltage to the third DC voltage. The power supply device according to any one of claims 1 to 3, wherein A switch for supplying or stopping the first DC voltage from the first converter to the first load;
2. The switch is turned on after the voltage output from the first converter is changed from the third DC voltage to the first DC voltage when the switch is turned on. 5. The power supply device according to any one of 4.   The power consumption when the third DC voltage is output from the first converter is smaller than the power consumption when the first DC voltage is output from the first converter. The power supply device according to any one of 1 to 5. An image forming means for forming an image;
In order to perform image formation by the image forming unit, the input DC voltage is switched to the first DC voltage by switching the input DC voltage by the first switching unit, and the converted first voltage of the first converter to output a DC voltage to the first load, said first DC voltage output from the first converter is inputted, the inputted said first DC voltage, the second A second converter for converting to a second DC voltage lower than the first DC voltage by switching by a switching means and outputting the converted second DC voltage to a second load; An image forming apparatus including a power source,
The first converter lowers the switching frequency of the first switching means to a switching frequency lower than the switching frequency when the first DC voltage is being output, and from the second DC voltage Output a low third DC voltage,
The second converter, by controlling the operation of said second switching means, an image forming apparatus and outputs the third DC voltage input before Symbol second load. When the first converter is outputting the third DC voltage, the second converter turns on the second switching means and supplies the third DC voltage to the second DC voltage. The image forming apparatus according to claim 7, wherein the image forming apparatus outputs to a load. In the energy-saving mode of the image forming apparatus, said first converter to claim 7 or 8, characterized in that outputs the third DC voltage to said second load via said second converter The image forming apparatus described. A switch for supplying or stopping the first DC voltage from the first converter to the first load;
After the switch is turned off and the supply of the first DC voltage to the first load is stopped, the voltage output from the first converter is changed from the first DC voltage to the third DC voltage. the image forming apparatus according to any one of claims 7 to 9, characterized in that changing to. A switch for supplying or stopping the first DC voltage from the first converter to the first load;
The switch is turned on after the voltage output from the first converter is changed from the third DC voltage to the first DC voltage when the switch is turned on. The image forming apparatus according to any one of 10 . Driving means for driving to form an image;
The first load, the image forming apparatus according to any one of claims 7 to 11, characterized in that it comprises the drive means. Control means for controlling the operation of the image forming means;
Said second load, the image forming apparatus according to any one of claims 7 to 12, characterized in that it comprises said control means.

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