Printer and switching power supply circuit

Abstract

To provide a printer that can reduce power consumption during a standby mode.SOLUTION: A printer comprises: a primary-side circuit that executes a switching operation; a secondary-side circuit that has a shunt regulator and outputs power to a load; a feedback circuit that feeds back, to the primary-side circuit, a result of comparison between output voltage output by the secondary-side circuit and reference voltage of the shunt regulator, and controls the output voltage from the secondary-side circuit; a control signal circuit that outputs a control signal input from the outside to the feedback circuit to control the output voltage from the secondary-side circuit; and a switching power supply circuit having a switch circuit that, when the output voltage from the secondary-side circuit becomes first low voltage or second low voltage lower than the first low voltage due to the input of the control signal, turns off supply of current to the shunt regulator, and a clamp circuit that is provided between the switch circuit and the ground.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a printing device and a switching power supply circuit. [Background technology]

[0002] A power supply circuit is known that compares the output voltage of a secondary circuit with a reference voltage of a shunt regulator and feeds back the result of the comparison to a primary circuit, thereby controlling the output voltage of the secondary circuit (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-166363 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the prior art, there is room for improvement in the power loss in the above-mentioned power supply circuit during standby mode. [Means for solving the problem]

[0005] In order to solve the above problem, one aspect is a printing device equipped with a switching power supply circuit having: a primary side circuit that performs switching operations; a secondary side circuit that has a shunt regulator and outputs power to a load; a feedback circuit that compares the output voltage output by the secondary side circuit with a reference voltage of the shunt regulator and feeds back the result of the comparison to the primary side circuit to control the output voltage of the secondary side circuit; a control signal circuit that outputs a control signal input from outside to the feedback circuit to control the output voltage of the secondary side circuit; a switch circuit that turns off the supply of current to the shunt regulator when the input of the control signal causes the output voltage of the secondary side circuit to become a first low voltage or a second low voltage lower than the first low voltage; and a clamp circuit that is provided between the switch circuit and ground.

[0006] In order to solve the above problem, one aspect is a switching power supply circuit having: a primary side circuit that performs switching operation; a secondary side circuit that has a shunt regulator and outputs power to a load; a feedback circuit that compares an output voltage output by the secondary side circuit with a reference voltage of the shunt regulator and feeds back the result of the comparison to the primary side circuit to control the output voltage of the secondary side circuit; a control signal circuit that outputs a control signal input from outside to the feedback circuit to control the output voltage of the secondary side circuit; a switch circuit that turns off the supply of current to the shunt regulator when the input of the control signal causes the output voltage of the secondary side circuit to become a first low voltage or a second low voltage lower than the first low voltage; and a clamp circuit provided between the switch circuit and ground. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a printing apparatus according to an embodiment. [Figure 2] 1 is a diagram showing a configuration of a switching power supply circuit according to an embodiment; [Figure 3]4 is a timing chart showing the state of each part of a printing device including each part of a switching power supply circuit according to an embodiment in an off mode. [Figure 4] 4 is a timing chart showing the state of each part of a printing device including each part of a switching power supply circuit according to an embodiment in a standby mode. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described with reference to the drawings. In this embodiment, the unit of voltage is volts, which may be written as [V].

[0009] FIG. 1 is a diagram showing the configuration of a printing device 1 according to an embodiment.

[0010] As shown in FIG. 1, the printing device 1 includes a switching power supply circuit 10, which is a power supply circuit for the printing device, a DC-DC converter circuit 11, and a printing control circuit 12.

[0011] The switching power supply circuit 10 is connected to a commercial AC power supply 2 via a cable 3. The switching power supply circuit 10 receives an AC voltage of, for example, 100 volts, rectifies, smooths, and converts the voltage, and outputs a DC voltage of 42 volts to a load. The switching power supply circuit 10 is configured to be detachable from the cable 3 that connects to the commercial AC power supply 2. Details of the switching power supply circuit 10 will be described later. Note that in this embodiment, the load refers to at least one of the DC-DC converter circuit 11, the printed control circuit 12, the logic circuit 13, and the printed unit 14, or a collective term for all of these.

[0012] The DC-DC converter circuit 11 steps down the input voltage and supplies the stepped-down power to the logic circuit 13, which will be described later. For example, the DC-DC converter circuit 11 steps down 42 volts to a voltage lower than 42 volts, such as 3.3 volts or 5 volts, and supplies the stepped-down power to the logic circuit 13.

[0013] The printing control circuit 12 is a circuit that controls the supply of power to the printing unit 14 based on the power input from the switching power supply circuit 10. For example, the printing control circuit 12 receives 42 volts of power and controls the supply of power to each part of the printing unit 14 based on the input power.

[0014] As shown in FIG. 1, the printing device 1 includes a logic circuit 13, a printing unit 14, and an input unit 15. The logic circuit 13 includes a SOC 131 that is a control circuit, and a memory 132 . The control circuit SOC 131 may be provided outside the printing device 1.

[0015] SOC 131 is an integrated circuit that controls each part of the printing device 1. SOC 131 includes a CPU (Central Processing Unit) and the like as an arithmetic execution part (not shown). A ROM (not shown) is connected to SOC 131, and this ROM stores control programs executable by the CPU and data related to the control programs in a non-volatile manner. SOC 131 controls the printing operation of printing unit 14 and each part of the printing device 1 by executing the control program stored in the ROM.

[0016] The memory 132 includes a semiconductor storage element such as an EEPROM or a flash memory, or a storage medium such as a hard disk, and stores various data in a rewritable, non-volatile manner.

[0017] The printing unit 14 includes a transport motor 141 , a carriage movement motor 142 , a cutter drive motor 143 , and a head drive circuit 144 .

[0018] The transport motor 141 is a motor that rotates the transport roller 141a and is connected to the transport roller 141a. The transport roller 141a is a roller that transports the print medium in the transport direction. The SOC 131 outputs a drive signal to the transport motor 141 to drive the transport motor 141. In response to the driving of the transport motor 141, the transport roller 141a rotates, and in response to the rotation of the transport roller 141a, the print medium is transported in the transport direction.

[0019] The carriage movement motor 142 is a motor that moves the carriage 142a in a scanning direction that intersects the transport direction of the print medium, and is connected to the carriage 142a. The carriage 142a is supported by a carriage shaft (not shown) that extends in the scanning direction that intersects the transport direction of the print medium, and the print head 144a scans in the scanning direction along this carriage shaft. The SOC 131 outputs a drive signal to the carriage movement motor 142, driving the carriage movement motor 142. In response to the driving of the carriage movement motor 142, the print head 144a mounted on the carriage 142a moves in the scanning direction.

[0020] The cutter drive motor 143 is a motor that moves the movable blade 143a and is connected to the movable blade 143a. The SOC 131 outputs a drive signal to the cutter drive motor 143 to drive the cutter drive motor 143. As the cutter drive motor 143 is driven, the movable blade 143a moves and the print medium is cut.

[0021] The head drive circuit 144 is connected to the print head 144a. The print head 144a is an inkjet head and includes nozzle rows for multiple colors, such as four colors C, M, and K. The print head 144a receives ink from ink cartridges (not shown) and ejects the ink from nozzles in each nozzle row to form dots on the printing surface of the printing medium, thereby printing characters, images, etc. Under the control of the SOC 131, the head drive circuit 144 drives actuators provided corresponding to the nozzles of the print head 144a, causing the nozzles to eject ink. Dots are formed on the printing surface of the printing medium in response to the ink being ejected from the nozzles.

[0022] The input unit 15 includes an input means (not shown), such as an operation switch or a touch panel, provided on the printing device 1, detects an operation performed by the user on the input means, and outputs the detected operation to the SOC 131. Based on the input from the input unit 15, the SOC 131 executes a process corresponding to the operation on the input means.

[0023] In this embodiment, the printing device 1 has three operating modes: a normal mode, a standby mode, and an off mode.

[0024] The normal mode refers to an operation mode in which power supply to each part of the printing device 1 is maintained and the printing device 1 can perform operations such as printing.

[0025] Standby mode refers to an operating mode in which the printer 1 waits for a command from the user to start printing. In standby mode, for example, the supply of power to various motors such as the transport motor 141 provided in the printing unit 14 is stopped. The printer 1 transitions from normal mode to standby mode when the input unit 15 detects an instruction to transition to standby mode based on the user's operation of an operation switch (not shown), or when a predetermined period of time has passed during which no operation such as printing is performed in normal mode. Standby mode consumes less power than normal mode. Also, when a predetermined condition is met in the off mode, the mode may be changed to the standby mode.

[0026] Off mode is a mode that reduces power consumption even more than standby mode. In off mode, the supply of power to components of the printing device 1 that consume a large amount of power is stopped, thereby further reducing the power consumption of the printing device 1. For example, in off mode, the RAM that constitutes the SOC 131, the RAM, and the memory 132 are stopped. When the input unit 15 detects an instruction to transition to off mode based on a user's operation of an operation switch (not shown), the printing device 1 transitions from normal mode or standby mode to off mode.

[0027] In this embodiment, the normal mode is a mode in which the output level is high, the off mode is a mode in which the output level is low, and the standby mode is a mode in which the output level is in the middle between high and low. That is, the output level in the normal mode is the highest, and the output level in the standby mode is higher than the output level in the off mode. In standby mode, power consumption is lower than in normal mode, but higher than in off mode. Any condition may be used as the condition for transitioning the operation mode between the normal mode, the standby mode, and the off mode.

[0028] As described above, the power consumption of the printer 1 differs depending on the operating mode of the printer 1. Therefore, the switching power supply circuit 10 varies the output voltage to be output to the load side at least between normal mode, standby mode, and off mode. For example, when the operating mode of the printer 1 is normal mode, the switching power supply circuit 10 outputs an output voltage of 42 volts to the load side; when the operating mode of the printer 1 is off mode, the switching power supply circuit 10 outputs an output voltage of 1 volt to 5 volts to the load side; and when the operating mode of the printer 1 is standby mode, the switching power supply circuit 10 outputs an output voltage of 10 volts to 20 volts to the load side. The load side refers to the side from which the switching power supply circuit 10 outputs power, and is the side where the DC-DC converter circuit 11, printing control circuit 12, logic circuit 13, printing unit 14, etc. are located.

[0029] FIG. 2 is a diagram showing the configuration of the switching power supply circuit 10 according to the embodiment. In this embodiment, in the printing device 1, the switching power supply circuit 10 outputs different output voltages to the load side in the normal mode, the standby mode, and the off mode.

[0030] 2, the switching power supply circuit 10 has a primary side circuit 5A and a secondary side circuit 5B. The switching power supply circuit 10 has a commercial AC power supply 2 connected to the primary side circuit 5A and a load 6 connected to the secondary side circuit 5B. The switching power supply circuit 10 converts an input voltage Vin input from the commercial AC power supply 2 to the primary side circuit 5A into an output voltage Vout and outputs the output voltage Vout to the load 6.

[0031] The primary circuit 5A includes a rectifier circuit S1 connected to the commercial AC power supply 2, a first electrolytic capacitor C1, a primary winding L1 of a transformer TR, and a switching circuit K1. In the primary circuit 5A, the input voltage Vin, which is an AC voltage, is rectified and smoothed by the rectifier circuit S1 and the first electrolytic capacitor C1. Furthermore, the primary side circuit 5A is configured as a switching type circuit in which the voltage applied to the primary winding L1 is controlled by the switching operation of the switching circuit K1.

[0032] The switching circuit K1 includes a control IC (Integrated Circuit) 51 and a first transistor Q1. In this embodiment, a FET is used for the first transistor Q1. The control IC 51 changes the voltage input to the gate of the first transistor Q1 according to the output of a photocoupler Pc (described later). Specifically, the control IC 51 outputs a pulse voltage to the gate of the first transistor Q1 to turn the first transistor Q1 on and off. This causes the first transistor Q1 to perform a switching operation.

[0033] The control IC 51 controls the on / off period of the first transistor Q1 by controlling the pulse width according to the output of the photocoupler Pc. The control IC 51 has an FB terminal to which a feedback voltage is applied, an OUT terminal that outputs a pulse voltage to the gate of the first transistor Q1, and a CS terminal to which a detection voltage indicating the detection result of the output current is applied. Note that the switching operation of the switching circuit K1 corresponds to the switching operation of the primary-side circuit 5A.

[0034] The secondary circuit 5B includes a secondary winding L2 which is a secondary winding of the transformer TR, a rectifying element S2, and a second electrolytic capacitor C2. When a voltage is applied to the primary winding L1 of the primary circuit 5A, a voltage is induced in the secondary winding L2 according to the ratio of the number of turns of the primary winding L1 to the number of turns of the secondary winding L2. The voltage induced in the secondary winding L2 is rectified and smoothed by the rectifying element S2 and the second electrolytic capacitor C2, and is output to the load 6.

[0035] In the switching power supply circuit 10, when the voltage applied to the primary winding L1 changes due to the switching operation of the switching circuit K1, the voltage induced in the secondary winding L2 changes, and the output voltage Vout of the secondary circuit 5B changes.

[0036] The secondary-side circuit 5B includes a first resistor R1 and a second resistor R2 between the first output terminal OUT1 and the ground output terminal GND. The first resistor R1 and the second resistor R2 are connected in series. One end of the first resistor R1 is connected to the first output terminal OUT1, and the other end is connected to one end of the second resistor R2 at a first node P1. One end of the second resistor R2 is connected to the first resistor R1 at the first node P1, and the other end is connected to the ground output terminal GND.

[0037] A shunt regulator SR is connected to the first node P1. The shunt regulator SR has an internal reference voltage circuit that generates a predetermined reference voltage, such as 2.5 volts. The shunt regulator SR is composed of, for example, an IC, and compares the voltage at the first node P1, which is obtained by dividing the voltage across the secondary winding L2 using a first resistor R1 and a second resistor R2, with the reference voltage generated by the internal reference voltage circuit. Hereinafter, the voltage at the first node P1 will also be referred to as the P1 voltage, which is the voltage obtained by dividing the output voltage Vout using the first resistor R1 and the second resistor R2. The cathode of the shunt regulator SR is connected to one end of the third resistor R3 at the second node P2, and the anode is connected to the ground output terminal GND.

[0038] One end of a third resistor R3, which is a supply resistor, is connected to the second node P2. The third resistor R3 is a resistor for supplying a constant current to the shunt regulator SR, and one end of the third resistor R3 is connected to the cathode of the shunt regulator SR at the second node P2. Generally, the shunt regulator SR needs to be supplied with a current of a predetermined value or more to ensure the accuracy of its operation. The resistance value of the third resistor R3 is set to a value that allows the shunt regulator SR to be supplied with a current of a sufficient value to ensure the accuracy of its operation. Here, the current value equal to or greater than the predetermined current value may be, for example, 1 mA. The operation is, for example, the generation and comparison of a reference voltage. A light-emitting diode Dp of a photocoupler Pc, which is a feedback circuit, is connected between the cathode of the shunt regulator SR and the first output terminal OUT1.

[0039] When the output voltage Vout on the secondary circuit 5B side rises and the divided voltage P1 voltage exceeds the reference voltage, the shunt regulator SR passes current from the cathode to the anode. This causes the shunt regulator SR to pass current through the light-emitting diode Dp that constitutes the photocoupler Pc. When current flows through the light-emitting diode Dp that constitutes the photocoupler Pc, the light-emitting diode Dp emits light. The light emitted from the light-emitting diode Dp is received by the phototransistor Qp that constitutes the photocoupler Pc together with the light-emitting diode Dp. When the phototransistor Qp receives light emitted from the light-emitting diode Dp, a feedback current flows between the collector and emitter of the phototransistor Qp. When a feedback current flows through the phototransistor Qp, a feedback voltage based on the feedback current is applied to the FB terminal of the control IC 51. Based on the feedback voltage applied to the FB terminal, the control IC 51 controls the pulse output to the first transistor Q1 so that the voltage applied to the primary winding L1 decreases, thereby lowering the output voltage Vout.

[0040] On the other hand, when the output voltage Vout drops and the divided voltage P1 voltage falls below the reference voltage, the shunt regulator SR does not allow current to flow through the photocoupler Pc. As a result, no feedback current flows between the collector and emitter of the phototransistor Qp. This causes the control IC 51 to control the first transistor Q1 so that the voltage applied to the primary winding L1 increases, thereby raising the output voltage Vout.

[0041] Note that the photocoupler Pc applying a feedback voltage to the FB terminal and not applying a feedback voltage to the FB terminal are equivalent to feeding back the comparison result between the P1 voltage and the reference voltage of the shunt regulator SR to the primary side circuit 5A.

[0042] In this way, the shunt regulator SR reduces the output voltage Vout when the P1 voltage exceeds the reference voltage, and increases the output voltage Vout when the P1 voltage falls below the reference voltage. In other words, the shunt regulator SR controls the output voltage Vout so that the P1 voltage and the reference voltage are equal, thereby performing constant voltage control to keep the output voltage Vout constant.

[0043] As described above, the control IC 51 has a CS terminal. A fourth resistor R4 is connected to the CS terminal. A current corresponding to the ratio of the number of turns of the primary winding L1 to the number of turns of the secondary winding L2 flows through the fourth resistor R4 relative to the output current. The fourth resistor R4 converts this current into a voltage, which is applied to the CS terminal as a detection voltage indicating the detection result of the output current. The control IC 51 compares the detection voltage applied to the CS terminal with the feedback voltage applied to the FB terminal and sets the period for which the first transistor Q1 is turned on based on the comparison result.

[0044] A control signal circuit K2 is connected to the second node P2. The control signal circuit K2 has a fifth resistor R5. One end of the fifth resistor R5 is connected to the second node P2 and the other end is connected to a control terminal ST. The control terminal ST is a terminal controlled by SOC131 or the input unit 15. SOC131 or the input unit 15 inputs a PSC signal, which is a control signal of a predetermined voltage level, to the control terminal ST. The control signal circuit K2 controls the output voltage Vout of the secondary-side circuit 5B by outputting the PSC signal, which is input from SOC131 or the input unit 15 via the control terminal ST, to the photocoupler Pc.

[0045] For example, when the SOC 131 or the input unit 15 inputs a "Low" or "Middle" level PSC signal to the control terminal ST, the control signal circuit K2 outputs the PSC signal to the photocoupler Pc. When the photocoupler Pc receives a "Low" or "Middle" level PSC signal, a current flows through the light-emitting diode Dp. This causes the light-emitting diode Dp constituting the photocoupler Pc to emit light. As described above, when the phototransistor Qp receives the light emitted from the light-emitting diode Dp, a feedback current flows between the collector and emitter of the phototransistor Qp. A feedback voltage is applied to the FB terminal, and the control IC 51 controls the pulse output to the first transistor Q1 based on the feedback voltage applied to the FB terminal to reduce the voltage applied to the primary winding L1, thereby lowering the output voltage Vout.

[0046] Here, when the operating mode of the printing device 1 is the off mode, the SOC 131 inputs a "low" level PSC signal to the control signal circuit K2. As a result, the output voltage Vout of the secondary side circuit 5B drops as described above, and the SOC 131 can lower the output voltage Vout. In this embodiment, the low voltage is a voltage lower than the output voltage Vout of the switching power supply circuit 10 in the normal mode, and more specifically, it refers to the output voltage Vout output by the switching power supply circuit 10 in the off mode. Furthermore, when the operating mode of the printing device 1 is standby mode, the SOC 131 inputs a "Middle" level PSC signal to the control signal circuit K2. As a result, the output voltage Vout of the secondary side circuit 5B drops as described above, so that the SOC 131 can set the output voltage Vout to a medium voltage. In this embodiment, the medium voltage is a voltage lower than the output voltage Vout of the switching power supply circuit 10 in normal mode, and more specifically, it refers to the output voltage Vout output by the switching power supply circuit 10 in standby mode. The medium voltage is higher than the low voltage.

[0047] Here, when the output voltage Vout of the secondary circuit 5B is a low or medium voltage due to the PSC signal, the output voltage Vout is controlled by the PSC signal, so control of the output voltage Vout by the shunt regulator SR is unnecessary. Therefore, when the output voltage Vout of the secondary circuit 5B is a low or medium voltage due to the PSC signal, supplying an operating current to the shunt regulator SR via the third resistor R3 results in unnecessary current being supplied to the shunt regulator SR. Furthermore, because current is supplied to the shunt regulator SR via the third resistor R3, unnecessary power is consumed by the third resistor R3 when the output voltage Vout of the secondary circuit 5B is a low or medium voltage due to the PSC signal. Furthermore, as described above, the third resistor R3 and the fifth resistor R5 are connected at the second node P2. Therefore, when the output voltage Vout of the secondary circuit 5B is a low voltage or a medium voltage due to the PSC signal, if current is supplied to the shunt regulator SR via the third resistor R3, that current will flow into the fifth resistor R5, and unnecessary power will be consumed by the fifth resistor R5 as well. The switching power supply circuit 10 of this embodiment solves this problem.

[0048] As shown in FIG. 2, a switch circuit K3 is connected between the first output terminal OUT1 and the ground output terminal GND. The switch circuit K3 includes a second transistor Q2, a sixth resistor R6, a seventh resistor R7, and a Zener diode TS. In this embodiment, a pnp-type bipolar transistor is used as the second transistor Q2. The second transistor Q2 has an emitter connected to the first output terminal OUT1, a base connected to a third node P3, and a collector connected to one end of the third resistor R3. One end of the sixth resistor R6 and one end of the seventh resistor R7 are connected to the third node P3. One end of the sixth resistor R6 is connected to the emitter of the second transistor Q2, and the other end is connected to the third node P3. The seventh resistor R7 has one end connected to the third node P3 and the other end connected to the cathode of the Zener diode TS. One end of the Zener diode TS is connected to the seventh resistor R7, and the other end is connected to the ground output terminal GND. That is, the sixth resistor R6, the seventh resistor R7, and the Zener diode TS are connected in series.

[0049] The second transistor Q2 turns on and off based on the voltage output to its base. The voltage output to its base here refers to the voltage at the third node P3. The voltage at the third node P3 is the output voltage Vout divided by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS, and is clamped at the saturation voltage between the base and emitter of the second transistor Q2. Hereinafter, this voltage will also be referred to as the P3 voltage. The second transistor Q2 turns on when the P3 voltage exceeds a predetermined voltage, and turns off when the P3 voltage is equal to or lower than the predetermined voltage. The P3 voltage, which is the boundary between on and off, is also referred to as the "threshold voltage" in the following description. The threshold voltage, which is the boundary between on and off of the second transistor Q2, is determined by the resistance values ​​of the sixth resistor R6, the seventh resistor R7, and the Zener diode TS. In this embodiment, the resistance values ​​of the sixth resistor R6, the seventh resistor R7, and the Zener diode TS are set so that the P3 voltage becomes the threshold voltage at which the second transistor Q2 turns off when the output voltage Vout is equal to or lower than 20 volts.

[0050] Here, the effect of the Zener diode TS will be described. In this embodiment, in the secondary circuit 5B, a clamp circuit is provided between the gate terminal of the second transistor Q2 in the switch circuit K3 that controls the conduction of the shunt regulator SR and the ground output terminal GND. In this embodiment, the clamp circuit is a Zener diode TS. The anode of the Zener diode TS is connected to the ground output terminal GND, and the cathode of the Zener diode TS is connected to the gate terminal of the second transistor Q2 via a seventh resistor R7.

[0051] In this embodiment, the provision of the Zener diode TS makes it possible to reduce power consumption in standby mode. That is, in this embodiment, the power consumption in standby mode can be reduced in the power supply circuit that controls the output voltage of the secondary circuit 5B by feeding back the comparison result between the output voltage output by the secondary circuit 5B and the reference voltage of the shunt regulator SR to the primary circuit 5A. Note that other circuit elements may be provided between the clamp circuit and the gate terminal of the second transistor Q2, and in this embodiment, a seventh resistor R7 is provided. Furthermore, other circuit elements may be provided between the clamp circuit and the ground output terminal GND.

[0052] Next, the operation of the printing device 1 having the switching power supply circuit 10 according to this embodiment will be described. FIG. 3 is a timing chart in off mode showing the state of each part of the printing device 1, including each part of the switching power supply circuit 10 according to the embodiment. Timing chart A in FIG. 3 shows the state controlled by the SOC 131 or the input unit 15. Timing chart B in FIG. 3 shows the state of the output voltage Vout of the secondary circuit 5B. Timing chart C in FIG. 3 shows the state of the P3 voltage. Timing chart D in FIG. 3 shows the on / off state of the second transistor Q2. Timing chart E in FIG. 3 shows the state of current flowing into the third resistor R3.

[0053] In the explanation of Fig. 3, it is assumed that the operating mode of the printer 1 is normal mode at the start of each timing chart. Also, in the explanation of Fig. 3, when the operating mode of the printer 1 is normal mode, the output voltage Vout is 42 volts. Also, in the explanation of Fig. 3, it is assumed that the operating mode of the printer 1 is off mode, and the output voltage Vout is 2 volts.

[0054] Assume that at first timing t1, the operating mode of the printer 1 starts to transition from normal mode to off mode. As described above, when the input unit 15 detects an instruction to transition to off mode based on a user's operation of an operation switch (not shown), the operating mode of the printer 1 transitions from normal mode to off mode.

[0055] As shown in timing chart A in FIG. 3, when the operating mode of the printing device 1 starts to transition from the normal mode to the off mode, the SOC 131 outputs a "Low" level PSC signal to the control terminal ST at a first timing t1. In the description of FIG. 3, it is assumed that the "Low" level to the control terminal ST in the off mode is 0 volts.

[0056] At first timing t1, when SOC 131 outputs a PSC signal to control terminal ST, control signal circuit K2 outputs a "Low" level PSC signal to photocoupler Pc. When photocoupler Pc receives the "Low" level PSC signal, current flows through light-emitting diode Dp, which constitutes photocoupler Pc. As a result, light-emitting diode Dp, which constitutes photocoupler Pc, emits light. When light-emitting diode Dp emits light, phototransistor Qp receives the light emitted from light-emitting diode Dp. When phototransistor Qp receives the light, a feedback current flows between the collector and emitter of phototransistor Qp. A feedback voltage is then applied to the FB terminal, and control IC 51 controls the pulse output to first transistor Q1 based on the feedback voltage applied to the FB terminal to reduce the power applied to primary winding L1.

[0057] When the power applied to the primary winding L1 decreases, the output voltage Vout drops from 42 volts at the second timing t2, as shown in timing chart B of FIG.

[0058] After the second timing t2, the output voltage Vout drops from 42 volts.

[0059] After the second timing t2, the output voltage Vout drops, and at the third timing t3, the output voltage Vout drops to 20 volts. Then, as shown in timing chart C of FIG. 3, the P3 voltage maintains the saturation voltage between the base and emitter of the second transistor Q2 until the third timing t3. Here, β volts is the voltage value of the P3 voltage divided by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS when the output voltage Vout is 20 volts, and in this embodiment, it is the threshold voltage.

[0060] As described above, in this embodiment, the resistance values ​​of the sixth resistor R6, the seventh resistor R7, and the Zener diode TS are set so that the P3 voltage becomes the threshold voltage at which the second transistor Q2 turns off when the output voltage Vout is 20 volts or less. Therefore, when the P3 voltage falls below the saturation voltage between the base and emitter of the second transistor Q2, the second transistor Q2 turns off at the third timing t3, as shown in timing chart D of FIG. 3. Then, when the second transistor Q2 turns off, current flow to the third resistor R3 is stopped at the third timing t3, as shown in timing chart E of FIG. 3.

[0061] After the third timing t3, the second transistor Q2 is turned off, and the current flowing into the third resistor R3 is stopped.

[0062] After the third timing t3, the output voltage Vout continues to drop, dropping to 2 volts, as shown in timing chart B of FIG. 3. As the output voltage Vout drops, the P3 voltage drops to γ ​​volts at the fourth timing t4. γ volts is the P3 voltage divided by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS when the output voltage Vout is 2 volts. γ volts is lower than β volts and is approximately 2 volts. At the fourth timing t4, the P3 voltage remains below β volts, so the second transistor Q2 remains off. Current flow to the third resistor R3 remains off.

[0063] In this way, when the output voltage Vout of the secondary circuit 5B is low due to the input of the PSC signal, the current flow to the third resistor R3 is turned off. That is, when the output voltage Vout of the secondary circuit 5B is low due to the input of the PSC signal, the switch circuit K3 including the second transistor Q2 turns off the supply of current to the third resistor R3, which controls the current of the shunt regulator SR, and reduces the current to the fifth resistor R5.

[0064] As described above, when the output voltage Vout of the secondary circuit 5B is low due to the PSC signal, the output voltage Vout is controlled by the PSC signal, making it unnecessary to control the output voltage Vout by the shunt regulator SR. Therefore, as described above, when the output voltage Vout of the secondary circuit 5B is low due to the PSC signal, the second transistor Q2 executes an off operation, thereby stopping the flow of current into the third resistor R3 and the supply of current to the shunt regulator SR, thereby reducing the current to the fifth resistor R5. This prevents unnecessary current from being supplied to the third resistor R3 and the fifth resistor R5, which control the current of the shunt regulator SR, when the output voltage Vout of the secondary circuit 5B is low due to the PSC signal.

[0065] Furthermore, when the output voltage Vout of the secondary circuit 5B is low due to the PSC signal, the second transistor Q2 turns off the flow of current into the third resistor R3. In other words, when the output voltage Vout of the secondary circuit 5B is low due to the PSC signal, no unnecessary power is consumed in the third resistor R3. Furthermore, because the flow of current into the third resistor R3 is turned off, no current flows into the fifth resistor R5 either. Therefore, when the output voltage Vout of the secondary circuit 5B is low due to the PSC signal, no unnecessary power is consumed in the fifth resistor R5. Furthermore, the reduction in the current into the fifth resistor R5 reduces the output voltage Vout. The reduction in the output voltage Vout reduces the current through the first resistor R1 and the second resistor R2. Therefore, the switching power supply circuit 10 can reduce power consumption when the output voltage Vout of the secondary circuit 5B is low due to the PSC signal.

[0066] In this embodiment, the case where the output voltage Vout of the secondary circuit 5B is low due to the PSC signal refers to the case where the operating mode of the printer 1 is in the off mode. The off mode is an operating mode in which power consumption is reduced. Therefore, an increase in power consumption is undesirable in the off mode. Therefore, in the off mode, the switching power supply circuit 10 reduces power consumption, so that an increase in power consumption can be prevented when the operating mode of the printer 1 is the off mode.

[0067] The switch circuit K3 also includes a second transistor Q2, a sixth resistor R6, a seventh resistor R7, and a Zener diode TS. When the output voltage Vout falls below a threshold voltage defined by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS, the second transistor Q2 turns off. More specifically, the switch circuit K3 turns off the second transistor Q2 when the output voltage Vout falls below 20 volts, which corresponds to the threshold voltage β volts. To turn off the second transistor Q2, an external off signal can be output to the base of the second transistor Q2. However, even if an external signal is output to turn off the second transistor Q2, power is consumed to output the signal. This increases power consumption in the off mode. To control the second transistor Q2 from outside the switch circuit K3, it may be necessary to provide a device for controlling the second transistor Q2 externally to the switch circuit K3. Therefore, in this embodiment, as the output voltage Vout drops, the second transistor Q2 is automatically turned off, which prevents the switching power supply circuit 10 from increasing power consumption in the off mode and enables the switching power supply circuit 10 to turn off the current supply to the shunt regulator SR with a simple configuration.

[0068] 3, let us assume that the operating mode of the printer 1 starts to transition from the off mode to the normal mode at the fifth timing t5. For example, when the input unit 15 detects an instruction to transition to the normal mode based on a user's operation of an operation switch (not shown), the printer 1 transitions the operating mode from the off mode to the normal mode.

[0069] As shown in timing chart A in FIG. 3, when the operating mode of the printing device 1 starts to transition from the off mode to the normal mode, the SOC 131 stops outputting the "High" level PSC signal to the control terminal ST at the fifth timing t5.

[0070] When SOC131 stops outputting the PSC signal to the control terminal ST, the control signal circuit K2 stops outputting the PSC signal to the photocoupler Pc. The light-emitting diode Dp that makes up the photocoupler Pc then stops emitting light, and feedback current no longer flows between the collector and emitter of the phototransistor Qp. Then, feedback voltage is no longer applied to the FB terminal, and the control IC 51 controls the pulse output to the first transistor Q1 so that the power applied to the primary winding L1 increases.

[0071] When the power applied to the primary winding L1 increases, the output voltage Vout rises from 2 volts at the sixth timing t6, as shown in timing chart B of Fig. 3. Also, when the output voltage Vout rises from 2 volts at the sixth timing t6, the P3 voltage rises from γ volts, as shown in timing chart C of Fig. 3.

[0072] After the sixth timing t6, the output voltage Vout rises from 2 volts. Furthermore, the P3 voltage rises from γ volts as the output voltage Vout rises after the sixth timing t6.

[0073] After the sixth timing t6, the output voltage Vout increases, and at the seventh timing t7, the output voltage Vout increases to 20 volts. Then, as shown in timing chart C of FIG. 3, the P3 voltage increases to β volts at the seventh timing t7.

[0074] As described above, in this embodiment, the resistance values ​​of the sixth resistor R6, the seventh resistor R7, and the Zener diode TS are set so that the P3 voltage becomes the threshold voltage that turns off the second transistor Q2 when the output voltage Vout is 20 volts or less. Therefore, when the P3 voltage rises to a voltage exceeding β volts, the second transistor Q2 turns on at the seventh timing t7, as shown in timing chart D of FIG. 3. Then, when the second transistor Q2 turns on, the supply of power to the third resistor R3 is turned on at the seventh timing t7, as shown in timing chart E of FIG. 3.

[0075] After the seventh timing t7, the second transistor Q2 is turned on. Also, after the seventh timing t7, the current flow to the third resistor R3 is turned on. As a result, after the seventh timing t7, current is supplied to the third resistor R3, which controls the current of the shunt regulator SR, and the shunt regulator SR can perform constant voltage control.

[0076] After the seventh timing t7, the output voltage Vout continues to rise, and as shown in timing chart B in Figure 3, the output voltage Vout rises to 42 volts. At timing t8, the voltage P3 is still the saturation voltage between the base and emitter of the second transistor Q2, so the second transistor Q2 remains on. Current flow to the third resistor R3 remains on.

[0077] FIG. 4 is a timing chart showing the state of each part of the printing device 1, including each part of the switching power supply circuit 10 according to the embodiment, in standby mode. Timing chart A in FIG. 4 shows the state controlled by the SOC 131 or the input unit 15. Timing chart B in FIG. 4 shows the state of the output voltage Vout of the secondary circuit 5B. Timing chart C in FIG. 4 shows the state of the P3 voltage. Timing chart D in FIG. 4 shows the on / off state of the second transistor Q2. Timing chart E in FIG. 4 shows the state of current flowing into the third resistor R3.

[0078] In the explanation of Fig. 4, it is assumed that the operating mode of the printer 1 is normal mode at the start of each timing chart. Also, in the explanation of Fig. 4, when the operating mode of the printer 1 is normal mode, the output voltage Vout is 42 volts. Also, in the explanation of Fig. 4, it is assumed that the operating mode of the printer 1 is standby mode, and the output voltage Vout is 13 volts. In this embodiment, the Zener voltage, which is the constant voltage of the Zener diode TS, is equal to or higher than the medium voltage, which is the output voltage Vout in the standby mode, and is higher than the medium voltage, for example. In the description of FIG. 4, the medium voltage is 13 volts.

[0079] For ease of explanation, the first timing t1 to the seventh timing t7 used in the explanation of FIG. 3 will also be shown in the explanation of FIG. 4, but for example, some or all of the first timing t1 to the seventh timing t7 may be different between the cases of FIG. 3 and FIG. 4.

[0080] Assume that at first timing t1, the operating mode of the printer 1 starts to transition from normal mode to standby mode. As described above, the operating mode of the printer 1 transitions from normal mode to standby mode when the input unit 15 detects an instruction to transition to standby mode based on a user's operation of an operation switch (not shown), or when a predetermined period of time has passed during which no operation, such as printing, is performed in normal mode.

[0081] As shown in timing chart A in FIG. 4, when the operating mode of the printing device 1 starts to transition from the normal mode to the standby mode, the SOC 131 outputs a PSC signal of "Middle" level to the control terminal ST at a first timing t1. In the explanation of FIG. 4, it is assumed that the "Middle" level to the control terminal ST in the standby mode is 11 volts. In the example of FIG. 4, "Middle" is abbreviated to "Mid."

[0082] At first timing t1, when SOC 131 outputs a PSC signal to control terminal ST, control signal circuit K2 outputs a "Middle" level PSC signal to photocoupler Pc. When photocoupler Pc receives the "Middle" level PSC signal, current flows through light-emitting diode Dp, which constitutes photocoupler Pc. This causes light-emitting diode Dp, which constitutes photocoupler Pc, to emit light. When light-emitting diode Dp emits light, phototransistor Qp receives the light emitted from light-emitting diode Dp. When phototransistor Qp receives the light, a feedback current flows between the collector and emitter of phototransistor Qp. A feedback voltage is then applied to the FB terminal, and control IC 51 controls the pulse output to first transistor Q1 based on the feedback voltage applied to the FB terminal to reduce the power applied to primary winding L1.

[0083] When the power applied to the primary winding L1 decreases, the output voltage Vout drops from 42 volts at the second timing t2, as shown in timing chart B of FIG.

[0084] After the second timing t2, the output voltage Vout drops from 42 volts.

[0085] After the second timing t2, the output voltage Vout drops, and at the third timing t3, the output voltage Vout drops to 20 volts. Then, as shown in timing chart C of FIG. 4, the P3 voltage maintains the saturation voltage between the base and emitter of the second transistor Q2 until the third timing t3. Here, β volts is the voltage value of the P3 voltage divided by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS when the output voltage Vout is 20 volts, and in this embodiment, it is the threshold voltage.

[0086] As described above, in this embodiment, the resistance values ​​of the sixth resistor R6, the seventh resistor R7, and the Zener diode TS are set so that the P3 voltage becomes the threshold voltage at which the second transistor Q2 turns off when the output voltage Vout is 20 volts or less. Therefore, when the P3 voltage falls below the saturation voltage between the base and emitter of the second transistor Q2, the second transistor Q2 turns off at the third timing t3, as shown in timing chart D of FIG. 4. Then, when the second transistor Q2 turns off, current flow to the third resistor R3 is stopped at the third timing t3, as shown in timing chart E of FIG. 4.

[0087] After the third timing t3, the second transistor Q2 is turned off, and the current flowing into the third resistor R3 is stopped.

[0088] After the third timing t3, the output voltage Vout continues to drop, dropping to 13 volts, as shown in timing chart B of FIG. 4. As the output voltage Vout drops, the P3 voltage drops to δ volts at the fourth timing t4. Here, δ volts is the voltage value of the P3 voltage divided by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS when the output voltage Vout is 13 volts. δ volts is lower than β volts. At the fourth timing t4, the P3 voltage remains below β volts, so the second transistor Q2 remains off. Current flow to the third resistor R3 remains off.

[0089] In this way, when the output voltage Vout of the secondary circuit 5B is a medium voltage due to the input of the PSC signal, the current flow to the third resistor R3 is turned off. In other words, when the output voltage Vout of the secondary circuit 5B is a medium voltage due to the input of the PSC signal, the switch circuit K3 including the second transistor Q2 turns off the supply of current to the third resistor R3, which controls the current of the shunt regulator SR, and reduces the current to the fifth resistor R5.

[0090] As described above, when the output voltage Vout of the secondary circuit 5B is a medium voltage due to the PSC signal, the output voltage Vout is controlled by the PSC signal, making it unnecessary to control the output voltage Vout by the shunt regulator SR. Therefore, as described above, when the output voltage Vout of the secondary circuit 5B is a medium voltage due to the PSC signal, the second transistor Q2 executes an off operation, thereby stopping the flow of current into the third resistor R3 and the supply of current to the shunt regulator SR, thereby reducing the current to the fifth resistor R5. This prevents unnecessary current from being supplied to the third resistor R3 and the fifth resistor R5, which control the current of the shunt regulator SR, when the output voltage Vout of the secondary circuit 5B is a medium voltage due to the PSC signal.

[0091] Furthermore, when the PSC signal causes the output voltage Vout of the secondary circuit 5B to be a medium voltage, the second transistor Q2 turns off the current flow to the third resistor R3. In other words, when the PSC signal causes the output voltage Vout of the secondary circuit 5B to be a medium voltage, no unnecessary power is consumed in the third resistor R3. Furthermore, because the current flow to the third resistor R3 is turned off, no current flows into the fifth resistor R5. Therefore, when the PSC signal causes the output voltage Vout of the secondary circuit 5B to be a medium voltage, no unnecessary power is consumed in the fifth resistor R5. Furthermore, the reduction in the current to the fifth resistor R5 reduces the output voltage Vout. The reduction in the output voltage Vout reduces the current to the first resistor R1 and the second resistor R2. Therefore, the switching power supply circuit 10 can reduce power consumption when the PSC signal causes the output voltage Vout of the secondary circuit 5B to be a medium voltage.

[0092] In this embodiment, the case where the output voltage Vout of the secondary circuit 5B is a medium voltage due to the PSC signal refers to the case where the operating mode of the printer 1 is standby mode. Standby mode is an operating mode in which power consumption is reduced. Therefore, an increase in power consumption is undesirable in standby mode. Therefore, in standby mode, the switching power supply circuit 10 reduces power consumption, so that an increase in power consumption can be prevented when the operating mode of the printer 1 is standby mode.

[0093] The switch circuit K3 also includes a second transistor Q2, a sixth resistor R6, a seventh resistor R7, and a Zener diode TS. When the output voltage Vout falls below a threshold voltage defined by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS, the second transistor Q2 turns off. More specifically, when the output voltage Vout falls below 20 volts, which corresponds to the threshold voltage β volts, the switch circuit K3 turns off the second transistor Q2. In other words, as the output voltage Vout drops, the supply of current to the third resistor R3, which controls the current of the shunt regulator SR, is automatically cut off. To turn off the second transistor Q2, it is possible to externally output an off-signal to the base of the second transistor Q2. However, even if an external signal is output to turn off the second transistor Q2, power is consumed to output the signal. This increases power consumption in standby mode. Furthermore, in order to control the second transistor Q2 from outside the switch circuit K3, it may be necessary to provide a configuration for controlling the second transistor Q2 outside the switch circuit K3. Therefore, in this embodiment, the second transistor Q2 is automatically turned off as the output voltage Vout drops. This prevents the switching power supply circuit 10 from increasing power consumption in standby mode, and enables, with a simple configuration, to turn off the supply of current to the third resistor R3, which controls the current of the shunt regulator SR.

[0094] 4, let us assume that the operation mode of the printer 1 starts to transition from standby mode to normal mode at fifth timing t5. For example, when the input unit 15 detects an instruction to transition to normal mode based on a user's operation of an operation switch (not shown), or when an instruction to perform an operation such as printing is received in standby mode, the printer 1 transitions its operation mode from standby mode to normal mode.

[0095] As shown in timing chart A of FIG. 4, when the operating mode of the printing device 1 starts to transition from standby mode to normal mode, SOC 131 stops outputting the "Middle" level PSC signal to the control terminal ST at the fifth timing t5.

[0096] When SOC131 stops outputting the PSC signal to the control terminal ST, the control signal circuit K2 stops outputting the PSC signal to the photocoupler Pc. The light-emitting diode Dp that makes up the photocoupler Pc then stops emitting light, and feedback current no longer flows between the collector and emitter of the phototransistor Qp. Then, feedback voltage is no longer applied to the FB terminal, and the control IC 51 controls the pulse output to the first transistor Q1 so that the power applied to the primary winding L1 increases.

[0097] When the power applied to the primary winding L1 increases, the output voltage Vout rises from 13 volts at the sixth timing t6, as shown in timing chart B of Fig. 4. Also, when the output voltage Vout rises from 13 volts at the sixth timing t6, the P3 voltage rises from δ volts, as shown in timing chart C of Fig. 4.

[0098] After the sixth timing t6, the output voltage Vout rises from 13 volts. Furthermore, in accordance with the rise in the output voltage Vout, the P3 voltage also rises from δ volts after the sixth timing t6.

[0099] After the sixth timing t6, the output voltage Vout increases, and at the seventh timing t7, the output voltage Vout increases to 20 volts. Then, as shown in timing chart C of FIG. 4, the P3 voltage increases to β volts at the seventh timing t7.

[0100] As described above, in this embodiment, the resistance values ​​of the sixth resistor R6, the seventh resistor R7, and the Zener diode TS are set so that the P3 voltage becomes the threshold voltage that turns off the second transistor Q2 when the output voltage Vout is 20 volts or less. Therefore, when the P3 voltage rises to a voltage exceeding β volts, the second transistor Q2 turns on at the seventh timing t7, as shown in timing chart D of FIG. 4. Then, when the second transistor Q2 turns on, the supply of power to the third resistor R3 is turned on at the seventh timing t7, as shown in timing chart E of FIG. 4.

[0101] After the seventh timing t7, the second transistor Q2 is turned on. Also, after the seventh timing t7, the current flow to the third resistor R3 is turned on. As a result, after the seventh timing t7, current is supplied to the shunt regulator SR, and the shunt regulator SR can perform constant voltage control.

[0102] After the seventh timing t7, the output voltage Vout continues to rise, and as shown in timing chart B of FIG. 4, the output voltage Vout rises to 42 volts. At timing t8, the voltage P3 is still the saturation voltage between the base and emitter of the second transistor Q2, so the second transistor Q2 remains on. The current flow into the third resistor R3 remains on.

[0103] Here, with regard to the normal mode, standby mode, and off mode, the output voltage Vout and the voltage of the PSC signal to the control terminal ST in each operating mode are not necessarily limited to the values ​​exemplified in this embodiment, and various values ​​may be used. Furthermore, various values ​​may be used as the Zener voltage that serves as the constant voltage of the Zener diode TS as long as they are effective in practice.

[0104] As described above, the printing device 1 includes a switching power supply circuit 10. The switching power supply circuit 10 includes a primary circuit 5A that performs switching operations, a secondary circuit 5B that has a shunt regulator SR and outputs power to the load 6, a photocoupler Pc that is a feedback circuit that compares the output voltage Vout output by the secondary circuit 5B with the reference voltage of the shunt regulator SR and feeds back the result to the primary circuit 5A to control the output voltage Vout of the secondary circuit 5B, a control signal circuit K2 that outputs a PSC signal, which is a control signal input from an external SOC 131, to the photocoupler Pc to control the output voltage Vout of the secondary circuit 5B, and a switch circuit K3 that turns off the supply of current to the shunt regulator SR when the output voltage Vout of the secondary circuit 5B is a medium voltage or a low voltage due to the input of the PSC signal.

[0105] As described above, when the output voltage Vout of the secondary circuit 5B is a medium or low voltage, the output voltage Vout is controlled by the PSC signal, making it unnecessary to control the output voltage Vout by the shunt regulator SR. Therefore, the switching power supply circuit 10 includes a switch circuit K3 that turns off the supply of current to the third resistor R3, which controls the current of the shunt regulator SR, when the output voltage Vout of the secondary circuit 5B is a medium or low voltage, using the PSC signal. This prevents unnecessary current from being supplied to the third resistor R3, which controls the current of the shunt regulator SR, when the output voltage Vout of the secondary circuit 5B is a medium or low voltage using the PSC signal. Therefore, the switching power supply circuit 10 can appropriately control the supply of current to the shunt regulator SR using the PSC signal when the output voltage Vout of the secondary circuit 5B is a medium or low voltage.

[0106] The printer 1 also includes a control circuit SOC131 that inputs a PSC signal to the control signal circuit K2. When the operating mode of the printer 1 is at least one of the standby mode and the off mode, the SOC131 outputs a PSC signal to the control signal circuit K2, causing the output voltage Vout of the secondary-side circuit 5B to be a medium voltage or a low voltage.

[0107] Thus, when the operating mode of the printer 1 is at least one of the standby mode and the off mode, the SOC 131 outputs a PSC signal to the control signal circuit K2, causing the output voltage Vout of the secondary circuit 5B to be a medium voltage or a low voltage. Therefore, when the operating mode of the printer 1 is at least one of the standby mode and the off mode, the switching power supply circuit 10 can appropriately control the supply of current to the shunt regulator SR.

[0108] The switch circuit K3 also includes a second transistor Q2, a sixth resistor R6, a seventh resistor R7, and a Zener diode TS. When the output voltage Vout of the secondary circuit 5B falls below a voltage corresponding to a threshold voltage determined by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS, the second transistor Q2 turns off the supply of current to the third resistor R3, which controls the current of the shunt regulator SR, thereby reducing the current to the fifth resistor R5.

[0109] Thus, when the output voltage Vout of the secondary circuit 5B falls below a threshold voltage defined by the sixth resistor R6, the seventh resistor R7, and the Zener diode TS, the second transistor Q2 turns off the current supply to the third resistor R3, which controls the current of the shunt regulator SR. In other words, the switching power supply circuit 10 automatically turns off the current supply to the third resistor R3, which controls the current of the shunt regulator SR, as the output voltage Vout of the secondary circuit 5B drops. Therefore, the printing device 1 does not need to include a configuration for controlling the second transistor Q2 from outside the switch circuit K3, and no power is consumed when controlling the second transistor Q2. Therefore, the switching power supply circuit 10 can prevent an increase in power consumption and appropriately control the current supply to the shunt regulator SR with a simple configuration. Furthermore, an increase in power consumption can be prevented in the off mode, where reduced power consumption is desired.

[0110] The secondary circuit 5B is configured to be able to supply current to the shunt regulator SR via a third resistor R3, which is a supply resistor for supplying a constant current to the shunt regulator SR. The switch circuit K3 turns off the flow of current to the third resistor R3 when the output voltage Vout of the secondary circuit 5B is a medium voltage or a low voltage due to the PSC signal.

[0111] This turns off the flow of current into the third resistor R3, preventing power consumption in the third resistor R3. Therefore, the switch circuit K3 can reduce the power consumption of the switching power supply circuit 10 when the output voltage Vout is a medium voltage or a low voltage due to the PSC signal input from the SOC 131.

[0112] The above-described embodiment merely shows one aspect of the present disclosure, and any modifications and applications are possible within the scope of the present disclosure.

[0113] For example, in the above-described embodiment, the switching power supply circuit 10 is exemplified as a power supply circuit built into the printing device 1. However, the switching power supply circuit 10 may also be a power supply circuit built into a device external to the printing device 1, such as an AC adapter. In this case, the PSC signal is output to an external device of the printing device 1. Even in such a case, the same effects as those described above can be achieved.

[0114] Furthermore, for example, in the above-described embodiment, the circuit configuration shown in FIG. 2 is one example, and the configuration can be changed by replacing the circuit elements shown in the figure with the same or a different number of ICs, and can be changed as desired within the scope of this disclosure.

[0115] Furthermore, the functional units shown in FIG. 1 are merely illustrative of their configurations, and the specific implementation form is not particularly limited. In other words, it is not necessary to implement hardware corresponding to each functional unit individually; it is of course possible to implement a configuration in which a single processor executes a program to realize the functions of multiple functional units. Furthermore, some of the functions realized by software in each of the above-described embodiments may be implemented by hardware, or some of the functions realized by hardware may be implemented by software. The specific detailed configurations of the other units of the printing device 1 may also be changed as desired without departing from the spirit of this disclosure.

[0116] Furthermore, for example, in the above-described embodiment, the printing device 1 is an inkjet printer, but is not limited to this. For example, the present disclosure can also be applied to other printers such as a thermal printer, a dot matrix printer, or a laser printer.

[0117] As described above, in the printing device 1 according to this embodiment, power consumption in standby mode can be reduced by reducing power consumption in the secondary voltage detection unit of the power supply circuit where power is consumed. In the off mode, the voltage is low and therefore the resistance loss in detecting the output voltage is very small, but in the standby mode, the voltage is higher than in the off mode and therefore the resistance loss is large. In this embodiment, the addition of a simple circuit such as a Zener diode TS can reduce power consumption in the standby mode.

[0118] The printing device 1 of this embodiment is equipped with a switching power supply circuit 10 having a primary side circuit 5A that performs switching operations, a secondary side circuit 5B that has a shunt regulator SR and outputs power to a load 6, a feedback circuit that compares the output voltage output by the secondary side circuit 5B with the reference voltage of the shunt regulator SR and feeds back the result to the primary side circuit 5A to control the output voltage of the secondary side circuit 5B, a control signal circuit K2 that outputs a control signal input from outside to the feedback circuit to control the output voltage of the secondary side circuit 5B, a switch circuit K3 that turns off the supply of current to the shunt regulator SR when the input of the control signal causes the output voltage of the secondary side circuit 5B to become a first low voltage or a second low voltage that is lower than the first low voltage, and a clamp circuit provided between the switch circuit K3 and ground. Therefore, in the printing device 1 according to this embodiment, it is possible to reduce the power consumption in the power supply circuit during standby mode. That is, in this embodiment, the power consumption during standby mode is reduced by the clamp circuit. In this embodiment, the feedback circuit is configured using a photocoupler Pc. In the standby mode, power is supplied to certain circuits so that they can operate. In this embodiment, the switching power supply circuit 10 is an example of a power supply circuit.

[0119] In the printing device 1 according to this embodiment, the switch circuit K3 includes a second transistor Q2. The clamp circuit is connected to the base terminal of the second transistor Q2. A clamp circuit holds the base terminal at a first holding voltage that is higher than a first low voltage. Therefore, in the printing device 1 according to this embodiment, the clamp circuit can hold the base terminal of the second transistor Q2 at the first hold voltage. Here, the third voltage held by the clamp circuit is higher than the first low voltage.

[0120] In the printing device 1 according to this embodiment, the clamp circuit includes a Zener diode TS. Therefore, in the printing device 1 according to this embodiment, power consumption in standby mode can be reduced using a simple circuit.

[0121] In the printing device 1 according to this embodiment, when the secondary circuit 5B outputs the first low voltage, the printing device 1 is in the standby mode.

[0122] In the printing device 1 according to this embodiment, when the secondary circuit 5B outputs the second low voltage, the printing device 1 is in the off mode.

[0123] Furthermore, this embodiment can provide a power supply circuit in addition to the printing device 1. In this case, the power supply circuit may be applied as a power supply circuit for any device.

[0124] Although the embodiments have been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of this disclosure.

[0125] [Note] Below, the dependent configuration examples may or may not apply. (Configuration example 1) a primary side circuit that performs a switching operation; a secondary circuit having a shunt regulator and outputting power to a load; a feedback circuit that feeds back to the primary side circuit a comparison result between an output voltage output by the secondary side circuit and a reference voltage of the shunt regulator, and controls the output voltage of the secondary side circuit; a control signal circuit that outputs a control signal input from an external source to the feedback circuit to control the output voltage of the secondary side circuit; a switching power supply circuit including: a switch circuit that turns off the supply of current to the shunt regulator when the output voltage of the secondary side circuit becomes a first low voltage or a second low voltage lower than the first low voltage due to input of the control signal; and a clamp circuit that is provided between the switch circuit and ground. Printing device.

[0126] (Configuration example 2) the switch circuit includes a transistor; the clamp circuit is connected to the base terminal of the transistor; the clamp circuit holds the base terminal at a first holding voltage higher than the first low voltage; The printing device described in (Configuration Example 1).

[0127] (Configuration example 3) the clamp circuit includes a Zener diode; The printing device according to (Configuration Example 1) or (Configuration Example 2).

[0128] (Configuration Example 4) When the secondary side circuit outputs the first low voltage, the printing device is in a standby mode. The printing device according to any one of (Configuration Example 1) to (Configuration Example 3).

[0129] (Configuration Example 5) When the secondary circuit outputs the second low voltage, the printing device is in an off mode. The printing device according to any one of (Configuration Example 1) to (Configuration Example 4).

[0130] (Configuration Example 6) a primary side circuit that performs a switching operation; a secondary circuit having a shunt regulator and outputting power to a load; a feedback circuit that feeds back to the primary side circuit a comparison result between an output voltage output by the secondary side circuit and a reference voltage of the shunt regulator, and controls the output voltage of the secondary side circuit; a control signal circuit that outputs a control signal input from an external source to the feedback circuit to control the output voltage of the secondary side circuit; a switch circuit that turns off the supply of current to the shunt regulator when the output voltage of the secondary side circuit becomes a first low voltage or a second low voltage lower than the first low voltage due to the input of the control signal; and a clamp circuit that is provided between the switch circuit and ground. A switching power supply circuit having a [Explanation of symbols]

[0131] 1...printing device, 2...commercial AC power supply, 3...cable, 5A...primary side circuit, 5B...secondary side circuit, 6...load, 10...switching power supply circuit, 11...DC-DC converter circuit, 12...printing control circuit, 13...logic circuit, 14...printing unit, 15...input unit, 51...control IC, 131...SOC, 132...memory, 141...conveyor motor, 141a...conveyor roller, 142a...carriage, 143a...movable blade, 142...carriage movement motor, 143...cutter drive motor, 144...head drive circuit, 144a...print head, C1...first electrolytic capacitor, C2...second electrolytic capacitor, Dp...light-emitting diode, GND...ground output terminal, K1...switching circuit, K2...control signal circuit, K 3...switch circuit, L1...primary winding, L2...secondary winding, OUT1...first output terminal, P1...first node, P2...second node, P3...third node, Pc...photocoupler, Q1...first transistor, Q2...second transistor, Qp...phototransistor, R1...first resistor, R2...second resistor, R3...third resistor, R4...fourth resistor, R5...fifth resistor, R6...sixth resistor, R7...seventh resistor, S1...rectifier circuit, S2...rectifier element, SR...shunt regulator, ST...control terminal, t1...first timing, t2...second timing, t3...third timing, t4...fourth timing, t5...fifth timing, t6...sixth timing, t7...seventh timing, TR...transformer, TS...zener diode

Claims

1. a primary side circuit that performs a switching operation; a secondary circuit having a shunt regulator and outputting power to a load; a feedback circuit that compares an output voltage output by the secondary circuit with a reference voltage of the shunt regulator and feeds back the result of the comparison to the primary circuit, thereby controlling the output voltage of the secondary circuit; a control signal circuit that outputs a control signal input from an external source to the feedback circuit to control the output voltage of the secondary side circuit; a switching power supply circuit including: a switch circuit that turns off the supply of current to the shunt regulator when the output voltage of the secondary side circuit becomes a first low voltage or a second low voltage lower than the first low voltage due to input of the control signal; and a clamp circuit that is provided between the switch circuit and ground. Printing device.

2. the switch circuit includes a transistor; the clamp circuit is connected to the base terminal of the transistor; the clamp circuit holds the base terminal at a first holding voltage that is higher than the first low voltage; The printing device of claim 1 .

3. the clamp circuit includes a Zener diode; The printing device of claim 1 .

4. When the secondary side circuit outputs the first low voltage, the printing device is in a standby mode. The printing device of claim 1 .

5. When the secondary side circuit outputs the second low voltage, the printing device is in an off mode. The printing device of claim 1 .

6. a primary side circuit that performs a switching operation; a secondary circuit having a shunt regulator and outputting power to a load; a feedback circuit that compares an output voltage output by the secondary circuit with a reference voltage of the shunt regulator and feeds back the result of the comparison to the primary circuit, thereby controlling the output voltage of the secondary circuit; a control signal circuit that outputs a control signal input from an external source to the feedback circuit to control the output voltage of the secondary side circuit; a switch circuit that turns off the supply of current to the shunt regulator when the output voltage of the secondary side circuit becomes a first low voltage or a second low voltage lower than the first low voltage due to the input of the control signal; and a clamp circuit that is provided between the switch circuit and ground. A switching power supply circuit having a

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