JP5786275B2 - Power supply control circuit - Google Patents

Description

  The present invention relates to a power supply control circuit that controls supply of power.

  Conventionally, this type of power supply control circuit includes a DC / DC converter circuit, a conversion control circuit that controls voltage conversion of the DC / DC converter circuit, and an overvoltage protection circuit provided on the output side of the DC / DC converter. Have been proposed (see, for example, Patent Document 1). In this device, when the overvoltage protection circuit is activated, the voltage conversion operation of the DC / DC converter is stopped by outputting a stop signal to the conversion control circuit.

JP-A-11-220871

  By the way, in the power supply control circuit, the circuit can be protected from the overvoltage by using the overvoltage protection circuit. However, in some cases, it is possible to detect a voltage drop in the circuit in order to prevent an unexpected malfunction of the circuit. It becomes important in. In this case, since the overvoltage protection circuit operates when the voltage exceeds the threshold value, the voltage drop cannot be detected as it is. On the other hand, it is conceivable to provide a dedicated circuit for detecting a voltage drop, but the circuit becomes complicated and large.

  The main object of the power supply control circuit of the present invention is to enable detection of a voltage drop at a power supply destination using an overvoltage protection circuit.

  The power supply control circuit of the present invention employs the following means in order to achieve the main object described above.

The power supply control circuit of the present invention is
A power supply control circuit for controlling power supply,
A power detection means having a voltage detection terminal connected to the voltage detection target, and cutting off the supply of the power when the voltage input to the voltage detection terminal exceeds a threshold;
A constant voltage source having a voltage exceeding the threshold;
A switch element having a switch control signal terminal connected to the first power supply destination, the switch element being turned on and off according to a voltage acting on the switch control signal terminal;
With
The gist of the invention is that the constant voltage source is connected to a voltage detection terminal of the power shut-off means via the switch element.

  In the power supply control circuit of the present invention, a power shut-off means for shutting off the power supply when the voltage input from the voltage detection target to the voltage detection terminal exceeds the threshold, a constant voltage source having a voltage exceeding the threshold, A switch element that is turned on and off in response to a voltage acting on the switch control signal terminal, and a constant voltage source is connected to the voltage detection terminal of the power shut-off means via the switch element. Thereby, the voltage drop of the first power supply destination can be detected using the power shut-off means for shutting off the power by detecting an overvoltage from the voltage detection target. As a result, the circuit can be made more compact.

  In such a power supply control circuit of the present invention, a first voltage conversion circuit that converts a power supply voltage into a first predetermined voltage and outputs the first voltage to the first power supply destination, and a power supply voltage from the first predetermined voltage. A second voltage conversion circuit that converts the second predetermined voltage to a second power supply destination that is different from the first power supply destination, and the second voltage conversion circuit includes: It can also serve as the constant voltage source. In this way, the device can be made more compact. In this aspect of the power supply control circuit of the present invention, the switch element has first and second switch terminals that can be connected and disconnected between the terminals, and the first switch terminal is connected via a resistor. Connected to the output terminal of the constant voltage source, the second switch terminal is grounded, and the power shut-off means is a connection point between the resistor and the first switch terminal. It can be connected to. In this case, a capacitor can be connected to the connection point in parallel with the switch element. By doing so, it is possible to more reliably suppress the constant voltage source from acting on the voltage detection terminal of the power shut-off means before the power supply of the first power supply destination is made when the power supply circuit is activated.

  Further, in the power supply control circuit of the present invention that supplies power to the electrical equipment, the first power supply destination may be a central processing unit of the electrical equipment. In this way, it is possible to detect an interruption of power to the central processing unit and suppress unexpected malfunctions to other power supply destinations.

  Further, in the power supply control circuit of the present invention, the power shut-off means is different from the first voltage supply circuit that divides and outputs the voltage of the first power supply destination, and the first power supply destination. A second voltage dividing circuit for dividing and outputting a voltage of a second power supply destination; and a second diode that is connected to an output terminal of the first voltage dividing circuit via a first diode. A second switch element for overvoltage determination having a second switch control signal terminal connected to the output terminal of the circuit via a second diode, and a second switch of the second switch element The constant voltage source may be connected to the control signal terminal via the switch element, and the power shut-off means divides and outputs the voltage of the first power supply destination. A third voltage dividing circuit and an output of the third voltage dividing circuit; A third switch element for overvoltage determination having a third switch control signal terminal connected to the child and a second power supply destination voltage different from the first power supply destination is divided and output. 4, and a fourth switch element for overvoltage determination in which a fourth switch control signal terminal is connected to an output terminal of the fourth voltage divider circuit, and the third switch element The constant voltage source may be connected to the third switch control signal terminal via the switch element.

1 is an external perspective view showing an external appearance of a printer 20 according to an embodiment of the present invention. FIG. 2 is a block diagram showing functional blocks of the printer 20 of the present embodiment. The block diagram which shows the outline of a structure of the power management part 70 of this embodiment. The block diagram which shows the outline of a structure of the overvoltage protection circuit 76 of this embodiment. The block diagram which shows the outline of a structure of the overvoltage protection circuit 76B of a modification. The block diagram which shows the outline of a structure of the power supply management part 70B of a modification. The circuit diagram at the time of arrange | positioning the diode D6 to the circuit of FIG. FIG. 6 is a circuit diagram when a diode D6 of the circuit of FIG. 5 is arranged.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view showing an external appearance of a printer 20 according to an embodiment of the present invention. FIG. 2 is a block diagram showing functional blocks of the printer 20 according to the present embodiment. FIG. FIG. 3 is a configuration diagram showing an outline of a configuration of a unit 70.

  The printer 20 of the present embodiment is configured as a photo printer that includes a printing mechanism 40 (see FIG. 2) and performs printing on L-size paper. As shown in FIG. A handle 22 for carrying the main body 21 is provided on the upper surface of the printer 21, an auto sheet feeder 23 for automatically feeding the set paper is provided on the rear surface of the main body 21, and a paper printed by the printing mechanism 40 is held on the front surface of the main body 21. A paper discharge tray 24 and a liquid crystal display (LCD) 25 for confirming settings at the time of photography and printing are provided, and a power button 26 for turning the power on and off is provided on the side of the main body 21. Further, an infrared communication port 28 (light receiving unit) is provided on the front surface of the main body 21 at a position adjacent to the paper discharge tray 24, and the remote control device 30 is operated with the light emitting unit 30a facing the infrared communication port 28. By doing so, the printer 20 can be remotely operated. The remote control device 30 includes a power button 31 for turning on / off the power as buttons for remotely operating the printer 20, and the printing is stopped when pressed during printing and the number of printed sheets when pressed on the photo selection screen. A stop / setting clear button 32 for canceling the selection of a photograph and a photo, a top menu button 33 for displaying a top menu screen, and a print number setting button for setting the number of prints (plus button and print for increasing the number of prints one by one) (A minus button for reducing the number of sheets one by one) 34, an up / down / left / right button 35 for selecting an item or setting value, an OK button 36 for determining an item or proceeding to the next screen, and a previous screen. A return button 37, a print button 38 for starting printing, a setting button 39 for displaying a setting screen, and the like are provided.

  As shown in FIG. 2, the printing mechanism 40 is driven by a carriage belt 43 that is looped in the left-right direction (main scanning direction) and reciprocates left and right along a guide 42. An ink cartridge 44 that supplies ink of each color such as magenta, yellow, and black; a print head 45 that applies pressure to each ink supplied from each ink cartridge 44 and discharges ink from the nozzle toward the paper S; A transport roller 46 that transports the paper S in the sub-scanning direction. The ink cartridge 44 is a so-called off-carriage type that is attached below the printing mechanism 40 and in which the ink cartridge 44 is not mounted on the carriage 41. Here, the print head 45 employs a method in which a voltage is applied to the piezoelectric element to deform the piezoelectric element and pressurize the ink. However, a voltage is applied to a heating resistor (for example, a heater) to heat the ink. A method of pressurizing the ink with the generated bubbles may be employed.

  The LCD 25 displays characters, figures, symbols, etc. under display control by the LCD controller 54. In the present embodiment, the LCD 25 is composed of pixels of 960 dots × 240 dots.

  As shown in FIG. 2, the printer 20 of the present embodiment has a main controller 60 that controls the entire printer, a printer ASIC 48 that controls the printing mechanism 40, and an infrared communication port 28. An infrared communication controller 52 that processes the input infrared signal as an operation signal, an LCD controller 54 that controls the display of the LCD 25, and a memory card controller that controls the writing and reading of data to and from the memory card MC inserted in the memory card slot 56 58 and a power management unit 70 as a power supply control circuit of the present invention that manages the power supply of the entire apparatus, and these are electrically connected to each other via a bus 59. The power management unit 70 is connected to a commercial power supply via an AC / DC power supply unit 90 that converts an AC voltage (for example, 100V) into a DC voltage V42 (for example, 42V). Although not shown in detail, the AC / DC power supply unit 90 rectifies the AC voltage of the commercial power supply, converts it into a DC voltage by switching the switching element, and steps down the converted AC voltage with a transformer to rectify and smooth the voltage. It is comprised as a switching power supply which performs. The AC voltage V42 converted by the AC / DC power supply unit 90 is supplied to a drive system of the printing mechanism 40 (a motor for driving the print head 45 and the carriage belt 43, a motor for driving the transport roller 46, etc.) The voltage is further stepped down by a DC / DC converter described later and supplied to various controllers.

  The main controller 60 is configured as a microprocessor centered on the CPU 61. The ROM 62 stores various processing programs, various data, various tables, etc., and the RAM 63 temporarily stores data. Even with this, a flash memory 64 for holding data and an interface (I / F) 65 for inputting an operation signal from the power button 26 are provided. An image file or the like is input to the main controller 60 from the memory card MC inserted into the memory card slot 56, an operation signal from the infrared communication controller 52, a detection signal from each part of the printing mechanism 40, or the like. The main controller 60 outputs a command signal to the printer ASIC 48, a control signal to the LCD controller 54, and the like.

  As shown in FIG. 3, the power management unit 70 includes a DC / DC converter 71 that converts a DC voltage V42 output from a commercial power supply via an AC / DC power supply unit 90 into a DC voltage V5 (for example, 5V); A DC / DC converter 72 that converts the DC voltage V5 from the DC / DC converter 71 into a DC voltage V3 (for example, 3.3V) and outputs it to the reset circuit 69, the power supply terminal of the memory card MC, and the DC / DC converter The DC voltage V5 from 71 is converted into a DC voltage V1 (eg, 1.1 V) and output to the CPU 61 of the main controller 60 and the DC voltage V5 from the DC / DC converter 71 is converted into a DC voltage. DC / DC converter that converts to V2 (for example, 1.8 V) and outputs to RAM 63 of the main controller 60 Overvoltage is detected by a barter 74, an overvoltage protection circuit 76 that detects an overvoltage of each of the outputs V5, V3, V1, and V2 of the DC / DC converters 71, 72, 73, and 74 and outputs an overvoltage signal. When the power supply control circuit 80 outputs a power supply stop signal for stopping the AC / DC power supply unit 90 and the overvoltage protection circuit 76, the output (voltage) drop of the DC / DC converter 73 is detected. A voltage drop detection circuit 78. Although not shown in detail, the reset circuit 69 is a circuit that resets the AC / DC power supply unit 90 (stops power supply) when the output of the DC / DC converter 72 is stopped.

  As shown in FIG. 3, the voltage drop detection circuit 78 has a base connected to the output terminal of the DC / DC converter 73 via a resistor R2, grounded to a ground via a resistor R3, and a collector connected via a resistor R1. A transistor Q1 (for example, a bipolar transistor) connected to the output terminal of the DC / DC converter 72 and whose emitter is grounded, and a connection point P between the collector of the transistor Q1 and the resistor R1 are arranged in parallel with the transistor Q1. A connected capacitor C and a diode D whose anode side is connected to the connection point P are provided. An overvoltage protection circuit 76 is connected to the connection point P via a diode D, and a drop in the output (voltage) of the DC / DC converter 73 is detected by the overvoltage protection circuit 76 detecting the potential at the connection point P. To do.

  FIG. 4 is a configuration diagram showing an outline of the configuration of the overvoltage protection circuit 76. As shown in the figure, the overvoltage protection circuit 76 includes series resistors R51 and R52 connected to the output terminal (V5) of the DC / DC converter 71 and a series connected to the output terminal (V3) of the DC / DC converter 72. Resistors R31, R32, series resistors R21, R22 connected to the output terminal (V2) of the DC / DC converter 74, and series resistors R11, R22 connected to the output terminal (V1) of the DC / DC converter 73. Diodes D5, D3, R12, a connection point between resistors R51 and R52, a connection point between resistors R31 and R32, a connection point between resistors R21 and R22, and a connection point between resistors R11 and R12, respectively. A transistor QF1 (eg, MOSFET) having a gate connected through D2 and D1 and a source grounded to ground, and a transistor It comprises, an inverter IN1 which is the output terminal to the power supply control circuit 80 outputs to the output terminal and inverting the signal input to the connected input terminal with a drain to an input terminal of F1 is connected. In the resistors R51 and R52, when the output V5 of the DC / DC converter 71 exceeds the allowable upper limit voltage, the voltage acting on the gate of the transistor QF1 is the gate threshold voltage (the lower limit value of the gate voltage for switching on the transistor QF1). In this embodiment, the resistance value is set to exceed approximately 2 V), and the resistors R31 and R32 are connected to the transistor QF1 when the output V3 of the DC / DC converter 72 exceeds the allowable upper limit voltage. A voltage dividing circuit in which the resistance value is set so that the voltage acting on the gate exceeds the gate threshold voltage described above, and the resistors R21 and R22 are used when the output V2 of the DC / DC converter 74 exceeds the allowable upper limit voltage. The resistance value is set so that the voltage acting on the gate of the transistor QF1 exceeds the gate threshold voltage described above. The resistors R11 and R12 have resistance values so that the voltage acting on the gate of the transistor QF1 exceeds the gate threshold voltage described above when the output V1 of the DC / DC converter 73 exceeds the allowable upper limit voltage. Is a voltage dividing circuit set. Therefore, when all of the outputs V5, V3, V2, and V1 of the DC / DC converters 71 to 74 are equal to or less than the allowable upper limit voltage, the transistor QF1 is switched off and the DC / DC converters 71 to 74 are switched off. When any one of the outputs V5, V3, V2, and V1 exceeds the allowable upper limit voltage, the transistor QF1 is switched on. As described above, since the ground of the transistor QF1 is grounded and the power supply control circuit 80 is connected to the drain via the inverter IN1, when the transistor QF1 is switched on, an on signal (overvoltage signal) is generated. When it is output to the power supply control circuit 80 and the transistor QF1 is switched off, an off signal is output to the power supply control circuit 80 side.

  The output terminal (V1) of the DC / DC converter 73 is connected to the cathode side of the diode D of the voltage reduction circuit 78, and the potential at the connection point P of the voltage reduction circuit 78 is the diode D, the voltage dividing resistor R11, It acts on the gate of the transistor QF1 through R22 in order. Therefore, when the potential at the connection point P is less than or equal to the allowable upper limit voltage of the DC / DC converter 73, the transistor QF1 is switched off and an off signal is output to the power supply control circuit 80 side. When the allowable upper limit voltage is exceeded, the transistor QF1 is switched on to output an on signal (overvoltage signal) to the power supply control circuit 80 side.

  As shown in FIG. 3 or FIG. 4, the power control circuit 80 inputs a signal from the inverter IN1 of the overvoltage protection circuit 76, a power on / off signal from the CPU 61 (see FIG. 3) of the main controller 60, and the like to each signal. A logic circuit 82 that outputs an output signal accordingly, and a transistor QF6 (for example, MOSFET) that is turned on and off by inputting the output signal from the logic circuit 82 to the gate. When an on signal (overvoltage signal) is input from the overvoltage protection circuit 76 or a power supply off signal is input, the logic circuit 82 switches off the transistor QF6 and stops the power supply (power supply stop signal). ) To the AC / DC power supply unit 90.

  Next, the operation of the printer 20 of the present embodiment configured as described above, particularly the operation of the power control unit 70 will be described. Consider a case where an abnormality occurs in the DC / DC converter 74 and an overvoltage is generated in the output. In this case, the output terminal of the DC / DC converter 74 is connected to the gate of the transistor QF1 via the voltage dividing circuit composed of the resistors R21 and R22 and the diode D2. The transistor QF1 is switched on, and an ON signal (overvoltage signal) is output from the drain of the transistor QF1 to the power supply control circuit 80 via the inverter IN1. The power supply control circuit 80 that has received the ON signal switches off the transistor QF6 and outputs a power supply stop signal to the AC / DC power supply unit 90, thereby cutting off the power supply of the AC / DC power supply unit 90. Therefore, it is possible to suppress the overvoltage exceeding the withstand voltage from acting on the power supply control unit 70 continuously.

  Next, consider a case where the output of the DC / DC converter 73 that supplies power to the CPU 61 of the main controller 60 is lower than the operating voltage necessary for the operation of the CPU 61 due to some abnormality. As described above, in the voltage drop detection circuit 78, the base of the transistor Q1 is connected to the output terminal of the DC / DC converter 73 via the voltage dividing circuit composed of the resistors R2 and R3, and the output terminal of the DC / DC converter 72 is connected. The collector of the transistor Q1 is connected via the resistor R1 and the connection point P, and the emitter of the transistor Q1 is grounded. Further, the output terminal of the DC / DC converter 73 is connected to the connection point P via a diode D, and the output terminal of the DC / DC converter 73 is connected to the overvoltage protection circuit 76 via voltage dividing resistors R11 and R12 and a diode D1. The gate of the transistor QF1 is connected. For this reason, if the output of the DC / DC converter 73 is normal, the potential at the connection point P becomes 0 when the transistor Q1 is switched on. Therefore, an overvoltage signal is output from the overvoltage protection circuit 76 when the transistor QF1 is switched off. When the output of the DC / DC converter 73 decreases, the potential at the connection point P becomes the output value V3 of the DC / DC converter 72 when the transistor Q1 is switched off. When the switch is turned on, an overvoltage signal (ON signal) is output from the overvoltage protection circuit 76. In this embodiment, the output drop of the DC / DC converter 73 is thus detected using the overvoltage protection circuit 76. When an overvoltage signal is output from the overvoltage protection circuit 76, the power supply control circuit 80 cuts off the power supply from the AC / DC power supply unit 90, so that power is not supplied to the CPU 61 but power is supplied to the drive system and the like. Inconveniences caused by continuing operations can be suppressed.

  Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. The overvoltage protection circuit 76 and the power supply control circuit 80 of the present embodiment correspond to the “power cutoff means” of the present invention, the DC / DC converter 72 corresponds to the “constant voltage source”, and the voltage drop detection circuit 78 (transistor Q1). ) Corresponds to the “switch element”.

  According to the power supply control circuit of the present embodiment described above, the base is connected to the output terminal of the DC / DC converter 73 via the resistor R2, grounded to the ground via the resistor R3, and the collector is connected via the resistor R1. The transistor Q1 is connected to the output terminal of the DC / DC converter 72 and the emitter is grounded to form a voltage drop detection circuit 78 to form a voltage drop detection circuit 78. Between the collector of the transistor Q1 in the voltage drop detection circuit 78 and the resistor R1 Since the connection point P is connected to the gate of the transistor QF 1 of the overvoltage protection circuit 76, the output drop of the DC / DC converter 73 can be detected using the overvoltage protection circuit 76. As a result, the apparatus can be made more compact as compared with the case where a dedicated detection circuit is separately provided for detecting the output decrease of the DC / DC converter 73. Moreover, since the capacitor C is connected to the connection point P in parallel with the transistor Q1, the DC / DC converter 72 starts operating earlier than the DC / DC converter 73 when the AC / DC power supply unit 90 is started. / DC converter 73 can prevent the potential at node P from rising to a potential for operating overvoltage protection circuit 76 over a period until transistor Q1 is turned on from the off state. False detection can be prevented more reliably.

  In the above-described embodiment, the cathode side of the diode D whose anode side is connected to the connection point P of the voltage drop detection circuit 78 is connected to the output terminal of the DC / DC converter 73. However, the connection when the transistor Q1 is off is used. If the potential at the point P exceeds the allowable upper limit voltage of the output of another DC / DC converter, it may be connected to the output terminal of the DC / DC converter, or the connection point P when the transistor Q1 is off. If the potential exceeds the gate threshold voltage of the transistor QF1, it may be directly connected to the gate of the transistor QF1.

  In the above-described embodiment, the voltage drop detection circuit 78, the overvoltage protection circuit 76, and the power supply control circuit 80 are configured as separate circuits. However, the voltage drop detection circuit 78 and the overvoltage protection circuit 76 are configured as a one-chip IC. Alternatively, the voltage drop detection circuit 78, the overvoltage protection circuit 76, and the power supply control circuit 80 may be integrated into a single chip.

  In the above-described embodiment, the output terminal (V1) of the DC / DC converter 73 is directly connected to the cathode side of the diode D whose anode side is attached to the connection point P of the voltage drop detection circuit 78. In consideration of the possibility that the potential of the DC / DC converter 73 (the output V3 of the DC / DC converter 72) acts on the output terminal of the DC / DC converter 73 may adversely affect the CPU 61 that is the output supply destination of the DC / DC converter 73. The diode D6 may be interposed so that the potential at the point P does not act on the output terminal of the DC / DC converter 73. A power management unit 70B of this modification is shown in FIG. 4 shows the case where the diode D6 is arranged in the circuit of FIG. 4, and FIG. 8 shows the case where the diode D6 is arranged in the circuit of FIG.

  In the embodiment described above, the output terminal of the DC / DC converter 72 is connected to the collector of the transistor Q1 of the voltage drop detection circuit 78 via the resistor R1. However, instead of the DC / DC converter 72, a DC / DC converter is used. The output terminal of 71 may be connected, the output terminal of the DC / DC converter 74 may be connected, or a constant voltage source corresponding to the output of the DC / DC converter 72 is provided separately. It does not matter if it is connected to

  In the embodiment described above, the overvoltage protection circuit 76 includes the output terminal of the DC / DC converter 71, the output terminal of the DC / DC converter 72, the output terminal of the DC / DC converter 74, and the output terminal of the DC / DC converter 73. Although each of the voltage dividing resistors R51 and R52, resistors R31 and R32, resistors R21 and R22, and resistors R11 and R12 is connected to the gate of one transistor QF1, it is not limited to this. As shown in the overvoltage protection circuit 76B of the modified example, the transistor QF5 whose gate is connected to the output terminal of the DC / DC converter 71 via the resistors R51 and R52 for voltage division, and the output terminal of the DC / DC converter 72 A transistor QF3 whose gate is connected via resistors R31 and R32 for voltage division, and DC / The transistor QF2 whose gate is connected to the output terminal of the C converter 74 via resistors R21 and R22, and the gate is connected to the output terminal of the DC / DC converter 73 via resistors R11 and R12. The transistor QF1 may be provided, and the sources of the transistors QF5, QF3, QF2, and QF1 may be grounded and the drain connected to the input terminal of the inverter IN1.

  In the above-described embodiment, the capacitor C is connected to the connection point P in the voltage drop detection circuit 78, but the capacitor C may be omitted. In this case, if the DC / DC converter 72 starts operating earlier than the DC / DC converter 73 when the AC / DC power supply unit 90 is activated, the overvoltage protection circuit 76 may erroneously detect a decrease in the output of the DC / DC converter 73. Therefore, it is desirable to provide a sequencer for controlling the starting order of the DC / DC converters 72 and 73.

  In the embodiment described above, the power supply control circuit of the present invention for supplying power has been described as being applied to the printer 20. However, the present invention is not limited to this, and voltage detection is performed from a voltage detection target such as a scanner, FAX, personal computer, or mobile phone. The present invention may be applied to any other device as long as it detects a decrease in the output of the power supply destination using an overvoltage detection circuit that determines an overvoltage when the voltage input to the terminal for use exceeds a threshold value.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  20 Printer, 21 Main body, 22 Handle, 23 Auto sheet feeder, 24 Output tray, 25 Liquid crystal display, 26 Power button, 28 Infrared communication port, 30 Remote control device, 30a Light emitting unit, 31 Power button, 32 Stop / Clear setting Button, 33 Top menu button, 34 Print number setting button, 35 Up / down / left / right button, 36 OK button, 37 Back button, 38 Print button, 39 Setting button, 40 Printing mechanism, 41 Carriage, 42 Guide, 43 Carriage belt, 44 Ink cartridge , 45 Print head, 46 Transport roller, 48 Printer ASIC, 52 Infrared communication controller, 54 LCD controller, 56 Memory card slot, 58 Memory card controller 60, main controller, 61 CPU, 62 ROM, 63 RAM, 64 flash memory, 65 interface (I / F), 69 reset circuit, 70, 70B power management unit, 71-74 DC / DC converter, 76 overvoltage protection circuit 78, voltage drop detection circuit, 80 power supply control circuit, 82 logic circuit, 90 AC / DC power supply, Q1, QF1 to QF6 transistors, R1, R2, R3, R11, R12, R21, R22, R31, R32, R51, R52 resistor, D, D1, D2, D3, D5, D6 diode, C capacitor, IN1 inverter.

Claims (1)

A plurality of DC / DC converters connected to an AC / DC power supply and powered;
A power shut-off means for inputting the output of the first DC / DC converter and shutting off the power supply to the AC / DC power supply unit when the output voltage exceeds a threshold;
Voltage drop detection means for detecting a drop in the output voltage of the first DC / DC converter and outputting a signal corresponding to the detection result;
With
The signal output from the voltage drop detecting means is input to the power shut-off means, and the power shut-off means is sent to the AC / DC power supply section when the output voltage drop of the first DC / DC converter occurs. And control to cut off the power supply to the plurality of DC / DC converters from the AC / DC power supply unit,
The AC / DC power supply unit is a power supply of the printer drive system, the first 1 DC / DC converter Ri power der printers CPU,
The first output of the first DC / DC converter is connected to the gate of a transistor included in the voltage drop detecting means, and the second output of the other DC / DC converter is connected to the collector of the transistor and connected to a diode. Connected to the first output, the emitter of the transistor being grounded,
The power shut-off means shuts off the power supply according to the second output as an input signal when the output voltage of the first output decreases and the transistor is turned off.
When the transistor exceeds the output voltage of the first output threshold is turned on, the potential of the collector becomes zero, the power supply characterized that you cut off the power supply according to the input first output Supply control circuit.

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