JP2013046501A - Power supply switching circuit and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To back up a load section for a longer time by means of an auxiliary power supply.SOLUTION: A power supply switching circuit of an embodiment includes a main power line, an auxiliary power line, a diode and a transistor. The main power line supplies power from a main power supply to the load section. The auxiliary power line supplies power from the auxiliary power supply to the load section when the supply of power from the main power supply to the load section drops. The diode has, on the auxiliary power line, an anode terminal connected to the auxiliary power supply and a cathode terminal connected to the load section. The transistor has, on the auxiliary power line, a source terminal connected to the anode terminal of the diode, a drain terminal connected to the cathode terminal of the diode, and a base terminal connected to the main power line.

Description

  Embodiments described herein relate generally to a power supply switching circuit and an electronic apparatus.

  As a backup power source for generating a DC power source from an AC power source (100 V or 200 V), operating the device by supplying the generated DC power source to various devices, and retaining important data in the device in the event of a power failure There are devices that supply power to the device from the mounted secondary battery. In a device equipped with a backup power source, a switching circuit for switching the power supply source is necessary to supply power from the secondary battery to the device only during a power failure.

  By the way, the secondary battery used as the backup power source tends to decrease the output voltage as the battery capacity decreases. Therefore, in order to lengthen the data backup time, the voltage at the switching circuit for switching the power supply source is used. By reducing the drop, it becomes possible to use the backup power source for a long time by one charge. However, conventionally, a diode is used to switch the power supply source to a secondary battery, and power is supplied from the secondary battery to the system. Therefore, the voltage drops due to the forward voltage drop of the diode. There is a problem that a loss occurs in the supply of power to the system. There are also switching-only ICs for switching the power supply source, but they are more expensive than diodes.

  The power supply switching circuit of the embodiment includes a main power supply line, an auxiliary power supply line, a diode, and a transistor. The main power supply line supplies power from the main power supply to the load unit. The auxiliary power line supplies power from the auxiliary power source to the load unit when the supply of power from the main power source to the load unit decreases. The diode has an anode terminal connected to the auxiliary power supply side and a cathode terminal connected to the load unit side in the auxiliary power supply line. In the auxiliary power line, the transistor has a source terminal connected to the anode terminal of the diode, a drain terminal connected to the cathode terminal of the diode, and a base terminal connected to the main power line.

FIG. 1 is a diagram illustrating an overview of a printer device and a POS terminal according to the present embodiment. FIG. 2 is a block diagram showing a functional configuration of the POS terminal. FIG. 3 is a diagram illustrating an electrical configuration of the power supply unit. FIG. 4 is a diagram for explaining an operation of supplying power from the 24V power supply line or the secondary battery line to the load unit. FIG. 5 is a diagram for explaining an operation of supplying power from the 24V power supply line or the secondary battery line to the load unit. FIG. 6 is a diagram for explaining an operation of supplying power from the 24V power supply line or the secondary battery line to the load unit.

  FIG. 1 is a diagram illustrating an overview of a printer device and a POS terminal according to the present embodiment. A POS (Point Of Sales) terminal 1 is an electronic device that supplies power to the printer device 7. The POS (Point Of Sales) terminal 1 is placed on a drawer 2 for storing cash and the like. The drawer 2 a of the drawer 2 is opened and closed. Control.

  The POS terminal 1 is provided with a keyboard 3 and a mode switch 4 for an operator to input a deposit amount and the like on the front side, and is connected with a main display 5 for the operator, and on the back side for a customer. A sub display 6 is connected. The mode switch 4 is a switch for selecting various business modes such as “registration”, “inspection”, “settlement”, “setting”, and is operated with a key, for example.

  The POS terminal 1 is connected to a printer device 7 that is driven by the POS terminal 1 supplied with power via a power cable C1. The power cable C1 includes a signal line for transmitting and receiving data in addition to wiring for supplying power from the POS terminal 1 to the printer device 7 (details will be described later). The power cable C1 that transmits data together with the power source may be a USB (Universal Serial Bus), for example.

  The printer device 7 is a thermal printer having a thermal head (printing unit) that prints on dedicated paper by heat, and prints receipts and journals based on power and data supplied from the POS terminal 1. Receipts printed by the printer device 7 are issued from a receipt issuing port 8. In this embodiment, a configuration having a printing unit that performs printing by a thermal method is illustrated, but the printing method of the printing unit may be other methods, for example, an inkjet method.

  The POS terminal 1 is connected to a barcode scanner 9 for reading a barcode printed on a product label at the time of product sales registration. The main display 5 and the sub display 6 are composed of a liquid crystal color display or the like equipped with a backlight, and display the product name and price of products registered for sale, the total amount of one transaction, the amount of change, and the like.

  FIG. 2 is a block diagram showing a functional configuration of the POS terminal. As shown in FIG. 2, a POS terminal 1 includes a CPU (Central Processing Unit) 10, a ROM (Read Only Memory) 11, a RAM (Random Access Memory) 12, a storage unit 13, a communication I / F 14, a speaker 15, an LED ( Light Emitting Diode) 16, cooling fan 17, main display 5, sub display 6, display control unit 23, keyboard 3, mode switch 4, keyboard control unit 32, printer control unit 42, serial port 52, barcode scanner 9, power supply Part 60 is provided.

  The CPU 10 centrally controls the processing of the entire POS terminal 1 by developing programs stored in the ROM 11 and the storage unit 13 in the work area of the RAM 12 and sequentially executing the programs. The ROM 11 and the storage unit 13 store programs of the POS terminal 1 and various setting data. The storage unit 13 may be a readable / writable storage medium such as a semiconductor memory or an HDD (Hard Disk Drive).

  The communication I / F 14 is a communication interface that transmits / receives data to / from an external device under the control of the CPU 10. The speaker 15 outputs a warning sound when an error occurs, various notification sounds to the user, and the like under the control of the CPU 10. The LED 16 notifies the user by blinking light under the control of the CPU 10. The cooling fan 17 is a fan for cooling the inside of the POS terminal 1.

  The display control unit 23 controls display of information on the main display 5 and the sub display 6. The keyboard control unit 32 controls the keyboard 3 and the mode switch 4. The printer control unit 42 controls the printer device 7. The serial port 52 is an interface of a serial communication system such as RS-232C or USB for connecting devices such as the barcode scanner 9.

  The power supply unit 60 supplies power to each unit of the POS terminal 1, the printer device 7 connected to the POS terminal 1, the barcode scanner 9, and the like. In the following description, each part (each part of the POS terminal 1, the printer device 7, the barcode scanner 9, and the like) that receives power supply from the power supply part 60 is collectively referred to as a load part.

  Here, details of the power supply unit 60 will be described with reference to FIG. 3. FIG. 3 is a diagram illustrating an electrical configuration of the power supply unit. As shown in FIG. 3, the power supply unit 60 includes an AC-DC conversion unit 61, a lithium ion battery 62, a power supply switching circuit 63, and the like.

  The AC-DC converter 61 converts the AC voltage of the commercial power source into a DC voltage (24V). The AC-DC conversion unit 61 is a main power source that supplies the power by applying the converted DC voltage to the load unit via the power supply switching circuit 63.

  When the power supply from the AC-DC converter 61 is stopped or lowered due to a power failure or the like, the lithium ion battery 62 applies an output voltage to the load unit via the power supply switching circuit 63 to supply power to the load unit. Backup power supply (auxiliary power supply). In the present embodiment, the lithium ion battery 62 is a secondary battery (battery) that is a two-cell battery with an output voltage of 8.0 V when fully charged and an output voltage of 6.0 V that stops discharging.

  The power supply switching circuit 63 applies the DC voltage converted by the AC-DC conversion unit 61 to the load unit during normal times when an AC voltage is applied from a commercial power supply. On the other hand, the power supply switching circuit 63 applies the output voltage from the lithium ion battery 62 to the load part at the time of a power failure when the application of the AC voltage from the commercial power supply is stopped.

  More specifically, the power supply switching circuit 63 includes a 24V power supply line 64, a secondary battery line 65, a first diode 66, a second diode 67, a transistor 68, and the like.

  The 24V power supply line 64 is a main power supply line to which a DC voltage is applied by the AC-DC conversion unit 61 and supplies power from the AC-DC conversion unit 61 to the load unit.

  The secondary battery line 65 is applied with an output voltage (a voltage lower than the DC voltage applied to the 24V power supply line 64) by the lithium ion battery 62, and a power failure or the like occurs and the AC-DC conversion unit 61 loads the load unit. This is an auxiliary power line for supplying power from the lithium ion battery 62 to the load section when the supply of power to the battery is reduced.

  In the 24V power supply line 64, the first diode 66 has an anode terminal 66a connected to the AC-DC conversion unit 61 side, a cathode terminal 66b connected to the load unit side, and from the AC-DC conversion unit 61 side to the load unit side. This is an electronic device having a rectifying action that allows a current to flow only toward.

  In the secondary battery line 65, the second diode 67 has an anode terminal 67a connected to the lithium ion battery 62 side, a cathode terminal 67b connected to the load part side, and from the lithium ion battery 62 side toward the load part side. It is an electronic device having a rectifying action that only allows current to flow.

  In the secondary battery line 65, the transistor 68 has a source terminal 68a connected to the anode terminal 67a of the second diode 67, a drain terminal 68b connected to the cathode terminal 67b of the second diode 67, and a base terminal 68c connected to the 24V power supply line. P-type FET (Field Effect Transistor) transistor connected to 64. That is, the transistor 68 functions as a bypass of the second diode 67 connected to the secondary battery line 65 that supplies power from the lithium ion battery 62 to the load section.

  Next, the operation of supplying power from the 24V power supply line 64 or the secondary battery line 65 to the load unit will be described in detail with reference to FIGS. 4-6 is a figure for demonstrating the operation | movement which supplies a power supply to a load part from a 24V power supply line or a secondary battery line.

  When power is supplied from a commercial power source and a DC voltage is applied to the 24V power line 64 by the AC-DC converter 61, the DC voltage applied to the 24V power line 64 is applied to the secondary battery line 65. As shown in FIG. 4, the 24V power supply line 64 supplies power to the load section via the first diode 66.

  Note that, when a DC voltage is applied to the 24V power supply line 64 by the AC-DC converter 61, the DC voltage applied to the 24V power supply line 64 is higher than the output voltage applied to the secondary power supply line 65. The secondary battery line 65 is provided with a second diode 67, so that the secondary battery from the 24V power line 64 to the secondary battery line 65. Current can be prevented from flowing into the line 65.

  When the power supply from the commercial power supply is cut off and a power failure occurs, and the DC voltage applied to the 24V power supply line 64 by the AC-DC converter 61 becomes lower than the output voltage applied to the secondary battery line 65 As shown in FIG. 5, the secondary battery line 65 supplies power to the load unit via the second diode 67. Immediately after the power supply from the commercial power supply is cut off and a power failure occurs, the DC voltage of the 24V power supply line 64 is not sufficiently lowered, and the predetermined voltage Vgs is added to the DC voltage of the 24V power supply line 64. The voltage becomes higher than the output voltage of the secondary battery line 65. Therefore, the transistor 68 is not turned on, and the secondary battery line 65 supplies power to the load unit via the second diode 67. Here, the predetermined voltage Vgs is a potential difference necessary for turning on the transistor 68.

  Note that while the power is supplied from the lithium ion battery 62, the DC voltage applied to the 24V power supply line 64 is lower than the output voltage applied to the secondary power supply line 65. Although the current tends to flow toward the power supply line 64, the first diode 66 is provided in the 24V power supply line 64, so that the current flow from the secondary battery line 65 to the 24V power supply line 64 is prevented. can do.

  After the supply of power from the commercial power supply is cut off and a power failure occurs, the voltage obtained by adding a predetermined voltage Vgs to the DC voltage of the 24V power supply line 64 becomes lower than the output voltage of the secondary battery line 65. Is turned on, and the secondary battery line 65 supplies power to the load section via the transistor 68 as shown in FIG. Since the voltage drop (several tens of mV) when power is supplied to the load part via the transistor 68 is smaller than the voltage drop (0.2 V) when power is supplied to the load part via the second diode 67, The loss of power supply to the load portion by the secondary battery line 65 can be reduced, and the load portion can be backed up by the lithium ion battery 62 for a longer time.

  As described above, according to the POS terminal 1 according to the present embodiment, the 24V power supply line 64 that supplies power from the AC-DC conversion unit 61 to the load unit, and the supply of power from the AC-DC conversion unit 61 to the load unit are provided. In the secondary battery line 65 that supplies power to the load section from the lithium ion battery 62 when the voltage drops, the anode terminal 67a is connected to the lithium ion battery 62 side in the secondary battery line 65, and the cathode terminal 67b is the load section. In the second diode 67 connected to the side and the secondary battery line 65, the source terminal 68a is connected to the anode terminal 67a of the second diode 67, the drain terminal 68b is connected to the cathode terminal 67b of the second diode 67, The base terminal 68c includes a transistor 68 connected to the 24V power supply line 64, thereby allowing AC-DC conversion. When the supply of power from the unit 61 to the load unit is stopped and a power failure occurs, the transistor 68 can function as a bypass of the second diode 67, so the power supply to the load unit by the secondary battery line 65 Loss can be reduced, and the load portion can be backed up by the lithium ion battery 62 for a longer time.

  Although the embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment is included in the scope and gist of the invention, and is also included in the invention described in the claims and the equivalent scope thereof.

DESCRIPTION OF SYMBOLS 1 POS terminal 7 Printer apparatus 9 Barcode scanner 60 Power supply part 61 AC-DC conversion part 62 Lithium ion battery 63 Power supply switching circuit 64 24V power supply line 65 Secondary battery line 66 1st diode 67 2nd diode 68 Transistor

JP 2001-142584 A

Claims (6)

A main power line for supplying power from the main power source to the load section;
An auxiliary power line for supplying power from an auxiliary power source to the load unit when supply of power from the main power source to the load unit is reduced;
In the auxiliary power line, a diode having an anode terminal connected to the auxiliary power source side and a cathode terminal connected to the load unit side;
In the auxiliary power line, a transistor having a source terminal connected to the anode terminal of the diode, a drain terminal connected to the cathode terminal of the diode, and a base terminal connected to the main power line;
Power supply switching circuit with   The power supply switching circuit according to claim 1, wherein the auxiliary power supply line supplies power to the load unit from a secondary battery that is the auxiliary power supply.   3. The power supply switching circuit according to claim 1, further comprising: a diode having an anode terminal connected to the main power supply side and a cathode terminal connected to the load unit side in the main power supply line. A load section;
A main power line for supplying power from the main power source to the load section;
An auxiliary power line for supplying power from an auxiliary power source to the load unit when supply of power from the main power source to the load unit is reduced;
In the auxiliary power line, a diode having an anode terminal connected to the auxiliary power source side and a cathode terminal connected to the load unit side;
In the auxiliary power line, a transistor having a source terminal connected to the anode terminal of the diode, a drain terminal connected to the cathode terminal of the diode, and a base terminal connected to the main power line;
With electronic equipment.   The electronic device according to claim 4, wherein the auxiliary power line supplies power to the load unit from a secondary battery that is the auxiliary power source.   6. The electronic device according to claim 4, further comprising: a diode having an anode terminal connected to the main power supply side and a cathode terminal connected to the load unit side in the main power supply line.

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