JP4626487B2 - Backup circuit - Google Patents

Description

  The present invention relates to a backup circuit that backs up a device having a liquid crystal display element when commercial power is shut off.

  Conventionally, this type of backup circuit is configured as shown in FIG. 3 (see, for example, Patent Document 1). Hereinafter, the configuration will be described.

  As shown in FIG. 3, the main power supply circuit 31a is connected to the commercial power supply 32a, and supplies the power supply current from the main power supply 31a to the Vdd terminal 47b of the microcomputer 46a. The power supply line to the Vdd terminal 47b forms a power supply circuit of a liquid crystal display element (hereinafter referred to as LCD) 11a composed of a resistor 41a, a resistor 42a, a resistor 42b, a resistor 42c, and a resistor 44a.

  The power supply line to the Vdd terminal 47b of the main power supply circuit 31a is connected to a series connection of a smoothing electrolytic capacitor 40a, a primary battery 36a that is a backup battery circuit, a diode 37a, and a resistor 38a. The zero cross circuit 45a monitors the commercial power supply 32a and outputs a zero cross signal to the microcomputer 46a.

  The operation at the time of backup in the above configuration will be described. When the commercial power supply 32a is cut off, the main power supply circuit 31a cannot supply the power supply current to the microcomputer 46a, and the voltage at the Vdd terminal 47b decreases as the smoothing electrolytic capacitor 40a is discharged.

When the voltage becomes equal to or less than (voltage of primary battery 36a−diode 37aVf), current is supplied from the primary battery 36a. This is the backup state.
Japanese Patent No. 3520280

  However, in such a conventional configuration, all the backup current is supplied from the primary battery 36a immediately after the commercial power supply 32a is cut off, and the primary battery 36a is consumed very much. .

  In addition, there is a method of increasing the capacity of the smoothing electrolytic capacitor 40a or changing to an electric double layer capacitor, but the output voltage gradually decreases from the start of backup according to the discharge, and the display density of the LCD 11a gradually changes. There was a problem that it became unsightly, such as crosstalk coming out.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems and aims to extend the life of a primary battery for backup and to make the liquid crystal display element display density at the time of backup substantially the same as when connected to a commercial power source. .

In order to achieve the above object, the present invention supplies a current to a second DC power supply circuit that is supplied with a current from a first DC power supply circuit connected to a commercial power supply, and a power failure is detected by a power failure detection means. Detecting and shutting off the output of the second DC power supply circuit, and connecting the first backup means comprising a series connection of a primary battery, a resistor and a charge blocking diode in parallel with the output of the first DC power supply circuit; A secondary battery having a rated voltage higher than that of the primary battery of the first backup means and a second backup means comprising a series connection of a resistor and a charge blocking diode are connected in parallel with the DC power supply circuit of the first backup circuit, The secondary battery of the second backup means is charged with the output current of the two DC power supply circuits, and the output voltage value of the first backup means is supplied to the microcomputer supplied with the power supply current by the first DC power supply circuit. A liquid crystal display element operating at the same voltage is connected, a divided voltage necessary for driving the liquid crystal display element is generated by a voltage dividing circuit, and the output voltage of the primary battery of the first backup means is prevented from flowing backward. A diode is connected so as to be supplied to the voltage dividing circuit, the output voltage of the second DC power supply circuit is stepped down to a constant voltage by a constant voltage circuit, and further supplied to the voltage dividing circuit via a diode for preventing reverse current flow. The output voltage of the constant voltage circuit when commercial power is supplied is configured to be higher than the voltage obtained by subtracting the forward voltage drop of the diode connected between the voltage of the primary battery and the voltage dividing circuit. The drive current of the liquid crystal display element is supplied from the primary battery even when the operating current of the microcomputer is supplied from the secondary battery .

  As a result, the secondary battery supplies backup current to the microcomputer and peripheral circuits from the start of backup until the voltage of the secondary battery drops below the voltage of the primary battery due to discharge, and only the power supply of the liquid crystal display element is backed up. By supplying a backup current from a primary battery with a stable voltage immediately after monitoring, the life of the primary battery for backup can be extended, and the darkness of the LCD display during backup is almost the same as when a commercial power supply is connected. Can be.

  The backup circuit of the present invention supplies a backup current from the secondary battery to the microcomputer and peripheral circuits until the voltage of the secondary battery becomes equal to or lower than the voltage of the primary battery due to discharge after the start of the backup. By supplying a backup current from a primary battery with a stable voltage immediately after backup monitoring, the power supply only can extend the life of the primary battery for backup, and connect the darkness of the LCD display during backup to the commercial power supply. It can be almost the same as time.

According to a first aspect of the present invention, there is provided a first DC power supply circuit connected to a commercial power supply, a second DC power supply circuit supplied with a current from the first DC power supply circuit, and detecting a power failure of the commercial power supply. A power failure detection means for cutting off the output of the second DC power supply circuit; and a first backup means connected in parallel to the output of the first DC power supply circuit and comprising a series connection of a primary battery, a resistor and a charge blocking diode. A secondary battery connected in parallel to the first DC power supply circuit and having a rated voltage higher than that of the primary battery of the first backup means; a second backup means comprising a series connection of a resistor and a charge blocking diode; A charging circuit for charging the secondary battery of the second backup means with an output current of the second DC power supply circuit; a microcomputer to which a power supply current is supplied by the first DC power supply circuit; and a microcomputer connected to the microcomputer. in front A liquid crystal display element that operates at the same voltage as the output voltage value of the first backup means, a voltage dividing circuit that generates a divided voltage necessary for driving the liquid crystal display element, and a primary battery of the first backup means The output voltage of the second DC power supply circuit is stepped down to a constant voltage and further supplied to the voltage dividing circuit via the diode for preventing the reverse current. A constant voltage circuit for supplying, and when the commercial power is supplied, the output voltage of the constant voltage circuit is a forward voltage drop of a diode connected between the voltage of the primary battery and the voltage dividing circuit The drive current of the liquid crystal display element is supplied from the primary battery even when the operating current of the microcomputer is supplied from the secondary battery . A secondary battery is installed in addition to the primary battery, and the backup current is supplied from the secondary battery to the microcomputer and peripheral circuits until the secondary battery voltage drops below the primary battery voltage after the backup starts. At the same time, only the power source of the liquid crystal display element can extend the life of the primary battery for backup by supplying the backup current from the primary battery whose voltage is stable immediately after the backup monitoring. The darkness can be made approximately the same as when a commercial power supply is connected.

  According to a second invention, in the first invention, the secondary battery in the second backup means is constituted by a capacitor such as an electrolytic capacitor or an electric double layer capacitor, and the commercial power supply is shut off and the backup operation is performed. Immediately after the start, the voltage of the electric field capacitor or electric double layer capacitor is larger than the voltage of the primary battery, and the backup current is supplied from the electric field capacitor or electric double layer capacitor. When the electric charge of the electric field capacitor or the electric double layer capacitor is discharged, the backup current can be supplied from the primary battery.

  According to a third aspect of the present invention, in the first or second aspect of the invention, when the power failure detection means detects a power failure of the commercial power source, it has a frame frequency changing means for reducing the frame frequency of the liquid crystal display element. When the means determines that there is a power failure, the liquid crystal display element lowers the frame frequency due to its characteristics by reducing the frame frequency of the liquid crystal display element. The supplied current can be reduced, and the consumption of the primary battery can be suppressed while the display density of the liquid crystal display element is made the same when the commercial power supply is connected and during the backup.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment)
FIG. 1 is a circuit diagram of a backup circuit according to an embodiment of the present invention.

  As shown in FIG. 1, the first DC power supply circuit 1 charges an electrolytic capacitor 14 from a commercial power supply 11 via a diode 12 and a resistor 13. The switching power supply IC 15 uses the resonance of the coil 16 to output a DC voltage of about 20V. The electrolytic capacitor 17 is an electrolytic capacitor for smoothing the output of the switching power supply IC15.

  The transistor 19 is a transistor that steps down the output 20V of the switching power supply IC 15 to 5V (Vdd21) by a series regulator method. The output 5V is a series between the resistor 18, the constant voltage diode 20, and the base emitter of the transistor 22. In the connection, the base-emitter voltage of the transistor 19 is subtracted from (the both-ends voltage of the constant voltage diode 20 + the base-emitter voltage of the transistor 22). Here, the voltage across the constant voltage diode 20 is 5V, the base-emitter voltage of the transistor 22 is 0.6V, the base-emitter voltage of the transistor 19 is 0.6V, and the voltage of Vdd21 is 5V + 0.6V-0. 6V = 5V is realized.

  The second DC power supply circuit 2 is also supplied with a current from the first DC power supply circuit 1 and has a part of a power failure detection means for cutting off the output of the second DC power supply circuit 2 when the commercial power supply 11 is interrupted. Is. In the second DC power supply circuit 2, the collector and emitter of the transistor 22 are connected in series with a resistor 23 and a resistor 24. The base of the transistor 25 is connected to the connection point between the resistor 23 and the resistor 24. When Vdd21 reaches 5V, the voltage across the resistor 24 exceeds 0.6V, and the collector-emitter becomes conductive. The resistor 26 is a resistor for stabilizing the voltage between the base and emitter of the transistor 22.

When Vdd is less than 5V, the voltage across the resistor 24 does not reach 0.6V, and the collector-emitter of the transistor 25 does not conduct. The resistance value of the resistor 24 is set to a value that can sufficiently overdrive the transistor 25. For this reason, when the collector-emitter becomes conductive, the collector-emitter voltage is at most about 0.1V. Therefore, the collector voltage of the transistor 25 when the commercial power supply 11 is connected is 5 V, which is substantially the same as Vdd21.

  When the commercial power supply 11 is connected, it is as described above. On the other hand, when the commercial power supply 11 is not connected, the switching power supply IC15 has an output of 0 V, the transistor 19 is not conductive, and the output is In addition to being 0 V, no current flows through the constant voltage diode 20 or the resistor 20, the transistor 22 is not conducted, and thus the transistor 25 is not conducted. Therefore, the collector voltage of the transistor 25 is 0V.

  The first backup means 3 is connected in parallel to the output of the first DC power supply circuit 1, and is constituted by a series connection of a charge prevention diode 31 of the primary battery 33, a resistor 32 and a primary battery 33. Hereinafter, the voltage of the primary battery 33 is referred to as Vbat35. In order to prevent a voltage drop, the diode 31 is a Schottky barrier type here. Reference numeral 34 denotes the Vf value. The value in the present embodiment is 0.15V.

  When the voltage of Vdd21 is smaller than the voltage Vbat35 of the primary battery 33 minus the forward voltage drop Vf34 of the charge prevention diode 31, a backup current is supplied from the primary battery battery 33 to Vdd21 via the charge prevention diode 31. Supply.

  The second backup means 4 is constituted by a series connection of an anti-charge diode 41 of a secondary battery, a resistor 42, and an electric double layer capacitor 43 constituting the secondary battery. Hereinafter, the voltage of the electric double layer capacitor 43 is referred to as Vc45. Again, the diode 41 uses a Schottky barrier type in order to prevent a voltage drop. 44 is the Vf value. The value in the present embodiment is 0.15V.

  When the voltage of Vdd21 is smaller than the voltage Vc45 of the electric double layer capacitor 43 minus the forward voltage drop Vf44 of the charge prevention diode 41, the electric double layer capacitor 43 passes through the charge prevention diode 41 to Vdd21. Supply backup current.

  Here, in the present embodiment, the rated voltage of the electric double layer capacitor 43 is set to a voltage higher than the rated voltage of the primary battery 33.

  Thus, immediately after the commercial power supply 11 is shut off and the backup operation starts, the voltage Vc45 of the electric double layer capacitor 43 is larger than the voltage Vbat35 of the primary battery 33, and the backup current is the electric double layer capacitor. 43. After the backup operation starts, time elapses, the electric double layer capacitor 43 is discharged to Vdd21, and the voltage Vc45 of the electric double layer capacitor 43 decreases (voltage Vc45 of the electric double layer capacitor 43−Vf44 of the diode 41). However, when the voltage falls below (voltage Vbat35 of the primary battery 33−Vf34 of the diode 31), the backup current is now supplied from the primary battery 33.

  The charging circuit 5 charges the secondary battery of the second backup means 4 with the output current of the second DC power supply circuit 2 and is supplied with current from the collector of the transistor 25 to charge the electric double layer capacitor 43. The diode 51 is connected so as to prevent backflow.

The microcomputer 6 is supplied with a power supply current from the first DC power supply circuit 1 and is connected to the LCD 7 for displaying various states. The drive voltage of the LCD 7 is the same as the output voltage value of the first backup means 3. A voltage having the same voltage as the rated voltage value of the primary battery 33 is used. In the present embodiment, a lithium battery is used as the primary battery 33, and its rated voltage is 3 V. Therefore, the LCD 7 is also of the 3 V specification.

  The voltage dividing circuit 8 generates a divided voltage necessary for driving the LCD 7, and is constituted by a series connection of a resistor 81, a resistor 82, and a resistor 83. 6 ports are connected. Hereinafter, the input voltage of the voltage dividing circuit 8 is referred to as Vlcd84.

  The diode 9 is a diode that supplies current from the primary battery 33 of the first backup means 3 to the voltage dividing circuit 8 and prevents charging of the primary battery 33 due to reverse current flow. Here, a Schottky barrier type is used to reduce the voltage drop, and its Vf is 0.15V.

  The constant voltage circuit 100 steps down the output voltage of the second DC power supply circuit 2 to a constant voltage and supplies the voltage to the voltage dividing circuit 8 via the reverse current blocking diode 103. From the collector current of the transistor 25, the resistor 101 And a constant voltage diode 102 are connected in series to generate a constant voltage, which is supplied to the voltage dividing circuit 8 via the backflow prevention diode 103. The output voltage of the constant voltage circuit 100 is set higher than the voltage Vbat35 of the primary battery 33 minus the forward voltage drop Vf91 of the diode 9 connected between the voltage dividing circuit 8. In the present embodiment, it is set to 3.2V.

  As a result, when the commercial power supply 11 is connected and current is supplied from the transistor 25 of the second DC power supply circuit 2, current is supplied to the voltage dividing circuit 8 from the constant voltage circuit 8. No current is supplied from 33.

  The crystal oscillation circuit 110 includes a crystal resonator 111, a capacitor 112, and a capacitor 113. The clock signal generated by the crystal oscillation circuit 111 is used as the main clock of the microcomputer 6 and is divided by the frequency dividing circuit 120 to generate the frame frequency of the LCD 7.

  The power failure detection means 130 constitutes part of the power failure detection and exists in the microcomputer 6. The collector voltage of the transistor 25, which is a power failure detection means existing in the second DC power supply circuit 2, is detected, and when it is 0V, it is determined that a power failure has occurred. For convenience, hereinafter, this 130 is referred to as a power failure detection means. The collector voltage of the transistor 25 becomes 0 V when the commercial power supply 11 is not connected, the switching power supply IC 15 is stopped, and no current flows through the constant voltage diode 20.

  The frame frequency changing unit 140 decreases the frame frequency of the LCD 7. When the power failure detection unit 130 determines that a power failure has occurred, the frame frequency changing unit 140 increases the frequency dividing ratio of the frequency dividing circuit 120 and decreases the frame frequency of the LCD 7. In general, because of the characteristics of the LCD, when the frame frequency is lowered, the current consumption is lowered. Therefore, the current supplied from the primary battery 33 to the voltage dividing circuit 8 during the backup can be reduced. Incidentally, 150 is a key input means, and 160 is various loads connected to the microcomputer 6.

  The operation and action of the above configuration will be described with reference to FIG. When the commercial power supply 11 is connected, the switching power supply IC 15 outputs a DC voltage of 20V. The 20 V DC voltage output from the switching power supply IC 15 is stepped down to Vdd 21 (5 V) by the transistor 19. This Vdd21 (5V) serves as a power source for the microcomputer 6, the key input means 150, and the various loads 160.

When the first DC power supply circuit 1 outputs Vdd21 (5 V), the transistor 22
Is conducted, and the collector current causes the transistor 25 of the second DC power supply circuit 2 to also conduct, and current is supplied to the constant voltage circuit 100. A power supply current is supplied from the constant voltage circuit 100 to the voltage dividing circuit 8, and display on the LCD 7 is performed.

  In addition, the electric double layer capacitor 43 is charged from the collector of the transistor 25 through the charging circuit 5 (here, the backflow prevention diode 51) and the resistor 42 of the second backup means 4. The electric double layer capacitor 43 is fully charged in about several tens of minutes after the commercial power supply 11 is connected. As described above, the transistor 25 is overdriven, and the voltage between Vce is about 0.1V. Yes, the voltage is about 5V, which is almost the same as Vdd21.

  Current is supplied to the voltage dividing circuit 8 from the collector of the transistor 25 through the constant voltage circuit 100, and the voltage Vlcd84 is higher than 2.85V which is (Vbat35 voltage 3V-Vf91 voltage 0.15V). Since the voltage is set to be 3.2 V, the power supply current of the voltage dividing circuit 8 which is the power supply of the LCD 7 is not from the primary battery 33 but from the Vdd 21 via the transistor 25 and the constant voltage circuit 100. Supplied.

  Next, a state where the commercial power supply 11 is turned off in this state will be described. When the commercial power supply 11 is turned off at time t, the switching power supply IC 15 of the first DC power supply circuit 1 is turned off, and the output of 20V is stopped. Then, the base current of the transistor 19 does not flow, the transistor 19 is also turned off, the current does not flow to the constant voltage diode 20, the transistor 22 is turned off, and the base current is supplied by the transistor 22 of the second DC power supply circuit 2 The transistor 25 is also turned off.

  At this time, the electric double layer capacitor 43 of the second backup unit 4 is charged to a voltage close to 5 V as described above, and supplies current to the Vdd 21 via the resistor 42 and the diode 41. Using this current as a power supply current, the microcomputer 6, the key input means 150, and the various loads 160 operate. Since the voltage at this time is small and the voltage across the resistor 42 can be ignored, the voltage across the electric double layer capacitor 43 is Vc45−diode Vf44.

  On the other hand, the current is supplied to the voltage dividing circuit 8 which is a power supply circuit of the LCD 7. However, since the transistor 25 is turned off, the current supply from the transistor 25 through the constant voltage circuit 100 is cut off. A current is supplied via the diode 9. The voltage at this time is 2.85V (3V which is the voltage Vbat84 of the primary battery 33-0.15V which is Vf91 of the diode 9).

  When the transistor 25 is turned off and its collector voltage becomes 0 V, the power failure detection means 130 in the microcomputer 6 determines that a power failure has occurred, and the frame frequency changing means 140 increases the frequency dividing ratio of the frequency dividing circuit 120 to increase the frame frequency of the LCD 7. Reduce. The LCD can reduce the current consumption and lower the display density by lowering the frame frequency.

  The LCD 7 is visible at the time of backup because the LCD power supply voltage Vlcd at the time of backup is 2.85 V, which is not much different from 3.2 V when the commercial power supply 11 is connected, and the display frequency is increased due to a decrease in the frame frequency. This is equivalent to when the commercial power supply 11 is connected.

  The above state continues until (voltage Vc45 of electric double layer capacitor 43−Vf44 of diode 41) falls below (voltage Vbat35 of primary battery 33−Vf34 of diode 31). In FIG. 2, it is the backup section T1 by the electric double layer capacitor.

  When (voltage Vc45 of electric double layer capacitor 43−Vf44 of diode 41) falls below (voltage Vbat35 of primary battery 33−Vf34 of diode 31), the backup current of Vdd21 is also supplied from primary battery 31. Become. It is the backup section T2 by the primary battery in FIG.

  At this time, the voltage of Vdd21 is 2.85V, which is a small current and the voltage at both ends of the resistor 32 is negligible (3V—the diode Vf34, which is the voltage Vbat35 at both ends of the primary battery 33).

  The power supply current of the LCD 7 is already supplied from the primary battery 33 even in the backup section by the electric double layer capacitor 43, and it does not change even in the backup section by the primary battery 33.

  The voltage Vbat of the primary battery 33 takes a relatively stable value until the end of its life. For this reason, the intensity of display on the LCD 7 during backup hardly changes until the end of the life of the primary battery 33.

  As described above, in the present embodiment, while (voltage Vc45 of electric double layer capacitor 43−Vf44 of diode 41) is higher than (voltage Vbat35 of primary battery 33−Vf34 of diode 31), The backup current to the microcomputer 6, key input means 150, and various loads 160 is supplied from the electric double layer capacitor 43 of the second backup means 4 to save current consumption of the primary battery 33 and to the LCD 7. Provides a stable power supply current in the vicinity of 3V from the primary battery 33, and lowers the frame frequency of the LCD 7 during backup, so that the display intensity of the LCD 7 is different between when the commercial power supply 11 is connected and during backup. Can be eliminated.

  Further, since the secondary battery in the second backup means 4 is composed of the electric double layer capacitor 43, the voltage of the electric double layer capacitor 43 is 1 immediately after the commercial power supply 11 is cut off and the backup operation starts. The backup current is larger than the voltage of the secondary battery 33 and is supplied from the electric double layer capacitor 43. After the time has elapsed since the start of the backup operation, when the electric double layer capacitor 43 is discharged, the backup current becomes the primary battery 33. Can be more supplied.

  In the present embodiment, the secondary battery is constituted by the electric double layer capacitor 43, but may be constituted by an electric field capacitor, and the same operation and effect can be obtained.

  As described above, the backup circuit according to the present invention supplies a backup current from the secondary battery to the microcomputer and peripheral circuits until the voltage of the secondary battery becomes equal to or lower than the voltage of the primary battery due to discharge after the backup starts. At the same time, only the power source of the liquid crystal display element can extend the life of the primary battery for backup by supplying the backup current from the primary battery whose voltage is stable immediately after the backup monitoring. Since the darkness can be made substantially the same as when a commercial power supply is connected, it is useful as a backup circuit for backing up a device having a liquid crystal display element when the commercial power supply is shut off.

The circuit diagram which made the backup circuit in one embodiment of this invention into a part block Time chart showing changes in voltage of each part of the backup circuit Circuit diagram of a part of the conventional backup circuit

DESCRIPTION OF SYMBOLS 1 1st DC power supply circuit 2 2nd DC power supply circuit 3 1st backup means 4 2nd backup means 5 Charging circuit 6 Microcomputer 7 Liquid crystal display element 8 Voltage dividing circuit 9 Diode 11 Commercial power supply 31 Charge prevention diode 32 Resistance 33 Primary battery 41 Charge prevention diode 42 Resistance 43 Electric double layer capacitor (secondary battery)
100 constant voltage circuit 130 power failure detection means

Claims (3)

A first DC power supply circuit connected to a commercial power supply; a second DC power supply circuit supplied with current from the first DC power supply circuit; and a second DC power supply circuit that detects a power failure of the commercial power supply. A power failure detection means for cutting off the output of the first DC power supply, a first backup means connected in parallel to the output of the first DC power supply circuit and comprising a series connection of a primary battery, a resistor and a charge blocking diode, and the first DC A second backup means comprising a secondary battery connected in parallel with the power supply circuit and having a rated voltage higher than that of the primary battery of the first backup means, a resistor and a charge blocking diode connected in series; and the second DC power supply circuit A charging circuit for charging the secondary battery of the second backup means with the output current of the second power supply, a microcomputer supplied with a power supply current by the first DC power supply circuit, and the first backup device connected to the microcomputer. A liquid crystal display element that operates at the same voltage as the output voltage value of the first means, a voltage dividing circuit that generates a divided voltage necessary for driving the liquid crystal display element, and an output voltage of the primary battery of the first backup means. And a diode connected to supply a voltage dividing circuit while preventing backflow, and a constant voltage supplied to the voltage dividing circuit via a diode that prevents the backflow and further reduces the output voltage of the second DC power supply circuit to a constant voltage. When the commercial power is supplied, the output voltage of the constant voltage circuit is obtained by subtracting the forward voltage drop of the diode connected between the voltage dividing circuit and the voltage of the primary battery. The drive current of the liquid crystal display element is supplied from the primary battery even when the operating current of the microcomputer is supplied from the secondary battery. circuit. 2. The backup circuit according to claim 1, wherein the secondary battery in the second backup means is constituted by a capacitor such as an electrolytic capacitor or an electric double layer capacitor. 3. The backup circuit according to claim 1, further comprising a frame frequency changing means for reducing the frame frequency of the liquid crystal display element when the power failure detecting means detects a power failure of the commercial power source.