Backup circuit

Abstract

To provide a highly reliable backup circuit.SOLUTION: A backup circuit according to an embodiment includes a backup capacitor, a charging circuit, a switching circuit, a detection circuit, and a discharge circuit. The backup capacitor stores power to be supplied to a load circuit. The charging circuit converts a voltage supplied from a power source to a predetermined voltage and charges the backup capacitor. The switching circuit switches a connection state between the backup capacitor and the load circuit. The detection circuit detects a value of the voltage of the power source, and when the value of the voltage of the power source is not more than a first threshold, outputs a signal to the switching circuit to connect the backup capacitor to the load circuit. The discharge circuit discharges the backup capacitor when power supply from the power source is stopped.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a backup circuit. [Background technology]

[0002] In devices that include load circuits that operate using power supplied from a power source, a very short power outage (momentary blackout) of about 10 ms can occur, for example, when switching between power sources, causing the voltage applied from the power source to temporarily fall below the lower limit of the operating voltage of the load circuit. For example, if the operation of a load circuit installed in a moving object such as an airplane or train temporarily stops, it becomes difficult to ensure the safety of the moving object. For this reason, a power supply backup circuit has been proposed as one of the means for supplementing the voltage supplied to the load circuit when the power supply is interrupted for a short period of time.

[0003] The backup circuit includes, for example, a capacitor for applying voltage to the load circuit when the power supply is stopped, and a charging circuit for charging the capacitor. When the power supply is operating, the capacitor is charged with power from the power supply, and when the power supply is stopped for a short period of time, the charged capacitor supplies voltage to the load circuit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-247146 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the equipment is stopped while the backup capacitor is still charged, the capacitor is put into no-load state, making it difficult to discharge the capacitor in a short time. In particular, if the backup circuit is located in a place where people may come into contact with it after the equipment is stopped, there is a risk of electric shock unless a sufficient amount of time has passed since the equipment was stopped.

[0006] Furthermore, if a capacitor and a resistor are connected in parallel to a charging circuit to discharge the backup capacitor, power always flows from the capacitor to the resistor, causing the charged power to be discharged, resulting in a decrease in power utilization efficiency. The risk of electric shock and reduced efficiency of power utilization can be factors that reduce the reliability of the backup circuit.

[0007] The embodiments of the present invention have been made in consideration of the above circumstances, and have an object to provide a highly reliable backup circuit. [Means for solving the problem]

[0008] The backup circuit in this embodiment includes a backup capacitor, a charging circuit, a switching circuit, a detection circuit, and a discharge circuit. The backup capacitor stores power to be supplied to the load circuit. The charging circuit converts the voltage supplied from the power supply to a predetermined voltage and charges the backup capacitor. The switching circuit switches the connection state between the backup capacitor and the load circuit. The detection circuit detects the voltage value of the power supply, and when the voltage value of the power supply is equal to or lower than a first threshold, outputs a signal to the switching circuit to connect the backup capacitor to the load circuit. The discharge circuit discharges the backup capacitor when power supply from the power supply is stopped. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a backup circuit according to an embodiment. [Figure 2] FIG. 2 is a diagram schematically illustrating an example of the configuration of a discharge circuit according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the backup circuit of the embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically illustrating an example of the configuration of a backup circuit according to this embodiment.

[0011] A backup circuit 1 of this embodiment is a circuit for backing up a power supply 2 that supplies DC power to a load circuit 3. The backup circuit 1, power supply 2, and load circuit 3 are mounted on, for example, an aircraft. The power supply 2 supplies power to the backup circuit 1 and the load circuit 3. For example, the power supply 2 is a DC power supply that outputs DC power obtained by rectifying and smoothing the AC power (115V AC) supplied from an aircraft engine generator. In this embodiment, the power supply 2 may momentarily stop supplying power or may supply a reduced amount of power, for example, when switching between generators. Such a momentary drop in power supply 2 is hereinafter referred to as a momentary power interruption.

[0012] The backup circuit 1 is connected to a power supply 2 and a load circuit 3, and supplies power to the load circuit 3 when the voltage applied from the power supply 2 to the load circuit 3 temporarily drops. The backup circuit 1 includes a backup capacitor 10, a charging circuit 20, a switching circuit 30, a detection circuit 40, and a discharging circuit 50.

[0013] Both ends of the backup capacitor 10 are connected to the charging circuit 20. One end (high potential end) of the backup capacitor 10 is electrically connected to the high potential output end of the charging circuit 20, and the other end (low potential end) of the backup capacitor 10 is electrically connected to the low potential output end of the charging circuit 20. The backup capacitor 10 is charged with DC power output from the charging circuit 20 and stores power. The backup capacitor 10 is also connected in parallel with the power source 2 to the load circuit 3 via a switching circuit 30, and supplies power to the load circuit 3 by the operation of the switching circuit 30.

[0014] The charging circuit 20 is connected to the power source 2 and the backup capacitor 10, and charges the backup capacitor 10 while power is being supplied from the power source 2. The charging circuit 20 converts the voltage of the DC power supplied from the power source 2 to a predetermined voltage, and charges the backup capacitor 10 with the converted DC power. For example, the charging circuit 20 boosts the voltage of 270 V DC applied from the power source 2 to 330 V DC, and charges the backup capacitor 10.

[0015] The switching circuit 30 is connected between the backup capacitor 10 and the load circuit 3 and switches the electrical connection state between the backup capacitor 10 and the load circuit 3. That is, the switching circuit 30 switches the electrical connection state of the path connecting the high-potential side end of the backup capacitor 10 and the load circuit 3. The switching circuit 30 is connected to a detection circuit 40 and switches the electrical connection state of the path connecting the backup capacitor 10 and the load circuit 3 based on a signal from the detection circuit 40. Specifically, based on the signal from the detection circuit 40, the switching circuit 30 is controlled to electrically disconnect the high-potential side end of the backup capacitor 10 from the load circuit 3 when the power supply 2 is operating normally, and to electrically connect the high-potential side end of the backup capacitor 10 to the load circuit 3 when the power supply 2 to the load circuit 3 drops. The switching circuit 30 includes a semiconductor element (self-arc-suppressing element) such as a field effect transistor (FET) or an insulated gate bipolar transistor (IGBT).

[0016] The detection circuit 40 detects the voltage of the power supply 2 by detecting the voltage value on the high potential side and the voltage value on the low potential side of the power supply 2, and outputs a signal (switching signal) to the switching circuit 30 when the voltage of the power supply 2 falls below a predetermined threshold. The detection circuit 40 is connected in parallel with the load circuit 3 relative to the power supply 2. The detection circuit 40 measures the voltage value of the power supply 2, and when the voltage value of the power supply 2 falls below a predetermined first threshold, outputs a signal (switching signal) to the switching circuit 30 to switch the connection. For example, the first threshold is a voltage value that is greater than the lower limit of the operating voltage of the load circuit 3 (the power supply voltage at which the load circuit 3 can operate) and less than the voltage value when the power supply 2 is operating normally.

[0017] The discharge circuit 50 is connected in parallel with the backup capacitor 10, and discharges the backup capacitor 10 when the power supply from the power source 2 to the load circuit 3 is stopped (or is reduced to such an extent that the operation of the load circuit 3 cannot be maintained). The discharge circuit 50 is also electrically connected to the high-potential output terminal of the power source 2.

[0018] FIG. 2 is a diagram schematically illustrating an example of the configuration of the discharge circuit 50 in this embodiment. The discharge circuit 50 includes a switching element 51 , a resistor 52 , and a gate voltage generating circuit 53 .

[0019] The switching element 51 conducts a path connecting one end (high potential end) and the other end (low potential end) of the backup capacitor 10 when the value of the voltage supplied from the power supply 2 falls below a second threshold. In this embodiment, the switching element 51 is an n-channel depletion-type MOSFET and includes a control terminal (gate terminal), a first terminal (source terminal), and a second terminal (drain terminal). The switching element 51 is turned on when the value of the voltage applied to the control terminal is equal to or greater than 0, and is turned off when the value of the voltage applied to the control terminal is negative. One main terminal (second terminal) of the switching element 51 is electrically connected to the high potential end of the backup capacitor 10, and the other main terminal (first terminal) of the switching element 51 is electrically connected to the low potential end of the backup capacitor 10 via a resistor 52. The control terminal of the switching element 51 is connected to a gate voltage generation circuit 53. The switching element 51 switches the connection between the backup capacitor 10 and the resistor 52 when a control voltage is applied from the gate voltage generating circuit 53 .

[0020] Resistor 52 is located in a path electrically connecting the low-potential end of backup capacitor 10 and the first terminal of switching element 51. When conduction occurs between the first terminal and the second terminal of switching element 51, the voltage of backup capacitor 10 is applied to resistor 52, and current flows through resistor 52, discharging backup capacitor 10. The resistance value of resistor 52 can be determined depending on the time required to discharge backup capacitor 10. For example, the resistance value of resistor 52 is determined so that discharge of backup capacitor 10 is completed (the voltage of backup capacitor 10 drops to a range where it is safe for a person to come into contact with backup circuit 1) within 10 seconds after power supply from power source 2 to load circuit 3 is stopped.

[0021] The gate voltage generation circuit 53 is connected to the power supply 2 and the switching circuit 30, and applies a negative control voltage to the control terminal of the switching element 51 when the voltage value of the power supplied from the power supply 2 (or the backup capacitor 10 via the switching circuit 30) to the load circuit 3 is equal to or greater than a second threshold. For example, the second threshold is the lower limit of the operating voltage of the load circuit 3. For example, the gate voltage generation circuit 53 transforms the voltage supplied from the power supply 2 and applies a negative control voltage to the switching element 51. Note that the second threshold is not limited to the lower limit of the operating voltage of the load circuit 3. The second threshold may be any value that is equal to or greater than the lower limit of the operating voltage of the load circuit 3 and smaller than the first threshold.

[0022] Next, the operation of the backup circuit 1 in this embodiment will be described for each operating state of the power supply 2. First, the operation of the backup circuit 1 when the power supply 2 is operating normally will be described. The power supply 2 supplies a voltage to the load circuit 3, causing the load circuit 3 to operate. The power supply 2 also supplies power to the charging circuit 20, which then charges the backup capacitor 10. At this time, the value of the voltage applied by the power supply 2 to the load circuit 3 exceeds the first threshold value in the detection circuit 40, so the detection circuit 40 does not output a signal (switching signal) to the switching circuit 30 to switch the connection, and the switching circuit 30 electrically disconnects the backup capacitor 10 from the load circuit 3. The power supply 2 also applies a voltage equal to or greater than the second threshold value to the gate voltage generation circuit 53 of the discharge circuit 50, causing the gate voltage generation circuit 53 to apply a negative control voltage to the control terminal of the switching element 51. Therefore, the switching element 51, to which a negative voltage is applied to the control terminal, is turned off, and the backup capacitor 10 is not electrically connected to the discharge path via the resistor 52, and the backup capacitor 10 is not discharged.

[0023] Next, the operation of the backup circuit 1 when a momentary interruption occurs in the power supply 2 will be described. When a momentary interruption occurs in the power supply 2, the value of the voltage applied from the power supply 2 to the load circuit 3 temporarily drops. The detection circuit 40 detects the voltage drop and inputs a signal to the switching circuit 30 to switch the connection. The switching circuit 30 receives the signal (switching signal) from the detection circuit 40 and electrically connects the high-potential end of the backup capacitor 10 to the load circuit 3. This causes the backup capacitor 10 to apply a voltage to the load circuit 3, and the load circuit 3 can operate with the voltage from the backup capacitor 10 before the voltage applied from the power supply 2 falls below the lower limit of the operating voltage. Since the first threshold value is greater than the second threshold value, the switching element 51 is not turned on at the timing when the switching circuit 30 switches.

[0024] Finally, the operation of the backup circuit 1 when the input power from the power source 2 is stopped will be described. When the input power supply is stopped, the application of voltage from the power supply 2 to the load circuit 3 and the backup circuit 1 stops. The detection circuit 40 detects a drop in the voltage of the power supply 2 and inputs a signal to the switching circuit 30 to switch the connection. The switching circuit 30 receives the signal from the detection circuit 40 and connects the backup capacitor 10 to the load circuit 3. For a certain period after the input power supply is stopped, the backup capacitor 10 supplies power to the load circuit 3, and the load circuit 3 operates on the voltage from the backup capacitor 10. During this period, a voltage equal to or greater than the second threshold is applied from the backup capacitor 10 to the gate voltage generation circuit 53 of the discharge circuit 50, causing the gate voltage generation circuit 53 to apply a negative voltage to the control terminal of the switching element 51. Therefore, the switching element 51 is turned off, the backup capacitor 10 is not connected to the resistor 52, and the backup capacitor 10 is not discharged.

[0025] When a certain period of time has passed since the input power supply was stopped, the charge stored in the backup capacitor 10 is released (the backup capacitor 10 is discharged), and the value of the voltage that the backup capacitor 10 applies to the load circuit 3 falls below the lower limit of the operating voltage of the load circuit 3. At this time, the load circuit 3 stops operating. Furthermore, the gate voltage generation circuit 53 of the discharge circuit 50 stops applying the control voltage to the control terminal of the switching element 51 because the value of the voltage applied from the backup capacitor 10 falls below the second threshold. Then, the voltage applied to the control terminal of the switching element 51 becomes 0 V, and the switching element 51 turns on. As a result, the backup capacitor 10 and the resistor 52 are connected, and the voltage remaining in the backup capacitor 10 is applied to the resistor 52, so that the backup capacitor 10 is discharged.

[0026] The detection circuit 40 may be configured to stop operating when the voltage applied from the power supply 2 to the load circuit 3 falls below a predetermined value (≦second threshold). In this case, when the detection circuit 40 stops, the output of the signal that switches the connection of the switching circuit 30 also stops, and the backup capacitor 10 is discharged by the discharge circuit 50 in a state where the high-potential side end of the backup capacitor 10 and the load circuit 3 are electrically disconnected.

[0027] With the backup circuit 1 configured as described above, the discharge circuit 50 does not operate during normal operation of the power supply 2 or when a momentary power interruption occurs due to the operation of the switching element 51, and the discharge circuit 50 operates only when the input power supply is stopped. Therefore, the backup circuit 1 can discharge the backup capacitor 10 only when the input power supply is stopped.

[0028] Furthermore, the time from when the input power supply is stopped until the discharge of the backup capacitor 10 is complete can be adjusted by changing the value of the resistor 52 of the discharge circuit 50.

[0029] Therefore, according to the backup circuit 1 of this embodiment, it is possible to discharge the backup capacitor only after the power supply is stopped without reducing power efficiency, and it is possible to provide a highly reliable backup circuit.

[0030] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0031] 1... backup circuit, 2... power supply, 3... load circuit, 10... backup capacitor, 20... charging circuit, 30... switching circuit, 40... detection circuit, 50... discharge circuit, 51... switching element, 52... resistor, 53... gate voltage generation circuit

Claims

1. A backup capacitor that stores electric power to be supplied to a load circuit, A charging circuit that converts the voltage supplied from a power source into a predetermined voltage and charges the backup capacitor, A switching circuit that switches the connection state between the backup capacitor and the load circuit, A detection circuit that detects the value of the voltage of the power source and outputs a signal for connecting the backup capacitor to the load circuit to the switching circuit when the value of the voltage of the power source is equal to or less than a first threshold value, A backup circuit comprising a discharge circuit that discharges the backup capacitor when the power supply from the power source stops.

2. The discharge circuit includes a switching element that conducts a path connecting one end and the other end of the backup capacitor when the voltage supplied from the power source falls below a second threshold value, and a resistor interposed in the path. The backup circuit according to claim 1.

3. The discharge circuit further includes a gate voltage generation circuit that applies a negative voltage to a control terminal of the switching element when a voltage is applied from the power source and the voltage of the power source is greater than a second threshold value. The backup circuit according to claim 2.

4. The switching element is an n-channel depletion-type MOSFET. The backup circuit according to claim 2.

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