JP2002082725A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably supply electric power and to reduce a voltage varying component before and after a momentary break. SOLUTION: If the power source 1 has a momentary break, electric charges accumulated in a capacitor 8 are supplied to a load 9 without passing through a resistance 21. When the voltage across the capacitor 8 drops below VN, an FET 6 turns off, but the electric power continues to be supplied to the load 9 through a diode 7. Further, a diode 10 prevents a current from flowing back to the power source 1. When the power source 1 recovers charging of the capacitor 8 is limited by a resistance 21 and when the charging voltage reaches VN, the FET 6 turns on to bypass the resistance 21. Consequently, the capacitor 8 functions as a low-pass filter which reduces voltage variation of Vin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device, and more particularly to a power supply device capable of reducing fluctuations in power supply voltage while ensuring stable operation of a load before and after an instantaneous interruption of power supply.

[0002]

2. Description of the Related Art In recent years, with the increase in demand for the Internet and the like, installation of communication devices such as large routers and exchanges which consume large amounts of power in communication stations has been increasing. In these communication devices, a large-capacity capacitor 8 is usually added to both ends of the power supply 1 for the load 9 as shown in FIG. If the charging operation of the capacitor 8 is improperly performed when the communication device is added, the power supply output Vin from the power supply equipment is short-circuited by the capacitor 8, and the power supply voltage Vin is reduced. As a result, for example, the power supply voltage of another device installed on the same floor and receiving power from the same power supply equipment fluctuates, causing a malfunction of the device or, in the worst case, a stoppage of a communication service. Will occur.

Therefore, as a general method for preventing the operation of the apparatus from being affected even when the power supply voltage from the power supply equipment is reduced, a backflow prevention diode 10 is provided on the power supply line as shown in FIG. A holding capacitor 8 is provided,
2. Description of the Related Art Circuits for preventing instantaneous interruption of input power are known. In this method, necessary energy is stored by the output holding capacitor 8, and even if the power supply 1 is short-circuited externally,
Output holding capacitor 8 by backflow prevention diode 10
To prevent energy from flowing out from the power supply.

However, in this conventional system, the influence of the voltage fluctuation of the power supply equipment can be avoided, but it affects other devices receiving power supply from the same power supply equipment. That is, since the output holding capacitor 8 usually has a large capacity,
When the instantaneous interruption of the input power supply is restored, an inrush current flows due to the charging operation of the output holding capacitor 8, which causes a drop in the power supply voltage Vin.

In order to solve the above problem, as a means for limiting the charging current to the output holding capacitor at the time of recovery from the momentary interruption of the input power supply, FIG. 9 shows a conventional system disclosed in Japanese Patent Application Laid-Open No. H10-14134. 2 shows a configuration of a stabilized power supply circuit. FIG.
In the charging / discharging circuit 50B of the stabilized power supply circuit, a parallel circuit of a resistor R and a diode D is connected in series to an output holding capacitor C2, an inrush current is prevented through the resistor R during charging, and a diode is connected during discharging. D controls the discharge timing. In addition, in FIG. 9, 30 is AC-
A DC converter, 40 is a DC-DC converter, C1 is a charge / discharge capacitor, 50A is a charge / discharge circuit, and 50 is an output holding circuit.

[0006]

However, in the conventional stabilized power supply circuit of FIG. 9 described above, the resistor R inserted to prevent the rush current during charging is always connected. , The effect of the low-pass filter is reduced. That is, originally C1 and C2
The filter characteristics are determined by the capacitance of the resistor R. However, a desired filter effect cannot be obtained by inserting the rush current prevention resistor R. Therefore, the configuration of FIG. 9 has a problem that the function of the low-pass filter for reducing the external input voltage fluctuation component is impaired.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and it is an object of the present invention to provide a stable power supply to a load when an instantaneous power interruption occurs and an instantaneous power interruption. An object of the present invention is to provide a power supply device having an effect as a low-pass filter for reducing an input voltage fluctuation component while limiting a charging current after restoration.

[0008]

According to the present invention, there is provided a power supply apparatus comprising: a power supply; and a low-pass filter configured to connect a resistor and a capacitor in series to supply a smoothed output of the power supply to a load. A bypass unit connected in parallel with the resistor to bypass the resistor, and the bypass unit is in a bypass state when the power supply is stable, and the voltage of the capacitor becomes lower than a predetermined value due to a decrease in the power supply. Sometimes, a power supply device is provided that includes control means for controlling the bypass means to a non-bypass state.

[0009] The power supply apparatus further comprises a backflow preventing diode provided between the power supply and the low-pass filter means for preventing a backflow current from the capacitor due to a decrease in the power supply.

The control means includes a comparison circuit for comparing the voltage of the capacitor with the predetermined value, and a control circuit for controlling the bypass means according to a result of the comparison. The means includes a switch element connected in parallel to the resistor and controlled to be turned on and off by the control circuit output, and a diode connected in parallel to the switch element and provided in a forward direction with respect to a discharge current from the capacitor. , Is further provided.

Further, a second capacitor charged by the power supply, and an auxiliary power supply for generating the predetermined value and the power supply for the comparison circuit based on an output of the second capacitor,
It is further characterized by including.

The operation of the present invention will be described. When the input power is momentarily interrupted, the charge stored in the output holding capacitor becomes
Power is supplied to the load without passing through the charging current limiting resistor. When it is detected that the voltage of the output holding capacitor has become equal to or less than the predetermined value, the switch element of the bypass unit is turned off. . Furthermore, since the discharge current does not flow backward in the direction of the input power supply, the energy stored in the output holding capacitor is supplied to the load without waste. When the instantaneous interruption is restored, the output holding capacitor is charged through the charging current limiting resistor. afterwards,
When the charging voltage of the output holding capacitor reaches a predetermined value,
The path of the charging current limiting resistor is bypassed. As a result, the output holding capacitor acts as a low-pass filter that reduces the voltage fluctuation component of the input power supply.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing a configuration of a power supply device as one embodiment of the present invention. Referring to FIG. 1, the power supply device according to the present invention includes an input power supply 1, an instantaneous interruption detection unit 100, a filter unit 200, and a load 9. The instantaneous interruption detection unit 100 mainly includes a backflow prevention diode 10, an auxiliary power supply 2, a comparator 3, a photocoupler (primary side) 4, and a photocoupler (secondary side) 5. Also, the filter unit 200 includes a P-channel MO
SFET 6, built-in diode 7, charging current limiting resistor 2
1 and an output holding capacitor 8. still,
11 is a diode, 12 and 18 are capacitors, 13-1
Reference numerals 7 and 19, 20 denote resistors, respectively.

Next, the function of each unit in FIG. 1 will be briefly described. The input power supply 1 supplies to the load 9 a voltage that is lower than the voltage Vin by the forward voltage of the backflow prevention diode 10. The auxiliary power supply 2 uses a capacitor 12 to stabilize a voltage further dropped by a forward voltage of the diode 11 from a supply voltage to the load 9 and uses the voltage as an input power supply. The comparator 3 uses the output of the auxiliary power supply 2 as a power supply, further uses the voltage VN obtained by dividing the output voltage of the auxiliary power supply 2 by the resistors 13 and 14 as a reference voltage, and sets the voltage of the output holding capacitor 8 to the resistance 15 and
The voltage VI divided at 16 is input as a comparison voltage, respectively.
The comparison result of VN and VI is output as VO.

The photocoupler (primary side) 4 is turned on and off in accordance with the output voltage VO of the comparator 3, and the photocoupler (primary side) 4
Is turned on, a current flows through the resistor 17, and the photocoupler (secondary side) 5 is turned on. In response to the on / off of the photocoupler (secondary side) 5, the P-channel MOSFET 6 biased by the resistors 19 and 20 and the capacitor 18 is turned on / off, and the bypass of the charging current limiting resistor 21 and the release of the bypass are controlled.

Next, the operation of the power supply device shown in FIG. 1 will be described with reference to FIGS. In FIGS. 3 to 5, the circuit elements indicated by dotted lines do not contribute to the actual circuit operation in each operation state. 3 to 5, the same parts as those in FIG. 1 are denoted by the same reference numerals. FIG. 2 shows the input voltage Vin, the reference voltage VN of the comparator 3, the comparison voltage (the voltage of the output holding capacitor 8) VI, and the output voltage of the comparator 3 at each timing from occurrence of an instantaneous interruption to recovery of the input power supply 1. V
FIG. 9 is a waveform chart showing the operation of O and P channel MOSFETs 6;

First, it is assumed that at time T = t1 in FIG. 2, the input voltage Vin becomes 0 [V] and an instantaneous interruption occurs. At t1 ≦ T <t2 during the instantaneous interruption period, the electric charge of the output holding capacitor 8 in FIG. 1 is prevented from being discharged to the outside by the backflow prevention diode 10 and power is supplied only to the load 9. VI is a discharge voltage characteristic to the load 9. At this time, VI (comparison voltage) <VN (reference voltage) due to discharge from the output holding capacitor 8, and the output voltage VO of the comparator 3 becomes "H". Therefore, the photocoupler (primary side)
A current flows from 4 through the resistor 17 and the photocoupler (secondary side) 5 is turned on, so that the P-channel MOSFET 6 is turned off. That is, the equivalent circuit of the power supply device of FIG. 1 in this state is as shown in FIG. 3, and the electric charge stored in the output holding capacitor 8 is supplied to the load 9 through the built-in diode 7 as shown by the arrow. .

Next, when the instantaneous interruption of the input voltage Vin is restored and returns to the normal value, that is, at time t2 ≦ T <t3 in FIG. 2, the output holding capacitor 8 in FIG. 2 is a charging voltage characteristic of the output holding capacitor 8 via the charging current limiting resistor 21. At this time, since the P-channel MOSFET 6 remains off, the equivalent circuit of the power supply device of FIG. 1 is as shown in FIG. 4, and the output holding capacitor is connected by the power supply 1 via the charging current limiting resistor 21 as shown by the arrow. 8 is charged and power is supplied to the load 9. Assuming that the voltage of the output holding capacitor 8 is VC8, the forward voltage of the backflow prevention diode 10 is VD10, and the resistance value of the charging current limiting resistor 21 is R21, the charging of the output holding capacitor 8 takes the current value ｛(Vin−VD10). −VC8｝ / R21.

Here, the auxiliary power supply 2 operates so that the output voltage VO of the comparator 3 can be accurately obtained even when the output holding capacitor 8 is discharged due to an instantaneous interruption of the input voltage Vin and the voltage of VI decreases. The reference voltage VN is supplied stably. In other words, the power supply voltage of the auxiliary power supply 2 must be equal to or higher than the voltage required to maintain the stable operation of the auxiliary power supply 2 itself. Therefore, even if the voltage of the output holding capacitor 8 drops, the diode 11
Thus, the voltage of the capacitor 12, that is, the power supply voltage of the auxiliary power supply 2 is not affected.

Further, when the voltage of the output holding capacitor 8 decreases, the reference voltage VN
It is necessary to set a value that inverts O. For example,
If Vin is DC + 48 ± 12 [V], the reference voltage V
N indicates that the voltage of the output holding capacitor 8 is DC + 36 [V]
The setting is made so that the output voltage VO of the comparator 3 changes as soon as the value becomes below.

Finally, when the input voltage Vin is stable,
That is, the time T in FIG. 2 is t0 ≦ T <t1 and t3 ≦ T
Consider the case At this time, since VN <VI, the output voltage VO of the comparator 3 becomes “L”. Therefore, the photocoupler (primary side) 4 is turned off, so that the photocoupler (secondary side) is turned off.
5 is open, and the P-channel MOSFET 6 is turned on. That is, the equivalent circuit of the power supply device in FIG. 1 in this state is as shown in FIG.
From the power supply 1 side, it looks as if the output holding capacitor 8 is directly connected to the power supply 1.

Generally, a capacitor added to a power supply input has a function of a low-pass filter (hereinafter referred to as LPF) for reducing an external input voltage fluctuation component. If the resistor 21 inserted to limit the current during charging is always inserted, a loss due to this resistor occurs and the effect of the LPF is reduced.

FIG. 6A shows the LPF characteristics depending on the capacitance of the output holding capacitor 8. The performance of this LPF is determined by the frequency characteristics of the output holding capacitor 8.
On the other hand, FIG.
No. 134, the charge / discharge circuit 50 of the stabilization circuit
A and 50B show LPF characteristics.

In the prior art, capacitors C1 and C1
The cutoff frequency of the LPF shifts to a higher frequency due to a factor other than the total capacitance of No. 2, that is, the presence of the resistor R.
Therefore, even if the combined capacitance of the capacitors C1 and C2 is set to be equivalent to the output holding capacitor 8 of the present invention, there is no means for bypassing the resistor R, so that an LPF effect equivalent to that of the present invention cannot be obtained. That is, according to the present invention, when the input voltage Vin is normal, the output holding capacitor 8 forms a low-pass filter, and greatly contributes to the reduction of the external input voltage fluctuation component.

It is apparent that the present invention is not limited to the above-described embodiment, but can be appropriately modified within the scope of the technical idea of the present invention. For example, in the above-described embodiment, the description has been made assuming that the polarity of the power supply of the input voltage is only the positive power supply (negative electrode ground). However, even when the power supply polarity is the negative power supply (positive electrode ground). Applicable.

In the above embodiment, nothing is connected to the end of the load, and the circuit is terminated by the load. However, this load acts as a power source for other devices. It can be widely applied even when other loads are connected.

[0027]

As described above, according to the present invention, when the power supply voltage is in a stable state, the charging current limiting resistor is bypassed, and the output holding capacitor is equivalently equivalent to a low-pass filter as viewed from the power supply side. Has the effect of contributing to the reduction of the external power supply voltage fluctuation component.

Further, according to the present invention, even when the power supply voltage decreases, power is supplied to the load without current flowing out of the output holding capacitor, so that the load operation is stabilized. And can continue. Further, even when the power supply voltage is restored, the output holding capacitor is charged via the resistor, so that an effect of preventing the occurrence of an inrush current can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device of the present invention.

FIG. 2 is a waveform diagram showing the state of each voltage and FET of the present invention.

FIG. 3 is an equivalent circuit diagram when an instantaneous interruption of an input power supply occurs according to the present invention.

FIG. 4 is an equivalent circuit diagram at the time of recovery from an instantaneous interruption of an input power supply according to the present invention.

FIG. 5 is an equivalent circuit diagram when the input power supply of the present invention is stable.

FIG. 6 is a diagram illustrating a low-pass filter characteristic of the present invention.

FIG. 7 is a circuit diagram of a power supply unit of a conventional communication device.

FIG. 8 is a circuit diagram of a conventional general instantaneous interruption prevention.

FIG. 9 is a circuit diagram of a conventional stabilized power supply circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply 2 Auxiliary power supply 3 Comparator 4 Photocoupler (primary side) 5 Photocoupler (secondary side) 6 P-channel MOSFET 7 Built-in diode 8 Output holding capacitor 9 Load 10 Backflow prevention diode 11 Diode 12, 18 Capacitor 13, 14, 15, 16, 17, 19, 20 Resistance 21 Charge current limiting resistance 100 Instantaneous interruption detection unit 200 Filter unit

Claims (6)

[Claims] 1. A power supply apparatus comprising: a power supply; and a low-pass filter configured to connect a resistor and a capacitor in series and configured to supply a smoothed output of the power supply to a load. A bypass means for making a bypass of the bypass means, and when the power supply is stable, the bypass means is in a bypass state. A power supply device, comprising: control means for controlling. 2. The semiconductor device according to claim 1, further comprising a backflow prevention diode provided between said power supply and said low-pass filter means, for preventing a backflow current from said capacitor due to a decrease in said power supply. The power supply as described. 3. The control device according to claim 2, wherein said control means includes a comparison circuit for comparing a voltage of said capacitor with said predetermined value, and a control circuit for controlling said bypass means in accordance with a result of the comparison. 3. The power supply device according to 1 or 2. 4. The power supply device according to claim 3, wherein said bypass means includes a switch element connected in parallel to said resistor and controlled to be turned on and off by an output of said control circuit. 5. The power supply device according to claim 4, wherein the bypass unit further includes a diode connected in parallel to the switch element and provided in a forward direction with respect to a discharge current from the capacitor. . 6. The power supply according to claim 1, further comprising: a second capacitor charged by the power supply; and an auxiliary power supply that generates the predetermined value and the power supply for the comparison circuit based on an output of the second capacitor. Item 6. The power supply device according to any one of Items 3 to 5.