JP2995962B2 - Power supply circuit for constant voltage power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supplying a DC voltage to a constant voltage power supply such as a so-called switching regulator while receiving an AC voltage from a commercial frequency power supply and intermittently controlling the current taken from the power supply into a sinusoidal waveform. A circuit,
The present invention relates to a power supply circuit for a constant voltage power supply that can continue power supply even during a short-term power failure or a momentary power failure.

[0002]

2. Description of the Related Art As is well known, since a constant voltage power supply such as a switching regulator is usually a so-called DC-DC converter, it is necessary to supply a DC voltage to the power supply. As the simplest power supply circuit, a rectifier circuit having a smoothing function is used.

In this rectifier circuit, it is necessary to use a capacitor for smoothing a pulsating rectified voltage. However, since a current taken from a commercial frequency power supply has a sharp peak waveform for charging the smoothing capacitor, invalid or apparent current is excessive. Problem. This can be mitigated by incorporating a current limiting reactor or choke coil into the rectifier circuit and dulling the peak of the charging current, but it is difficult to completely eliminate it. Harmonics associated with the remaining reactive current adversely affect the power supply side The risk remains, and complete removal of harmonics requires a rather large noise filter.

For this reason, recently, as described above, an active smoothing filter circuit for intermittently controlling a current from a commercial frequency power supply so as to have a sinusoidal shape is often incorporated in a line operated type power supply circuit as described above. The present invention also relates to this type of power supply circuit. Hereinafter, the configuration of a conventional example of a power supply circuit having an active smoothing filter function and the essential points of its operation will be described with reference to FIG.

[0005] The right half of FIG. 2 is a constant voltage power supply 10, and the left half is a power supply circuit including a rectifier circuit 20 receiving an AC voltage Va from the power supply 1 and an active smoothing filter circuit 30. The active smoothing filter circuit 30 receives the rectified voltage Vr of the full-wave rectified waveform from the rectifier circuit 20 to its choke coil 31, turns on the high-frequency field effect transistor 32, accumulates energy in this choke coil 31, and sets the transistor 32 The main circuit configuration of a so-called step-up DC-DC converter that supplies the voltage stabilized by the capacitor 34 via the diode 33 to the constant voltage power supply 10 as its input voltage Vi while repeating the operation of turning off and releasing energy. Transistor 32 so that the current taken from the commercial frequency power supply 1 becomes sinusoidal.
A control circuit 35 for the gate, which controls the timing of the on / off operation of the gate, is incorporated therein. This control circuit 35
Is the actual value of the supply voltage at the output of the diode 33,
The full-wave rectified voltage waveform on the input side of the choke coil 31, the actual value of the current flowing through the transistor 32 during the charging time detected by the resistor 32a, and the zero point of the current flowing through the choke coil 31 are calculated by the auxiliary coil 31a. The detected timing signal is given as shown.

The control circuit 35 receives these signals and generates a target value of the current flowing through the transistor 32 which is similar to the rectified voltage waveform so as to keep the actual voltage at the target value. The operation of turning off 32 and turning it on at the zero point of the current of the choke coil 31 is repeated. Due to the frequent on / off operation of the transistor 32, the current flowing through the choke coil 31 has a waveform in which a triangular wave whose peak value changes sinusoidally repeats at a high frequency,
Therefore, the current drawn from the power supply 1 via the rectifier circuit 20 has a waveform in which a high frequency of several tens of kHz usually overlaps a sine waveform of the commercial frequency. That is, the active smoothing filter circuit 30 functions as an active filter for smoothing a sharp peak-shaped waveform into a sine wave shape as described above in principle from the current supplied from the power supply 1. The high frequency on the current waveform is not usually harmful, but can be easily removed if necessary by inserting a very small noise filter on the power supply 1 side.

Since the constant voltage power supply 10 which receives a substantially constant DC voltage from the power supply circuit of FIG. 2 is a normal switching power supply, a brief description will be given. In the example shown in the figure, the input voltage Vi is input to the flyback type transformer 11, the current of the primary coil 11a is turned on and off by the transistor 12, and the AC voltage of the secondary coil 11b is rectified by the diode 13 and stabilized by the capacitor 14. Then, for example, the DC voltage of 5 V is output as the output voltage Vo. The voltage control circuit 15 receives the output voltage Vo, sends a switching command according to the actual value to the drive circuit 17 via the photocoupler 16 in the illustrated example, and turns the transistor 12 on and off to keep the output voltage Vo constant. To keep. The constant-voltage power supply 10 shown in FIG. 2 is insulated and its input-side ground point Ei and output-side ground point Eo are separated from each other.

[0008]

A power supply circuit having an active smoothing filter function as described above has an advantage that a sine-wave current can be obtained from a commercial frequency power supply. However, there is a problem in that the operation of the commercial frequency power supply is interrupted even if the commercial frequency power supply is interrupted within a very short time of 1 cycle or less, and the electronic circuit or the like supplied with power from the constant voltage power supply malfunctions.

That is, in a normal power supply circuit, such a short-time power failure or instantaneous power failure can be sufficiently coped with by using a capacitor having large stored energy in the capacitor 34 shown in FIG. Since the high-frequency operation is performed under self-excited oscillation that controls the timing of turning on and off the transistor 32 according to the waveform of the current in the coil 31, the capacitance value of the capacitor 34 cannot be increased so much in relation to the high-frequency operation. is there. Further, even if the amount of stored energy in the stabilizing capacitor 14 is increased on the side of the constant voltage power supply 10, it is possible to cope with a momentary power failure.
Since the output voltage Vo is low, the required capacitance value becomes extremely large, which is not practical.

SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem and to improve a power supply circuit having an active smoothing filter function so that the output voltage of a constant voltage power supply is not interrupted or reduced even when the commercial frequency power supply stops momentarily. .

[0011]

SUMMARY OF THE INVENTION According to the present invention, there is provided a rectifier circuit for receiving an AC voltage from a commercial frequency power supply, and an active smoothing filter for receiving the rectified output and controlling a current taken from the commercial frequency power supply in a sinusoidal manner. The power supply circuit is composed of a circuit, an energy storage circuit that charges the capacitor with the rectified output of the rectifier circuit, and an instantaneous power failure detection circuit that detects a short-time power failure of the commercial frequency power supply. When a power failure is detected by the instantaneous power failure detection circuit, This is achieved by supplying the charging voltage of the capacitor from the storage circuit to the constant voltage power supply.

It is advantageous to incorporate a charging diode that conducts in the direction of charging the capacitor into the energy storage circuit of the above configuration. In addition, in order to supply power to the constant voltage power supply from the energy storage circuit during an instantaneous power failure, a transistor switch that is turned on by the detection signal of the instantaneous power failure detection circuit is incorporated in the energy storage circuit, and the power is fixed from the interconnection point between the charging diode and the energy storage capacitor. Power may be supplied to a voltage power supply. Furthermore, it is advantageous to prevent the current from flowing into the side of the active smoothing filter circuit when the power is supplied from the energy storage circuit to the constant voltage power supply by using a diode.

Although the instantaneous interruption detection circuit may monitor the voltage on the input side or the output side of the rectifier circuit, it is easiest and practical to monitor the almost constant output voltage of the active smoothing filter circuit. This may be configured to generate a detection signal indicating a power failure or a momentary power failure when the monitoring voltage falls below a predetermined limit value. In order to eliminate the difference between the voltage supplied from the active smoothing filter circuit and the power supply from the energy storage circuit to the constant voltage power supply using this detection signal, the point that the active smoothing filter circuit is of a boost type is used. Preferably, the output voltage is set to about the peak value of the AC voltage of the commercial frequency power supply, which is the charging voltage of the capacitor of the energy storage circuit.

[0014]

According to the present invention, there is provided an energy storage circuit for accumulating necessary energy in a capacitor in order to guarantee power supply to a constant voltage power supply in the event of an instantaneous interruption of a commercial frequency power supply, and connecting this to the output side of a rectifier circuit. Therefore, the capacitor can always be charged by the rectified output without affecting the operation of the active smoothing filter circuit, and the rectified voltage of the commercial frequency power supply is much higher than the output voltage of the constant voltage power supply. This is to reduce the capacitance of the capacitor of the energy storage circuit necessary for energy storage by two orders of magnitude or more than when the energy is stored on the output side of the constant voltage power supply.

Since the energy storage circuit maintains the energy storage state without power consumption immediately after the capacitor is charged immediately after the commercial frequency power supply is turned on, the energy storage circuit immediately detects a power failure by the instantaneous power failure detection circuit. Power can be supplied to the constant voltage power supply. The capacitance required for the capacitor is, for example, 1 to
Even if power supply to a constant-voltage power supply having a current capacity of several tens of A during a two-cycle power failure is guaranteed, it can be reduced to about several hundred μF.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in FIG. 1 will be described below. 1 corresponding to FIG. 2 in FIG. 1 are denoted by the same reference numerals, and the description of the overlapping portions will be omitted as appropriate. The constant voltage power supply 10 shown in FIG. 1 is the same as that shown in FIG.

The energy storage circuit 40 of FIG. 1 is connected between the rectifier circuit 20 and the active smoothing filter circuit 30, and the commercial frequency power supply 1 generally uses a 100 V AC voltage Va to perform a full-wave rectification type rectifier circuit.
A pulsating rectified voltage with a peak value of about 140 V rectified by 20
Receive Vr. In the power supply circuit of the present invention, since the waveform of the current taken from the power supply 1 is controlled in a sinusoidal manner by the active smoothing filter circuit 30, the rectifying output side of the rectifying circuit 20 has a smoothing capacitor or a smoothing reactor as in FIG. Is not connected.

The energy storage circuit 40 of this embodiment comprises an energy storage capacitor 41 and a charging diode which conducts only in its charging direction.
And a power supply transistor switch 43 connected to the interconnection point between the two. Thus, the energy storage capacitor 41
Is charged via the charging diode 42, the capacitor 41 is charged to the peak value of the rectified voltage Vr, and discharge is prevented during the pulsation. Therefore, after the capacitor 41 is charged immediately after the power supply 1 is turned on, the energy storage circuit 40 always maintains the energy storage state without consuming any power. The transistor switch 43 may be composed of, for example, a field effect transistor and may be turned on by the instantaneous power failure detection signal DS.

The active smoothing filter circuit 30 has the same configuration as that of FIG. An energy storage circuit 40 is connected between this and the rectifier circuit 20, but since the capacitor 41 is initially charged and does not take current as described above, the active smoothing filter circuit 30 The operation described with reference to FIG. 2 that takes a sinusoidal current from the power supply 1 can be performed without any influence from the power supply 1.

The instantaneous stoppage detection circuit 50 of this embodiment is connected to the output side of the active smoothing filter circuit 30. The instantaneous power failure detection circuit 50 may be connected to any place where a power failure can be detected based on the voltage on the input side or output side of the rectifier circuit 20, for example, but the active smoothing filter circuit 30 having the most stable voltage in the power supply circuit. It is advantageous to connect to the output side, and to detect the substantially constant DC voltage by, for example, resistance voltage division, and to generate a detection signal DS indicating a power failure or an instantaneous interruption when the voltage falls below a predetermined limit value. .

When a power failure is detected by the instantaneous power failure detection circuit 50, the energy storage circuit 40 receives the detection signal DS, immediately turns on the transistor switch 43, and supplies the charging voltage of the capacitor 41 to the constant voltage power supply 10. . The power supply path at this time is preferably connected from the transistor switch 43 to the output side of the diode 33 of the active smoothing filter circuit 30 as shown in the figure, whereby the power supply current from the energy storage circuit 40 is shifted to the active smoothing filter circuit 30 side. Backflow can be prevented.

In order to minimize the fluctuation of the input voltage Vi of the constant voltage power supply 10 when the power supply is switched from the active smoothing filter circuit 30 to the energy storage circuit 40, the output of the active smoothing filter circuit 30 must be minimized. The voltage is preferably set in accordance with the peak value of the rectified voltage Vr which is the charging voltage of the capacitor 41 in the energy storage circuit 40. Since the active smoothing filter circuit 30 is a step-up DC-DC converter as described above, the output voltage can be easily set, for example, setting the inductance value of the choke coil 31 and the capacitance value of the capacitor 34 and adjusting the operation of the control circuit 35. This condition can be satisfied by the above method.

In the power supply circuit of FIG. 1 described above, the amount of energy stored in the energy storage circuit 40 is set so that power supply can be guaranteed against a power outage of the commercial frequency power supply 1 for, for example, one or two cycles. When the output voltage Vo of the constant voltage power supply 10 is 5 V and the current capacity is 20 A, the capacitor of FIG.
When trying to accumulate power supply energy in
A minimum of 80,0 to guarantee power supply during the momentary interruption of the cycle
It is necessary to have an extremely large capacitance of 00 μF.
However, in the present invention, the capacitor 41 of the storage circuit 40 is charged to the peak value of the rectified voltage Vr, and the AC voltage Va of the power
Assuming that the peak value of the rectified voltage Vr is 0 V and the peak value of the rectified voltage Vr is 140 V, the amount of energy storage is proportional to the square of the charging voltage.
That is, it is sufficient to have a capacitance of 1/800.
Although the required reduction rate of the capacitance depends on the rated voltage, of course, in the present invention, the capacitor of the storage circuit 40 is used.
By reducing the capacitance required for 41 by at least two digits, the practicality of the power supply circuit with power supply guarantee at the time of a momentary power failure can be improved.

[0024]

As described above, according to the present invention, a power supply circuit that receives an AC voltage from a commercial frequency power supply and supplies a DC voltage to a constant voltage power supply includes a rectifier circuit that receives an AC voltage, and a rectifier circuit that receives a rectified output of the rectifier circuit. An active smoothing filter circuit for controlling the current taken from the commercial frequency power supply into a sinusoidal waveform, an energy storage circuit for charging a capacitor with the rectified output of the rectifier circuit, and an instantaneous blackout detection circuit for detecting a short-time power failure of the commercial frequency power supply The following effects can be obtained by supplying the charging voltage of the capacitor from the storage circuit to the constant voltage power supply when the power failure is detected by the momentary power failure detection circuit.

(A) By storing and storing energy in the capacitor of the energy storage circuit and supplying the charging voltage of the capacitor to the constant voltage power supply according to the detection signal of the instantaneous power failure detection circuit, The interruption of the operation can be reliably prevented, and the malfunction of the electronic circuit or the like to which the power is supplied can be reliably prevented. (b) By connecting the storage circuit to the rectification output side of the rectification circuit, the capacitor can be constantly charged without affecting the operation of the active smoothing filter circuit. (c) Utilizing that the rectified voltage of the commercial frequency power supply is usually at least one digit higher than the output voltage of the constant voltage power supply, the capacitance of the capacitor of the storage circuit required for energy storage is stored at the output side of the constant voltage power supply. The power supply circuit with power supply guarantee at the time of a momentary power failure can be more practically used. As described above, the present invention can provide a remarkable effect in adding a power supply function at the time of an instantaneous power failure to a power supply circuit for a constant voltage power supply having an active smoothing filter function for taking a sinusoidal current from a commercial frequency power supply. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of a power supply circuit for a constant voltage power supply according to the present invention.

FIG. 2 is a circuit diagram showing a conventional power supply circuit together with a content example of a constant voltage power supply.

[Explanation of symbols]

 1 Commercial frequency power supply 10 Constant voltage power supply 20 Rectifier circuit 30 Active smoothing filter circuit 40 Energy storage circuit 41 Energy storage capacitor 42 Charging diode 43 Power supply transistor switch at momentary power failure 50 Instantaneous power failure detection circuit DS Detection signal of instantaneous power failure detection circuit Va AC voltage of commercial frequency power supply Vr Rectified voltage of rectifier circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02M 3/00 H02M 7/06

Claims (3)

(57) [Claims] 1. A circuit for receiving an AC voltage from a commercial frequency power supply and supplying a DC voltage to a constant voltage power supply, wherein the rectifier circuit receives the AC voltage and receives the rectified output of the rectifier circuit from the commercial frequency power supply. An active smoothing filter circuit that controls the current in a sine wave form; an energy storage circuit that charges a capacitor with a rectified output of a rectifier circuit; and an instantaneous power failure detection circuit that detects a short-time power failure of a commercial frequency power supply. A power supply circuit for a constant-voltage power supply, wherein a charging voltage of a capacitor is supplied from a storage circuit to a constant-voltage power supply when a power failure is detected. 2. The power supply circuit for a constant voltage power supply according to claim 1, wherein a charging diode that conducts only in a direction for charging the capacitor is incorporated in the energy storage circuit. 3. The circuit according to claim 1, wherein a current is prevented from flowing into the active smoothing filter circuit side by a diode during power supply from the energy storage circuit to the constant voltage power supply. Power supply circuit for voltage power supply.