JP3056179B2 - Instantaneous interruption prevention circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for obtaining a constant voltage output by rectifying a commercial input, and more particularly, to a circuit for preventing an instantaneous interruption of a power supply circuit in which an instantaneous power failure of a commercial input voltage is taken.

[0002]

2. Description of the Related Art In a power supply circuit having two or more types of outputs having different voltage accuracy standards, a commercial AC input (hereinafter referred to as AC
In the event of an instantaneous power failure (hereinafter referred to as input), the output capacitor of the rectifier circuit, that is, the power supply circuit, is designed so that the voltage accuracy of the output circuit with the highest voltage accuracy standard does not fall below the standard. The capacity of the input capacitor is determined. For this reason, the capacitance of the input capacitor has a large enough value when viewed from an output circuit having a low voltage accuracy standard value. That is, in a power supply circuit having two or more outputs, for example, an output having a low voltage such as +5 V has a high voltage accuracy standard of about ± 5%, and the capacity of the input capacitor is determined so as not to fall below the voltage accuracy standard value. ing. On the other hand, an output having a high voltage such as +24 V has a voltage accuracy standard of about ± 10%. In the case of this output, the above-mentioned capacitor has a sufficient value with respect to the voltage accuracy standard value.

As a method of reducing the capacitance of an input capacitor as much as possible, for example, Japanese Patent Laid-Open No.
No. 0 is disclosed. According to this technology, when an instantaneous interruption occurs, only the most important output circuit of the multiple outputs is utilized, and the other output circuits transmit instantaneous interruption detection signals to individually provided logic gate circuits, Output is stopped. Thus, the power consumption at the momentary interruption is reduced, and the capacity of the input capacitor is reduced.

[0004]

However, when the input capacitor has a large capacitance as described above, the rise time of the power supply at startup is delayed, and the timing of operating the load is delayed. In addition, the cost increases.
Further, in the method of reducing the capacitance of the capacitor by the technique as disclosed in Japanese Patent Application Laid-Open No. 8-181740,
One of the output circuits is stopped, and each time the power is restarted, some action must be taken on these loads. Furthermore, when a large number of loads that cannot be stopped are connected, it is difficult to cope with the load.

[0005] The present invention has been made in view of such circumstances, and its object is to solve the problem when an instantaneous interruption occurs.
It is an object of the present invention to provide an instantaneous interruption prevention circuit of a power supply circuit capable of satisfying a voltage accuracy standard without stopping any output and reducing the capacity of an input capacitor.

[0006]

SUMMARY OF THE INVENTION According to the present invention, there is provided a circuit for preventing instantaneous interruption of a power supply circuit in a power supply circuit having two or more outputs having different voltage accuracy standards, having a margin in output voltage accuracy based on an instantaneous interruption detection signal. Forcibly lower the voltage of the output circuit to the limit value of the voltage accuracy. This suppresses the discharge consumption of the input capacitor of the power supply circuit, and replenishes the energy of the input capacitor to the output circuit with high output voltage accuracy.
In this way, the input capacitor is kept to a minimum so that the output circuit with high output voltage accuracy does not fall below the voltage accuracy in the event of an instantaneous interruption.

[0007]

According to a first aspect of the present invention, there is provided a power supply circuit for generating a predetermined DC voltage from a commercial AC voltage. Equipped with a plurality of output circuits with different accuracy specification values, the voltage of the output circuit with sufficient voltage accuracy is reduced to the lower limit of voltage accuracy during a momentary interruption of commercial AC input, and the charging energy of the input capacitor of the power supply circuit is reduced to the voltage accuracy. Is supplied to an output circuit with no margin. Further, the instantaneous interruption countermeasure circuit of the power supply circuit according to claim 2 is:
In the instantaneous interruption prevention circuit according to the first aspect, the voltage of the output circuit having a margin of the voltage accuracy standard value is higher than the voltage of the output circuit having no margin of the voltage accuracy standard value.

According to a third aspect of the present invention, there is provided an instantaneous interruption prevention circuit for a power supply circuit, wherein the instantaneous interruption detection means for detecting an instantaneous interruption of a commercial input and an instantaneous interruption from the instantaneous interruption detection means are provided. Instantaneous interruption countermeasure means for varying the signal voltage level based on the detection signal; an error signal for controlling the voltage of the output circuit having a margin of voltage accuracy at a constant voltage; a signal voltage level from the instantaneous interruption countermeasure means; Switching control means for comparing and controlling the triangular wave, when an instantaneous interruption detection signal is input from the instantaneous interruption detection means and the signal voltage level from the instantaneous interruption countermeasure means becomes higher than the voltage level of the error signal, The switching control means stops the constant voltage control based on the error signal, compares and controls the signal voltage level of the instantaneous interruption countermeasure means and the reference triangular wave, and outputs the voltage of the output circuit having a margin of voltage accuracy to the voltage accuracy standard value. lower limit It characterized in that in lowering.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of a power supply circuit using an instantaneous interruption prevention circuit according to an embodiment of the present invention.
First, the configuration of the power supply circuit of FIG. 1 will be described.

The AC input 1 is full-wave rectified by a rectifier circuit 3,
It is smoothed by the input capacitor 5 and supplied to the input of the power supply circuit. The power supply circuit uses the input capacitor 5 as an input, and a primary winding of a transformer 7 and a switching element (FE in the figure).
T) A switching circuit is constituted by the series circuit of 9. Further, a first output circuit 11 having a built-in rectifier circuit (not shown) is connected to a secondary winding of the transformer 7.
The first output circuit 11 has, for example, an output voltage of +24 V and a voltage accuracy of ± 10%, and is an output having a high voltage and relatively high output voltage accuracy. A second output circuit 13 including a rectifier circuit (not shown) is connected to the tertiary winding of the transformer 7. The second output circuit 13 outputs, for example, an output voltage +5
V, voltage accuracy ± 5%, output with low voltage and relatively high output voltage accuracy. Therefore, the rectifier circuit (not shown) of the second output circuit 13 is constituted by a constant voltage control rectifier circuit that satisfies this voltage accuracy.

The switching circuit detects the output voltage of the first output circuit 11 with a photodiode 15 composed of a photocoupler, and feeds it back to a phototransistor 17 to perform constant voltage control. That is, the switching regulator 19 is controlled by the feedback voltage to perform constant voltage control of the first output circuit 11. On the other hand, the ACLOW detection circuit 21 detects the voltage drop of the input capacitor 5 due to the instantaneous interruption of the AC input, activates the instantaneous interruption countermeasure circuit 23, and sends a signal for lowering the output voltage to the switching regulator 19. Have been.

Next, the operation of the power supply circuit shown in FIG. 1 will be schematically described. Normally, the switching circuit is a photodiode 15
, The output voltage of the first output circuit 11 is detected and fed back to the switching regulator 19 for PW
M (Pulse Width Modulation) control is performed, and constant voltage control is performed so that the output voltage of the first output circuit 11 falls within a predetermined voltage accuracy. On the other hand, the second output circuit 13
A constant voltage control circuit (not shown), based on the voltage reduced by the tertiary winding of the transformer 7 from the controlled voltage,
It outputs a more accurate constant voltage.

When an instantaneous interruption occurs in the AC input 1 and the voltage of the input capacitor 5 drops to a predetermined value, ACLOW
The detection circuit 21 detects a voltage drop of the input capacitor 5,
A signal for operating the instantaneous interruption countermeasure circuit 23 is sent from the ACLOW detection circuit 21. When the instantaneous interruption countermeasure circuit 23 operates, a signal for lowering the voltage of the first output circuit 11 is sent to the switching regulator 19, and the first output circuit 1
1 is forcibly reduced. The range in which the voltage is reduced may be reduced to the lower limit value of the output voltage accuracy of the first output circuit 11 (therefore, to the limit of -10%).
On the other hand, since the output voltage of the second output circuit 13 is set lower than that of the first output circuit 11, even if the voltage of the first output circuit 11 is reduced by narrowing the duty width of the PWM control,
It is still within the range of voltage accuracy (± 5%).

The discharge energy of the input capacitor 5 is reduced by the amount by which the voltage of the first output circuit 11 is reduced. Therefore, the energy charged in the input capacitor 5 can be supplied to the second output circuit 13, so that the voltage of the second output circuit 13 can be stabilized within the accuracy during the instantaneous interruption time. . Further, if the input capacitor 5 is used in this manner, the capacitance of the capacitor for instantaneous interruption countermeasures can be determined based on the voltage drop limit value of the first output circuit 11 having low voltage accuracy. Capacity can be reduced.

FIG. 2 is a circuit example of the instantaneous interruption prevention circuit and the switching regulator in the power supply circuit of FIG. 1, and FIG. 3 is an operation waveform of each part in the circuit of FIG. Therefore, the embodiment of the present invention will be described in detail with reference to FIGS. First, the configuration of the circuit in FIG. 2 will be described. In the instantaneous interruption prevention circuit 23, a Zener diode ZD1 is connected from a power supply Vcc through a limiting resistor R0, and resistors R1 and R2 are connected in series with the Zener diode ZD1. Furthermore, a resistor R3 and a transistor Q1 are connected in parallel with the resistor R2.
Are connected in series. Then, a signal from the ACLOW detection circuit 21 is supplied to the base of the transistor Q1.
The signal is transmitted to the switching regulator 19 from the voltage dividing node between R1 and the resistors R2 and R3. Note that the capacitor C1 connected to the base of the transistor Q1 is
The transistor caused by noise from the LOW detection circuit 21
This is to prevent Q1 from malfunctioning.

Next, the switching regulator 19
The triangular wave oscillation circuit 27 is connected to the reference input terminal (-terminal) of the PWM comparator 25, and the first control input terminal (+1
Terminal) is connected to the output of the error amplifier 29. In the error amplifier 29, the reference voltage 31 is input to the reference input terminal (+ terminal), and the feedback voltage of the output voltage of the first output circuit 11 shown in FIG. And an error signal is output. Further, an output signal from the instantaneous interruption countermeasure circuit 23 is input to a second control input terminal (+2 terminal) of the PWM comparator 25. And PWM
The output signal of the comparator 25 is input to the gate of the FET 9 of the switching circuit of FIG.

Next, the operation of this circuit will be described with reference to the circuit diagram of FIG. 2 and the operation waveforms of FIG. The symbols of the waveforms of the respective parts in FIG. 3 are indicated by (a) to (f), and the periods T1, T2,
A description will be given in chronological order in the order of T3. First, an operation when the AC input (d) is supplied in the period T1 will be described. A triangular wave (a) is supplied from a triangular wave oscillation circuit 27 to a reference input terminal (− terminal) of the PWM comparator 25.
, The first control input terminal (+1 terminal)
, An error amplifier output voltage (b), which is an error signal, is input from the output of the error amplifier 29. On the other hand, since the AC input is supplied, the voltage from the AC input detection circuit 21 is applied to the base of the transistor Q1, and
1 turns on, and the resistor R3 is added in parallel with the resistor R2.
The voltage level at the voltage dividing point in the resistor R1 has a low value. Therefore, the dead time control voltage (c) input to the second control input terminal (+2 terminal) of the PWM comparator 25 is lower than the error amplifier output voltage (b) input to the first control input terminal (+1 terminal). Value.

Thus, the PWM comparator 25
Is controlled by comparing the error amplifier output voltage (b), which is the higher control input voltage, with the triangular wave (a). As a result, the output of the PWM comparator 25 becomes H (high) during a period when the level of the triangular wave (a) is higher than the level of the error amplifier output voltage (b), so that the voltage of the first output circuit 11 becomes a predetermined value. The PWM comparator output waveform (e) having the duty width to be controlled is output. Since the FET 9 of the switching circuit of FIG. 1 is switched by the PWM comparator output waveform (e), a predetermined constant voltage is output to the first output circuit 11.

Next, when the AC input (d) is momentarily interrupted in the period T2, the voltage from the ACLOW detection circuit 21 disappears, so that the transistor Q1 is turned off and the resistance R3 of the resistance voltage dividing circuit is changed from the parallel connection of the resistance R1. It is released. For this reason,
The divided voltage level of the resistors R1 and R2 increases. Therefore, the level of the dead time control voltage (c) is
The value becomes higher than the error amplifier output voltage (b). As a result, the triangular wave (a) and the dead time control voltage (c) are compared and controlled, and the output of the PWM comparator 25 is H (high) only during the period when the level of the triangular wave (a) is higher than the dead time control voltage (c). So,
The duty ratio P is reduced so that the voltage of the first output circuit 11 is reduced to the lower limit value (−10%) of the output voltage accuracy.
The WM comparator output waveform (e) is output.

By switching the FET 9 of the switching circuit with this PWM comparator output waveform (e), the output voltage of the first output circuit 11 drops to the lower limit of the standard. As a result, the discharge energy of the input capacitor 5 can be minimized, and the energy of the input capacitor 5 is supplied to the second output circuit 13 during the instantaneous interruption, so that the output voltage of the second output circuit 13 is stabilized. Can be achieved. Here, the output voltage of the second output circuit 13 is set to such a low voltage value that stabilization can be achieved even when the output voltage of the first output circuit 11 drops to the lower limit of the specification. Further, the level of the dead time control voltage (c) at the moment of the instantaneous interruption of the AC input is set to a level at which the voltage of the first output circuit 11 does not exceed the limit value of the output voltage accuracy.

Next, when the AC input recovers in the period T3, the output voltage (b) of the error amplifier and the triangular wave (a) are compared and controlled by the same operation as in the period T1, so that the first voltage is output.
A PWM comparator output waveform (e) having a duty width for controlling the voltage of the output circuit 11 to a predetermined value is output.

The embodiment described above is an example for describing the present invention, and the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the invention. is there. For example, the instantaneous interruption countermeasure circuit is not limited to the circuit of the present embodiment,
An instantaneous interruption signal may be transmitted when the C input voltage falls below the reference voltage. The voltage control circuit is not limited to the PWM control method, but may be a frequency control method in which the ON width is fixed and the frequency is changed. In this case, the control may be performed such that the frequency is reduced so that the voltage of the first output circuit is reduced to the standard lower limit value by the instantaneous interruption signal, and the duty ratio is reduced. In short, in a power supply circuit having two or more outputs with different voltage accuracy specification values, at the moment of instantaneous interruption of input, the voltage of the output circuit with sufficient output voltage accuracy is reduced to the lower limit of the specification value to limit the discharge energy of the input capacitor. It goes without saying that any configuration that supplies the energy of this input capacitor to an output circuit that does not have sufficient output voltage accuracy falls within the scope of the present invention.

[0024]

As described above, according to the instantaneous interruption countermeasure circuit of the present invention, at the moment of instantaneous interruption, the voltage of the output circuit having a margin of output voltage accuracy is reduced to the lower limit of the standard value, so that extra output can be obtained. Since the energy can be reduced and the input energy can be given a margin, the instantaneous interruption resistance can be improved. Furthermore, the capacitance of the input capacitor can be reduced by transferring excess energy of the output circuit having a margin of output voltage accuracy to an output circuit having a margin of output voltage accuracy. This can reduce the size and cost of the power supply.

[Brief description of the drawings]

FIG. 1 is a block diagram of a power supply circuit using an instantaneous interruption prevention circuit according to an embodiment of the present invention.

FIG. 2 is a circuit example of an instantaneous interruption prevention circuit and a switching regulator in the power supply circuit of FIG.

FIG. 3 is an operation waveform of each part in the circuit of FIG. 2;

[Explanation of symbols]

1 AC input, 3 rectifier circuit, 5 input capacitor, 7
... Transformer, 9 ... Switching element (FET), 11 ...
1st output circuit, 13 ... 2nd output circuit, 15 ... photodiode, 17 ... phototransistor, 19 ... switching regulator, 21 ... ACLOW detection circuit, 23 ... instantaneous interruption prevention circuit, 25 ... PWM comparator, 27 ... triangular wave oscillation circuit , 29: Error amplifier, 31: Reference voltage, C0: Capacitor, ZD1: Zener diode, R0, R1, R2, R3
... resistor, Q1 ... transistor

Claims (3)

(57) [Claims] 1. A power supply circuit for generating a predetermined DC voltage from a commercial AC voltage, wherein the power supply circuit includes a plurality of output circuits having different voltage accuracy standard values. When the commercial AC input is momentarily interrupted, the voltage of the output circuit with margin of voltage accuracy is reduced to the lower limit of voltage accuracy, and the charging energy of the input capacitor of the previous power supply circuit is supplied to the output circuit with margin of voltage accuracy. An instantaneous interruption countermeasure circuit in a power supply circuit characterized by the following. 2. The power supply circuit according to claim 1 , wherein a voltage of the output circuit having a margin of the voltage accuracy standard value is higher than a voltage of an output circuit having no margin of the voltage accuracy standard value. Countermeasure circuit. 3. An instantaneous interruption detection means for detecting the commercial input instantaneous interruption, an instantaneous interruption countermeasure means for varying a signal voltage level based on an instantaneous interruption detection signal from the instantaneous interruption detection means, and a sufficient voltage accuracy. Switching control means for comparing and controlling an error signal for controlling the voltage of a certain output circuit with a constant voltage, a signal voltage level from the instantaneous interruption countermeasure means, and a reference triangular wave; When the detection signal is input and the signal voltage level from the instantaneous interruption countermeasure unit becomes higher than the voltage level of the error signal, the switching control unit stops constant voltage control based on the error signal,
The signal voltage level of the instantaneous interruption countermeasure means and the reference triangular wave are compared and controlled to lower the voltage of an output circuit having a margin of voltage accuracy to a lower limit of a voltage accuracy standard value . Instantaneous interruption prevention circuit in power supply circuit.