JPH06237579A - Switching power supply - Google Patents

Abstract

(57) [Summary] [Purpose] To extend the output holding time during an instantaneous power failure without increasing the capacitance of the input electrolytic capacitor. [Structure] A power failure detection circuit 5 for detecting an AC input and a voltage controlled oscillator 6 whose oscillation frequency changes according to the voltage are provided, and a power failure detection signal from the power failure detection circuit is used to temporarily In addition, the frequency of the control signal (switching frequency) is changed to a frequency higher than that in normal operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device having a function of extending the output holding time in the event of a momentary power failure or the like.

[0002]

2. Description of the Related Art In recent years, with the progress of semiconductor technology, electronic devices have been reduced in size and weight, and power sources used therein have also been required to be reduced in size and weight. Therefore, switching power supplies featuring small size and high efficiency are rapidly becoming popular. Further, a switching power supply mounted in an information processing device such as a computer is also required to have high reliability, and protection against surges, instantaneous power failures, etc. is becoming important.

For example, after the AC input is cut off, the time during which the output voltage is held within the standard range of the input fluctuation is defined as the output holding time. In information processing devices, etc., this output holding time is used. In order to protect the data and the operation of the device, the switching power supply is required to have an output holding time longer than a certain time. Generally, in order to extend the output holding time, there are methods such as (1) increasing the capacitance of the input smoothing capacitor and (2) increasing the conversion efficiency.

The operation during a momentary power failure in the conventional switching power supply will be described with reference to FIGS. 3 and 4. Figure 3
In the figure, 1 is a rectifier circuit for rectifying an AC input, 2 is an inrush current prevention circuit for suppressing an inrush current, 3 is a smoothing circuit for smoothing a rectified input, 4 is a power conversion circuit for converting power, and 8 is a switching frequency. An oscillator 7 that determines the output voltage is a control circuit that controls the output voltage of the power conversion circuit by changing the duty at a constant frequency.

In the normal state, the charging current to the input smoothing capacitor of the smoothing circuit 3 flows from the AC input source through the rectifying circuit 1 and the inrush current preventing circuit 2. The electric charge accumulated in the capacitor of the smoothing circuit 3 is consumed through the power conversion circuit 4, and the input smoothing capacitor of the smoothing circuit 3 is discharged through this path. In the normal state, the control circuit 7
The frequency of the output control signal 10 is constant, and the DC output voltage is stabilized by changing the duty of the control signal 10 according to the state of the input voltage and the load. Here, when an instantaneous power failure or the like occurs, the charging current from the AC input source to the smoothing circuit 3 is cut off and the accumulated charge in the capacitor of the smoothing circuit 3 is consumed, so that the voltage of the smoothing circuit 3 decreases and the output After the holding time has elapsed, the DC output falls outside the standard range (Fig. 4).

[0006]

However, in the configuration of the above-mentioned conventional example, since the power conversion circuit 4 is driven at a constant frequency by the control signal 10 at the momentary power failure of the AC input source, the conversion efficiency is almost constant. The output holding time mainly depends on the capacitance of the capacitor of the smoothing circuit 3.
Therefore, a large electrolytic capacitor is required to secure a predetermined output holding time, which has been an obstacle to downsizing of the power supply and cost reduction. The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a switching power supply device that extends the output holding time during an instantaneous power failure without increasing the capacitance of the input electrolytic capacitor. is there.

[0007]

In order to achieve the above-mentioned object, the present invention is provided with a power failure detection circuit for detecting an AC input and a voltage controlled oscillator whose oscillation frequency changes according to the voltage. In addition, the frequency of the control signal (switching frequency) is temporarily changed to a frequency higher than that during normal operation by a power failure detection signal from the power failure detection circuit.

[0008]

According to the present invention, the output holding time can be extended by temporarily improving the efficiency in the case of a momentary power failure or the like due to the above configuration.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a switching power supply device showing an embodiment of the present invention, and FIG. 2 is a time chart for explaining the operation in FIG. Further, the description of the same parts as those in FIGS. 3 and 4 of the conventional example will be omitted. That is, in the present embodiment, as shown in FIG. 1, a power failure detection circuit 5 for detecting an AC input and a frequency signal of a control signal 10 for controlling the power conversion circuit 4 whose oscillation frequency changes according to the voltage. The output voltage-controlled oscillator 6 (having the function of increasing the switching frequency by the power failure detection signal 14 compared to the normal operation) is provided, and the power failure detection signal 14 causes the occurrence of an instantaneous power failure,
By increasing the oscillation frequency of the voltage controlled oscillator 6, the frequency of the control signal 10 (switching frequency) is temporarily increased.
Is set higher than that during normal operation.

The power failure detection circuit 5 uses the negative logical product of the input detection signal output from the input voltage detection circuit 11 and the reset signal output from the reset circuit 12 as the power failure detection signal 14 so that the power is turned on. The power failure detection signal is set to H level (false) (period td in FIG. 2), and the power failure detection signal 14 is set to L level (true) only during power failure.

Since the power failure detection signal 14 is at the H level (false) in the normal operation state after the power is turned on, the voltage controlled oscillator 6 oscillates at the frequency in the normal state, and the power conversion circuit is similar to the conventional example. 4 is controlled by a control circuit 7 with a predetermined frequency signal. Here, when the AC input is cut off due to an instantaneous power failure at time t1, the input voltage detection circuit 11 detects this after a predetermined time and outputs a power failure detection signal 14.
Upon receiving the power failure detection signal 14, the voltage controlled oscillator 6 changes the oscillation frequency to a higher frequency than usual according to the input voltage and outputs it to the control circuit 7. The control circuit 7 controls the power conversion circuit 4 with the control signal 10 having a higher frequency than the normal operation state. Therefore, after time t1, it is equivalent to a temporary improvement in efficiency as compared with the normal operation state, and the output holding time is extended. If the instantaneous power failure continues for more than the output hold time, D
C output decreases. After that, when the power is restored from the power failure at the time t2, the same operation as when the power is turned on is performed. Further, when the power is turned off from the normal state, it can be considered that the power failure continues for the output holding time or longer.
The same operation as the operation from t2 to t2 is performed.

[0012]

According to the present invention, the output holding time during an instantaneous power failure can be extended without increasing the capacitance of the input electrolytic capacitor, and the power supply can be downsized and the cost can be reduced. Have an effect.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a switching power supply device according to an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the switching power supply device according to the embodiment of the present invention.

FIG. 3 is a configuration diagram of a switching power supply device according to a conventional example.

FIG. 4 is an operation explanatory diagram of a switching power supply device according to a conventional example.

[Explanation of symbols]

1 ... Rectifier circuit, 2 ... Inrush current prevention circuit, 3 ... Smoothing circuit, 4 ... Power conversion circuit, 5 ... Blackout detection circuit, 6 ...
Voltage controlled oscillator, 7 ... Control circuit, 8 ... Oscillator, 10
... control signal, 11 ... input voltage detection circuit, 12 ... reset circuit, 13 ... AND circuit (negative logic), 14 ... power failure detection signal.

Claims (1)

[Claims] 1. A rectifying circuit for rectifying an AC input, a smoothing circuit for smoothing a voltage rectified by the rectifying circuit, an inrush current prevention circuit for suppressing a charging current (inrush current) to the smoothing circuit, A power conversion circuit that converts the voltage of the smoothing circuit, a power failure detection circuit that detects the stop of the AC input, and a voltage controlled oscillator that changes the oscillation frequency to a high frequency by a power failure signal output from the power failure detection circuit, The switching power supply device, wherein the voltage controlled oscillator changes the frequency of the control signal of the power conversion circuit to a frequency higher than that during normal operation by the power failure signal when the AC input is momentarily cut off.