JPH05236736A - Power source circuit - Google Patents

Abstract

PURPOSE:To constitute a great part of components of digital circuits by turning on a switching element when the current flowing to an inductance is zero, and turning it off after a counter counts a specified time, in a switching power source which gets high output by bringing input current waveform close to input voltage waveform. CONSTITUTION:At the same time the power on, an oscillator 14 starts oscillation, and a frequency dividing counter 9 also starts dividing, and a current detection means 8 sets a flip flop 11 and turns on a switch element 4, and lets a current flow to an inductance 3. The frequency dividing counter 9 is reset at the same time as the setting of the flip flop 11, and when the output of the frequency dividing counter 9 becomes the decode value of a decoder 13, the flip flop 11 is reset, and the switch element 4 is turned off. During the on period of the switch element 4, the energy accumulated in the inductance generates counter-electromotive force, and the energy is supplied to load 7, and when a current becomes zero, the current detection means 8 sets the flip flop 11 again.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for converting alternating current into direct current, and more particularly to a power supply circuit suitable for obtaining a high power factor.

2. Description of the Related Art In order to obtain a high power factor, a current waveform flowing through an inductance may be made close to a voltage waveform. Therefore, conventionally, as described in Transistor Technology 1988-3 488, after turning on a switching element, the current flowing through the inductance is converted into a voltage and turned off when it matches the waveform of the input voltage, and the current flowing through the inductance is zero. Then, the switch element was controlled to be turned on again. As a result, the current waveform as shown in FIG. 2 was obtained and the power factor was improved. In the figure, 20 is the output voltage of the rectifier, and 21 is the current flowing through the inductance. Further, conventionally, a start circuit for forcibly turning on the switch element is provided. In the conventional example, since the switch element does not turn on unless the current becomes zero from the state where the current is flowing through the inductance in advance, the current waveform and the voltage waveform during the period when the input voltage is low and the current hardly flows. And the switch element turns off, the current does not flow through the inductance and the switch element turns on.
It is because it will not be done.

Since a start circuit for starting the control is required, the number of parts increases. Moreover, since the ON period of the switch element is controlled in an analog manner, it is difficult to configure the logic circuit. Therefore, it is difficult to achieve miniaturization by an integrated circuit and intelligence by a microcomputer.

A means for detecting a current flowing through an inductance is provided, and if the current is zero, the switch element is turned on and a predetermined time is counted by a counter that divides the source oscillation frequency, and then the switch element is turned on. I decided to turn it off.

With the above construction, when the current flowing through the inductance becomes zero after the switch element is turned off, the switch element is turned on again, so that the switch element can be repeatedly turned on and off. In the present invention, the ON period of the switch element is made constant in order to bring the current waveform closer to the rectified voltage waveform. The reason for this is as follows. When the output voltage of the rectifier at the moment when the switch element is turned on is Vin, the inductance is L, and the ON period of the switch element is Ton, the current I flowing through the inductance after Ton is I =
(Vin / L) × Ton. Since Ton is sufficiently shorter than the cycle of the output voltage of the rectifier, it can be considered that Vin is constant during the ON period. Further, in order to bring the current waveform close to the voltage waveform, a proportional relationship must be established between I and Vin in any case. Therefore, I = K × Vin (K
Is constant), and from the above two equations, Ton = K × L
Becomes Since both K and L are constants, the ON period Ton of the switch element must be constant. Further, if the current flowing through the inductance is zero, the switch element is turned on, so a start circuit is not required. Also T
The power supplied to the load can be controlled by making on variable, but this only needs to change the count value of the counter. That is, since many of the constituent elements are logic circuits, miniaturization by an integrated circuit and intelligence by a microcomputer are easy.

FIG. 1 shows an embodiment of the present invention. In the figure, 1 is an AC power supply, 2 is a rectifier, 3 is an inductance, 4 is a switching element, 5 is a diode, 6 is a smoothing capacitor, 7 is a load, 8 is a current detecting means for the inductance 3, 9 is a frequency dividing counter, and 11 is Flip-flop, 13 is a decoder, 1
4 is an oscillator. When the power is turned on, the oscillator 14 starts oscillating. As a result, the frequency division counter 9 also starts frequency division. Therefore, when the power is turned on, the current flowing through the inductance 3 remains zero, so that the current detecting means 8 sets the flip-flop 11 to turn on the switch element 4 to flow the current through the inductance 3. The frequency division counter 9 is reset at the same time when the flip-flop 11 is set. After that, the output of the frequency division counter 9 becomes the decode value of the decoder 13 and the flip-flop 11 is reset. Therefore, the ON time of the switch element 4 becomes a constant value until the frequency division counter 9 counts the decoded value of the decoder 13. In the OFF period of the switch element 4, the energy stored in the inductance 3 in the ON period generates counter electromotive force and passes through the diode 5. Further, it is smoothed by the smoothing capacitor 6 and supplied to the load 7. When the supply of energy is completed, the current flowing through the inductance 3 decreases, and the current detecting means 8 detects that it has become zero and sets the flip-flop 11 again. As described above, the current waveform of the inductance 3 becomes close to the output voltage waveform of the rectifier 2 when the ON period of the switch element 4 is constant. Therefore, by repeating the above operation, the DC voltage can be supplied to the load 7 with a high power factor. In order to control the voltage to be supplied, the inductance 3 is applied during the ON period of the switch element 4.
The ON period of the switch element 4 may be controlled by changing the energy stored in. Another embodiment of the present invention will be described with reference to FIG. This is an example in which the DC voltage is fed back to stabilize the voltage. In the figure, the same blocks as in FIG. 1 are assigned the same numbers. The current detecting means 8 is a differentiating circuit and detects that the current flowing through the inductance 3 has become zero. 10 is an OR gate,
12 is a decoder, 30 is an A / D converter, 31 is a comparator, 32 is a filter circuit, 33 is an up / down counter, 34 is a comparator, and 35 is a reference generation circuit. The output voltage is converted into digital data by the A / D converter 30 and input to the comparator 31. Comparator 31
Then, the A / D conversion result of the output voltage is compared with a predetermined reference value. The filter circuit 32 is a filter composed of a logic circuit, and integrates the output of the comparator 31 that arrives in time series and discretely on the time axis to remove the influence of noise and the like, and the current output voltage becomes the reference value. Outputs whether it is larger or smaller. The up-down counter 33 performs up-counting when the output voltage from the output of the filter circuit 32 is smaller than the reference value, and performs down-counting when the output voltage is opposite. The comparator 34 is the frequency division counter 9
And the outputs of the up / down counter 33 are compared with each other, and when both outputs match, the flip-flop 11 is reset. That is, the output of the up / down counter 33 is in the ON period of the switch element 4 as it is, and the output voltage increases when up-counting and decreases when down-counting. With the configuration described above, the output voltage can be stabilized by the feedback control. Further, since the current detecting means 8 is a differentiating circuit, it is possible that the current detecting means 8 does not operate during a period when the output voltage of the rectifier 2 is low, that is, during a period when the current of the inductance 3 is small or immediately after the power is turned on. In this case, since the flip-flop 11 is set by the decode value of the decoder 12, the switch element 4 is turned off.
There is no continuous FF. Therefore, no special start circuit is required. In this case, the OF of the switch element 4
Although the F period increases, the output voltage of the rectifier 2 is low, so there is almost no deterioration in the power factor. In this embodiment, most of the circuits within the dotted line in FIG. 3 are composed of logic circuits, which is suitable for integration into an integrated circuit. Further, since the output voltage can be controlled only by changing the reference value, it is easy to realize intelligence by the microcomputer. Further, if an inverter circuit of a fluorescent discharge lamp is connected to the load, dimming can be easily performed by the present invention. Furthermore, it is obvious that the effect of the present invention will not change even if a transformer is used instead of the inductance of the embodiment and the output voltage is obtained from the secondary side.

According to the present invention, the switch element is turned on.
Since OFF is generated from the output of the counter that divides the source oscillation frequency, a start circuit for starting control is not required. Further, since many of the constituent elements are logic circuits, it is possible to supply a power supply circuit which can be easily miniaturized by an integrated circuit and made intelligent by a microcomputer and which has a high power factor.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the present invention used in (Example 1).

[Fig. 2] Current waveform of rectifier output voltage and inductance

FIG. 3 is a schematic diagram of the present invention used in (Example 1).

[Explanation of symbols]

 1 ... AC power supply 2 ... Rectifier 3 ... Inductance 4 ... Switch element 5 ... Diode 6 ... Capacitor 7 ... Load 8 ... Current detection means 9 ... Dividing Counter 10 ... OR gate 11 ... Flip-flop 12, 13 and 34 ... Decoder 14 ... Oscillator 20 ... Rectifier output voltage 21 ... Inductance current 30 ... A / D converter 31. ..Comparator 32 ... Filter circuit 33 ... Up-down counter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhisa Senba 69 Wakashiba-cho, Ryugasaki-shi, Ibaraki Hitachi Lighting Co., Ltd.Ryugasaki Factory (72) Inventor Ikuo Nakazawa 69 Wakashiba-cho, Ryugasaki-shi, Ibaraki Hitachi Lighting Co., Ltd. Ryugasaki Plant (72) Inventor Naoto Nakagawa 69 Wakashiba-cho, Ryugasaki-shi, Ibaraki Hitachi Lighting Co., Ltd. Ryugasaki Plant

Claims (1)

[Claims] A switching power supply including a rectifier for rectifying an AC voltage, an inductance, a switch element, a diode, and a capacitor has detection means for detecting a current flowing through the inductance, and the switch element has a detection means for detecting that the current is not flowing through the inductance. ON when detected
However, the power supply circuit is characterized in that it is turned off after a predetermined time has passed.