JPH0715951A - Switching power supply - Google Patents

Abstract

PURPOSE:To provide a switching power supply that achieves the same high power factor and efficiency as conventional self-excited types in spite of its simpler circuit constitution and that allows the significant simplification of noise preventive measures and the significant cost reduction for the purpose of practical use. CONSTITUTION:This switching power supply consists of a control circuit 3 that supplies driving signals to the switching element 22 of a DC-DC converter 2; a comparator 31 that compares the input pulsating voltage from a rectifier 1 with reference voltage; and a oscillation circuit 32 the oscillation frequency of which is switchable between two different frequencies f and 3f (or f modified by '5'). The power supply is so constituted that the switching element 22 is turned on/off at a frequency of f when input pulsating voltage is above the reference voltage and at 3f (or 5f) when the former is below the latter.

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 for converting an alternating current input into a direct current by interposing, for example, a discharge lamp between an inverter circuit for high frequency lighting and an alternating current input.

[0002]

2. Description of the Related Art Full-wave rectification of an AC input by a rectifier,
Generally, a so-called capacitor input type in which a smoothing capacitor is connected is often used as a switching power supply device that smoothes after converting power at a high frequency.

The capacitor input type rectifying and smoothing circuit has a large peak value of the input current and a conduction angle t _{1 as} shown in the input voltage waveform and the input current waveform in FIG.
Has a drawback that not only the input power factor is poor due to narrowing, but also the content rate of harmonic components is high.

Therefore, in recent years, in order to solve such a drawback, as shown in the circuit diagram of FIG. 8, a choke coil 21, a switching transistor 22, a diode 23 and a smoothing capacitor 24 are connected to an output terminal of the rectifier 1. A system in which the DC-DC converter 2 is connected and the input current waveform is controlled to have almost the same shape as the input voltage waveform has been put into practical use (eg, transistor technology 1988, March issue).

In the circuit of FIG. 8, a control circuit for supplying a drive signal to the switching transistor 22 of the DC-DC converter 2 (for example, TDA manufactured by Siemens Co., Ltd.)
4814) 300, the pulsating voltage from the rectifier 1 is divided by the resistors R ₁ and R ₂ , a detection signal V ₀ of the output voltage, a detection signal A _{S of the} current flowing through the switching transistor 22, and the coil 21. As shown in FIG. 9, the current detection signal is used to regulate the maximum value A _MAX of the current (switching current) flowing in the switching transistor 22 so that the switching current A _S as shown in the drawing flows in the switching transistor 22. , Drive the switching transistor 22 in a self-excited manner. Therefore, this drive signal becomes a signal as illustrated in FIG.

[0006]

By the way, according to the circuit shown in FIG. 8, the waveform of the AC input current is controlled in a sine wave shape which is substantially similar to the waveform of the AC voltage, and the input power factor approaches 1 as well. It becomes possible.

However, since the switching transistor 22 operates in a self-excited manner, its drive signal is as shown in FIG.
As is clear from 0, various frequencies are included, and various noises are generated from the transistor 22 switching-controlled by such a signal. When such noise is sent to the line,
The noise from each electric device affects each other and causes an unexpected big accident. A filter is necessary to prevent such an accident, but due to the wide variety of noise frequencies, the filter inevitably requires a large amount of cost, which is a major obstacle to practical economics. Has become.

The present invention has been made in view of the above circumstances, and a high power factor equivalent to this can be obtained with a simple circuit configuration as compared with the self-excited type described above. Moreover, it is an object of the present invention to provide a switching power supply device capable of significantly simplifying noise countermeasures and significantly reducing cost particularly during mass production.

[0009]

In order to achieve the above object, the switching power supply device of the present invention comprises a DC power supply in which an AC input is full-wave rectified by a rectifier 1 and a choke coil 2.
1, a DC-DC converter 2 including a switching element 22, a diode 23, and a smoothing capacitor 24 is connected, the switching element 22 is switched by a drive signal from the control circuit 3, and a constant DC voltage is applied from the smoothing capacitor 24. In the power supply device for obtaining the above, the control circuit 3 is switched to the comparison circuit means 31 for comparing the input voltage from the DC power supply with the reference voltage, and the oscillation frequency to either of two frequencies f and 3f or f and 5f different from each other. The oscillating circuit 32 is capable of turning on / off the switching element 22 at the frequency f when the input voltage exceeds the reference voltage, and at the frequency 3f or 5f in the following states. To be

[0010]

In the conventional switching power supply device illustrated in FIG. 8, the switching operation is self-excited because the peak value of the current flowing through the switching transistor 22 is changed to the input voltage waveform so that the input current waveform is a sine wave. In order to change each period according to
This is to gain the reverse recovery time of 3. That is, when the peak value of the current flowing through the switching transistor 22 is large, the next switching cycle is started before the reverse recovery time of the diode 23 elapses, and the switching transistor is switched before the current flowing through the coil 21 becomes zero. 22 is turned on, a short-circuit current flows through the diode 23, which causes noise, and a large switching loss occurs. To prevent this, after the current flowing through the coil 21 becomes zero, This is because the next switching operation is started.

In the present invention, the switching transistor 2
2 switching frequencies f and 3f (or f and 5f)
In the state where the peak value of the current flowing through the switching transistor 22 is small, that is, when the pulsating voltage from the rectifier 1 is equal to or less than a predetermined value, the time when the current flowing through the coil 21 becomes 0 is short. Use the switching frequency of the switching transistor 22 to 3
It is set to f (or 5f), and when the pulsating voltage exceeds a predetermined value, the switching frequency is slowed down to f to prevent switching by the reverse recovery time of the diode 23. This prevents the short-circuit current from flowing through the diode 23 and the occurrence of switching loss without performing the self-excited operation.

By fixing the switching frequency of the switching transistor 22 to two types and setting the frequency to f and 3f or f and 5f in this way, noise countermeasures can be made as compared with the circuit configuration of FIG. Greatly facilitated.

[0013]

FIG. 1 is a circuit diagram of an embodiment of the present invention. The AC input 10 is input to the DC-DC converter 2 after being full-wave rectified by the rectifier 1 via the line filter 11. The DC-DC converter 2 is the same as that shown in FIG. 8, and is composed of a choke coil 21, a switching transistor 22 shunt-connected to the choke coil 21, a diode 23 for preventing backflow, and a smoothing capacitor 24. ing.

The switching transistor 22 of the DC-DC converter 2 is turned on / off in a separately excited manner by a drive control signal from the control circuit 3 at either a constant frequency f or a frequency 3f which is three times as high as described later. .

The control circuit 3 compares the pulsating voltage from the rectifier ₁ with the voltage signal V ₁ obtained by dividing the pulsating voltage by the resistors R1 and R2 and the reference voltage V _R, and the output of the comparator 31 causes the oscillating frequency. Mainly includes an oscillation circuit 32 that switches to f or 3f, and a signal from the oscillation circuit 32 serves as a drive signal for the switching transistor 22.

The reference signal V _R of the comparator 31 is the pulsating voltage from the rectifier 1 and the Zener diode 33 and the resistor R.
It is obtained by making the voltage constant at 3. Further, the capacitors 41 and 42, the diode 43, and the resistor R40 are for obtaining the constant voltage power source of the control circuit 3.

The oscillating circuit 32 is a relaxation oscillating circuit whose output is a square wave, and the resistance which is a factor for determining the frequency together with the capacitor 32b is changed by the output from the comparator 31, and its oscillating frequency is either f or 3f. Has been adjusted to be. That is, the output of the comparator 31 is transmitted through the resistor R4 and the diode 35 to the transistor 32.
When a is turned on / off and the transistor 32a is in the off state, the resistor R5 and the adjusting resistor R6 function as elements for determining the oscillation frequency of the oscillation circuit 32 to set the oscillation frequency to f, and the transistor 32a is turned on. Only in the state of 1), the resistors R7 and R8 are connected in parallel to the resistors R5 and R6, and the oscillation frequency is increased to 3f.

With the above configuration, as shown in the example of the time chart of the signal waveform of each part in FIG. 2, the output of the oscillation circuit 32, that is, the frequency of the drive signal of the switching transistor 22 is the pulsating voltage V ₁ from the rectifier _1. 3f in the following state reference voltage V _R, becomes f is in a state of exceeding the reference voltage V _R.

As described above, the time until the current flowing in the choke coil 21 becomes zero becomes long when the input pulsation voltage is large and becomes short when the input pulsation voltage is small.
Even if the switching transistor 22 is switched by the drive signal of FIG. 2, a short-circuit current does not occur in the diode 23 and a switching loss does not occur.

Moreover, since the switching operation of the switching transistor 22 is of the separately excited type and its frequency is fixed at f and 3f, not only the circuit structure is simple, but also its noise countermeasure is lower than that of the circuit of FIG. Greatly simplified.

In the above embodiment, one switching frequency f of the switching transistor 22 is set to 23.3.
The input current is measured at 6 kHz (the other frequency 3f is 70.08 kHz) in FIG. 3, and in FIG. The result of actually observing a portion with a large pulsating voltage in a short cycle (B) is shown. As is clear from these figures, it was confirmed that the input current waveform could be a waveform close to a sine wave although it was not perfect, and that no short-circuit current was flowing through the diode 23.

Further, at this time, the load is set to 1 kΩ, the input power is changed in the range of 90 to 110%, and the power factor and the output power at that time are measured.

[0023]

[Table 1] As is clear from Table 1, both the power factor and the efficiency were close to 1, and it was found that there were no problems such as switching loss.

Then, the harmonic content was measured, and the results shown in FIG. 5 were obtained. These results are summarized in the table and the T of IEC standard 77A (Secretariat) 82 is obtained.
able

Table 2 is shown together with 2.

[Table 2] As shown in Table 2, it was confirmed that all the harmonics with respect to the fundamental wave satisfied the above-mentioned standards.

FIG. 6 is a circuit configuration diagram of another embodiment of the present invention. In this figure, elements equivalent to those in FIG. 1 are assigned the same reference numerals and explanations thereof are omitted, but the characteristic of the embodiment of FIG. 6 is that the pulsating voltage from the rectifier 1 is applied to resistors R1 and R2. The voltage signal V ₁ divided by is connected to the cathode of the Zener diode 33, and the anode of the Zener diode 33 is connected to the base of the transistor 36 via the resistor R9. The emitter of the transistor 36 is -D via the resistor R10.
In addition to being connected to C, the collector is connected to the base of the transistor 32a via the resistor R4 and the diode 35 and to the positive voltage level via the resistor R3.

According to this structure, only when the pulsating voltage exceeds the Zener voltage of the Zener diode 33, the reverse current turns on the transistor 36, and the forward voltage applied to the transistor 32a is removed. 32a is turned off. That is, the transistor 32a is turned on / off depending on whether or not the pulsating voltage is higher than the Zener voltage of the Zener diode 33, and the oscillation circuit 32 becomes large at the frequency 3f while the pulsating voltage is small, as in the previous embodiment. It oscillates at the frequency f and drives the switching transistor 22 of the DC-DC converter 2.

In each of the above embodiments, the switching frequency of the switching transistor 22 is set to f and 3.
Although an example in which f is set is shown, the present invention is not limited to this, and f and 5
The switching frequency of f may be used, and in this case as well, it is possible to obtain substantially the same operational effects including efficiency and measures against noise.

[0029]

As described above, according to the present invention,
Switching transistor of DC-DC converter,
Two different frequencies f and 3f (or f and 5)
The frequency is 3f (or 5f) when the pulsating voltage from the rectifier is less than or equal to the predetermined value, and the frequency is 1/3 (or 1/5) when the pulsating voltage from the rectifier is less than or equal to the predetermined value. Since it is configured to be turned on / off by f, it has a simple circuit configuration compared to the conventional self-excited operation type switching power supply device, and is short-circuited to the diode for preventing reverse current in the DC-DC converter. The input current waveform can be approximated to the input voltage waveform without causing current flow or switching loss, and the power factor and efficiency can be made equal to those of the conventional self-excited type.

Moreover, the switching frequencies are f and 3f.
(Or f and 5f) because it is fixed to two types,
The noise countermeasure can be greatly simplified as compared with the self-excited type, and in addition to the simple circuit configuration described above, it is also extremely advantageous in terms of practical cost.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a time chart showing an example of signal waveforms of respective parts in the control circuit 3.

FIG. 3 is a graph showing an actual measurement result of an input current waveform according to an embodiment of the present invention.

FIG. 4 is a graph showing a measurement result of a current flowing through the diode 23 in the embodiment of the present invention.

FIG. 5 is a graph showing the actual measurement result of the harmonic content rate of the example of the present invention.

FIG. 6 is a circuit configuration diagram of another embodiment of the present invention.

FIG. 7 is a graph showing an input voltage waveform and an input current waveform together in a conventional capacitor input type switching power supply device.

FIG. 8 is a circuit configuration diagram showing an example of a self-excited operation type switching power supply device using a conventional DC-DC converter.

9 is an explanatory diagram of the operation of the conventional device of FIG.

10 is a graph showing an example of a drive signal waveform of a switching transistor in the conventional device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 rectifier 11 line filter 2 DC-DC converter 21 choke coil 22 switching transistor 23 backflow prevention diode 24 smoothing capacitor 3 control circuit 31 comparator 32 oscillator circuit 32a transistor 33 zener diode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H05B 41/24 F 9249-3K

Claims (2)

[Claims] 1. A DC-DC converter including a choke coil, a switching element, a diode, and a smoothing capacitor is connected to a DC power source obtained by full-wave rectifying an AC input with a rectifier, and the switching element is connected to a control circuit. In a power supply device that is switched by a drive signal to obtain a constant DC voltage from the smoothing capacitor,
The control circuit includes a comparison circuit means for comparing the input voltage from the DC power supply with a reference voltage, and an oscillation circuit capable of switching the oscillation frequency between two different frequencies f and 3f or f and 5f. A switching power supply device, which is configured to turn on / off the switching element at a frequency f when the input voltage exceeds the reference voltage and at a frequency 3f or 5f in the following states. 2. The switching power supply device according to claim 1, wherein the frequency f is 20 to 29.5 kHz.