JP3287651B2 - Switching 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 switching power supply for converting an AC input to DC by interposing an AC input between an inverter circuit for lighting a discharge lamp at high frequency and the like.

[0002]

2. Description of the Related Art AC input is full-wave rectified by a rectifier,
In a switching power supply device that performs smoothing after power conversion at a high frequency, generally, a so-called capacitor input type in which a smoothing capacitor is connected is often used.

A capacitor input type rectifying / smoothing circuit has a large input current peak value and a conduction angle t ₁ , as shown in FIG.
However, not only the input power factor is poor due to the narrowing, but also the content of the harmonic component is high.

In recent years, in order to solve such a disadvantage, as shown in a 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 a rectifier 1. A method of connecting a DC-DC converter 2 and controlling the input current waveform to be substantially the same as the input voltage waveform has been put into practical use (for example, Transistor Technology, March 1988).

In the circuit shown in FIG. 8, a control circuit (for example, a TDA manufactured by Siemens Corporation) for supplying a drive signal to the switching transistor 22 of the DC-DC converter 2 is used.
In 4814) 300, flows through the pulsating voltage from the rectifier 1 dividing the signal by the resistor R ₁ and R _2, the detection signal V ₀ which output voltage detection signal A _S of the current flowing through the switching transistor 22, and the coil 21 As shown in FIG. 9, the maximum value A _MAX of the current (switching current) flowing through the switching transistor 22 is regulated using the current detection signal so that the switching current _AS flows as shown in the switching transistor 22. , The switching transistor 22 is driven in a self-excited manner. This drive signal is therefore 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 sinusoidal waveform substantially similar to the AC voltage waveform, and the input power factor is also brought close to 1. It becomes possible.

However, since the switching transistor 22 operates in a self-excited manner, its drive signal is
As is clear from 0, various frequencies are included, and various noises are generated from the transistor 22 that is switching-controlled by such a signal. When such noise is sent out on the line,
Noise from each electrical device interacts with each other and causes an unexpected large accident. Filters are required to prevent such accidents, but due to the wide variety of noise frequencies, the filters inevitably require a large amount of cost, which poses a major problem in practical economics. Has become.

The present invention has been made in view of such circumstances, and can obtain a high power factor equivalent to the self-excited type under a simple circuit configuration as compared with the self-excited type. In addition, it is an object of the present invention to provide a switching power supply device that can greatly simplify noise countermeasures and can achieve a significant cost reduction particularly in mass production.

[0009]

In order to achieve the above object, a switching power supply according to the present invention includes a choke coil 2 connected to a DC power supply obtained by full-wave rectifying an AC input by a rectifier 1.
1, a DC-DC converter 2 composed of a switching element 22, a diode 23, and a smoothing capacitor 24 is connected, and the switching element 22 is switched by a drive signal from a control circuit 3 so that a DC constant voltage is output from the smoothing capacitor 24. In the power supply device, the control circuit 3 is switched to one of two different frequencies f and 3f, or f and 5f, of a comparison circuit means 31 for comparing an input voltage from a DC power supply with a reference voltage. The switching element 22 is configured to be turned on and off at a frequency f when the input voltage exceeds the reference voltage, and at a frequency 3f or 5f in the following states when the input voltage exceeds the reference voltage. Can be

[0010]

The reason why the switching operation of the conventional switching power supply device illustrated in FIG. 8 is self-excited is that 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 becomes a sine wave. When changing in each cycle according to the
In order to gain the reverse recovery time of No. 3. In other words, if the peak value of the current flowing through the switching transistor 22 is large, the next switching cycle is entered before the reverse recovery time of the diode 23 elapses, and the switching transistor is switched until the current flowing through the coil 21 becomes zero. 22 is turned on, a short-circuit current flows through the diode 23, causing noise and causing a large switching loss. 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
The switching frequency of 2 is f and 3f (or f and 5f)
When 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 during which the current flowing through the coil 21 becomes 0 is short. The switching frequency of the switching transistor 22 is set to 3
When the pulsating voltage exceeds a predetermined value, the switching frequency is reduced to f to prevent switching by the reverse recovery time of the diode 23. This prevents a short circuit current from flowing through the diode 23 and prevents the occurrence of switching loss without performing the self-excited operation.

By thus fixing the switching frequency of the switching transistor 22 to two types and setting the frequencies to f and 3f or f and 5f, noise countermeasures can be reduced as compared with the circuit configuration of FIG. It is 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 subjected to full-wave rectification by the rectifier 1 via the line filter 11. The DC-DC converter 2 is the same as that shown in FIG. 8 and includes 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 one of a constant frequency f and a frequency 3f three times as high as described later. .

A control circuit 3 compares a reference voltage V _R with a voltage signal V ₁ obtained by dividing the pulsating voltage from the rectifier 1 by resistors R ₁ and _{R 2,} and an oscillation frequency based on an output of the comparator 31. Mainly includes an oscillation circuit 32 that switches to f or 3f, and a signal from the oscillation circuit 32 becomes a drive signal for the switching transistor 22.

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

The oscillation circuit 32 is a relaxation oscillation circuit in which the output is a square wave, and the resistance, which determines the frequency of the oscillation together with the capacitor 32b, changes according to the output from the comparator 31, and the oscillation frequency is either f or 3f. It has been adjusted to be. That is, the output of the comparator 31 is connected to the transistor 32 via the resistor R4 and the diode 35.
is turned on / off, and when the transistor 32a is in the off state, the resistor R5 and the adjusting resistor R6 function as a deciding element of the oscillation frequency of the oscillation circuit 32, and the oscillation frequency is set to f, and the transistor 32a is turned on. Only when it is located, the resistors R7 and R8 are connected in parallel with the resistors R5 and R6, and the oscillation frequency increases to 3f.

[0018] With the above arrangement, the output of the oscillation circuit 32 as an example of a time chart of signal waveforms in Figure 2, i.e. the frequency of the drive signal of the switching transistor 22, the pulsating voltages 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 required for the current flowing through the choke coil 21 to become 0 becomes longer when the input pulsation voltage is large and becomes shorter when the input pulsation voltage is small.
Even when the switching transistor 22 is switched by the drive signal of FIG. 2, no short-circuit current occurs in the diode 23, and no switching loss occurs.

Further, since the switching operation of the switching transistor 22 is separately excited and its frequency is fixed at f and 3f, not only the circuit configuration is simple, but also its noise countermeasures are smaller than those of the circuit of FIG. It is greatly simplified.

In the above embodiment, one switching frequency f of the switching transistor 22 is set to 23.3.
FIG. 3 shows the result of actually measuring the input current at 6 kHz (the other frequency 3f is 70.08 kHz), and FIG. 4 shows the current flowing through the diode 23 in the long period (A) by changing the time axis. The result of actually observing a portion having a large pulsation voltage in a short cycle (B) is shown. As is clear from these figures, the input current waveform was not perfect, but could be substantially a sine wave, and it was confirmed that no short-circuit current was flowing through the diode 23 at all.

Further, at this time, the load was set to 1 kΩ, the input power was changed between 90% and 110%, and the power factor and output power at that time were 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 was no problem such as switching loss.

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

FIG. 6 is a circuit diagram of another embodiment of the present invention. In this figure, the same reference numerals are given to the same elements as those in FIG. 1 and the description thereof is omitted. However, the feature of the embodiment of FIG. 6 is that the pulsating voltage from the rectifier 1 is changed by resistors R1 and R2. The voltage signal V ₁ divided by the above 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 connected to -D via a resistor R10.
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 configuration, 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 and off depending on whether or not the pulsation voltage is greater than the zener voltage of the zener diode 33. As in the previous embodiment, the oscillation circuit 32 operates at the frequency 3f while the pulsation voltage is small and increases when the pulsation voltage is large. 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.
The switching frequency may be f, and in this case, substantially the same operation and effect can be obtained as well as the efficiency and noise countermeasures.

[0029]

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

Moreover, the switching frequency is f and 3f
(Or f and 5f)
The noise countermeasures can be greatly simplified as compared with the self-excited type, which is extremely advantageous in terms of practical costs in addition to the simplicity of the circuit configuration described above.

[Brief description of the 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 a signal waveform of each unit in the control circuit 3;

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

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

FIG. 5 is a graph showing the results of actual measurement of the harmonic content in 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 diagram showing an example of a self-excited operation type switching power supply device using a conventional DC-DC converter.

FIG. 9 is an explanatory diagram of the operation of the conventional device of FIG. 8;

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 Oscillation circuit 32a Transistor 33 Zener diode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-91731 (JP, A) JP-A-4-212812 (JP, A) JP-A-3-195355 (JP, A) JP-A-63- 265562 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/00-3/44 H02M ^7/ 00-7/40

Claims (1)

(57) [Claims] 1. A DC-DC converter comprising a choke coil, a switching element, a diode, and a smoothing capacitor is connected to a DC power supply obtained by performing full-wave rectification on an AC input by a rectifier, and the switching element is supplied from a control circuit. A power supply device that switches by a drive signal to obtain a constant DC voltage from the smoothing capacitor,
The control circuit includes a comparison circuit unit that compares an input voltage from the DC power supply with a reference voltage, and an oscillation circuit that can switch an oscillation frequency between two different frequencies f and 3f or f and 5f. A switching power supply device for turning on / off the switching element at a frequency f when the input voltage exceeds the reference voltage, and at a frequency 3f or 5f when the input voltage is below the reference voltage.