JPH05260750A - Ac/dc converter - Google Patents

Abstract

PURPOSE:To increase a power factor of an AC/DC converter which receives a commercial AC power supply and generates a DC output. CONSTITUTION:In an AC/DC converter wherein a main circuit is constructed of a rectifier circuit RC1, a field-effect transistor Q1, a transformer Tr1 and a rectifier circuit RC2, a choke coil L1 and a diode D1 are inserted between the rectifier circuit RC1 and a smoothing capacitor C1, and a capacitor C3 and a parallel circuit of a choke coil L3 and a capacitor C4 are connected between the node of the choke coil L1 and the diode D1 and the node of the field-effect transistor Q1 and a primary winding n1. A time ratio control for stabilizing an output and a phase control for preventing an excess of a charging voltage of the capacitor C1 are applied to a control circuit U1 executing a control to drive the field-effect transistor Q1, so as to improve further an input power factor.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC / DC converter for converting a commercial AC input power supply voltage into a stable DC output voltage, and more particularly to a high power factor AC / DC converter.

2. Description of the Related Art Conventionally, as an AC / DC converter which receives a commercial AC power source and converts it into a DC voltage, for example, there is one shown in FIG. In the figure, the AC input voltage Ei
Input rectifier circuit RC1 for full-wave rectification, smoothing capacitor C1,
AC input voltage Ei by AC / DC converter composed of field effect transistor Q1, which is a switching element, transformer Tr1, transformer reset diode D4, output rectifying diode D2, flywheel diode D3, output smoothing choke coil L2, and output smoothing capacitor C2 Is converted to a stable DC output voltage Eo. However, in such a conventional AC / DC converter, although the output DC voltage has a desirable characteristic, the waveform of the input current corresponds only to the peak value of the input AC voltage as shown in FIG. Since it does not flow, the power factor is low, around 0.5 to 0.7. There is a method of inserting and connecting a sufficiently large choke coil in the rectifier circuit to improve the power factor, but it has the drawback of large size and weight. In recent years, a method of electronically improving the power factor by providing a front converter for power factor improvement has been partially used. However, the number of components is increased, the size is increased, the price is high, and the mutual interference of switching elements is large. There was a problem of inviting.

SUMMARY OF THE INVENTION It is an object of the present invention to obtain a compact, lightweight and economical high power factor AC / DC converter circuit with a simple circuit configuration.

In order to solve this problem, the present invention rectifies / smooths an AC input voltage and turns on / off this rectified voltage at a high frequency by means of a semiconductor switching element so that the primary voltage of a transformer is changed. In a converter circuit that is applied to the winding to obtain a high-frequency AC voltage in the secondary winding and rectifies and smoothes this high-frequency AC voltage to obtain a predetermined voltage, the input rectifier circuit and the input smoothing capacitor A choke coil for boosting and a diode are inserted between them, and a resonance capacitor is connected to the connection point of this boosting choke coil and diode and the connection point of the transformer and switching element.
The first means is to provide another parallel resonant circuit of a choke coil and a capacitor. The second means is to drive the semiconductor switching element at an ON / OFF drive frequency that increases in accordance with an increase in the terminal voltage of the smoothing capacitor. The present invention proposes a high power factor AC / DC converter having such characteristics.

The AC / DC converter of this construction is one switching element, and the former stage is a so-called chopper circuit, which forms a converter which receives the output capacitor of this chopper circuit and switches at a high frequency. The input current waveform of the chopper circuit in the previous stage operates with a waveform close to the input voltage which is a sine wave. According to the above-mentioned first means, the parallel resonant circuit becomes almost capacitive when the transfer energy is large, and equivalently, there is no limitation on the charging energy to the chopper circuit, and conversely when the transfer energy is small, the parallel resonant circuit is parallel. The impedance of the resonance circuit becomes large and equivalently limits the charging energy to the chopper circuit. According to the second means, the frequency rises as the voltage of the smoothing capacitor rises, and the conduction of the chopper is cut off in the short ON period, so that the input current is correspondingly limited. Either means acts to further correct the excess or deficiency of the charging energy of the smoothing capacitor, thus reducing the distortion of the input AC current.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An AC / DC converter according to the present invention will be described with reference to FIG. As shown in Fig. 1, the commercial AC power supply Ei is connected to the input terminals X1 and X2 in a bridge type rectifier circuit.
Connect to RC1. The DC output terminal of the rectifier circuit RC1 is supplied to the smoothing capacitor C1 via the choke coil L1 and the diode D1. At the connection point between choke coil L1 and diode D1, capacitor C3 and choke coil L3 are connected.
The drain electrode of the field effect transistor Q1 is connected through a parallel circuit of the capacitor C4 and the capacitor C4, and its emitter is connected to the negative electrode of the capacitor C1. The gate terminal of the field effect transistor Q1 is turned on / off at a high frequency of 100 kHz to 200 kHz by the control circuit U1 for the switching regulator. Here, the terminal voltage of the capacitor C1 is connected to the input terminal of the detection / comparison circuit DET2, in which the terminal voltage of the capacitor C1 is compared with the reference voltage and the error voltage is amplified and output. The output voltage of the detection / comparison circuit DET2 is connected to the terminal 6 of the control circuit U1 via the resistor R1. Here, the control circuit U1 is a TL49 from Texas Instruments, which is an integrated circuit for switching power supplies that is widely used.
This is a general circuit configured by adding an output current amplifier circuit and some auxiliary components to 4 or equivalent. The terminal 6 of the control circuit U1 is a terminal for setting the charging rate of the internal relaxation oscillation circuit. When the voltage injected to this terminal becomes high, the charging cycle becomes long, the oscillation frequency drops to 100kHz, and vice versa. The oscillating frequency is set to increase up to about 200kHz when the voltage is low. These parts are rectifier chopper circuits. That is, input commercial AC power supply Ei (100V 50H
The field effect transistor Q1 is repeatedly turned on and off at a high frequency of 100 kHz to 200 kHz via the choke coil L1 and the capacitor C3 and the parallel circuit of the choke coil L3 and the capacitor C4 by rectifying z) by the rectifier circuit RC1. The operation of the parallel circuit of the choke coil L3 and the capacitor C4 will be described later, so short circuit will be considered here. Here, the choke coil L1 is about 500 μH, the capacitor C3 is 0.02 μF,
C1 was chosen to be 200 μF. First, field effect transistors
When Q1 is on, current that charges capacitor C3 flows from choke coil L1. This current is the capacitor C3
The voltage flows to the voltage of capacitor C1 until it reaches the voltage of capacitor C1, and energy is stored in these choke coil L1 and capacitor C3. Next, when the field effect transistor Q1 is turned off, the current energy stored in the choke coil L1 charges the capacitor C1 through the diode D1. The capacitance of the capacitor C1 is large enough,
In the steady state, the DC voltage Eb is kept almost constant. Since the input AC current always passes through the choke coil L1, the current is continuous. The positive terminal of the capacitor C1 is then connected to the drain of the field effect transistor Q1 via the primary winding n1 of the transformer Tr1. The secondary winding n2 of the transformer Tr1 is connected to the smoothing capacitor C2 via the rectifying diode D2 and the smoothing choke coil L2, and the DC output terminals Y1, Y
Also connected to 2. These DC output terminals Y1 and Y2 are
The comparison circuit DET1 is connected, and its output is connected to the detection input terminal of the control circuit U1 via the photocoupler Q2. Here, the detection / comparison circuit DET1 is composed of a resistance voltage divider and a constant voltage diode. The photocoupler Q2 selects a withstand voltage sufficient to insulate the commercial AC power supply Ei. A diode D3 acting as a flywheel is connected between the other terminal of the secondary winding n2 of the transformer Tr1 and the connection point between the diode D2 and the choke coil L2. This part has a so-called forward converter function and a reset function for the transformer Tr1 due to the natural vibration of the capacitor C3 and the primary winding n1 of the transformer Tr1. When the field effect transistor Q1 is on, the accumulated charge in the capacitor C1 supplies power to the output terminal through the primary winding n1 of the transformer Tr1 and the subsequent circuits, and the field effect transistor Q1 is off. At this time, the energy of the current flowing through the primary winding n1 of the transformer Tr1 flows through the path of the capacitor C3 and the diode D1 and the transformer Tr1
And the voltage of the capacitor C3 is inverted. Next, the operation will be described in detail. First, the internal oscillation frequency of the control circuit U1 is fixed, and the parallel circuit of the choke coil L3 and the capacitor C4 is omitted. It is assumed that the switching frequency of the field effect transistor Q1 is sufficiently higher than the frequency of the input AC power supply. Therefore, the input voltage is considered to be constant during one cycle of switching, and since the choke coil L1 is sufficiently large with respect to the switching frequency, it can be considered to be almost constant current. Therefore, although the integrated amount of the input current in one switching cycle is affected by the AC input voltage, if a simulation is performed for one cycle of the AC frequency, a waveform like a DC component superimposed on a sine wave is obtained. The waveform has a power factor of about 0.98, and the distortion factor of the input current corresponds to 20%. The output voltage of the forward coupling converter is determined by the voltage applied to the primary winding n1 of the transformer Tr1 and its duty ratio in the range where the current of the filter choke coil L2 is not cut off. Therefore, the control circuit U1 performs duty ratio control to compensate the voltage fluctuation of the converter circuit so that the output voltage is kept constant with respect to the load fluctuation. In this converter circuit, field effect transistor Q1 which is a switching element
The duty ratio control is performed so that the output voltage is constant with only one. On the other hand, the field-effect transistor Q1 is controlled by the same duty ratio as the switching element of the chopper circuit against the fluctuation of the AC input voltage, but as a result, the internal circuits are mutually controlled so as to maintain a stable DC output voltage. .. However, the charging voltage of the smoothing capacitor C1 tends to rise when the load is light. The reason why the voltage of the smoothing capacitor C1 rises when the load is light is that the energy stored in the choke coil L1 is charged to the voltage of the capacitor C1 every cycle of the field effect transistor Q1 regardless of the load power. This is because the amount does not change much. Therefore, if the charge amount of the capacitor C3 can be controlled, the voltage of the capacitor C1 can be controlled. This state will be described with reference to FIG. 2. The charge amount of the capacitor C3 is determined by the potential difference between the negative output terminal of the rectifier circuit and the point b when the field effect transistor Q1 is on. Therefore, the larger the potential difference between the points a and b with reference to the point b, the smaller the potential difference. Therefore, the voltage of the capacitor C1 can be controlled by controlling this potential difference. Field effect transistor Q1
There are two means for controlling the potential difference between the points a and b when the switch is turned on. First, the free vibration of the capacitor C4 and the choke coil L3 is used as the first means. By controlling the on-phase of field effect transistor Q1 during free oscillation of capacitor C4 and choke coil L3 according to the voltage of capacitor C1, capacitor C3
Control the amount of charge. For example, when the load becomes lighter and the voltage of C1 becomes higher, the ON phase of the field effect transistor Q1 is moved to the one where the voltage of the capacitor C4 and the choke coil L3 becomes higher with reference to the point b, that is, the ON point is delayed. As a result, the potential difference between the points a and b is reduced, and the charge amount of the capacitor C3 is reduced. Then, the amount of energy stored in the choke coil L1 is reduced and the voltage rise of the capacitor C1 is suppressed. Here, the operation of the parallel circuit of the choke coil L3 and the capacitor C4 will be described in more detail. Generally, the frequency characteristic of a parallel resonant circuit of an inductance and a capacitor has an impedance maximum at its natural frequency fn, is capacitive at frequencies higher than the natural frequency fn, and is inductive at frequencies lower than the natural frequency fn. And by utilizing this characteristic, it is linked with the magnitude relation of the transmitted energy. That is, the operating frequency fo of the converter is operated in a range higher than the natural frequency fn. Using the impedance characteristics of the parallel resonant circuit, the parallel resonant circuit becomes almost capacitive when the transfer energy is large, and equivalently, there is no limit on the charging energy to the chopper circuit.
On the contrary, when the transfer energy is small, the impedance of the parallel resonant circuit becomes large and equivalently limits the charging energy to the chopper circuit. In this way, the charging amount of the smoothing capacitor C1 is automatically controlled according to the transmitted energy. Next, as a second means for controlling the potential difference between the points a and b when the field effect transistor Q1 is switched on, a means corresponding to the phase φ1 and the phase φ2 shown in FIG.
There is a means for utilizing the change in the potential difference Vab between the point and the point b.
In order to change the phase, the drive frequency of the switching element Q1 is changed. As a configuration for this, the terminal voltage of the smoothing capacitor C1 is connected to the input terminal of the detection / comparison circuit DET2, in which the terminal voltage of the capacitor C1 is compared with the reference voltage and its error voltage is amplified and output. This is sent to the terminal 6 of the control circuit U1 via the resistor R1, and the internal oscillation frequency of the control circuit U1 changes. This second
According to this means, the internal oscillating frequency of the control circuit U1 increases in accordance with the increase in the voltage of the smoothing capacitor C1, and the conduction of the chopper is cut off in the short ON period, so that the input current is correspondingly limited. When the frequency is changed, the voltage at the output terminals Y1 and Y2 of this converter is kept constant by controlling while keeping the on / off ratio constant. Either means acts to further correct the excess or deficiency of the charging energy of the smoothing capacitor, thus reducing the distortion of the input AC current. In this embodiment, both the first means and the second means are provided, but either one means naturally works. The connection location of the detection / comparison circuit DET1 is not limited to the output terminal but may be directly connected to both ends of a remote load. Alternatively, the transformer Tr1 may be provided with a winding for voltage detection to detect the output voltage. Also transformer Tr
It is also possible to provide a plurality of secondary windings in 1 and to provide a rectifying / smoothing circuit and an output terminal for each.

[Second Embodiment] FIG. 4 shows a second embodiment of the present invention.
This embodiment has the same structure as the embodiment shown in FIG.
The difference in configuration is that the connection polarity of the transformer Tr1 is
The reverse polarity of the case, the secondary side rectifier circuit is a half-wave rectifier circuit consisting only of the diode D2 and the capacitor C2, and the diode is connected in series with the primary winding n1 of the transformer Tr1.
The point is that D4 is provided with the polarity shown. This difference in structure corresponds to the operation in that the converter operation part is replaced with the so-called forward type from the flyback type. Other than that, it is common to obtain the high power factor targeted by the present invention. The diode D4 in the second embodiment can be omitted because it is not an essential component, but the diode D4 is effective for the desired operation. On the other hand, in the first embodiment, there is no part corresponding to the diode D4, but the basic operation does not change even if a component corresponding to this is included.

The present invention has the features described above,
The output voltage is stabilized and controlled by one switching element, and at the same time, the waveform of the AC input current can be improved and the power factor is zero.
It can be improved to about 996. Moreover, since there is only one switching element, there is no mutual interference as in the case where the conventional pre-converter is provided. Furthermore, due to the resonance action of the converter, the switching element becomes zero-volt switching, the resonance capacitor plays the role of a lossless snubber, and the snubber circuit of the switching element becomes unnecessary. Furthermore, the resonance action of the converter also plays the role of the reset circuit of the transformer, and the converter transformer does not require the reset winding and reset diode. As described above, the AC / DC converter according to the present invention has a simple structure and has effects of small size, light weight, high power factor, and high efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an AC / DC converter according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the AC / DC converter according to the present invention.

FIG. 3 is a diagram showing a relationship between an operating frequency and transfer energy of the AC / DC converter according to the present invention.

FIG. 4 is a partial view showing a configuration of a second embodiment of an AC / DC converter according to the present invention.

FIG. 5 is a diagram showing an example of a configuration of a conventional AC / DC converter.

FIG. 6 is an AC input current waveform diagram of a conventional AC / DC converter.

[Explanation of symbols]

 Co, C1, C2, C3, C4… Capacitor D1, D2, D3, D4… Diode DET1, DET2… Comparison detection circuit Ei… Commercial AC power supply L1, L2, L3… Choke coil Q1… Field effect transistor Q2… Photocoupler Ro , R1… Resistor RC1, RC2… Rectifier circuit Tr1… Transformer U1… Control circuit X1, X2… Input terminal Y1, Y2… Output terminal

Claims (6)

[Claims] 1. A bridge-type rectifier circuit comprising a pair of input terminals to be connected to a commercial AC power source, a pair of AC input terminals and a pair of DC output terminals, the AC input terminals of the rectifier circuit. A bridge-type rectifier circuit connected to the pair of input terminals, a choke coil, a diode, and a capacitor connected in series with each other, which are connected to the output terminals of the bridge-type rectifier circuit, and the frequency of the commercial AC power supply. And a switching circuit having a pair of main electrodes and a control terminal, the control circuit generating an on / off drive signal having a frequency sufficiently higher than that of the above-mentioned capacitor and increasing with the rise of the terminal voltage of the capacitor. , Its control terminal is driven on and off by the control circuit, and one end of its main electrode is at a second point at a connection point between the choke coil and the diode. A transformer comprising a switching element connected through a capacitor and the other end of the main electrode connected to one end of the capacitor, and a primary winding and a secondary winding. A transformer having a wire connected between the connection point of the capacitor and the diode and the main electrode of the switching element; rectifying means connected to the secondary winding of the transformer; and connecting to the rectifying means AC / D consisting of a connected output terminal
C converter. 2. A bridge-type rectifier circuit having a pair of input terminals to be connected to a commercial AC power source, a pair of AC input terminals and a pair of DC output terminals, the AC input terminals of the rectifier circuit. A bridge-type rectifier circuit connected to the pair of input terminals, a choke coil, a diode, and a capacitor connected in series with each other, which are connected to the output terminals of the bridge-type rectifier circuit, and the frequency of the commercial AC power supply. A switching element having a control circuit for generating an on / off drive signal of a sufficiently high frequency as compared with the above, and a pair of main electrodes and a control terminal, the control terminal being driven on / off by the control circuit, One end of the main electrode is composed of a second capacitor, a second choke coil and a third capacitor at the connection point between the choke coil and the diode. Is a transformer having at least a primary winding and a secondary winding, which are connected through a series circuit with a parallel circuit, and the other end of the main electrode is connected to one end of the capacitor. And a transformer whose primary winding is connected between the connection point between the capacitor and the diode and the main electrode of the switching element, and a rectifying means connected to the secondary winding of the transformer. , AC / D consisting of an output terminal connected to this rectifying means
C converter. 3. A bridge-type rectifier circuit comprising a pair of input terminals to be connected to a commercial AC power supply, a pair of AC input terminals and a pair of DC output terminals, the AC input terminals of the rectifier circuit. A bridge-type rectifier circuit connected to the pair of input terminals, a choke coil, a diode, and a capacitor connected in series with each other, which are connected to the output terminals of the bridge-type rectifier circuit, and the frequency of the commercial AC power supply. And a switching circuit having a pair of main electrodes and a control terminal, the control circuit generating an on / off drive signal having a frequency sufficiently higher than that of the above-mentioned capacitor and increasing with the rise of the terminal voltage of the capacitor. , Its control terminal is driven on and off by the control circuit, and one end of its main electrode is at a second point at a connection point between the choke coil and the diode. A switching element connected through a series circuit of a capacitor and a parallel circuit including a second choke coil and a third capacitor, and the other end of the main electrode connected to one end of the capacitor; A transformer comprising a winding and a secondary winding, the primary winding of which is connected between the connection point of the capacitor and the diode and the main electrode of the switching element, AC / D composed of a rectifying means connected to the secondary winding of the transformer and an output terminal connected to the rectifying means.
C converter. 4. The rectifying means connected to the secondary winding of the transformer transfers energy corresponding to when the switching element is turned on.
Alternatively, the AC / DC converter according to claim 3. 5. The rectifying means connected to the secondary winding of the transformer transfers energy corresponding to the time when the switching element is off.
Alternatively, the AC / DC converter according to claim 3. 6. The diode according to claim 1, wherein a diode is connected in series with the primary winding of the transformer.
Or A according to claim 3 or claim 4 or claim 5.
C / DC converter.