JPH05236749A - Ac/dc converter - Google Patents

Abstract

PURPOSE:To increase the power factor of an AC/DC converter which generates a DC output upon receiving commercial AC power. CONSTITUTION:In the title AC/DC converter the main circuit of which is constituted of a rectifier circuit RC1, a field effect transistor Q1, a transformer Tr1, and rectifier circuit RC2, a choke coil Ll and a diode D1 are connected between the circuit RC1 and a capacitor C1 and a capacitor C3 is connected between the connecting point of the coil L1 and diode D1 and the connecting point of the transistor Q1 and the primary winding n1 of the transformer Tr1. In addition, the input power factor of the AC/DC converter is further improved by making a control circuit U1 stabilize the output voltage of the converter by making time ratio control on the output voltage with a signal obtained through a detection/comparator circuit DET1 and phase control by using the output voltage of the circuit RC1.

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 boost choke coil and a diode are inserted between them, and a resonance capacitor is connected to the connection point between the boost choke coil and the diode and the connection point between the transformer and the switching element. With regard to the on / off drive frequency of the semiconductor switching element, the present invention proposes a high power factor AC / DC converter characterized by being driven at a frequency corresponding to the instantaneous value of the voltage immediately after rectification of an AC input.

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. The drain electrode of the field effect transistor Q1 is connected to the connection point between the choke coil L1 and the diode D1 via the capacitor C3, and the emitter thereof 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, a voltage divider consisting of resistors R1 and R2 is connected to the output terminal of rectifier circuit RC1, and this divided voltage is connected to terminal 6 of control circuit U1 via series resistor R3. Here, the control circuit U1 is a popular TL494 of Texas Instruments, which is an integrated circuit for switching power supply.
Alternatively, it is a general circuit configured by adding an output current amplifier circuit and some auxiliary components to an equivalent product. 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 50Hz)
Is rectified by the rectifier circuit RC1 and passes through the choke coil L1 and the capacitor C3, and the field effect transistor Q1 is repeatedly turned on and off at a high frequency of 100 kHz to 200 kHz. 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 transistor Q
When 1 is on, the current that charges the capacitor C3 flows from the 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 function called a so-called forward converter, a capacitor C3 and a transformer.
There is a reset function for the transformer Tr1 due to natural vibration with the primary winding n1 of 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 to reset the transformer Tr1 and reverse the voltage of the capacitor C3. Next, the operation will be described in detail. First, consider that the internal oscillation frequency of the control circuit U1 is constant. 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 large enough for the switching frequency, it can be regarded as a constant current. Therefore,
The integrated amount of the input current in one switching cycle is
Although affected by the AC input voltage, if a simulation is performed for one cycle of the AC frequency, the sine wave as shown in Fig. 3 (f) has a waveform in which the DC component is superimposed. This 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, the time ratio is controlled so that the output voltage is kept constant with only one field effect transistor Q1 which is a switching element. 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. .. Next, the internal oscillation frequency of the control circuit U1 is
A case will be described in which the voltage changes immediately after the rectification according to the instantaneous value. In this case, the internal oscillation frequency of the control circuit U1 increases / decreases according to the waveform of the input AC voltage Ei as shown in FIG. 2 (b). The output drive signal of the control circuit U1 has a waveform corresponding to this waveform and having the above-mentioned duty ratio, as shown in FIG. 2 (c). Even in this case, the field effect transistor Q1 which is a switching element
If the ON / OFF duty ratio is controlled as described above, a stable DC output voltage can be obtained. Then, the charge amount of the capacitor C3 changes in accordance with the phase of the input voltage Ei, the internal oscillation frequency is high in the low voltage phase, and the charge amount of the capacitor C3 in the short cycle becomes small. Further, in the high voltage phase, the internal frequency is low, and the amount of charge to the capacitor C3 in the longer cycle is large, so the waveform of the input current Ii is improved and comes closer to the waveform of the input AC voltage Ei. .. In this example, the waveform shown in FIG. 3 (e) was obtained. In this waveform, the power factor was 0.996 and the distortion factor of the input current was about 5%.
In this embodiment, the instantaneous value of the output terminal of the rectifier circuit is injected into the oscillator circuit as a proportional value via the resistor, but it is possible to control the oscillator circuit via another waveform shaping circuit or function generating circuit. The input power factor can be made even closer to 1. Further, in order to obtain the voltage value corresponding to the instantaneous value of the AC input voltage, the voltage value is not limited to the output of the rectifier circuit of the main circuit as in the present embodiment, but is obtained from the input terminal through another rectifier circuit or a transformer. You can also 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. It is also possible to provide a plurality of secondary windings on the transformer Tr1 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 illustrating the operation of the first embodiment of the AC / DC converter according to the present invention.

FIG. 3 is an AC input current waveform diagram of the AC / DC converter according to the present invention.

FIG. 4 is a diagram 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… Capacitor D1, D2, D3, D4… Diode DET1… Comparison detection circuit Ei… Commercial AC power supply L1, L2… Choke coil Q1… Field effect transistor Q2… Photocoupler Ro, R1, R2, R3 … Resistors RC1, RC2… Rectifier circuit Tr1… Transformer U1… Control circuit X1, X2… Input terminals Y1, Y2… Output terminals

Claims (4)

[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 AC input terminal and corresponding to the instantaneous value of the voltage at the AC input terminal. The control terminal is driven on and off by the control circuit, and one end of the main electrode is connected to the connection point of the choke coil and the diode with a second coil. 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. The AC / D according to claim 1, wherein the rectifying means connected to the secondary winding of the transformer transfers energy corresponding to when the switching element is turned on.
C converter. 3. The AC / D according to claim 1, wherein the rectifying means connected to the secondary winding of the transformer transfers energy corresponding to when the switching element is off.
C converter. 4. A diode is connected in series with the primary winding of the transformer.
Alternatively, the AC / DC converter according to claim 3.