JPH04197080A - Ac-dc converter - Google Patents

Abstract

PURPOSE:To realize free setting of output voltage while sustaining the rectified input current in sinusoidal waveform by providing a function for regulating the peak value of a voltage obtained by full-wave rectifying a sine wave and for stabilizing the output voltage. CONSTITUTION:A DC input voltage V1 is converted through a first choke coil 4 and a switching transistor 5 into an AC high frequency voltage which is then applied through a first capacitor 7 onto a second choke coil 8. A flyback voltage induced in the second choke coil 8 is then rectified and smoothed through a diode 9 and a second capacitor 10 thus producing an output voltage V0. Since the relation between input and output is similar to that in a step up/down converter, the output voltage V0 can be set freely.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an AC-DC converter whose purpose is to suppress harmonics and improve the input power factor by making the input current waveform sinusoidal.

Conventional technology In recent years, AC-DC converters, represented by switching power supplies, have become increasingly unnecessary due to their widespread use in various electronic devices, but harmonic suppression and input power factor improvement are now required for these converters. It has become.

Below is a conventional A for the purpose of harmonic suppression and input power factor improvement.
The C-DC converter will be explained.

Figure 3 shows the circuit configuration factors of a conventional AC-DC converter.
This is an application of a boost converter.

In FIG. 3, 1.1' is an input terminal, which receives input AC voltage. 2 is a full-wave rectifier, which performs full-wave rectification of the received input AC voltage. 3 is a capacitor, 4 is a choke coil, 5 is a switching transistor, 6 is a current detection resistor, 9 is a diode, 10 is a capacitor, 11.
11' is an output terminal. Reference numeral 20 denotes a control drive circuit, which includes a reference voltage source 21, an error amplifier 22, a multiplier 23, a comparator 24, an oscillator 25, and a drive circuit 26.

The operation of the conventional AC-DC converter configured as described above will be explained below.

First, the input AC voltage is input to the full-wave rectifier 2 and the capacitor 3.
It is rectified and smoothed by and converted into a DC voltage v1. The capacitance of the capacitor 3 may be small or may be absent. That is, the DC voltage V1 is a full-wave rectified waveform that sufficiently includes the pulsating current of the input AC voltage. This DC voltage V1 is returned to a high frequency AC voltage by a choke coil 4 and a switching transistor 5, and then rectified and smoothed by a diode 9 and a capacitor 10, and is output as an output voltage vO. The output voltage vO is compared with the reference voltage source 21 and amplified by the error amplifier 22. The output of the error amplifier 22 and the DC voltage 1 are multiplied by the multiplier 23, resulting in a full-wave rectified waveform voltage v2 having a predetermined magnitude and proportional to the waveform of the DC voltage v1.

The current flowing through the switching transistor 5 is detected by the current detection resistor 6, and the detected voltage v3 is detected by the comparator 24.
It is compared with the full-wave rectified waveform voltage v2 by. Comparator 2
The output of 4 is sent to the drive circuit 26 along with the output 4 of the oscillator 25.
The drive circuit 26 outputs a drive output V5 that drives the switching transistor 5 at a predetermined on/off ratio. This situation is shown in FIG. In FIG. 4, (al is the output V4 of the oscillator 25, (bl is the full-wave rectified waveform voltage V2
and the detection voltage (3) of the current detection resistor 6, fcl is the drive output V5 of the drive circuit 26, and fd) is the choke current I2 flowing through the choke coil 4. In this way, by placing the peak value of the current flowing through the switching transistor 5 on a predetermined full-wave rectified waveform, the choke current 12 is made as shown in FIG. The input power factor can be at or near unity.

Problem to be Solved by the Invention However, since the above conventional configuration is a step-up converter system, insulation between input and output is not possible, and the output voltage is always set higher than the input voltage to obtain the desired output voltage. Therefore, the AC-DC converter installed in the latter stage is forced to meet strict input specifications. As a conventional method other than the above, a buck-boost converter can also be used,
In this case, the input current after rectification becomes discontinuous, and in order to convert the AC input current into a sine wave, the AC
-A filter circuit installed before the DC converter,
This has the problem that it becomes very large.

The present invention solves the above-mentioned conventional problems, and is a power factor improvement method that allows the output voltage to be freely set while making the input current continuous after rectification in the form of a sine wave, and also enables isolation between input and output. The purpose is to provide an AC-DC converter.

Means for Solving the Problems In order to achieve this object, the AC-DC converter of the present invention includes a first rectifier that rectifies an AC input, and a first choke connected to the input voltage rectified by the first rectifier. A series circuit of a coil, a switching means, and a current detecting means is connected in parallel, and a high frequency AC voltage obtained from the input voltage by the switching means is applied to a second choke coil via a first capacitor, and the switching a second rectifier and a second capacitor for rectifying and smoothing the voltage generated in the second choke coil or a separate winding applied to the second choke coil during the off period of the means and supplying an output voltage; determining the on-off ratio of the switching means by comparing the peak value of the current obtained from the current detection means with a sinusoidal full-wave rectified waveform voltage synchronized with the input voltage in order to make the input current sinusoidal;
The control drive circuit includes a control drive circuit having a function of adjusting the peak value of the sinusoidal full-wave rectified waveform voltage in order to stabilize the output voltage.

Effect By having the above configuration, the output voltage can be freely set while the rectified double input current is continuous in a sine wave shape, and
Insulation between input and output can also be achieved. EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit configuration diagram of an AC-DC converter in a first embodiment of the present invention.

In FIG. 1, 1.1' is an input terminal, which receives an input AC voltage. Reference numeral 2 denotes a full-wave rectifier as a first rectifier, which performs full-wave rectification of the received input AC voltage. 3 is a capacitor, 4 is a first choke coil, 5 is a switching transistor as a switching means, 6 is a current detection resistor as a current detection means, 7 is a first capacitor, 8 is a second choke coil, 9 is a Diode as second rectifier, 10 second capacitor, 11.11'
is the output terminal. Reference numeral 20 denotes a control drive circuit, which includes a reference voltage source 21, an error amplifier 22, a multiplier 23, a comparator 24, an oscillator 25, and a drive circuit 26.

The operation of the AC-DC converter configured as above will be described below.

First, the input AC voltage is input to the full-wave rectifier 2 and the capacitor 3.
It is rectified and smoothed by , and converted into a DC voltage (1). The capacitance of the capacitor 3 may be small or may be absent. That is, the DC voltage (1) is a full-wave rectified waveform that sufficiently includes a pulsating current component of the input voltage. This DC voltage v1 is converted into a high frequency AC voltage by the first choke coil 4 and the switching transistor 5, and then applied to the second choke coil 8 via the first capacitor 7. The generated flyback voltage is rectified and smoothed by the diode 9 and the second capacitor 10, and is output as an output voltage VO. The output voltage ■0 is compared with the reference voltage source 21 and amplified by the error amplifier 22. The output of the error amplifier 22 and the DC voltage V1 are multiplied by the multiplier 23, resulting in a full-wave rectified waveform voltage v2 having a predetermined magnitude and proportional to the waveform of the DC voltage V1. The current flowing through the switching transistor 5 is detected by the current detection resistor 6, and the detected voltage V3 is compared with the full-wave rectified waveform voltage 2 by the comparator 24. The output of the comparator 24 is inputted to the drive circuit 26 together with the output V4 of the oscillator 25, and the drive circuit 26 outputs a drive output V5 that drives the switching transistor 5 at a predetermined on/off ratio. This situation is almost the same as that shown in FIG. 4 used to explain the conventional example.

By placing the peak value of the current flowing through the switching transistor 5 on the predetermined full-wave rectified waveform in this way,
Conventionally, it is possible to make the current flowing through the first choke coil 4 as shown in Fig. 4fd), to make the input AC current a sine wave with suppressed harmonic components, and to make the input power factor 1 or close to it. Similar to the example.

However, in the case of this embodiment, the input DC voltage V1 is
choke coil 4 and switching transistor 5
After being converted into a high frequency AC voltage by
Since it is rectified and smoothed by the diode 9 and the second capacitor 10 and output as the output voltage VO, the relationship between the input and output is the same as that of a buck-boost converter.
The output voltage VO can be set freely.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a circuit configuration diagram of an AC-DC converter in a second embodiment of the present invention.

In FIG. 2, 1.1' is an input terminal which receives an input AC voltage. Reference numeral 2 denotes a full-wave rectifier as a first rectifier, which performs full-wave rectification of the received input AC voltage. 3 is a capacitor, 4 is a first choke coil, 5 is a switching transistor as a switching means, 6 is a current detection resistor as a current detection means, 7 is a first capacitor, and the above is the same as the configuration shown in FIG. It is. The configuration differs from that shown in Fig. 1 in that a separate winding 8' is provided in the second choke coil 8, and a diode 9 as a second rectifier and a second capacitor 10 are connected to the separate winding 8, and the control drive circuit 20
However, the reference voltage source 21, the error amplifier 22, and the multiplier 23
, a comparator 24 , an oscillator 25 , a drive circuit 26 , a photocoupler 27 , and a 1/V converter 28 .

11.11' is an output terminal.

The operation of the AC-DC converter configured as above will be described below.

First, the input AC voltage is input to the full-wave rectifier 2 and the capacitor 3.
It is rectified and smoothed by and converted into a DC voltage v1. The capacitance of the capacitor 3 may be small or may be absent. That is, the DC voltage (1) is a full-wave rectified waveform that sufficiently includes a pulsating current component of the input AC voltage. This DC voltage V1 is converted into a high frequency AC voltage by the first choke coil 4 and the switching transistor 5, and then the first capacitor 7
The flyback voltage generated in the separate winding 8' of the second choke coil 8 is rectified and smoothed by the diode 9 and the capacitor 10, and is output as the output voltage VO. Output.

The output voltage ■0 is output from the reference voltage source 21 by the error amplifier 22.
It is compared and amplified. The output of the error amplifier 22 is isolated and transmitted by a photocoupler 27, and is multiplied by a DC voltage v1 via an I/V converter 28 by a multiplier 23 to produce a full wave of a predetermined magnitude and proportional to the waveform of the DC voltage v1. The rectified waveform voltage becomes v2. The current flowing through the switching transistor 5 is detected by the current detection resistor 6, and the detected voltage V3 is compared with the full-wave rectified waveform voltage 2 by the comparator 24. The output of the comparator 24 is sent to the drive circuit along with the output V4 of the oscillator 25. 26, and the drive circuit 26 outputs a drive output V5 that drives the switching transistor 5 at a predetermined on/off ratio. This situation is almost the same as that shown in FIG. 4 used to explain the conventional example. In this way, by placing the peak value of the current flowing through the switching transistor 5 on the predetermined full-wave rectified waveform, the current flowing through the first choke coil 4 is made as shown in FIG. As in the conventional example, a sine wave with suppressed components can be formed, and the input power factor can be made to be 1 or close to it.

However, in the case of this embodiment, the second choke coil 8
The flybank voltage generated in the separate winding 8' is
It is rectified and smoothed by the diode 9 and the capacitor 10 and output as an output voltage vO, thereby insulating the input and output. The relationship between input and output is the same as that of a buck-boost converter, and the second choke coil 8 and separate winding 8'
The degree of freedom in setting the output voltage VO can be further increased by changing the turns ratio.

Although a resistor is used as the current detecting means in the first and second embodiments, it goes without saying that a current detecting means such as a current transformer may be used.

As shown in the above embodiment, during the period when the switching means 5 is on, the input voltage rectified by the first rectifier 2 is applied to the first choke coil 4, and the input voltage rectified by the first rectifier 2 is applied to the first choke coil 4.
A voltage is applied across the first capacitor 7 to energize each choke coil 4.8. Switching means 5
is off, the first choke coil 4 and the second
The demagnetizing current of the choke coil 8 is output from the second capacitor 10 to the load via the second diode 9.

The input voltage Ei1 rectified by the first rectifier 2, the voltage across the first capacitor 7 is Ec, the output voltage is EO, and the first
The inductances of the choke coil 4 and the second choke coil 8 are Ll and L2, respectively, and the on period and off period of the switching means 5 are Ton and Tof, respectively.
Let it be f.

The amount of increase in the excitation current flowing through the first choke coil 4 while the switching means 5 is on is Ei·T on
/ L 1 , during the period when the switching means 5 is off, the first
The amount of decrease in the demagnetizing current flowing through the choke coil 4 is (Ec
+Eo-E i) ・To f f/Ll, if the current flowing through the first choke coil 4 is continuous, the amount of increase and the amount of decrease will be equal, and the following formula % formula % (Ec + Eo) ・Toff=Ei・(Ton+T
off) = - = 111 Similarly, since the amount of increase and amount of decrease in the current flowing through the second choke coil 8 are equal, Ec -Ton = Eo ・Toff
−−−−−−(2) (From formula 11+21, Ec=Ei Eo=(Ton/Toff)・Ei −−−−−−
(31. In other words, the input voltage Ei rectified by the first rectifier 2 and the voltage Ec across the first capacitor 7 are equal, and as can be seen from equation (3), the relationship between the input and output voltages of the buck-boost converter is Therefore, in the configuration of the present invention, the output voltage can be set freely while the input current after rectification is continuous in a sinusoidal waveform.Furthermore, the separate winding 8' of the second choke coil 8 can be set as desired. By rectifying and smoothing the voltage generated therein to obtain an output voltage, it is possible to provide insulation between input and output.

Effects of the Invention As described above, the present invention provides a series circuit including a first rectifier for rectifying an AC input, a first choke coil for the input voltage rectified by the first rectifier, a switching means, and a current detection means. are connected in parallel, and a high frequency AC voltage obtained from the input voltage by the switching means is applied to the second choke coil via the first capacitor, and during the period when the switching means is off, the second choke coil Alternatively, a second rectifier and a second capacitor that rectify and smooth the voltage generated in the second choke coil and supply the output voltage, and a second rectifier and a second capacitor that rectify and smooth the voltage generated in the second choke coil, and a second capacitor and a second capacitor that rectify and smooth the voltage generated in the second choke coil, and a second capacitor and a second capacitor that rectify and smooth the voltage generated in the second choke coil, and a second capacitor and a second capacitor that rectify and smooth the voltage generated in the second choke coil, and a second capacitor and a second capacitor that rectify and smooth the voltage generated in the second choke coil, and a second capacitor and a second capacitor that rectify and smooth the voltage generated in the second choke coil; The on-off ratio of the switching means is determined by comparing the peak value with a sinusoidal full-wave rectified waveform voltage synchronized with the input voltage, and the peak value of the sinusoidal full-wave rectified waveform voltage is determined in order to stabilize the output voltage. By having a configuration consisting of a control drive circuit with an adjustment function, the output voltage can be freely set while the input current after rectification is continuous in a sinusoidal waveform, and it is also possible to isolate the input and output. AC for power factor improvement
It is possible to realize a DCC-type data.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of the AC-DC converter in the first embodiment of the present invention, FIG. 2 is a circuit diagram of the AC-DC converter/z+-converter in the second embodiment of the present invention, and The figure is a circuit diagram of a conventional AC-DC converter/sl-controller.
The figure is an operation waveform diagram. 1-1'...Input terminal, 2...Full-wave rectifier, 4...First choke coil, 5...
... Switching transistor, 6 ... Current detection resistor, 7 ... First capacitor, 8 ...
...Second choke coil, 9...Diode, 10...Second capacitor, 11-11
'... Output terminal, 20... Control drive circuit. Name of agent: Patent attorney Haruaki Koebi and two others 2 - Principal J
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Claims (2)

[Claims] (1) A first rectifier that rectifies an AC input, and a series circuit including a first choke coil, a switching means, and a current detection means are connected in parallel to the input voltage rectified by the first rectifier, and the input voltage is A high frequency AC voltage obtained from the voltage by the switching means is applied to a second choke coil through a first capacitor, and the voltage generated in the second choke coil during a period when the switching means is off is rectified and smoothed. a second rectifier and a second capacitor that supply an output voltage, and a sine wave full-wave rectifier that synchronizes the peak value of the current obtained from the current detection means with the input voltage to make the AC input current sinusoidal. AC-DC comprising a control drive circuit having a function of determining an on-off ratio of the switching means by comparison with a waveform voltage and adjusting a peak value of the sinusoidal full-wave rectified waveform voltage in order to stabilize the output voltage. converter. (2) A separate winding is provided in the second choke coil to serve as an output winding, and a second rectifier and a second capacitor are connected to the output winding to supply the output voltage. AC-DC converter.