JP2005006398A - Ac/dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive lightweight and compact AC-DC converter. <P>SOLUTION: The AC-DC converter comprises a means for rectifying an input AC voltage having such properties as an amplitude increases as a frequency increases, a smoothing means having a plurality of smoothing capacitors of different capacities and breakdown voltages and outputting a DC voltage by smoothing a rectified voltage from the rectifying means, and a capacity control means for monitoring the state of the rectified voltage and switching the total capacity of the smoothing means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AC / DC converter, for example, an AC / DC converter that inputs a DC voltage and outputs a DC voltage by changing the voltage and frequency output from a generator or the like (for example, changing according to the number of revolutions). It can be applied to a device.
[0002]
[Prior art]
There are many AC / DC converters for obtaining a DC power supply by inputting a commercial AC power supply having a substantially constant frequency and voltage, and various devices have been made (see Patent Document 1).
[0003]
However, there is also an AC / DC conversion device in which an AC voltage whose frequency and voltage fluctuate is input. For example, there is a power supply device (AC / DC converter) that starts a gasoline engine and converts an AC voltage output from a charge coil (corresponding to a generator) into a stable DC voltage. The effective value and frequency of the AC voltage from such a generator are substantially proportional to the number of revolutions of the generator.
[0004]
The AC / DC converter applied in such a use also rectifies the AC voltage and converts it to DC by smoothing with a smoothing capacitor, as in the case of a normal AC / DC converter.
[0005]
Here, the smoothing capacitor has a large capacity to respond to a low frequency and a low voltage when the rotational speed is slow, and has a high withstand voltage to respond to a high frequency and a high voltage when the rotational speed is fast. Has been made. That is, a high withstand voltage and large capacity capacitor is applied.
[0006]
[Problems to be solved by the invention]
However, a high-withstand-voltage, large-capacity capacitor is practically bulky and heavy, and is expensive, limiting the downsizing of an AC / DC converter.
[0007]
The present invention has been made in view of the above points, and an object of the present invention is to provide a lightweight, compact, and inexpensive AC / DC converter that converts an AC voltage whose frequency and voltage fluctuate into a DC voltage.
[0008]
[Means for Solving the Problems]
In order to solve such a problem, the AC / DC converter of the present invention includes (1) a rectifying means for rectifying an input AC voltage having the property that the amplitude increases as the frequency increases, and (2) the rectifying means. Smoothing means having a plurality of smoothing capacitors with different capacities and withstand voltages, and smoothing the rectified voltage from the output, and (3) monitoring the state of the rectified voltage and determining the overall capacity of the smoothing means. And switching capacity control means.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
(A) First Embodiment Hereinafter, a first embodiment of an AC / DC converter according to the present invention will be described in detail with reference to the drawings.
[0010]
FIG. 1 is a circuit diagram illustrating a configuration of the AC / DC converter according to the first embodiment. The AC / DC converter according to the first embodiment includes a rectifier circuit 3, a reference power supply 4, a comparison circuit 5, a switch 6, a low breakdown voltage large capacity capacitor 7, a high breakdown voltage small capacity capacitor 8, and a voltage stabilization circuit 9. The AC power source 1 input via the input terminals 2A and 2B is converted to DC.
[0011]
The AC power supply 1 corresponds to, for example, a generator, and the AC voltage has a small amplitude (in other words, an effective value) when the frequency is low and a large amplitude when the frequency is high. When the generator (AC power supply 1) gradually increases the rotation speed from the rotation speed 0 to a predetermined rotation speed, the frequency of the AC voltage gradually increases (the amplitude is the same). On the contrary, when the generator (AC power supply 1) gradually decreases the rotation speed from the predetermined rotation speed to the rotation speed 0, the frequency of the AC voltage also gradually decreases (the amplitude is the same). .
[0012]
The rectifier circuit 3 rectifies the AC voltage having the above-described properties input via the input terminals 2A and 2B, and either a full-wave rectifier circuit or a half-wave rectifier circuit may be applied.
[0013]
The low withstand voltage large capacity capacitor 7 and the high withstand voltage small capacity capacitor 8 are both provided as smoothing capacitors. The low withstand voltage large capacity capacitor 7 has, for example, a withstand voltage of 35 V and a capacity of 1000 μF, and the high withstand voltage small capacity capacitor 8 has, for example, a withstand voltage of 100 V and a capacity of 180 μF. The withstand voltage of the low withstand voltage large capacity capacitor 7 may be lower than the maximum value voltage that the output voltage (pulsating voltage) of the rectifier circuit 3 can take.
[0014]
The low withstand voltage large capacity capacitor 7 is provided with a switch 6 in series. When the switch 6 is in an ON state, the low withstand voltage large capacity capacitor 7 and the high withstand voltage small capacity capacitor 8 constitute a parallel circuit.
[0015]
The comparison circuit 5 compares the voltage of the output line LH on the high voltage side of the rectifier circuit 3 with the voltage of the reference power source 4 and controls on / off of the switch 6.
[0016]
For example, the comparison circuit 5 may use an operational amplifier or the like, and its specific configuration is not limited. The comparison circuit 5 turns on the switch 6 when the voltage of the output line LH is equal to or lower than the voltage of the reference power supply 4, and causes the low withstand voltage large-capacitance capacitor 7 to function as smoothing. Further, when the voltage of the output line LH is larger than the voltage of the reference power supply 4, the comparison circuit 5 turns off the switch 6 and disconnects the low withstand voltage large capacity capacitor 7. In this case, only the high withstand voltage small capacity capacitor 8 functions for smoothing.
[0017]
The voltage stabilization circuit 9 corresponds to, for example, a three-terminal regulator or a switching regulator, and further stabilizes the smoothed DC voltage. As the voltage stabilizing circuit 9, one constituted by an integrated circuit can be applied, and this can contribute to miniaturization.
[0018]
When the AC power source 1 is a generator, the rotation speed is slow immediately after the generator is started, and the output AC voltage is small in both frequency and amplitude (effective value), and the output voltage from the rectifier circuit 3 (pulsating voltage ( RMS value)) is also small. Therefore, the comparison circuit 5 keeps the switch 6 in the ON state, and smoothing is performed by the parallel circuit of the low withstand voltage large capacity capacitor 7 and the high withstand voltage small capacity capacitor 8, and the smoothed voltage is stabilized by the voltage stabilizing circuit 9. Is output.
[0019]
As the rotational speed of the generator gradually increases, the frequency and amplitude (effective value) of the output AC voltage gradually increase, and the output voltage (pulsating voltage (effective value)) from the rectifier circuit 3 gradually increases. Become bigger. Due to the increase in the output voltage from the rectifier circuit 3, the timing at which the magnitude relationship with the voltage of the reference power supply 4 is reversed occurs. At this time, the comparison circuit 5 switches the switch 6 to OFF. As a result, the low withstand voltage large capacity capacitor 7 is disconnected, and smoothing is performed only with the high withstand voltage small capacity capacitor 8, and the smoothed voltage is stabilized and output by the voltage stabilizing circuit 9.
[0020]
The smooth state using only the high withstand voltage small capacity capacitor 8 continues even after the rotational speed of the generator reaches a predetermined speed.
[0021]
At the time of transition to stop the generator, the rotational speed gradually decreases, and there is a point in time during which the switch 6 is turned on. After that point, the low withstand voltage large capacity capacitor 7 and the high withstand voltage small capacity capacitor Smoothing is performed by eight parallel circuits.
[0022]
According to the first embodiment, since smoothing is performed using the low withstand voltage large capacity capacitor 7 and the high withstand voltage small capacity capacitor 8, compared with the conventional case where the high withstand voltage large capacity capacitor is applied, the parts Although the number of points is increased, a lightweight, compact and inexpensive AC / DC converter can be realized.
[0023]
When the input AC voltage has a low frequency and a low amplitude, it is necessary to increase the time constant (in other words, increase the capacity) of the smoothing circuit in order to respond to the low frequency. This requirement is satisfied because the parallel circuit of the high-voltage small-capacitance capacitor 8 functions.
[0024]
When the input AC voltage has a high frequency and a high amplitude, the time constant of the smoothing circuit may be reduced (in other words, the capacity may be reduced). Therefore, the high withstand voltage small capacity capacitor 8 can be sufficiently smoothed. When the input AC voltage has a high frequency and a high amplitude, only the high withstand voltage small capacity capacitor 8 functions and the low withstand voltage large capacity capacitor 7 does not function. There is nothing.
[0025]
(B) Second Embodiment Next, a second embodiment of the AC / DC converter according to the present invention will be described in detail with reference to the drawings. The second embodiment has a more specific configuration than the first embodiment.
[0026]
FIG. 2 is a circuit diagram showing the configuration of the AC / DC converter according to the second embodiment, and the same and corresponding parts as in FIG.
[0027]
The output AC voltage of the AC power supply 1 is input to the diode bridge circuit (3) including four diodes D1 to D4 via the input terminals 2A and 2B and is full-wave rectified.
[0028]
The source and drain of the PMOS transistor Q1 are inserted in series as a series switching element in the low withstand voltage large capacity capacitor C1 (7). A high voltage small capacitor C2 (8) is connected in parallel to the series circuit of the low voltage large capacitor C1 and the PMOS transistor Q1 (6).
[0029]
Between the output line LH on the high voltage side and the output line LL on the low voltage side of the diode bridge circuits D1 to D4, the resistor R1 and the collector and emitter of the N-type bipolar transistor Q2 are connected in series. In addition, one or a plurality of zener diodes ZD (4) and a resistor R2 are connected in series between the output line LH and the output line LL. A connection point between the Zener diode ZD and the resistor R2 is connected to the base of the transistor Q2 via the resistor R3. A connection point between the resistor R1 and the collector of the transistor Q2 is connected to the gate of the transistor Q1.
[0030]
The one or more Zener diodes ZD functionally provide the reference voltage described in the first embodiment.
[0031]
When the voltage between the output lines LH and LL (pulsating voltage) is small, no current flows through the Zener diode ZD, the base voltage of the transistor Q2 becomes almost the potential of the output line LL, and the transistor Q2 is turned off. As a result, a high potential is applied to the gate of the transistor Q1 via the pull-up resistor R1, and the transistor Q1 is turned on.
[0032]
On the other hand, when the voltage (pulsating voltage) between the output lines LH and LL is large (when the voltage exceeds the breakdown voltage of the Zener diode ZD), a Zener current flows through the Zener diode ZD, and the voltage across the resistor R2 increases. The transistor Q2 is turned on, and as a result, the transistor Q1 is turned off.
[0033]
Although the second embodiment is shown more specifically than the first embodiment, the same operation as the first embodiment can be performed, and the same effect as the first embodiment can be obtained.
[0034]
(C) Third Embodiment Next, a third embodiment of the AC / DC converter according to the present invention will be briefly described with reference to the drawings.
[0035]
FIG. 3 is a circuit diagram showing the configuration of the AC / DC converter according to the third embodiment. The same reference numerals are given to the same and corresponding parts as in FIG.
[0036]
The AC / DC converter of the third embodiment is one in which a changeover switch 6 is applied instead of the on / off switch 6 of the first embodiment. When the output voltage from the rectifier circuit 3 is small, the changeover switch 6 functions only the low withstand voltage large capacity capacitor 7, and when the output voltage from the rectifier circuit 3 is large, only the high withstand voltage small capacity capacitor 8 functions. Switching operation is performed.
[0037]
According to the third embodiment, the same effect as that of the first embodiment can be obtained.
[0038]
(D) Fourth Embodiment Next, a fourth embodiment of the AC / DC converter according to the present invention will be briefly described with reference to the drawings.
[0039]
In the first embodiment described above, the capacitance in the smoothing circuit is switched in two steps. In the fourth embodiment, the capacitance in the smoothing circuit is switched in three steps.
[0040]
FIG. 4 is a circuit diagram showing the configuration of the AC / DC converter according to the fourth embodiment, and the same or corresponding parts as those in FIG. 1 are given the same reference numerals.
[0041]
In the case of the fourth embodiment, in addition to the low withstand voltage large capacity capacitor 7 and the high withstand voltage small capacity capacitor 8, a medium withstand voltage medium capacity capacitor 10 is provided. A switch 11 is connected in series to the medium-voltage medium-capacitance capacitor 10, and this switch 11 is on / off controlled by the functions of the reference power supply 12 and the comparison circuit 13.
[0042]
In the case of the fourth embodiment, the input AC voltage is divided into three ranges according to the frequency and amplitude. In a range where the frequency and amplitude are small, both the switches 6 and 11 are turned on, and the low withstand voltage large capacity capacitor 7, the medium withstand voltage medium capacity capacitor 10 and the high withstand voltage small capacity capacitor 8 are all functioned and smoothed. In a range where the frequency and amplitude are intermediate, the switch 6 is turned off and the switch 11 is turned on, and the medium withstand voltage medium capacity capacitor 10 and the high withstand voltage small capacity capacitor 8 are functioned and smoothed. In a range where the frequency and amplitude are large, both the switches 6 and 11 are turned off, and only the high withstand voltage small-capacitance capacitor 8 is functioned and smoothed.
[0043]
According to the fourth embodiment, the same effect as that of the first embodiment can be obtained. Furthermore, in the fourth embodiment, it can be expected that the capacitance in the smoothing circuit is switched more smoothly.
[0044]
(E) Fifth Embodiment Next, a fourth embodiment of the AC / DC converter according to the present invention will be briefly described with reference to the drawings.
[0045]
FIG. 5 is a circuit diagram showing the configuration of the AC / DC converter according to the fifth embodiment, and the same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals.
[0046]
In the fifth embodiment, the voltage stabilization circuit 9 is omitted, and a rotation control unit 14 is provided instead. In the fifth embodiment, the AC power source 1 is a generator.
[0047]
The rotation control unit 14 is composed of, for example, a microcomputer and controls the rotation speed of the generator (AC power supply 1) based on the voltage between the output lines LH and LL or the AC frequency.
[0048]
For example, when the output voltage needs to be stabilized after the rotation speed reaches a predetermined speed, the rotation control unit 14 increases the rotation speed when the voltage between the output lines LH and LL becomes lower than the predetermined voltage. When the voltage between the output lines LH and LL becomes higher than a predetermined voltage, the rotational speed is controlled to be lowered. That is, the voltage between the output lines LH and LL is stabilized through control of the rotation speed. Thereby, the voltage stabilization circuit 9 can be omitted.
[0049]
According to the fifth embodiment, the same effect as that of the first embodiment can be obtained. Furthermore, in the fifth embodiment, further reduction in size can be expected by omitting the voltage stabilizing circuit 9.
[0050]
(F) Other Embodiments In each of the above embodiments, the switching timing of a switch or the like is determined based on the rectified voltage. However, it may be determined based on other parameters. For example, the AC input voltage itself may be monitored to determine the switching timing of the switch or the like. When the AC power supply 1 is a generator, the rotational speed is monitored and the switching timing of the switch or the like is determined. You may make it judge.
[0051]
The application of the AC / DC converter of the present invention is not limited as long as the AC input voltage has the property of increasing (in proportion to) the frequency and increasing the amplitude.
[0052]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a lightweight, compact, and inexpensive AC / DC converter that converts an AC input voltage whose frequency and voltage fluctuate into a DC voltage.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an AC / DC converter of a first embodiment.
FIG. 2 is a circuit diagram showing an AC / DC converter according to a second embodiment.
FIG. 3 is a circuit diagram showing an AC / DC converter according to a third embodiment.
FIG. 4 is a circuit diagram showing an AC / DC converter according to a fourth embodiment.
FIG. 5 is a circuit diagram showing an AC / DC converter according to a fifth embodiment.
[Explanation of symbols]
1: AC power supply, 3: rectifier circuit, 4, 12: reference power supply, 5, 13: comparison circuit, 6, 11: switch, 7: low withstand voltage large capacity capacitor, 8: high withstand voltage small capacity capacitor, 9: voltage stability Circuit: 10: medium-voltage medium-capacitance capacitor; 14: rotation control unit.

Claims (5)

Rectifying means for rectifying the input AC voltage, having the property that the amplitude increases as the frequency increases,
Smoothing means that smoothes the rectified voltage from the rectifying means and outputs a DC voltage, and has a plurality of smoothing capacitors having different capacities and withstand voltages;
An AC / DC converter comprising: capacity control means for monitoring the state of the rectified voltage and switching the overall capacity of the smoothing means. The smoothing means is a parallel circuit of a large capacity capacitor with a low withstand voltage and a small capacity capacitor with a high withstand voltage,
The capacitance control means smoothes the entire parallel circuit when the rectified voltage is lower than a reference voltage, and smoothes only with the small capacitor when the rectified voltage is larger than the reference voltage. The AC / DC converter according to claim 1. The AC / DC converter according to claim 1, further comprising a generator that inputs an AC voltage to the rectifying means. The AC / DC converter according to any one of claims 1 to 3, further comprising a voltage stabilizing circuit at a subsequent stage of the smoothing means. 4. The AC / DC converter according to claim 3, further comprising a feedback unit that feeds back information on a smoothed voltage by the smoothing unit to a rotation control unit that performs rotation control of the generator.

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