JP3456583B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention relates to a DC-DC converter.
Data, especially high-frequency components contained in switching control signals.
DC-DC that can reduce noise generated at low cost
It concerns a converter. [0002] 2. Description of the Related Art Conventionally, it has been widely used in fields such as electronic and electric equipment.
Flyback type DC-DC converter used
Is shown in FIG. The DC-DC converter shown in FIG.
Bridge rectifier circuit 2 connected to a commercial AC power supply 1
And the rectification output terminal of the bridge rectification circuit 2
Input smoothing capacitor 3, primary winding 4a and secondary winding 4b
And the primary winding 4a is connected in series with the input smoothing capacitor 3.
, And a primary winding 4a of the transformer 4
MOS- as a switching element connected in series to
FET 5 and an output connected to the secondary winding 4b of the transformer 4.
Consisting of a power rectifier diode 6 and an output smoothing capacitor 7
Rectifying / smoothing circuit 8 and DC output voltage V of rectifying / smoothing circuit 8_O
A constant frequency is applied to the gate terminal of the MOS-FET 5 according to
ON / OFF control signal V_GAnd a control circuit 9 for giving
ing. [0003] The control circuit 9 is a DC output of the rectifying and smoothing circuit 8.
Voltage V_OOutput voltage detection circuit 10 for detecting the
A light emitting unit 11a driven by an output of the detection circuit 10;
Controls the current flowing to itself according to the light output of the light emitting unit 11a
A photocoupler 11 comprising a light receiving portion 11b
On / off control signal V applied to the gate terminal of FET5
_GOf the on / off period of the
Control is performed according to the current flowing through the light receiving portion 11b of the coupler 11.
PWM modulation circuit 12 and output from PWM modulation circuit 12
ON / OFF control signal V_GResistor to set the frequency of
13 and a frequency setting circuit 15 comprising a capacitor 14.
It is composed of The PWM modulation circuit 12
The light output of the light emitting portion 11a of the plastic 11 increases and the light receiving portion 11b
Current flowing through the light-receiving portion 11b increases.
ON / OFF control signal V when the voltage between_G
Of the photocoupler 11 to reduce the ON period of
The light output of the portion 11a decreases and the current flowing to the light receiving portion 11b becomes
And the voltage between the collector and the emitter of the light receiving portion 11b decreases.
On-off control signal V when rising_GBroaden the on period
Behave as if Also, the on / off control signal V_GFrequency
The number is the number of capacitors 14 constituting the frequency setting circuit 15.
Pressure V_CTAnd the set value is generally 150k
It is around Hz. In the DC-DC converter shown in FIG.
During the ON period of OS-FET5, whether the commercial AC power supply 1
Through the bridge rectifier circuit 2 and the input smoothing capacitor 3
As a result, energy is stored in the transformer 4. MOS-FET
When 5 goes from on to off, it is stored in the transformer 4
Energy is released and rectified and smoothed from the secondary winding 4b
DC output voltage V via circuit 8_OIs output. Also,
DC output voltage V of rectifying / smoothing circuit 8_OIn the control circuit 9
Output voltage detection circuit 10
According to a signal input from the
On / off control applied to the gate terminal of MOS-FET5
Control signal V_GIs changed by the PWM modulation circuit 12
Control at constant frequency set by wave number setting circuit 15
I do. Thereby, the DC output voltage V of the rectifying and smoothing circuit 8 is_O
The ratio of the ON / OFF period of the MOS-FET 5
Since it is controlled at a constant frequency, the secondary winding 4 of the transformer 4
b through the rectifying / smoothing circuit 8 to output a fixed level DC output voltage.
Pressure V_OIs obtained. [0005] By the way, commercial AC power
As a standard for noise generated from equipment connected to the
International standard CISPR, US FCC, European
Inputs such as EN55022 of PA community and VCCI of Japan
Return conduction noise standards are generally known. These
The noise standard is specified for frequencies above 150 kHz.
ing. Recently used as DC-DC converter
Switching power supplies have been switching
Higher frequency is being promoted, and now 150kHz
Before and after is common. For these reasons, FIG.
In the DC-DC converter shown in
The wave number, that is, from the control circuit 9 to the gate terminal of the MOS-FET 5
ON / OFF control signal V applied to the_GFrequency of 15
It is set around 0 kHz. On the other hand, the input feedback conduction noise
The voltage level of the noise is 150 kHz before as shown in FIG.
Since the noise voltage of the subsequent frequency becomes the largest,
The noise voltage whose main component is the wave number
Appears between AC input terminals. This noise voltage is
To the DC-DC converter
Both propagate to electronic devices and the like connected to the commercial AC power supply 1,
This may cause malfunction of these electronic devices and the like.
Therefore, in the DC-DC converter shown in FIG.
Reduces conducted noise within the limits of the above noise standards
In fact, the input side of the bridge rectifier circuit 2 is
Many router circuits are inserted. Therefore, noise countermeasures
Therefore, many parts such as a filter circuit are required,
Since the design is complicated, there is a disadvantage that the manufacturing cost is high.
Was. On / off control by dedicated low-frequency oscillator
Signal V_GModulate the frequency of the input feedback conducted noise
There is a way to lower the level, but in this case,
Also requires a dedicated low-frequency oscillator, reducing manufacturing costs.
A soaring problem arises. Therefore, the present invention provides a switching control signal.
Noise generated by high frequency components included at low cost
Aim to provide a DC-DC converter that can be reduced
And [0007] SUMMARY OF THE INVENTION DC-DC according to the present invention
The converter consists of an AC power supply (1) and a rectifier circuit (2).
And a primary winding (4a) connected in series with the DC power supply.
Transformer (4) having a secondary winding (4b) and a primary winding (4a)
The switching element (5) connected in series with the
Rectification connected to the primary winding (4a) or secondary winding (4b) in (4)
The smoothing circuit (8) and the switch according to the output voltage of the rectifying and smoothing circuit (8).
An on / off control signal (V) is supplied to the control terminal of the switching element (5).
_G) Is provided. Control circuit (9)
Switch according to the output voltage of the rectifying and smoothing circuit (8).
Control the ratio of the on / off period of the
Rectifying and smoothing from the primary winding (4a) or secondary winding (4b)
A DC output of a constant voltage is taken out via a path (8). In this DC-DC converter, the control circuit
(9) is an on-state applied to the control terminal of the switching element (5).
・ Off control signal (V_G) Controls the ratio of the on / off period.
Connected to the PWM modulation circuit (12) and the PWM modulation circuit (12).
Frequency setting circuit (15). AC power supply (1)
Series resistor (18) connected between the circuit and the frequency setting circuit (15)
Is provided in the modulation means (19), and the frequency is set through the series resistor (18).
The AC voltage of the AC power supply (1) is applied to the constant circuit (15). PW
On / off control signal output from M modulation circuit (12)
(V_G) Is modulated according to the AC voltage of the AC power supply (1).
You. A control circuit according to the AC voltage of the AC power supply (1)
On / off control signal (V_G)
By modulating, the on / off control signal (V_G) Frequency
Number fluctuates in a certain range and its frequency component is in a certain range
Disperse in. As a result, the on / off control signal (V_G)of
Frequency component of input feedback conducted noise whose main component is frequency
Are distributed over a certain range, and the noise voltage at these frequencies
Since they are not superimposed, the noise voltage level decreases. this
Therefore, the circuit design is simplified by reducing the number of parts such as filter circuits.
Can be simplified and the manufacturing cost can be reduced.
You. Therefore, the high frequency included in the switching control signal
To reduce noise generated by wave components at low cost
Becomes possible. [0010] DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a DC-DC converter according to the present invention will be described.
One embodiment of an inverter will be described with reference to FIGS.
You. However, in FIG. 1, substantially the same parts as those shown in FIG.
The same reference numerals are given to the minutes and the description is omitted. In FIG.
As shown, the DC-DC converter of the present embodiment
In the DC-DC converter shown in FIG.
One and the other of the output terminals of the source 1 are rectifying elements, respectively.
Rectifier diodes 16 and 17 are connected, and each rectifier diode is connected.
The cathode terminals of the nodes 16 and 17 are connected via a series resistor 18.
The connection of the resistor 13 and the capacitor 14 of the frequency setting circuit 15
It is connected to the continuation point. That is, the rectifier diode 1
6, 17 and the series resistor 18 are connected to the AC input of the commercial AC power supply 1.
Force voltage V_ACRectified by rectifier diodes 16 and 17
Pulsating voltage V_RCIs output from the control circuit 9 in accordance with
ON / OFF control signal V_GModulating means 1 for modulating the frequency of
9. The other circuit configuration is the DC-D shown in FIG.
It is almost the same as the C converter. Next, the DC-DC converter shown in FIG.
The noise reduction operation will be described. From commercial AC power supply 1
50Hz AC input voltage V output_ACIs every half cycle
2 is rectified by the rectifier diodes 16 and 17, and FIG.
Ripple voltage V shown in (A)_RCIs converted to As shown in FIG.
Ripple voltage V of each rectifier diode 16, 17_RCIs the series resistance
Frequency setting circuit 15 in control circuit 9 via 18
The voltage V of the capacitor 14_CTIs superimposed on This
The voltage V of the capacitor 14 shown in FIG._CTTop right
Of the pulsating current V of each of the rectifier diodes 16 and 17._RC
Changes according to the instantaneous value of, as shown in FIG.
Voltage V of capacitor 14_CTFrequency changes. This result
As a result, the on / off control signal V in the frequency setting circuit 15
_GIs set to 140k around 150kHz
Since the frequency changes in the range of Hz to 160 kHz, the PWM modulation
ON / OFF control signal V output from the path 12_GFrequency
Is the pulsating voltage V of each rectifier diode 16, 17_RCIn response to the
The modulation is performed in a range of 140 kHz to 160 kHz. But
Therefore, as shown in FIG._GFrequency
The frequency component of input feedback conducted noise whose main component is number is 1
Averagely dispersed in the range of 40 kHz to 160 kHz,
Since noise voltages of these frequencies are not superimposed, noise
The pressure level decreases. The DC-DC converter shown in FIG.
Regarding the basic operation of the barter, the D shown in FIG.
The description is omitted because it is almost the same as that of the C-DC converter.
Abbreviate. A DC-DC converter according to the embodiment shown in FIG.
The pulsating voltage V of each rectifier diode 16, 17_RC
Of the frequency setting circuit 15 in the control circuit 9
Voltage V_CTSuperimposed on each rectifier diode
Pulse voltage V _RCPWM modulation circuit according to
ON / OFF control signal V output from_GThe frequency of
140 kHz to 160 kHz centering on 150 kHz
Modulated in range. This reduces the input feedback conducted noise
Frequency components average in the range of 140kHz to 160kHz
And noise voltages of these frequencies are not superimposed
Therefore, the noise voltage level decreases. Because of this,
If the circuit design can be simplified by reducing parts such as
In both cases, manufacturing costs can be reduced. Accordingly
The switching control signal, that is, the on / off control signal V
_GNoise generated by high frequency components contained in
Can be reduced. The embodiment of the present invention is limited to the above-described embodiment.
It is not specified and various changes are possible. For example,
In the embodiment, the rectifying / smoothing circuit is provided from the secondary winding 4b of the transformer 4.
A constant level DC output voltage V_OHow to get
Although the DC-DC converter of FIG.
From the primary winding 4a through the rectifying and smoothing circuit 8
DC output voltage V_ODC-DC converter that obtains
The present invention can also be applied to Also,
In the above embodiment, the case of the single-phase commercial AC power supply 1 is described.
In the case of three-phase and three-phase or higher polyphase AC power supply
The present invention can also be applied to Furthermore,
In each of the above embodiments, the flyback type DC-DC
Although the present invention has been applied to an inverter,
Forward type or resonant type etc.
The present invention is also applied to other types of DC-DC converters.
It is possible. [0014] According to the present invention, the AC voltage of the AC power supply is
Of the on / off control signal output from the control circuit
By modulating the wave number, the voltage of the input feedback conducted noise
Since the level can be reduced, the number of components such as filter circuits is reduced.
It is possible and there is no need to provide a dedicated low-frequency oscillator,
Measures for noise of DC-DC converter at low cost
Input feedback noise of electronic equipment connected to AC power supply
It is possible to prevent malfunction due to noise. In addition,
DC-DC due to input feedback conduction noise with easy noise countermeasures
It is also possible to suppress fluctuations in the DC output voltage of the converter
Becomes Therefore, higher switching frequency
Switching power supply such as DC-DC converter by wave
Can greatly contribute to the miniaturization and weight reduction of
You.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electric circuit diagram showing an embodiment of a DC-DC converter according to the present invention. FIG. 2 is a waveform diagram showing voltages of respective parts of the DC-DC converter shown in FIG. 3 is a waveform diagram showing a frequency spectrum of input feedback conducted noise of the DC-DC converter shown in FIG. 1 [FIG. 4] An electric circuit diagram showing a conventional DC-DC converter [FIG. 5] The DC-DC converter shown in FIG. Waveform diagram showing frequency spectrum of input feedback conducted noise [Explanation of symbols] 1. Commercial AC power supply (AC power supply), 2. Bridge rectifier circuit (rectifier circuit), 3. Input smoothing capacitor, 4.
..Transformer, 4a..primary winding, 4b..secondary winding, 5..MOS-FET (switching element),
6 ··· Output rectifying diode, 7 ··· Output smoothing capacitor, 8 ··· Rectifying smoothing circuit, 9 ··· Control circuit, 10
..Output voltage detection circuit, 11 Photocouplers, 1
1a ··· Light-emitting unit, 11b ··· Light-receiving unit, 12 ··· PWM
Modulation circuit, 13 ... resistor, 14 ... capacitor, 1
5 ··· Frequency setting circuit, 16,17 ··· Rectifier diode (rectifier element), 18 ·· Series resistance, 19 ·· Modulation means,

Claims (1)

(57) Claims 1. A DC power supply comprising an AC power supply and a rectifier circuit; a transformer having a primary winding and a secondary winding connected in series to the DC power supply; A switching element connected in series to the secondary winding, and a primary winding or 2
A rectifying / smoothing circuit connected to the next winding; and a control circuit for applying an on / off control signal to a control terminal of the switching element according to an output voltage of the rectifying / smoothing circuit. A DC-controller for controlling a ratio of an on / off period of the switching element in accordance with an output voltage of a circuit and extracting a constant-voltage DC output from the primary winding or the secondary winding of the transformer via the rectifying / smoothing circuit; In the DC converter, the control circuit includes: a PWM modulation circuit that controls a ratio of an on / off period of an on / off control signal applied to a control terminal of the switching element; and a frequency setting circuit connected to the PWM modulation circuit. And a series resistor connected between the AC power supply and the frequency setting circuit is provided in the modulating means, and the frequency setting circuit is connected to the frequency setting circuit through the series resistor. Grant AC voltage flow supply, DC-DC converter, characterized in that modulates the frequency of the on-off control signal outputted from the PWM modulation circuit to an AC voltage of the AC power source.