JPH09154278A - Primary smoothing circuit of switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the power factor by using a primary smoothing circuit having the compact and simple constitution, and suppressing noises and the peak value of an input current. SOLUTION: A charging circuit comprising a tertiary winding N3 of a transformer 6 and a high-frequency choke coil CH and a charging diode D1 are connected respectively between a smoothing capacitor C1 and points A and B on a hot line 4p. When a transistor Q is on, electromotive force is generated in the tertiary winding N3, and the capacitor C1 is charged. At the same time, the choke coil CH is excited. When the transistor Q1 becomes off, counter- electromotive force is generated in the choke coil CH, and the capacitor C1 is charged by the same way. Therefore, even if the instantaneous value of the full-wave rectified voltage is lower than the voltage across the terminals of the capacitor C1, the electromotive force of the tertiary winding N3 or the counter-electromotive force of the choke coil CH is applied, the current is inputted from a commercial AC power supply 1 and the capacitor C1 is charged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primary smoothing circuit in a switching power supply unit, which smoothes primary DC power obtained by full-wave rectifying primary AC power input from a commercial AC power source and supplies the smoothed primary DC power to a switching converter.

[0002]

2. Description of the Related Art A switching power supply device is widely used as a power supply device for various electronic devices because of its low cost, small size and light weight, and its excellent conversion efficiency. FIG.
FIG. 1 is a circuit diagram showing an example of a configuration of a most general and widely known conventional switching power supply device.

The switching power supply device shown in FIG.
After the primary AC power input from the commercial AC power source 1 via the input terminals 20a and 20b is full-wave rectified by the diode bridge 21 and smoothed by the smoothing capacitor C5,
Switching is performed by the transistor Q5 connected in series with the primary winding Np of the transformer 22, and the secondary AC power induced in the secondary winding Ns of the transformer 22 by the switching is rectified and smoothed by the secondary rectifying and smoothing circuit 23. The secondary DC power is output to the load 9 from the positive and negative output terminals 24a and 24b.

The switching control circuit (SWC) 25 is
By outputting a drive pulse having a pulse width corresponding to the output voltage detected in the vicinity of the output terminals 24a and 24b to the transistor Q5 to turn it on and off, the output voltage of the switching power supply device becomes a preset voltage. Control.

However, 1 for smoothing the primary DC power
Since the next smoothing circuit is a capacitor input type smoothing circuit consisting of only the capacitor C5 as shown in FIG. 13, the conduction angle of the input AC current is narrow and the peak value of the current is large, so that the commercial AC power supply 1 In addition, it adversely affects other devices connected to the power source 1, and since the input current contains a large amount of high-frequency components of the commercial frequency, the ripple component also increases and heat generation or the like shortens the life of the capacitor C5.

In order to solve the problem of such a capacitor input type smoothing circuit, a choke input type smoothing circuit in which a choke coil is inserted between the diode bridge 21 and the capacitor C5 of FIG. 13 is known. There is. The choke input type smoothing circuit has a wider AC current conduction angle and a smaller current peak value than the capacitor input type smoothing circuit. Therefore, the commercial AC power supply 1 and other devices and capacitors connected to the power supply 1 The adverse effect on the life of C5 is greatly reduced.

However, in order for the choke coil for low frequencies such as the frequency of the commercial AC power source 1 to effectively operate, a large inductance of several mH to several tens of mH is required, so the choke coil is large and heavy. Become,
Not only the cost is greatly increased, but also the resistance of the coil is increased. Further, there is a problem that the phase delay due to the inductance becomes large and the power factor is rather lowered.

Therefore, as shown in FIG. 14, between the diode bridge 21 and the capacitor C5, a choke coil CH6 for high frequency, a diode D6, a transistor Q6, a drive pulse generating circuit (DPG) 27 and a current detecting means, for example, a current. There has been a switching power supply device in which an active filter 26 including a transformer (CT) 28 is inserted to shape a waveform of an input current to improve a power factor and reduce a high frequency component.

That is, in the active filter 26 shown in FIG. 14, when the transistor Q6 is on, the direct current output from the diode bridge 21 flows in the series circuit composed of the choke coil CH6, the current transformer 28, and the transistor Q6. The choke coil CH6 is excited. When the transistor Q6 turns off, the stored excitation energy is reconverted into a current, and the choke coil CH6
And the output voltage of the diode bridge 21 are added to charge the capacitor C5 via the diode D6.

The drive pulse generating circuit 27 includes a capacitor C
In order to detect the voltage between the terminals of 5 and stabilize the voltage,
The output voltage of the diode bridge 21 is detected to form a reference waveform proportional to the full-wave rectified voltage waveform, and the excitation current flowing in the choke coil CH6 when the transistor Q6 is on is detected by the current transformer 28 to detect the excitation current. The drive pulse whose duty ratio is controlled so that the peak value follows the reference waveform is output, and the transistor Q
Turn 6 on and off.

Therefore, the AC current input to the diode bridge 21 from a commercial AC power supply (not shown) has a sine waveform proportional to the AC voltage (both positive and negative), so that the power factor is almost 100% and half of the input current. The conduction angle for each wave is approximately 1
The angle becomes 80 °, the high peak component of the input current disappears and the high frequency component disappears, and the adverse effect on the commercial AC power source side becomes almost zero.

[0012]

However, FIG.
In the switching power supply device shown in FIG. 2, the switching converter has a two-stage configuration, and particularly since the drive pulse generating circuit 27 is more complicated in configuration and operation than the switching control circuit 25, the number of components is increased and the cost is increased. However, increasing size is inevitable.

Further, the drive pulses output by the switching control circuit 25 and the drive pulse generation circuit 27 are
Not only are the frequencies independent of each other, but the pulse width also changes, so the high-frequency components also change intricately, and they interfere with each other, generating broadband noise that extends from the low-frequency region to the high-frequency region. . Therefore, there is a problem that troubles related to EMI such as radio interference easily occur.

The present invention has been made in view of the above points, and simplifies the configuration of the primary smoothing circuit of the switching power supply device to prevent cost increase and size increase, and also causes noise and peak value of input current. The purpose is to suppress power consumption and improve the power factor.

[0015]

In order to achieve the above-mentioned object, the present invention is a primary equipped with a smoothing capacitor for smoothing primary DC power obtained by full-wave rectifying the input primary AC power by a primary rectifier circuit. A smoothing circuit, in which primary DC power smoothed by the smoothing circuit is applied to a series circuit of a primary winding of a transformer and a switching element, and the switching element is switched to induce a secondary winding of the transformer. The secondary smoothing circuit is a primary smoothing circuit for rectifying and smoothing the generated secondary AC power by a secondary rectifying and smoothing circuit and outputting the resulting secondary DC power to a load as follows.

That is, both output terminals of the primary rectifier circuit,
A tertiary winding independent from the primary winding and the secondary winding of the transformer, with one of the lines connecting the primary winding of the transformer and both ends of the series circuit of the switching element as a hot line and the other as a common line. Is provided, and the hot side output terminal of the primary rectifier circuit and the hot side terminal of the smoothing capacitor whose common side terminal is connected to the common line are connected by the series circuit of the tertiary winding and the choke coil, and the smoothing is performed. A charging circuit for charging the capacitor is formed, and a discharging diode is connected between the hot line and the hot side terminal of the smoothing capacitor in a direction to discharge the smoothing capacitor.

In the above primary smoothing circuit, between the point where the hot line charging circuit is connected and the point where the discharging diode is connected, one of the current passing through the discharging diode is
It is advisable to insert a backflow prevention diode that prevents backflow to the next rectifier circuit side.

A commutation diode may be connected between the common line and the connection point between the tertiary winding of the transformer and the choke coil.

Alternatively, in the charging circuit, a stabilizing diode for stabilizing the operation of each part of the charging circuit may be inserted in series with the tertiary winding and the choke coil of the transformer.

Further, at least one of high frequency due to switching is provided between both output terminals of the primary rectifier circuit, between both terminals of the smoothing capacitor, and between the hot line side of the discharging diode and the common line side of the smoothing capacitor. It is better to connect a small-capacity capacitor for bypassing noise.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a circuit diagram showing an example of the configuration of a switching power supply device using a primary smoothing circuit according to a first embodiment of the present invention.

The switching power supply device 10 shown in FIG.
Are input terminals 2a and 2b for primary AC power, a diode bridge 3 which is a primary rectifier circuit, a tertiary winding N3 of a transformer 6, a choke coil CH for high frequency, a capacitor C1 which is a smoothing capacitor, and a discharge Primary smoothing circuit composed of diode D1 which is a diode, primary winding N1 and secondary winding N2 of transformer 6, transistor (may be FET) Q which is a switching element, switching control circuit (SWC) 5 and secondary A switching converter composed of a rectifying and smoothing circuit 7, a positive / negative output terminal 8p of the secondary DC power,
And 8n.

The primary AC power input from the commercial AC power supply 1 via the input terminals 2a and 2b is the diode bridge 3
Is full-wave rectified by and is output from the positive and negative output terminals 3p and 3n, and the positive line 4 is a hot line.
It is supplied to the series circuit of the primary winding N1 of the transformer 6 of the switching converter and the transistor Q via p and the negative line 4n which is a common line.

One end of the tertiary winding N3 of the transformer 6 is connected to the line 4p at the connection point A, and the other end of the tertiary winding N3 is connected to the line through the choke coil CH and the capacitor C1 which are connected in series. 4n. Further, at the connection point between the choke coil CH and the capacitor C1, the diode D1 is placed in the direction of discharging the capacitor C1.
Is connected to one end and the other end is connected to the line 4p at the connection point B to form a primary smoothing circuit.

In the switching converter following the primary smoothing circuit, the transistor Q switches the current flowing through the primary winding N1 of the transformer 6 at high speed to induce a high-frequency secondary AC power in the secondary winding N2. Is rectified and smoothed by the secondary rectifying / smoothing circuit 7, converted into secondary DC power, and output to the load 9 connected to the output terminals 8p and 8n.

The switching control circuit 5 has an output terminal 8
The output voltage of the secondary DC power is detected in the vicinity of p and 8n, the detected voltage is compared with a preset voltage, and if the detected voltage is high, the duty ratio of the drive pulse output to the transistor Q is lowered to reduce it. For example, the output voltage is held at the set voltage by increasing the duty ratio and controlling the on / off of the transistor Q.

FIG. 2 shows the secondary rectifying / smoothing circuit 7 shown in FIG.
FIG. 3 is a circuit diagram showing an example of the configuration of FIG. In the secondary rectifying / smoothing circuit 7 shown in FIG. 2, as is generally well known, the transistor Q (FIG. 1) is turned on, and a current flows in the primary winding (not shown) of the forward type transformer 6. When it flows,
The upper end becomes positive due to the secondary AC power induced in the secondary winding N2, and the current flows through the rectifying diode D7 and the choke coil CH2 to charge the smoothing capacitor C2 and excite the choke coil CH2. .

When the transistor Q is turned off, the electromotive force of the secondary winding N2 becomes 0 and the diode D7 is turned off, but the counter electromotive force is generated in the choke coil CH2 and the right end becomes positive, and the charge is accumulated. The generated excitation energy is reconverted into a current, flows through the capacitor C2 and the commutation diode D8, and charges the capacitor C2. The smoothed secondary DC power charged in the capacitor C2 is output to the load 9 (FIG. 1) connected via the output terminals 8p and 8n.

In FIG. 1, the tertiary winding N3 of the transformer 6
The winding direction of is substantially the same as the winding direction of the primary winding N1. However, hereinafter, when the transistor Q is turned on and a current flows through the primary winding N1, The case where an electromotive force is induced in the direction in which the lower end of the tertiary winding N3 becomes positive will be described as an example. In addition, the negative line 4n, which is a common line, is used as a reference (0 V) for the voltage of each part.
And set the instantaneous value of the output voltage of the diode bridge 3 to V
i, the voltage between the terminals of the capacitor C1 is Vc.

The instantaneous value Vi changes with the fundamental wave having a frequency twice the frequency of the commercial AC power source 1 (commercial frequency).
With respect to such a low frequency, the choke coil CH for a high frequency hardly acts as an inductor, and with respect to the switching frequency of the transistor Q which is turned on / off according to the drive pulse output from the switching control circuit 5. Is
The choke coil CH acts as an inductor.

The current flowing through the primary winding N1 of the transformer 6 when the transistor Q is on is supplied from the diode bridge 3 while the instantaneous value Vi is higher than the terminal voltage Vc,
Needless to say, in the opposite case, the power is supplied from the capacitor C1 through the diode D1, but the primary winding N1
Since an electric current flows through the third winding N3, an electromotive force is generated in the direction in which the lower end of the tertiary winding N3 is positive with respect to the upper end.
The voltage at the lower end of the tertiary winding is higher than the connection points (hereinafter also simply referred to as “points”) A and B by the electromotive force.

Therefore, whether the current source of the primary winding N1 is the diode bridge 3 or the capacitor C1, a part of the supplied current is from the point A to the tertiary winding N.
3. It flows through the choke coil CH and the capacitor C1 to charge the capacitor C1 and act to excite the choke coil CH which acts as an inductor in this case.

When the transistor Q is turned off, the electromotive force of the tertiary winding N3 becomes zero, but a counter electromotive force is generated in the choke coil CH, so that the voltage at the connection point between the choke coil CH and the capacitor C1 is a point. The current becomes higher than that of A and B and the excitation energy accumulated in the choke coil CH is reconverted to flow into the capacitor C1 to be charged. That is, during a period in which the voltage Vc across the terminals of the capacitor C1 is higher than the instantaneous value Vi of the output voltage of the diode bridge 3, the above-described action acts to reduce a part of the discharge current of the capacitor C1.

During a period when the instantaneous value Vi is higher than the inter-terminal voltage Vc, a part of the current output from the diode bridge 3 passes from the point A through the tertiary winding N3 to the choke coil CH that does not act as an inductor. The capacitor C1 is charged by passing in a short circuit, but the current from the diode bridge 3 is switched to the tertiary winding N3 by switching.
And the choke coil CH acting as an inductor, the current described above generated in the charging circuit is superposed to charge the capacitor C1.

Therefore, the peak value of the AC current input from the commercial AC power supply 1 is suppressed, the power factor is improved, and noise is not generated. Further, since the choke coil CH used in the switching power supply device 10 is a high frequency choke coil corresponding to the switching frequency of the transistor Q, compared to the low frequency choke coil used in the conventional choke input type smoothing circuit. , Much smaller and lighter and cheaper.

FIG. 3 is a circuit diagram showing an example of the configuration of a switching power supply device using a primary smoothing circuit according to a second embodiment of the present invention. The switching power supply device 11 shown in FIG. 3 is different from the switching power supply device 10 shown in FIG.
Therefore, the same parts are denoted by the same reference numerals and the description thereof will be omitted.

The primary smoothing circuit of the switching power supply device 11 shown in FIG. 3 differs from the primary smoothing circuit of the switching power supply device 10 in that it is a positive line 4p which is a hot line.
And the tertiary winding N3 and the diode D of the transformer 6, respectively.
1 of the connection points A and B with respect to 1, the point A is arranged on the diode bridge 3 side and the point B is arranged on the primary winding N1 side.
A diode D2, which is a backflow prevention diode, is connected between points A and B so that the current goes from point A to point B so that the discharge current of the capacitor C1 does not flow back to the diode bridge 3 side. .

Since the diode D2 is provided to prevent the reverse flow of the discharge current of the capacitor C1, while the instantaneous value Vi of the output voltage of the diode bridge 3 is higher than the inter-terminal voltage Vc of the capacitor C1, both points A and B have the same value. The voltage becomes the instantaneous value Vi, and conversely, when the voltage is low, the voltage at the point A is the instantaneous value Vi.
However, the voltage at the point B is held at the inter-terminal voltage Vc.

Therefore, the voltage at the terminal of the choke coil CH on the side of the capacitor C1 is higher than the electromotive force generated in the tertiary winding N3 according to the on / off state of the transistor Q rather than the point A where the voltage is always the instantaneous value Vi. Choke coil CH
The voltage is increased by the voltage of the back electromotive force generated at.

Therefore, even if the output voltage of the diode bridge 3, that is, the instantaneous value Vi which is the absolute value of the voltage of the primary AC power is lower than the inter-terminal voltage Vc of the capacitor C1, the instantaneous value Vi and the tertiary winding are obtained. If the sum of the voltage of the electromotive force of the line N3 or the voltage component of the counter electromotive force of the choke coil CH is higher than the terminal voltage Vc, the AC current is input from the commercial AC power source 1 to charge the capacitor C1. In addition to the effect of the primary smoothing circuit of No. 10, the conduction angle becomes wider, and the peak value of the input AC current becomes lower accordingly, the power factor is further improved, and the generation of noise is suppressed.

4 and 5 are circuit diagrams respectively showing an example of the configuration of a switching power supply device using a primary smoothing circuit according to a third embodiment of the present invention. 4 and 5
The switching power supply devices 12 and 13 shown in FIG. 3 are the same as the switching power supply devices 10 and 11 shown in FIG. 1 and FIG. Are denoted by the same reference numerals and description thereof will be omitted.

The primary smoothing circuits of the switching power supply devices 12 and 13 shown in FIGS. 4 and 5 are different from the primary smoothing circuits of the switching power supply devices 10 and 11, respectively.
Between the connection point X of the tertiary winding N3 of the transformer 6 and the choke coil CH and the negative line 4n which is a common line,
The diode D3, which is a commutation diode, is connected in the direction in which the current flows from the line 4n to the connection point X.

As described above, by connecting the diode D3 in parallel to the series circuit of the choke coil CH and the capacitor C1 in the direction of charging the capacitor C1, the excitation energy of the choke coil CH when the transistor Q is turned off. The current reconverted into the direct current charges the capacitor C1 directly through the diode D3 without passing through the diode bridge 3 and the tertiary winding N3.

Therefore, the influence of the voltage fluctuation of the primary AC power input to the diode bridge 3 also affects the primary winding N1 of the transformer 6 through the tertiary winding N3.
Since the secondary winding N2 is not affected, the capacitor C1 is reliably charged by the charging circuit including the tertiary winding N3 and the choke coil CH, and the operation of the switching power supply device 12 or 13 is switched. It is more stable than the power supply device 10 or 11.

FIGS. 6 and 7 are waveform charts showing an example of changes in voltage and current in each part of the switching power supply device 13 shown in FIG. 5, and FIG. 6 shows a capacitor C1.
7 is a voltage waveform and a current when the inter-terminal voltage Vc is higher than the maximum value of the instantaneous value Vi of the output voltage of the diode bridge 3, and when the inter-terminal voltage Vc is lower than the maximum value of the instantaneous value Vi. The waveform is shown.

FIGS. 6 and 7A show changes in the DC voltage of the inter-terminal voltage Vc and the instantaneous value Vi, respectively, and FIGS. 6B and 7B respectively show the commercial AC power supply 1 to the diode bridge. 3 shows the change in the current of the primary AC power input to 3. 6 (A) and 7 (B) each show an example in which the frequency of the commercial AC power supply 1 is 50 Hz, and thus the full-wave rectified instantaneous value Vi of the fundamental wave is 100 Hz. The time axis is 5 ms per scale.

When the load 9 is a light load and a small direct current is supplied, as shown in FIG. 6A, the instantaneous voltage Vi of the output voltage of the diode bridge 3 is always higher than the inter-terminal voltage Vc of the capacitor C1. Is also low. However, in the primary smoothing circuit 13 (FIG. 5) according to the present invention, the instantaneous Vi is
If is not 0, the AC current is input as shown in FIG. 6B, and the waveform is almost proportional to the AC voltage. Therefore, the power factor is extremely high and almost 100%. I understand.

When the load 9 becomes a heavy load and the supplied DC current increases, the terminal voltage Vc of the capacitor C1 decreases and the diode bridge 3 increases, as shown in FIG.
The output voltage becomes lower than the maximum value of Vi at the moment. The waveform of the terminal voltage Vc in this case is very similar to the waveform of the terminal voltage of the capacitor in the conventional capacitor input type smoothing circuit.

However, as shown in FIG. 7B, the waveform of the alternating current to be input is such that the instantaneous value Vi is such that no alternating current is input in the case of the conventional capacitor input type smoothing circuit. Even if the voltage is lower than the voltage Vc, if it is not 0, the AC current is input from the commercial AC power supply 1. Therefore, when the capacity and load of the smoothing capacitor are the same, the decrease in the inter-terminal voltage Vc, that is, the ripple in the voltage of the primary DC power is far greater than that in the conventional capacitor input type smoothing circuit. It's getting less.

The period during which the instantaneous value Vi shown in FIG. 7A exceeds the terminal voltage Vc, that is, the period corresponding to the charging period of the smoothing capacitor in the conventional capacitor input type smoothing circuit, is the same. As shown in (B) of the figure,
An increase in the input AC current is observed, but the peak value is also greatly suppressed. Therefore, the power factor is slightly lower than that shown in FIG. 6, but its fluctuation range is also small.

Although the example of the switching power supply device 13 shown in FIG. 5 has been described above, the switching power supply devices 10 to 12 shown in FIGS. 1 and 3 and 4 respectively correspond to the weight of the load 9. Terminal voltage Vc, instantaneous value Vi
The respective voltage waveforms and the waveform of the input AC current are the same as the respective waveforms shown in FIGS. 6 and 7.

FIG. 8 and FIG. 9 are circuit diagrams respectively showing an example of the configuration of a switching power supply device using a primary smoothing circuit according to a fourth embodiment of the present invention. The switching power supply devices 14 and 15 shown in FIGS. 8 and 9 are different only in the parts constituting the primary smoothing circuit, and other parts are the same as those in FIG.
3 and the same as the switching power supply devices 10 and 11 shown in FIG.

The primary smoothing circuits of the switching power supply devices 14 and 15 shown in FIGS. 8 and 9 are different from the primary smoothing circuits of the switching power supply devices 10 and 11, respectively.
That is, a diode D4, which is a stabilizing diode, is connected between the connection point A and the tertiary winding N3 of the transformer 6 in a direction to charge the capacitor C1.

The diode D4 is not limited to the above and illustrated positions, but the choke coil CH,
Between the common connection point Y of the diode D1 and the capacitor C1 and the connection point A, that is, at any position in the charging circuit, as long as the polarity direction is the same (direction in which current flows from point A to point Y) , And the same action and effect are obtained, respectively.

By connecting the diode D4 in series in the charging circuit, the transistor Q is turned on.
Even if an electromotive force is generated in the tertiary winding N3 or a back electromotive force is generated in the choke coil CH depending on the off state, the voltages at points A and B with respect to the common line 4n and both terminals of each element are stable. As a result, the primary smoothing circuit, and thus the switching power supply devices 14 and 15 are each more stabilized, and the operation is ensured.

10 and 11 are circuit diagrams respectively showing another example of the configuration of the switching power supply device using the primary smoothing circuit according to the fourth embodiment of the present invention. The switching power supply devices 16 and 17 shown in FIG. 10 and FIG. 11 are different from each other only in the parts constituting the primary smoothing circuit.
Others are the switching power supply device 1 shown in FIGS. 4 and 5.
Since they are the same as 2 and 13, respectively, the same parts are designated by the same reference numerals and the description thereof will be omitted.

The primary smoothing circuits of the switching power supply devices 16 and 17 shown in FIGS. 10 and 11 differ from the primary smoothing circuits of the switching power supply devices 12 and 13, respectively, in that the tertiary winding N3 and the choke coil CH are used. The diode D5, which is a stabilizing diode, is connected between the choke coil CH and the connection point X between the line connecting the line and the commutation diode D3.

The diode D5 is not limited to the above and illustrated positions, but the choke coil CH,
At any position between the common connection point Y and the connection point X of the diode D1 and the capacitor C1, as long as the polarity direction is the same (the direction in which the current flows from the point X to Y), the same operation is performed. And the effect is obtained.

The diode D5 connected in this manner is the same as the stabilizing diode D4 (see FIG. 8,
Since the position of 9) is limited between the point X and the point Y, the operation is exactly the same. However, when the commutation diode D3 is provided, it is more stable when the stabilizing diode is connected between the point X and the point Y than when it is connected between the point A and the point X. Was confirmed experimentally.

FIG. 12 is a circuit diagram showing an example of the configuration of the switching power supply device according to the fifth embodiment of the present invention. The switching power supply device 18 shown in FIG. 12 is the same as the switching power supply device 10 shown in FIG. 1 except that the positive and negative output terminals 3p and 3n of the diode bridge 3 or both terminals of the smoothing capacitor C1 or the discharging diode D are used.
1 hot line 4p side connection point B and smoothing capacitor C
A small-capacity capacitor Cp for bypassing high-frequency noise is connected to at least one of the connection points on the common line 4n side, as shown by the broken line.

As described above, by connecting the capacitor Cp, the high frequency noise generated by the switching of the transistor Q can be bypassed, and troubles related to EMI such as electromagnetic interference to other parts can be easily prevented. I can. Note that FIG. 12 shows a case where the present invention is applied to the switching power supply device 10 as the fifth embodiment, but is applied to the switching power supply devices 11 to 17 shown in FIGS. 3 to 5 and 8 to 11, respectively. However, it goes without saying that the same effect can be obtained.

[0062]

As described above, the primary smoothing circuit of the switching power supply device according to the present invention has a simple structure, is small in size, is light in weight, and is inexpensive, while suppressing the generation of noise and the peak value of the input alternating current, The rate can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a configuration of a switching power supply device using a primary smoothing circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a configuration of a secondary rectifying / smoothing circuit shown in FIG.

FIG. 3 is a circuit diagram showing an example of a configuration of a switching power supply device using a primary smoothing circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing an example of a configuration of a switching power supply device using a primary smoothing circuit according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing another example of the configuration of the switching power supply device using the primary smoothing circuit according to the third embodiment of the present invention.

FIG. 6 is a waveform diagram showing an example of changes in voltage and current in each part of the switching power supply device shown in FIG.

FIG. 7 is a waveform diagram showing another example of changes in voltage and current in each part of the switching power supply device shown in FIG.

FIG. 8 is a circuit diagram showing an example of a configuration of a switching power supply device using a primary smoothing circuit according to a fourth embodiment of the present invention.

FIG. 9 is a circuit diagram showing another example of the configuration of the switching power supply device using the primary smoothing circuit according to the fourth embodiment of the present invention.

FIG. 10 is a circuit diagram showing still another example of the configuration of the switching power supply device using the primary smoothing circuit according to the fourth embodiment of the present invention.

FIG. 11 is a circuit diagram showing still another example of the configuration of the switching power supply device using the primary smoothing circuit according to the fourth embodiment of the present invention.

FIG. 12 is a circuit diagram showing an example of a configuration of a switching power supply device using a primary smoothing circuit according to a fifth embodiment of the present invention.

FIG. 13 is a circuit diagram showing an example of a configuration of a switching power supply device using a conventional capacitor input type smoothing circuit.

FIG. 14 is a circuit diagram showing an example of a configuration of a switching power supply device using a conventional active filter as a smoothing circuit.

[Explanation of symbols]

 1: Commercial AC power supply 3: Diode bridge (primary rectification circuit) 4p: (Positive) line (hot line) 4n: (Negative) line (common line) 6: Transformer 7: Secondary rectification smoothing circuit 9: Load 10 to 18: Switching power supply device A, B, X, Y: Connection point C1: Capacitor (smoothing capacitor) CH: Choke coil Cp: Small-capacity capacitor D1: Discharge diode D2: Backflow prevention diode D3: Commutation diode D4, D5: Stabilizing diode N1: Primary winding N2: Secondary winding N3: Tertiary winding Q: Transistor (switching element) Vi: Instantaneous value of output voltage of diode bridge 3 Vc: Between terminals of capacitor C1 Voltage

Claims (5)

[Claims] 1. A primary smoothing circuit comprising a smoothing capacitor for smoothing primary DC power obtained by full-wave rectifying the input primary AC power by a primary rectifying circuit, the primary smoothing being smoothed by the smoothing circuit. The DC power is applied to the series circuit of the primary winding of the transformer and the switching element, and the secondary AC power induced in the secondary winding of the transformer by switching the switching element is converted by the secondary rectifying and smoothing circuit. In a primary smoothing circuit of a switching power supply device that performs rectification and smoothing and outputs to a load as secondary DC power, both output terminals of the primary rectification circuit, and both ends of a series circuit of a primary winding of the transformer and a switching element. A third winding independent of the primary winding and the secondary winding is provided in the transformer by using one of the lines connecting the A series circuit of a winding and a choke coil connects the hot side output terminal of the primary rectifier circuit and the hot side terminal of the smoothing capacitor whose common side terminal is connected to the common line to form the smoothing capacitor. A charging circuit for charging the capacitor is formed, and a discharging diode is connected between the hot line and a hot-side terminal of the smoothing capacitor in a direction to discharge the smoothing capacitor. Smoothing circuit. 2. The primary smoothing circuit of the switching power supply device according to claim 1, wherein the hot line is connected between the point where the charging circuit is connected and the point where the discharging diode is connected. A primary smoothing circuit of a switching power supply device, characterized in that a reverse current preventing diode for preventing a reverse current of a current passing through the diode to the primary rectifying circuit side is inserted. 3. The primary smoothing circuit of the switching power supply device according to claim 1, wherein a commutation diode is connected between a connection point between the tertiary winding of the transformer and the choke coil and the common line. A primary smoothing circuit for a switching power supply device characterized in that 4. The primary smoothing circuit of the switching power supply device according to claim 1, wherein in the charging circuit, the tertiary winding of the transformer and the choke coil are connected in series. A primary smoothing circuit of a switching power supply device, wherein a stabilizing diode for stabilizing the operation of each part of the charging circuit is inserted. 5. The primary smoothing circuit of the switching power supply device according to claim 1, wherein the output terminals of the primary rectifying circuit, the terminals of the smoothing capacitor, and the discharge are provided. A switching power supply device characterized in that a small-capacity capacitor for bypassing high-frequency noise due to switching is connected to at least one of the hot line side of the diode and the common line side of the smoothing capacitor. Primary smoothing circuit.