JP2640741B2 - Noise reduction circuit in switching power supply circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a noise reduction circuit in a switching power supply circuit. More specifically, recently, in order to downsize a switching power supply circuit, a high-frequency switching system has been generally adopted. The present invention
An object of the present invention is to reduce noise caused by a reverse current at the time of turning off an output rectifier and / or a commutation rectifier as an output rectifier of such a switching power supply circuit.

2. Description of the Related Art As shown in FIG. 9, a switching power supply circuit using a so-called forward converter circuit includes a primary winding (4) of a transformer (3) between input DC power supply terminals (1) and (2). ), A MOSFET (5) which is a semiconductor switching element is connected, and rectifiers (7) and (8) for output and commutation on the output side are connected to the secondary winding (6) of the transformer (3). Connected to the output terminal (1) via the filtering reactor (9) and the capacitor (10).
1) (12) connected to this output terminal (11) (12)
The output voltage is detected and amplified by a detection amplifier circuit (13), and this detection signal is passed through an isolator (14) to the MOSFET.
In addition to (5), the switching of the MOSFET (5) is controlled to stabilize the output voltage.

In the switching power supply as described above, the noise appearing at the output terminals (11) and (12) is the most important trouble.

In the switching power supply circuit shown in FIG. 9, the largest noise source is when the rectifiers (7) and (8) on the output side connected to the secondary winding (6) of the transformer (3) are turned off. is there. This is the output rectifier (7) (8)
Is discharged as a reverse current, a pulse-like surge current flows, and a large noise voltage is generated between the output terminals (11) and (12) due to the surge current. Also,
Even when a shot barrier diode is used, similar noise is generated due to the junction capacitance between the semiconductor and the metal. More specifically, in FIG. 10 (b), Ii indicates the secondary current Ii in FIG. 9, and T _{1 in} FIGS. 10 (a) and 10 (b).
-T ₄ is a time on the MOSFET (5). MOSFET (5)
Power Ii than at T ₁ of the turn-on is increased, it reached the time T _2,
T ₂ is commutated current is cut off between the previously rectifier (8) and the reactor (9), between T ₂ -T _3, the recovery current Ir ₂ at the turn-off of the commutation rectifier (8) is added And flows as a reverse current of the commutation rectifier (8).

Next, when T ₄ at MOSFET (5) is turned off, the applied voltage of the output rectifier (7) is reversed current decreases, further flows as the recovery current Ir ₁ is reverse current also the output rectifier (7) . Output rectifier and absorbs recovery current somewhat (7) is led to have a reverse voltage blocking capability, T ₅ -T ₆ between rapid recovery current Ir ₁ to becomes zero decreases. The _{T 5 -T 6, T 2 -T} 3 , etc. of the rectifier (7) (8)
The output voltage V _O at the time of reduction of the recovery current of equal, the noise voltage Vn ₁ by commutating rectifier (8) as shown in FIG. 10 (a), the noise voltage Vn ₂ by output rectifier (7) Appear.

As shown in FIG. 9, the output and commutation rectifiers (7) and (8) for reducing these noise voltages Vn ₁ and Vn ₂ include:
Usually, a so-called RC snubber circuit in which resistors (15) and (16) and capacitors (17) and (18) are connected in series is added. When the accumulated charges of the rectifiers (7) and (8) for output and commutation are discharged as reverse currents, these resistors (15)
(16) and capacitors (17) and (18).

"Problems to be solved by the invention" These measures reduce noise considerably,
Elements such as the resistors (15) and (16) and the capacitors (17) and (18) generate power loss. In particular, this causes a large loss when the switching frequency of the MOSFET (5) is increased, and reducing this loss and effectively reducing noise has been a serious problem in designing and manufacturing a power supply.

A different approach to this solution is to use a reactor (19) having a square saturation characteristic in series with the rectifier (7) as shown in FIG.
(See, for example,
-147982).

In the following, the reason for improvement by the reactor (19) will be clarified, the disadvantages thereof will be described, and then, means for overcoming the disadvantages while retaining this characteristic according to the present invention will be described.

FIG. 12 shows the secondary side voltage Vi of the transformer (3), the applied voltage Vs of the saturable reactor (19) and the passing current Ii of FIG.

In these drawings, first, when T ₄ at voltage Vi is reversed, Vi is applied in the direction in which the output terminal (12) side of Figure 11 is positive. This moment rectifier (7) does not have a reverse blocking capability, current Ii is not only lower than the peak value, T ₄ Recovery reverse current Ii of -T rectifier between ₅ (7)
r passes. The magnitude and shape of this reverse current are limited by the magnetic flux φ of the reactor (19) in FIG. 13 and the characteristics shown in the current Ii curve, and the peak value thereof is also Ir in FIG. 10 (b).
Not only does it significantly decrease than ₁ , but the waveform at the time of the decrease becomes gentle. Therefore, the noise indicated by Vn ₂ in FIG. 10A generated at the time of the voltage reversal is significantly reduced.

Note that noise generated when the current Ii between T _{2 and} T ₃ rises is also reduced as compared with FIG. 10A. This is a reactor (1
This is because the rise of Iir becomes slow due to the residual inductance at the time of 9) saturation.

The above is an advantage of inserting the square-shaped saturation reactor (19). However, in the reactor (19), the high inductance that blocks the reverse current of the rectifier (7) on the output side also blocks the forward current of the rectifier (7), and conversely, the MOSFET ( Excessive surge voltage is generated at both ends of 5). The disadvantages of this circuit are that the available pulse width is limited to between T _{3 and} T ₄ , and that the power loss of the reactor (19) reduces the overall efficiency as compared with the conventional system of FIG. I do.

`` Means for solving the problem''The present invention provides a switching power supply circuit including an output-side rectifier that operates in synchronization with opening and closing of a semiconductor switching element for power conversion. A reactor having square-shaped saturation characteristics inserted in series with the rectifier on the output side, and a rectifier connected in parallel to both ends of the reactor and opposite to the rectifier on the output side inserted in series with the reactor; A noise reduction circuit in a switching power supply circuit, wherein a magnetic snubber circuit including a series circuit of a linear reactor connected in series is connected.

[Operation] The reactor is connected in series with the rectifier on the output side, and a magnetic snubber circuit including a rectifier in the opposite direction to the rectifier and a series circuit of a linear reactor connected in series to the rectifier is connected. The recovery current when the charge stored in the rectifier flows as a reverse current is suppressed by the magnetic snubber circuit, reducing the noise caused by the recovery current and reducing the power loss. Can be

Embodiment An embodiment of the present invention will be described below with reference to FIGS. The same parts as those of the conventional circuit are denoted by the same reference numerals.

In FIG. 1, (1) and (2) are input terminals of a DC power supply, and between the input terminals (1) and (2), a primary winding (4) of a transformer (3) and a semiconductor switching element. MOSFET (5)
Are connected in series.

One end of the secondary winding (6) of the transformer (3) is connected to an anode of an output rectifier (7) for rectifying an induced voltage of the reactor (19) and the secondary winding (6) having a square saturation characteristic. , Cathode,
Filtering reactors (9) are connected in series to one output terminal (11) in series. The other end of the secondary winding (6) is connected to the cathode of the output rectifier (7) via the anode and cathode of a commutation rectifier (8) for rectifying the induced voltage of the filtering reactor (9). As well as
The output terminal (12) is connected, and a filtering capacitor (10) is connected between the output terminals (11) and (12). further,
A detection amplifier circuit (13) for detecting and amplifying the output voltage is coupled to the output terminals (11) and (12). The detection amplifier circuit (13) is connected via an isolator (14) for insulation. It is coupled to the gate of the MOSFET (5).

In such a circuit, the output rectifier (7) is connected to the reactor (19) having the square-shaped saturation characteristic and both ends of the reactor (19), and has a direction opposite to that of the output rectifier (7). An improved snubber circuit (hereinafter referred to as a magnetic snubber circuit) according to the present invention, comprising a series circuit of a rectifier (20) having a forward direction and a linear reactor (21) is connected.

A series circuit of a resistor (16) and a capacitor (18) is provided at both ends of the commutation rectifier (8), and a rectifier connected to the both ends of the resistor (16) in the opposite direction to the commutation rectifier (8). The general RCD snubber circuit configured by (22) is connected for convenience.

The operation of the above configuration will be described with reference to FIG.

When the voltage Vi of the secondary winding (6) is (+), it is blocked by the rectifier (20) and no voltage or current exists in the linear reactor (21).

The operation between T _{4 and} T ₇ when the voltage Vi is applied with (−) will be described.

Output rectifier (7) does not recover reverse blocking function T ₄ -T ₅
Between the voltage the same between T ₄ -T ₅ of the Figure 12 it is applied. It is assumed that the forward voltage drop of the rectifier (20) is zero.

The voltage of T ₄ −T ₅ causes a current to flow to the linear reactor (21).
I ₄ flows, T _5:00 increases. T ₅ output rectifiers in time (7) is recovered to the voltage V ₄ becomes zero reverse blocking function, the current I ₄ during the next T ₅ -T ₅ 'decreases. During this time, the voltage V ₄ Is induced, which is the voltage product between T _{4 and} T ₅ , and the following equation is naturally satisfied as the characteristic of the linear inductance.

V ₄ of the right term becomes the power supply of the reactor (19). This T ₅
During −T ₅ ′, since the reactor (19) is in the unsaturated region and has high impedance, almost the same amount of the voltage V ₄ is applied to the reactor (19), and the magnetic flux equivalent to the voltage-time product of the right term is generated. Set.

To explain this third diagram, the magnetic flux which is set at T ₅ point means that it is pulled back almost located close to the saturation point at T ₅ 'point.

When the voltage Vi turns positive at the point T ₇ (T ₁ ), at this time, as is apparent from FIG. 3, since the characteristic curve of the magnetic flux φ-current Ii is almost near the saturation point, In Figure 13 Neither the volt-time product nor the time T ₁ -T ₂ is needed, and immediately the reactor (19) saturates and the current Ii starts to rise.

In this way, in the method of FIG. 11, T ₁ −
Dead time exists between T ₂ are, it will not exist in the manner of Figure 1.

As described above, not only can the effective pulse width be expanded, And Is directly related to the power loss of the reactor (19), but in the system of FIG. Because There is minimum, the power loss of the reactor (19) is halved, Note that the rectifier (20) and reverse current is passed through the I ₄ between a non-existent when the T ₁ -T ₄ of the reactor (21) This rectifier (20) is a necessary condition of the present invention because it not only overheats but also makes the above operations impossible.

The operation described above works exactly the same in the full-wave output type shown in FIGS. That is, in FIG. 4, the input DC power supply terminals (1) and (2) are connected to a primary winding (4) of a transformer (3) and two MOSFETs (5a) (5b) that open and close alternately. ) And connect a capacitor,
The secondary winding (6) of the transformer (3) is coupled with two output rectifiers (7a) (7b), a filtering choke (9) and a capacitor (10), and furthermore an output terminal (11). The output voltage detection and amplification circuit (13) coupled to (12) is coupled to the gates of the MOSFETs (5a) and (5b) through isolators (14a) and (14b) to alternately perform open / close control operations and output. In a so-called half-bridge, full-bridge, push-pull, etc. full-wave output type converter circuit for stabilizing a voltage, a center tap type secondary winding (6) of a transformer (3) includes:
Output rectifiers (7a) and (7b) are connected in series, and these output rectifiers (7a) and (7b) are connected to reactors (19a) (19b) and rectifiers (20a) (20b) each having square saturation characteristics. And a magnetic snubber circuit comprising linear reactors (21a) and (21b).

In FIG. 5, as in FIG. 4, in a full-wave output type converter circuit such as a half bridge, a full bridge, a push-pull, etc., the secondary winding (6) of the transformer (3) is connected to the secondary winding (6).
The output rectifiers (7a) (7b) (7c) (7d) are combined in a so-called bridge type, and each output rectifier (7a) (7b) (7
c) In (7d), a reactor with square-shaped saturation characteristics (19a)
(19b) (19c) (19d) and rectifiers (20a) (20b) (20
c) (20d) and linear reactors (21a) (21b) (21
c) A magnetic snubber circuit consisting of (21d) is connected to each other.

It is obvious that the operations in FIGS. 4 and 5 are exactly the same as those in FIG.

In FIGS. 1, 4 and 5, the reactor (1
9), (19a), (19b), (19c), and (19d) desirably have square characteristics, but the operation of the present invention is also possible with a ferrite core reactor other than a linear reactor with a gap. .

Further, according to the circuit configuration of the present invention, the resistor (15) and the capacitor (17) connected to the output rectifier (7) of FIG.
Becomes unnecessary, and this power loss is eliminated. Further, as will be described below, if the snubber circuit of the commutation rectifier (8) is improved and used together, these losses are remarkably reduced, and not only the noise but also the efficiency are greatly improved as compared with the circuit of FIG. This is also more pronounced with higher frequencies.

 This will be described in more detail.

FIG. 7 shows that a snubber circuit composed of a resistor (16) and a capacitor (18) is added to the commutation rectifier (8) in the same way as the conventional circuit of FIG. the turn-on of T ₃ at the reactor due to saturation (19)
As shown in FIG. 6 (b), a spike voltage about three times the steady voltage is generated due to the resonance between the residual inductance and the capacitor (18), which also increases the noise at the output end. When the commutation rectifier (8) and the reverse rectifier (22) are connected in parallel with the resistor (16), the spike voltage effectively reduces the steady applied voltage as shown in FIG. 6 (c).
It is suppressed to about 1.2 to 1.5 times. This utilizes the residual inductance of the reactor (19) conversely, thereby greatly reducing output noise. This is shown in FIGS. 7 and 8.
This is because the constants of the resistor (16) and the capacitor (18) in the figure are also significantly different.

For example, in an output 15V, 3A, 500KHz circuit, in FIG. 7, a resistor (16): 220Ω (2W), a capacitor (18): 200pF In FIG. 8, a resistor (16): 20KΩ (1 / 2W), a capacitor (18) ): 1000pF.

The circuit inserted in parallel with the commutation rectifier (8) on the output side in FIG.
In the figure, the power loss of the resistor (16) and the capacitor (18) was 1.5 W, but was 0.25 W in the method of FIG. Further, in the system of FIG. 7, the loss increases in proportion to the increase of the frequency, but in the system of FIG. 8, the loss is almost independent of the frequency due to the characteristics of the voltage clamp circuit.

In FIG. 8, the commutation rectifier (8) on the output side
In parallel, a rectifier (22) is added to the resistor (16) and the capacitor (18), and a general example in which a snubber circuit improved from the snubber circuit of FIG. 7 is used. However, the present invention does not intend the improved snubber circuit of FIG. 8 which is an improvement of the circuit of FIG.

In the present invention, this commutation rectifier (8) on the output side
And a rectifier connected in parallel to both ends of the reactor and opposite to the commutation rectifier (8) inserted in series with the reactor, and connected in series with the rectifier. And a magnetic snubber circuit composed of a series circuit of the linear reactors.

Next, FIG. 14 shows an example in which the present invention is applied to a so-called chopper type switching power supply circuit. That is, in the conventional circuit, when the semiconductor switching element (5) is turned on, a large reverse recovery current flows through the commutation rectifier (8), which is the rectifier on the output side, and this generates a large noise voltage on the output side. In the example of FIG. 14, a square-shaped saturation characteristic reactor (19) inserted in series with the commutation rectifier (8) and rectifiers (20) inserted at both ends of the reactor (19) are installed in the commutation rectifier (8). And a magnetic snubber circuit comprising a series circuit of a linear reactor (21).

With this configuration, the recovery current of the commutation rectifier (8) is suppressed without impairing the characteristics of the commutation rectifier (8) when it is turned on (when the semiconductor switching element is turned off). The drastically reduced output noise is similar to the above-described operation.

“Effects of the Invention” (1) The present invention relates to a reactor having square-shaped saturation characteristics and an output side connected in parallel to both ends of the reactor to an output rectifier in a switching power supply circuit and having the reactor inserted in series. A magnetic snubber circuit consisting of a rectifier in the opposite direction to the rectifier and a series circuit of a linear reactor connected in series to the rectifier is connected, so that the output noise suppression effect due to the recovery current of the output rectifier is reduced. The power loss is more than twice that of the conventional system, and the power loss in that portion is about one third, and a more remarkable effect can be obtained with the increase in frequency.

(2) The present invention suppresses the noise caused by the recovery current when the accumulated charge of the rectifier is discharged as a reverse current, so that the output is used to rectify the voltage induced in the secondary winding on the output side. The present invention can be used not only in a rectifier but also in a commutation rectifier in a chopper type switching power supply circuit of a type of a switching power supply circuit.
That is, a pulse signal chopped by the semiconductor switching element is obtained through a filtering reactor, a filtering capacitor and a commutation rectifier for rectifying a voltage induced in the filtering reactor, to obtain a smooth DC output voltage, and the output voltage is detected and amplified. A commutation rectifier in a chopper-type switching power supply circuit configured to obtain a desired output by controlling the switching period of a semiconductor switching element by detecting and amplifying in a circuit also includes a square-shaped saturation characteristic reactor, a rectifier, and a linear reactor. By inserting a magnetic snubber circuit, noise caused by the recovery current of the commutation rectifier can be reduced.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a first embodiment of a noise reduction circuit in a converter circuit according to the present invention, FIG. 2 is an output waveform diagram of each part in FIG. 1, FIG. FIG. 4 is an electric circuit diagram showing a second embodiment of the present invention,
FIG. 5 is an electric circuit diagram showing a third embodiment of the present invention, FIG. 6 is an output waveform diagram of FIGS. 7 and 8, and FIG. 7 is a case where a magnetic snubber circuit is connected to an output rectifier to form a commutator. FIG. 8 is an electric circuit diagram in which a conventional snubber circuit is connected to a rectifier, FIG. 8 is an electric circuit diagram in which a snubber circuit obtained by improving the conventional snubber circuit in FIG. 7 is connected, FIG. 9 is a conventional converter circuit diagram, and FIG. 9 is an output waveform diagram of each part in FIG. 9, FIG. 11 is a circuit diagram of a main part in FIG. 9, FIG. 12 is an output waveform diagram of each protection in FIG. 11, and FIG.
FIG. 14 is an electric circuit diagram showing a fourth embodiment of the present invention. (1) (2) ... input power terminal, (3) ... transformer,
(4)… Primary winding, (5) (5a) (5b)… Semiconductor switching element (MOSFET), (6)… Secondary winding, (7) (7a)
(7b) (7c) (7d) (8) (20) (20a) (20b) (20
c) (20d) (22) rectifier, (9) (19) (19a) (1
9b) (19c) (19d) ... reactor, (10) (17) (18)
…… Capacitor, (11) (12) …… Output terminal, (13)…
… Output voltage detection amplifier circuit, (14) (14a) (14b)… Isolator, (15) (16)… Resistance.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tokunari Inoue 2559-1 Honmachida, Machida-shi To 3-404 (56) References JP-A-55-147982 (JP, A) JP-A-60-31624 (JP, A) JP-A-61-280769 (JP, A) Journal of the Japan Society of Applied Magnetics, 12 [2] (1988), p. 389-394

Claims (5)

(57) [Claims] 1. A switching power supply circuit comprising an output rectifier which operates in synchronization with the opening and closing of a semiconductor switching element for power conversion, wherein the switching rectifier is inserted in series with the output rectifier. And a linear reactor connected in parallel to both ends of the reactor and opposite to the output rectifier inserted in series with the reactor and a linear reactor connected in series with the rectifier. A noise reduction circuit in a switching power supply circuit, wherein a magnetic snubber circuit including a series circuit is connected. 2. A switching power supply circuit comprising: a semiconductor switching element (5) for power conversion connected to DC power input terminals (1) and (2) via a primary winding (4) of a transformer (3). The secondary winding (6) of the transformer (3) is turned on and off in synchronization with the turning on and off of the semiconductor switching element (5) to apply an induced voltage of the secondary winding (6). An output rectifier (7) as a rectifier on the output side to be rectified, a filtering reactor (9), a filtering capacitor (10), and a commutating rectifier for commutating a voltage induced in the filtering reactor (9). (8) and a converter circuit for controlling the switching time of the semiconductor switching element (5) to stabilize the output voltage. The output rectifier (7) includes the output rectifier ( 7) a reactor (19) having a square saturation characteristic inserted in series with the reactor (19); A rectifier (20) connected in parallel to both ends of the rectifier (19) and opposite to the output rectifier (7) inserted in series with the reactor (19);
2. A noise reduction circuit in a switching power supply circuit according to claim 1, wherein a magnetic snubber circuit comprising a series circuit of a linear reactor (21) connected in series to the switching power supply circuit is connected. 3. A switching power supply circuit comprising two semiconductor switching elements which alternately open and close to DC power input terminals (1) and (2) via a primary winding (4) of a transformer (3). (Five
a) and (5b) are connected, and the semiconductor switching element (5a) is connected to a center tap type secondary winding (6) of the transformer (3).
(5b) output rectifiers (7a) and (7b) as output-side rectifiers that perform on and off operations in synchronization with the on and off operations of each of the (5b) and rectify the induced voltage of the secondary winding (6); Combine the filtering reactor (9) and the filtering capacitor (10),
A full-wave output type converter circuit configured to alternately control the switching time of the semiconductor switching elements (5a) and (5b) to stabilize the output voltage, and the output rectifier (7a);
In (7b), reactors (19a) with square-shaped saturation characteristics inserted in series with output rectifiers (7a) and (7b), (1
9b) and output rectifiers (7a) and (7b) connected in parallel to both ends of the reactors (19a) and (19b) and inserted in series with the reactors (19a) and (19b). Claims comprising connecting a magnetic snubber circuit comprising a rectifier (20a), (20b) and a series circuit of linear reactors (21a), (21b) connected in series to the rectifier (20a), (20b). 3. A noise reduction circuit in a switching power supply circuit according to claim 1. 4. A switching power supply circuit comprising: two semiconductor switching elements that alternately open and close via DC coil input terminals (1) and (2) via a primary winding (4) of a transformer (3). (Five
a) and (5b) are connected, and the secondary winding (6) of the transformer (3) is turned on and off in synchronization with the on and off of the semiconductor switching elements (5a) and (5b). An output rectifier (7a) (7d), (7b) (7c) as an output-side rectifier that operates to rectify the induced voltage of the secondary winding (6), a filtering reactor (9), and a filtering rectifier (7). A full-wave output type converter circuit, which is connected to a capacitor (10) and alternately controls the switching time of the semiconductor switching elements (5a) and (5b) to stabilize the output voltage; Rectifier (7a) (7
d), (7b) and (7c) are connected to the output rectifier (7a) (7
d), (7b), (7c), and reactors (19a) (19d), (19b) (19c) having a square saturation characteristic inserted in series with the reactors (19a) (19d), (19b) (19c) ) Are connected in parallel to both ends of the reactor (19a) (19d), (19b) (19)
Output rectifiers (7a) (7d), (7)
b) Rectifiers (20a) (20d), (20b) opposite to (7c)
(20c) and this rectifier (20a) (20d), (20b) (20
The linear reactor (21a) (21
2. A noise reduction circuit in a switching power supply circuit according to claim 1, wherein a magnetic snubber circuit comprising a series circuit of d), (21b) and (21c) is connected. The switching power supply circuit outputs a pulse signal chopped by turning on and off a semiconductor switching element (5) for power conversion to a DC output via a filtering reactor (9) and a filtering capacitor (10). And a voltage induced in the filtering reactor (9) is changed to a direct current through a commutation rectifier (8) as an output-side rectifier that operates on and off in synchronization with on and off of the semiconductor switching element. The chopper rectifier (8) includes a chopper-type switching power supply circuit configured to obtain an output and control a switching period of the semiconductor switching element (5) to obtain a desired output. ) And a reactor (19) having a square-shaped saturation characteristic inserted in series with a commutation rectifier connected in parallel to both ends of the reactor (19) and inserted in series with the reactor (19) 2. A magnetic snubber circuit comprising a rectifier (20) having a direction opposite to that of (8) and a series circuit of a linear reactor (21) connected in series to the rectifier (20). A noise reduction circuit in the switching power supply circuit described in the above.