JPS60174064A - Dc/dc converter circuit - Google Patents

Abstract

PURPOSE:To separate a digital channel terminating unit from the high impedance of a subscriber by separating the primary and secondary sides via the high impedance from DC over to high frequency range. CONSTITUTION:Electrostatic shielding layer 46p is provided between the primary winding 27 and the secondary winding 28, and connected with the primary side 18a of the stationary end of the primary winding 27, and the switching voltage e1 generated across the primary winding 27 is not generated as a voltage (in phase mode switching noise) between the primary side 18a and the secondary side 19a. An electrostatic shielding layer 46s is provided between the layer 46p and the secondary winding 28, and connected with the secondary side 19a of the stationary end side of the secondary winding 28, thereby similarly eliminating the generation of the switching voltage e2 generated across the secondary winding 28.

Description

[Detailed Description of the Invention] [Field to which the invention pertains] This inventor switches DC power and supplies it to the primary winding of a transformer, rectifies and smoothes the output of the secondary winding of the transformer, and obtains a y DC output. DC-DC converter circuit (hereinafter referred to as DO7)
It is called a DO conversion circuit. ) regarding.

In particular, the present invention relates to a DC-DC conversion circuit in which input and output are separated by high impedance and generation of common-mode switching noise is suppressed.

This invention is based on the earlier patent application filed in 1983-132 filed by the same applicant.
564 and Japanese Patent Application No. 57-132365.

[Description of prior art]

FIG. 1 shows a digital line termination device installed inside a subscriber's premises in a digital subscriber line transmission system. DC-D
The o conversion circuit is used, for example, as the power supply circuit 17 of the line termination device 11.

This circuit 17 has a conventional configuration as shown in FIG.
When a DC conversion circuit is applied, the following drawbacks occur.

(a) Between the primary side and the secondary side of the D C-DC conversion circuit 17, that is, between the circuit-to-next-side terminal 18a and the circuit secondary-side terminal 19a, or between the circuit-to-next-side terminal 18b and the circuit secondary side ICDC-DC conversion circuit 17 between side terminals 19t1
A switching noise, so-called common-mode switching noise, occurs as a result of switching. This common mode switching noise is converted into differential mode noise according to the amount of unbalanced attenuation determined by the subscriber line 12 and the digital line termination device 11, etc. This can cause code errors in digital signals. Therefore, it is necessary to sufficiently reduce the occurrence of common-mode switching noise, but the conventional D'0-DC conversion circuit cannot satisfy this requirement. ,,,7.
. Since various longitudinal noises such as 71-1.6o and impulsive noise are induced and cause code errors in digital signals, the amount of unbalanced attenuation of the digital line termination device 11 needs to be sufficiently high. In order to eliminate the drawback described in the above item (a), l'c D O-D as shown in FIG.
An external capacitor blade with sufficiently low impedance at the switching frequency of the C conversion circuit 17 is connected to the circuit-next terminal 18.
a and the circuit secondary side terminal 19a (or between the circuit and the circuit secondary side terminal 18'b and the circuit secondary side terminal 191). However, in the case where such an external configuration is adopted and the circuit secondary side terminal 19a or 191) of the Do-Do conversion circuit 17 is connected to the ground with low impedance as is generally implemented, the power separation filter 16
Coil and external capacitor 23 for a (or 16b)
Because of this, a resonance point is formed in the vertical circuit, and since the impedance becomes low at this resonance point, the unbalanced attenuation of the digital line termination circuit 11 is extremely degraded, causing a code error due to external noise. For this reason, it is necessary to set the resonance point to a frequency sufficiently higher than the Barne transmission band.
It is necessary to separate the circuit secondary side terminals 1ga + 18b from the circuit secondary side terminals 19a and 19b with a high impedance equivalent to the stray capacitance of the transformer 14.

However, in this case, in the conventional circuit configuration, the above (
The disadvantages mentioned in section a) arise.

[Purpose of the invention]

It is an object of the present invention to eliminate the above-mentioned drawbacks, and to provide a DC-DC converter that isolates the primary side and the secondary side with high impedance over a high frequency range including DC and switching frequencies, and that generates less common mode switching noise. An object of the present invention is to provide a DC conversion circuit.

[Key points of the invention]

The present invention provides a DC-DC conversion circuit that switches DC power and supplies it to the primary winding of a transformer, rectifies and smoothes the output of the secondary winding of the transformer, and obtains a DC output. a first electrostatic shielding layer inserted between a secondary winding and connected to a stationary end of the secondary winding; and a first electrostatic shielding layer inserted between the electrostatic shielding layer and the secondary winding; and a second electrostatic shielding layer connected to the stationary end of the secondary winding.

[Explanation based on examples]

Hereinafter, a circuit according to an embodiment of the present invention will be explained based on the drawings. Fourth
The figure is a circuit configuration diagram showing the configuration of this embodiment circuit.

First, the configuration and connections of this embodiment circuit will be explained.

This embodiment circuit has circuit-next terminals 18a and 18b.
, circuit secondary side terminals 19a and 19b, and transformer 2
6, an input capacitor 37, a switch element 25, a switch element drive circuit 38, a diode 34, and an output capacitor section, where the transformer 26 is -
Each secondary winding is composed of the secondary winding 28, electrostatic shielding layers 46p and 46B, transformer secondary terminals 4 and 31, transformer secondary terminal 32, and wings.

The circuit-next terminal 18a is connected to the positive pole of the external DC power supply 24, and the circuit-next terminal 18b is connected to the negative pole of the external DC power supply 24. The circuit-next terminal 18a is connected to one terminal of the input capacitor 37 and the transformer-next terminal 29 of the transformer 26, and the circuit-next terminal 18b is connected to the other terminal of the input capacitor 37 and the switch element drive. The circuit is connected to that input and to the emitter of a switch element 25, which is an NPN type transistor. The output of the switch element drive circuit blade is connected to the base of the switch element 250, and the collector of the switch element 25 is connected to the transformer-next terminal 31.

One end of the primary winding 11127 of the transformer 26 and one end of the electrostatic shielding layer 46p are connected to the transformer-next terminal 29, and the other end of the primary winding of the transformer 26 is connected to the transformer-next terminal 31. . One end of the secondary winding iwx of the transformer 26 and one end of the electrostatic shielding layer 46 are connected to the transformer secondary terminal 32, and the other end of the transformer secondary winding #1128 of the transformer 26 is connected to the transformer secondary terminal 32. 33.

The transformer secondary terminal 32 is connected to one terminal of the output capacitor 35 and the circuit secondary terminal 19a, and the transformer secondary terminal 33 is connected to the anode of the diode 34. The cathode of the diode 34 is connected to the output capacitor 3
5 and the circuit secondary side terminal 19b. The circuit secondary side terminal 19a is connected to one terminal of the load 36, and the circuit secondary side terminal 19b is connected to the other terminal of the load 36.

The feature of this invention is that, as shown in this embodiment circuit, an electrostatic shielding layer 46p is provided between the primary winding 27 and the secondary winding line of the transformer 26, and this electrostatic shielding layer 46
p is connected to terminal 29, which is the stationary end of the negative winding n,
Further, an electrostatic shielding layer 46S is provided between the electrostatic shielding layer 46p and the secondary winding line, and this electrostatic shielding layer 468ti is connected to the terminal 32, which is the stationary end of the secondary winding 28. Here, the stationary end of the secondary winding 27 is an alternating current zero potential point on the primary side, and may be, for example, one of the terminals 18a and tab of the input capacitor 37, or the stationary end of the secondary winding 28. The end is an AC zero potential point in the secondary side pressure, for example, the terminals 19a, 1 of the output capacitor.
9b may be used.

Now, in the embodiment circuit configured in this way, the negative side 1
The fact that the switching voltage generated between 8a and the secondary side 19a, that is, the common mode switching noise, is reduced will be explained below.

In the case of the conventional DC-Do conversion circuit shown in Fig. 3,
The common mode switching noise can be expressed as:

However, vl is the common mode switching noise amplitude value 1, C1
and C2 represent the equivalent capacitance between the transformer secondary terminal 29 and the transformer secondary terminal 32, and the equivalent capacitance between the transformer primary terminal 31 and the transformer secondary terminal 33, and their values are the transformer 26 primary winding 27 and secondary winding 28
C1 is the switching voltage induced between the transformer secondary terminals 29 and 31, and C2 is the value of the stray capacitance distributed between the transformer secondary terminals 32 and 33. represents the induced switch voltage. − From the above equation, the common mode switching noise ■ is the switching voltage θ1 induced across the primary winding 27,
It is known that - is produced due to the influence of both the switching voltage θ2 induced on both sides of the secondary winding line. However, in the example circuit shown in FIG. 4, (1) -th winding n-
Since the electrostatic shielding layer 46p is provided between the secondary winding lines and is connected to the primary side 18aK, which is the stationary end of the negative winding n, the switching voltage e1 generated across the negative winding 27 is Voltage between primary side 18a and secondary side 19a (
(ii) an electrostatic shielding layer 468 is provided between the electrostatic shielding layer 46p and the secondary winding 28, and this is the stationary end of the secondary winding 28 on the secondary side; By being connected to 19alC,
The switching voltage e2 generated at both ends of the secondary winding 28 is not generated as a voltage between the primary side 18a and the secondary side 19a (in-phase moat one-to-one leg noise).

These points will be explained in more detail using FIG. 5. FIG. 5 shows the DC-DC conversion circuit shown in FIG. 4, focusing on the alternating current component that is involved in reducing the common mode switching noise. The symbols in FIG. 5 correspond to those in FIG. 4. Symbol θ1. e2 and ■1
indicates the switching voltage between each terminal at any given time, and the arrows indicate the mutual relationship of each voltage polarity. capacitor 4
7 and 48 represent the number I-ray capacitance distributed between the negative winding 27 and the electrostatic shielding layer 46p using a lumped constant circuit,
Capacitors 47 and 48 are connected between both ends 4 and 31 of the secondary winding 27 and the electrostatic shielding layer 46p, respectively. Capacitors 49 and 51 are secondary windings and electrostatic shielding layer 461i
Capacitors 49 and 51 are connected between both ends 32 and 33 of the secondary winding and the electrostatic shielding layer 468, respectively.

Here, the capacitor n, the - next winding lm27, the closed circuit of the switch element is set as the closed circuit I, the - next winding, the capacitor 47
, 48, the closed circuit of the electrostatic shielding layer 46p is a closed circuit ■, the closed circuit of the secondary winding part, the electrostatic shielding layer 46B, and the capacitor 49.51 is a closed circuit V, and the secondary winding 92B, capacitor word, and diode are Let the closed circuit be closed circuit ■.

First, the above item (1) will be explained. First, cycle I in Figure 5
Focus on. The input capacitor 37 has sufficiently low impedance to the switching frequency component, and has a sufficiently low impedance for the switching frequency component.
Since this is almost equivalent to a short circuit, no switching voltage is generated across it. - A switching voltage e1 is induced in the secondary winding 27. Here, from the Kirchhoff voltage period in the closed circuit l, a switching voltage with an amplitude equal to the switching voltage elK induced between both ends 29 and 31 of the -order winding η is generated at both ends of the switch element in opposite phases. . Next, focusing on the closed circuit IVK, capacitor 47
Since both ends of 0 are short-circuited by the electrostatic shielding layer 46p, no switching voltage is generated. Therefore, the cycle ■
From the Kirchhoff voltage 11j in
Resulting switching voltages et K Switching voltages of equal amplitude occur in opposite phases.

Therefore, the switching voltage e generated on the -next side is closed only to the primary side by the electrostatic shielding layer 46P, and the -next side 1
It is known that the voltage KFi change between the secondary side 8a and the secondary side 19a is not affected.

Next, the above item (11) will be explained. First, focus on the cycle ■busy in Figure 5. The output capacitor has a sufficiently low impedance to the switching frequency component, which is equivalent to a short circuit, so no switching voltage is generated across it. Therefore, from the Kirchhoff voltage period, the secondary winding l!
A switching voltage having an amplitude equal to the switching voltage e2 induced between the ends 32 and 33 of the edict is generated in opposite phase.

Next, focusing on the closed circuit V, both ends of the capacitor 490 are
Since it is shorted by electrostatic shielding layer 468, no switching voltage is generated. Therefore, from the Kirchhoff voltage period in the closed circuit VK, the voltage across the capacitor 51 is as follows.
A switching voltage having an amplitude equal to the switching voltage e2 generated between both ends 32 and 33 of the secondary winding section is generated in opposite phase. Therefore, the switching voltage e2 generated on the secondary side is closed only to the secondary side by the electrostatic shielding layer 46,
It is known that the voltage between the secondary side 18a and the secondary side 19a is not affected.

As described above, with the configuration shown in FIG. 4, the negative side Is a #
18b and the secondary sides 19'a and 19b are separated by high impedance, less common mode switching noise is generated, and a 0-DC conversion circuit can be provided.

In the above explanation, it is a so-called current transmission type DC-DC conversion in which the diode for half-wave rectification on the secondary side conducts when the switch element 25 on the primary side is off in Figure 4. Although this invention was applied to a circuit, the invention is also applied to a so-called voltage transmission type Do-DC conversion circuit, in which a diode for half-wave rectification on the next side conducts when a primary switch element is on. can. An example thereof is shown in FIG. 6, corresponding to FIG. 4. The difference between these two figures is that the polarity of the rectifier diodes has been reversed.

Now, the following is an application example circuit in which the secondary side as shown in Fig. 4 and Fig. 6 has multiple outputs and multiple secondary windings, a 0-DC conversion circuit, and the present invention is applied. Explain.

First, in a DO-Do conversion circuit in which the secondary windings are separated by high impedance, an electrostatic shielding layer is also provided between the secondary windings, and each electrostatic shielding layer is connected to the corresponding secondary winding. The configuration in which the coil is connected to the dead end of the winding is advantageous in reducing the generation of common mode switching noise.

FIGS. 7 and 8 show circuits according to an embodiment of the present invention in which the secondary side has dual force, and parts corresponding to those in FIG. 4 are given the same reference numerals.

Next, in a DC-DC conversion circuit in which the secondary windings are coupled with low impedance (including DC coupling), the common-mode The effect of reducing switching noise remains unchanged. FIGS. 9 and 10 show circuits according to an embodiment of the present invention in which there is a double force on the secondary side and this double force is DC coupled, and no electrostatic shielding layer is provided between the secondary windings. , FIG. 11 and FIG. 12 show an embodiment circuit of the present invention in the same case as above, in which an electrostatic shielding layer is provided between the secondary windings, and parts corresponding to those in FIG. 4 are designated by the same reference numerals. It is attached.

〔Effect of the invention〕

As explained above, the present invention can cover high frequency ranges including direct current and switching frequencies.

The input side and output side are isolated with high impedance, and the generation of common mode switching noise is suppressed.
-DC conversion circuit can be provided. Therefore, for example, in a digital subscriber line transmission system using balanced cables, the present invention can be applied as a power receiving power source for a digital line termination device installed inside a subscriber's premises that is operated by a remote supply voltage from a station. For example, the switching noise generated by the DC-DC conversion circuit is less likely to enter the pulse transmission system circuit, and high impedance separation between the digital line termination device and the subscriber line is possible. This has the effect of obtaining a high unbalanced attenuation amount of the terminating device, and also has the effect of suppressing as much as possible the sign error of the digital signal with respect to the large vertical noise induced on the subscriber line.

[Brief explanation of drawings]

1 and 2 are connection diagrams showing the configuration of a digital line termination device installed inside a subscriber's premises. FIG. 3 is a connection diagram showing the basic configuration of a conventional current transfer box type DC-DC conversion circuit. Fig. 4 is a connection diagram showing an example circuit in which the present invention is applied to a current transmission type D (!-DC conversion circuit). An explanatory diagram of the switching noise reduction effect. Fig. 6 is a connection diagram showing an embodiment circuit in which the present invention is applied to a voltage transmission type DC-DC conversion circuit. Figs. Connection diagram showing an example circuit applied to a current transmission type DC-DC conversion circuit with double power on the side. 11... Digital line termination device, 12... Subscriber line, 13... Connection point, 14...・Trance, 15...
- Pulse transmission circuit, 15a, 16b...Power separation filter, 17...DC-DC conversion circuit, 18a, 1
8b +++ circuit-next terminal, 19 a e 19 b
...Circuit secondary side terminal, 21...DC blocking capacitor, 22a, 22b...Transformer secondary side terminal, 23...
・External capacitor, U...DC power supply, 2i...switch element, 26...-transformer, n...-th order winding, imperial order...secondary winding, tomb, 31...transformer −Next terminal,
32.33...Transformer secondary side terminal,...Diode, blade...Outgoing capacitor, 36...Load, 37
...Input capacitor, wing...Switch element drive circuit, 46p, 46s...electrostatic shielding layer. Patent Applicant Nippon Telegraph and Telephone Public Corporation Agent Patent Attorney Naotaka Ide, ¥) 12 11 +sb 62 Ama 7th Ara 121

Claims (1)

[Claims] <1) In a DC-DC conversion circuit that switches If, H, and power and supplies it to the primary winding of a transformer, rectifies and smoothes the output of the secondary winding of this transformer, and obtains a DC output. a third electrostatic shielding layer inserted between the secondary winding and the secondary winding and connected to the stationary end of the secondary winding; A DC-DC conversion circuit comprising: a second electrostatic shielding layer inserted between the electrostatic shielding layer and the secondary winding and connected to a stationary end of the secondary winding.