JPS6059856A - Direct current supply circuit - Google Patents

Abstract

PURPOSE:To eliminate an in-phase composition noise by inserting a semiconductor flowing a current unidirectionally between both ends of a load side winding of a pulse transformer and both ends of a recrifier capacitor in the direct current supply of the DC-DC converter system. CONSTITUTION:The rectifiers D100, D400 flowing a current unidirectionally only are inserted between the terminals 3, 4 of the load side winding of the pulse transformer T100 and the terminals (g), (f) of a rectifier capacitor C100, in the DC supply circuit of the floating type DC-DC converter system where a DC talking current is supplied via a subscriber line connecting an exchange and a terminal device. Thus, the load side winding and the rectifier circuit are constituted as a balanced circuit network from a DC up to high frequencies to make the circuit network coarse from ground over the entire frequencies. Thus, a voltage induced in the winding of the load side is applied equally to the D100 and D400 entirely, no signal to ground is produced at the terminals (f), (g) and no in-phase composition noise is outputted to the subscriber line.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a DC-DC converter system without impairing the high ground balance characteristics and high efficiency power supply characteristics, which are the advantages of the floating DC-DC converter type DC supply circuit. This invention relates to the configuration of a DC supply circuit that can eliminate switching noise, especially common-mode component noise, generated by the DC power supply circuit.

A DC supply circuit is a circuit that supplies DC communication current from an exchange to terminals such as telephones via subscriber lines.

Currently, the DC supply circuit commonly used in switchboards is
This is realized by the winding of a relay switch. The performance required for a DC supply circuit is (1) a power supply function that supplies M current, (2) a loop monitoring function that detects the flow of DC, (3) an interface function with voice calls, and (4)
) High balance characteristics and absorption ability for AC induced noise, which is in-phase component noise. In the case of a relay switch winding, the winding has a large inductance and 2
The divided windings are wound in a piphalar manner so that the characteristics of both windings match. In addition, the winding direction of the two-divided winding is specified, and the impedance of 11 becomes low for common-mode component noise, absorbing this noise into the station power supply.
For balanced component signals such as voice calls, ltJ has a high impedance and the presence of the winding can be ignored. The performance of the relay switch winding listed above satisfies the above-mentioned performance requirements for the DC supply circuit.

Although the relay switch for direct current supply has such excellent performance, there is a limit to miniaturization because the relay switch is an electromagnetic component and has an inductance that provides high impedance up to low frequencies.

Furthermore, since there are four requirements for matching the characteristics of the two divided windings, there is a limit to the reduction in manufacturing costs.

Furthermore, the communication current supplied to the terminal using the DC -48V local power supply ranges from 20 mA to 100 mA or more. Conventional relay switches and DC supply circuits that simulate them using electronic circuits have an internal DC resistance of 440Ω, so if a current of 100mA or more flows, the internal power consumption is 4.4W or more. The heat generated is too large to be pumped into the circuit. In addition, the DC supply circuit is a subscriber-compatible circuit, and a large number of circuits are installed in the exchange, so the large power consumption in the circuit is due to the thermal design of the mounting surface. There are a number of items that require consideration from the perspective of implementation.

In recent years, studies have been made to reduce the size of direct current supply circuits by computerizing them, and to reduce costs by mass producing integrated circuits. One of the directions under consideration is a high-efficiency DC supply circuit using a KDC-DC converter system. Conventional relay switches and direct current supply circuits that are simulated by electronic circuits have the disadvantages mentioned above, but DC-DC converter type direct current supply circuits require 440Ω to achieve the same supply current characteristics.
Since the desired characteristics are obtained by using the inductance of a coil such as a transformer without using the voltage drop of the resistor, it is a highly efficient supply circuit that does not generate heat in the supply circuit in principle.

There are several types of DC-DC: lamper type, but what all types have in common is that a pulsed current is supplied from the primary power source through an inductance element and a switch that opens and closes in a circular manner. This means that the current flowing through the rectifier circuit on the opposite side of the inductance element is rectified into a DC power supply to be supplied to the subscriber line. By using the winding of a transformer as an inductance element, the winding to which the switching confectionery and the local power supply are connected and the winding to which the rectifier circuit and subscriber line are connected can be realized using separate windings of the transformer. Alternatively, the latter winding can be electrically floating from earth. The former winding will be referred to as the primary side winding, and the latter winding will be referred to as the load side winding. If the winding on the load side and the load circuit are made floating, the impedance to the ground (also called longitudinal impedance or common-mode component impedance) becomes extremely high, so it is easy to realize a large unbalanced attenuation characteristic to the ground. This shows that among the performances required of the DC supply circuit described above, (4) high balance characteristics and absorption capacity for AC induced noise, which is in-phase component noise, can be easily achieved.

For this reason, research has been carried out on the practical application of this floating type DC-DC converter type DC supply circuit, but the floating type had the disadvantage that switching noise, especially common-mode component noise, could not be suppressed until now. . This situation will be explained using drawings.

FIG. 1 shows the configuration of a conventional floating DC-DC converter type DC supply circuit. Further, FIG. 2 shows typical waveforms of each part of FIG. 1.

In FIG. 1, 1oo is a clock generation circuit, 101 is a pulse width modulation (PWM) circuit, 1o2 is a rectifier circuit,
103 is a filter circuit 5WIOθ is a switch element, Tl
00 is a pulse transformer, D1θ0 is a rectifying diode, C1oo is a rectifying capacitor, and A and B are terminals.

The operation of the circuit will be explained according to FIGS. 1 and 2.

The clock generation circuit 100 generates a clock that determines the primary side switching frequency of the DC-DC converter,
This clock is input to a pulse width &M (PWM) circuit 101 and becomes the PWM timing.

This PWM signal is shown in the waveform example of voltage a in Figure 2.
The timing is right. The PwM signal is applied as a drive signal to the switch element SW7θ0.

When the voltage is at a high level in the waveform of Figure 2, the switch element 5
W100 is conductive, and when the voltage is at a low level, switch element S W lθ0 is made non-conductive, and pulse transformer T1θθ is connected via switch element SWIθ0.
A current as shown by tT' and I in FIG. 2 flows from the ground potential to the local power supply potential -VB in the primary winding (between terminals No. 2). - When the current ■ flows in the next winding, the current will try to flow in the other windings, but in the case of the winding on the load side (between terminals 3 and 4), The direction of the induced current from the winding direction is terminal 4 of the winding.
This is the direction in which the fluid flows out from to the load. Since this current direction reverse biases the rectifier diode D100, as a result, while the current (2) is flowing through the primary side wire, the load impedance of the winding on the load side is extremely low, and no current flows. On the other hand, when the switch element 5W100 becomes non-conductive and the current in the sequential winding becomes zero, a current in the opposite direction tends to flow in the winding on the load side. This direction is the direction in which the fluid flows out from the terminal 3 toward the load side.

At this time, the diode D100 becomes 1 forward biased and conducts, and the current indicated by the single arrow in FIG. 1 flows through the rectifying capacitor C100.

An example of the waveform of current 1 is shown in FIG. Current i charges capacitor C100 with the polarity shown in FIG.

The capacitor C100 is charged while the current l is flowing, and the operation of discharging the charge toward the load while the current i is not flowing is repeated every clock cycle. Current due to this discharge flows to the load and becomes a supply current to the terminal.

Another winding of Norst U/S T100 (terminal 5-
6) and the rectifier circuit 102, a PWM modulation signal C is created and sent to the pulse width modulation circuit 101. terminal 5
The relationship between the winding direction of the winding between -6 and the current switching polarity in the rectifier circuit 102 is the same as the winding direction of the load side winding and the current switching polarity of the rectifier diode D100. When the occupancy rate of the signal indicated by the voltage, which is the control signal of the switching element SWIθO, is constant,
- The total amount of power transferred via the transformer T100 is constant regardless of the size of the load. Therefore, the voltage across the rectifying capacitor C1θ0 changes in proportion to the square root of the DC resistance of the load. This voltage appears between terminals 5 and 6 in proportion to the ratio of the number of turns between the winding on the load side and the winding between terminals 5 and 6, so the voltage information between terminals 5 and 6 is transferred to the rectifier circuit.
The voltage e obtained through 02 has information on the DC resistance f1 of the load winding on the load side. Furthermore, by comparing the voltage e with an appropriate threshold voltage, it is also possible to perform a DC loop detection function.

The filter circuit 103 has a characteristic of allowing direct current to pass through but blocking alternating current, so terminals A and B to which subscriber lines are connected are
When viewed from above, in the case of direct current, the rectifying capacitor C1, which is a battery,
00 is visible and the impedance is low, but in the case of AC, the filter circuit 10.9 becomes high impedance, so the DC supply circuit is no longer visible. Although not shown in FIG. 1, the alternating current audio signal is terminated and processed by the audio signal processing circuit.

Common mode component noise is generated as follows. In the operating principle described so far, while the current I flows through the primary winding, the rectifier diode D100 becomes reverse biased, and no current flows through the load winding, but in reality Since stray capacitance exists in the lead wire portions of the terminals 3, 4 and other parts, the flow in the shape of a nockle flows through the stray capacitance. In principle, all the voltage induced in the winding on the load side is applied across the rectifier diode D1θθ, and if the system on the load side is a floating type, this voltage will not go out to the subscriber line, but there is stray capacitance. is divided by the ratio of the reciprocal of the stray capacitance of each of terminals 3 and 4, and a voltage waveform is generated between the ground and each terminal. FIG. 3 is a diagram illustrating this situation.

FIG. 3 is a diagram in which the rectifying capacitor C1θO is extracted from the winding on the load side in FIG. 1, and stray capacitance is added. The arrow indicated by a dashed line in the figure indicates the stray capacitance C, ? o o~C3
02 shows a path through which leakage current flows. Third
The intersection point 3.4 of the circuit shown in the figure is the pulse transformer T1 of Fig. 1.
1 diode 100, matched with terminals 3 and 4 of 00
Even if C is reverse biased and in a cutoff state, if there is a path shown by the dashed-dotted line in Figure 3, then the stray capacitance C, ? 00~C302
According to the impedance ratio of the rectifying capacitor C100 to the pulse, a ground voltage waveform is generated at the terminals 3, 4 and the terminal f. Here, stray capacitance C3θ0 ~ C3θ2
Since the capacitance of the rectifying capacitor C1θO is generally extremely large compared to the above, the voltage waveform of the terminal 3 and the voltage waveform of the terminal f match sufficiently. As shown in Figure 1, this terminal 3
is directly connected to one of the pair of subscriber lines, and the terminal f is also connected to the other pair of subscriber lines via the filter circuit 103. Since the ground impedance of the subscriber line and the terminal equipment is large, substantially the same voltage waveforms at terminals 3 and f are output to the subscriber line as in-phase component noise.

The level of common mode component noise is the voltage induced in the winding on the load side of the pulse transformer Tl 00 and the stray capacitance C' 300~C3
Depending on the capacitance ratio of 02, it may reach several tens of V. When this common-mode component noise is applied to a pair of wires with a finite ground balance, the common-mode component is converted into a balanced component according to the degree of unbalance, resulting in noise that is difficult to remove. The problem was that it often mixed in as induced noise on lines and lines, degrading quality.

The present invention aims to solve these drawbacks by connecting both ends of the winding on the load side of a pulse transformer and both ends of a rectifying capacitor via a semiconductor device that allows current to flow in only one direction. In particular, the large amplitude signal induced in the winding on the load side of the pulse transformer is prevented from being transmitted to either terminal of the rectifying capacitor, even if there is stray capacitance. Examples will be described below with reference to the drawings.

FIG. 4 shows an embodiment of the present invention. This corresponds to Figure 1 showing the conventional circuit configuration, but the difference is that there is a connection between terminal 3 of the winding C on the load side of the pulse transformer T100 (between terminals s and 4) and terminal g of the rectifying capacitor C100. The second rectifying diode D400 is connected, and the terminal 3 - the second rectifying diode D40θ - the rectifying capacitor c1θ0 - the first
+7)! This is the point where current flows through the path between the diode D100 and the terminal 4. The second rectifying diode D400 in the DC-DC converter circuit performs the same rectifying operation as the first rectifying diode D1oo.

Furthermore, since the impedance of the second rectifying diode D400 shows the same change as that of the first rectifying diode DI00, the influence that this second diode D4θθ has on the formation of the side flow path of the pulse signal due to stray capacitance is Extremely large.

FIG. 5 is a circuit diagram showing the circuit from the winding on the load side to the rectifying capacitor in the circuit configuration according to the present invention, and (2) showing the influence of stray capacitance.

The configuration shown in FIG. 5 differs from that shown in FIG. 3 in that the impedance of each element from the winding on the load side to the rectifying capacitor CIOθ trench is balanced. The winding on the load side and the rectifier circuit directly connected to the winding have a balanced circuit network configuration from direct current to high frequency, and the circuit network is sparsely isolated from the ground over the entire frequency range.

Since there are rectifier diodes D100 and D4oo, when these rectifier diodes D, 7θ0, and D400 are in the cutoff state, the rectifier capacitor C is
The distance between IOθ and the winding on the load side is extremely sparse), and there is no path for current to flow through terminals f and g to terminal 3. Therefore, all the voltage induced in the winding on the load side is applied equally to the rectifying diodes D100 and D4oθ, and no ground signal is generated at the wide terminals f and g. and,
It is possible to eliminate in-phase component noise from being output to the subscriber line.

In the embodiment, a rectifier diode D400 with a resistance of 2 is used, but the present invention is not limited to this, and when the switching element 5W100 on the negative winding side is conductive, it has an extremely large impedance, and the switching element 5WI00 is cut off. Any element may be used as long as it operates so as to have an extremely small impedance when in the state. For example, this purpose can be achieved by switching transistors.

Since the DC supply circuit is a circuit placed to support subscribers, it is extremely densely mounted, but it has a noise resistance of -70 dB.
m or less is required. According to the present invention, it is possible to suppress in-phase component noise, which is a cause of noise increase, through the practical use of a floating DC-DC converter type DC supply circuit, which inherently has many advantages, and the miniaturization of the DC supply circuit thereby. , which has a great effect on realizing low power consumption.

[Brief explanation of drawings]

Figure 1 is a diagram of a conventional floating DC-DC converter type DC supply circuit, Figure 2 is an example of waveforms at each point in Figure 1, and Figure 3 is common-mode component noise generation in the conventional configuration of Figure 1. FIG. 4 is a circuit diagram showing an embodiment of the present invention, and FIG. 5 is a diagram showing the state of leakage current in the configuration of FIG. 4. 1θθ... Clock generation circuit, 10... Pulse width modulation (PWlvI) circuit, 102... Rectifier circuit, 7
03=filter circuit, SWlθθ...switching element, TiO2...nogle transformer, Dloo, D4
θθ... Rectifier diode. Patent applicant Oki Electric Industry Co., Ltd. Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] In a floating DC-DC converter type DC supply circuit that supplies DC communication current through subscriber lines that connect exchanges and terminal equipment, both ends of the winding on the load side of the pulse transformer and both ends of the rectifying capacitor 1. A DC supply circuit characterized in that the DC supply circuit is connected through a semiconductor element that allows current to flow in only one direction.