JPS63232742A - Constant current supplying circuit - Google Patents

Abstract

PURPOSE:To equivalently enlarge the inductance of an electronized choke coil by using a supplying circuit having a constant current system, and increasing the impedance of the circuit without using a capacitor so that an alternate current signal is prevented from getting in. CONSTITUTION:A voltage generator 2 impresses a constant voltage to the positive input of an operational amplifier in a constant current circuit 1, and a supplying current (i), corresponding to the impressing voltage of the voltage generator 2, flows from the constant current circuit 1, towards -VE potential from an earthing potential. In such the constant current suppling circuit, a current supplying resistance is requested to be kept always at a constant value. Then, the voltage generator 2 detects the voltage between both the terminals of the constant current circuit, and varies the voltage to be impressed to the constant current circuit 1 so that the current supplying resistance is constant. For instance, if a supplying voltage V is increased, it increaes the current, as well correspondingly to it, and keeps the feed resistance value constant.

Description

[Detailed Description of the Invention] [Required 111] A constant current power supply circuit that increases the inductance of an electronic choke coil for alternating current signals and prevents the power supply resistance from changing depending on the amount of current flowing. .

[Industrial Field of Application] The present invention relates to a constant current power supply circuit, and more particularly to a constant current power supply circuit that is installed in an electronic exchange and supplies power to telephones and the like.

In a system using an electronic exchange, each telephone is supplied with power (power supply current) from a power source within the electronic exchange.

FIG. 5 is a block diagram of such an electronic switching system. As shown in the figure, a power supply current i as shown in the figure flows from the ground potential to the -48V potential, and power is supplied to the subscriber telephone device. Here, the feeding current i flows out into the line via the ground side choke coil L1 and flows into the -48V side via the choke coil L2.

On the other hand, the audio signal is 24i! It is connected to the station side via a hybrid transformer T for IL/4-wire conversion. Here, A
I+Δ2 is a gain adjustment amplifier inserted into each line, and BN is a balancing network for preventing the received signal from the 4 wires from going around to the transmitting side.

In a system having such a configuration, choke coils Lz and Lz, which have a high resistance to AC signals, are connected to the current supply section to prevent audio signals from entering. Therefore, the inductance of the choke coils L1+L2 needs to be as high as possible.

[Prior Art] FIG. 6 is a diagram showing a conventional circuit example of a current feeding circuit. The circuit shown in the figure corresponds to the part in FIG. 5 that supplies the power supply current from the choke coil L+. The supply voltage V is divided by the resistors R2 and R3 connected between the ground potential and the COMO 29124, and the voltage at the point A (the positive input point of the operational amplifier U) in the figure is determined. A load resistor RL is connected between the common line 1 and the -48V line. Here, A
If the potential at the point is VA, then the supplied current i is given by the following equation, assuming that R1 is used as it is as the resistance value of resistor R1.

1=vA/R+ This feed current i is supplied from a current boosting transistor Q driven by an operational amplifier U.

Here, the capacitor C connected to both ends of the resistor R3 is for bypassing the audio signal (AC signal) entering the power supply circuit, so that the influence of the AC signal does not appear at the point A. That is, the circuit shown in the figure can be equivalently represented by a series circuit of a resistor R and a choke coil L as shown in FIG. The inductor has a high impedance for AC signals, making it difficult for AC signals to pass through. In this sense, the circuit shown in FIG. 6 can be called a power supply circuit (electronic choke circuit) using an electronic choke coil.

[Problems to be Solved by the Invention] In the tm current feeding circuit shown in FIG. 6, the capacitance of the capacitor C must be increased in order to increase the inductance of the electronic choke coil with respect to the AC signal. Since capacitors are not suitable for integration into an integrated circuit, that is, they cannot be miniaturized, there is a problem in integrating the circuit shown in FIG. If you tried to force integration, you would have to connect only the capacitor externally, which was a problem.

The present invention has been made in view of these points, and
It is an object of the present invention to provide a constant current power supply circuit that can equivalently increase the inductance of an electronic choke coil without using a capacitor.

[Means for Solving the Problems] FIG. 1 is a block diagram of the principle of the present invention. In the figure,
1 is a constant current circuit that has a built-in operational amplifier and outputs a constant current according to the voltage applied to its positive input; 2 is a voltage generator that applies a voltage that changes in steps to the positive input of the constant current circuit 1; It is.

The voltage generator 2 applies a constant voltage to the positive input of an operational amplifier (not shown) in the constant current circuit 1, and the constant current circuit 1 supplies power based on the applied voltage of the voltage generator 2. A current i flows from the ground potential to the -VE'lli level. In such a constant current power supply circuit, it is required that the power supply resistance (the voltage across the constant current circuit 1 divided by the power supply current 1) is always kept at a constant value. In the conventional circuit shown in FIG. 6, the relationship between the power supply voltage V and the power supply current 1 is always linear, and therefore the power supply resistance (V/i) is always constant. If a constant current circuit is used, a high-impedance power supply circuit for AC signals can be realized, but the relationship between V and : is no longer linear, and the power supply resistance changes depending on the noise of the flowing current. Therefore, the voltage generator 2 detects the voltage across the constant current circuit and varies the voltage applied to the constant current circuit 1 so that the power supply resistance becomes constant. For example, when the power supply voltage V increases, the current is also increased accordingly to keep the power supply resistance value constant.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is an electrical circuit diagram showing one practical example of the present invention. Components that are the same as those in FIG. 6 are designated by the same reference numerals. The difference from the conventional example shown in FIG. 6 is that a constant voltage is applied to the positive input of the operational amplifier U, so that the circuit shown in the figure becomes a constant current circuit. The point is that the output of the voltage generator 2, which applies a voltage to the positive input of the operational amplifier U (point B in the figure), is made variable so that the power supply resistance remains constant. A resistor R4 is connected between the point B and the common line 4. Common line I
A resistor RL (load) is connected between the negative potential -■ε. The operation of the circuit configured in this manner is as follows.

In the circuit shown in the figure, if the potential of point B with respect to the common line is Va, the feeding current i is 1=VB/R1 using R1 as the resistance value of the reference resistor R1, and in the circuit shown in the figure, Va is constant. It operates as a constant current circuit when This Va is given to point B from the voltage generator 2. By using such a constant current circuit,
Since it has a high impedance with respect to AC signals, it is possible to prevent AC signals from entering the power supply circuit.

Here, when the voltage (power supply voltage) (2) across the power supply circuit changes depending on the state of the load, the power supply resistance R (-V/l) changes.

If the power supply voltage V increases, the power supply resistance will also increase. Therefore, the voltage generator 2 detects the increase in voltage V from the potential VA at point A, and increases the potential Vs at point B by the increased amount.
The power supply current i is increased by increasing the power supply resistance 1, and the value of the power supply resistance 1 is kept constant.

FIG. 3 is a diagram showing the relationship between VA and Va. As VA increases, ve also increases in a stepwise manner to keep the change in f8 resistance constant.

FIG. 4 is a diagram showing a specific example of the configuration of the voltage generator 2. As shown in FIG.

VA is converted into digital data by a Δ/D converter 21, and then converted into an analog voltage according to the input data by a D7/Δ converter 22, which outputs a potential Va to be applied to point B. Assuming that VA and VB have a linear relationship as shown in FIG. 3, the configuration shown in FIG. 4 can be used.

[Effects of the Invention] As explained in detail above, according to the present invention, by using a constant current type power supply circuit, it is possible to increase the impedance of the circuit without using a capacitor and prevent the intrusion of AC signals. , it is possible to provide a constant current power supply circuit that can equivalently increase the inductance of an electronic choke coil. According to the present invention, since the output current of the constant current circuit is varied according to the power supply voltage, the power supply resistance can also be kept constant. Furthermore, since the circuit of the present invention does not use a capacitor, it is easy to integrate.

[Brief explanation of the drawing]

Fig. 1 is a principle block diagram of the present invention, Fig. 2 is an electric circuit diagram showing an embodiment of the present invention, Fig. 3 is a diagram 1J showing the relationship between VA and VB, and Fig. 4 is a voltage generator diagram. 5 is a block diagram of an electronic exchange system, FIG. 6 is a diagram showing an example of a conventional circuit, and FIG. 7 is an equivalent circuit diagram of FIG. 6. In FIG. 1, 1 is a constant current circuit, and 2 is a voltage generator. -Vε 1 Current circuit angle ■ 2 Diagram showing the relationship between Figure A and VB (7) Figure 3 Figure 4

Claims (2)

[Claims] (1) A constant current circuit (1) that outputs a constant current according to the voltage applied to the positive input of an operational amplifier, and a voltage generator that applies a voltage that changes in steps to the positive input of the constant current circuit (1). A constant current power supply circuit configured by a device (2). (2) The voltage generator (2) is an A/D converter (21)
2. The constant current power supply circuit according to claim 1, wherein the constant current power supply circuit comprises a D/A converter (22) and a D/A converter (22).