JPH077308B2 - Constant current circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current circuit, and more particularly to a load for stabilizing load sharing when connected to another constant current circuit in series and supplying a current to the load. The present invention relates to a constant current circuit having a sharing resistor.

Prior Art As shown in FIG. 1, a plurality of constant current circuits are provided for a load 6.
When 1,1 'is connected in series and constant current is supplied to the load 6, load sharing is stabilized by connecting the load sharing resistor 5 to the output circuit of the constant current circuit 1,1'. I am letting you. That is, the constant current circuit 1 includes the constant current source 4 and the load 6
And a control circuit 3 for controlling the constant current source 4 so that the output voltage of the current detector 2 becomes a constant value, and the load sharing resistor 5. Has been done.

FIG. 2 is a circuit diagram showing a conventional example of the constant current circuit 1.
That is, the current detector 2 has a winding with a winding number N ₁ connected in series between the constant current source 4 and the load 7, and the product of the current I ₁ flowing through the winding and the winding number N _1. , Ie ampere turn
A voltage proportional to I ₁ N ₁ is output and supplied to the control circuit 3.
Figure 3 shows the DC excitation ampere-turn AT of the current detector 2.
It is a graph showing the relationship between the output voltage V _D and. When the DC excitation ampere-turn AT-output voltage conversion ratio is g, the output voltage V _D of the current detector 2 is V _D = g · I ₁ · N ₁ (1) This output voltage V _D is compared with the reference voltage E by the comparison amplifier A incorporated in the control circuit 3, and a control signal such that V _D = E ... Is given to the constant current source 4, and the constant current source 4 outputs the control signal. The output current I ₁ is controlled to have a predetermined constant value. Here, assuming that the voltage across the load 7 is V _L , the current flowing through the load 7 is I _L , the resistance value of the load sharing resistor 5 is R _P , and the current flowing through the load sharing resistor 5 is I ₂ , I _L = It can be expressed as I ₁ −I ₂ = I ₁ −V _L / R _P (3). Therefore, the loss W due to the load sharing resistor 5 is W = V _L ² / R _P (4) That is, by connecting the load sharing resistor 5, the output impedance of the constant current circuit becomes a finite value R _P.
And the output characteristic becomes the characteristic shown by the solid line in FIG. If the load sharing resistor 5 is not connected, the constant current source 4
Output current I ₁ and load current I _L are equal to each other and are constant currents, the output impedance of the constant current circuit is equal to the output impedance of the constant current source 4 and an infinite output impedance. Connecting 5 results in a finite output impedance R _P. This makes it possible to stabilize the load sharing when a plurality of constant current circuits are connected in series, as described below.

FIG. 5 shows two constant current circuits 1, 1'as shown in FIG.
It is a figure which shows the load sharing characteristic at the time of connecting to the load 6 in series. The straight lines a and c shown by the solid lines respectively show the output characteristics of the constant current circuits 1, 1 ', the vertical axis shows the output current, and the horizontal axis shows the output voltage. However, the output voltage V _A of the constant current circuit 1 is from the left end to the right in the figure, and the output voltage V _B of the constant current circuit 1'is from the right end to the left.
Now, the output current I _A of the constant current source 4 of the constant current circuit 1 and the output current I _B of the constant current source 4 of the constant current circuit 1 ′ are I _A = I _B (5) Assuming that the slopes of a and c are equal, the output voltages V _A and V _B of the constant current circuits 1 and 1'are determined by the intersections of the straight lines a and c, and as shown in the figure, V _A = V _B , A load current I _L flows through 6. At this time, the voltage across the load 6 is 2V
_L is V _A + V _B. Therefore, V _A = V _B = V _L (6), and the load is evenly shared.

Next, due to temperature fluctuations, fluctuations in the input power supply, etc., the output currents I _A and I _B of the constant current source 4 of the constant current circuits 1 and 1 ′ each have the maximum fluctuation within the allowable range ± ΔI ₁ , the output current of the constant current source 4 of the constant current circuit 1 is increased by △ I _1, the output characteristic of the constant current circuit 1 becomes as shown by the straight line b shown by a chain line in FIG. 5, the constant current circuit 1 The output of the constant current source 4 of ′ is ΔI ₁
When the output decreases from the constant current circuit 1'as shown by the straight line d, the voltage shared by the constant current circuits 1 and 1'is ΔV.
Fluctuations occur. The allowable accuracy of the output current of the constant current source 4 is ±
When B%, the output current variation value, because it is _{± △ I 1 = ± B ·} I 1/100 ...... (7), the shared voltage difference △ V _{is, △ V = R P · △} I 1 = _{R P · B · I 1/} 100 ...... is (8). That is, the shared voltage difference is proportional to the accuracy B of the output currents I ₁ and I ₁ of the constant current source 4 and the output impedance R _P of the constant current circuit. In order to reduce this sharing difference,
The larger the output current I ₁ , the higher the accuracy of I ₁ and the smaller R _P must be.

At present, the power supply method for the submarine coaxial transmission system, which is an analog communication system, installs a constant current device including the constant current circuit as described above at both end stations, and a 100mA to a repeater connected in the middle of the submarine coaxial line. (For 5MHz system) or 156mA (36MH
The constant current of z method) is supplied. When such a constant current circuit is used in a submarine optical transmission system of a digital transmission system that needs to supply a current of 1A to 2A, the voltage sharing difference ΔV is about the same as in the submarine coaxial transmission system. In order to achieve the above, it is necessary to lower the output impedance R _P of the constant current device. However, lowering the output impedance R _P increases the loss in the load-sharing resistor 5 as is apparent from the equation (4), and the amount of heat generated increases, which makes the load-sharing resistor 5 large. I have to turn it on.

OBJECT OF THE INVENTION The object of the present invention is to solve the above-mentioned drawbacks of the related art and to make it possible to maintain the output impedance at a predetermined value by means of a load-sharing resistor having a large resistance value. It is to provide a reduced constant current circuit.

Configuration of the invention, a constant current circuit of the present invention, a current detector connected in series between a constant current source and a load, a control circuit for controlling the constant current source by the output of the current detector, In a constant current circuit including a load sharing resistor connected to an output of the constant current source, the current detector includes a first winding connected in series between the constant current source and the load. A second winding connected between the constant current source side of the first winding and the load sharing resistor and having a larger number of turns than the first winding, A voltage proportional to the sum of the ampere-turn of the first winding and the ampere-turn of the second winding is output, and the control circuit controls the output voltage of the current detector to be a predetermined value. It is characterized by controlling a current source.

Embodiments of the Invention Next, the present invention will be described in detail with reference to the drawings.

FIG. 6 is a circuit diagram showing an embodiment of the present invention. That is, as the current detection winding of the current detector 2 ′, the first winding having the same number of turns N ₁ as the conventional one is connected in series between the constant current source 4 and the load 7, and the first winding is connected. A _second winding having a winding number N ₂ larger than the winding number N _{1 of the first} winding is connected to the constant current source 4 side of the winding, and the other end of the second winding is for load sharing. Connect the resistor 5. Therefore, a part of the output current I ₁ ′ of the constant current source 4 is the first
Becomes the load current I _L supplied to the load 7 through the second winding, and the remaining current I ₂ flows through the second winding through the load sharing resistor 5
Flow to. The current detector 2 outputs an output voltage V _D proportional to the total of the ampere-turns of the two windings and inputs the output voltage V _D to the control circuit 3. The control circuit 3 compares the input voltage V _D with the reference voltage E. Then, the constant current source 4 is controlled so that the equation (2) is satisfied.

FIG. 7 shows the DC excitation ampere-turn of the current detector 2 '.
Is a diagram showing a relationship between AT and the output voltage V _D, the characteristics of,
This is the same as the conventional characteristic shown in FIG. However, the 7th
In the figure, the sum of the ampere turns of the first and second windings, ie I _L N ₁ + I ₂ N _2, is plotted on the horizontal axis. Therefore, V _D = E = g (I _L N ₁ + I ₂ N ₂ ) (9) holds. When I ₂ = 0, that is, when the load current I _L when the second winding is opened is I ₁ , the relationship of Expression (1) holds, and from Expression (1) and Expression (9), I ₁ N ₁ = I _L + I ₂ N ₂ (10) holds. Therefore, I _L = I ₁ −I ₂ N ₂ / N ₁ = I ₁ −V _L N ₂ / R _P N ₁ = I ₁ −V _L / R _P ′ (11) where R _P ′ = R _P N ₁ / N ₂ (12) Since N ₂ is larger than N ₁ , R _P ′ <R _P (13). Therefore, the characteristic of this embodiment is as shown by the straight line f in FIG. In order to obtain the characteristic shown by the straight line e in the same figure, the resistance value R _P of the load sharing resistor 5 should be N ₂ / N ₁ times that of the conventional example shown in FIG. You can
That is, the present embodiment has an effect that the loss due to the load sharing resistor 5 can be reduced to N ₁ / N ₂ as compared with the conventional case.

EFFECTS OF THE INVENTION As described above, in the present invention, the current detector is provided with the first winding and the second winding, and the second winding is wound more times than the first winding. Connected to the constant current source side of the first winding, supplying a current to the load through the first winding, and connecting the other end of the second winding to one end of the load sharing resistor, Since the constant current source is controlled so that the output voltage of the detector becomes equal to the reference voltage, the output impedance of this circuit can be lowered even if the resistance value of the load sharing resistor is increased. Therefore, there is an effect that the loss of the load sharing resistor can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a power supply system in which two constant current circuits are connected in series to supply a constant current to a load, and FIG. 2 is a conventional example of a constant current circuit used in the power supply system. FIG. 3 is a circuit diagram showing the characteristics of the current detector of the conventional example, FIG. 4 is a diagram showing the output characteristics of the conventional constant current circuit, and FIG. FIG. 6 is a characteristic diagram showing the load sharing of each constant current circuit, FIG. 6 is a circuit diagram showing one embodiment of the present invention, FIG. 7 is a diagram showing characteristics of the current detector of the above embodiment, and FIG. FIG. 4 is a diagram showing output characteristics of the above-mentioned embodiment. In the figure, 1,1 ': constant current circuit, 2,2': current detector,
3: Control circuit, 4: Constant current source, 5: Load sharing resistor, 6: Power supply type load, 7: Load.

Front page continuation (72) Inventor Katsuhiko Yamamoto 3-9-11 Midoricho, Musashino City, Tokyo Inside the Nippon Telegraph and Telephone Public Corporation Musashino Electro-Communications Research Laboratory (56) Reference JP-A-54-36557 (JP, A)

Claims (1)

[Claims] 1. A current detector connected in series between a constant current source and a load, a control circuit for controlling the constant current source by the output of the current detector, and an output of the constant current source. In a constant current circuit with a load sharing resistor connected to
The current detector includes a first winding connected in series between the constant current source and a load, and between the constant current source side of the first winding and the load sharing resistor. A second winding that is connected and has more turns than the first winding;
Output a voltage proportional to the sum of the ampere-turn of the winding and the ampere-turn of the second winding, and the control circuit controls the current source so that the output voltage of the current detector becomes a predetermined value. A constant current circuit characterized by controlling the.