JPH077310B2 - Constant current circuit - Google Patents

Description

The present invention relates to a constant current circuit, and more particularly to a constant current source having a constant current source whose current value is independently controlled and which is connected in series to supply a constant current to a load. Regarding the circuit.

FIGS. 1A and 1B are block diagrams showing a configuration example and a usage example of a conventional constant current circuit, respectively. The constant current circuit 1 controls the current I ₁ sent from the constant current source 3 to a predetermined value by the current detection circuit 4 and the control circuit 6, and supplies the current I _L to the load 7. That is, a magnetic amplifier (not shown) having a saturable reactor is used for the current detection circuit 4, and the current I ₁ sent from the constant current source 3 passes through the DC winding W _D for current detection, The current is divided into a current I ₂ flowing to the load sharing resistor R _P and a current I _L flowing toward the load 7. The current detection circuit 4 is ampere-turns N · I ₁ (where N of the DC winding W _D DC winding W _D
The output voltage V _d proportional to
This is sent to the control circuit 6. Therefore, the relationship between the output voltage V _d of the current detection circuit 4 and the current I ₁ is expressed as V _d = g · N · I ₁ (1), and the proportional constant g is a DC excitation ampere-turn.
It is the output voltage conversion ratio. The control circuit 6 includes a comparison amplifier 61, one of the pair of input terminals of which the output voltage V _d of the current detection circuit 4 is applied and the other of which has a reference voltage V _{0 serving as} a reference for constant current control. Is printed. The reference voltage V ₀ is set to satisfy the relationship of V ₀ = g · N · I ₁₀ (2) with respect to the current I _{10 having} a predetermined value for the current I ₁ . The control circuit 6 sends a control signal of a voltage proportional to the difference between the output voltage V _d and the reference voltage V ₀ to the constant current source 3 so that the difference between the two becomes zero, that is, the current I ₁ is equal to the current I ₁₀ . The constant current source 3 is controlled so that

When power is supplied to a coaxial cable type or optical fiber type repeater using such a constant current circuit 1,
A plurality of them are connected in series as shown in Fig. 1 (b) (two in series are shown in Fig. 1 (b). Note that the diodes D ₁ and D ₂ are the operations of the constant current circuits 1A and 1B, respectively. It is for bypass at the time of interruption.) A redundant configuration that operates simultaneously is used to improve reliability and share the load. Constant current circuit
Both 1A and 1B have the same configuration as in FIG. In this case, even if the current I ₁ sent from the constant current source 3 of each of the constant current circuits 1A and 1B fluctuates within the range of the constant current control accuracy, one of the constant current circuits 1A and 1B has excessive power. In order not to share the load, it is necessary to set the resistance R _P to a certain value or less, as described below.

FIG. 2 is a characteristic diagram showing operation characteristics at the time of connection in FIG. 1 (b). The horizontal axis represents the output voltage V _A of the constant current circuit 1A, and the vertical axis represents the supply current I _L to the load 7. Voltage V _L0
The current I _L0 and the current I _L0 indicate the value of the voltage and the current during the standard operation of the load 7, respectively. The characteristics A ₀ and B ₀ shown by the solid lines represent the output voltage vs. output current characteristics when the current I ₁ sent from the constant current source 3 of the constant current circuits 1A and 1B is equal to the predetermined current I ₁₀ , respectively. Both currents I _A0 and I _B0 are equal to current I ₁₀ . As is clear from FIG. 1 (a), I _L = I ₁ −I ₂ = I ₁ − (V / R _P ) ... (3) holds, and I ₁ = I ₁₀ If it is applied to the constant current circuit 1A in this case, I _L = I _A0 − (V _A / R _P ) ... (4) holds. This is shown in the characteristic A0. Also,
In the standard operation of the load 7, V _B = V _L0 −V _A is established, and if this relational expression and the expression (3) are applied to the constant current circuit 1B, I _L = I _B0 − (V _L0 / R _P ) + (V _A / R _P ) ... (5) holds. This is shown in the characteristic B ₀ . The operating point in this case is given by the intersection point P ₀ of the characteristics A ₀ and B ₀ , but the voltage V _{A0 at} this time is obviously just half the voltage V _A0 , and the load sharing of the constant current circuits 1A and 1B is It is even.

On the other hand, the characteristics A ₁ and B ₁ shown by the broken lines show the case where the sending current I ₁ of the constant current source 3 of the constant current circuits 1A and 1B fluctuates up to the upper limits I _B1 and I _{B1 of the} constant current control accuracy range. . As is apparent from equation (3), characteristic A ₁ and B ₁ is in each of the characteristics A ₀ and B ₀ △ and translation I ₁ only upward and downward properties _{(however, △ I 1 = I A1 -I} A0 = I _B0 −
I _B1 ). Along with this change in the operating characteristics, the operating point also moves to the intersection point P ₁ of the characteristics A ₁ and B ₁ , and the voltage V _A changes from the voltage V _A0 when the load is evenly shared to the voltage V _A1 to change the load. The sharing will be uneven. Variation of this voltage V _A ΔV _A =
V _A1 −V _A0 is expressed as ΔV _A = R _P · ΔI ₁ = R _P · b · I ₁₀ (6) using the constant current control accuracy b = ΔI ₁ / I ₁₀ . The magnitude is proportional to the sending current I ₁₀ of the constant current source 3, its control accuracy b, and the resistance R _P. Normally, the control accuracy b cannot be reduced below a certain limit due to restrictions in terms of accuracy and stability of parts used. Therefore, when the load current is necessary to increase the current I ₁₀ in large systems, in order to suppress a voltage variation △ V _A within the desired range, small no Senebanara resistance R _P. For example, the load current in the case of the analog transmission method using the coaxial cable is about 50 to 100 mA, whereas the load current in the case of the digital transmission method using the optical fiber reaches 1 to 2 A, which is one digit higher than that. . In order to suppress the voltage fluctuation ΔV _A in the latter case within the same range as in the former case, it is necessary to lower the resistance R _P by one digit. Fig. 1 (a)
As is clear from the above, since the power consumed by the resistor R _P , that is, the power loss W is expressed as W = V ₂ / R _P (7), the resistor R _P is lowered by one digit as described above. Then, the power loss W increases by one digit, the resistance R _P becomes large, and the heat dissipation cooling means becomes large in order to cope with the increase in the heat generation amount of the resistance R _P , and the constant current circuit must be made large. I don't get. Further, if the resistance value is lowered as described above, when one of the two constant current circuits 1A and 1B connected in series as shown in FIG.
The variation amount of the current I _L generated along with this increase. For example, when the operation of the constant current circuit 1B is interrupted and the diode D ₂ becomes conductive and the voltage V _B becomes zero, the operating point shifts to the point Q ₀ on the characteristic A _{0 in} FIG. However, the point Q ₀ is
Characteristic A _0, a straight line showing the operation characteristics of the load _{7 I L = (V L0 /} I
_L0 ) · _VA (not shown in Fig. 2). Since characteristic A ₀ is the linear absolute value of the right edge of the 1 / R _P slope, the point Q ₀ if R _P is decreased, the process proceeds to the lower left on the diagram the same, from a standard operation point of the load 7 The gap increases.

As described above, in the conventional constant current circuit, especially when the load current is large, the power loss in the load sharing resistor is large, the circuit becomes large, and the load current fluctuation when a failure occurs in a part of the redundant configuration. Has the drawback of being large.

An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a constant current circuit in which the power loss of the load sharing resistor is smaller than in the prior art and the load current fluctuation is small when a failure occurs in a part of the redundant configuration. .

The circuit of the present invention has a current detection circuit for detecting a current at a predetermined location in the circuit and a sending current controlled so that the detection value converges to a predetermined value in response to a signal indicating the detection value of the current detection circuit. In the constant current circuit having a constant current source and a load-sharing resistor, the current detection circuit has at least first and second windings for current detection and winding of the second winding. The number of selections is set to be larger than the number of turns of the first winding, and the first flow path and the resistor for guiding the sending current of the constant current source to the external load through the first winding. A second flow path which is connected to the resistor in series and which causes a current in the second flow path to flow side-by-side. Is a circuit provided with a current limiting circuit that is connected so as to lead to the current limiting circuit and limits the sideward current to a predetermined value or less.

The present invention will now be described in detail with reference to the drawings.

FIG. 3 is a block diagram showing the first embodiment of the present invention. The difference between the constant current circuit 2 shown in the figure and the conventional constant current circuit 1 shown in FIG.
Add the DC winding W _D2, further diversion of the current I ₂ to the resistor R _P performed between the current detection circuit 5 and the constant current source 3 is provided with a current control circuit 8 to the resistor R _P connected in series That is. The current sent from the constant current source 3 is the load sharing resistor R.
It is split into a current I ₂ flowing to _P and a current I _L flowing toward the load through the first DC winding W _D1 . Current limiting circuit 8
Has a configuration in which both ends of a Zener diode ZD connected in series to the resistor R _P are connected to the second DC winding W _D2 via the resistor R _P for side-flowing the current I ₃ .

The output voltage V _d of the current detection circuit 5 is proportional to the sum of the ampere-turns of the first and second DC windings W _D1 and W _D2 , that is, (N ₁ · I _L + N ₂ · I ₃ ), and V _d = G (N ₁ · I _L + N ₂ · I ₃ ) ... (6) However, N ₁ and N ₂ indicate the number of _turns of the first and second DC windings W _{D 1} and W _D2 , respectively. The control circuit 6 receives this output voltage V _d and, with respect to this and a current I ₁₀ having a predetermined value, V ₀ = g · N ₁ · I ₁₀ (7) A control signal of a voltage proportional to the difference from ₀ is sent to the constant current source 3, and an ampere turn (N ₁ · I _L + N ₂
-The sending current I ₁ of the constant current source 3 is controlled so that (I ₃ ) becomes equal to ampere-turn (N ₁ · I ₁₀ ). By this control, I _L = I ₁₀ − (N ₂ / N ₁ ) · I ₃ (8) holds.

On the other hand, in the current I ₃ shunted to the second DC winding W _D2 , the voltage across the zener diode ZD (V _Z ) is the zener voltage (V
When it is less than _B ), it is equal to the current I _2, and when the voltage across the Zener diode ZD (V _Z ) reaches the Zener voltage (V _B ), the winding resistance of the second DC winding W _D2 is very small. Therefore, when ignored, it becomes a constant value equal to (V _B / R _S ). Therefore, when V _Z <V _B holds, equation (8)
Since the winding resistance of the first DC winding W _D1 is very small, I _L = I ₁₀ − (N ₂ / N ₁ ) · I ₂ = I ₁₀ − (V / R) ... ... (9) _{where, R = (R P + R} S) / (N 2 / N 1) ...... is (10) holds, and when the vice is _V Z = _{V B is, I L = I 10 - (} N 2 / N ₁ ) ・ (V _B / R _S ) …… (11) holds. The following figure shows equations (9) and (11) as in FIG.

FIG. 4 is a characteristic diagram showing the operating characteristics of this embodiment, and shows the operating characteristics when two constant current circuits 2 are connected in series as shown in FIG. 1 (b). The characteristics A ₀ and B ₀ shown by the solid lines respectively indicate the operating characteristics of the two constant current circuits 2A and 2B connected in series, and the currents I _A0 and I _B0 are both the predetermined current I.
Equal to ₁₀ . That is, the characteristic A ₀ (or B ₀ ) is shown by applying the equations (9) and (11) to the constant current circuit 2A (or 2B). The voltage V _AC is the voltage V _A at the operating point at which the characteristic A ₀ shifts from the characteristic of the equation (9) to the characteristic of the equation (11), Is represented. As is clear from the equations (9) and (11), the absolute value of the slope of the characteristic A ₀ is 1 / R if V _A <V _AC
And if V _A <V _AC , then it is zero. Referring to the equation (12), the voltage V _AC is _{calculated by} setting the intersection point P ₀ of the characteristics A ₀ and B ₀ to be 1 / R.
Intersection Q ₀ of the gradient portion has and characteristics A ₀ and load characteristics (absolute value) (i.e. the straight line _{I L = (V L0 / I} L0) · V Ao illustration is omitted) is in the portion of the slope of zero You can choose to Fig. 4 shows an example of such selection. As a result, the power loss in the resistors R _S and R _P can be reduced more than before, and one of the constant current circuits 2A and 2B operates. The fluctuation amount of the current I _L when interrupted can also be reduced as compared with the conventional case. First, the variation △ V _A voltage V _A due to the variation of the current I ₁ in the constant current control range, the slope of 1 / R of the variation characteristic A ₀ and B ₀ in the present embodiment the voltage V _A ( If it occurs within the portion of (absolute value), it is expressed as ΔV _A = R · ΔI ₁ = R · b · I ₁₀ (13). As is clear by comparing the equation (6) and the above equation (13) in the case of the conventional circuit and referring to the equation (10), the resistance value (R _S + R _P ) in this embodiment can be calculated as follows. Of the resistor R _{P in} the circuit The same voltage fluctuation ΔV _A is obtained when they are equal to. Therefore, the power loss in the resistors R _S and R _P is N _{1 in} this embodiment.
If the number of turns is set so that <N ₂ is satisfied, Reduce to. Further, since the characteristic A ₀ in the conventional circuit becomes a straight line as shown by the broken line a ₀ , the operating point of the constant current circuit 1A at the time of the interruption of the operation of the constant current circuit 1B is the point q ₀ , but in the present embodiment, , Constant current circuit when the operation of constant current circuit 2B is interrupted
The operating point for 2A is point Q ₀ . The point Q ₀ is located on the upper right side of the point q ₀ and therefore approaches the standard operating point of the load 7.

As described above, the second DC winding W _D2 having a larger number of turns than the first DC winding W _D1 is additionally provided in the current detection circuit 5 to provide the first and second DC windings W _D1 and By controlling the current so that the ampere-turn of W _D2 becomes a predetermined value, the power loss of the load sharing resistors R _S and R _P can be reduced, and the current flowing through the load sharing resistor R _P can be current limited. The current shunted by the circuit 8 is applied to the second DC winding W _D2.
Flow into the circuit, it is possible to reduce load current fluctuations when one circuit is disconnected during series operation.

FIG. 5 is a block diagram showing a second embodiment of the present invention. In the circuit of this embodiment, the current limiting circuit 8 is connected to the ground side when one output end is grounded in the circuit of the first embodiment. Obviously, the operating principle is the same as that of the first embodiment, but the voltage applied to the second DC winding W _D2 in FIG. 3 is lower in this embodiment, so that the DC winding wire W There is an advantage that it is not necessary to subject the _D2 to high withstand voltage processing as in the conventional case, and the number of manufacturing steps of the current detection circuit 5 can be reduced.

FIG. 6 is a block diagram showing a third embodiment of the present invention. In the circuit of this embodiment, constant current control is performed by the current detection circuit 15 additionally provided with the reference current winding W _S for flowing the reference current I _S. The reference current winding W _S has a sum of ampere-turns of the first and second DC windings W _D1 and W _D2 (N ₁
The reference current I _S for canceling (I _L + N ₂ · I ₃ ) is supplied from the constant current source 13. Assuming that the number of turns of the reference current winding W _S is N _S , the current detection circuit 15 outputs the output voltage V proportional to the combined value of ampere turns (N ₁ · I _L + N ₂ · I ₃ −N _S · I _S ). _d is generated and sent to the control circuit 6. In this embodiment, the constant current control reference voltage V ₀ in the control circuit 6 is set to zero. That is, the control circuit 6 outputs a control signal having a voltage proportional to the voltage V _d to the north of the constant voltage source 3 so that the voltage of the control signal becomes zero, that is, I _L = (N _S / N ₁ ) · I _S (N ₂ / N ₁ ) ・ I ₃ …… (14) The constant current source 3 is used to send out the current I ₁ that satisfies the relationship.
To control. In the equation (14), I ₁₀ in the equation (8) is changed to (N
_{Since S} / N ₁ ) · I _S is replaced by the expression, constant current control similar to that in the first embodiment can be performed in this embodiment, and therefore the same effect as that in the first embodiment can be obtained. it can.

It is clear that the same effect can be obtained when three or more circuits of this embodiment are operated in series. The current limiting circuit 8 is Fig. 3 without limiting to the illustrated circuit form, when the current I ₂ flowing the current I ₂₀ below a predetermined intact second
DC winding W _D2 flowed side, the current I current I ₂ is determined in advance
If circuit constructed only of which current I ₂₀ so as to flow side to the second DC winding W _D2 when it exceeds _20, it will be obvious that the same effect can be obtained.

As is apparent from the above description, the present invention has a smaller power loss in the load sharing resistor than the conventional one, and a small fluctuation in the load current when a part of the resistance occurs during serial operation, and a small fluctuation in the constant current. The effect is that a constant current circuit can be realized.

[Brief description of drawings]

1A and 1B are block diagrams showing a configuration example and a usage example of a conventional constant current circuit, respectively, and FIG. 2 is a characteristic diagram showing an operation of the conventional constant current circuit, FIGS. 3 and 4 respectively. FIG. 5 is a block diagram and a characteristic diagram showing the first embodiment of the present invention, and FIG. 5 and FIG. 6 are the second diagram of the present invention.
It is a block diagram which shows and 3rd Example. 1,1A, 1B, 2,2A, 2B ... constant current circuit, 3,13 ... constant current source,
4,5,15 ...... current detection circuit, 6 ...... control circuit, 7 ...... load, 8 ...... current limiting _{circuit, W D, W D1, W} D2 ...... DC winding,
W _S …… Reference current winding, R _S , R _P …… Resistance, D ₁ , D ₂ ……
diode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiko Yamamoto 3-9-11 Midoricho, Musashino-shi, Tokyo Inside Nippon Telegraph and Telephone Public Corporation Musashino Telecommunications Research Laboratories (56) Reference JP-A-54-36557 (JP, A)

Claims (1)

[Claims] 1. A current detection circuit for detecting a current at a predetermined location in a circuit, and a sending current controlled so that the detection value converges to a predetermined value in response to a signal indicating the detection value of the current detection circuit. In a constant current circuit having a constant current source and a load sharing resistor, the current detection circuit has at least first and second windings for current detection, and the number of turns of the second winding is The number of windings is set to be larger than the number of turns of the first winding, and the first current flowing through the constant current source through the first winding to an external load and the resistor flows through the resistor. A second flow path, the second flow path is connected in series with the resistor, and the current in the second flow path is diverted to be guided to the second winding. A constant current circuit comprising a current limiting circuit which is connected and limits the side-flowing current to a predetermined value or less.