JPH077309B2 - 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 P _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 Vd is generated in proportion to the number of turns of the output voltage Vd and is sent to the control circuit 6. Therefore, the relationship between the output voltage Vd of the current detection circuit 4 and the current I ₁ is expressed as Vd = gN · I ₁ (1), and the proportional constant g is the 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 Vd of the current detection circuit 4 is applied, and the other of which a reference voltage V _{0 serving as} a reference for constant current control. Is being applied. The reference voltage V _O is set so as to satisfy the relationship of V _O = 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, so that the difference between them sends a control signal of a voltage proportional to the difference between the output voltage Vd and the reference voltage V _O to the constant current source 3 becomes zero, that is, the current I ₁ is equal to current I ₁₀ To control the constant current source 3.

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 pieces are connected in series in FIG. 1 (b). The diodes D ₁ and D ₂ are constant current circuits 1 _A and 1 _{B, respectively.}
It is for bypass when the operation of the. ) Use a redundant configuration that operates simultaneously to improve reliability and share the load. Both the constant current circuit 1 _A and 1 _B have the same configuration as FIG. (A). In this case, even when the current I ₁ that is transmitted from each of the constant current source 3 of the constant current circuit 1 _A and 1 _B is varied within the range of the constant current control precision, the constant current circuit 1 _A and 1 _B
To prevent one side from sharing an excessive power load,
As described below, it is necessary to set the resistance R _P to a certain value or less.

FIG. 2 is a characteristic diagram showing operation characteristics at the time of connection in FIG. 1 (b). Output voltage V _A of the abscissa the constant current circuit 1 _A
And the vertical axis represents the supply current I _L to the load 7. Voltage V
_LO and current I _LO indicate the voltage and current values during the standard operation of load 7, respectively. The characteristics A ₀ and B ₀ shown by the solid lines are the output voltage vs. output current characteristics when the current I ₁ sent from the constant current source 3 of the constant current circuits 1 _A and 1 _B is equal to the predetermined current I _{10. Shown} and currents I _AO and I
_BO is equal to the 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 1 _A in this case, I _L = I _AO − (V _A / R _P ) ... (4) holds. This is shown in the characteristic A _O. Further, holds the _V B = _{V LO} -V _A at the time of normal operation of the load 7, applying the this relation and Equation (3) to the constant current circuit _{1 B, I L = I BO} - (V _LO / R _P ) + (V _A / R _P ) ... (5) holds. This is illustrated in the characteristic BO. The operating point in this case is given by the intersection point P _O of the characteristics AO and B _O , but the voltage V _{AO at} this time is obviously just half of the voltage V _LO , and the load sharing of the constant current circuits 1 _A and 1 _B. 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 1 _A and 1 _B fluctuates up to the upper limit I _A1 of the constant current control accuracy. Formula (3)
As is clear from the characteristics, the characteristics A ₁ and B ₁ are
_O and B _O only △ I ₁ becomes characteristic translated upward and downward (provided that _{△ I 1 = I A1 -I AO} = I BO -I B1.) In accordance with this operating characteristic variations, the operation The 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 _AO when the load is evenly distributed to the voltage V _A1 and the load distribution becomes uneven. Variation of this voltage V _A ΔV _A = V _A1 −V
_AO 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 , and the constant current source 3 Of the sending current I ₁₀ , 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 for coping with the increase in the heat generation amount of the resistance R _P becomes large in scale, and the constant current circuit becomes large. I have no choice. Further, if the resistance value is lowered as described above, two constant current circuits _1A connected in series as shown in FIG.
When one of _B and 1 _B causes a failure to interrupt the operation, the amount of fluctuation of the current I _L accompanying this becomes large. For example, when the operation of the constant current circuit 1 _B 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 the characteristic A ₀ and the straight line I _L = showing the operating characteristic of the load 7.
It is the intersection with (V _LO / I _LO ) · _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. A constant current source 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 delivery current of the constant current source Has a connection such that after passing through the first winding, the current is shunted to a first flow path that flows to the resistor and a second flow path that flows to an external load, and the first flow path is A current limiting circuit that is connected in series with the resistor and is connected so as to cause the current in the first flow path to flow into the second winding and to limit the current flowing into the second winding to a predetermined value or less. Circuit.

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.
The DC winding W _D2 is additionally provided, and the current limiting circuit 8 is provided in series with the resistor R _P. The current I ₁ sent from the constant current source 3 is led to the first DC winding W _D1 of the current detection circuit 5 as in the conventional case. After passing through the first DC winding W _D1 , the current I ₁ is split into a current I ₂ flowing to the load sharing resistor R _P via the current limiting circuit 8 and a current I _L flowing toward the load. To do. The current limiting circuit 8 has a configuration in which both ends of the Zener diode ND connected in series with the resistor R _P are connected to the second DC winding W _D2 via the resistor R _S for side current I ₃ .

The output voltage Vd 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 ₁ + N ₂ · I ₃ ), and Vd = g (N ₁ · I ₁ + N ₂ · I ₃ ) ... (8) However, N ₁ and N ₂ indicate the number of _turns of the first and second DC windings W _D1 and W _D2 , respectively. The control circuit 6 receives this output voltage Vd and, with respect to the current I ₁₀ having a predetermined value, a reference voltage V ₀ represented by V ₀ = g · N ₁ · I ₁₀ (9) The control signal of the voltage proportional to the difference of is sent to the constant current source 3, and the ampere turn (N ₁ · I ₁ + N ₂ · N
The sending current I ₁ of the constant current source 3 is controlled so that I ₃ ) becomes equal to the ampere-turn (N ₁ · I ₁₀ ). By this control, I ₁ = I ₁₀ − (N ₂ / N ₁ ) · I ₃ (10) holds.

On the other hand, the current I ₃ shunted to the second DC winding W _D2 is equal to the current I ₂ when the voltage (V _Z ) across the Zener diode ZD is less than the Zener voltage (V _B ), and the Zener diode ZD When the voltage across both ends (V _Z ) reaches the Zener voltage (V _B ), the winding resistance of the second DC winding W _D2 is very small, and therefore has a constant value equal to (V _B / R _S ). Therefore, when V _Z <V _B holds, referring to the equation (10), When V _Z = V _B holds, L _L = I ₁ −I ₂ = I ₁₀ − (N ₂ / N ₁ ) · (V _B / R _S ) − (V−V _B ) / R _P
(13) is established. FIG. 4 shows the equations (11) and (13) 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 _AO and I _BO are both the predetermined current I.
Equal to ₁₀ . That is, the characteristic A ₀ (or B ₀ ) is expressed by the equation (1
1) and (13) are applied to the constant current circuit 2A (or 2B) for illustration. The voltage V _AC has the characteristic A ₀ expressed by the formula (1
The voltage V _A at the operating point at which the characteristic of 1) shifts to the characteristic of formula (13), Is represented. As is clear from the equations (11) and (13), 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 1 / R _P.

Referring to the equation (12), the winding number ratio N ₂ / N ₁ can be selected so as to satisfy 1 / R _P <1 / R. Further, referring to the equation (14), the voltage V _AC is set such that the intersection P ₀ of the characteristics A ₀ and B ₀ is at the slope (absolute value) of 1 / R and the characteristic A ₀ and the load characteristic (that is, the straight line I). _{L = (V LO / I LO} ) · V AO shown can be chosen so that the portion of the gradient of the intersection Q ₀ is 1 / R _P of omitted) (absolute value). 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 variation of the current I _L at the time of interruption can be reduced than conventionally. First, the fluctuation ΔV of the voltage V _A caused by the fluctuation of the current I ₁ within the constant current control range.
_A indicates that the variation of the voltage V _A is 1 / of the characteristics A ₀ and B ₀ in this embodiment.
If it occurs within the gradient (absolute value) part of R, it can be expressed as ΔV _A = R · ΔI ₁ = R · b · I ₁₀ (15). As is clear by comparing the equation (8) and the above equation (15) in the case of the conventional circuit and referring to the equation (12), it is clear that the resistance value (R _P + R _P ) in the present embodiment is Resistance in the circuit The same voltage fluctuation ΔV _A is obtained when they are made equal to each other. Therefore, the power loss in the resistors R _S and R _P is reduced to N ₁ / (N ₁ + N ₂ ) times that in the conventional circuit in this embodiment. Furthermore,
Since the characteristic A ₀ in the conventional circuit is a straight line as shown by the broken line a ₀ , the constant current circuit when the operation of the constant current circuit 1B is interrupted
The operating point of 1A is point q ₀ , but in this embodiment, the constant current circuit 2B
The operating point of the constant current circuit 2A at the time of the interruption of the operation is the 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, so that the size of the ampere turns predetermined first and second DC windings W _D1 and W _D2 provided by adding a second DC winding W _D2 to the current detection circuit 3 By controlling the current, the power loss of the load sharing resistors R _S and R _P can be reduced, and the load sharing resistor R _S can be further reduced.
The current flowing in the current limiting circuit 8 to the second current
By causing the current to flow into the DC winding W _D2 of, the load current fluctuation when one circuit is disconnected during series operation can be reduced.

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 constant current source 13 supplies the reference current I _S for canceling (I ₁ + N ₂ · I ₃ ). Set the number of turns of the reference current winding W _S to N
If _S, the current detection circuit 15 outputs a voltage proportional to the combined value of the ampere turns _{(N 1 · I 1 + N} 2 · I 3 -N S · I S) V
_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 sends a control signal having a voltage proportional to the voltage V _d to the constant current source 3 so that the voltage of the control signal becomes zero, that is, I ₁ = (N _S / N ₁ ) · I _S (N _The constant current source 3 is controlled so as to deliver the current I ₁ expressed as ₂ / N ₁ ) · I ₃ (16). The formula (16) is obtained by changing I ₁₀ in the formula (10) to (N _S / N ₁ ) ·
Since the equation is replaced with I _S , constant current control similar to that of the first embodiment can be performed in this embodiment as well, and therefore the same effect as that of the first embodiment can be obtained.

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 formation, 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
It is obvious that the same effect can be obtained if the circuit is configured so that only the current I ₂₀ is diverted to the second DC winding W _D2 when it exceeds ₂₀ .

As is apparent from the above description, the present invention can realize a constant current circuit in which the power loss of the load sharing resistor is smaller than that in the prior art and the fluctuation of the load current is small when a partial failure occurs during serial operation. There is an effect.

[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 control _{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 delivery current of the constant current source is The first flow path has a connection for branching into a first flow path that flows through the resistance and a second flow path that flows through an external load after passing through the first winding. A current limiting circuit that is connected in series with the resistor and is connected so as to cause the current in the first flow path to flow to the second winding and to guide the current to the second winding; Constant current circuit characterized by.