JPH0715652B2 - Constant current circuit - Google Patents

Description

The present invention relates to a constant current circuit, and in particular, it has a constant current source whose current value is independently limited, and a plurality of constant current sources are connected in series to provide a constant current to a load. The present invention relates to a constant current circuit for supplying a current.

[Conventional technology]

FIGS. 5A and 5B are block diagrams showing a configuration example of a conventional constant current circuit and an example of use thereof, respectively.
5 (a) and 5 (b), the constant current circuit 1 controls the current I ₁ sent from the constant current source 3 by the current detection circuit 4 and the control circuit 6 so as to have a predetermined value, and the load 7 Supply a current I _L to. 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 and then the load. The current is divided into a current I ₂ flowing through the 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 denotes the number of turns of the DC winding W _D) of the DC winding W _D to generate an output voltage V _d which is proportional to this control circuit 6 Send to. 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 being applied. 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,
As shown in Fig. 5 (b), a plurality of them are connected in series (Fig. 5 (b) shows an example in which two of them are connected in series. The diodes D ₁ and D ₂ are the constant current circuits 1A and 1B, respectively. This is for bypass when operation is interrupted.) 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 structure as in FIG. 5 (a). 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. 6 is a characteristic diagram showing operating characteristics when the conventional constant current circuit shown in FIG. 5 (b) is connected. 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. The voltage V _L0 and the current I _L0 indicate the voltage and current values during the standard operation of the load 7, respectively.
The characteristics A ₀ and B ₀ shown by the solid line are for the constant current circuit 1A, respectively.
And the output voltage vs. output current characteristics when the current I ₁ sent from the constant current source 3 of 1B is equal to the predetermined current I ₁₀ .
Both currents I _A0 and I _B0 are equal to current I ₁₀ . Fifth
As is clear with reference to the figure (a), I _L = I ₁ −I ₂ = I ₁ (V / R _P ) ... (3) holds, and this is determined when I ₁ = I _10. When applied to the current circuit 1A, I _L = I _A0 − (V _A / R _P ) ... (4) holds. This is shown in the characteristic A ₀ . 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 half of the voltage V _L0 , 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 indicated by the broken lines are obtained when the sending current I ₁ of the constant current source 3 of the constant current circuits 1A and 1B fluctuates up to the upper limit I _B0 and the lower limit I _{B1 of the} constant current control accuracy range. Show. As is clear from the equation (3), the characteristics A ₁ and B ₁ are characteristics obtained by translating the respective characteristics A ₀ and B ₀ upward and downward by ΔI ₁ (where ΔI 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 ΔV _A of this voltage _{V 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 , and the constant current The magnitude is proportional to the output current I ₁₀ of the 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 it is necessary to increase the current I ₁₀ in a large load current system, the resistance R _P must be reduced in order to keep the voltage fluctuation ΔV _A within a desired range. 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, the resistance R _P may be lowered by one digit. Fig. 5 (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, 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 _L0 / I _L0 ) · V _A (not shown in FIG. 6). Since the dynamic A ₀ is a straight line to the right of the absolute value 1 / R _P of the gradient, the point Q ′ ₀ shifts to the lower left in the figure when R _P decreases, and from the standard operating point of the load 7. The distance between them increases.

[Problems to be Solved by the Invention]

In the conventional constant current circuit described above, 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 is large when a failure occurs in a part of the redundant configuration. It has the drawback.

[Means for Solving the Problems]

The constant current circuit of the present invention is configured to detect a current at a predetermined location in the circuit and a current detection circuit so that the detection value converges to a predetermined value in response to a symbol indicating the detection value of the current detection circuit. In a constant current circuit having a constant current source for controlling a sending current and a load sharing resistor, the current detection circuit has at least first and second windings for current detection. The number of windings of the winding is set to be larger than the number of windings of the first winding, and the first flow path for guiding the delivery current of the constant current source to the external load through the first winding. And a second flow path that flows through the resistor, and a connection path is formed so as to be shunted to the second flow path. The second flow path is connected in series with the resistance and the current in the second flow path is side-flowed. An electric current which is connected so as to be guided to the second winding and which limits the side-current flowing within a preset value. And it includes a limiting circuit.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention.

The difference between the constant current circuit 2 shown in FIG. 1 and the conventional constant current circuit 1 shown in FIG. 5 (a) is that a second DC winding W _D2 is added to the current detection circuit 5 and the resistance is further increased. the shunt current I ₂ to R _P performed between the current detection circuit and the constant current source 3, a resistor R _P
That is, the current limiting circuit 8 is connected in series. The current sent from the constant current source 3 is split into a current I ₂ flowing through the load sharing resistor R _P and a current I _L flowing through the first DC winding W _D1 toward the load. The current limiting circuit 8 includes a Zener diode ZD ₁ and a resistor R _q connected in series with the resistor R _P.
The parallel circuit is composed of two resistors connected to the second DC winding W _D2 via a resistor R _s and a Zener diode ZD ₂ 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 _D1 and W _D2 , respectively. The control circuit 6 receives this output voltage V _d and, with respect to this and the current I ₁₀ of a predetermined value, the reference voltage V ₀ represented by V ₀ = g · N ₁ · I ₁₀ (7) A control signal of a voltage proportional to the difference between the 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.

Now, assuming that the Zener voltages of the Zener diodes ZD ₁ and ZD ₂ are V _B1 and V _B2 , respectively, and V _B1 > V _B2 (9), the current I ₃ shunted to the second DC winding W _D2 is Since the voltage across the resistor R _q (V _Z1 ) is zero when the Zener voltage of the Zener diode ZD ₂ is less than V _B2 , I _L = I ₁₀ (10) holds, and the voltage across the resistor R _q is satisfied. (V _Z1 ) is the Zener diode ZD ₂
R is equal to or higher than the Zener voltage (V _B2 ) of the zener diode and is equal to or lower than the Zener voltage (V _B1 ) of the zener diode ZD _{1.
Since p} > R _q > R _s and the winding resistance of the DC winding W _D2 is very small, I _L = I ₁₀ − (N ₂ / N ₁ ) · I ₃ = I ₁₀ − (N ₂ / N ₁ ) · (V _Z1 −V _B2 ) / R _s (11) holds, and when V _Z1 = V _B1 , I _L = I ₁₀ − (N ₂ / N ₁ ) · (V _B1 Similarly to FIG. 6, FIG. 2 (b) shows equations (10), (11) and (12) for which −V _B2 ) / R _s (12) holds.

FIGS. 2A and 2B are a block diagram showing an application example of the first embodiment and a characteristic diagram showing operation characteristics of the application example, respectively.

2 (b) shows the constant current circuit 2 as shown in FIG. 2 (a).
The operating characteristics when connected in series are shown below.

The characteristics A ₀ and B ₀ shown by the solid line in FIG. 2 (b) show the operating characteristics of the constant current circuits 2A and 2B of the first embodiment shown in FIG. Current I _A0
And I _B0 are both equal to the predetermined current I ₁₀ . That is, the characteristic A ₀ (or B ₀ ) is shown by applying the equations (10), (11) and (12) to the constant current circuit 2A (or 2B). The voltage V _AC is a constant current circuit at the operating point where the characteristic A ₀ shifts from the characteristic of equation (11) to the characteristic of equation (12).
2A is the output voltage V _A , V _B is the output voltage of the constant current circuit 2B, Is represented. As is apparent from equation (11) and (12), the absolute value of the gradient of the characteristic A _0, if V A _{<V AC} (N ₂
/ N ₁ ) / R _s (= 1 / R) and is zero if V _A > V _AC . With reference to the equation (13), the voltage V _AC is set such that the intersection P ₀ of the characteristics A ₀ and B ₀ is in the portion of the slope (absolute value) of 1 / R and the characteristic A ₀ and the load characteristic (that is, the straight line I _L = (V _L0 /
I _L0 ) ・ V _A. The intersection point Q _{0 (not} shown) can be selected so as to be in a portion having a slope of zero. FIG. 2B shows an example of such selection, and as a result, the resistance R
_s and can reduce than conventional power loss in the R _p, further amount of variation of the current I _L when either is interrupted operation of the constant current circuits 2A and 2B also can be reduced than conventionally. First, the variation [Delta] V _A voltage V _A due to the variation of the current I ₁ in the constant current control range, in the first embodiment variation of the voltage V _A is 1 / R of the characteristic A ₀ and B ₀ If it occurs within the gradient (absolute value) part, ΔV _A = R · ΔI ₁ = R · b · I ₁₀ (14) As is clear by comparing the equation (6) and the above equation (14) in the case of the conventional circuit and referring to the equation (11), the resistance value (R _s + R _p ) in the present embodiment can be calculated as follows. The same voltage fluctuation ΔV _A results when the resistance R _p in the constant current circuit is made equal to (N ₂ / N ₁ ) times. Therefore, the resistances R _s and R
If the number of turns is set so that N ₁ <N ₂ is satisfied in this embodiment, the power loss at _p is (N ₂ / N in the case of the conventional constant current circuit 1).
₁ ) Double reduction. Furthermore, the characteristic A in the conventional constant current circuit 1
_{Since 0} is a straight line as shown by the solid line in FIG. 6, the operating point of the constant current circuit 1A when the operation of the constant current circuit 1B is interrupted is the point q ₀ in FIG. 2 (b). In this embodiment, the operating point of the constant current circuit 2A when the operation of the constant current circuit 2B is interrupted 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, 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 magnitude, 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 is 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. 3 is a block diagram showing a second embodiment of the present invention.

In the constant current circuit of the second embodiment, the current limiting circuit 8 is connected to the ground side when one output end of the constant current circuit 2 of the first embodiment is grounded. 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. 1 is lower in the case of the second embodiment. There is no need to subject the line W _D2 to high withstand voltage processing as in the conventional case, and there is an advantage that the number of manufacturing steps of the current detection circuit 5 can be reduced.

FIG. 4 is a block diagram showing a third embodiment of the present invention.

In the constant current circuit of the third embodiment, a current detection circuit 15 additionally provided with a reference current winding W _s for flowing the reference current I _s is provided.
Constant current control by. The reference current winding W _s has a first
And the reference current I _s for canceling the sum (N ₁ · I _L + N ₂ · I ₃ ) of the ampere-turns of the second DC windings W _D1 and W _D2.
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 an 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 the third embodiment, the constant current control reference voltage in the control circuit 6
V ₀ is set to zero. That is, the control circuit 6 controls the voltage V
a control signal voltage proportional to _d feed to the constant-current source 3, so that the voltage of the control signal becomes zero, i.e. _{I L = (N s / N} 1) · I s - (N 2 / N 1) · I ₃ ... Constant current source 3 to send out current I ₁ that satisfies the relationship of (15)
To control. In the equation (15), I ₁₀ in the equation (8) is changed to (N
_s / N ₁ ) · I _s , the constant current control similar to that of the first embodiment can be performed in the third embodiment, and therefore, the same effect as that of the first embodiment can be obtained. Obtainable.

It is apparent that the same effect can be obtained when three or more constant current circuits of the third embodiment are operated in series. Further, the current limiting circuit 8 is not limited to the circuit form illustrated in FIG. 1, and when the inflowing current I ₂ is equal to or less than the predetermined current I ₂₀ , it is caused to flow to the second DC winding W _D2 as it is, and the current I 2 if circuit constructed only of which current I ₂₀ so as to flow side to the second DC winding W _D2 when _{the 2} exceeds the current I ₂₀ determined in advance, it will be obvious that the same effect can be obtained.

〔The invention's effect〕

As described above, in the present invention, the current detection circuit is additionally provided with the second DC winding having a larger number of turns than the first DC winding, and the ampere-turns of the first and second DC windings are predetermined. By controlling the current so that the load sharing resistance becomes large, the power loss of the load sharing resistor can be reduced, and the current flowing in the load sharing resistor is side-flowed by the current limiting circuit to the second DC winding. The inflow has an effect that the load current fluctuation when one of the constant current circuits is disconnected during the two-series operation can be reduced as compared with the related art. As a result, the constant current characteristic can be improved compared to the conventional one,
This has the effect of making it possible to reduce the influence on the load operating at a constant current as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing the first embodiment of the present invention, and FIG.
FIGS. 3A and 3B are a block diagram showing an application example of the first embodiment and a characteristic diagram showing the operation characteristics of the application example, and FIGS. 3A and 3B are the second and the second of the present invention, respectively. 3 is a block diagram showing the third embodiment, FIGS. 5 (a) and 5 (b) are block diagrams showing a configuration example and a usage example of a conventional constant current circuit, and FIG. 6 is a conventional diagram shown in FIG. 5 (b). FIG. 7 is a characteristic diagram showing operating characteristics when the constant current circuit of FIG. 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.

Claims (1)

[Claims] 1. A current detection circuit for detecting a current at a predetermined location in a circuit, and a sending current 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 for controlling the current and a load sharing resistor, the current detection circuit has at least first and second windings for current detection, and the second winding Is set to be larger than the number of turns of the first winding, and the first flow path for guiding the sending current of the constant current source to the external load through the first winding and the A second passage having a connection passage for branching to the second passage flowing in the resistance;
Is connected in series to the resistor and is connected so as to cause the current in the second flow path to flow to the second winding and to flow to the second winding, and the current flowing to the side is within a preset value. A constant current circuit, characterized in that it is provided with a current limiting circuit for limiting to.