JP2593692Y2 - Series load protection device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a series load protection device suitable for connecting various load circuits in series.

[0002]

2. Description of the Related Art When driving various loads by applying a voltage, if the voltage obtained by a power supply circuit is too high, it is necessary to reduce the voltage applied to the load. An example is shown in FIG. In the figures, 1 to 10 are lamps having a rated voltage of "6" volts, which are connected in parallel with each other. Reference numeral 12 denotes a Zener diode having a Zener voltage of "6" volts, and is connected in parallel to these lamps 1 to 10. Reference numeral 11 denotes a resistor which is connected in series to the Zener diode 12 and to which a power supply voltage V _C (= “12” volts) is applied. Therefore,
The voltage across Zener diode 12 is "6" volts, and a voltage of "6" volts is applied to each of lamps 1-10.

In the configuration shown in FIG. 7, two lamps 1 to 10 are connected in series, and a power supply voltage V _C is applied to these series circuits. Therefore, the power supply voltage V _C
Is divided by each of the lamps 1 to 10, and each of the lamps 1 to 1
A voltage of "6" volts is applied to zero. Further, in the configuration shown in FIG. 8, the connection points of the lamps connected in series are further connected to each other.

[0004]

In the configuration of FIG. 6, since "1/2" of the power supplied from the power supply (not shown) is consumed by the resistor 11, the power is wasted. Problem. Further, in the configuration shown in FIG. 7, if one of the two lamps connected in series (for example, the lamp 1) is disconnected, the other lamp (the lamp 6) cannot be turned on. On the other hand, in the configuration of FIG. 8, even if one of the lamps is disconnected, the other lamps are not turned off immediately. However, in the configuration shown in FIG. 8, when any one of the lamps is disconnected, the balance between voltage and current is lost. For example, when the lamp 1 is disconnected, the terminal voltages of the lamps 2 to 5 become higher than “6” volts, and the possibility that the lamps 2 to 5 are disconnected early increases. The present invention has been made in view of the above-described circumstances, and provides a series load protection device that can prevent, even when a part of a load is damaged, from adversely affecting other normal loads. It is intended to be.

[0005]

According to the present invention, in order to solve the above-mentioned problems, a first load and a first load are provided.
A second load connected in series with the first and second loads;
The emitter end is connected to the connection end of the load, and the first load
A first transistor having a collector connected to the other end,
An emitter terminal is connected to a connection terminal between the first and second loads.
And the collector end is connected to the other end of the second load.
In both cases, the second transistor has a different polarity from the first transistor.
And the first and second transistors
And a voltage holding means for holding the voltage between the base ends of the first and second terminals constant .

[0006]

Either the first or second load fails,
When the terminal voltage rises, the corresponding first or second
The transistor turns on and the terminal voltage of the failed load
The pressure is suppressed.

[0007]

Embodiment A. First Embodiment A first embodiment of the present invention will be described below with reference to FIG. In the drawings, parts corresponding to the respective parts in FIGS. 6 to 8 are denoted by the same reference numerals, and description thereof will be omitted. In the figure, lamps 1 to 10 are connected in the same manner as the circuit of FIG. That is, two lamps 1 to 10 are connected in series, and the power supply voltage V _C is applied to these series circuits. The connection points of the lamps connected in series are further connected to each other.

In the configuration shown in FIG.
The collector and the emitter of the NPN transistor 20 are connected in parallel with 5, and the collector and the emitter of the PNP transistor 21 are connected in parallel with the lamps 6-10. Further, the resistor 13, the diode 14, and the resistor 1
5 are connected in series, a power supply voltage V _C is applied to the resistor 13, and the resistor 15 is grounded. The connection point between the resistor 13 and the diode 14 is connected to the base end of the transistor 20, and the connection point between the diode 14 and the resistor 15 is connected to the base end of the transistor 21. The resistance values of the resistors 13 and 15 are the same.

Next, the operation of this embodiment will be described.
First, when the power supply voltage V _C is applied to the resistor 13, a current flows sequentially through the resistor 13, the diode 14, and the resistor 15, and a forward voltage drop V _D occurs in the diode 14. This voltage drop V _{D is referred} to as “0.
6 "volts, resistor 13 and diode 1
Voltage V _A at the fourth connection point, and the voltage V _B is at the junction of diode 14 and the resistor 15, resistor 13,
If the resistance values of 15 are equal, the following equations (1) and (2) are obtained. V _A = V _C /2+0.3...... formula _{(1) V B = V C} /2-0.3...... formula (2)

Here, assuming that all of the lamps 1 to 10 are normal, the voltage V _{Q at} the connection point between the transistor 20 and the transistor 21 becomes equal to “V _C / 2”.
Therefore, both the emitter-base voltage V _BE of the transistors 20 and 21 becomes “0.3” volt. In a general silicon transistor, the emitter-base voltage V _BE
Is turned off when the voltage becomes equal to or less than "0.6" volt. That is, as shown in FIG. 9, the emitter-base voltage V
_{When BE} is less than "0.6" volts, the emitter current _IE of transistor 20 hardly flows. Therefore,
When all of the lamps 1 to 10 are normal, the transistors 20 and 21 are turned off, and a voltage of “V _C / 2” is applied to each of the lamps 1 to 10.

Next, the operation when some lamps are disconnected will be described. For example, when the lamp 1 is disconnected, the lamp 1
Since the combined resistance of the parallel circuit composed of 5 is _{high, V Q <V C / 2} ...... (3) the relationship is established. Further, when the V _A -V _Q> 0.6 ...... formula (4) is satisfied, because the emitter-base voltage V _BE of the transistor 20 is "0.6" volts, transistor 20 is turned on .

Here, since the emitter current _IE of the transistor 20 is equal to the difference between the current flowing through the lamps 6 to 10 and the current flowing through the lamps 2 to 5, it becomes a current substantially corresponding to one lamp. By the way, referring to FIG.
Irrespective of the magnitude of the emitter current _IE, the emitter-base voltage V _BE is substantially constant at “0.6” volts. Therefore, the voltage _VQ is as shown in the following equation (5).

[0013]

(Equation 1)

Next, assuming that the lamps 2 to 5 are sequentially disconnected, the emitter current _IE increases each time the disconnection occurs, but the voltage V _BE is substantially constant. ) Holds. The transistor 21 is shown in FIG.
It has the characteristic of reversing the positive and negative of the graph of
When the lamps 6 to 10 are disconnected, they operate similarly to the transistor 20. Therefore, the voltage applied to both ends of each of the lamps 1 to 10 is maintained substantially in the range of “V _C /2±0.3” regardless of the disconnection state of the other lamps.

As described above, in this embodiment, the voltage applied to both ends of each of the lamps 1 to 10 is substantially equal to “V _C / 2 ±
Therefore, even if some lamps are disconnected, it is possible to prevent other lamps from being disconnected.

The present embodiment can be variously modified as shown in FIGS. In the configuration shown in FIG.
A resistor 16 is provided instead of the diode 14 in FIG. Other configurations are the same as those in FIG. In the following description, the lamps 1 to 5 are connected to the load L ₁ ,
The lamp 6 to 10 that the load L _2. In FIG. 2, when the resistance values of the resistors 13, 15, and 16 are selected so that the voltage drop in the resistor 16 becomes "0.6" volt, FIG.
1 operates in the same manner as that of FIG.

In the configuration shown in FIG. 3, Darlington-connected transistors 22 and 23 are provided instead of transistor 20, and Darlington-connected transistors 24 and 25 are provided instead of transistor 21. ing. Further, diodes 17 to 19 connected in series are provided instead of the diode 14. According to the configuration of FIG. 3, V _A = V _C /2+0.9...... formula _{(6) V B = V C} /2-0.9...... formula (7) is satisfied, but the transistors 22 and 23 is V _a -V _Q> 0.6 × turned on when the 2 ...... formula (8) is satisfied, the transistor 24,
25 is similar, the circuit of FIG. 3 operates in the same manner as that of FIG.

B. Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. In the figure, L _{1 to} L _(2n) are loads, which are sequentially connected in series. Supply voltage V _C load L ₁ is at one end
Is applied, and the load L _(2n) is grounded. Next, Q ₁ , Q ₃ ,..., Q _(2n-1) are NPN transistors and Q ₂ , Q ₄ ,..., Q _(2n) are PNP transistors. It is connected in parallel with the corresponding loads L _{1 to} L _(2n) . Further, the resistor R ₁ ~R (n _{+ 1)} and the diode D ₁ ~D _(n) are connected alternately in series, together with the power supply voltage V _C is applied to the resistor R _1, R _{(n + 1)} is grounded. The resistors R _{1 to} R _{(n + 1)} and the diodes D ₁ to
The bases of the transistors Q _{1 to} Q _(2n) are sequentially connected to each connection point of D _(n) .

Here, the forward voltage drop of the diodes D _{1 to} D _(n) is “0.6” volt, and the loads L _{1 to} L
The power supply voltage side of the terminal voltage of the _(2n) and V _L1 ~V L _(2n),
The base voltages of the transistors Q _{1 to} Q _(2n) are V _{B1 to} V
_{Assuming that B (2n)} , the resistance value of each of the resistors R _{1 to} R _{(n + 1)} is
It is set so as to satisfy the following equation (9).

[0020]

(Equation 2)

For example, when the voltage V _L2 in the normal state is “1”
0 "volts, the voltage V _B1 is" 10.3 "volts,
Each resistor R is adjusted so that the voltage V _B2 becomes “9.7” volts.
Resistance values of _{1 to} R _{(n + 1)} are set.

In the above configuration, when the loads L _{1 to} L _(2n) are all normal, the emitter-base voltages V _BE of the transistors Q _{1 to} Q _(2n) are all “± 0.3” volts. become. That is, the transistors Q _{1 to} Q _(2n) are turned off. On the other hand, if any of the loads L _{1 to} L _(2n) fails, the balance between the voltages V _{L1 to} V _{L (2n)} is lost. When any of the voltages V _{L1 to} V _{L (2n)} fluctuates by more than “0.3” volts from the normal value, the emitter-base voltage V _{BE of} the corresponding transistor Q _{1 to} Q _(2n) becomes “ ±
0.6 "volts and the transistor is turned on. Thus, the voltage V _L1 ~V L _(2n), in a case where the maximum variation also becomes approximately "normal value ± 0.3" volts, the loads L ₁ ~L _(2n) is protected.

In the configuration of FIG. 4, a circuit is shown in which an even number of loads L _{1 to} L _(2n) are connected in series.
When connecting an odd number of loads L _{1 to} L _{(2n + 1)} , the configuration shown in FIG. 5 may be used. In the figure, the load L _(2n)
The collector end and the emitter terminal of the NPN transistor Q _a is connected in parallel with the PNP transistor Q _(2n). Moreover, the load L _{(2n + 1)} is the collector end and the emitter terminal of the transistor Q _b are connected in parallel. Between the power supply and ground, resistors R _a, diode D _a and a resistor R _b and are connected sequentially in series, the anode end of the diode D _a is the base of the transistor Q _a, cathode end transistor They are respectively connected to the base of the Q _b. Resistors R _a, the resistance value of R _b is
The base voltage of the transistor Qa in _a normal state is set to be equal to the base voltage of the transistor Q _(2n) .

According to the above configuration, when the load L _(2n) fails and the voltage balance is lost, the transistors Q _a and Q _(2n) are turned on, and the fluctuation of the terminal voltage of each load is suppressed. Further, if the load L _{(2n + 1)} fails, the transistor Q _b is turned on, variations in the terminal voltage of each load can be suppressed. Therefore, in the configuration of FIG. 5, similarly to the configuration of FIG. 4, the loads L _{1 to} L _{(2n + 1)} are protected. In each of the embodiments described above, the case where a lamp is used as a load has been described. However, the present invention is not limited to a lamp and can be applied to various loads.

[0025]

As described above, according to the series load protection device of the present invention, any one of the first and second loads can be used.
If the load fails, the terminal voltage of the failed load is suppressed.
As a result, fluctuations in the voltage applied to the other loads are reduced, so that adverse effects on these other loads can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a modification of the first embodiment.

FIG. 3 is a circuit diagram of another modification of the first embodiment.

FIG. 4 is a circuit diagram of a second embodiment of the present invention.

FIG. 5 is a circuit diagram of a modification of the second embodiment.

FIG. 6 is a circuit diagram of a conventional lamp lighting circuit.

FIG. 7 is a circuit diagram of a conventional lamp lighting circuit.

FIG. 8 is a circuit diagram of a conventional lamp lighting circuit.

FIG. 9 is a characteristic diagram of a general NPN transistor.

[Explanation of symbols]

 1 to 10 Lamp (load) 20, 21 Transistor (switching element)

Claims (1)

(57) [Scope of request for utility model registration] And 1. A first load, the second load connected in series with the first load, the emitter terminal connected to said first and second load connecting end
And a collector end connected to the other end of the first load.
One transistor and an emitter terminal connected to a connection terminal between the first and second loads.
And the collector end is connected to the other end of the second load.
In both cases, the second transistor has a different polarity from the first transistor.
And a voltage between base terminals of the first and second transistors
And a voltage holding means for holding the voltage constant .