JPS61184918A - Switching device - Google Patents

Abstract

PURPOSE:To prevent malfunction of a load due to an input current and to increase in power consumption and to protect the input circuit and load to a load current exceeding the upper limit value or over by providing a switch means supplying a current to the load only when the input current is less than a threshold value and setting the threshold value to a desired level and a current suppressing means to the load current. CONSTITUTION:When the input current I is a threshold value or below, since the emitter area of a TrQ4 is larger than that of a Q5, a collector current Ic has a relation of Ic4>Ic5. A current equal to the Ic4 flows to a TrQ3 biased by a TrQ2, the collector potential of the TrQ5 rises near the power supply voltage and a TrQ7 keeps the off state. When the current I is increased, the current Ic4 is increased and the voltage drop across a resistor R2 is increased, so long as the current I does not reach the threshold value Ith decided the emitter area ratio (n) of the Trs Q4, Q5 and the resistor R2, the TrQ7 keeps the off-state. When the current I exceeds the value Ith, the relation of Ic4<Ic5 is obtained, the collector potential of the TrQ5 is lowered and the TrQ7 is turned on. When the current I is increased further, the collector current of the TrQ6 is increased, the Ic4, Ic5 are decreased and then the current I is decreased. Further, the relation of Ic4>Ic5 is obtained to limit the load current.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a switching device, and in particular, a switching device that controls current to a load by setting a threshold value for the current flowing to an input terminal,
Also, it is a switching device that sets the upper limit of the current flowing to the load and suppresses the current flowing to the input circuit and load.
related.

[Objective of the Invention] The object of the present invention is to prevent malfunction of the load due to current flowing through the input terminal and increase in power consumption of the entire device, and also to be able to arbitrarily set the current level according to the current level of the input circuit. An object of the present invention is to provide a switching device having a function of protecting an input circuit and a load when the current flowing to the load exceeds a limit value.

[Summary of the invention] The purpose of the above is.

a switch means that supplies current to a load only when a current flowing through an input terminal reaches or exceeds a certain threshold value, and is capable of setting the threshold value to a desired level; Current suppressing means for setting a certain upper limit on the flowing current.

This is achieved by a switching device characterized in that it consists of:

[Embodiments of the invention] Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

FIG. 1 is a circuit diagram of an embodiment of a switching device according to the present invention.

In the figure, PNP transistors Q2 and Q3 form a current mirror type constant current circuit, and the collector electrodes of Q2 and Q3 are connected to the collector electrodes of NPN transistors Q4 and Q5 by t1c, respectively. However, the ratio of the emitter areas of Q4 and Q5 is nil. The base electrodes of Q4 and Q5 are both NPN transistors Q
The resistor R1 is connected to the collector electrode of R1.
Q4 and Q5 are biased. The resistor R1 only needs to have a high resistance, but a constant current element such as an FET may also be used.

The emitter electrode of Q4 is connected to the input terminal l via the resistor R2, and the emitter electrode of Q5 is directly connected to the input terminal l.

Also, the collector electrode of Q5 is a PNP transistor Q6
and connected to the base electrode of Q7. The emitter electrodes of Q6 and Q7 are connected to the positive electrode of power supply 2, and Q6
The collector electrode of Q7 is grounded via the resistor R3, and the collector electrode of Q7 is grounded via the load circuit 3. Also,
The base electrode of Ql is also grounded via R3, and the emitter electrode is directly grounded.

Since the negative electrode of power supply 2 is grounded, load circuit 3 has Q
It is driven by the on/off operation of 7. Further, the emitter electrodes of Q2 and Q3 are both connected to the positive electrode of the electrode 2, and a current is supplied thereto.

In such a circuit configuration, when the current flowing to the input terminal l is less than the difficult value Ith, Q7 is in the off state, and when it is above the threshold value Ith, it is in the on state.
As will be described later, is set by the emitter area ratio n of Q4 to Q5 and the resistor R2 connected to the emitter electrode of Q4.

Further, the upper limit value of the current flowing through the load circuit is set by Ql and R3.

Next, the switch operation of this embodiment having such a configuration will be explained.

First, when the current I is smaller than the threshold value, the emitter area of Q4 is larger than that of Q5, so the collector current Ic4 of Q4 is larger than the collector current Ic5 of Q5 (Ic4>Ic5), L Since Q3 and Q3 form a current mirror type constant current circuit, Q3 biased by Q2 is in a state where a current equivalent to the collector current Ic4 of Q4 flows, and as a result, the collector potential of Q5 is the same as that of the Trt source 2. It rises to near the voltage. For this,
Q7 remains off and no current is supplied to the load circuit 3. At this time, since the base of Q6 is also at the same potential as Q7, the off state is maintained.

As the electric current gradually increases, the current Ic4 also increases and R
The voltage drop at 2 increases. Therefore, the base-emitter voltage of Q5 gradually becomes larger than the base-emitter voltage of Q4. However, as long as the current I does not reach the threshold value Ith determined by the emitter surface edge ratio n of Q4 and Q5 and R2, the state of IC4>IC5 continues, and Ql remains off.

Next, when the four-current current exceeds the threshold value Ith, a state of I c4 <Ic5 occurs with respect to the collector currents of Q4 and Q5. However, since the collector voltage state of Q3 biased by Ql is Ic4, the collector potential of Q5 decreases, Ql is turned on, and current is supplied to the load circuit 3 from the voltage TA2. At this time, collector current I'' also flows through Q6, and a voltage of IrφR3 is applied to the base of Ql.

When the current ■ flowing into the input terminal 1 further increases, the current flowing into the load circuit 3 through Ql increases, and
The collector current Ir of Q6 also increases, raising the base potential of Ql. When the base potential of Ql increases, the collector current of Ql increases, lowering the base potentials of Q4 and Q5.

As the base potentials of Q4 and Q5 decrease, Ic4 and Ic5 decrease, and the input terminal current I decreases. Also,
When the base potential of Q4 and Q5 decreases, Ic4<I
The state changes from the cs state to I c4 >Ic5, increasing the collector potential of Q5 and suppressing the current flowing into the load circuit. That is, when the base potential of Q6 increases due to the increase in the collector potential of Q5, and the collector current of Q6 is suppressed, the base potential of Ql decreases.

This puts Ql in the off state, and Q4 and Q5
increases the base potential of IC4, Q4 and Q5 again
<IC5 state is reached. This operation sets an upper limit of 1 on the current flowing into the load circuit 3.

A method for determining the threshold value rth in the above switch operation will be explained using the current relational expression and FIG. 2.

FIG. 2 is a graph showing the relationship between base-emitter voltage and collector current of two transistors having different emitter areas.

Since the emitter area of Q4 is n times that of Q5, Q
Collector currents Ic4 and IC5 of Q4 and Q5 are expressed by the following equations.

I c4 = n Is exp (qVbe4 /↑
) --- (1) IC5; ISe! p(qvbe5/nicho) (2) where k is Portzmann's constant, q is unit charge, T is absolute temperature, and V be4 and V be5 are the base-01577 voltages of Q4 and Q5, respectively.

By the way, since the resistor R2 is connected to the emitter of Q4, the following relationship exists between Vbe4 and Vbe5.

Vbe4 +I c4 *R2=Vbe5 m * *
(3) Therefore, by substituting equation (3) into equation (1), the following equation is obtained.

I C4=nf exp (q(Vbe5- I C
40R2)/kT) (4) Curves 101 and 102 in FIG. 2 graphically represent the relational expressions (2) and (4) above. However, the curve 103 represents Equation (1) with Vbe4 as the horizontal axis.

As is clear from the graph, the curve 102 representing the collector current Ic4 of Q4 and the curve 101 representing the collector current Ic5 of Q5 intersect when Vbe5 = Vt (7). That is, after this time, IC4 and I
The magnitude relationship with c5 is reversed. At this time, Ic4=I
Since c5=It, the following relational expression is obtained by combining equations (2) and (4).

T-log n = I t * R2 meeting (5)
Therefore, the threshold value 1 is twice the current It when Vbe5=Vt, where the magnitude relationship of the currents Ic4 and Ic5 changes.
It can be th. That is, the threshold value 1th can be set to a desired level by determining the emitter area ratio n and the resistance value of the resistor R2 using the relational expression (5) above.

Note that, as is clear from equation (5), the threshold value I th
= 2 I t is a function of temperature T. Therefore, if the current I is kept constant, it can also be used as a temperature switch that turns Q7 on and off depending on temperature changes.

Note that in order to reduce power consumption in this embodiment, Q4 and Q
In order to determine the current consumption of this embodiment without depending on the voltage of the power supply 2 and the voltage of the input terminal l, , a constant current element or a constant current circuit using a JFET or the like may be used instead of the resistor R1.

FIG. 3 is a block diagram showing an example of how to use this embodiment.

In the figure, switching devices 110a, 10b, φ
* has the circuit configuration shown in FIG. 1, and a plurality of them are provided. Loads 3a, 3b, . Further, a voltage Vcc is applied to each switching device as the power supply 1 in FIG. 1, and control signals from the CPU 11 are input to input terminals 2a, 2b, . . . of each switching device.

As can be seen from the operation explanation already described, the current flowing through each input terminal 2a, 2b, . . . changes when a high-level or low-level control signal is input from the CPU 11, and the current is set. Each switching device is turned on or off depending on whether it is below the threshold value Ith or above the threshold value Ith.

With this configuration, for example, in a mode in which the amplifier as the load 3a is not operated and only the motor as the load 3b is operated, the CPU u is switched to the switching device 1.
0a is turned off and switching device 10b is turned on, current can be supplied only to motor 3b. Therefore, current can be supplied only to the circuits and devices necessary for the intended function, and overall power consumption can be saved.

In addition, since the threshold value Ith can be easily set,
It is also compatible with CPUs with different current levels of control signals, and can be widely used as a switch means.

In addition, when the current value flowing through the load circuit exceeds the upper limit, a means is provided to suppress the input current and the current flowing to the load circuit, so it has a protection function for the load circuit and input circuit against overcurrent. For example, even if an overcurrent flows through the amplifier of the load 3a, the current at the input 2a of the switching device is only limited, and the operation of the CPU II is not affected, and the motor of the load 3b can be operated normally.

Note that the NPN transistor Ql in FIG.

A switching device in which Q4 and Q5 are replaced with PNP transistors, PNP transistors Q2, Q3, Q6, and Q7 are replaced with NPN transistors, and the polarity of the power supply 2 is reversed so that the current flowing to the input terminal l is in the opposite direction is the first switching device. This can be easily arrived at from the circuit shown in the figure.

[Effects of the Invention] As explained in detail above, the switching device according to the present invention closes the load circuit only when the thickness of the current flowing through the input terminal reaches or exceeds a set threshold value. In order to supply current to the load circuit, even if there is a small current such as leakage current at the input terminal, or even if current is generated due to noise etc., current will not be supplied to the load circuit, ensuring reliable switch operation. In addition, power consumption can be reduced. Further, all currents other than those flowing into the load flow to the input terminals.

Further, since the threshold value can be set to a desired level, there is no need to consider the current level of an external device connected to the input terminal, and the device can be used in a wide range of applications as a switching means.

In addition, when the upper limit of the current flowing through the load is exceeded, in order to suppress the current flowing to the input circuit and load, protect the input circuit and load from overcurrent to the load, and when driving multiple loads. Furthermore, it is possible to provide a switching device that does not cause damage to one load to affect the operation of other loads and can be easily applied to a wide variety of loads.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a switching device according to the present invention. FIG. 2 is a graph showing the relationship between base-emitter voltage and collector current of two transistors with different emitter areas. FIG. 1 is a block diagram showing an example of how to use this embodiment. l...Input terminal 3...Load circuit Q2, Q3. Q
6, Ql...PNP) Transistor Ql, Q4, Q5...NPN) Transistor R1, R2, R3/Dispute/Resistance Agent Patent Attorney Sekihira Yamashita Figure 1 Figure 2 l

Claims (3)

[Claims] (1) Supplying current to the load only when the current flowing to the input terminal reaches or exceeds a certain threshold,
A switching device comprising: a switch device that can set the threshold value to a desired level; and a current suppressor device that sets a certain upper limit on the current flowing through the load. (2) The switch means includes two transistors with different emitter areas, a first resistor connected to the emitter of the transistor with a large emitter area, and a control electrode connected to the collector side of the transistor with a small emitter area. and a constant current circuit that attempts to supply equal current to the two transistors, the bases of the two transistors are equally biased at a constant level, and the current flowing to the emitters of the two transistors is is a current flowing to the input terminal, and when the current exceeds the threshold value, the magnitude relationship between the collector current characteristics of the two transistors changes, and based on this change, the transistor with a small emitter area The drive transistor is operated by a potential change on the collector side of the drive transistor to control the current supply to the load, and the current suppressing means is configured to operate the drive transistor when the current flowing through the load reaches the upper limit value or exceeds the upper limit value. When
Claim 1, wherein the current flowing through the load and the input terminal is suppressed by detecting the current flowing through the load and reducing the base current of the two transistors. switching device. (3) The threshold value is set to a desired level by the emitter area ratio of the two transistors and the resistance value of the first resistor. switching device.