JPS6096919A - Overcurrent detection circuit of electronic switch - Google Patents

Abstract

PURPOSE:To decrease a residual voltage at ON state as an electronic switch by controlling the output state of a controller with the output of an overcurrent detection circuit and controlling a current switching element of a load current depending on this output state. CONSTITUTION:The emitter of a transistor (TR)22 is connected to the terminal of a power supply 19 via a resistor (R) 33 and the emitter of a TR23 is connected to the other terminal of the power supply 19 via a resistor R31. Then collectors of both the TRs 22, 23 are connected. Emitters of TRs 24, 25 are connected respectively to the power supply 19 and the collectors are connected together. Then the emitter and collector of a TR21 are connected respectively to the power supply 19 via a current source 20. Then the TRs 21, 22 and 24, and the TRs 23, 25 are constituted to be current mirror circuits respectively. A signal output terminal is provided to the connecting point G between the TRs 24 and 25, the terminal is connected to the controller 17 so as to control the output state of the controller 17.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcurrent detection circuit for electronic switches, such as proximity switches.

Conventionally, this type of overcurrent detection circuit inserts an emitter resistor to the emitter of the output transistor Tr1 as shown in FIGS. This is a simple method for detecting overcurrent, and is used in many applications. Although this method can be easily implemented, it has the drawback that the remaining voltage at the output terminal at 8 o'clock becomes extremely large. That is, the remaining voltage Von when the transistor Trl is turned on depends on the output current value and the output current capacity of the transistor Tr1.
n is Van = 0.2 (V), output current It =
150 (mA), including the overcurrent detection circuit, 2
When a current of 00 mA or more flows, this is considered an overcurrent. When the base-emitter voltage Vbe of the transistor Try is detected to be 0.7 (V) or more, the value of the emitter resistance R1 becomes. Also, when the output current It=:150 (mA), the voltage Vrl across the emitter resistor R1 is Vrl ==
35 x 0.15-0.525 (V,], so the voltage Vx of the series circuit of transistor Trl and emitter resistor R, is Vx2 Von + Vr, = 0.2-t-0,525
:0,725 (V:]. By inserting the overcurrent output in this way, the O as an electronic switch
The remaining output voltage at N-time is more than 3 times 1, and as is clear from the calculation formula, no matter how much the output power capacity of the output transistor Trl is increased and the remaining output voltage Yon at ON-time is decreased, the overcurrent detection circuit is not included. In addition, in the conventional overcurrent detection circuit, the output residual voltage hardly decreases when the transistor is turned on.
Since the emitter voltage was the overcurrent detection voltage, it had a large negative temperature coefficient.

This invention attempts to eliminate such conventional drawbacks, and the first purpose of this invention is to
Compared to those that detect overcurrent using an emitter voltage, the detection voltage is lowered, thereby reducing the overcurrent detection resistance of the electronic switch and reducing the remaining voltage when the electronic switch is turned on. It is.

A second object of the present invention is to enable overcurrents of both current sink and current source output types to be detected by the same overcurrent detection circuit.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram when the overcurrent detection circuit according to the present invention is applied to a proximity switch.
1 is composed of a proximity sensor IC circuit 1 and a current switching element 26, such as an output transistor, for supplementing the output current capacity of this IC circuit. And the IC circuit 1
has internal oscillation 00 circuit 2, comparator 3, and integration circuit 4.
, comparator 5, output circuit 6. It has a constant voltage circuit 7, a power supply reset circuit 8, an output roller 14, and an overcurrent detection circuit 16, and the output circuit 6. The power supply reset circuit 8 and the output controller 14 constitute an electronic switch controller 17. Further, a detection coil, a 1% resonant capacitor C3, a sensitivity adjustment variable resistor R22, a bypass capacitor C28, an integrating capacitor 024, a power supply reset capacitor 025, a load 9, and the like are externally attached.

Therefore, when a metal body approaches or separates from the detection coil, the oscillation circuit 2 starts or stops oscillating, and an output of logic I or H is obtained from the output circuit 6.

An overcurrent detection circuit 16, which will be described later, is provided between the current switching element 26 and the output controller 14.

FIG. 4 is a circuit diagram showing the main part of the present invention, which basically consists of four transistors, namely a first transistor 22, a second transistor 22, and a second transistor.
transistor 23, third transistor 24, and fourth transistor 25, resistor 31.33, and current source 2
The overcurrent detection circuit 16 is constituted by a block including the transistor 21 and the transistor 21. Diode 27 and resistor 3
5 constitutes an overvoltage protection circuit 18, which protects the overcurrent detection circuit 16 when a large voltage is applied to the node 41. This overvoltage protection circuit is for a current sink, but the circuit composed of the diode 28 and the resistor 36 is an overvoltage protection circuit for a current source. 19
is the power supply. Note that the current switching element 26 is connected to the load 9
It controls the current flowing through the circuit, and is made up of, for example, a transistor. Each transistor 22.23 and each resistor 3
A connection terminal an C is pulled out to the connection point with 1.33,
A signal output terminal G is provided at the connection point between the transistors 24 and 25, and this output terminal is further connected to the main end of the controller 17 that controls the transistor 26, thereby controlling the output state of the controller 17. ing. In FIG. 4, the overcurrent detection circuit 16 and the overvoltage protection circuit 18 are integrated into ICs.

Now, in Fig. 4, the current I0 from the current source 2o is ■o=
5 [μA], resistance value of resistor 31.33 R31* R33
If 几s+=Rss=10 [KΩ], then 7-do4
The voltages V41 and Vat of 1 and 42 become overcurrent detection voltages, and their values are V, , =V, , = 1. XR,,=
I. XR5, = 5 X 10 = 50 (mV). This is because when nodes 41 and 42 are both open, transistors 24 and 25 are balanced and output node 46 is in a critical state.

Now, when the node 41 is connected to the output current detection resistor R, the voltage generated across this resistor is 50 (mV).
If it is smaller, resistor R4 is connected from node 41 through resistor 35.
A current starts to flow toward the resistor 32, so the current flowing through the resistor 32 decreases, and the emitter voltage of the transistor 25 decreases.
Transistors 24 and 25 become unbalanced, and node 4
The potential of 6 becomes L. At this time, the output of the electronic switch controller 17 becomes, for example, H, and the current switching element 26 is in the on state.

Further, for some reason, the current flowing through the current switching ligature 26 exceeds a predetermined value, and the voltage generated across the stone and the resistor R exceeds 50 (mV), and the voltage at the node 46 becomes H.

At this time, the output of the electronic switch controller 17 becomes, for example, L, and the current switching element 26 is substantially turned off. Therefore, the current flowing through the resistance island decreases, the potential of the energizing node 41 decreases, and the potential of the node 46 also decreases. When the potential of the node 46 eventually reverses to L, the output of the electronic switch controller 17 becomes H, and the current switching element 26 is turned on.

Furthermore, when the voltage of resistor R9I is 50 (mV), resistor 3
No current flows through 5, which becomes the threshold voltage.

In this way, the voltage generated across the resistor R1 is 50 (mV)
When the overcurrent detection circuit 16 exceeds this point, the overcurrent detection circuit 16 detects that point.

The above explanation is an example of how the current sink appears,
In the case of the current source output type, the node 46 becomes H when an overcurrent is detected. An example of the output format of the current source is shown in FIG. In this figure, external connection terminal C is used.

The circuit shown in FIG. 6 is a current source output type circuit similar to that shown in FIG. 5, but the difference from the circuit shown in FIG. 5 is that the current switching element 26 is composed of a PNP transistor. FIG. 7 shows a modified example of the current mirror circuit.
The modifications shown in (c) are well known.

In Fig. 4, when the detection voltage is 50 (mV) and the overcurrent is 200 [n1A], the resistance R4 becomes 0mV 20 mA - 2" [Ω], and therefore the output current J1 = 150 (m^ ] ON
The remaining voltage Vx is Vx =v(B1 +Vr, :=:0.2 +〇,2
5 X 0115::0.2 +○, 0375:0.2
375 (V ), which is a great improvement compared to the conventional one.As is clear from this calculation example, in the conventional example, the resistance 8
．． The voltage Vr across the resistor 1'L was quite large, but in this invention, the voltage Vr across the resistor 1'L becomes smaller than the remaining voltage VOQ when the transistor 26 is turned on, and therefore the remaining voltage when the transistor 26 is turned on. In addition to using a transistor with a large capacity to reduce Von, it is also possible to reduce the remaining voltage Vx when the output terminal is turned on.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing conventional overcurrent detection circuits, FIG. 3 is a block diagram when the overcurrent detection circuit according to the present invention is applied to a proximity switch, and FIG. 4 is a circuit diagram showing the overcurrent detection circuit according to the present invention. A circuit diagram showing one embodiment of the detection circuit, FIG. 5 is a circuit diagram showing a second embodiment of this invention, FIG. 6 is a circuit diagram showing a third embodiment of this invention, and FIG. 7 is a circuit diagram showing a third embodiment of this invention. FIG. 7 is a circuit diagram showing a modification of the mirror circuit. DESCRIPTION OF SYMBOLS 1...IC circuit, 2...Oscillation circuit, 3...Comparator, 4...Integrator circuit, 5...Comparator, 6
... Output circuit, 7... Constant voltage circuit, 8... Power supply reset circuit, 9... Load, xo... Switch, 14
...output controller, ...detection coil s"
n...variable resistor, C1...resonant capacitor s C2
4... Integrating capacitor, C2,... Capacitor, 1
6... Overcurrent detection circuit, 17... Electronic switch controller, 1B... Overvoltage protection circuit, 19... Power supply, 20... Current source, 21-25... Transistor. 26... Current switching element, 27... Diode, 28... Diode, 31. :33,3! 'i・
・Resistance, BI...Resistance, 41.42...Node, 4
6...Output node. Patent applicant Yamatake Honeywell Co., Ltd. Figure 4 Figure 5 Figure 8 Figure 6 18 Figure 7 (a) Procedural amendment (method) % formula % 1. Indication of the case Japanese Patent Application No. 58-205666 2. Title of the invention Electronic switch overcurrent detection circuit 3, person making the correction Drawing 7, correction content drawing (no change in content)

Claims (1)

[Claims] +11 A load, a current switching element that controls the current flowing through the load, and an overcurrent detection resistor are connected in series to a power supply, and a first terminal is connected to one terminal of the power supply. The emitters of the transistors are connected via a resistor, and the collectors thereof are respectively connected via a current source to the other terminal of a power supply, and the emitter of a second transistor is connected to one terminal of the power supply via a resistor. the emitter of the third transistor is connected to the other terminal of the power source via a resistor, the collectors of both transistors are connected to each other, and the emitter of the third transistor is connected to the other terminal of the power source through a resistor; and the emitter of the fifth transistor is connected to the other terminal of the power supply, and the collectors of both transistors are connected to each other, and the emitters of the first transistor, the second transistor, and the fourth transistor are connected to each other. The transistor, the third transistor, and the fifth transistor are connected to each constitute a current mirror circuit, and a connection terminal is drawn out from a connection point between the second and third transistors and each of the resistors. , this terminal is selectively connected to the connection point between the current switching element and the overcurrent detection resistor, and a signal output terminal is provided at the connection point between the fourth transistor and the fifth transistor, and this output terminal An overcurrent detection circuit for an electronic switch, characterized in that the overcurrent detection circuit is connected to an input terminal of a controller that controls the current switching element, and controls an output state of the controller. (2) Overcurrent detection of the electronic switch according to claim 1, wherein an overvoltage protection circuit is connected between one of the connection terminals and the connection point between the overcurrent detection resistor and the current switching element. circuit.