JPS5899031A - Switching circuit - Google Patents

Abstract

PURPOSE:To reduce the number of elements in use and the number of required terminals, by connecting a bias circuit having switching control terminals to the base of a transistor (TR) and switching the conduction/interruption of the TR according to the potential of the terminal. CONSTITUTION:A bias circuit consisting of a constant current CS and a TRQ7 and including a switching control terminal 3 is connected to the base of a TRQ8. The cathode of a light emitting diode LED1 is connected to the collector of the TRQ8, a resistor R8 and an LED2 are connected in series between the LED1 and the emitter of the TRQ8, and the emitter of the TRQ8 is grounded. The anodes of the LEDs1, 2 are connected in common and connected to a positive voltage VCC via a resistor R7. When the bias circuit is set inoperative by a changeover switch SW connected between the terminal 3 and a positive power supply voltage terminal 5, since the TRQ8 is interrupted, the LED2 is driven. In turning on the SW, the TRQ8 is conductive, a current is supplied from the terminal 5 to the LED1 to drive said LED1. This circuit has circuit and terminal numbers and is suitable for circuit integration.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching circuit, and particularly to a light emitting diode (hereinafter referred to as L).
This invention relates to a switching circuit suitable for display switching circuits such as ED.

FIG. 1 shows an example of a conventional LED display switching circuit. 1st
In the figure, a differential circuit is configured with transistors Qt-'-h, and the base bias potential at one point of the base of one transistor Q is fixed at a value obtained by dividing the power supply voltage Vcc by a resistor R8. Similarly, the 6th point of the other transistor q has a resistance of 1. Although it is given by dividing the resistance of a melon, it is kept at a sufficiently high potential with respect to the potential of one point. In this state, the base of transistor q
The current l supplied from the constant current source C8 is supplied to the transistor Q. be done. As a result, 147 registers Q, , Qa are in the suspended state, and Q,, Q, are in the active state.
5LBD drive terminal 1, second light emitting diode LE
Supplies current to D and drives it.

Next, when the selector switch SW connected to the base 5 points of transistor q is closed, and the point b is grounded through the resistor island, the potential at the point b becomes the resistance R1 and the resistance H, , R,
The value is resistance-divided by the parallel combined resistance value of Q, and the potential is set to 1/(, which is sufficiently low with respect to the potential at point a. In this state, the base and emitter of transistor Q are reverse biased. The current 1 supplied from the constant current source C8 flows through the transistor Q, since the current 1 supplied from the constant current source C8 is in a cut-off state, and on the other hand, the transistor Q is in an active state with a forward bias between its base and its base.

supplied to As a result, transistor %, Q4 is in the cutoff state, cb, QAFi is in the active state, 9. A current is supplied to the first light emitting diode LED through the LED drive terminal 2 to drive it. In FIG. 1, the circuit within the dotted line can be integrated into an integrated circuit, and in that case, the switching control terminal 3 and the LED are used as the LED switching terminal.

A total of three terminals, drive terminal 2, LED, and drive terminal 1, are safe.

It is an object of the present invention to provide a switching circuit that is an electronic switch that can be easily integrated into an integrated circuit by reducing the number of elements used and the number of terminals required compared to the prior art.

According to the present invention, a bias circuit having a switching control terminal is connected to the base of the transistor, the collector (or emitter) of the transistor is connected to one end of a first load having a threshold, and the emitter (or emitter) of the transistor is connected to one end of a first load having a threshold value. A resistive element or a diode and a second load having a threshold are connected in series between the other end of the first load (collector) and the other end of the first load, and a bias power source is connected. , there is obtained a switching circuit characterized in that it has means for switching the conduction/discontinuation state of the transistor.

Therefore, when a circuit including a bias circuit and the transistor is integrated into an integrated circuit, the number of parts can be reduced because the circuit is extremely simple compared to a differential circuit. As switching terminals, three terminals are required: a switching control terminal, the collector terminal of the transistor, and an entrant terminal. However, since the emitter terminal is grounded directly or through a load, compared to the conventional method, it is necessary to use three terminals including the Fih ground terminal. In other words, one less terminal is required.

Next, the present invention will be described in detail according to embodiments using the drawings.

FIG. 2 is a circuit connection diagram showing an embodiment of the present invention, in which the same functional parts as in FIG. 1 are denoted by the same numbers or symbols. In Figure 2, the switching control terminal 3 is connected to the base of the transistor.
A bias circuit consisting of a constant current source C81 and a transistor Q is connected to its collector, and a first light emitting diode LED.

The cathode side of the light emitting diode 1, ED
, and the emitter of the transistor, a second light emitting diode l, ED, and a resistive island are connected in series, the emitter of the transistor q is grounded, and the emitter of the transistor q is grounded. Second light emitting diode 1. The common connection point on the anode side of ED, LP, and D is connected to the positive power supply voltage Vcc via a resistor. A changeover switch SW connected between the changeover control terminal 3 and the positive power supply voltage terminal 5
The conduction/discontinuation state of the light emitting diode 1. is switched. ED,,LED.

can be switched.

When the bias circuit consisting of the constant current source C8 and the transistor Q is set to an inoperable state by the changeover switch SW, the transistor q is not supplied with
Since it is in the cutoff state, current is supplied from the positive power supply voltage terminal 5 to the light emitting diode LED via the resistor, and the light emitting diode LED is driven. When the changeover switch SW is then connected to the terminal 3, the bias circuit is switched into operation, the base of the transistor 1 is biased, and sufficient current is supplied to the base to bring it into saturation. When the saturation resistance of the transistor becomes sufficiently smaller than the resistor R1, a current is supplied from the positive power supply voltage terminal 5 to the light emitting diode LED1 to drive it in order to absorb the stain current from the collector. At this time l
The current flowing to , ED, is made sufficiently small so that no light is emitted. Also, if you use the horse as a constant current source, it will produce an LED! Figure 3 is a circuit connection diagram showing another embodiment using a current mirror circuit composed of a resistor R1·e''11 and a transistor Qo*Q+o as a constant current source C8. , FIG. 4 is a circuit connection diagram showing still another implementation/:A using an expanded resistor Rxt and a diode D in place of the resistor R1. In addition, in FIG. 4, the diode D is replaced as necessary. It goes without saying that a plurality of diodes may be connected in parallel or in series.

Compared to the case where the resistor Rs is used, the diode D also has a threshold value, so that sharp switching is performed.

As is clear from the above description, a load having a threshold value, such as an LED, can be easily switched by the voltage applied to the switching control terminal.

In the switching circuit according to the present invention, if the circuit inside the dotted line in FIG. The number of pins can be reduced compared to conventional circuits, and the number of elements used can be greatly reduced, which is advantageous in terms of cost and scale factor, and it is possible to create circuits that are effective for integrated circuits. In addition, in the above explanation,
Although the display of a light emitting diode has been described, it will be explained once again that the present invention is not limited to the above embodiments, and that the present invention can be applied to a switching circuit that drives a load having a transistor value of 1 in general, as shown in Fig. 2.3. No need to do it.

[Brief explanation of drawings]

FIG. 1 is a circuit connection diagram showing an example of a conventional LED display switching circuit. 2 to 4 are circuit connection diagrams of LED display switching circuits showing embodiments of the present invention, respectively. Q1~Q,. ...Transistor, D...Group diode, 8~R0...Resistor, 3.Old...Switching control terminal, 6.Old...Bias circuit.

Claims (1)

[Claims] A bias circuit having a switching control terminal is connected to the base of the transistor, and a resistive element or diode is connected between the collector (or emitter) of the transistor and a first negative terminal having a threshold value. 1. A switching circuit, comprising means for connecting a load in series, connecting a bias power supply, and switching the conduction/discontinuation state of the transistor according to the potential of the switching control terminal.