JPH05268033A - Digital signal output device - Google Patents

Abstract

PURPOSE:To obtain an output current at an Lo level in excess of the absolute maximum rating of a transistor(TR) in use as required by providing an output control circuit for a digital signal, plural TRs outputting the digital signal externally depending on its control signal, and a switch used to selectively add the digital signals outputted from the TRs to the output device. CONSTITUTION:When a moving contact (a) of a switch 41 is connected to a normally open contact (b), TRs 21, 22 are connected in parallel with an output terminal 31. Thus, an output current sum of the two TRs 21, 22 is outputted at the output terminal 31 by turning simultaneously on the TRs 21, 22 and a double output current is obtained when the TRs of an identical characteristic are employed. Furthermore, since an output terminal 32 is connected to nowhere, the output terminal 32 cannot be used and should the output terminal 32 be connected to somewhere, a problem such as short-circuit is not caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal output device, and more particularly to improvement of a digital signal output device using a transistor.

[0002]

2. Description of the Related Art FIG. 4 is a connection diagram showing an example of a digital signal output device using a transistor. In the figure,
Reference numeral 1 is an output control circuit for digital signals, 2 is a plurality of transistors for outputting digital signals to the outside, 3 is an output terminal, and the collectors of the transistors are directly output. A control signal is input to the base of the transistor 2 from the output control circuit 1, each emitter is commonly connected to the ground, and an output terminal 3 is connected to each collector. Various loads according to the application are connected to the output terminal 3 and are selectively driven.

[0003]

However, such a problem
Output current I of the Lo-level transistor 2 in the device
_OLDepends on the absolute maximum ratings of the transistors used.
Be restricted.

Therefore, it is impossible to drive a relay, a lamp or the like which requires a drive current of _IOL max or more. The present invention has been made in view of such conventional problems, and an object thereof is a digital signal output device capable of supplying a Lo level output current exceeding the absolute maximum rating of a transistor used as necessary. To provide.

[0005]

A digital signal output device according to the present invention includes a digital signal output control circuit, a plurality of transistors for outputting a digital signal to the outside according to a control signal of the output control circuit, and outputs from these transistors. And a switch for selectively adding the digital signals to be generated.

[0006]

The digital signals output from the transistors are selectively added according to the opening / closing of the switch, and the transistors are connected in parallel, so that an output current larger than that of a single transistor can be obtained.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the principle of a digital signal output device according to the present invention, and parts common to those in FIG. In the figure, 4 is a switch, which is provided to selectively add the digital signals output from the transistor 2. The switch 4 is selectively driven by the output control circuit 1.

FIG. 2 is a connection diagram showing an embodiment of the present invention. In the figure, as the switch 4, a changeover switch having a normally open contact b and a normally closed contact c is used. The collector of the transistor 2 ₁ is connected is connected directly to the output terminal 3 ₁ a normally open contact b of the switch 4 _1. The collector of the transistor 2 ₂ is connected to the movable contact a of the switch 4 _1, normally closed contact c of the switch 4 ₁ is connected to the normally open contact b of the switch 4 ₂ is connected to an output terminal an output terminal 3 ₂ ing. The collector of the transistor 2 ₃ is connected to the movable contact a of the switch 4 _2, normally-closed contact c of the switch 4 ₂ is connected is connected to the output terminal 3 ₃ a normally open contact b of the switch 4 ₃ . The collector of the transistor 2 ₄ is connected to the movable contact a of the switch 4 _3, the normally open contacts of the next stage switch (not shown) with a normally closed contact c of the switch 4 ₃ is connected to an output terminal an output terminal 3 ₄ Connected.

The movable contact a of each of these switches 4 is normally connected to a normally closed contact c as shown in the figure. In this state, each transistor 2 is driven and controlled by the control signal of the output control circuit 1,
Although the digital signal to the output terminal 3 is output, the magnitude of the output current I _OL is limited by the absolute maximum rating of the transistor 2.

On the other hand, consider the case where the movable contact a of the switch 4 is connected to the normally open contact b by the control signal of the output control circuit 1. For example, switch 4
_When the movable contact a of _{No. 1} is connected to the normally open contact b, the transistors 2 ₁ and 2 ₂ are connected in parallel to the output terminal 3 ₁ . Therefore, by turning on these transistors 2 ₁ and 2 ₂ simultaneously, the output terminal 3
Two transistors 2 ₁ and 2 ₂ of the output current is to be output is added to _1, 2 times the output current is obtained in the case of using the same transistor characteristics. In addition,
In this case, can not be used because the output terminal 3 ₂ has not been where both the connection, there is no problem such as a short circuit also as something if it was connected to the output terminal 3 _2.

FIG. 3 is a connection diagram showing another embodiment of the present invention. In FIG. 3, a two-pole relay having a normally open contact d and a normally closed contact e is used as the switch 4. The collector of the transistor 2 ₁ is directly connected to the output terminal 3 ₁ and is also connected to the collector of the transistor 2 ₂ via the normally open contact d of the switch 4 ₁ . The collector of the transistor 2 ₂ is connected through the normally open contact d of the switch 4 ₂ is connected via the normally closed contact (e) of the switch 4 ₁ to the output terminal 3 ₂ to the collector of the transistor 2 _3. The collector of the transistor 2 ₃ is connected to the output terminal 3 ₃ via the normally closed contact e of the switch 4 _2.
It is connected to the.

Each of these switches 4 is normally in the state shown in the figure. In this state, each transistor 2 is driven and controlled by the control signal of the output control circuit 1, so that a digital signal is output to the output terminal 3. that is, the magnitude of the output current I _OL is limited by the absolute maximum rating of the transistor 2.

[0013] In contrast, by opening the normally-closed contact e closes the respective switches 4 ₁ and 4 ₂ of the normally open contacts d by a control signal output control circuit 1, the output terminal 3 ₁ transistor 2 ₁ And 2 ₂ and 2 ₃ are connected in parallel.

Therefore, by simultaneously turning on these transistors 2 ₁ , 2 ₂ and 2 ₃ , the output currents of the _three transistors 2 ₁ , 2 ₂ and 2 ₃ are added and output to the output terminal 3 _1. Therefore, when transistors having the same characteristics are used, a triple output current can be obtained. In addition,
At this time, the output terminals 3 ₂ and 3 ₃ cannot be used because they are not connected to anything, but if something happens to these output terminals 3 ₂ and 3 3.
₂ and there is no problem such as a short circuit even if it is connected to a 3 _3.

Similarly, four or more pieces can be connected in parallel. Alternatively, a plurality of transistors having different characteristics may be used and combined.

[0016]

According to the present invention described above, L exceeding the absolute maximum rating of the transistor used as necessary is provided.
It is possible to provide a digital signal output device capable of supplying an o-level output current, and it is effective for driving elements such as relays and lamps that require a drive current exceeding the absolute maximum rating of a single transistor.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a connection diagram showing an embodiment of the present invention.

FIG. 3 is a connection diagram showing another embodiment of the present invention.

FIG. 4 is a connection diagram showing an example of a conventional digital signal output device.

[Explanation of symbols]

 1 Output control circuit 2 Transistor 3 Output terminal 4 Switch

Claims (1)

[Claims] 1. A digital signal output control circuit, a plurality of transistors for outputting a digital signal to the outside according to a control signal of the output control circuit, and a switch for selectively adding the digital signals output from these transistors. A digital signal output device characterized by being configured.