JPS6029007A - Output circuit - Google Patents

Abstract

PURPOSE:To prevent generation of breakdown by providing a transistor (TR) whose collector is connected to a power supply, and whose emitter and base are connected respectively to an emitter and a base of an output TR. CONSTITUTION:The collector of a TR2 is connected to the power supply voltage Vcc and the emitter and the base are connected respectively to the emitter and base of the output TR1. When a base voltage of a TR3 is larger, although the TR1 is cut off, the TR2 is conductive. As a result, the emitter-base voltage is not increased more than the base-emitter forward voltage of the TR2, thereby preventing the breakdown of the TR1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an output circuit such as an IC, and relates to an output circuit in which breakdown of an output transistor is prevented.

Conventionally, there has been a circuit of this type as shown in FIG.

In the figure, Tri and Tr3 are transistors whose emitters are commonly connected and form an output circuit, and whose collectors are connected to the power supply Vcc. 1 is an input terminal connected to the base of transistor Tr3, R'e is a resistor connected between the common emitter of transistor Tri and Tr3 and the ground, and O is an output terminal connected to the common emitter of transistor Tri and Tr3. .

Further, Io is a current source provided between the base of the transistor Tri and the ground, and T r 4 is a transistor driven by the bias power supply vb, whose collector is connected to the above power supply V.
connected to cc. Further, R is a resistor connected between the emitter of the transistor Tr4 and the base of the transistor Tr1.

Next, the operation will be explained. Now, when the base voltage of transistor Tr3, that is, the input voltage is lower than the base voltage of transistor Tri, the output voltage taken out from terminal 0 is V
b-Vbe4-RIo-Vbel. However, Vbe4
．． Vbe1 are respectively connected to transistors Tr4. This is the base-emitter voltage of Tri.

In this way, when the base voltage of the transistor Tr3 is lower than the base voltage of the transistor Tri, the transistor T
Although only rl operates and transistor Tr3 is cut off, transistor Tr3 applied to input terminal 1
When the base voltage of the transistor Tri becomes larger than the base voltage of the transistor Tri, the transistor Tri becomes a cut-off state, and the base-emitter of the transistor Tri is reverse biased.

The conventional output circuit is configured as described above, and when the base voltage applied to the transistor Tr3 becomes extremely large, the reverse bias voltage applied between the emitter and base of the transistor Trl also increases, and this increases the breakdown voltage Veb. If the voltage exceeds that level, the transistor Tri will break down, resulting in the generation of noise and the like.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by providing a breakdown prevention transistor whose base and emitter are respectively connected to the emitter and base of the output transistor, the output transistor It is an object of the present invention to provide an output circuit that can prevent the reverse bias voltage applied between the base and emitter of a semiconductor device from becoming larger than a certain level, thereby preventing the occurrence of breakdown.

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

FIG. 2 shows an output circuit according to an embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate the same components. Tr
2 is an output transistor T whose emitter and base are respectively
This is a breakdown prevention transistor connected to the base and emitter of r1.

Next, the operation will be explained. When the base voltage of the transistor Tr3 increases, the transistor Tr1 is cut off, but at this time, the transistor Tr2 is conductive, and as a result, the emitter-base voltage of the transistor Tri is equal to the base-emitter forward voltage Vbe2 of the transistor Tr2. The transistor T
Breakdown of ri can be prevented.

Note that the present invention is not limited to the above embodiments, but can be applied to various output circuits.

As described above, according to the present invention, the base and emitter are respectively emitters of output transistors.

A breakdown prevention transistor connected to the base is provided to prevent the reverse bias voltage applied between the base and emitter of the output transistor from exceeding a certain value, which prevents breakdown of the output transistor. This has the effect of preventing the occurrence of accompanying noise.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional output circuit, and FIG. 2 is a circuit diagram showing an output circuit according to an embodiment of the present invention. Tri...output transistor, 0...output terminal,
Vcc: Power supply, Tr2: Breakdown prevention transistor. In the drawings, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa Figure 1 Figure 2 Procedural amendment (voluntary) March 27, 1939 2, Name of the invention output circuit 3, Representative Hitoshi Katayama of the person making the amendment Department 4, Agent 5, Amendment Column 6 of Detailed Explanation of the Invention of the Subject Specification, Contents of Amendment (1) In the 3rd page, line 12 of the specification, "breakdown" was replaced with "breakdown, resulting in deterioration or deterioration of the transistor Tri." ” is corrected. (2) In the 7th line of page 5, ``accompanying this'' is corrected to ``accompanying deterioration of the transistor.''that's all

Claims (1)

[Claims] (11 An output transistor to which an input voltage is applied to the base, the collector connected to a power supply, and the output taken out from the emitter; the collector connected to the power supply, the base connected to the emitter of the output transistor, and the emitter connected to the base of the transistor. An output circuit comprising: a breakdown prevention transistor connected to a breakdown prevention transistor;