JPH07263970A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To suppress the emitter current to protect an output transistor TR from destruction due to a large current by bypassing a part or the base current at the time when the voltage between the base and the emitter of the output TR exceeds a prescribed value. CONSTITUTION:If the emitter current of an output TR Q4 is increased by output short-circuit and a voltage VBE between the base and the emitter exceeds a prescribed voltage, a PNP TR Q5 and a Schottky barrier diode on constituting a monitor bypass circuit are turned on together, and a part of the base current flowing to the output TR Q4 is bypassed through the TR Q5. Consequently, a large current is prevented from flowing to the output TR Q4 to protect the output TR from degradation and destruction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit having an emitter follower output circuit, and more particularly to a semiconductor integrated circuit having high reliability capable of protecting the emitter follower output circuit from a large current at the time of output short circuit. .

[0002]

2. Description of the Related Art FIG. 4 shows a circuit diagram of a conventional semiconductor integrated circuit. This is a configuration in which an emitter follower output transistor Q4 is added to any circuit.

In such a conventional emitter follower output circuit of the ECL circuit, there is no circuit for limiting the output current when the output is short-circuited, and a large current flows to the output transistor Q4 when the output is short-circuited, which causes deterioration or destruction of the element. There is a risk.

[0004]

As described above, the conventional semiconductor integrated circuit has a problem that a large current flows through the output transistor when the output is short-circuited, and there is a risk that the element is deteriorated or destroyed.

The present invention solves the above problems,
An object of the present invention is to provide a semiconductor integrated circuit capable of preventing a large current from flowing through the output transistor when the output is short-circuited and protecting the output transistor from destruction.

[0006]

In order to solve the above-mentioned problems, the semiconductor integrated circuit of the first feature of the present invention is a semiconductor integrated circuit having an output transistor Q4 of an emitter follower as shown in FIG. Output transistor Q
4 monitors the base-emitter voltage V _BE of, when the base-emitter voltage V _BE is greater than the specified value, a monitoring bypass circuit for bypassing a part of the base current of the output transistor Q4 Constitute.

The semiconductor integrated circuit according to the second aspect of the present invention is the semiconductor integrated circuit according to claim 1, wherein the monitoring bypass circuit is a Schottky barrier diode D.
1, the emitter electrode is connected to the base electrode of the output transistor Q4, the collector electrode is connected to the power supply V _EE , and the base electrode is connected to the emitter electrode of the output transistor Q4 via the Schottky barrier diode D1. And is configured.

The semiconductor integrated circuit according to the third aspect of the present invention is the semiconductor integrated circuit according to claim 1, wherein the monitoring bypass circuit includes a PN junction diode D2 and an emitter electrode as a base of the output transistor Q4. On the electrode
A PNP transistor Q whose collector electrode is connected to the power source V _EE and whose base electrode is connected to the emitter electrode of the output transistor Q4 through the PN junction diode D2.
5 and 5.

[0009]

In the semiconductor integrated circuit of the first, second and third features of the present invention, the output transistor Q of the emitter follower is used.
4. A monitoring bypass circuit having a function of monitoring the base-emitter voltage V _BE of 4 and a current bypass function between the base electrode of the output transistor Q4 and the power supply line V _EE is connected to form the base of the output transistor Q4. When the emitter-to-emitter voltage V _BE exceeds a specified value, the monitoring bypass circuit is turned on to bypass a part of the base current flowing into the output transistor Q4 and control the emitter current (output current) flowing through the output transistor Q4. I am trying to do it.

Therefore, the monitoring bypass circuit monitors the base-emitter voltage V _BE of the output transistor Q4, and the output current increases due to an output short circuit or the like, and the base-emitter voltage V _{BE of the} output transistor Q4 exceeds a specified value. When it rises to, the current bypass function in the monitoring bypass circuit is actuated to bypass a part of the base current flowing into the output transistor Q4 and reduce the base current of the output transistor Q4. As a result,
An abnormal increase in the emitter current (output current) of the output transistor Q4 can be controlled, and the output transistor Q4 can be protected from destruction.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 shows a circuit diagram of a semiconductor integrated circuit according to a first embodiment of the present invention. In the figure, the same parts as those in FIG. 4 (conventional example) are designated by the same reference numerals.

In the circuit configuration of the conventional semiconductor integrated circuit (FIG. 4), when the base-emitter voltage V _BE exceeds a specified value, a monitoring function is provided for monitoring the base-emitter voltage V _BE of the output transistor Q4. This is a configuration in which a monitoring bypass circuit having a current bypass function for bypassing a part of the base current of the output transistor Q4 is added.

The monitoring bypass circuit has a Schottky barrier diode D1 and an emitter electrode connected to the output transistor Q.
No. 4, the collector electrode is connected to the power supply V _EE , and the base electrode is connected to the emitter electrode of the output transistor Q4 via the Schottky barrier diode D1.
It is composed of an NP transistor Q5.

Next, the operation of the semiconductor integrated circuit of this embodiment will be described. In the ECL, the output circuit of the emitter follower normally has an output current of several [mA] to several tens [mA].
Used in the area of degree. In this case, the base-emitter voltage V _{BE (Q4)} of the output transistor Q4 is 0.8
V _{BE (Q4)} <V _{BE (Q5)} + V between the base-emitter voltage V _{BE (Q5) of} the PNP transistor Q5 and V _{F (D1)} of the Schottky barrier diode D1. The relationship of _{F (D1)} (1) is established.

Therefore, both the PNP transistor Q5 and the Schottky barrier diode D1 are turned off, the base current of the output transistor Q4 is not bypassed, and the same operation as that of the conventional semiconductor integrated circuit (FIG. 4) is possible. Become.

Next, the output current (emitter current of the output transistor Q4) increases due to output short circuit, and the relationship of V _{BE (Q4)} ≧ V _{BE (Q5)} + VF _(D1) (2) is established. In that case, both the PNP transistor Q5 and the Schottky barrier diode D1 are turned on, and a part of the base current flowing into the output transistor Q4 is bypassed by the PNP transistor Q5.

Therefore, the base current flowing into the output transistor Q4 decreases, and as a result, the output transistor Q4.
The emitter current of 4 also decreases, a large current is prevented from flowing through the output transistor Q4, and the element can be protected from deterioration or destruction.

FIG. 2 shows the output characteristic V _CC = in the semiconductor integrated circuit of this embodiment and the conventional semiconductor integrated circuit (FIG. 4).
It is the figure which compared by simulation the (output current with respect to output voltage) when 5.0V and _VEE = 0V. Figure 2
2A is an output characteristic diagram when the output is at "H" level, and FIG. 2B is an output characteristic diagram when the output is at "L" level.

Also in the figure, the semiconductor integrated circuit of this embodiment has an output current (several [mA] to several tens [mA]) of normal operation.
In the range of (about), the same operation as in the conventional example is performed, and when the output current increases due to an output short circuit or the like, it can be confirmed that the output current is suppressed more than in the conventional example. Second Embodiment Next, FIG. 3 shows a circuit diagram of a semiconductor integrated circuit according to a second embodiment of the present invention.

The semiconductor integrated circuit of this embodiment also has a configuration in which a monitoring bypass circuit is added to the circuit configuration of the conventional example (FIG. 4), and the monitoring bypass circuit is a PN junction diode D.
2, the emitter electrode is connected to the base electrode of the output transistor Q4, the collector electrode is connected to the power supply VEE, and the base electrode is connected to the emitter electrode of the output transistor Q4 via the PN junction diode D2.
It consists of and.

The semiconductor integrated circuit of this embodiment is different from that of the first embodiment in that a PN junction diode D2 is used in place of the Schottky barrier diode D1, and the principle of operation, action and effect thereof are basically the same. The same as the first embodiment.

However, the Schottky used in the first embodiment
About the barrier diode D1, V _FIs small and also made
While it has the feature of increasing the number of manufacturing processes,
Regarding the PN junction diode D2 used in the embodiment,
Usually V_FIs about 0.7 [V], and the area must be reduced
Need to be larger, and it is the same as other transistors.
Features that can be realized by one manufacturing process
There are some differences in points.

The PN junction diode D2 can also be realized by diode connection of transistors.

[0024]

As described above, according to the present invention,
The monitoring bypass circuit allows the output transistor base
When the emitter-to-emitter voltage (V _BE ) is monitored and the output current increases due to output short-circuiting, etc., and the base-emitter voltage (V _BE ) of the output transistor rises above a specified value, the current bypass function in the monitoring bypass circuit concerned. The output transistor's emitter current (output current) because the output transistor's base current is reduced by bypassing a part of the base current flowing into the output transistor.
It is possible to control the abnormal increase in the device, and as a result, it is possible to prevent the deterioration or destruction of the device due to the large current, and it is possible to provide a semiconductor integrated circuit having high reliability.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a semiconductor integrated circuit according to a first embodiment of the present invention.

FIG. 2 is a comparative explanatory diagram by simulation of output characteristics (output current with respect to output voltage) in the semiconductor integrated circuit of the first embodiment and the semiconductor integrated circuit of the conventional example (FIG. 4), and FIG. At "H" level, Fig. 2 (b)
FIG. 4 is an output characteristic diagram when the output is at “L” level.

FIG. 3 is a circuit diagram of a semiconductor integrated circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional semiconductor integrated circuit.

[Explanation of symbols]

Q1, Q2, Q3 ... NPN transistor R1, R2, R3 ... Resistor Q4 ... Output transistor Q5 ... PNP transistor D1 ... Schottky barrier diode D2 ... PN junction diode IN ... Input signal (voltage) _VBB , _VCS ... Bias power supply ( Voltage) V _CC , V _EE ... Power supply (voltage) OUT ... Output signal (voltage)

Claims (3)

[Claims] 1. A semiconductor integrated circuit having an output transistor of the emitter follower (Q4), monitors the base-emitter voltage of the output transistor (Q4) (V _BE), the base-emitter voltage (V _BE ) Exceeds a specified value, the semiconductor integrated circuit has a bypass circuit for bypassing a part of the base current of the output transistor (Q4). 2. The monitoring bypass circuit comprises a Schottky barrier diode (D1), an emitter electrode as a base electrode of the output transistor (Q4), a collector electrode as a power supply (V _EE ), and a base electrode as the Schottky. Through the barrier diode (D1), the output transistor (Q
4. A PNP transistor (Q5) connected to the emitter electrode of 4), respectively.
The semiconductor integrated circuit according to 1. 3. The monitoring bypass circuit comprises a PN junction diode (D2), an emitter electrode for a base electrode of the output transistor (Q4), a collector electrode for a power source (V _EE ), and a base electrode for the PN junction diode. (D
PNP transistor (Q5) connected to the emitter electrode of the output transistor (Q4) via 2)
The semiconductor integrated circuit according to claim 1, further comprising: