JPH11136049A - Semiconductor integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor integrated circuit which does not need other circuit elements or external terminals in the case of externally connecting a transistor in parallel with an internal control transistor. SOLUTION: A transistor Q1 operates when voltage that exceeds the sum voltage of voltage that is generated by a diode which is connected to a base of a control transistor Q1 and voltage between the base and emitter of the transistor Q1 is applied to a connection point between the emitter of the transistor Q1 and a control circuit of the diode. Even when voltage between the base and emitter of a transistor Q2 that is externally connected disperses, because the voltage always becomes smaller than the voltage of the sum, it stops the operation of the transistor Q1 and can surely operate only the external transistor Q2.

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 configured to connect an external transistor in parallel with a control transistor inside a semiconductor integrated circuit when a large output is to be obtained.

[0002]

2. Description of the Related Art For example, in a semiconductor integrated circuit in which a series regulator is formed, a transistor having a large current capacity is provided as necessary in order to obtain an output larger than an output obtained by controlling a control transistor in the integrated circuit. It is configured to be connectable to the outside in parallel with the control transistor.
FIG. 3 is a circuit diagram of a conventional semiconductor integrated circuit having such a configuration. Between the input terminal 1 and the output terminal 2, a control transistor Q1 is connected in series inside a semiconductor integrated circuit 6 indicated by a dotted line, and the transistor Q1 is controlled by a control circuit 5 connected to the base. The base of the transistor Q1 is led out to the terminal 3. When another transistor Q2 is connected outside the integrated circuit 6 to obtain a large output, the transistor Q1 is connected between the input terminal 1 and the output terminal 2.
And connected in parallel. When the transistor Q2 is connected, its base is connected to the control circuit 5 through the terminal 3 together with the base of the transistor Q1. And
The operation of the transistor Q1 inside the integrated circuit 6 is stopped, and only the external transistor Q2 is operated as a control transistor.

However, when the base-emitter voltage V _{BE2 of} the external transistor Q2 is higher than the base-emitter voltage V _{BE1 of the} internal transistor Q1,
The transistor Q1 operates without the transistor Q2 operating.
Only still works and an overload condition occurs. Then, the temperature rises, and the base-emitter voltage V _BE1 further falls, so that oscillation or damage is likely to occur. In any case, if the transistor Q2 does not operate, the intended large output cannot be obtained.

FIG. 4 is a circuit diagram of a conventional semiconductor integrated circuit capable of stopping operation of an internal control transistor Q1 and reliably operating an externally connected transistor Q2. An external terminal 7 is provided outside the integrated circuit 6, and the transistor Q2 is connected between the external terminal 7 and the output terminal 2. A resistor R3 is connected between the external terminal 7 and the input terminal 1 of the integrated circuit 6, and capacitors C1 and C2 each having one side grounded are connected to both ends of the resistor R3. Integrated circuit 6
Are formed in the same manner as in FIG.
And the base of transistor Q2 are commonly connected to control circuit 5 by terminal 3 of integrated circuit 6. The input is external terminal 7
Supplied to

In FIG. 4, by making the emitter voltage of the transistor Q1 lower than the emitter voltage of the transistor Q2 by the resistor R3, the voltage applied between the base and the emitter of the transistor Q1 becomes the voltage applied between the base and the emitter of the transistor Q2. It is made to be smaller than that. By doing so, the transistor Q2
Is connected, the base-emitter voltage V
_{Even if BE2} varies, the initial purpose of always operating the external transistor Q2 to increase the output can be achieved. However, it is necessary to connect the resistor R3 to the outside in addition to the transistor Q2, and it is also necessary to connect the capacitors C1 and C2 to prevent the input impedance from increasing due to the connection of the resistor R3. Further, an external terminal 7 is required. Providing an external terminal outside the integrated circuit 6 and requiring a plurality of circuit elements to be connected in addition to the transistor connected to the outside of the integrated circuit 6 means that only a minimum number of circuit elements can be externally connected when the purpose of the integrated circuit cannot be achieved. This is undesirable from the point of view of connecting to

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor integrated circuit which does not require other circuit elements or external terminals when an external transistor is connected in parallel with an internal control transistor. .

[0007]

According to the present invention, there is provided a semiconductor integrated circuit in which a control transistor is connected in series between an input terminal and an output terminal and whose output is controlled by the transistor. PN
One end of the junction is connected, and the other end of the PN junction is connected to a control circuit of the transistor and is led out to a terminal.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a semiconductor integrated circuit according to the present invention, a voltage exceeding a sum of a voltage generated by a PN junction connected to a base of a control transistor and a base-emitter voltage of the transistor is applied to the control transistor. When applied between the connection point of the emitter and the control circuit of the PN junction,
The transistor is formed to operate. Even if the voltage between the base and the emitter of the transistor connected to the outside varies, the voltage always becomes smaller than the sum voltage, so that the operation of the control transistor is stopped and only the external transistor can be reliably operated.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of a semiconductor integrated circuit according to the present invention. 4 and 5 are denoted by the same reference numerals. In FIG. 1, a PNP-type control transistor Q1 is connected in series between an input terminal 1 and an output terminal 2 of a semiconductor integrated circuit 6. The base of the transistor Q1 is connected to the anode of the diode D1, and the cathode is connected to the collector of the transistor Q3 and to the terminal 3 different from the input terminal 1 and the output terminal 2 exposed outside the semiconductor integrated circuit 6.
Note that the diode D1 is generally formed by a so-called diode-connected transistor connected between the collector and the base. The base of the NPN transistor Q3 is connected to the output side of the error amplifier 4, and the emitter is grounded. A series circuit of the resistors R1 and R2 is connected between the output terminal 2 and the ground, and the connection point between the resistors R1 and R2 is connected to the non-inverting input terminal of the error amplifier 4. A reference voltage V _RE is applied to the inverting input terminal of the error amplifier 4. Transistor Q
1 operates when a voltage equal to or higher than the sum of the base-emitter voltage V _BE1 and the voltage generated by the PN junction of the diode D1 is applied between the cathode of the diode D1 and the emitter of the transistor Q1. Each voltage is 0.6V
Therefore, the sum voltage is about 1.2V.

The semiconductor integrated circuit 6 detects a voltage corresponding to the output voltage of the output terminal 2 by a series circuit of resistors R1 and R2. Error amplifier 4 compares the detected voltage with reference voltage V _RE to increase or decrease the collector current of transistor Q3. If the output voltage obtained at output terminal 2 is lower than the set value, the collector current of transistor Q3 increases, and the base current of transistor Q1 also increases. If the output voltage is higher than the set value, the transistor Q3
And the base current of the transistor Q1 decreases. As described above, the error amplifier 4 and the transistor Q3 form a control circuit, and control the base current of the control transistor Q1 to obtain the output voltage set at the output terminal 1.

When the transistor Q2 having a large current capacity is externally connected, its emitter is connected to the input terminal 1, its collector is connected to the output terminal 2, and its base is connected to the connection point between the cathode of the diode D1 and the collector of the transistor Q3. By connecting to the connecting terminal 3, the transistor Q2 is connected in parallel with the transistor Q1. in this case,
The transistor Q2 operates with the base-emitter voltage V _BE2 , while the transistor Q1 operates with the sum voltage as described above. Even if the base-emitter voltage V _{BE2 of the} transistor Q2 varies, it is apparent that the voltage is smaller than the sum of about 1.2V, so that the externally connected transistor Q2 operates reliably and the internal The transistor Q1 does not operate. Therefore, a large output can be obtained at the output terminal 2 by controlling the transistor Q2 having a large current capacity by the control circuit.

FIG. 2 is a circuit diagram showing another embodiment of the semiconductor integrated circuit of the present invention. The control transistor Q1 is connected in series between the input terminal 1 and the output terminal 2, and the transistor Q1 forms a Darlington circuit with another transistor Q4. The base of the transistor Q4 is connected to the collector of the transistor Q3 forming the control circuit and to the terminal 3. Transistor Q2
Is formed by the base-emitter junction of the transistor Q4. External transistor Q
2 is connected to the input terminal 1, the output terminal 2, and the terminal 3 as in the case of FIG.

In the case of FIG. 2, the base of the transistor Q1
A voltage equal to or higher than the sum of the emitter-to-emitter voltage V _BE1 and the base-emitter voltage V _BE4 of the transistor Q4
The transistor Q1 and the transistor Q4 operate when applied between the emitter of one and the base of the transistor Q4. When the transistor Q2 is connected in parallel, its base-emitter voltage V _BE2 is clearly smaller than the sum voltage, so that the externally connected transistor Q2 operates reliably. Although the series regulator has been described as an example in the embodiment, the present invention can be applied to other general circuits for controlling current. As the diode, various diodes such as a Schottky diode can be used in addition to a general diode.

[0014]

As described above, in the semiconductor integrated circuit of the present invention, one end of the PN junction of the semiconductor circuit element is connected to the base of the internal control transistor, and the other end is connected to the control circuit and to the terminal. If another transistor is externally connected, the base of the other transistor is connected to the control circuit via the terminal. A voltage is generated between the base of the control transistor and the control circuit due to a voltage drop due to the PN junction, but is not generated in an externally connected transistor. Therefore, the externally connected transistor can be reliably operated, and the operation of the internal control transistor can be stopped. As a result, a large output by the control of the transistor connected to the outside can be reliably obtained at the output terminal. In addition, there is no need to connect external terminals or other circuit elements except for transistors, and this is a practical invention from the viewpoint of connecting only the minimum number of circuit elements to the outside of the integrated circuit as necessary.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a semiconductor integrated circuit of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the semiconductor integrated circuit of the present invention.

FIG. 3 is a circuit diagram of a conventional semiconductor integrated circuit.

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

[Explanation of symbols]

 1 input terminal 2 output terminal 3 terminal Q1 control transistor

Claims (3)

[Claims] 1. A semiconductor integrated circuit in which a control transistor is connected in series between an input terminal and an output terminal and whose output is controlled by the transistor, one end of a PN junction of a semiconductor circuit element is connected to a base of the transistor. The other end of the PN junction is connected to a control circuit of the transistor and is led to a terminal exposed outside the semiconductor integrated circuit. 2. The semiconductor integrated circuit according to claim 1, wherein said PN junction is formed by a diode. 3. The semiconductor integrated circuit according to claim 1, wherein said PN junction is formed by another transistor forming a Darlington circuit together with a control transistor.