JPH0644206B2 - Constant voltage circuit for semiconductor integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention is a constant voltage circuit of a semiconductor integrated circuit, and by providing a protection transistor, destruction of the output transistor at the time of power-off is prevented.

[Industrial application field]

The present invention relates to a constant voltage circuit composed of a semiconductor integrated circuit, and more particularly to a circuit in which an output transistor in the constant voltage circuit of the semiconductor integrated circuit prevents damage and protects it.

Conventionally, a semiconductor integrated circuit using a bipolar transistor constitutes a constant voltage circuit for controlling an output voltage constant.

A bipolar transistor may be destroyed if a reverse overcurrent flows through the PN junction, and it is necessary to have a circuit configuration in which a reverse current does not flow through the PN junction of the bipolar transistor forming the constant voltage circuit.

[Conventional technology]

FIG. 4 shows a circuit diagram of an example of a conventional constant voltage circuit. In the figure, the power supply voltage V _IN is applied to the input terminal 10. The constant current source 11 supplies the base current of the output transistor Tr ₁ . For example, when the load connected to the output terminal 12 is large and the output voltage V ₀ is low, the divided voltage of the output voltage V _{0 by} the resistors R ₂ and R ₃ is also reduced, and this divided voltage is the reference voltage from the voltage source 13. the output voltage of the operational amplifier 14 is the voltage V _R and the differential amplifier is increased, the constant current source 11
As a result, the current supplied to the base of the transistor Tr ₁ increases and the output voltage V ₀ is raised to a constant value.

Further, when the load current output from the collector of the transistor Tr ₁ becomes excessive, the transistor Tr ₂ becomes conductive due to the voltage drop due to the resistor R ₁ , and the collector current of the transistor Tr ₁ flows through the diode D ₁ ,
The base current of the transistor Tr ₁ is reduced and the load current is suppressed.

In the figure, the portion surrounded by the broken line is composed of the semiconductor integrated circuit 15, and the output terminal 12 is connected with the capacitor C _L for stabilizing the output voltage V ₀ .

[Problems to be solved by the invention]

The operation power source of each circuit in the semiconductor integrated circuit 15 is the input terminal 1
It is derived from a power supply voltage V _{IN of} zero.

Therefore, when the power supply is cut off and the voltage of the input terminal 10 falls to 0V, the output terminal of the operational amplifier 14, that is, the base of the transistor Tr ₁ becomes 0V. However, the capacitor C
_{Since the} electric charge is accumulated in _L , the transistor Tr ₁
There is a problem in that the transistor Tr ₁ is destroyed because the reverse current flows between the emitter and the base of the transistor due to reverse bias.

The present invention has been made in view of these points,
It is an object of the present invention to provide a constant voltage circuit for a semiconductor integrated circuit which prevents the output transistor from being destroyed with a simple configuration.

[Means for solving problems]

A constant voltage circuit of a semiconductor integrated circuit according to the present invention has an emitter connected to an output terminal (12), a base connected to a base of an output transistor (Tr ₁ ), a collector grounded, and an output transistor ( tr ₁₎ has a protection transistor to protect the conductive to the output transistor (Tr ₁₎ when reverse biased (Tr _3), the protection transistor (Tr _3), the output transistor (Tr
₁ ) between the output terminal and the protection transistor (Tr ₃ )
The element formation region (23) of the resistor (R ₁ ) which is provided in common with the emitter region of the transistor is connected to the base of the output transistor (Tr ₁ ) to have the same potential, and the region of the resistor (R ₁ ) and the element The formation region (23) and the element isolation region (24) grounded are equivalently configured.

[Action]

According to the present invention, when the power supply of the semiconductor integrated circuit is cut off and the PN junction of the output transistor is reverse-biased, the protection transistor becomes conductive, the charge accumulated in the capacitor connected to the output terminal is discharged, and the output The protection transistor can be prevented from being destroyed, and the protection transistor can be formed without newly providing an element formation region.

〔Example〕

FIG. 1 shows a principle diagram of a constant voltage circuit according to the present invention. In the figure, those parts which are the same as those corresponding parts in FIG. 4 are designated by the same reference numerals, and a description thereof will be omitted.

In FIG. 1, a PNP transistor Tr ₃ for protection is used.
The emitter is connected to the output terminal 12, the collector is grounded, and the base is connected to the output terminal of the operational amplifier 14. The transistor Tr ₃ is for discharging the capacitor C _L when the power is cut off.

The power supply voltage V _IN is applied to the terminal 10, and the constant current source 11,
Operational amplifier 14, when the transistor Tr ₁ or the like is performing the operation is a voltage output voltage is 0V or more of the operational amplifier 14, only the value base-emitter voltage of the transistor Tr ₃ is turned the transistor Tr ₃ (For example
0.7V), the transistor Tr ₃ does not operate.

Here, when the power supply is cut off and the voltage of the terminal 10 falls to 0V, the output voltage of the operational amplifier 14 becomes 0V, and the voltage of the output terminal 12 is held at approximately the voltage V ₀ by the capacitor C _L. The base-emitter voltage of the transistor Tr ₃ becomes, for example, 0.7 V or higher. As a result, the transistor Tr ₃ is turned on, and the electric charge accumulated in the capacitor C _L is discharged via the transistor Tr ₃ .

This prevents the transistor Tr ₁ from being broken and protected. It is also easy as the circuit configuration Add transistor Tr ₃ for protection.

FIG. 2 shows a circuit diagram of an embodiment of the circuit of the present invention. In the figure, those parts which are the same as those corresponding parts in FIG. 4 are designated by the same reference numerals, and a description thereof will be omitted.

In FIG. 2, the element forming region of the resistor R ₁ formed in the semiconductor integrated circuit 15 is connected to the base of the transistor Tr ₁ as shown in FIG.

FIG. 3 shows the transistor Tr ₁ of the semiconductor integrated circuit 15.
3 is a sectional view of a portion of the resistor R ₁ and the resistor R ₁ . In FIG.
An n ⁺ type buried layer 21 is formed on a P type substrate 20, and further n type element formation regions 22 and 2 are formed by epitaxial growth.
3 is formed. The element formation regions 22 and 23 are separated from other element formation regions by a P ⁺ -type element isolation region 24.

The element formation region 22 includes a P-type region 25 and an n ⁺ -type region 2
6 is provided, an n ⁺ type region 27 is further provided in the P type region 25, and electrodes 28, 29 and 30 are provided in the P type region 25 and n ⁺ type regions 26 and 27, respectively. In addition, 31 is an insulating layer. The element forming region 22 is composed of electrodes 28, 29, 3
0 forms a second illustrated NPN-type transistor Tr ₁ having a base, a collector and an emitter, respectively, and an electrode 2
8 is connected to the output terminal of the operational amplifier 14, the electrode 29 is connected to the terminal 10, and the electrode 30 is connected to one end of the resistor R ₁ , that is, the electrode 34 described later.

In the element formation region 23, the P-type region 32 and the n ⁺ -type region 33 are provided.
Is provided, electrodes 34 and 35 are provided at both ends of the P-type region 32, and an electrode 36 is provided at the n ⁺ -type region 33. The P-type region 32 forms the resistance R ₁ shown in FIG.
4 is connected to the electrode 30 which is the emitter of the transistor Tr ₁ , and the electrode 35 is connected to the output terminal 12.

Generally, the electrode 36 is connected to the terminal 10 and the potential of the element formation region is the power supply voltage V _IN , but in the present embodiment, the electrode 36 is connected to the electrode 28 which is the base of the transistor Tr ₁ . In addition, the electrode 3 provided in the element isolation region 24
7 is grounded.

Here, the element formation region 23 constitutes a substrate PNP transistor having the n-type region 33 as a base, the P-type region 32 as an emitter, and the P ⁺ -type element isolation region 24 as a collector. Further, since the electrode 36 in the n ⁺ type region is connected to the base of the transistor Tr ₁ , the electrode 35 in the P type region is connected to the output terminal 12, and the element isolation region 24 is grounded by the electrode 37, the element formation is performed. Area 2
3 and the substrate PNP type transistor of the element isolation region 24 or the transistor Tr ₃ of the circuit shown in the first figure performs the same operation. That is, the circuit shown in the second diagram is equivalent to the circuit shown in the first diagram.

Therefore, the circuit shown in FIG. 2 performs exactly the same operation as the principle diagram, and prevents the transistor Tr ₁ from being broken when the power is cut off. In the above embodiment, the transistor Tr
_It is not necessary to provide an element forming region for ₃ and the circuit configuration is very simple.

〔The invention's effect〕

As described above, according to the present invention, it is possible to prevent destruction of the output transistor and protect it with a simple circuit configuration in which only the protection transistor is provided, and the resistance between the output transistor and the output terminal is improved. The protection transistor can be formed very simply by connecting the element formation region of 1 to the base of the output transistor, which is extremely useful in practice.

[Brief description of drawings]

1 and 2 are a principle diagram of the circuit of the present invention and a circuit diagram of an embodiment, FIG. 3 is a sectional view of an embodiment of the semiconductor integrated circuit shown in FIG. 2, and FIG. 4 is an example of a conventional circuit. It is a circuit diagram of. In the figure, 10 is an input terminal, 12 is an output terminal, 14 is an operational amplifier, 15 is a semiconductor integrated circuit, 22 and 23 are element formation regions, 24 is an element isolation region, 25 and 32 are P-type regions, 26 and 27. , 33 are n ⁺ type regions, 28, 29, 30, 34 to 37 are electrodes, C _L is a capacitor, R ₁ is a resistor, and Tr _{1 to} Tr ₃ are transistors.

Claims (1)

[Claims] 1. A constant voltage circuit of a semiconductor integrated circuit, which variably controls an output current of an output transistor (Tr ₁ ) according to a voltage of an output terminal (12) to hold the voltage of the output terminal (12) constant. The emitter is connected to the output terminal (12), the base is connected to the base of the output transistor (Tr ₁ ), and the collector is grounded.
₁ ) is turned on when it is reverse biased, the transistor for protection (T ₁ ) is turned on to protect the transistor for output (Tr ₁ ).
In the constant voltage circuit of the semiconductor integrated circuit having r ₃ ), the protection transistor (Tr ₃ ) has an emitter of the protection transistor (Tr ₃ ) between the output transistor (Tr ₁ ) and the output terminal. An element forming region (23) of a resistor (R ₁ ) provided in common with the region is connected to the base of the output transistor (Tr ₁ ) to have the same potential,
A constant voltage circuit for a semiconductor integrated circuit, which is equivalently constituted by a region of the resistor (R ₁ ), the element forming region (23) and a grounded element isolation region (24).