JPS61216505A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To suppress the power consumption in a circuit according to the state of a load by forming the 1st and the 2nd transistors (TR) of a Darlington connection circuit in separated conductive area on a semiconductor substrate individually and setting the reverse current amplification factor of the 1st TR low. CONSTITUTION:Epitaxial layers 46 and 48 are formed at adjacent positions electrically separately and individually so as to constitute the Darlington connection circuit 6 on the semiconductor substrate 21. Then, the area of the emitter area 30 of a TR 2 formed in the epitaxial layer 46 is set smaller than the area of its collector electrode part 28 and the reverse current amplification factor HPE of the TR 2 is set to a small value. Consequently, the reverse current amplification factor of the TR 2 decreases and the absorption of a current from a TR 8 to the emitter of the TR 2 is accelerated, so that the current is absorbed to the base of a TR 4 efficiently.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an amplifier circuit using a Darlington connection circuit, and in particular to an amplifier circuit suitable for a drive output circuit that drives a load such as a motor. be.

[Conventional technology]

An amplifier circuit constructed by connecting a pair of transistors in a Darlington connection is used as an output circuit for driving a load such as a motor, as shown in Japanese Patent Application No. 58-238461, for example.

As shown in FIG. 2, this amplifier circuit has a Darlington connection circuit 6 made up of first and second transistors 2.4, and a third transistor 8 added thereto. That is, the base of each transistor 2.8 has a resistor 10
．． An input signal is applied from input terminal 14 via 12;
The base current of each transistor 2.8 flows in response to this input signal.

A load 20 such as a motor is connected between the output terminal 16 formed on the collector side of the transistor 2.4 and the power supply terminal 18 to which the drive power source is connected. A drive voltage Vcc is applied from a drive power supply between the drive power supply and the ground side through a resistor 18.

In such an amplifier circuit, if we assume that a DC motor is connected as the load 20, the internal impedance of the motor is low at the time of startup and when the motor is at steady rotation. However, during steady rotation, the current required for rotation is smaller than the starting current.

In this case, assuming that there is no transistor 8, when a large current is required at the time of starting the motor, the collector-emitter voltage VCt of the transistor 4 of the Darlington connection circuit 6 is the base-emitter voltage v of the transistor 4. ■ and the collector-emitter saturation voltage vc of transistor 2! □□ sum (VCt” v,, + Vcz
smt+).

As a result, even when the motor is under a light load, such as when the motor shifts to steady rotation, power consumption occurs inside the circuit regardless of changes in the motor current, and there is an inconvenience that unnecessary power consumption occurs inside the Darlington connection circuit 6. .

Therefore, in order to solve this problem, a transistor 8 is added, and in a specific operating range, the base current is supplied from the transistor 8 to the transistor 4 instead of the transistor 2. That is, during heavy loads such as when starting a motor, the base current of the transistor 4 is supplied by the transistor 2.8, and the transistor 4
is driven, but when the motor shifts to steady rotation, its load current ■. decreases and transistor 4 goes into saturation, transistor 2 also goes into saturation, but
At this time, since transistor 8 is not saturated, base current is supplied from transistor 8 to transistor 4.

In this case, the collector-emitter voltage vc! of the transistor 4! is its collector-emitter saturation voltage VC! □
, becomes.

Due to this operation, the load current I with respect to the collector-emitter voltage VCt of the transistor 4 of the Darlington connection circuit 6 becomes characteristic A shown in FIG. 3, compared to characteristic B when the transistor 8 is not added. , the collector-emitter voltage V4 of the transistor 4 changes stepwise as in the operating ranges a and b, with a specific value of the load current 1c set as a threshold. Therefore, according to such an amplifier circuit, it is possible to flow the load current IC in accordance with the state of internal impedance of the load 20, and effects such as being able to suppress the current consumption inside the circuit when the load is light can be expected.

[Problem that the invention seeks to solve]

However, when such an amplifier circuit is usually realized using a semiconductor integrated circuit, as shown in FIG. Generally, the transistor 8 is formed in one epitaxial layer 22, and the transistor 8 is formed in another epitaxial layer 24. That is,
In the transistor 2, 26 is a base region, 28 is a collector electrode portion formed in the collector region made of the epitaxial layer 22, 30 is an emitter region, and the transistor 4
In the transistor 8, 32 is a base region, 34 is a collector electrode portion formed in the collector region made of the epitaxial layer 22, and 36 is an emitter region.
a collector electrode portion formed in the collector region consisting of 4;
42 is an emitter region.

The emitter region 30° of the transistor 2, the base region 32 of the transistor 4, and the emitter region 42 of the transistor 8 are connected to each other by a conductive wiring 44 through electrodes (not shown) as shown by broken lines.

In such a semiconductor integrated circuit, the reverse current amplification factor (when the HF ratio increases) when looking from the emitter region 30 of the transistor 2 to the collector electrode portion 28 is 3.

In this case, the current supplied from the emitter of transistor 8 to the base of transistor 4 will be absorbed in the operating range where transistor 2 is saturated, and there is a risk that the effect of adding transistor 8 as shown in characteristic A shown in FIG. 3 may not be obtained. In particular, if the characteristics differ between manufacturing lofts, the function of the transistor 8 will be hindered.

Therefore, the present invention provides an amplifier circuit in which a third transistor is added to the Darlington connection circuit made up of the first and second transistors to supply a drive current to the Darlington connection circuit in a certain operating region. The purpose is to reliably realize characteristic A shown in FIG.

[Means for solving problems]

That is, the present invention provides a Darlington connection circuit consisting of a first transistor to which an input signal is applied to the base and a second transistor to which a base current is applied by the first transistor. In an amplifier circuit including a third transistor that flows a base current according to a signal, the first and second
transistors are individually formed in separate conductive regions on a semiconductor substrate, and the reverse current amplification factor of the first transistor is set to be low.

[For production]

By separately forming the first and second transistors in different epitaxial layers, interference of the common collector region of each transistor is avoided, and by reducing the reverse current amplification factor of the first transistor, the third The drive current from the emitter region of the transistor is efficiently flowed into the base region of the second transistor.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the amplifier circuit of the present invention, and parts common to the layout of the amplifier circuit shown in FIG. 2 and the semiconductor integrated circuit shown in FIG. 4 are given the same reference numerals.

In FIG. 1, epitaxial layers 46 and 48 are electrically isolated at adjacent positions as conductive regions of a specific conductivity type for configuring the Darlington connection circuit 6 with respect to the semiconductor substrate 21. The first transistor 2 is formed in the epitaxial layer 46, and the second transistor 4 is formed in the epitaxial layer 48.

The area of the emitter region 30 of the transistor 2 formed in the epitaxial layer 46 is set smaller than the area of its collector electrode portion 28, and the reverse current amplification factor (H□) of the transistor 2 is set to a low value.

In this case, epitaxial layer 24 is formed adjacent to each epitaxial layer 46, 48, and third transistor 8 is formed in the same way.

The emiff region 30 of the transistor 2, the base region 32 of the transistor 4, and the emitter region 42 of the transistor 8 are connected by a conductor wiring 50 to form an amplifier circuit as shown in FIG.

With this configuration, the reverse current amplification factor of the transistor 2 is reduced, and in a specific operating range, absorption of the current from the transistor 8 into the emitter of the transistor 2 is suppressed, and the current is efficiently absorbed into the base of the transistor 4. be able to. That is, when transistor 2 is saturated, the base current of transistor 4 is supplied only from transistor 8, and as shown in characteristic A shown in FIG. Operating ranges a and b are realized in which the collector-emitter voltage ve+r of the transistor 4 changes.・Although the amplifier circuit shown in FIG. 2 has been described as a drive circuit that drives a load such as a motor, the present invention is applicable not only to such a drive circuit but also to supply various signal amplification outputs to various loads. It can be used as an amplification means.

〔Effect of the invention〕

As explained above, according to the present invention, the following effects can be obtained.

(a) Transfer the current from the third transistor to the second transistor.
, the power can be efficiently supplied to the transistor, the effect of adding the third transistor can be fully exhibited, and power consumption inside the circuit can be suppressed depending on the load state.

(b) Since absorption of the current from the third transistor by the first transistor can be suppressed, the supply current from the third transistor is reduced by that amount, reducing power consumption and reducing heat generation in the semiconductor integrated circuit. It can be suppressed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the amplifier circuit of the present invention, FIG. 2 is a circuit diagram showing the amplifier circuit that is the premise of the invention, FIG. 3 is a graph showing its operating characteristics, and FIG. FIG. 2 is an explanatory diagram showing a semiconductor integrated circuit that realizes the amplifier circuit shown in FIG. 2; 2... First transistor, 4... Second transistor, 6... Darlington connection circuit, 8... Third transistor, 28... Collector electrode portion, 30...
Emitter region, 46.48...Epitaxial layer. FIG. 1 I 2...First transistor 2B...Collector electrode portion 6...Darlington connection circuit 46.
48...Epitaxial layer 8... Third transistor Fig. 2 Fig. 3-, Ic Fig. 4

Claims (2)

[Claims] (1) The input signal is applied to the base of the second transistor in a Darlington connection circuit consisting of a first transistor to which the input signal is applied to the base, and a second transistor to which the base current is supplied by the first transistor. In an amplifier circuit including a third transistor that flows a base current according to An amplifier circuit characterized by having a low reverse current amplification factor. (2) The amplifier circuit according to claim 1, wherein the first transistor has a smaller emitter area than a collector electrode portion.