JPH0846449A - Current amplifier circuit - Google Patents

Abstract

PURPOSE:To increase maximum output power without increasing the size of an output transistor by providing a second level shift means on a level shift loop circuit equalizing input voltage with output voltage. CONSTITUTION:Input voltage Vin is supplied to the input of an inverted Darlington circuit 1 via a first level shift means D 3. By providing a second level shift means D4 corresponding to the first level shift means D3 on a level shift loop circuit equalizing input voltage Vin with output voltage Vout, the base potential of the driving transistor of the inverted Darlington circuit can be made high even when the input voltage lowers down to the same potential as the ground potential of the circuit. As a result, because a saturation opeartion is hardly generated, the base current required for an NPN output transistor Q1 is sufficiently supplied and the transisitor Q1 an be operated in a saturation area, the amplitude of output voltage can be made large on the ground potential side of the circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current amplifier circuit, and more particularly to a technique effective for use in a circuit using a push-pull output circuit composed of an inverted Darlington circuit and a normal Darlington circuit.

[0002]

2. Description of the Related Art In an audio amplifier circuit mounted on an automobile, there is a strong demand for a high output specification, but since the power source is taken from 12V of an on-vehicle battery, an ordinary current amplifier circuit must obtain a sufficiently high output. I can't. Therefore, as shown in FIG. 4, the inverted Darlington circuit 1 is provided in the output stage.
And the normal Darlington circuit 2 is often used. In this circuit, the base-emitter voltages of the NPN output transistor Q1 and the PNP drive transistor Q2 of the inverted Darlington circuit 1 are offset in the opposite potential directions. The output voltage V is increased by the extremely large current amplification factors of the normal Darlington circuit 1 and the inverted Darlington circuit 1.
A large amplitude range of out can be secured. Regarding such an Inverted Darlington circuit,
For example, CQ publisher, "Transistor Technology Special" No. 18, page 12 to page 29, issued November 1, 1989.

[0003]

In order to widen the output voltage range on the pull drive side (ground potential side of the circuit) in the current amplification circuit as described above, the NPN output transistor Q1 is operated in a saturated operation, and the collector, It is necessary to reduce the voltage between the emitters. However, when the input voltage Vin is lowered to the ground potential side of the circuit, the PNP drive transistor Q
Since the voltage between the emitter and collector of No. 2 becomes saturated and the current amplification factor h _FE decreases, the NPN
There is a problem that the base current required by the output transistor Q1 cannot be supplied.

Therefore, in the conventional current amplifier circuit, it is impossible to operate up to the operating region where the collector-emitter voltage of the NPN output transistor Q1 becomes sufficiently small, and the amplitude range (dynamic range) of the output voltage Vout is increased. That is what makes it narrower. When trying to obtain a wider amplitude range of the output voltage Vout, the NPN output transistor Q1 or the PNP drive transistor Q2 is used.
Although it is conceivable to increase the transistor size of the semiconductor integrated circuit device, the chip size is increased in the semiconductor integrated circuit device, and the number of chips constituting a current amplifier circuit that can be formed from one semiconductor wafer is reduced, which leads to mass productivity. It is disadvantageous in terms.

An object of the present invention is to provide a current amplification circuit which can increase the maximum output power without increasing the size of the output transistor. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0006]

The outline of a typical one of the inventions disclosed in the present application will be briefly described as follows. That is, in the output circuit in which the normal Darlington circuit and the inverted Darlington circuit are push-pull connected, the input voltage is supplied to the input of the inverted Darlington circuit through the first level shift means, and The level shift loop circuit for equalizing the voltage and the output voltage is provided with the second level shift means corresponding to the first level shift means.

[0007]

According to the above-mentioned means, even when the input voltage is lowered to the same potential as the ground potential of the circuit, the base potential of the drive transistor of the inverted Darlington circuit can be increased, so that the saturation operation is less likely to occur,
Since the base current required for the NPN output transistor is sufficiently supplied and can be operated in the saturation region, the amplitude of the output voltage can be increased to the ground potential side of the circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit diagram of essential parts of an embodiment of an audio amplifier using a current amplifier circuit according to the present invention. Each circuit element in the figure is formed on one semiconductor substrate such as single crystal silicon by a known semiconductor manufacturing technique together with an amplifier circuit provided in a preceding stage as described later. In this embodiment, an example in which two current amplifier circuits are connected by BTL (balanced transformerless) to drive a load is shown.

The BTL output circuit is composed of two current amplifier circuits AMP1 and AMP2 having the same structure. The two current amplifier circuits AMP1 and AMP2 are
Input voltages Vin and Vin 'that are in opposite phase to each other are supplied. The output voltages Vout and Vout 'obtained from the current amplifier circuits AMP1 and AMP2 are supplied to the speaker SP.

One of the current amplification circuits AMP1 shown as a representative example includes a normal Darlington circuit 2 for push-driving the speaker SP, an inverted Darlington circuit 1 for pull-driving, and a level shift loop circuit. Bias circuit including. The other current amplifier circuit AM shown as a black box
P2 is also composed of a similar circuit.

In the one current amplifier circuit AMP1 described above, the normal Darlington circuit 1 that push-drives the speaker SP includes an NPN drive transistor Q6 and an NP.
It is composed of an N output transistor Q7. The input voltage Vin is applied to the diode D1 at the base of the transistor Q6.
And D2 are level-shifted and supplied. A bias current is supplied from the constant current source I2 to the diodes D1 and D2.

In the one current amplifier circuit AMP1 described above, an inverted inverter for pull-driving the speaker SP is used.
The Darlington circuit 1 comprises a PNP drive transistor Q2 and an NPN output transistor Q1. Above NP
The input voltage Vin is supplied to the base of the N-transistor Q2 through the level shifting diode D3 in order to prevent the operation in the saturation region.

A level shift loop circuit is provided for equalizing the output voltage Vout and the input voltage Vin, in other words, for allowing an idling current to flow through the Darlington circuits 1 and 2. The level shift loop circuit is configured to include the transistor Q2. That is, the emitter of the transistor Q2 is
The emitter of the NPN transistor Q3 is connected, a bias current is made to flow from the constant current source I1 to the base of the transistor Q3, and the collector is the power supply voltage VCC.
Connected to.

A diode-shaped NPN transistor Q corresponding to the transistors Q2 and Q3 is provided between the base of the transistor Q3 and the output terminal.
4 and a PNP transistor Q5 are provided. Further, as described above, the input voltage Vin is level-shifted and supplied to the base of the transistor Q2 through the level shift diode D3.
A diode D4 for level shifting is provided between the collector and the base of the. That is, the diode-type transistor Q4 has a base and a collector connected through the diode D4.

Such current amplifier circuits AMP1 and AMP
In No. 2, the snubber circuit 3 including a capacitor having a good high frequency characteristic and a small resistance is connected to each output terminal because oscillation easily occurs in the high frequency region. In such an oscillation prevention measure by the snubber circuit 3, it is necessary to increase the capacitance value of the capacitor to some extent in order to surely prevent the oscillation operation, and since it cannot be built in the semiconductor integrated circuit, it is constituted by an external component. .

In the circuit of this embodiment, the output voltage Vout
Is level-shifted by the transistors Q5 and Q4 and the diode D4 by 2VBE (VBE is the voltage between the base and emitter of the transistor) + VF (VF is the forward voltage of the diode) to the power supply voltage VCC side and transmitted to the base of the transistor Q3. And such a transistor Q3
2VBE + with transistor Q2 and diode D3
Only VF is level-shifted to the ground potential side of the circuit and fed back to the input terminal (input voltage Vin). As a result, the output voltage Vout is made equal to the input voltage Vin.

Here, the collector-emitter voltage VCE (Q2) of the PNP transistor Q2 is obtained by the following equation (1). VCE (Q2) = VBE (Q1)-[Vin + VF (D3) + VBE (Q2)] = -Vin-VF (D3) ..... (1)

According to the above equation (1), since VCE (Q2) =-VF (D3) remains even when Vin = 0, the transistor Q2 does not operate in saturation. Then, the transistor Q2 can sufficiently supply the base current to the NPN transistor Q1. As a result, the output transistor Q1 is saturated and the collector,
Since the emitter-to-emitter voltage VCE is reduced and the amplitude range of the output voltage Vout is widened, the maximum output voltage can be increased.

FIG. 2 shows a circuit diagram of another embodiment of the current amplifier circuit according to the present invention. In this embodiment, a resistor R1 is inserted in series with a level shifting diode D3 that supplies the input voltage Vin to the base of the transistor Q2 of the inverted Darlington circuit 1. Corresponding to this, also in the level shift loop circuit, a similar resistor R2 is connected in series to the diode D4. Such an increase in the impedance of the level shift loop circuit may deteriorate the oscillation stability of the negative feedback loop composed of the level shift loop circuit and the inverted Darlington circuit. For this reason, in this embodiment, the capacitor C1 is connected in parallel with the diode D4 and the series resistor R2 to bypass the high frequency component and perform phase compensation, thereby preventing oscillation in the high frequency region. .

Since the other structure is the same as that of the embodiment shown in FIG. 1, the description thereof will be omitted. By providing the oscillation preventing capacitor C1 in the level shift loop circuit as described above, the snubber circuit 3 constituted by an external component can be omitted if the oscillation can be reliably prevented. As a result, the number of external parts can be reduced.

FIG. 3 shows a block diagram of an embodiment of a 4-channel BTL amplifier circuit to which the present invention is applied. Each circuit block in the figure is formed on a single semiconductor substrate such as single crystal silicon by a known semiconductor integrated circuit manufacturing technique.

In the semiconductor integrated circuit device IC, the same B
TL amplifier circuit is channel CH1 to channel CH
4 circuits are provided like 4. One circuit is the drive amplifier circuit DA and the current amplifier circuits AMP1 and AM as described above.
It is composed of P2. The drive amplifier circuit DA has an input voltage v
In is voltage-amplified to form input voltages Vin and Vin ′ having opposite phases. Specifically, each current amplifier circuit AMP1 and AM
It is composed of a differential amplifier circuit for amplifying the voltage corresponding to P2, and the output voltages Vout and Vout 'are fed back to the feedback input through a feedback circuit for gain setting. Then, a first-stage circuit for supplying a signal having the same phase as the input voltage vin of the differential amplifier circuit and the input voltages Vin and Vin 'having the opposite phase is provided.

The operation and effect obtained from the above embodiment are as follows. That is, (1) In the output circuit in which the normal Darlington circuit and the inverted Darlington circuit are push-pull connected, the input voltage is supplied to the input of the inverted Darlington circuit via the first level shift means. At the same time, by providing the level shift loop circuit for equalizing the input voltage and the output voltage with the second level shift means corresponding to the first level shift means, the input voltage becomes the same potential as the ground potential of the circuit. Even if it drops like this, the base potential of the drive transistor of the inverted Darlington circuit can be made high, so that the saturation operation is unlikely to occur, and the base current necessary for the NPN output transistor is sufficiently supplied to operate it in the saturation region. The output voltage amplitude can be Effect that can be increased to the side is obtained.

(2) In the above (1), it is possible to obtain a large power output even at a low power supply voltage by driving the load by connecting the BTL.

(3) By connecting a capacitor in parallel with the level shift circuit provided in the level shift loop circuit so as to bypass the high frequency component, it is possible to realize the stabilization of the operation. can get.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention of the present application is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the current amplification circuit according to the present invention may be used as a single-ended current amplification circuit or the like, in addition to the BTL connection used as described above. It goes without saying that the level shift diode may use a diode-connected transistor. The present invention
It can be widely used as a current amplifier circuit.

[0027]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, in the output circuit in which the normal Darlington circuit and the inverted Darlington circuit are push-pull connected, the input voltage is supplied to the input of the inverted Darlington circuit through the first level shift means, and By providing the level shift loop circuit for equalizing the voltage and the output voltage with the second level shift means corresponding to the first level shift means, the input voltage is lowered to the same potential as the ground potential of the circuit. Even when the NPN is used, the base potential of the drive transistor of the inverted Darlington circuit can be made high, which makes it difficult for the saturation operation to occur.
Since the base current required for the output transistor is sufficiently supplied and can be operated in the saturation region, the amplitude of the output voltage can be increased to the ground potential side of the circuit.

By driving the load by connecting the above current amplifier circuit to the BTL, it is possible to obtain a large power output even at a low power supply voltage.

Stabilization of the operation can be realized by connecting a capacitor in parallel with the level shift circuit provided in the level shift loop circuit to bypass the high frequency component.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a current amplifier circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the current amplifier circuit according to the present invention.

FIG. 3 is a block diagram showing an embodiment of a 4-channel BTL amplifier circuit to which the present invention is applied.

FIG. 4 is a circuit diagram showing an example of a conventional current amplifier circuit.

[Explanation of symbols]

AMP1, AMP2 ... Current amplification circuit, 1 ... Inverted Darlington circuit, 2 ... Normal Darlington circuit, 3 ... Snubber circuit, Q1-Q17 ... Transistor,
I1 to I2 ... Constant current source, D1 to D4 ... Diode, SP
… Speaker, DA… Drive amplifier circuit.

Front Page Continuation (72) Inventor Masanori Iechu 5-20-1 Kamimizuhonmachi, Kodaira-shi, Tokyo Hitachi, Ltd. Semiconductor Division

Claims (3)

[Claims] 1. A first-conductivity-type first output transistor on a power supply voltage side, in which an input voltage is level-shifted corresponding to a voltage between its base and emitter and supplied to the base, and such a first output transistor. The same first conductivity type, the second connected to the ground potential side of the circuit connected in series
Output transistor, the input voltage is supplied to the base through the first level shift means, and the second conductivity type drive transistor for transmitting the collector output to the base of the second output transistor, and the emitter of the drive transistor And an input voltage and an output voltage including a base and an emitter of the drive transistor and a second level shift means corresponding to the first level shift means, which are connected to a connection point of the first and second output transistors. And a level shift loop circuit that equalizes and, and a current amplification circuit. 2. The current amplifying circuit according to claim 1, wherein a drive transistor of a first conductivity type connected in a Darlington form is provided at the base of the first output transistor. 3. The level shift means provided at the base of the drive transistor of the second conductivity type includes a diode, and the level shift means provided in the level shift loop performs the level shift corresponding thereto. 3. The current amplifier circuit according to claim 1, wherein a phase compensation capacitor is provided in parallel with the diode in addition to the diode.