JPS61105916A - Push-pull amplifier - Google Patents

Abstract

PURPOSE:To attain the operation at a low power supply voltage by setting a maximum output current with an output current I0 of two constant current sources and using a current I2 flowing to the 3rd constant current source so as to set an idling current in a push-pull amplifier circuit used for the output stage of an acoustic power amplifier. CONSTITUTION:In increasing the level of an input signal fed to an input terminal 9 in the negative direction, a collector current of a drive transistor (TR) 11 is decreased and when the drive TR11 is turned off, a base current of an output TR19 reaches a maximum value I0. Thus, the maximum current flowing to the collector of the output TR19 is I0.hFE (hFE is a current amplification factor of the output TR19), and the maximum current is as large as 150mA with I0=500muA and hFE=300, resulting in driving sufficiently a speaker 20 being a load. That is, the push-pull amplifier circuit is activated by a low power supply voltage and a sufficient output current is obtained, then this circuit is suitable for an operational amplifier, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION B) Industrial Application Field The present invention relates to a push-pull amplifier circuit used in the output stage of an audio power amplifier, etc. The present invention relates to a suitable push-pull amplifier circuit.

(b) Conventional technology As a pushinable amplifier circuit that operates with a low power supply voltage,
For example, a current-driven push-pull amplifier circuit is known, as shown in FIG. 2 of Japanese Utility Model Application Publication No. 55-87017. The pushinable amplifier circuit is as shown in FIG.
An input signal applied to input terminal (1) K is current-amplified by a pre-drive transistor (2) of class A operation and first and second drive transistors (3) and (4) of class B push-pull operation, and First and second output transistors (5
) and (6) to amplify the voltage to obtain a push/pull output signal at the output terminal (7). For example, input terminal (
When a positive input signal IIK is applied, a negative signal is generated at the collector of the predrive transistor (2), turning on the second drive transistor (4) and the second output transistor (6), and turning on the first drive transistor (4) and the second output transistor (6). The transistor (3) and the first output transistor (5) are turned off and a negative output signal is generated at the output terminal (η).

Also, when a negative input signal is applied to the input terminal +1)K,
A positive signal is generated at the collector of the predrive transistor (2), which turns on the first drive transistor (3) and the first output transistor (5), and turns on the second drive transistor (4) and the second output transistor (6). ) is turned off and the output terminal (7
) produces a positive output signal. Therefore, if the push-pull amplifier circuit shown in Fig. 3 is used, the push-pull amplifier circuit according to the input signal can be
A pull output signal can be obtained from the output terminal +7)K.

Problems to be Solved by the Invention H However, the pushinable amplifier circuit has a drawback in that it cannot be used at a low power supply voltage.

That is, the voltage drop of the constant current source (8) is expressed as Vex (sa
t ), then the push-pull amplifier circuit in FIG.
V,, +2Vc, (sat) (However, ■1
．． is the base-emitter voltage of the transistor, Vcm
(Sat) requires the voltage of the collector-emitter saturation voltage of the transistor, V, , : 0.7V, Ve,
If (sat) = 0.1■, the voltage is 1
, 6V, so 3V power supply (1,8V compensation) or 4.5V
■It can be used for equipment that uses a power supply (2.7V compensation), but it cannot be used for equipment that uses a 1.5V power supply (0.9V compensation). In addition, in the push-pull amplifier circuit shown in Figure 3, the maximum output current and idle link current are determined according to the current flowing through the constant current source (8), so if the maximum output current is increased, the idle link current is decreased. This has the disadvantage that it becomes difficult to set the desired value, making it difficult to design an amplifier circuit for a low current consumption board.

B) Means for Solving the Problems The present invention has been made in view of the above-mentioned points, and includes a common emitter type first drive transistor to which an input signal is applied to the base, and a common emitter type first drive transistor whose base and emitter are connected to the first drive transistor. a second dynamic transistor commonly connected to the base and emitter of the transistor; a first constant current source that supplies the collector current of the first drive transistor; and a second constant current source that supplies the collector current of the second drive transistor. a first output transistor driven by a signal obtained at the collector of the first drive transistor; and a second output transistor driven by a signal obtained at the collector of the second drive transistor. do.

(E) Effect According to the present invention, the base-emitter voltage V□ (=o, 7) of the drive transistor and the voltage drop Van of the constant current source
(sat) (= 0. I V ) sum voltage (= 0.
It is possible to provide a push-pull amplifier circuit that operates with a power supply voltage of 8V or higher.

(f) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which (9) is an input terminal to which an input signal is applied, and Ql is the input terminal (9).
), the first drive transistor having its base connected to U])
is a second drive transistor whose base and emitter are commonly connected to the base and emitter of the first drive transistor aα, and the west side is a current source a3 and a diode-connected transistor α, and the transistor α4) is connected as a current mirror. A first constant current source consisting of a transistor (15), a first constant current source consisting of the current source αJ, the transistor α
A second constant current source consisting of a transistor (1η) connected in a current mirror to
A PNP type first output transistor operates according to the current, which is the difference between the collector current of OI and the output current of the first leg current source @ (19 is the difference between the collector current of the second drive transistor (11) and the an NPN type second output transistor that operates according to the difference current from the output current of the first leg current source 4;
and (2) are speakers serving as a load connected via the output point AK output capacitor f2]) of the push-inable amplifier circuit.

In Figure 1, the current flowing through the current source (131) is calculated.

Then, the collector NH of the transistor α is also constructed.

If the mirror ratio is 1, then the transistor (14
) and current mirror connected transistor Q5I and (1
The collector current of 7) is also Io. Therefore, the output currents of the first and second constant current sources 0 and the horse mackerel are equally Io
becomes. In addition, the first and second drive transistors (IC
By adding the base biases E and 0υ to predetermined values, the collector currents of the first and second drive transistors a [and α1) can be set to Io, respectively. For that reason,
In a no-signal state where no input signal is applied to the input terminal (9), the output current of the first constant current source and the collector current of the first drive transistor α, the output current of the second constant current source and the second The collector currents of the drive transistors (11) are equal to each other, the base currents of the first and second output transistors α and al do not flow, and the true output transistors are turned off.

Next, when a positive input signal is applied to the input terminal (9),
The collector currents of the first and second drive transistors (1G and α1) increase to 0+ΔIK, the base current of the first output transistor (18) KΔ flows, and the first output transistor (18) turns on. , all the output current of the second constant current source flows into the collector of the second drive transistor (11), so the second output transistor α is turned off.Therefore, the collector current of the first output transistor αυ is The signal flows into the speaker (2), and a sound corresponding to the positive input signal is generated from the speaker (2).

Moreover, when a negative input signal is applied to the input terminal (9),
The collector currents of the first and second drive transistors αQ and α1) decrease to Io−ΔI, a base current of ΔI flows through the base of the second output transistor α9, and the second output transistor I is turned on. At that time, the output current of the first current source 4 is smaller than the collector current of the first drive transistor a, so the first output transistor (1B is turned off. Therefore, the collector current of the second output transistor (Il) is The signal flows to the speaker ■, and sound corresponding to the negative input signal is generated from the speaker ■.Therefore, if the push-pull amplifier circuit shown in FIG. 1 is used, the positive and negative input signals applied to the input terminal (9) K It is possible to drive the speaker (2), which acts as a load, according to the

As the level of the input signal applied to the input terminal (9) increases in the positive direction, the base current of the first output transistor αS increases accordingly, and the collector current also increases. Therefore, the upper limit of the current flowing through the collector of the first output transistor (18) is IcmaX (maximum collector current). As time goes on, the collector current of the second drive transistor all decreases, and when the second drive transistor (11) is turned off, the second output transistor
The base current of the transistor (19) is the maximum value I.K. Therefore, the maximum current flowing to the collector of the second output transistor (2) is I, h□ (however, ham is the current of the second output transistor (19) amplification factor), and for example, factor o=5
00 μA.

)1. , = 300, the maximum current is 150mA
Since this is a large value, it is possible to sufficiently drive the speaker (2), which is the load.

As mentioned above, the pushinable amplifier circuit of FIG. 1 operates with a low power supply voltage and can obtain a sufficient output current, so it is suitable for use with an equal voltage operational amplifier. However, the push-pull circuit shown in FIG.
Since the second output transistor is turned off and the idle link current becomes zero, there is a risk of generating crossover distortion, which may cause problems when used in the final stage amplifier of audio equipment.

FIG. 2 shows another embodiment of the present invention in which the push-pull amplifier circuit of FIG. 1 is improved to prevent the occurrence of crossover distortion.
The feature is that a third constant current source is inserted between the 0 base and the ground. In FIG. 2, circuit elements that are the same as those in FIG. 1 are given the same figure numbers and their explanations will be omitted. In FIG. 2, if it is assumed that an idle link current of 11 flows through the collector of the first output transistor Q8 in a no-signal state due to the connection of the third constant current source @, then the equation becomes as follows.

Further, if it is assumed that all the idling current flowing into the collector of the first output transistor Q81 flows into the collector of the second output transistor Ql, then the second
The output transistor (110) has a first rotating transistor whose base and emitter are commonly connected to the base and emitter of the second drive transistor (1G's collector current also becomes 10,0L).

The output current of the first constant current source 4 is 0, which is the first current.

Therefore, the current flowing through the third constant current source @ is LK
If set, the bias of all the transistors composing the push-pull amplifier circuit in Fig. 2 will be appropriate, and the idling current of I will flow through the first and second output transistors and 0. It is possible to measure the reduction of crossover distortion. In other words, if the current flowing through the third constant current source @ is determined (=stop), then the first and second output transistors (18 and a9
Idling current of 1. (=Lnil1) can be arbitrarily determined. In the case of Fig. 2, the third constant current source is inserted between the base of the first output transistor (1) and the ground, and the third constant current source is inserted between the base of the second output transistor (19). Exactly the same result can be obtained even if the current amplification factor h of the transistor is
Since em changes depending on the ambient temperature, with the circuit configuration shown in FIG. 2, the idle link current I also changes depending on the ambient temperature. In order to improve this point, the first and second output run sisters and the housing 9 are each connected as current mirrors, and the mirror ratio n is the current amplification factor h2. All you have to do is make it equal to . Current mirror connection, n=h□
Then, the idle link current I flowing through the first and second output transistors, na8 and αIK becomes 〒, and a stable idle link current can be set.

(1) Effects of the Invention As described above, according to the present invention, it is possible to provide a push-pull amplifier circuit that operates with a low power supply voltage.

Further, according to the present invention, it is possible to provide a push-nible amplifier circuit that can obtain a sufficiently large maximum output current. Further according to the present invention, the output currents of the first and second constant current sources.

The maximum output current can be set by , and the idle link current can be set by the current flowing to the third constant current source, so both 1! The advantage is that the current can be set independently, the idle link current can be set independently of the maximum output current, and as a result, the reduction in current consumption can be easily measured.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a circuit diagram showing a conventional push-nable amplifier circuit. Explanation of main drawing numbers (1υ...drive transistor, ■, 4...constant current source, t1 seconds, (19...output transistor). Applicant: Sanyo Electric Co., Ltd. and 1 other representative: Patent attorney Shizuo SanoFigure 1Figure 2

Claims (1)

[Claims] (1) a common-emitter first drive transistor whose base is connected to the input terminal; a second common-emitter drive transistor whose base and emitter are respectively connected to the base and emitter of the first drive transistor; a first constant current source that supplies a constant current to the collector of the first drive transistor; a second constant current source that supplies a constant current to the collector of the second drive transistor; and a signal obtained at the collector of the first drive transistor. P driven by
an NP type first output transistor and an NP driven by a signal obtained at the collector of the second driving transistor;
and an N-type second output transistor, the collectors of the first and second output transistors are commonly connected to form an output point, and a push-pull output signal is generated at the output point. Pull amplifier circuit.