JPS59140706A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To remove the switching distortion of a class ''B'' SEPP power amplifier with a small idling current by controlling the idling current according to an output DC potential. CONSTITUTION:When an input signal S is positive, a transistor (TR) 4 is off, so a TR36 is off and a driving control circuit 52 connected to an output terminal 28 detects the output DC potential to flow a collector current to a TR54; and a base current is flowed to a TR44, and consequently the power TR42 is supplied with a constant bias current in a positive half cycle of the input signal S according to the output DC potential. At the moment when the input signal S becomes negative, the power TR42 turns on, so the switching is performed smoothly to prevent the generation of distortion, and the current flowing through the TR54 has a value corresponding to the output DC potential, so the current is reduced while the input signal S is negative, eliminating unnecessary current consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and particularly to improvements in class B power amplifiers.

Bwks E P P (Sf
ngle Ended Pu5h-Pull) power amplifier is used. This BiS E P P power amplifier consists of a pair of transistors whose operating states are alternately switched between the positive and negative half cycles of the input signal waveform, but each transistor has a constant Bias current is passed as idling current.

This idling current increases power consumption, lower voltage,
This may hinder driving with low current consumption. In particular, the idling current is low in battery-powered portable audio equipment.
This may cause unnecessary battery consumption.

However, in order to reduce this idling current and eliminate switching distortion, if this type of amplifier is configured with a -product circuit, it becomes necessary to attach an external capacitor, which increases the number of components in the circuit configuration. It also has the disadvantage of being expensive.

An object of the present invention is to provide an amplifier circuit that reduces idling current and suppresses the occurrence of switching distortion.

The present invention includes a pair of transistors constituting a class B push-pull amplifier, a drive circuit that supplies a base current to one of these transistors, and a drive circuit that applies a base current to one of the transistors in accordance with an output DC potential when the transistor is in an inactive state. The present invention is characterized by comprising a drive control circuit that controls a drive circuit and supplies a base current to the transistor.

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

The figure shows an embodiment of the amplifier circuit of the present invention.

In the figure, a differential amplifier 2 is installed at the input stage of this amplifier circuit. That is, the emitters of the pair of transistors 4.6 are made common, a constant current source 10 is connected between this emitter and the power supply terminal 8, and a constant current source 10 is connected between the collector of the transistor 4 and the reference potential point terminal 12. is transistor 14
is connected.

In addition, the collector of the transistor 6 and the reference potential point terminal 12
A diode 16 is connected between the two, and the anode of the diode 16 and the base of the transistor 14 are connected in common, and the transistor 14 and the diode 16 constitute a current mirror circuit.

An input terminal 18 is formed at the base of the transistor 4, as well as resistors 20, 22, 24 and a capacitor 2.
A constant bias is set from a bias circuit composed of 6. Further, a feedback circuit composed of resistors 30, 32 and a capacitor 34 is inserted between the base of the transistor 6 and the output terminal 28, so that the output signal is negatively fed back to the base of the transistor 6. There is.

The output of the differential amplifier 2 is taken out from the collector of the transistor 4, and this collector output is given to the base of the transistor 36. The transistor 36 is connected between the power supply terminal 8 and a reference potential point via a constant current source 38 on the collector side. That is, the output of the differential amplifier 2 is transferred from the collector side of the transistor 36 to the power transistor 40.
and the base of a drive transistor 44 for driving the power transistor 42. The power transistors 40 and 42 are connected in series between the power supply terminal 8 and the reference potential point terminal 12 with their emitters facing the reference potential point side, forming a 5EPP circuit.

Further, a constant current source 4 is connected between the power supply terminal 8 and the output terminal 28.
6 and diodes 48 and 50 are connected in series, the emitter of the transistor 44 is connected to the anode side of the diode 48, and the collector of the transistor 44 is connected to the base of the power transistor 42. That is, transistor 44, constant current source 46 and diode 48.5
0 constitutes a drive circuit for the power transistor 42.

A drive control circuit 52 is installed which detects the DC potential of the output terminal 28, causes a base current to flow through the transistor 44 in accordance with this DC potential, and controls the power transistor 42 into an operating state. That is, the power transistor 40
A transistor 54 is connected to the emitter side between the base and the reference potential point via a resistor 56, and the base of this transistor 54 is connected to the output point via a resistor 58 and a diode 60. Connected to a reference potential point.

The operation will be explained based on the above configuration. Input terminal 1
When an AC signal S is applied to AC signal S, transistor 4 becomes non-conducting when a positive half cycle is applied to AC signal S, so that transistors 36 and 44 become non-conducting. As a result, the power transistor 40
becomes conductive, while power transistor 42 becomes non-conductive. At this time, in a class B amplifier, if the idling current is small, the power transistor 42 will certainly become non-conductive, which will cause switching distortion.

In this case, the base of the transistor 54 is connected to the output terminal 28.
An output DC potential occurring at the terminal is applied, and a current flows according to this potential. A collector current flows through the transistor 54 in response to this base current, and a base current flows through the transistor 44 due to this collector current. This base current corresponds to the output DC potential. A bias current is applied from the transistor 44 to the base of the power transistor 42, and the power transistor 42 is controlled to a constant bias state according to the output DC potential during the positive half cycle period of the input signal. As a result, the input signal S enters the negative half cycle and becomes conductive at the same time, so that the switching operation is performed smoothly and the occurrence of switching distortion can be reliably prevented. Therefore, even if the idling current for suppressing the occurrence of switching distortion is reduced, the occurrence of switching distortion can be similarly suppressed.

Further, since the current flowing through the transistor 54 is given at a value corresponding to the output DC potential, when the input signal S is in a negative half cycle, it decreases in accordance with the potential, thereby suppressing wasteful current consumption. Furthermore, the current flowing through the transistor 54 can be arbitrarily adjusted by the value of the resistor 56.

As described above, according to the present invention, it is possible to suppress switching distortion, reduce idling current, and reduce power consumption.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the amplifier circuit of the present invention. 40.42... Power transistor, 44... Drive transistor, 52... Drive control circuit.

Claims (1)

[Claims] A pair of transistors constituting a class B push-pull amplifier, a drive circuit that supplies a base current to one of these transistors, and a drive circuit that controls the drive circuit according to an output DC potential when the transistor is in an inactive state. and a drive control circuit for applying a base current to the transistor.