JPS59147505A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To prevent abnormal sound from being produced by providing a switching control circuit and the 1st and the 2nd switching circuits to a drive circuit of an amplifier for an output circuit of which a bootstrap circuit is used so as to prevent the leakage of power supply ripple at application of a power switch. CONSTITUTION:The bootstrap circuit comprising output transistors (TR) 6, 8 and a bootstrap capacitor 18 is provided to an output stage of an amplifier circuit and the TRs 6, 8 are switched alternately by the drive circuit 10. The 1st switching circuit 28 is connected between the circuit 10 and a power supply terminal 2 and the 2nd switching circuit 32 is connected between the base of the TR8 and the power supply terminal 2 via a constant current source 30. Further, a switching control circuit 34 is connected between the power supply terminal 2 and a reference potential terminal 4 and the time constant of the circuit 34 is decided by the capacitor 38. Moreover the circuits 28, 32 are controlled by the circuit 34 so as to prevent the leakage of ripple and the generation of abnormal sound at application of the power supply switch 40.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and more particularly to an amplifier circuit having an internal bootstrap circuit in which the generation of transients is prevented.

FIG. 1 shows the configuration of an amplifier circuit in which the output circuit is composed of a bootstrap circuit. A driving type (1) voltage Vcc is applied to the power supply terminal 2 via a power switch (not shown), and an output l-range screen 8 is connected in series between the power supply terminal 2 and the reference potential side terminal 4. It is connected. A drive circuit 10 is connected to the base of each output transistor 8, and each output transistor 8 alternately performs a switching operation based on the output signal of the drive circuit 10. A drive circuit 10 is connected to the power supply terminal 2 via a resistor 12, and a drive voltage Vcc is connected to the drive circuit 10 through a resistor 12.
is applied and a bootstrap terminal 14 is formed. Between this bootstrap terminal 14 and the output terminal 16, a capacitor 1 for bootstrap is connected.
B is inserted. Further, a load 22 is connected between the output 11b1 terminal 16 and the reference potential side terminal 4 via a capacitor 20. Further, a resistor 24 is connected to the output point of this amplifier circuit, and a feedback signal is given to a pre-stage amplifier (not shown) via this resistor 24. Further, a signal input terminal 2G is formed in the drive circuit 10, and a signal from the previous stage amplifier is applied to this signal input terminal 26.

In this way, when the output circuit is configured with a bootstrap I/wrap circuit (2), the drive circuit 10 is configured with a certain time delay after turning on the power switch in order to prevent the occurrence of a transient stage due to turning on the power switch. After that, it is configured to be operational. However, since the impedance of the output terminal 16 is maintained in a high state from the time when the power switch is turned on until the drive circuit 10 starts operating, an abnormal signal current easily flows through the load 22, which causes pop noises. etc., may cause abnormal noise. In particular, the influence from the power supply line is applied to the load 2 through the resistor 12 and capacitor 18.
2, and shocks when the power switch is turned on, fluctuations and ripples in the power supply voltage, etc., become causes of abnormal signals.

An object of the present invention is to provide an amplifier circuit that prevents abnormal noise from occurring when a power switch is turned on when an output circuit is configured with such a bootstrap I/wrap circuit.

The present invention provides an amplifier circuit in which the output circuit is composed of a boots I/ramp circuit, and a first (third) switching circuit inserted between a drive circuit that drives the output circuit and a power supply; and a switching control circuit that controls the first switching circuit to be in a conductive state and the second switching circuit to be in a non-conductive state for a certain period of time from the start of power supply. It is characterized by having the following.

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

FIG. 2 shows an embodiment of the amplifier circuit of the present invention, and the same parts as the circuit of FIG. 1 are designated by the same symbols. In the figure, a first switching circuit 28 is inserted into the power supply line for supplying power to the drive circuit 10, and a constant current source 3 is inserted between the output transistor 8 and the power supply line.
A second switching circuit 32 is inserted through 0. And, between the power supply line and the reference potential side terminal 4,
Ct, said first and second switching circuit 28.32
A switching control circuit 34 is installed for controlling. Control terminal 36 of this switching control circuit 34
A capacitor (4) 38 is connected to the capacitor (4) for setting a time constant. The first and second switching circuits 28 and 32 are composed of switching elements such as switching L-transistors, and the switching control circuit 34
The conduction and non-conduction states are controlled based on the control output.

Further, a power source 42 composed of a battery or the like is connected to the power source terminal 2 via a power switch 40.

The operation will be explained based on the above configuration. When the power switch 40 is placed in a conductive state, a power supply 42 is applied to the switching control circuit 34 via the power supply line. As the power supply 42 is supplied, a constant charging current flows through the capacitor 38, and after a certain period of time, the capacitor 38 is charged to a constant potential.

That is, from the start of conduction of the power switch 40, the capacitor 38
During a certain period of time until the is charged to a certain potential, the first
The second switching circuit 28 is controlled to be non-conductive, and during this period, the second switching circuit 32 is controlled to be conductive. In this case, a constant (5) bias is applied to the base of the output transistor 8 from the constant current source 30, and the output transistor 8 is controlled to be conductive. As a result, the output terminal 16 and the reference potential side terminal 4 are short-circuited by the output transistor 8, and the potential of the output terminal 16 is maintained at approximately the same level as the reference potential +1llll level. Therefore 1. Even though the switching circuit 28 is kept in a non-conducting state to stop the operation of the drive circuit 10 in order to prevent the occurrence of a transient stage when the power switch is turned on, the DC level of the output element 16 remains at the reference potential. Since the output terminal 16 is maintained at a low level, the output terminal 16 is in a very low impedance state, and the transient stage and power ripple caused by the conduction of the conventional power switch 40 are transmitted through the resistor 12 and capacitors 18 and 20. Therefore, inconveniences caused to the load 22 can be effectively prevented. That is, the conventional abnormal sound signal current path is formed on the reference potential side via the output transistor 8, and the abnormal signal current flowing to the load 22 is blocked.

According to such a configuration, even in the output circuit of the low frequency power amplifier, even when a relatively light load such as a hesodophone is connected, abnormal noise can be prevented from being generated from the power supply line.

As described above, according to the present invention, it is possible to prevent the occurrence of a transient stage and the leakage of power supply ripples when the bootstrap source switch is turned on.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional amplifier circuit, and FIG. 2 is a circuit diagram showing an embodiment of the amplifier circuit of the present invention. 6, 8... Output I transistor, IO... Drive circuit, 28... First switching circuit, 32... Second
switching circuit, 34... switching control circuit. (7)

Claims (1)

[Claims] In an amplifier circuit in which an output circuit is configured with a bootstrap circuit, a first switching circuit inserted between a drive circuit that drives the output circuit and a power supply, and a first switching circuit inserted between the output circuit and the power supply. 2 switching circuit;
An amplifier circuit comprising: a switching control circuit that controls a first switching circuit to be in a conductive state and controls a second switching circuit to be in a non-conductive state for a certain period of time from the start of power supply.