JPH04332206A - Power amplifier - Google Patents

Abstract

PURPOSE:To stop an output transistor from deviating from a safe operating range even when a terminal at the output capacitor load side of a B-class push-pull output circuit is erroneously connected a power supply terminal. CONSTITUTION:When the terminal at the side of speaker 46 is connected to the terminal to which power supply voltage has been applied, a voltage that is a sum of charging voltage of output capacitor 45 and the power supply voltage is applied to an output terminal 44. This overvoltage conducts transistors 40 and 41, and a safe operating range detecting circuit 101 detects erroneous connection. When the transistor conducts, transistors 43 and 39 conduct, while a transistor 24 is shut off. Thus, transistors 25 and 28 are turned off, are stopped from deviating from the safe operating range, and are protected from being destroyed by erroneous connection.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to power amplifiers, and more particularly to power amplifiers including class B push-pull output circuits.

0002

2. Description of the Related Art In conventional power amplifiers, power amplifiers including a class B push-pull output circuit in which a load is connected to an output terminal via an output capacitor have been widely used.

0003

[Problem to be Solved by the Invention] In this type of power amplifier, if the load side terminal of the output capacitor is mistakenly connected to the power supply terminal, the voltage due to the accumulated charge in the capacitor and the power supply voltage will be applied to the collector of the output transistor. A voltage equal to the sum of is applied. As a result, a large current flows through the output transistor, often exceeding its safe operating area (ASO) and destroying it.

The present invention seeks to provide a power amplifier in which the output transistor does not deviate from the safe operating area even if the load side terminal of the output capacitor is mistakenly connected to the power supply terminal.

[0005]

[Means for Solving the Problems] The power amplifier of the present invention includes:
A push-pull output circuit that supplies output to the load via a capacitor, a safe operating area detection circuit that detects the output terminal voltage and operates when the output terminal voltage exceeds a set voltage, and the output of the push-pull output circuit. The control circuit controls the output of the push-pull output circuit in response to the output of the safe operating area detection circuit when the output terminal voltage of the push-pull output circuit exceeds the set voltage. This puts the transistor in a non-operating state.

[0006]

[Operation] In the power amplifier of the present invention, the safe operating area detection circuit detects the output terminal voltage of the push-pull output circuit, and when it exceeds the set voltage, operates the control circuit to output the output of the push-pull output circuit. By disabling the transistor, the output transistor always operates in a safe operating area.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the power amplifier of the present invention will be described below with reference to FIG.

In the figure, 1 is a power supply terminal, 2 is a ground terminal, and a resistor 3 and a Zener diode 4 are connected in series between these terminals 1 and 2. Note that the cathode of the Zener diode 4 is connected to the resistor 3 side, and its anode is connected to the ground terminal side.

5 is an NPN transistor, 6 is a resistor, 7 is a PNP transistor whose base and collector are connected,
8 is a resistor, 9 is an NPN transistor, 10 is a resistor, 11
are PNP transistors, which are connected in series between a power supply terminal 1 and a ground terminal 2. Reference numeral 12 denotes an input terminal, which is connected to the base of the transistor 11. Also,
The base of the transistor 5 is connected to the connection point between the resistor 3 and the Zener diode 4.

13 is a resistor, 14 is a PNP transistor,
A constant current source 15 forms a series connection and is inserted between the emitter of the transistor 5 and the ground terminal 2. The base of the transistor 14 is connected to the base of the transistor 7.

16 is a constant current source, 17, 18, 19 are PN
The P transistor and 20 are resistors, which are connected in series between the power supply terminal 1 and the ground terminal 2. The collectors and emitters of both transistors 17 and 18 are connected.

21 is a resistor, 22 is a PNP transistor,
23 is a resistor, which is connected to the constant current source 16 and the transistor 1.
It is inserted and connected in series between the connection point with the collector of No. 7 and the ground terminal 2. The base of the transistor 22 is connected to the connection point between the collector of the transistor 14 and the constant current source 15, and the connection point between the emitter and the resistor 21 is connected to the base of the transistor 19.

24 is a PNP transistor, 25 is an NPN
The transistor 26 is a resistor, and these are connected in series between the power supply terminal 1 and the ground terminal 2. The base of transistor 25 is connected to the connection point between the emitter of transistor 18 and the collector of transistor 19.

Reference numerals 27 and 28 indicate NPN transistors, which are connected in series between the power supply terminal 1 and the ground terminal 2. The base of the transistor 28 is connected to the connection point between the collector of the transistor 25 and the resistor 26.

29 is an NPN transistor, and the power supply terminal 1
and the base of the transistor 27,
Its base is connected to the connection point between the constant current source 16 and the collector of the transistor 17. A resistor 30 is inserted and connected between the base and collector of the transistor 27. Diodes 31 and 32 are connected in series in the same direction, and the anode of diode 31 is connected to the base of transistor 24, and the cathode of diode 32 is connected to the emitter of transistor 27 and the collector of transistor 28, respectively.

33 and 34 are resistors, and 35 is a constant current source, which connect the emitter of the transistor 27 and the transistor 28.
It is inserted and connected in series between the connection point with the collector and the ground terminal 2.

A negative feedback terminal 36 is connected to the connection point between the resistor 34 and the constant current source 35, and is further grounded via a capacitor 37.

38 is a constant current source, and 39 is an NPN transistor, which are connected in series between the power supply terminal 1 and the ground terminal 2, and their connection point is connected to the base of the transistor 24 and the anode of the diode 31. has been done.

PNP transistors 40 and 41 constitute a current mirror circuit, with the collector of the transistor 40 connected to the power supply terminal 1, and the emitter connected to the emitter of the transistor 27 and the collector of the transistor 28 through a resistor 42, respectively. It is connected. ASO with these
A detection circuit 101 is configured.

Reference numeral 43 denotes an NPN transistor, the collector of which is connected to the power supply terminal 1, and the emitter connected to the base of the transistor 39. These transistors 39 and 43 constitute a bias control circuit 102.

Reference numeral 44 denotes an output terminal, which is connected to the emitter of the transistor 27 and the collector of the transistor 28, and is connected to an output capacitor 45 and a speaker 46 as a load.
It is grounded through a series connection with.

In the embodiment with the above configuration, during normal operation, the transistor 40 constituting the current mirror circuit
, 41 are in the off state, the input signal is input to input terminal 1.
2, the transistors 27 and 28 perform class B push-pull operation, and an amplified output signal is obtained at the output terminal 44. This output signal is supplied to a speaker 46 via a capacitor 45.

If the load side of the output capacitor 45, that is, the speaker 46 side terminal is connected to the terminal to which the power supply voltage is applied by mistake, the sum of the charging voltage of the output capacitor 45 and the power supply voltage will be applied to the output terminal 44. applied, A
Exceeds SO detection level. This excessive voltage is applied between the collector and emitter of transistor 28. On the other hand, this voltage causes the emitter potentials of the transistors 40 and 41 to rise, thereby making these transistors 40 and 41 conductive, and the ASO detection circuit 101 detects a misconnection. When the transistor 41 becomes conductive, a base current is supplied to the transistor 43, and the transistor 39 connected to it in Darlington becomes conductive, so that the bias control circuit 102 prevents the ASO deviation. That is, if the collector current of the transistor 39 is configured to be a sufficiently larger value than the current from the constant current source 38, the base potential of the transistor 24 becomes approximately equal to the ground potential, and the transistor 24 becomes cut off. . This turns off transistors 25 and 28, prevents them from deviating from the ASO, and prevents damage due to incorrect connection. Furthermore, the transistor 27 becomes inoperative due to the rise in its emitter potential.

[0024]

[Effects of the Invention] In the power amplifier of the present invention, the output terminal voltage of the push-pull output circuit that supplies output to the load via the capacitor is detected by the safe operating area detection circuit, and the voltage at the output terminal of the push-pull output circuit is detected by the safe operating area detection circuit. When the set voltage is exceeded, the safe operating area detection circuit activates the control circuit and disables the output transistor of the push-pull output circuit, so this output transistor always operates in the safe operating area and prevents excessive current from flowing. flow is prevented and there is no risk of destruction.

[Brief explanation of drawings]

[Fig. 1] Fig. 1 is a circuit diagram of an embodiment of a power amplifier of the present invention.

[Explanation of symbols]

1 Power terminal 2 Ground terminal 3, 6, 8, 10, 13, 20, 21, 23, 26, 3
0, 33, 34, 42 resistance 4 Zener diode 5, 9, 25, 27, 28, 29, 39, 43 NP
N transistors 7, 11, 14, 17 to 19, 22, 24, 40, 41
PNP transistor 12 Input terminals 15, 16, 35, 38 Constant current sources 31, 32 Diode 36 Negative feedback terminal 37 Capacitor 44 Output terminal 45 Output capacitor 46 Speaker 101 Safe operating area (ASO) detection circuit 102
bias control circuit

Claims (1)

[Claims] 1. A push-pull output circuit that supplies an output to a load via a capacitor; and a safety operation that detects the output terminal voltage of the push-pull output circuit and operates when the output terminal voltage exceeds a set voltage. an area detection circuit; and a control circuit that controls the operating state of the output transistor of the push-pull output circuit according to the output of the safe operation area detection circuit, and the output terminal voltage of the push-pull output circuit exceeds a set voltage. The power amplifier in which the control circuit disables the output transistor of the push-pull output circuit in accordance with the output of the safe operating area detection circuit when the power amplifier is activated.