JPS5910011A - Power amplifier - Google Patents

Abstract

PURPOSE:To maintain the bias current flowing to an output transistor TR at a fixed level in response to a rise of temperature due to the sudden generation of heat of the output TR, by compensating the bias voltage of a constant voltage bias circuit in response to the output electric power and the heat generating temperature of the output TR. CONSTITUTION:A temperature sensor 16 is thermally connected to output transistors TR1 and TR2, and an output signal detecting circuit 17 is provided. A control circuit 18 supplies the detecting signals of the sensor 16 and the circuit 17 and works based on a certain prescribed logic to control the current of a constant current source 12. Then the output electric power and the heat generating temperature of the output TR which is suddenly changed by the output electric power are detected. The current of the current source 12 varies in response to the output electric power and the heat generating temperature of the output TR. Therefore the voltage drop component of a register 19 varies. Then the supply voltage is compensated for a constant voltage bias circuit consisting of bias setting resisters 8 and 9 and a TR10 in order to obtain a fixed level of the bias current flowing to the output TR1 and TR2.

Description

[Detailed description of the invention] Industrial applications The present invention relates to audio power amplifiers.

FIG. 1 shows an example of a general configuration of a power amplifying section in a conventional amplifier of this type. In Figure 1, 1°2 is the output trannostar, 3.4 is the emitter resistance of the output trannostar,
5 and 6 are drive transistors that drive the output transnoster 1゜2, 7 is a resistor, 8゜9 is a bias setting resistor,
Both Toranostar and O make up a constant voltage/gauss circuit. 11 is a voltage signal source, and 12 is a constant current source. Furthermore, 13 is the output terminal, and 14.15 are the positive and negative connection terminals, respectively.

In the conventional example configured in this way, the constant voltage bias circuit is biased by the constant current a, 12, and therefore always supplies a constant bias voltage.

It is thermally coupled to the output transistor 1 or 2 of the constant voltage bias circuit, and the output transistor 1゜20 which changes as J- is connected to the output transistor 1 or 2 of the constant voltage bias circuit.
Although the bias voltage is designed to change depending on the temperature, its thermal time constant 9 is generally large, so the constant voltage bias circuit changes its bias due to the sudden heat generation of the output transistor 1.2. There was a problem in that the voltage could not be corrected instantaneously, and an excessive bias current would flow through the output trannostar 1.2 during that transient time.Purpose of the InventionThe present invention therefore aims to correct the output power The power amplifier is designed to fully follow the heat generation temperature of the output transnoster, which changes rapidly due to this, and corrects the bias voltage of the constant voltage bias circuit so that the bias current of the output transistor is always constant. This is what we provide.

In order to achieve the above object, the invention includes a temperature change sensor that detects the crystallinity of an output transistor, an output signal detection circuit, and a constant voltage that processes each detection signal of the temperature sensor and the output signal detection circuit. A means for correcting the bias circuit pressure is provided. 1: Examples will be explained in detail with reference to the drawings.

DESCRIPTION OF THE EMBODIMENT FIG. 2 shows an embodiment of the present invention, in which the same reference numerals as in FIG.
is a temperature sensor thermally coupled to the output transistors 1 and 2, which detects, for example, the temperature of the heat sink of the output transistor. 17 is an output signal detection circuit; 18 is an input circuit for each detection signal of the temperature sensor 16 and the output signal (Vτ output circuit 17);
A constant current source 12 operates according to a certain determined function.
This is a control circuit that controls the current of the current. Further, J9 is a resistor connected in series to the constant voltage bias circuit.

In this embodiment configured in this way, the output power and the heat generation temperature of the output trannostar which changes rapidly due to the output power are detected, and the current of the constant current source 2 is changed in accordance with the detected output power. The supply voltage of the constant voltage bias circuit is set to Mn
IE Sari, Ru.

Note that if the transistor IO of the constant voltage bias circuit is thermally coupled to the output trannostar 1 or 2 and -C is set, then J
The voltage supplied to the constant voltage bias circuit can be changed in response to the temperature of the output transistor, which varies depending on the temperature.

As described in detail, according to the present invention, steady temperature changes due to environmental temperature etc. in the output transistor can be prevented.
Output that follows temperature rise due to sudden heat generation
・It has the effect of being able to always maintain a constant flow of ・Guiasumi flowing to Rannosta.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the general configuration of a conventional power width section, and FIG. 2 is a circuit diagram of an embodiment of the present invention. J, 2 Output 1-Lannostar, 5, 6...IM
5. Nostar, 8.9 Bias setting resistor of constant voltage bias circuit, 10. Transistor, 11. Voltage signal U source, 12. Constant current source, 16. Temperature sensor, 17
-Output signal detection circuit, 18 system [sum circuit.

Claims (2)

[Claims] (1) In a power amplifier including an output transnostar, a drive transistor that drives the output transistor, and a constant voltage bias circuit that varies a bias voltage to the drive transistor, a temperature sensor that detects the temperature of the output transistor; Output signal (6! output circuit and the yxx
and means for correcting the bias voltage supplied by the constant voltage and bias circuit so that the bias current of the output transistor is constant by processing each detection signal of the output signal detection circuit. power amplifier. (2) The constant voltage bias circuit is thermally coupled to the output transistor, and the constant voltage bias circuit supplies a voltage corresponding to the temperature of the output transistor, which varies depending on the environmental temperature. The power amplifier according to claim 1, wherein the bias voltage j is changed.