JPS5977707A - Bias circuit device - Google Patents

Abstract

PURPOSE:To suppress the change in a bias current due to the fluctuation in the collector loss by fitting an output transistor (TR) and its bias circuit to a radiator and controlling the bias circuit with a bias voltage in response to the temperature difference detected at a heat sensing resistive element. CONSTITUTION:The output TRs1, 2 and a TR3 giving a bias to the TRs1, 2 are fitted to a radiator 13. A resistive element 11 of negative temperature dependancy is fitted to the vicinity of the output TRs 1, 2 of the radiator 13, and a negative characteristic temperature dependancy resistive element 12 is fitted apart from the output TRs1, 2 of the radiator 13. A difference of resistance of the elements 11, 12 is detected by a comparator amplifier 10 and a detecting output controls a bias voltage variable device 9. The fluctuation in the bias current is suppressed because of the fluctuation in the collector loss of the output TRs1, 2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a bias circuit device that can be used in a 5EPP output stage of a low distortion power amplifier for audio.

1. Structure of conventional example and its problems FIG. 1 shows an example of a conventional bias circuit. In Figure 1, 1 and 2 are output transistors, 3 is a bias transistor, 4 and 6 are DC power supply terminals, 6.7 is a signal input terminal, 8 is an output terminal, and R1 and R2 are bias setting resistors. . Then, the bias voltage vb applied between the base and emitter of the output transistors 1 and 2 is as follows, where Vbe3 is the voltage between the base and emitter of the bias transistor 3.
(1) becomes.

Here, when the voltages between the base and emitter of output transistors 1 and 2 required to flow a constant bias current through output transistors 1 and 2 are respectively Vbe1 + Vbe2, "bel = Vbe2""Vbe3 = Vo 2 (T5- To) However, vO: Voltage between the base and emitter when the junction temperature of each transistor 1.2.3 is To: Tj: Assuming that the temperature characteristic is the junction temperature of each transistor 1.2.3, the output transistor 1 ，
If the temperature difference between the output transistor 2 and the bias transistor 3 is always constant, it will be Vb - (Vbe1"Vbe2), and a constant bias current can flow. However, the output signal changes and the output transistor 1. When the collector loss changes, since there is always thermal resistance between the output transistors 1 and 2 and the bias transistor 30, the temperature difference between the output transistors 1 and 2 and the bias transistor 3 changes, so the bias current changes. There are drawbacks to doing so.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks and to suppress variations in the bias current due to variations in the collector loss of the output transistor.

A first heat-sensitive resistance element is mounted on the heatsink near the output transistor, a second heat-sensitive resistance element is mounted on the heatsink away from the output transistor; A bias circuit is provided to generate a bias voltage according to the difference in temperature detected by the second heat-sensitive element and the second heat-sensitive element, and both bias circuits are connected in series.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a circuit diagram showing one embodiment of the present invention, and the same parts as those in FIG. 1 are given the same numbers and the explanation thereof will be omitted.

In FIGS. 2 and 3, 9 is a bias variable device, 10 is a comparison amplifier, 11° and 12 are negative temperature-dependent resistance elements,
13 is a heat sink. Since the resistor element 11 is installed near the output transistors 1 and 2, and the resistor element 12 is installed at a location away from the output transistors 1 and 2, there is no negative characteristic even if the temperature of the heat sink 13 changes due to changes in the ambient temperature. Although the difference in the resistance values of the temperature-dependent resistance elements 11 and 12 does not change,
Since the collector losses of the output transistors 1 and 2 change, when the temperature of the radiator 13 changes, the difference in the resistance values of the negative characteristic temperature dependent resistance elements 11 and 12 changes. Therefore, in the circuit configuration as shown in FIG. The bias voltage is compensated by the bias transistor 3 for the change in the junction temperature of the output transistors 1 and 2 due to a change in temperature, and the change in the junction temperature of the output transistors 1 and 2 due to the change in the collector loss of the output transistor 1゜2. Bias voltage variable device 9 corrects the bias voltage for 1.
can be controlled by

Effects of the Invention As described above, according to the present invention, even if the collector loss of the output transistor changes with temperature, the bias current changes as a matter of course.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a bias circuit device in a conventional example, FIG. 2 is a circuit diagram of a bias circuit device in an embodiment of the present invention, and FIG. 3 is a perspective view of a portion of the same device. 1.2... Output transistor, 3...
Bias transistor, 4, 6...DC power supply terminal, 6゜end...Signal input terminal, 8...
・Output terminal, 9...Bias voltage variable device, 10.
... Comparison amplifier, 11゜12 ... Negative characteristic temperature dependent resistance element, 13 ... Heat sink, R1,
R2...Resistance for bias setting. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3

Claims (1)

[Claims] An output transistor and a bias circuit that applies a bias to the output transistor are attached to a heat sink, a first heat-sensitive resistance element is attached to the heat sink near the output transistor, and a first heat-sensitive resistance element is attached to the heat sink away from the output transistor. A second heat-sensitive resistance element is attached to the above-mentioned first
A bias circuit device is provided with a bias circuit that generates a bias voltage according to the difference in temperature detected by a second heat-sensitive element and a second heat-sensitive element, and the two bias circuits are connected in series.