JPH04139908A - Bias circuit for push-pull amplifier - Google Patents

Abstract

PURPOSE:To reduce power consumption and to reduce the cost of a transformer by devising the circuit so that a DC bias flows to two transistors(TRs) in series so as to make a bias current nearly a half. CONSTITUTION:Other terminal of a coil 19 connecting to a feeding terminal (power supply terminal) 18 connects to a collector of a TR 5 and an emitter of the TR 5 is connected to a collector of a TR 6 through the series connection of a resistor 21 and a coil 20. The emitter of the TR 6 connects to ground via a resistor 12, the collector of the TR 5 connects to one terminal of a primary winding of an output transformer 2 via a capacitor 22 and the collector of the TR 6 is connected to the other terminal of the primary winding of the output transformer 2 via a capacitor 23. Thus, the DC bias flows to the two TRs 5, 6 in series. Thus, the current is halved in comparison with a current of a conventional circuit, a tap of the output transformer 2 is not required to reduce the cost of the transformer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bias circuit for a push-pull amplifier, and particularly to a bias circuit for a push-pull amplifier that operates with low power consumption and has low distortion.

[Conventional technology]

An example of a conventional push-pull amplifier is shown in FIG. 2 and will be described.

In this Figure 2, 1 is an input transformer, 2 is an output transformer, 3 is an input terminal, 4 is an output terminal, 5.6 is a transistor, 7, 8, 9, 10, 11° 12 is a resistor, 13.
14, 15, 16, and 17 are capacitors, and 18 is a power supply terminal that is a power supply terminal.

The collectors of transistors 5 and 6 are connected to both ends of the primary winding of output transformer 2, and power is supplied to the intermediate tap of the primary winding of output transformer 2, and the emitters of transistors 5 and 6 are connected to each other. Each is grounded via a resistor 11, 12.

In the push-pull amplifier configured in this manner, in order to use the transistors 5 and 6 with good distortion, it is necessary to allow sufficient collector current to flow in both transistors. In order to cause this current to flow in the opposite direction from the intermediate tap of the primary winding of the output transformer 2, the magnetic flux of the transformer caused by this bias current is generated in the opposite direction, and the overall effect of the primary winding of the output transformer 2 cancels out. This prevents magnetic saturation of the transformer due to direct current.

In FIG.
However, at this time, the same amount of current flows from the center tap in the opposite direction of the winding, so that the magnetic flux due to this power supply 'ft flow is canceled out for the winding of the output transformer 2 as a whole.

[Problem a that the invention seeks to solve]

In the push-pull amplifier described above, in order to improve distortion characteristics, collector current is passed through both transistors in parallel, so there is a problem that current consumption is large. Furthermore, since the output transformer requires an intermediate tap, there is a problem that the transformer becomes expensive.

[Means to solve the problem]

The bias circuit of the push-pull amplifier of the present invention connects the other terminal of the first coil connected to the power supply terminal to the collector of the first transistor, and connects the emitter of the first transistor to the first resistor. the second through the second coil
The emitter of this second transistor is grounded through a second resistor, and the collector of the first transistor is connected to the primary winding of the output transformer through a first capacitor. The collector of the second transistor is connected to the other terminal of the primary winding of the output transformer via a second capacitor.

[Effect]

In the present invention, a DC bias current supplied from a power supply terminal flows through two transistors in series.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a bias circuit for a push-pull amplifier according to the present invention.

In Fig. 1, the same numbers as in Fig. 2 indicate corresponding parts, 19.20 is a coil, 21 is a resistor, 22.2
3 is a capacitor.

Then, the other terminal of the coil 19 connected to the power supply terminal (power supply terminal) 18 is connected to the collector of the transistor 5, and the emitter of the transistor 5 is connected to the collector of the transistor 6 through the resistor 21 and the coil 20 in series. The emitter of transistor 6 is connected to ground via resistor 12, the collector of transistor 5 is connected to one terminal of the primary winding of output transformer 2 via capacitor 22, and the collector of transistor 6 is connected to ground via resistor 12. 23 to the other terminal of the primary winding of the output transformer 20.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

The DC bias current supplied from the power supply terminal (power supply terminal) 18 passes through the coil 19 to the transistor 5 and the resistor 21.
．． Coil 20. The current flows into transistor 6.

With this, two DC bias expansion transistors 5 and 6
Because the two flow in series, the current can be halved compared to conventional ones. Further, the middle tap of the output transformer 2 can be eliminated, and the transformer can be made inexpensive.

〔Effect of the invention〕

As explained above, in the present invention, since the DC bias is caused to flow through two transistors in series, the bias current can be halved and power consumption can be reduced. Moreover, the intermediate tap of the output transformer can be eliminated, and the cost of the transformer can be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a bias circuit for a push-pull amplifier according to the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional push-pull amplifier. 2...Output transformer, 5,6...Transistor, 12...Resistor, 18...Power supply terminal (power supply terminal), 19.21-...Coil, 21
...resistor, 22.23...capacitor.

Claims (1)

[Claims] The other terminal of the first coil connected to the power supply terminal is
The emitter of this first transistor is connected to the collector of a second transistor through a first resistor and a second coil, and the emitter of this second transistor is connected to a collector of a second transistor. grounded through a resistor, the collector of the first transistor is connected to one terminal of the primary winding of the output transformer through a first capacitor, and the collector of the second transistor is connected to a second capacitor. A bias circuit for a push-pull amplifier, characterized in that the bias circuit is connected to the other terminal of the primary winding of the output transformer via.