JPS6042645B2 - amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit used in the output stage of audio equipment.

Amplifying circuits used in the output stage of audio equipment employ class B operation with high power efficiency.

However, if the power efficiency is good, it will always be about 7
The power efficiency is approximately 0%, and the power efficiency further decreases when the signal is small. The present invention has been made in view of the above points, and
It is an object of the present invention to provide an amplifier circuit that can increase power efficiency, reduce transistor loss, and thereby enable miniaturization of transformers and heat sinks.

Embodiments of the present invention will be described below based on the drawings.

First, in FIG. 1, reference numeral 11 denotes an input signal source, and this input signal source 11 is connected to the base of an NPN type transistor 12, which is a first transistor. The emitter of this transistor 12 is connected to the movable terminal 1 of the switch 14 through the load 13.
4a, and this movable terminal 143 is grounded. Further, the first DC power supply 15 and the second DC power supply 16 are connected in series, and the common connection between the negative electrode of the first DC power supply 15 and the positive electrode of the DC power supply 16 is connected to the first fixed terminal of the switch 14. Further, the negative terminal of the DC power supply 16 is connected to the second fixed terminal 140 of the switch 14, and the main power of the first DC power supply 15 is connected to the collector of the transistor 12. Next, the operation of the above amplifier circuit will be explained. When the signal is small, the movable terminal 1 of the switch 14
43 is connected to the first fixed terminal 14, and the movable terminal 143 switches to the second fixed terminal 140 when a large signal is received.

Therefore, when the signal is small, the transistor 12 operates with a low power supply voltage from only the first DC power supply 15, and when a large signal is generated, the transistor 12 operates at a high power supply voltage from the first DC power supplies 15 and 16. Therefore, according to such an amplifier circuit,
Since the transistor 12 operates with a low power supply voltage when the signal is small, and operates with a high power supply voltage when the signal is large, the power efficiency is increased, and the loss of the transistor swatter 12 is reduced. Miniaturization becomes possible.

Output stage amplifier circuits are often configured so that a positive signal is amplified by one transistor and a negative signal is amplified by another transistor (push-pull configuration), and the present invention is applied to this amplifier circuit. The first embodiment shown in FIG. 2 is applied.

Therefore, a PNP type transistor 17, which is a second transistor whose base is connected to the input signal source 11 in the same way as the NPN type transistor 12, is added to the amplifier circuit of FIG. 1, and its emitter is connected to the transistor 12. Common connection with emitter. Further, a second DC power supply 18 is connected in series to the third DC power supply 16, and the negative pole of the second DC power supply 18 is connected to the collector of the transistor 17. With this configuration, a positive signal is amplified by the NPN type transistor 12;
The related operations are the same as in the principle diagram above. On the other hand, the negative signal is amplified by the PNP transistor 17, and at this time, when the signal is small, the movable terminal 143 of the switch 14
is connected to the second fixed terminal 142, and the movable terminal 143 is connected to the first fixed terminal 141 at the time of a large signal. That is, the transistor 17 is connected to the second DC power supply 1 when the signal is small.
It operates with a low power supply voltage consisting of only 8, and the second
and third DC power supplies 16 and 18, which operate at a high power supply voltage. Note that the second to fourth embodiments described below all have a push-pull configuration.

The second implementation shown in Figure 3 divides the current power source into a low-voltage DC power source and a high-voltage DC power source, and automatically connects and disconnects the low-voltage DC power source to a transistor using the switching action of a diode. This is an example. Therefore, this. In the embodiment, first and second DC power supplies 19 and 20 with low voltage are provided, and a third DC power supply 21 with high voltage is provided, and the positive electrode of the first DC power supply 19 is connected to the It is connected to the collector of the NPN type transistor 12 and connected to I.
The collector of P-type transistor 17 is connected to the negative electrode of second DC power supply 20 via diode 23 . Also,
The negative pole of the first DC power supply 19 and the positive pole of the second DC power supply 20 are connected to the movable terminal 143 of the switch 14, and the third DC power supply 21 is connected to the first fixed terminal 141 of the switch 14.
The positive electrode of the third DC power supply 21 is connected to the second fixed terminal 142 , and the negative electrode of the third DC power supply 21 is connected to the second fixed terminal 142 . Further, the positive electrode of the third DC power supply 21 is connected to the collector of the transistor 12 via a diode 24 as a switch means, and the collector of the transistor 17 is connected to the third DC power supply 21 via a diode 25 as a switch means. connected to the negative terminal of That is, when the signal is small, the movable terminal 143 of the switch 14 is not connected to either the first or second fixed terminal 141, 142, and therefore, at this time, the first and second DC power supplies 19, 20 act as switching means. diode 22,
It is connected to transistors 1J2 and 17 via 23, and these transistors 12 and 17 operate at a low power supply voltage.

On the other hand, when a large signal occurs, the movable terminal 14 of the switch 14
3 is connected to the second or first fixed terminal 142, 1, and the third DC power supply 21 is connected to the transistors 12, 17 via the diodes 24, 25, so that the transistors 12, 17 are connected to the high power supply. Operates on voltage. At this time, the diodes 22 and 23 are reverse biased and turned off, and by turning off the diodes 22 and 23, the first and second
DC power supplies 19 and 20 are disconnected from transistors 12 and 17. The third embodiment shown in FIG. 4 uses a DC power source as shown in FIG. 2 and embodies switching of the power source. Therefore, in this embodiment, the emitter of the transistor 28 is connected to the common connection portion (first common connection portion) between the positive electrode of the second DC power source 18 and the negative electrode of the third DC power source 16, The emitter of the transistor 33 is connected to a common connection between the negative electrode of the first DC power supply 15 and the positive electrode of the third DC power supply 16 (second common connection), and the cathode of the diode 29 is connected to the second common connection. The anode of the diode 34 is connected to the first common connection. That is, when the signal is small, the first and second DC power supplies 15 and 18 are connected to the transistors 12 and 17 via the diodes 29 and 34, and the transistors 12 and
17 operates with a low power supply voltage. On the other hand, when the signal is large, the transistors 28 and 33 are turned on, while the diodes 29 and
34 is turned off, the first and second DC power supplies 15,
18, second and third DC power supplies 18, 16 are connected to transistors 12, 17 via transistors 28, 33, and these transistors 12, 17 operate at a high power supply voltage. In the configuration shown in FIG. 3, at the time of a large signal, the third DC power supply 21 having a high power supply voltage is connected to the transistor 12,
The fourth embodiment shown in FIG. 5 is designed to automatically connect to 17.

Therefore, in this embodiment, the input signal source 11 is connected to the base through the diode 26 and the Zener diode 27 serving as the detection means. NPN type transistor 28 connected to
The emitter of the PNP type transistor 33 is connected to the negative electrode of the third DC power supply 21, and the emitter of the PNP type transistor 33 whose base is connected to the input signal source 11 via the diode 31 and the Zener diode 32 serving as the detection means is connected to the negative electrode of the third DC power supply 21. It is connected to the positive terminal of the DC power supply 21, and further connected to the collectors of the transistors 28 and 33, the negative terminal of the first DC power supply 19,
The positive terminal of the second DC power supply 20 and the other end of the load 13 (the side opposite to the transistors 12 and 17) are grounded. That is, when a large signal is generated, the transistors 28 and 33 are positively biased and turned on via the Zener diodes 27 and 32, so that the high power supply voltage of the third DC power supply 21 is applied to the transistors 12 and 33 via the transistors 28 and 33. 17
will be supplied to The first to fourth embodiments have been described above, and in each of these embodiments, the transistor is operated at a low power supply voltage when a signal is small, and switched to a high power supply voltage when a large signal is operated. Power efficiency can be increased and transistor loss can be reduced, thereby making it possible to downsize the transformer and heat sink.

Furthermore, in either case, the power supply voltage can be switched in the push-pull configuration that is currently widely used, and its practicality is high. As detailed above, the present invention provides an amplifier circuit that can increase power efficiency and reduce transistor loss, thereby making it possible to downsize transformers and heat sinks. can.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the principle of an amplifier circuit according to the present invention, and FIGS. 2 to 5 are circuit diagrams showing other embodiments of the present invention. 12: first transistor, 13: load, 14: switch, 15, 19: first DC power supply, 16, 21: third DC power supply, 17: second transistor, 18, 20: second DC power supply Power supply, 22, 23, 26, 31: diode,
24, 25, 29, 34: Diode as switch means, 27, 32: Zener diode as detection means,
28: Transistor, 33: Transistor.

Claims (1)

[Claims] 1 first and second transistors connected in a push-pull manner, first and second power supplies correspondingly connected to the first and second transistors, output levels of input signals to each of the transistors, and a detection means for detecting polarity; and a third power source different from the first and second power sources is switched and connected to the first or second power source according to a determination signal from the detection means, and the third power source is switched to the first or second power source. An amplifier circuit characterized in that it comprises switch means adapted to increase the voltage supplied to the first or second transistor.