Sanyo Electric Co., Ltd.

Kenichi Kokubo

Takayuki Taira

Masanori Fujisawa

Koji Tatani

There is disclosed a power amplification device for BTL-driving a load with a half-wave signal whose output direct current level is set close to an earth level, in which output signals of first and second output amplifiers (2) and (3) are added in an adder circuit (10). A higher output signal is selected from the two output signals and generated as an output signal c. Output currents of variable current sources (8) and (9) of the first and second output amplifiers (2) and (3) are controlled in response to the output signal c to change operating currents of the first and second output amplifiers (2) and (3). The operating currents are enlarged only when the output signals of the first and second output amplifiers (2) and (3) are enlarged. Thereby, the efficiency of the operating current of BTL drive type output amplifier is enhanced.

Power amplification device

When first and fourth output transistors (15) and (18) are turned on, the voltage at the connecting point between the first and second driving transistors (19) and (20) drops. When second and third output transistors (16) and (17) are turned on, the voltage at the connecting point between third and fourth driving transistors (21) and (22) drops. As a result, voltage differences between the collectors and emitters of the first and second input transistors (2), (3) and the first and second current source transistors (13) and (14) increase so that saturation of the first and second current source transistors (13) and (14) can be prevented. Since a resistor is connected between a connecting point between upper and lower output transistors and a connecting point between upper and lower driving transistors having inverted phases from the former two transistors, current is limited and oscillation can be prevented.

BTL amplifying circuit

In a power amplifier apparatus comprising four amplifiers, each amplifier is adapted to amplify the half-wave output signal of a first differential amplifier by means of second and third output amplifiers (2, 3) to drive load (4) by their output amplifying signals and add the output amplifying signals by means of a non-linear circuit (5) in order to control the output DC voltage with the output signal of a second differential amplifier (6) according to the difference between the signal obtained by the non-linear addition and reference value Vref. Feedback signals X and Y of the left front first differential amplifier (1LF) and feedback signals X' and Y' of the right rear first differential amplifier (1RR) are applied to a single clip detection circuit 9 so that any clip in the output signal of the first and second output amplifiers can be detected by means of the feedback signals X, Y, X' and Y'.

Power amplifier apparatus

In a power amplifier apparatus, a positive output signal of left front output amplifier (2LF), a negative output signal of left rear output amplifier (3LR), a negative output signal of right front output amplifier (3RF), and a positive output signal of right rear output amplifier (4RR) are applied to an adder (9), which selects the signal showing the highest level out of the four signals and generates a voltage corresponding to the selected signal. Switching power source (10) is adapted to operate according to the output signal of the adder (9) and produces a power source voltage to each of the high efficiency amplifiers. The positive output signal of the left front output amplifier and that of the right rear output amplifier are identical and substantially in-phase, whereas the negative output signal of the left rear output amplifier and that of the right front output amplifier are identical and substantially in-phase. Thus, a power source voltage is generated for each of the high efficiency amplifiers while providing fewer adders than the number of loads.

The present invention provides a B class push-pull amplifying circuit suitable for use in a headphone type tape recorder and the like. The amplifying circuit utilizes a current mirror circuit system in its output transistors to provide an idling current for compensating for crossover distortion by using the mirror ratio. The current mirror circuit system includes a pair of output current mirror circuits complimentarily coupled with each other. One branch of these output current mirror circuits includes a diode-connected transistor, the emitter current path of which is ON-OFF controlled by a drive transistor in the other branch. Thus, when no signal is input, the respective one of the current mirror output circuits complimentarily coupled with each other functions as a current mirror circuit such that the small idling current determined by the mirror ratio will pass therethrough. On the other hand, the inputting of a signal causes the output of the opposite side drive transistor to make the current mirror circuit inoperative. The output transistor functions as a normal amplifying circuit. An amplification factor h.sub.FE provided at this time can reliably assure a sufficiently large amplification degree.

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Ota, Japan

Kenichi Kokubo