JPS6153889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an output transformerless direct coupling power amplifier.

As shown in FIG. 1, a conventional output transformerless directly coupled power amplifier has transistors 12 and 1.
5 and a resistor 14 constitute a differential amplifier circuit, and the power supply 7
The voltage passed through switch 6 is removed by resistor 16 and capacitor 1 to remove unnecessary alternating current components.
A bias voltage is applied to the base of a transistor 12 which is divided by 1 and 11, and its output is outputted from a single-ended push-pull circuit consisting of complementary transistors 21 and 22 through a drive transistor 18. transistor 12
The collector is connected to a ground terminal through a load resistor 13, and the output is taken out from this collector and applied to a drive transistor 18. The emitter of the drive transistor 18 is grounded, and the collector is connected to the power supply terminal d through a level shift circuit 20 having a resistor 19 and a plurality of (three in this case) diodes connected in series in the forward direction. Further, at both ends of the level shift circuit 20, complementary transistor configurations 21 and 2 connected to Darlington are connected.
The terminal corresponding to the base of No. 2 is connected. Terminals corresponding to the emitters of the complementary transistor structures 21 and 22 are connected to each other (terminal e) to form a single-ended push-pull circuit, which is outputted to a load 5 via a capacitor 4. Terminal e is connected to the base of transistor 15 through resistor 17. Furthermore, in terms of AC, a negative feedback circuit is formed by resistors 17, 2 and capacitor 3, and the gain is adjusted.

In such a power amplifier, when the power switch 6 is closed, the power supply voltage is applied to the complementary transistor structure 21 through the resistor 19, so that the terminal corresponding to its emitter rises. Capacitor 4 quickly connects terminal e to supply voltage with low impedance of complementary transistor arrangement 21.
The potential of increases. This voltage is applied to terminal c via resistor 17. At this time, capacitor 3 resistor 2
The time constant determined by resistor 17 and capacitor 3 is designed to be sufficiently large for the frequency normally used, and on the other hand, resistor 17 is set sufficiently larger than resistor 2 to obtain the necessary voltage gain, so the time constant determined by resistor 17 and capacitor 3 The constants are designed to be quite large. Also, considering the moment when the power switch 6 is closed, a voltage that increases with a time constant determined by the resistor 16 and the capacitor 1 is applied to the terminal b, which is divided by the resistors 10 and 11, and is applied to the base of the transistor 12. resistance 1
The time constant determined by the resistor 17 and the capacitor 1 is generally not very large and is sufficiently smaller than the time constant determined by the resistor 17 and the capacitor 3. Therefore, the voltage at terminal c rises later than the voltage at terminal b, and the voltage at output terminal e rises almost to the power supply voltage, and then the voltage at terminal c rises to the voltage at terminal b, and they match. At this point, transistor 12 becomes conductive, a voltage is applied across resistor 13, drive transistor 18 becomes conductive, its collector potential drops, and complementary transistor arrangement 22 becomes conductive, starting normal operation.

As described above, in the conventional output transformerless type direct coupling power amplifier, the output transistor is driven at the same time as the power is turned on, so a voltage close to the power supply voltage appears at the output terminal, and this is caused by the resistance of the speaker's voice coil. A large pulse-like voltage is applied to the speaker's voice coil after being differentiated by the coupling capacitor, producing abnormal noise and often causing the voice coil to break due to excessive current.

An object of the present invention is to obtain a direct coupling power amplifier that does not output an abnormally excessive current when the power is turned on.

According to the present invention, a single-ended push-pull power amplifier, a driving amplifier circuit for driving the single-ended push-pull power amplifier, a pre-stage amplifier, and a line voltage fluctuation removal circuit serving as a power supply circuit for the pre-stage amplifier are provided. In the direct-coupled power amplifier, a transient voltage variation of the power supply voltage is detected based on a transient variation of the power supply voltage applied to the direct-coupled power amplifier and a voltage generated by a filter time constant circuit of the line voltage removal circuit. The output of the detection means is used to connect the input terminal of the single-ended push-pull power amplifier to the reference voltage position, and the switch means conducts during the voltage transient fluctuation period when the direct coupling power amplifier is turned on and shuts off during normal operation. to obtain a power amplifier which suppresses a transient output of the direct coupling power amplifier during a period of transient fluctuation of the power supply voltage.

In other words, in order to prevent an abnormally excessive current from being output when the power is turned on, the collector potential of the drive transistor that drives the push-pull circuit should gradually rise when the power is turned on, and the voltage at the output terminal should also be set slowly. It is sufficient to prevent an excessive pulse-like current from being output to the voice coil of the speaker by increasing the current.

The present invention will be explained below with reference to the drawings.

In FIG. 2 showing an embodiment of the present invention, the same parts as in the conventional power amplifier (see FIG. 1) are given the same reference numerals, and the different parts are the transistor 23.
The collector of the transistor is connected to the power supply terminal d, the emitter is connected to the resistors 10 and 14, and the base is connected to the power supply terminal d through the resistor 24 and grounded through the terminal a and the capacitor 1. 25 has its base connected to terminal a, its collector connected to power supply terminal d, and its emitter connected to the base of transistor 26 and grounded via switch means 27 and current source 28. The emitter is connected to the connection point between the resistor 19 and the level shift circuit 20, and the collector is grounded.

In the power amplifier having the above configuration, the transistor 23, the resistor 24, and the capacitor 1 constitute a line voltage fluctuation removal circuit, and the switch means 27 is closed during a voltage transition period when the power is turned on, and is opened during normal operation. When the power is turned on, the voltage at terminal a changes to resistance 24.
is applied to the base of the rising transistor 25 with a time constant determined by the capacitor 1. Switch means 2
7 is closed, the emitter of transistor 25 rises with a time constant equal to the time constant of the voltage at terminal a, and since this voltage is applied to the base of transistor 26, its emitter rises in the same way as the voltage at terminal a. , current is supplied from the power supply terminal d through the resistor 19. Therefore, complementary transistor configuration 2
The voltage at the base of resistor 2 is similar to the voltage at terminal a.
4 and the time constant of capacitor 1, and as a result, the output terminal e rises slowly, and the capacitor 4 is charged across both ends of the capacitor 4, and no pulse-like excessive current flows through the voice coil of the speaker, causing abnormal sound. It doesn't even come out. The voltage at the output terminal e charges the capacitor 3 through the resistor 17, and when the voltages at the terminals b and c match, the complementary transistor structure 22 becomes conductive and starts steady operation as described in the description of the prior art. In the embodiment of FIG. 2, resistor 24
The time constant determined by the resistor 17 and the capacitor 1 is set to a value almost close to the time constant determined by the resistor 17 and the capacitor 3. In the line voltage fluctuation removal circuit, even if the capacitance value of capacitor 1 is not very large, the resistor 24
Since the resistance value of can be made large, the time constant becomes a relatively large value. This is because the voltage drop across the resistor 24 during steady operation is determined only by the base current of the transistor 23, which is sufficiently small. Also, during normal operation, the switching means 27 is open, so that the transistor 26 is always cut off and does not disturb the base bias of the complementary transistor arrangement 21.

FIG. 3 shows another embodiment of the present invention, characterized in that the switching means 27 in the embodiment of FIG. 2 is implemented electronically, providing a power amplifier advantageous for semiconductor integrated circuits. . The difference between FIG. 3 and FIG. 2 is that transistors 31 and 33 and a resistor 32 constitute a differential amplifier circuit, and the voltage applied to the power supply terminal d is divided by resistors 29 and 30 to the base of the transistor 31. The base of transistor 33 is connected to terminal a, the emitters of transistors 31 and 33 are commonly connected and connected to power supply terminal d through resistor 32, and the collector of transistor 33 is connected to terminal a. The emitter of the transistor 35 is grounded, and the collector is connected to the emitter of the transistor 25 and the transistor 26.
It is connected to the base connection point.
The operation of the switching means using this differential amplifier circuit is such that the potential at the connection point between the resistors 29 and 30 and the potential at the terminal a are compared, and the transistor whose base is connected to the lower potential side becomes conductive, and the current source transistor 35
When the power is turned on, the transistor 33 becomes conductive, driving the current source transistor 35 and making the transistors 25 and 26 conductive. During normal operation, the potential of the terminal a changes to the resistor 2.
Since the potential is higher than the potential at the connection point between 9 and 30, transistors 33, 35, 25 and 26 are cut off.
During steady operation, a voltage greater than the voltage of the AC component (hum component) applied to power supply terminal d is applied to terminal a.
Since the potential is set between the potential of the current source transistor 35 and the potential of the connection point between the resistors 29 and 30, the current source transistor 35 will not malfunction and the base bias of the complementary transistor configuration 21 will not be disturbed. By means of the above-mentioned switch means, the rise of the output terminal e when the power is turned on is gradual, similar to the rise of the potential of the terminal a, and no excessive current is output to the voice coil of the speaker.

FIG. 4 shows another embodiment of the present invention, in which the present invention is implemented in a power amplifier equipped with a bootstrap capacitor and capable of obtaining an output signal with little voltage loss. The difference in FIG. 4 from FIG. 2 is that the collector of the drive transistor 18 is connected to the power supply terminal d through load resistors 19 and 36, and is also connected to the bases of transistors 38 and 39, and the connection between the load resistors 19 and 36. The point is connected to output terminal e through terminal g and bootstrap capacitor 8, the emitter of transistor 38 is connected to terminal g through resistor 37 and to terminal e through level shift circuit 20, and the collector is connected to transistor 41. The emitter of the transistor 41 is grounded, the collector of the transistor 39 is connected to the terminal e, the collector of the transistor 39 is connected to the terminal g, and the emitter of the transistor 41 is connected to the base of the transistor 40. The collector of the transistor 40 is connected to the power supply terminal d, and the emitter is connected to the terminal e.
The emitter of the transistor 26 is connected to the connection point between the load resistors 36 and 19. In the power amplifier having the above configuration, when the power is turned on, the potential at the terminal g rises slowly with a time constant determined by the resistor 24 and the capacitor 1, similar to the potential at the terminal a, so the voltage at the output terminal e also gradually rises, and the voltage at the output terminal e increases gradually. Excessive current is not output to the voice coil.

As described above, according to the present invention, it is possible to suppress the transient voltage when the power is turned on without impairing the functions of the conventional power amplifier.

Furthermore, since the present invention utilizes the transient voltage of the circuit for removing line voltage fluctuations, there is no increase in the number of capacitor parts, and the present invention is suitable for converting circuit elements in terminals into semiconductor integrated circuits, and the number of external lead-out terminals can also be increased. do not have.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional power amplifier, FIG. 2 is a circuit diagram showing one embodiment of the present invention, and FIGS. 3 and 4 are circuit diagrams showing other embodiments of the present invention. It is. 1, 3, 4, 8...Capacitor, 5...Load,
2, 10, 11, 13, 14, 16, 17, 1
9, 24, 29, 30, 32, 36, 37...Resistance, 12, 15, 18, 23, 25, 26, 3
1, 33, 35, 38, 39, 40, 41...Transistor, 20,34...Diode, 21,
22... Complementary transistor configuration, 7... Power supply, 2
7... Switch means, 28... Current source.

Claims (1)

[Claims] 1. In a power amplifier comprising a signal input stage, a push-pull output stage, a means for coupling these, and a line voltage fluctuation removal circuit as a power supply circuit to the signal input stage, the line voltage removal when a power supply voltage is applied. receives a voltage change based on a time constant of a filter circuit in the circuit for driving the push-pull output stage, and changes the potential of the signal output terminal with substantially the same time constant as the voltage change. 1. A power amplifier comprising: means for activating the power amplifier; and means for deactivating the means during steady state operation.