JPS637045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier that prevents excessive current from flowing through a transistor when a voltage is applied from the output side.

Conventionally, when a large output power amplifier is required, such as when a broadcast system has a large number of speakers, multiple small-capacity power amplifiers are used instead of a single power amplifier to satisfy the above requirements. The above requirements are generally met by connecting them in parallel. Such a device is advantageous in manufacturing, management, transportation, etc. because the weight of the amplifier itself can be reduced.

However, this configuration in which a plurality of amplifiers are connected in parallel has the following drawbacks. In other words, if some of the power amplifiers out of multiple power amplifiers fail to output the desired signal due to a malfunction or the like, the outputs of the other normal amplifiers are added from the output side of the failed amplifier (hereinafter referred to as reverse). Transistors as power amplification elements consume a large amount of power. As a result, the load impedance of a normal power amplifier decreases and overload occurs, resulting in a problem that even this normal amplifier breaks down. Especially if it is an amplifier with a negative feedback circuit,
When a signal is applied from the output end, the signal applied to the output end and the signal amplified by the amplifier via the negative feedback loop are in opposite phase, so the internal impedance seen from the output side of this amplifier was so low that it would overload an otherwise normal amplifier.

Also, by disconnecting the failed amplifier,
The one that attempts to solve the above drawbacks is
This is shown in Publication No. 15254. However, this method has a problem with the configuration for detecting amplifier failure.
In other words, amplifier failures can be caused by a variety of things, such as failures in the amplification elements, blown fuses, failures in the power supply circuit, or failures in the input section, but all of these failures can be detected by one type of failure detector (for example, a current-limiting relay). However, it is difficult to detect this problem by using various fault detectors, and the configuration inevitably becomes complicated.

The present invention has been made in order to eliminate the drawbacks of the above-mentioned conventional devices, and while having a simple configuration, it can cope with any failure of a power amplifier and prevents a failed amplifier from overloading other normal power amplifiers. Therefore, it is an object of the present invention to provide a power amplifier that does not cause failure of other normal power amplifiers.

When a failed power amplifier fails to output the desired signal and is reverse driven, the present invention limits the short-circuit current that tends to flow through the transistor, thereby allowing other normal power amplifiers connected in parallel to It is characterized by the fact that it does not overload the vehicle.

An embodiment of the present invention will be described below with reference to the drawings. A1, A2, . . . An are power amplifiers, and are connected in parallel. These amplifiers A
1, A2, ...An are all the same, so
Only A1 shows the configuration in detail, and the others are omitted.
1 is an input signal terminal, and 2 is an output terminal.
3 is a driver amplifier circuit connected to the input signal terminal 1, and the output terminal of this amplifier circuit 3 is connected to the primary winding of a driver transformer 4. These driver amplifier circuit 3 and driver transformer 4 form an input signal circuit I. The amplifier circuit 3
is connected to power supply 5 via fuse F1. Reference numerals 6 and 7 indicate first transistors, each having its collector connected to the positive terminal of the power source 5. In addition, impedance elements 8 and 9 are connected to the primary windings of an output transformer 10 in sequence, and the intermediate point of the primary windings is connected to the negative pole of the power source 5 via fuses F2 and F3, respectively. are doing. These first transistors 6, 7
An input signal is supplied from the input signal circuit I to the base emitter of. 11 and 12 are bias circuits, respectively, and each of the first transistors 6 and 7
It is set up correspondingly. These bias circuits 11 and 12 constantly supply a predetermined amount of bias to each of the first transistors 6 and 7 from the power supply 5, thereby controlling the first transistors 6 and 7.
This is to operate in a region where the V _BE - I _C characteristics are linear, thereby eliminating crossover distortion. Therefore, even when the transistors 6 and 7 are not supplied with an input signal from the input signal circuit I, a small base current flows through these bias circuits 11 and 12, and therefore a small collector current flows. . However, this bias value may be small, and when transistors 6 and 7 are turned on by being supplied with an input signal of the polarity shown, and a voltage is present in the primary winding of output transformer 10 (for example, in the figure, transistor 6 is (when it is turned on and a voltage of the polarity shown is occurring in the primary winding),
This is done so that the potential at point C (point D) in the figure does not exceed the potential at point A (point B). Each of these bias circuits 11 and 12 includes resistors 13 and 14, a common resistor 15, and first diodes 16 and 17 for preventing backflow. 18 and 19 are second diodes,
It is connected between the collectors and emitters of the first transistors 6 and 7 so that the polarity is opposite to that of the collectors and emitters. In this embodiment, second diodes 18 and 19 are connected in parallel with the series circuit of transistors 6 and 7 and impedance elements 8 and 9, and the present invention includes this embodiment. A second diode 1 like this
8 and 19 prevent a reverse voltage from being applied between the collector and emitter of the first transistors 6 and 7;
This is for bypassing the power supply 5. 2
Reference numerals 0 and 21 designate second transistors, which are provided corresponding to the first transistors 6 and 7. That is, these second transistors 20, 21
The collector emitter is connected to the output transformer 10.
and the connection point A (point B) between the primary winding and the impedance elements 8 and 9, and the bias circuits 11 and 1.
2 and the bias supply point C (point D). Further, its base is connected to the bases of the first transistors 6 and 7. 22, 23
is the third diode for backflow prevention. Then, as described above, the input signal is supplied from the input signal circuit I, and the power amplifier A1 operates normally.
When transistor 6 or 7 is on, a voltage whose peak value is close to the voltage of power supply 5 is generated in the primary winding of output transformer 10, so that the potential at point C or D in the figure is equal to A in the figure. It is set so that the potential does not become higher than the potential at point or point B.

Next, the operation of this embodiment will be described. When all amplifiers A1, ...An are normal, driver transformer 4's 2
Positive and negative input signals are generated alternately in the next winding, and the first
The transistors 6 and 7 operate alternately to cause the output transformer 10 to generate an amplified signal. That is, when a signal of the polarity shown appears in the driver transformer 4, a signal in the positive direction is applied to the base of the first transistor 6 to the emitter, so it is activated.
Power supply 5 - Fuse F1 - First transistor 6 -
A current flows through the impedance element 8 - the primary winding of the output transformer 10 - the fuse F2 - the power supply 5 circuit. The other first transistor 7 does not operate because a negative signal is applied to its base and emitter. At this time, the second transistor 20 is also turned on and a current attempts to flow between its collector and emitter, but its collector potential is fixed by the bias circuit 11, and its emitter potential is the same as that of the first transistor. When transistor 6 operates, the potential at point A in the figure of the primary winding of output transformer 10 becomes higher than the potential at point C in the figure, so that the collector-emitter current does not flow. Next, when a signal of the opposite polarity appears on the driver transformer 4, one first transistor 6 becomes inactive, and the other first transistor 7 becomes active. In this way, all the power amplifiers A1, . . . An operate and output the desired signals, so that a total output appears at the output terminal 2.

Then, for example, if the power amplifier A1 stops outputting a signal due to a failure in the driver amplifier circuit 3,
The output of another normal power amplifier is applied to the secondary winding of the output transformer 10. For example, when a voltage with the polarity shown is applied, voltage also appears in the primary winding,
It will be applied to each transistor 6, 7.
Therefore, one first transistor 6 does not turn on, but the other first transistor 7 tries to turn on because its emitter has a lower potential than the base fixed by the bias circuit 12. Therefore, a closed circuit of power supply 5 - fuse F1 - first transistor 7 - impedance element 9 - primary winding of output transformer 10 - fuse F3 - power supply 5 is formed, and a large amount of current tends to flow.
However, at this time, the second transistor 2
1 turns on because the emitter potential of the first transistor 7 falls below its base potential, similarly to when the emitter potential of the first transistor 7 falls below its base potential. As a result, a circuit including power supply 5 - fuse F1 - resistor 14 - diode 23 - second transistor 21 - primary winding of output transformer 10 - fuse F3 - power supply 5 is formed. As a result, the first transistor 7
bias and limit base current.
Therefore, it is possible to prevent a large amount of current from flowing through the first transistor 7. Note that the resistor 14 performs a current limiting effect on the current flowing through the second transistor 21. When a voltage with a polarity opposite to that shown in the figure appears, a similar effect occurs in one of the first transistors 6 to prevent a large amount of current from flowing. Therefore, power consumption in the failed power amplifier A1 is small, and other normal power amplifiers are not overloaded.

For example, if the collector-emitter of the first transistors 6 and 7 is broken and short-circuited,
Fuses F2 and F3 are disconnected to protect the amplifier, and the reverse drive signal can be disconnected, so that normal amplifiers are not overloaded.

Note that it is clear that the same effect will occur even if other power amplifiers fail. In addition, the details of the failure are
Even if it is not a failure of the driver amplifier circuit, for example, one of the amplification elements is destroyed, the power supply circuit is broken, or a fuse is blown, the expected signal cannot be output, and as a result, the output terminal It is the same in that output signals from other power amplifiers can be added to it, and it functions as described above to prevent overloading.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways. For example, the power amplifier of the present invention can be used alone, and is applicable both when used alone and when a plurality of power amplifiers are connected in parallel.

As detailed above, the present invention is capable of reducing the bias of the first transistor and preventing a large amount of current from flowing through the first transistor when a voltage is applied to the output transformer from the outside. be. Therefore, even if one of the multiple units fails when multiple units are connected in parallel,
It does not overload other normal power amplifiers and does not cause other normal power amplifiers to malfunction. Moreover, the configuration is extremely simple,
It can handle any kind of breakdown.

[Brief explanation of the drawing]

The figure is a partially omitted circuit diagram showing an embodiment of the present invention. A1,... An... Power amplifier, 6, 7... First transistor, 8, 9... Impedance element, 1
0... Output transformer, 11, 12... Bias circuit,
16, 17...First diode, 18, 19... Second diode, 20, 21... Second transistor, I... Input signal circuit.

Claims (1)

[Claims] 1. An impedance element and a primary winding of an output transformer are sequentially connected to each emitter side, and each collector/emitter is connected in parallel to a power supply via the impedance element and the primary winding. a pair of bias circuits each including a first diode for backflow prevention and constantly supplying a predetermined amount of bias from the power supply to the base of each of the first transistors; an input signal circuit that supplies an input signal to the base of each of the first transistors; a pair of second diodes connected in parallel with the collector and emitter of each of the first transistors and having opposite polarity; ; A collector-emitter is provided between the connection point of each of the primary windings and the impedance element and a bias supply point of the bias circuit to each of the first transistors, and the base is connected to the base of the first transistor. It is connected to the base, and a voltage is applied to the output transformer from the outside.
When a voltage is induced in the next winding, it turns on and the first
A power amplifier comprising: a pair of second transistors that reduce the bias of the transistors;