JP2565819B2 - BTL amplifier protection circuit and audio device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to storage of a BTL amplifier.
Protection circuit and an audio device using this circuit ,
Specifically, in an amplifier using the BTL (Balanced Transformer Less) method, when the output terminal to the load is short-circuited to the ground side (ground fault) or short-circuited to the power supply side (power fault), the ground fault The present invention relates to a protection system that protects an amplifier circuit for output from a short circuit.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram mainly showing a protection circuit of a BTL amplifying device in a conventional audio device . Here, 1 is an amplifier, 2 is a positive phase side amplification circuit, 3 is a negative phase side amplification circuit, 4 is a speaker, 5 and 6 are comparators,
7 is an OR gate. Amplifier 1, Positive phase side amplification circuit 2,
The negative phase side amplification circuit 3 constitutes one BTL amplifier as a whole, and drives the speaker 4 as a load. To elaborate,
Upon receiving the input signal A, the amplifier 1 outputs a pair of signals including a positive phase input signal B having the same phase and a reverse input signal C having an inverted phase.

Then, the positive phase input signal B is amplified by the positive phase side amplifier circuit 2 to be a positive phase output signal C, and the positive phase output signal C is inputted to one end of the speaker 4. Further, the anti-phase input signal D is amplified by the anti-phase side amplifier circuit 3 to be an anti-phase output signal E, and the anti-phase output signal E is input to the other end of the speaker 4. The positive-phase output signal C and the negative-phase output signal E thus generated are voltage signals whose phases are mutually inverted, and the output current C ′ by the positive-phase output signal C and the output by the negative-phase output signal E are output. The current E ′ is also a current having the same value but having different directions.

Therefore, by adopting the pair of amplifier circuits 2 and 3, the voltage and current applied to the speaker 4 are both doubled as compared with the case where the amplifier circuit is independent. That is,
Output power to load is quadrupled. Due to these advantages, the BTL method is widely used to increase the output of car stereos and other audio equipment.

By the way, in the BTL system having such a configuration, the speaker 4 is driven in a state of being floated from a reference potential such as a ground potential. If the speaker 4 is short-circuited to the ground for some reason, the load voltage will not be generated. Therefore, the positive phase side amplification circuit 2 and the negative phase side amplification circuit 3 flow an excessive current in an attempt to increase the output voltage. Therefore, there is a risk that the output transistors 2b and 2c of the amplifier circuit 2 and the output transistors 3b and 3c of the amplifier circuit 3 will be destroyed due to overload, and a protection circuit for preventing the destruction is required. In particular, in a car stereo for a vehicle, the installation environment and the usage environment are harsh and the probability of accidents is high, so a protection circuit is essential.

The comparators 5 and 6 and the OR gate 7 form a part of such a protection circuit and are circuits for detecting the state of the ground fault. In principle, the speaker 4 is driven in a state of being floated from the ground potential in the steady state, and it is detected whether or not any one of the output signals C and E is the ground potential to detect the ground fault state. It is to determine whether or not. However, since it is difficult for the output signals C and D to completely reach the ground potential due to the presence of wiring resistance and contact resistance, a comparison voltage of 2VF is generated by the two diodes connected in series in this example. The output signals C and E are compared and detected.

That is, the comparator 5 detects that the normal output signal C is below the comparison voltage (2VF), or the comparator 6 detects that the reverse output signal E is below the comparison voltage (2VF). Then, the OR gate 7 outputs the cutoff signal F as if there is a ground fault. Then, in response to the cutoff signal F, the positive phase side amplification circuit 2 and the negative phase side amplification circuit 3 stop outputting the positive phase output signal C and the negative phase output signal E, respectively. This allows
Output transistors 2b, 2c, 3b of the amplifier circuits 2 and 3,
Prevent the destruction of 3c.

[0008]

[Problems that the Invention is to Solve] In this way, conventional Oh
In the protection circuit of the BTL amplifier in the audio device,
The ground fault is detected by using a comparison voltage slightly higher than the ground potential (2VF in the above example). Therefore, if the ground fault detection is to be made reliable, this comparison voltage is raised rapidly. On the other hand, when a voltage smaller than the above-mentioned comparison voltage is output as the positive-phase output signal and the negative-phase output signal, it is erroneously detected as a ground fault state, and therefore the positive-phase amplifier circuit and the negative-phase amplifier circuit cover the entire voltage range of the power supply. Amplitude output signal cannot be output.

For this reason, the advantage of the BTL method for the purpose of increasing the output power is offset for protection, which is inconvenient in the conventional protection circuit. In addition, conventional B
The protection circuit of the TL amplifier is insufficient because it can detect the ground fault but cannot detect the power fault. The purpose of this invention is
In order to solve the problems of the conventional technology,
It is an object of the present invention to realize a protection circuit for a BTL amplifying device which can output a large power corresponding to a power supply voltage and can detect not only a ground fault but also a power fault, and an audio device having this circuit .

[0010]

The structure of the protection circuit of the BTL amplifying apparatus and the audio apparatus therefor according to the present invention which achieves the above object is a positive phase generated by amplifying an input signal.
The first of the push-pull that outputs the output signal to one end of the load
Amplification circuit and negative phase output signal generated by amplifying input signal
Second push-pull amplifier circuit that outputs the voltage to the other end of the load
And a positive phase output signal from the first amplifier circuit to one end of the load
Generating a first detected current corresponding to the current flowing to
1 current detection circuit and the positive phase output signal
Second detection corresponding to the current flowing from the first to the first amplifier circuit
The second current detection circuit that generates the current and the negative phase output signal
The current flowing from the second amplifier circuit to the other end of the load
A third current detection circuit for generating a corresponding third detection current
And a second amplifier circuit from the other end of the load by the reverse-phase output signal
A fourth current detection circuit that generates a fourth detection current corresponding to the current flowing into the first, second, third
And the fourth detected current is a current in the same direction,
When the unbalanced current, which is the difference between the sum of the detected current and the third detected current and the sum of the second detected current and the fourth detected current is equal to or greater than a predetermined value, the first and second amplifier circuits The output operation of is stopped.

The specific configuration is that a positive-phase output signal generated by amplifying an input signal is output to one end of a load, and a current to the load due to the positive-phase output signal is supplied through a first output transistor. A first current receiving a current from the load due to the positive-phase output signal via a second output transistor;
Of the positive phase output signal, the negative phase output signal having the same amplitude and the phase inverted with respect to the positive phase output signal is generated from the input signal by amplification, and is output to the other end of the load to output the negative phase output signal. A second amplifier circuit which supplies a current to the load by a signal through a third output transistor and receives a current from the load by the anti-phase output signal through a fourth output transistor; A first detection transistor whose bases and emitters are connected to the output transistor and a collector flows a first detection current, and a base and emitters which are connected to the second output transistor and whose collector is a first A second detection transistor for flowing the second detection current and a third output transistor for connecting the bases to each other and the emitters to each other so that the collector flows the third detection current. The detection transistor, the fourth detection transistor in which the bases and the emitters are connected to the fourth output transistor, and the collector causes the fourth detection current to flow, and the first detection current and the third detection current are combined. Unbalanced current detection in which the second detected current and the fourth detected current are combined into the first sum and the difference between the first and second sums is output as the unbalanced current A cutoff signal generation circuit that receives the unbalanced current and generates a cutoff signal when the absolute value of the unbalanced current is greater than or equal to a predetermined value, and the positive phase output signal and the reverse phase signal based on the cutoff signal. The output of the output signal is stopped.

[0012]

In the push-pull type BTL amplifier, the positive phase output
The current discharged on the side is sinked on the negative phase output side. That
Flows as a speaker and has the same current value logically. So
Here, in the steady state, the output current of the positive phase and the sink of the negative phase side
There is no difference in the current value. Paying attention to this point, spout on the normal phase side
Output current and sink current on the opposite phase side
Is detected by detecting the difference between these current values.
Detect normal state. In addition, for this
The same operation is performed, and the sum of the outputs on the positive phase side and the negative phase side and the sync
Take the sum of the samurai and take the difference of these sums. Like this, positive
Set the discharge side of the phase side and the opposite phase side and the sync state in the same direction.
It is detected as a current and is output to the discharge side and sink side respectively.
Detection circuit by taking the sum and then taking the difference of the sum
Can be simplified and a reliable protection operation can be performed. Ingredient
Physically, each output transistor of the push-pull and the detection transistor are connected to each other between the bases and the emitters, so that the first detection current substantially corresponds to the current flowing out by the positive-phase output signal, The second detected current substantially corresponds to the inflow current due to the positive phase output signal, and the third detected current substantially corresponds to the outflow current due to the negative phase output signal. The fourth detected current substantially corresponds to the generated current. The unbalanced current is obtained as the difference between the sum of the first detected current and the third detected current and the sum of the second detected current and the fourth detected current.

By the way, in the BTL amplifying device in the steady state, the phases of the positive-phase output signal and the negative-phase output signal are inverted to each other, and a single load is driven from the opposite side with the same output current. As a general rule, the first detected current and the fourth detected current obtained as described above have the same current value, and the directions of the currents are only reversed. Also, the second
The same applies to the detection current of and the third detection current. Therefore, the unbalanced current obtained by the above relationship theoretically does not flow at all in the steady state except for the error current caused by the variation of the circuit elements and the like and the slight difference of the amplification factor.

On the other hand, when the output terminals of both output signals are arbitrarily grounded or short-circuited to each other, the first to fourth
The balance between the detection currents of 1 is lost, and a significant unbalanced current flows. Therefore, when such a ground fault or a power fault occurs, an unbalanced current having a current value larger than the error current is detected and a cutoff signal is generated, so that the output of both output signals is stopped and the circuit is protected. .

As long as the positive-phase output signal and the negative-phase output signal are balanced, the unbalanced current does not flow.
The second amplifier circuit spans the entire voltage between ground and the power supply,
Further, for example, when bootstrapped, an output signal exceeding the range can be output. Therefore, the BTL of the audio device of the present invention is increased.
In the protection system wide device, it is possible to output sufficient large power corresponding to the power supply voltage, moreover, it is possible to detect a point short circuit is not limited to the ground, cell due to incorrect wiring or the like
It is possible to prevent the destruction of the unit.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION B in the audio apparatus of the present invention
An embodiment of the protection circuit of the TL amplifier will be described. A block diagram of a specific configuration centering on the protection circuit is shown in FIG.
Shown in Here, 1 is an amplifier, 2 is a positive phase side amplification circuit, 3
Is a negative phase side amplification circuit, 4 is a speaker, 20b, 20c, 3
0b and 30c are detection transistors, 56 is an unbalanced current detection circuit, and 70 is a cutoff signal generation circuit. As described above, the amplifier 1, the positive phase side amplification circuit 2, and the negative phase side amplification circuit 3 form a BTL amplifier to drive the speaker 4. Further, in a steady state, the positive-phase output signal C and the negative-phase output signal E have opposite phases to each other, and the output current C ′ and the output current E ′ are currents having the same value but different directions. Is.

The positive phase side amplification circuit 2 includes a drive circuit 2a which receives a positive phase input signal B and a normal phase output signal C which is controlled by the drive circuit 2a.
And an output transistor 2b for supplying an output current C'which outputs to the speaker 4 and an output current C'which outputs a positive phase output signal C together with the transistor 2b under the control of the drive circuit 2a and flows in from the speaker 4. It is composed of an output transistor 2c for receiving. Since the bases of the detection transistor 20b and the output transistor 2b are connected to each other and the emitters of the detection transistor 20b are connected to each other, the detection current Gb proportional to the output current C'outflows.
Can be flowed through the collector.

Further, since the detection transistor 20c and the output transistor 2c are connected to each other at their bases and also at their emitters, the inflowing output current C '.
A detection current Gc proportional to can be passed through the collector. The negative-phase side amplifier circuit 3 includes a drive circuit 3a that receives the negative-phase input signal D, an output transistor 3b that receives the negative-phase output signal E under the control of the driving circuit 3a, and that supplies an output current E ′ that flows out to the speaker 4. The output transistor 3c is also controlled by the drive circuit 3a and outputs the reverse-phase output signal E together with the transistor 3b and receives the output current E ′ flowing from the speaker 4.

Since the bases of the detection transistor 30b and the output transistor 3b are connected to each other and the emitters of the detection transistor 30b are connected to each other, the output current E'outflows there.
A detection current Hb proportional to can be made to flow through the collector. Furthermore, the detection transistor 30c is output since the transistors 3c and base together to each other is also connected further emitters of which are connected, the detection current Hc proportional to the output current E that flows', can flow through the collector.

The unbalanced current detection circuit 56 is composed of, for example, a current mirror 56b, and the sum current I obtained from the detection current Gb and the detection current Hb by simple connection.
Is the input side current of the current mirror 56b, and the detection current G
The sum current J obtained by simple connection from c and the detected current Hc is used as the output current of the current mirror 56b. As a result, the unbalanced current K is output as the current on the signal line branched from the signal line of this output current. That is, it is possible to output the unbalanced current K which is the difference between the sum of the detection current Gb and the detection current Hb with respect to the sum of the detection current Gc and the detection current Hc.

The cutoff signal generation circuit 70 is formed of a full-wave rectifier circuit with a dead zone, etc., and generates a cutoff signal F when the absolute value of the unbalanced current K is a predetermined value or more. Here, the above-mentioned predetermined value indicates the width of the dead zone for preventing erroneous detection in response to an error current caused by variations in circuit elements. Note that FIG. 2 shows a specific configuration example of the cutoff signal generation circuit 70.

In this way, the output transistors 2b, 2c,
3b and 3c respectively have detection transistors 20b and 20
Since the detection currents Gb, Gc, Hb, and Hc are generated by connecting c, 30b, and 30c in parallel to detect the output state, these configurations and setting values are the original output. (C, E, C ', E') is not adversely affected. Therefore, the positive phase output signal C and the negative phase output signal E
Since it is not necessary to limit the range of the output value itself, the positive phase side amplification circuit 2 and the negative phase side amplification circuit 3 output the output signals C and E over the entire voltage (Vcc) between the ground and the power supply. it can. Further, when bootstrapped, for example, a large power exceeding that range can be output.

Under such a configuration, in the steady state, the detection current Gb, the detection current Hc, and the detection current G are detected.
c and the detection current Hb are currents of the same value whose directions are different from each other similarly to the output currents C ′ and E ′.
The input side current (I) and the output side current (J) of 6 are balanced. Therefore, since the unbalanced current H basically does not flow,
The shutoff signal F is not generated. Therefore, the speaker 4 is bidirectionally driven by the positive phase output signal C in which the positive phase input signal B is amplified and the negative phase output signal E in which the negative phase input signal D is amplified.

By the way, in an abnormal state, that is, when the output terminals of both output signals C and E are arbitrarily grounded or short-circuited to each other, in such a case, the positive-phase output signal C and the negative-phase output signal E are generated. And the balance with Further, the balance between the output current C'and the output current E'is also lost, so that the detection currents Gb, Gc, Hb, Hc generated by simulating them are generated.
Also loses the balance. For this reason, an unbalanced current K having a magnitude corresponding to how the balance is lost flows. As a result, the cutoff signal F is generated, and in response to this, the positive phase side amplification circuit 2 and the negative phase side amplification circuit 3 stop the output of the output signals C and E, respectively. , 2c, 3b, 3c, etc. are protected.

As a special case, the transistor 2
b, the amplification factor of the transistor 20b, the amplification factor of the transistor 2c, the amplification factor of the transistor 20c, the amplification factor of the transistor 3b, and the amplification factor of the transistor 30b.
When the design is such that the ratio of the amplification factor of the transistor 3c and the ratio of the amplification factor of the transistor 3c and the amplification factor of the transistor 30c are all equal, one of the output terminals of the output signals C and E is Although it is difficult to detect a special state in which a ground fault occurs and the other is a power fault, it is generally effective.

[0026]

As can be understood from the foregoing description, in the audio apparatus of the present invention, As a BTL amplifying device
In the protection system, the unbalanced current is obtained from the detected current generated by simulating the output currents of the positive phase output signal and the negative phase output signal. Then, in the steady state, the positive-phase output signal and the negative-phase output signal are balanced and the unbalanced current does not flow,
When the output terminals of both output signals are arbitrarily grounded or short-circuited, it is detected that an unbalanced current flows and the output of both output signals is stopped. As a result, there is an effect that a large power corresponding to the power supply voltage can be output and that not only the ground fault but also the power fault can be detected.

[Brief description of drawings]

FIG. 1 is a block diagram of an audio device B of the present invention.
It is an example of the protection circuit of a TL amplifier, and is a block diagram centering on it.

FIG. 2 is a detailed circuit diagram of an interruption generating circuit in the protection circuit.

FIG. 3 is a BTL in a conventional audio device.
It is a block diagram centering on the protection circuit of an amplifier.

[Explanation of symbols]

 1 Amplifier 2 Positive phase side amplification circuit 2b, 2c Output transistor 3 Reversed phase side amplification circuit 3b, 3c Output transistor 4 Speaker 5, 6 Comparator 7 OR gate 20b, 20c, 30b, 30c Detection transistor 56 Unbalanced current detection circuit 70 Break Signal generation circuit

Claims (3)

(57) [Claims] 1. A positive phase output signal generated by amplifying an input signal.
Push-pull first amplifier circuit that outputs the voltage to one end of the load
The negative phase output signal generated by amplifying the input signal
A second push-pull amplifier circuit that outputs the other end of the load,
The positive phase output signal causes the load from the first amplifier circuit to the load.
Generates the first detection current corresponding to the current flowing out to one end
The first current detection circuit, and the positive phase output signal
It corresponds to the current flowing from one end of the load into the first amplifier circuit.
That a second current detecting circuit for generating a second detection current, the other of the load from the second amplifier circuit by the negative-phase output signal
Generate a third detected current corresponding to the current flowing out to the end
The third current detection circuit and the negative output signal
Corresponds to the current flowing from the other end of the load to the second amplifier circuit
A fourth current detection circuit for generating a fourth detection current , wherein the first, second, third and fourth detection currents have the same direction.
And the unbalanced current, which is the difference between the sum of the first detected current and the third detected current and the sum of the second detected current and the fourth detected current, is greater than or equal to a predetermined value, BT characterized by stopping the output operation of the first and second amplifier circuits
L amplifier protection circuit. 2. A positive-phase output signal generated by amplifying an input signal is output to one end of a load, and a current to the load due to the positive-phase output signal is supplied via a first output transistor to output the positive-phase output. A first amplifier circuit for receiving a current from the load by a signal via a second output transistor, and a negative phase output signal having the same amplitude and a phase reversed with respect to the positive phase output signal, the input signal From the load to the other end of the load, the current to the load due to the negative-phase output signal is supplied through the third output transistor, and the current from the load due to the negative-phase output signal is generated. A second amplifier circuit for receiving via a fourth output transistor; a first amplifier circuit;
The first detection transistor whose bases and emitters are connected to the output transistor and the collector flows the first detection current, and the base and emitters are connected to the second output transistor and the collector is A second detection transistor for flowing a second detection current; a third detection transistor in which bases and emitters of the third output transistor are connected to each other so that a collector flows a third detection current; The bases and the emitters are connected to the output transistor, and the collector is the fourth
And a fourth detection transistor for flowing the detection current of No. 1, and the first detection current and the third detection current are combined to obtain a first sum, and the second detection current and the fourth detection current are combined to generate a second sum. Sum and first
Unbalanced current detection circuit that outputs the difference between the sum of the unbalanced current and the second sum as an unbalanced current, and a cutoff signal that receives the unbalanced current and generates a cutoff signal when the absolute value of the unbalanced current is greater than or equal to a predetermined value. A protection circuit for a BTL amplifying device, which stops the output of the positive phase output signal and the negative phase output signal by the cutoff signal. 3. A positive phase output signal generated by amplifying an input signal.
Push-pull first amplifier circuit that outputs the voltage to one end of the load
The negative phase output signal generated by amplifying the input signal
A second push-pull amplifier circuit that outputs the other end of the load,
The positive phase output signal causes the load from the first amplifier circuit to the load.
Generates the first detection current corresponding to the current flowing out to one end
The first current detection circuit, and the positive phase output signal
It corresponds to the current flowing from one end of the load into the first amplifier circuit.
That a second current detecting circuit for generating a second detection current, the other of the load from the second amplifier circuit by the negative-phase output signal
Generate a third detected current corresponding to the current flowing out to the end
The third current detection circuit and the negative output signal
Corresponds to the current flowing from the other end of the load to the second amplifier circuit
A fourth current detection circuit for generating a fourth detection current , wherein the first, second, third and fourth detection currents have the same direction.
And the unbalanced current, which is the difference between the sum of the first detected current and the third detected current and the sum of the second detected current and the fourth detected current, is greater than or equal to a predetermined value, An audio device having a protection circuit for a BTL amplifying device for stopping the output operation of the first and second amplifying circuits.