JPS6218978Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a protection circuit that automatically shuts off the circuit to prevent damage to speakers when an amplifier fails and outputs direct current.

Conventionally, various so-called DC protection circuits have been devised to protect speakers from DC output caused by amplifier failure. There are devices that detect when the level difference becomes excessive by comparing the input audio signals, but in any case, the protection circuit is activated for excessive input audio signals, and the protection circuit is activated for input audio signals that are useful. However, it was not an ideal protection circuit that required the protection circuit to not operate.

The present invention eliminates such conventional drawbacks and provides a protection circuit that operates only with the DC signal output due to an amplifier failure and automatically cuts off the signal path connecting the amplifier output terminal and the speaker. be. Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of an amplifier protection circuit showing an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the circuit shown in FIG.

The audio signal input from input terminal I, amplified by amplifier _A0 , and appearing at output terminal O is sent to speaker SP via switch SW, which is a signal path breaker, and is emitted into the space. The contact is opened by the output signal of the first level comparator _COM1 .

Further, a part of the audio signal input from the input terminal I is input to the input terminal 11 of the subtraction circuit 1, and a part of the audio signal appearing at the output terminal O is input to the second level comparator COM ₂ . It is also input to another input terminal 12 of the subtraction circuit 1 via an attenuator R. The subtracter R attenuates a part of the audio signal appearing at the output terminal O to make it at the same level as the audio signal input from the input terminal I and input to the input terminal 11 of the subtraction circuit 1. It is something.

The output terminal 13 of the subtraction circuit 1 is an inverting/non-inverting switchable amplifier circuit (hereinafter referred to as a switching amplifier circuit).
The switching amplifier circuit 2 is connected to the input terminal 21 of the switching amplifier circuit 2.
The output terminal 23 of is connected to the anode of the diode _D1 . The cathode of the diode _D1 is grounded via a resistor, and the cathode of the diode D1 is connected to a first level comparator via a low-pass filter F.
Connected to the COM ₁ input terminal. The output signal of the first level comparator COM ₁ is switched
As described above, it is used as a control signal for the SW.

Further, the output terminal of the second level comparator COM ₂ is connected to the control signal input terminal 22 of the switching amplifier circuit 2.

In the configuration shown in the above diagram, the circuit operation when an audio signal is input from input terminal I is divided into cases such as when the amplifier is operating normally, when it is malfunctioning and outputting DC current, etc. This will be explained in detail with reference to the waveform diagram in FIG.

(1) When amplifier A ₀ is operating normally, when an audio signal of an appropriate level is input from input terminal I, input terminals 11 and 12 of subtraction circuit 1
Audio signals of the same level as 2-1 and 2-2 in FIG. 2 are respectively input to , and the signal in FIG. 2-1 is subtracted from the signal in FIG.
The two audio signals cancel each other out at point a on the output side of
The state will be as follows. On the other hand, the level at point b on the output side of the second level comparator COM ₂ switches between low (L) and high (H) states every positive and negative half cycle of the input audio signal, as shown in Figure 2-4.
The signal appearing at the point b is applied to the control signal input terminal 22 of the switching amplifier circuit 2, and when the signal is at low level (L), the switching amplifier circuit 2 is operated as a non-inverting amplifier circuit, and the signal is When the level is high (H), the switching amplifier 2 works as an inverting amplifier circuit.

As a result, the audio signal appearing at point a is in phase with the switching amplifier circuit 2 when point b is at low level (L).
When point b is at a high level (H), it is inverted and appears at point c in the opposite phase. However, the signal waveform at point a is at 0 level as shown in Figure 2-3, and regardless of whether the level at point b is high (H) or low (L), the signal appearing at point c is as shown in Figure 2-5. It becomes a 0 level state. Therefore, _D1 is not conductive and the level at point d is also level 0 as shown in Figure 2-6, so the first level comparator _COM1 does not output a control signal to open the switch SW. The switch SW remains on, and the amplifier A ₀
The output audio signal is sent to the speaker SP and emitted into the space.

If the level of the input audio signal is excessive, an audio signal as shown in Figure _2-11 is input to the input terminal 11 of the subtraction circuit 1, and the amplification operation of the amplifier _A0 is saturated to the other input terminal 12. to do 2
An audio signal with a waveform with a flattened head as shown in Figure _2-21 is input, and a signal waveform as shown in Figure _2-31 , which is the difference between the two audio signals, appears at point a. On the other hand, since the level at point b on the output side of the second level comparator COM ₂ is high level (H) in the negative half cycle of the input signal, the switching amplifier circuit 2 is operated as an inverting amplifier circuit. The audio signal waveform appearing at point a is 2-3 at point a.
2-5 where the positive half cycle of the waveform in Figure ₁ is reversed
It will look like the one shown in Figure ₁ . Therefore diode D ₁
is not conductive and the level at point d remains at level 0 as shown in Figure _2-61 , the first level comparator COM ₁ does not output the control signal to open the switch SW, and the input audio signal is input to the amplifier.
After being amplified by _A0 , the sound is emitted into the space via speaker SP.

(2) When amplifier A ₀ is out of order and outputs DC current. If the input audio signal is at an appropriate level, the input terminal 11 of subtractor circuit 1 will have 2-1 ₂ in Figure 2.
Or, an audio signal with a waveform as shown in 2-1 ₃ is input, but if the DC current is positive, a positive DC voltage as shown in 2-2 ₂ is applied to the other input terminal 12, and the point a is _2-3 An audio signal waveform raised to the positive side as shown in Figure 2 appears, and the second level comparator COM ₂ inputs the above positive DC current and the level at point b is in the low (L) state. Therefore, the audio signal waveform appearing at point c is in phase with the signal waveform _2-3 at point a.
5 It appears as a signal waveform of the same shape and level as shown in Figure ₂ . Therefore, the diode _D1 becomes conductive, and a positive voltage waveform as shown in Fig. _2-62 appears at the point d.As a result, this voltage waveform is input to the first level comparator _COM1 via the low-pass filter F. The output voltage of the first level comparator COM ₁ is applied to the switch SW.
SW is turned off or cut off, and the purpose of preventing the DC current generated due to the failure of amplifier A ₀ from flowing into the speaker SP and damaging the amplifier A ₀ as well as the speaker is achieved.

In addition, if the above DC current is negative, 2
A negative DC voltage as shown in Figure _2-3 is applied to the input terminal 11, and an audio signal waveform pulled to the negative side as shown in Figure _2-33 appears at point a, resulting in a second level. Since the comparator COM ₂ inputs the above-mentioned negative DC current and the level at point b is in a high (H) state, the switching amplifier circuit 2 operates as an inverting amplifier circuit, and the above-mentioned audio signal waveform 2-3 at point a ₃ is reversed and becomes 2 at point c
-5 It appears as a waveform raised to the positive side as shown in Figure ₃ . Therefore, a positive voltage waveform as shown in Figure _2-63 appears at point d, and similarly to the above, the output voltage of the first level comparator COM ₁ is applied to the switch SW, which is turned off, and the amplifier and The purpose of protecting the loudspeaker from damage is achieved.

The above-mentioned low-pass filter F is provided to prevent malfunctions caused by the phase difference between the input and output audio signals of the amplifier _A0 in the low or high frequency range of the audio signal.
The time constant is set to 100msec.

If the amplifier A ₀ is an inverting amplifier, an adder circuit can be used instead of a subtracter circuit. If an excessive audio signal is input when amplifier A ₀ fails, the positive potential at point d seems to be canceled out by the excessive input, but the change in amplitude of the audio signal is complex, and the input at point d always occurs. There is a moment when the potential appears positive, and the switch SW is accurately shut off.

FIG. 3 is a circuit diagram showing an embodiment of an amplifier protection circuit which is a more specific embodiment of the present invention, and it is assumed that resistors with the same symbols in the circuit diagram have the same resistance value.

To briefly explain the circuit operation with reference to FIG. 3, two differential amplifiers connected to the first differential amplifier _A1
Since the resistors R ₁ have the same value and the attenuation ratio of the attenuator R is set to 1/2A, the first differential amplifier A ₁
performs the same operation as the subtraction circuit 1, and a signal waveform as shown in FIG. 2 appears at point a. (However, A is the amplification degree of the amplifier _A0 .) Also, the two resistors _R2 connected to the second differential amplifier _A2 have the same value, and the output signal of the second level comparator _COM2 is low level (L), that is, point b is low level (L), the diode
D ₂ conducts, field effect transistor T turns off and the second differential amplifier A ₂ operates as a non-inverting amplifier, and the second level comparator COM ₂
When the output signal of is at a high level (H), that is, the point b is at a high level (H), the diode _D2 is cut off and the field effect transistor T is turned on.
The second differential amplifier _A2 operates as an inverting amplifier.

Therefore, the second differential amplifier _A2 performs the same operation as the switching amplifier circuit 2, and a signal waveform as shown in FIG. 2 appears at point c, and a DC signal due to the failure of amplifier _A0 appears at point d. When a positive voltage waveform corresponding to the output appears, the first level comparator
COM ₁ outputs a control signal, switch SW is cut off, and both amplifier A ₀ and speaker SP can be protected.

As described above, the amplifier protection circuit according to the present invention does not operate even in response to excessive input of useful audio signals, and promptly cuts off the signal path when DC current is output due to amplifier failure. This is an ideal protection circuit that can protect both the amplifier and the speaker.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an amplifier protection circuit showing one embodiment of the present invention, Fig. 2 is a waveform diagram for explaining the circuit operation of Figs. 1 and 3, and Fig. 3 is a more specific example of the present invention. FIG. 2 is a circuit diagram showing an example of a protection circuit for an amplifier, which is a typical example. I...Input terminal, A ₀ ...Amplifier, SP...Speaker, SW...Switch, O...Output terminal, 1...
...Subtraction circuit, 2...Inverting/non-inverting switchable amplifier circuit, F...Low pass filter, COM ₁ ...First level comparator, COM ₂ ...Second level comparator, R...Attenuator, D ₁ , D ₂ ... diode, A ₁ ... first differential amplifier, A ₂ ... second differential amplifier, T ... field effect transistor,
_R1 , _R2 ...Resistance, a, b, c, d...Points in the circuit.

Claims (1)

[Scope of utility model registration request] Subtraction or addition in which a part of the input signal of an amplifier that amplifies the audio signal and supplies it to the speaker is input to one input terminal, and a part of the output signal of the amplifier is input to the other input terminal via an attenuator. A circuit consisting of a circuit, an inverting/non-inverting switchable amplifier circuit to which the output signal of the subtraction or addition circuit is input, and a unidirectional element and a low-pass filter connected in series to input the output signal of the inverting/non-inverting switchable amplifier circuit. a first level comparator that inputs the input via the amplifier; and a circuit breaker that is interposed in a signal path connecting the output terminal of the amplifier and the speaker and is applied with the output voltage of the first level comparator to interrupt the signal path. , and a second level comparator inputting a part of the output signal of the amplifier, and the output voltage of the second level comparator is used as a switching control signal for the inverting/non-inverting switchable amplifier circuit. Amplifier protection circuit.