JPH0145152Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a protection circuit, and particularly to a protection circuit that is optimal for use in a low frequency amplifier such as an audio amplifier.

(Prior art) Generally, an audio amplifier has a configuration as shown in Fig. 1, in which a signal input from the input section IN is passed through the voltage amplification section VA to the power amplification section PA.
After the power is amplified, it drives the speaker SP. The power amplification unit PA is configured to be supplied with power by a single power supply circuit suitable for the rated output.

However, in the conventional audio amplifiers mentioned above, the output from the amplifier is always applied directly to the speakers, so it is possible for the amplifier to malfunction due to incorrect connections in the audio system, howling, or operational errors by the user. When an excessive signal is input to the input terminal, this signal is directly amplified, and a voltage comparable to the power supply voltage is applied to the speaker. Moreover, modern amplifiers have the ability to output a maximum output that is approximately twice the rated output, so if speakers with insufficient maximum allowable input are used, accidents such as voice coil burnout often occur, especially when the maximum output is reached. is in a clipped state, so the high-frequency spectrum increases greatly,
In particular, there were problems such as the tweeter being easily destroyed. In order to prevent such accidents, standards for matching amplifiers and speakers have been established by IEC.
(INTERNATIONAL ELECTRONICAL
COMMISSON).
Conventional ASO detection type protection circuits are mainly intended to protect the amplifier, and are not only largely ineffective against speaker damage caused by amplifier clipping, but also have disadvantages such as deterioration in performance and sound quality, so they are not sufficient. Ta.

(Purpose of the invention) The present invention was made in view of the above points, and its purpose is to eliminate the problem only when the output of the amplifier is in a clip state, without causing deterioration of the original performance or sound quality of the amplifier. An object of the present invention is to provide a protection circuit capable of performing an appropriate protection operation.

(Structure of the invention) The protection circuit according to the invention includes two sets of power supply circuits on the low voltage side and high voltage side, a power amplifier circuit that selectively uses each power supply, and a voltage control circuit provided in the preceding stage of the power amplifier circuit. In an amplifier having an amplifier circuit and a control section that selectively connects the two sets of power supply circuits to the power amplifier circuit, the control section detects the output voltage from the power amplifier circuit, and detects the output voltage saturation for a certain period of time. It is equipped with a detection circuit that outputs a signal only when the power supply circuit continues to be used, and a distribution circuit that is activated by the signal from the detection circuit and selects which power supply circuit to use. is configured to limit the voltage applied to the

(Example) An example of the protection circuit according to the present invention will be described based on FIGS. 2 to 4. Fig. 2 shows a basic block diagram, Fig. 3 shows a specific circuit example, and Fig. 4 shows another embodiment. PH, it is designed to drive the low voltage side amplifier PL. 1 is a detection circuit that detects the output voltage from the voltage amplification circuit VA and outputs a signal only when the output voltage is saturated for a certain period of time, and includes a clip detection section 2 and an integrator. 3. Shaking width control section 4
It is composed of. S is a distribution circuit,
It is composed of a switch control section SC and a switch section _S1 , and can distribute and supply the output from the voltage amplification circuit VA to the high voltage side amplifier PH or the low voltage side amplifier PL. As a result,
Power supply that should supply power to each amplifier PH or PL
BH or BL will be used selectively.
Therefore, if the output from the voltage amplifier circuit VA clips while the high-voltage amplifier PH is operating, the output from the high-voltage amplifier PH is automatically switched to the low-voltage amplifier PL, and the power at the output section OUT is reduced. do. Figure 3 shows a specific circuit example,
Transistors Q ₁ , Q ₂ and resistor R ₂₆ constitute a driver stage; transistors Q ₃ to _{Q 6} and resistors R ₁ to _{R 5}
are switch circuits, transistors Q ₇ to _{Q 9} , diodes D ₁ and D ₂ , resistors R ₇ to _{R 11} , and power supplies E ₁ and E ₂ are circuits and transistors configured to perform output level detection and switch control. Q ₁₁ , Q ₁₂ are circuit transistors Q ₁₃ , which constitute a high output amplifier stage.
_Q14 is a power amplification stage for low output, transistor _Q15 ,
Resistor R ₁₅ , bias circuit BI is pre-driver stage,
Transistor Q ₁₆ , resistor R ₁₇ , R ₁₈ is a clip detection circuit, transistor Q ₁₇ ~Q ₂₁ , diode D ₅ ~
D ₈ , resistors R ₁₉ to R ₂₅ , and capacitor C ₁ each constitute an output limiting circuit.

Below, an example of its operation will be explained for the positive half cycle. First, when the output amplitude is small, transistors Q ₃ , Q ₇ , and Q ₉ are off;
Q ₅ turns on, so transistor Q ₁₃ operates,
Power is supplied to the load through transistor _Q13 from the power supply +BL. Here, the output amplitude is the reference voltage
When E ₁ rises by about 1.2V (the threshold level of transistor Q ₉ and diode D ₁ ), the transistor
Q ₉ is turned on, and transistors Q ₇ and Q ₃ are turned on. Therefore, power to the load (speaker SP) is supplied from the power supply +BH through transistor _Q11 . In short, the above operation selects a power source and a power element according to the output amplitude, and has the effect of reducing power loss of the output element.

At this point, the amplitude becomes even larger, and when the output starts to clip, the transistor in the pre-driver stage
The emitter potential of _Q16 suddenly rises and the transistor
Turn on _Q16 . Then transistor Q ₂₁
is off, transistors Q ₁₇ to Q ₂₀ are on,
The potential of the base of transistor Q ₁ is limited to approximately 0.6 V higher than the power supply voltage E ₁ (diode D ₅ ,
D ₇ , determined by the threshold voltage of transistor Q ₁₇ ). Output voltage must be transistor Q ₁
Since it _is designed to operate at a voltage that is 1.2V or more lower than the base _{voltage of} Transistor _Q9 , which is set to be in the on state, will not turn on. Therefore, transistor _Q5 is turned on, and the circuit shown in Figure 3 operates with the power supply on the low voltage side (+BL) and the amplifier on the low voltage side, and the output power is completely suppressed to protect the speaker SP. I can do it. Resistor _R21 ~ _R23 , capacitor
The integration circuit consisting of _C1 is for preventing chattering and is for preventing the output from being limited by short-term peak voltage clips of normal musical tone input signals. That is,
It has a delay function that performs the above-mentioned protective operation only when the output is in a clipped state for a certain period of time or more, to prevent malfunctions.

FIG. 4 shows another embodiment, in which low-voltage or high-voltage power supplies BL, BH are selectively supplied to the power amplifying section PA, and the switching is performed by a switch section _S2 . This is what I did.

(Effects of the invention) According to the protection circuit according to the invention, even if an excessive input signal is received due to incorrect connection of the audio system, generation of howling, or incorrect operation, an abnormal output will not occur, and the amplification element or There is no risk of speaker deterioration or destruction. Moreover, since the protection circuit operates only when the clipping state continues for a certain period of time or more, the inherent performance and sound quality of the amplifier will not deteriorate, making it particularly suitable as a protection circuit for audio amplifiers.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a general amplifier circuit.
2 to 4 show examples in which the protection circuit according to the present invention is implemented in an amplifier circuit, and FIG. 2 is a block diagram,
FIG. 3 is a concrete circuit example, and FIG. 4 is a block diagram showing another embodiment. BL: Low voltage side power supply, BH: High voltage side power supply, PA: Power amplifier, PL: Low voltage side amplifier, PH: High voltage side amplifier, 1: Detection circuit, 2: Clip detection section, 3: Integrator, 4: Amplitude control section.

Claims (1)

[Claims for Utility Model Registration] Two sets of power supply circuits on the low-voltage side and high-voltage side, a power amplification circuit that selectively uses each power supply, a voltage amplification circuit provided in the preceding stage of the power amplification circuit, and the above-mentioned. In an amplifier having a control section that selectively connects two sets of power supply circuits to a power amplifier circuit, the control section is composed of a clip detection section, an integrator, and an amplitude control section, and the control section includes a clip detection section, an integrator, and an amplitude control section. A detection circuit that detects the output voltage from the voltage amplification circuit provided in the previous stage and outputs a signal only when the output voltage remains saturated for a certain period of time; What is claimed is: 1. A protection circuit comprising: a distribution circuit for selecting which power supply circuit to use;