JPH0141220Y2 - - Google Patents

Description

[Detailed description of the invention] (Technical field) The present invention detects whether the output terminal is short-circuited during the muting time, which cuts off the load for several seconds after the power amplifier is turned on, and connects the amplifier configuration to BTL connection. It is related to a circuit that changes from 1 to 2 to parallel connection.

(Background technology) In general, in a power amplifier, the current flowing through the output power transistor greatly increases or decreases depending on the impedance of the load. When the transistor is short-circuited, an overcurrent flows into the transistor, causing destruction or characteristic deterioration. By the way, a BTL amplifier connects a speaker between two power amplifiers, and unlike a normal amplifier, neither output terminal is grounded, so if you mishandle it, one side may be grounded like a normal amplifier. It is possible to connect the type of load that will be used. This means that the output of one of the power amplifiers is short-circuited, leading to destruction of the transistor and deterioration of characteristics as described above.

(Purpose) The purpose of this invention is to improve the shortcomings of BTL amplifiers by detecting the load impedance immediately after turning on the power and switching the configuration to a parallel amplifier if one end is grounded. This protects the amplifier.

(Example) A detailed explanation will be given below with reference to the drawings. 1st
In the figure, 12a, 12b and 12c are BTL-
With the parallel switch, the output of the power amplifier 2 is transferred to the muting switch 4 by the BTL-parallel switch 12b.
It is selected whether to connect to one fixed terminal 4a of the power amplifier 1 or to the output terminal of the power amplifier 1. The output of the power amplifier 1 reaches a hot side speaker connection terminal (Hot terminal) 5 via one fixed terminal 3a of the muting switch 3. The fixed terminal 3b of the switch 3 is grounded. The load is connected between the Hot terminal 5 and the cold side speaker connection terminal (Cold terminal) 6. The detector 10 includes a voltage source 9, a resistor 8, and a level detection circuit 7, the other fixed contact 4b of the switch 4 is connected to the terminal 10a, and the output terminal 10b is connected to the control circuit 11. A control signal is outputted by the control circuit 11 and sent to the BTL-parallel switchers 12a, 12b and 12c. The muting circuit 13 switches the muting switches 3 and 4 to the fixed contacts 3b and 4b, respectively, during a muting period of several seconds from when the power is turned on.

In the above configuration, when the speaker is connected between terminals 5 and 6 and the power is turned on, during the muting period immediately after that, the switches 3 and 4 are connected to the fixed contact 3.
Since it is switched to the b and 4b sides, the speaker is connected between the fixed contact 4b and the ground. At this time, the output of the reference voltage source 9 is divided by the resistor 8 and the speaker impedance and appears at the terminal 10a, but since this voltage is adjusted to exceed a predetermined value, the output of the level detection circuit 7 is low. level. In this case, the control signal from the control circuit 11 switches the switches 12a, 12b and 12c to the BTL connection side A. After the mutating period, the switches 3 and 4 are switched to the fixed contacts 3a and 4a, but since the output of the detector 10 is still above the predetermined voltage, the amplifiers 1 and 2 are switched to the fixed contacts 3a and 4a.
Remains a BTL connection.

Next, if we connect a type of speaker that is designed for use with an amplifier with one end grounded, such as one that uses terminal 6 to be grounded, between terminals 5 and 6,
Since the terminal 10a of the detector 10 is grounded and the voltage is below a predetermined voltage, the output of the detection circuit 7 becomes a high level, and the control signal from the control circuit 11 is transferred to the switch 12.
Switch a, 12b and 12c to parallel connection side B. As a result, the amplifier 1 is separated from the fixed terminal 4a, so that the amplifier 1 is not destroyed.

The detector 10 is not limited to the one described above. 2 and 3 show other embodiments of the detector 10, respectively.

FIG. 2 uses a photocoupler 7a, and as mentioned above, a speaker is connected between the terminal 10a and the ground during the muting period, so a bridge circuit is formed by resistors 8a and 8b, resistor 8c, and the speaker. . In this case the bridge circuit is balanced and therefore no current flows through the photocoupler. When the terminal 6 is grounded, the balance is disrupted, current flows through the photocoupler 7a, and grounding of the terminal 6 is detected. Note that the resistors 8b and 8c may be omitted.

In FIG. 3, a voltage serving as a detection reference is obtained by a Zener diode 9d.

(Effects) As described above, according to the power amplifier circuit according to the present invention, the impedance of the load can be detected with high sensitivity, and reliable protective operation can be performed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the power amplifier circuit according to the present invention, and FIGS. 2 and 3 are circuit diagrams showing other embodiments of the detector used in the present invention. 1, 2... Power amplifier, 3, 4... Muting switch, 5... Hot terminal, 6... Cold terminal, 9... Reference voltage source, 10... Detector, 11...
...control circuit, 12a, 12b, 12c...BTL
-Parallel switching circuit.

Claims (1)

[Scope of utility model registration request] means for deriving the output of the first amplifier to the first output terminal; and means for deriving the output of the second amplifier to the first output terminal for parallel connection or for deriving it to the second output terminal for BTL connection; a selection means for selecting whether to
In a power amplifier having muting means for cutting off output for a predetermined period immediately after power is turned on, and speaker impedance detection means, the muting means connects the first speaker connection terminal to the first speaker impedance detection means.
a first switching means for selecting whether to connect the second speaker connection terminal to the second output terminal or to ground; and a second switching means for selecting whether to connect the second speaker connection terminal to the second output terminal or to the speaker impedance detection means. 2 switching means so that speaker impedance is detected during the muting period, and when the speaker impedance is below a predetermined value, the selecting means is controlled to connect the power amplifiers in parallel. power amplifier.