JP2000152367A - Speaker protection circuit for btl power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a speaker protection circuit that protects a speaker by detecting a DC abnormal voltage of an input signal in a balanced transformerless BTL power amplifier so as to automatically turn off an output. SOLUTION: This protection circuit consists of a clip detection circuit 1 that detects clips which exceed the saturation level of an output voltage waveform Vout, due to saturation of a BTL power amplifier 30 to provide an output of a clip detection signal Scp, a timer circuit 4 that receives the clip detection signal Scp of the clip detection circuit 1 to provide an output, when a clip CP is consecutive for a prescribed time Toff or longer, and a control circuit 5 that controls an output on/off circuit 3 that receives an output of the timer circuit 4 to turn off the output Vout of the BTL power amplifier 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speaker protection circuit in a BTL (balanced transfomerless) power amplifier which is frequently used for car audio which requires a large output particularly at a low power supply voltage. The present invention relates to a circuit for detecting an abnormal voltage by a clip appearing in an output voltage waveform and automatically turning off an output of a BTL amplifier to protect a speaker so that an excessive DC current does not continuously flow to the speaker.

[0002]

2. Description of the Related Art At present, power amplifiers of audio equipment including car audio have a BTL (differential) output type (complementary SEPP circuit;
mentary single ended push-pull circuit).

That is, SEPP (single ended push-pul)
l) Two sets of S
OTP circuit of EPP (output transformerless circui
t: A circuit in which an output transformer is omitted in a power amplifier and a load speaker is directly connected to the power amplifier or an output is applied through a capacitor. ) Are operated in opposite phases, and a load (speaker) is connected between the output points. In this method, the voltage utilization is twice as high as when the SEPP circuit is used alone, and a large output can be obtained with a low power supply voltage.

[0004] In the complementary SEPP circuit using the ± power supply (± Vcc) of the power stage A in the basic circuit diagram of the BTL power amplifier shown in FIG. 4, the average DC potential of the output VOUT is 0 V, and the Since the impedance is low, it is directly connected without cutting the DC component with a capacitor. Therefore, if the balance is lost due to some factor such as destruction of the element, the power transistors Q1 to Q4 and the load Z
Since a large DC current would flow through the left speaker and damage it, protection measures were required more than before.

The most frequent accident is the destruction of the power transistor due to excessive current. For example, in the circuit diagram of FIG.
In order to prevent the destruction of Q4 due to excessive current, the voltage between both ends of RE by the power transistor's collector Q3 and Q4 current Ic is divided by a resistor and added to the bases of the detection transistors Q5 and Q6. Q5,
A protection circuit in which Q6 is turned on to limit the current by suppressing the bases of the power transistors Q1 and Q2, and a load ZL
There is a protection circuit or the like in which a fast-blow fuse or a breaker circuit is connected in series to the output so as to cut off the output VOUT when an excessive current flows through the speaker.

In some cases, means for detecting the average DC potential of the output VOUT and operating the relay circuit when the average DC potential exceeds a predetermined potential width to disconnect the speaker is employed.

[0007]

However, since the above-mentioned conventional protection circuit is provided especially as an additional circuit,
Whether it is built in the LSI chip of the BTL power amplifier in advance,
It is necessary to attach a relay circuit externally, and an increase in cost is inevitable.

Further, since the bias voltage of the preceding stage is not equal to the input side of the BTL power amplifier, a DC cut capacitor is usually connected. However, the DC signal leakage of the DC cut capacitor causes the input signal VIN to be input. Is fixed to the + side or the − side in a DC manner (extremely, in the case of an input short-to-supply or an input ground-fault), the BTL power amplifier operates so that the output voltage is DC-amplified and output according to the gain of the amplifier. Would. At this time, if the conventional protection circuit for the power transistor and the excessive current of the speaker does not operate, the DC current will continue to flow to the speaker and the voice coil of the speaker will be burnt, and in some cases, the whole speaker will be burnt. You could end up doing it.

In particular, smoke or ignition of car audio in a vehicle compartment is highly likely to lead to a serious accident. Therefore, it is highly necessary to take measures against the abnormal DC voltage of the input signal VIN of the BTL power amplifier.

The present invention has been made in view of the need for protection of a speaker when an abnormal DC voltage is generated in an input signal of the above-described conventional BTL power amplifier, and detects an abnormal DC voltage of the input signal of the BTL power amplifier. And a speaker protection circuit in a BTL power amplifier that automatically turns off the BTL power amplifier to protect the speaker.

[0011]

In order to solve the above-mentioned problems, the present invention detects a clip CP of an output voltage waveform Vout due to saturation of a BTL power amplifier and outputs a clip detection signal Sc.
a clip detection circuit that outputs p, a timer circuit that receives a clip detection signal Scp of the clip detection circuit, and outputs when a clip continues for a predetermined time Toff or more,
And a control circuit for receiving the output St of the timer circuit and outputting a control signal Ssb for turning off the output Vout of the BTL power amplifier. A speaker protection circuit in the BTL power amplifier is provided.

It should be noted that, as shown in FIG. 3, the maximum amplitude level of the output voltage waveform Vout of the BTL power amplifier is limited by the power supply voltage Vcc (saturation level Vs
BT), the input voltage waveform Vin exceeding a certain
When the signal is input to the L power amplifier, the signal waveform of the output voltage waveform Vout is saturated, a clip CP appears, and the sound becomes distorted. Therefore, many of the current integrated circuit chips (LSI chips) of BTL power amplifiers incorporate the above-described clip detection circuit (also referred to as an output saturation detection circuit). Waveform Vout is saturated (that is, clip CP has occurred)
This is detected, and a clip detection signal Scp is output as a control signal, whereby the sound quality control circuit and the volume control circuit are controlled to improve the sound quality.

The present invention focuses on the clip detection signal Scp and uses the signal as a sensor of a protection circuit for a DC abnormal voltage of a speaker.

[0014]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block circuit diagram for explaining a configuration of a speaker protection circuit in a BTL power amplifier according to the present invention.

FIG. 2 shows an input signal waveform Vin, an output voltage waveform Vout, a clip detection signal Scp, and a control signal when a DC abnormal voltage occurs in the input signal waveform Vin in the BTL power amplifier having the speaker protection circuit according to the present invention. FIG. 7 is a waveform diagram showing a correspondence of each waveform of the standby signal Ssb as the example.

In FIG. 1, the speaker protection circuit in the BTL power amplifier 30 according to the present invention includes a clip C in a state where the output voltage waveform Vout due to the saturation of the BTL power amplifier 30 exceeds the saturation level Vs as shown in FIG.
A clip detection circuit 1 that detects P (saturated) and outputs a clip detection signal Scp (usually high and saturated and low)
A timer circuit 4 which receives the clip detection signal Scp of the clip detection circuit 1 and outputs when the clip CP has continued for a predetermined time Toff or more, and an output of the BTL power amplifier 30 which receives the output St of the timer circuit 4 And a control circuit 5 for turning off Vout (other circuits are omitted).

More specifically, the timer circuit 4 and the control circuit 5 are built in a control microcomputer chip 10, and the clip detection circuit 1 is built in a BTL power amplifier 30 integrated on an LSI chip. . As means for turning on / off the output of the BTL power amplifier 30, the BTL power amplifier 30 is controlled by turning on / off the standby signal Ssb of the BTL power amplifier 30.
That the output on / off circuit 3 is controlled.

In FIG. 1, the LSI of the BTL power amplifier 30 is
The clip detection signal Scp at the chip is an open collector output (active low) of the NPN transistor Qcp, and when the output voltage waveform Vout is clipped,
The clip detection circuit 1 in the LSI operates to turn on the NPN transistor Qcp (Scp goes low). The clip detection signal Scp is also used as a control signal of the sound quality control circuit and the volume control circuit 7 as in the prior art. In the present invention, however, the clip detection signal Scp is newly used as a DC abnormal voltage detecting means for the speaker protection circuit. .

As described above, when a DC voltage is superimposed on the input voltage waveform Vin of the BTL power amplifier 30 as in the case of a short-to-supply or a ground fault, the output voltage waveform Vout is also amplified by a factor of amplification to reduce the DC voltage. Abnormal voltage is output. Normal,
If this state continues, excessive DC current will continue to flow through the voice coil of the speaker SP, and if left unattended, the voice coil will burn out.

Accordingly, as shown in FIG. 2, the timer circuit 4 sets the clip detection signal Scp to a predetermined time Toff.
(Considering the discrimination from a normal audio signal and the permissible limit of the speaker SP, 1 to 10 seconds is appropriate, for example, about 5 seconds.) When the audio signal is continuously output, the normal audio signal is output to the BTL power amplifier. The control signal St that determines that the DC abnormal voltage has not been input to the input terminal 30 but has been input is output.

Next, the control circuit 5 receives the output St of the timer circuit 4 and activates the output on / off circuit 3 of the BTL power amplifier 30 (turns off the output of the BTL power amplifier) as a control signal. The standby signal Ssb is transmitted to the amplifier 30.

Due to the operation of the speaker protection circuit, the output of the BTL power amplifier 30 is automatically turned off before the speaker SP overheats even if the abnormal DC voltage is input, and the speaker SP does not become important.

It goes without saying that a control signal for turning off the output of the BTL power amplifier 30 may be another control signal for turning off the output, in addition to the above-mentioned standby signal.

The speaker protection circuit according to the present invention uses the clip detection circuit 1 of the output voltage waveform Vout used for the purpose of improving the sound quality in the conventional LSI chip of the BTL power amplifier 30 for controlling it. Since only the timer circuit 4 and the control circuit 5 of the BTL amplifier built in the microcomputer 10 are used, there is almost no increase in cost as compared with the prior art, and the smoke-based and ignition of the speaker SP can be avoided beforehand. There is no doubt that it will be a great speaker protection measure.

[0026]

The speaker protection circuit in the BTL power amplifier according to the present invention detects the abnormal DC voltage input to the input of the BTL power amplifier and turns off the output. Therefore, smoke is generated by the application of the abnormal DC voltage of the speaker. There is an excellent effect that ignition is prevented beforehand, and the safety of car audio, which requires particularly severe environmental resistance, is improved.

In addition, the above speaker protection circuit is usually built in a control microcomputer by using a clip detection circuit used for controlling a volume control circuit in an LSI circuit of a conventional BTL power amplifier. There is an excellent design and manufacturing advantage that it can be realized extremely simply and at low cost using only the timer circuit and the control circuit of the BTL power amplifier.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram for explaining a configuration of a speaker protection circuit in a BTL power amplifier according to the present invention.

FIG. 2 is a waveform diagram of Vin, Vout, Scp, and Ssb when an abnormal DC voltage occurs in the BTL power amplifier according to the present invention.

FIG. 3 is a waveform diagram of Vin in a BTL power amplifier, Vout where a clip has occurred, and a clip detection signal Scp.

FIG. 4 is a circuit diagram showing an example of a basic circuit and a protection circuit of a conventional BTL power amplifier.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 clip detection circuit 3 output on / off circuit 4 timer circuit 5 control circuit 7 volume control circuit 10 control microcomputer chip 30 BTL power amplifier CP clip (saturation) Scp clip detection signal Ssb control signal (standby signal) St timer circuit Output SP Speaker Toff Predetermined time Vin Input signal waveform Vout Output voltage waveform Vs Saturation level

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) KA22 KA33 KA62 SA05 TA01 TA06

Claims (1)

[Claims] 1. A clip detection circuit for detecting a clip of an output voltage waveform due to saturation of a BTL power amplifier and outputting a clip detection signal, and receiving the clip detection signal of the clip detection circuit and continuing the clip for a predetermined time or more. A speaker protection circuit for a BTL power amplifier, comprising: a timer circuit for outputting a signal in a case; and a control circuit for receiving a output of the timer circuit and outputting a control signal for turning off an output of the BTL power amplifier.