DE2337705A1 - PROTECTIVE CIRCUIT FOR ELECTROACOUSTIC DEVICES - Google Patents

Description

Applicant IV: Beltek Corporation

13-'7, P chome, Nishi-Ko.'i;, ^, OtaVu, T ο k: ο / Japa.n

Protection circuit for electroacoustic devices

The invention relates to a protective circuit in particular for loudspeakers and the output stage transistors of Amplifiers in any electroacoustic devices, or sound devices for short.

There are a number of devices and circuits to protect the output stage transistors of audio frequency amplifiers against abnormally high current loads, namely overloads by overcurrent, and to protect speakers against unwanted Voltage fluctuations at the output from the amplifier to the speaker have been suggested. The previously known However, protection devices and circuits use a very large number of transistors and other circuit elements, are therefore very complex in terms of construction, their installation in sound equipment consequently causes undesirably high levels Koster :.

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Based on the known prior art, it is primarily the aim of the invention to provide a new and improved one To propose protective circuit for sound equipment, which is characterized by a simpler and less complex structure, which manages in particular with a limited number of transistors and other circuit elements.

It is a further object of the invention to propose a protection circuit of the type in question, which the Output stage transistor. of audio frequency amplifiers from current overloads protects, which can occur, for example, in the event of a short circuit in the output contacts of the amplifier.

In addition, it is the object of the invention to propose such a protective circuit that is similar to that of an audio frequency amplifier assigned loudspeakers against voltage fluctuations on the amplifier, such as those from the unavoidable wear and tear or fatigue of the circuit elements can be attributed to disruptive effects protection.

Finally, it is the object of the invention to provide such a protective circuit to create the speaker against unwanted effects

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shields from temporary voltage fluctuations on the Amplifier output originate, as they can occur, for example, when the switch is operated.

In order to achieve the objects outlined above and further problems which will be shown below, the invention is based on the invention a protective circuit for electroacoustic devices with a transistor-operated amplifier and a Loudspeaker provided. According to the invention, the protective circuit has a pair between loudspeaker and amplifier output inserted relay contacts. In addition, a relay circuit is provided, which has one of the relay contacts assigned, Has relay coil and transistors monitoring the puncture of the relay coil. The component of the relay circuit forming transistors is also assigned a delay circuit in such a way that an application of the Relay coil in the sense of a closure of the relay contacts only takes place after a specified period of time after closure of the switch has elapsed, so that the loudspeaker is affected by interference effects caused by voltage fluctuations at the amplifier output when the device is switched on is spared. The protection circuit also has an overload detector circuit, which in turn has Transistors is populated with the output stage transistors

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of the amplifier acting overcurrent in the sense of influencing the relay coil of the relay circuit in this way respond that the relay coil is de-energized via the delay circuit and the transistors associated with this circuit will. The interruption between loudspeaker and amplifier caused by the open relay contacts is maintained for a specified period of time in which the output stage transistors remain unstressed.

Finally, the protective circuit can alternatively or additionally be provided with a DC voltage detector circuit, which is also equipped with transistors that respond to voltage fluctuations at the output of the amplifier in such a way, that the relay coil of the relay circuit via the delay circuit and its associated transistors of the Relay circuit is made currentless. The relay contacts opened to separate the loudspeaker from the amplifier are then again held in the open position for a predetermined period of time in order to protect the loudspeaker from voltage fluctuations.

A major advantage of the protective circuit according to the invention over previously known solutions is the small number of

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electrical components, especially transistors, with which it gets by. Further advantages are their functional reliability as much as the extent of the protection it provides,

The features or combinations of features which are believed to be new and characteristic of the invention are outlined in detail in the claims. Design and puncture method of the circuit according to the invention emerge from the following description of a plurality of preferred embodiments shown in the drawings of the circuit, wherein like reference numerals identify the same electrical components. Show it:

Figure 1 shows the electrical circuit diagram of a preferred embodiment of the invention Protection circuit,

Figure 2 shows the circuit diagram of a modified embodiment,

FIG. 5 shows the circuit diagram of a third embodiment,

FIG. 4 shows the circuit diagram of a fourth embodiment.

The protective circuit according to the invention in Figure 1 is a

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Pair of relay contacts LS assigned, which are provided between the loudspeaker SP and a point P between the emitter resistors Rl and R2 of the corresponding output stage transistors Q6 and Q7 of the sound device amplifier, and consist of a detector circuit that reacts to the transistors QjS and Q7 applied overcurrent.

A DC voltage detector circuit that detects voltage fluctuations in the aforementioned point P, from which the amplifier power is delivered, reacts and a relay circuit, the one depending on the detector circuit responding to the overcurrent and on the voltage fluctuations Detector circuit opens the relay contacts LS if necessary.

The overload detector circuit has in particular a transistor Ql, the base of which with the amplifier between the output point P and the transistor Q6 and Q7, respectively is. The current level to be monitored by the transistor Ql is predetermined by the resistors R3 and R4.

The one that responds to the voltage fluctuations at point P. The DC voltage detector circuit is equipped with transistors Q2, Q3 and QS. Deviations from the normal, on 0 volts

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The set potential in the positive sense is indicated by the transistor Q2, those in the negative sense by the Transistor QJ. The bases of the respective transistors Q2 and QJ are at point P via the current limiting resistor R5 connected. The voltage level to be monitored by transistors QJ and Q8 is given by the Resistors R6, R7 and R8. The transistors Ql, Q2 and Q8 are connected to a current limiting resistor R9.

The relay circuit includes a relay coil LC and transistors Q4 and Q5. The function of the transistor q4 is monitored by a delay circuit, which is through a con-. capacitor Cl and resistor Rio, RIl and R12 is formed. The transistor Q4 is also with the current limiting resistor RlJ connected.

A transformer T with two secondary windings is used as the voltage source T2 and TJ provided. The outputs A and B of the secondary winding T2 are connected to the terminals A and B of the amplifier connected, while the outputs C and D of the secondary winding TJ still provided to the terminals C and D of the Protection circuit according to the invention are connected. Only one secondary winding can also be provided,

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their outputs both to the terminals of the amplifier and are connected to the terminals of the protective circuit.

When the switch SW1 is closed, DC voltage is applied to the outputs AB and. CD of the secondary windings T2 and T ^ des Transformer. At this point the speaker remains SP, however, initially still separated from the point P of the amplifier by the open relay contacts LS, and onto this Shielded from interfering effects due to voltage fluctuations at point P. The relay contacts LS close only when there are no more voltage fluctuations at point P, which is achieved as follows.

After the switch SW1 is closed, the current from the secondary winding T3 flows through the resistor Rio, the capacitor Cl to ground. While the capacitor Cl is charged in this way, the voltage in Point b of the protection circuit is lowered to such an extent that no current flows through the transistors QA and Q5. So there is initially no excitation of the relay coil LC, the relay contacts LS remain open and the loudspeaker SP remains separate from the amplifier. According to the invention, the point in time up to which the relay contacts LS remain open,

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are exactly synchronized with the time at which the temporarily occurring at the outputs A and B of the transformer following the closing of the switch SWl Voltage fluctuations come in port case.

As soon as the capacitor Cl is charged, a feedback voltage is applied to the transistor q4, whereby this Transistor as well as transistor Q5 become conductive. As a result the relay coil LC is now also excited, the relay contacts LS are closed and the electrical Connection established between the amplifier and the loudspeaker. The sound device equipped with the protective circuit according to the invention is now in the operating state.

In the event that an abnormally large signal is applied to the output stage transistors Q6 and QCJ of the amplifier, for whatever reason, or if the outputs ti and t2 of the amplifier are short-circuited, an increased current flowing through transistor Q6 causes both ends of the Resistance Rl produces a voltage. This voltage passes through resistors Rj5 and R4 to transistor Ql and causes a short circuit between the collector and emitter of this transistor. This results in a discharge of the initially charged capacitor Cl through a short circuit, the

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from the capacitor Cl, the resistor R9, the diode D4, Collector and emitter of the transistor Ql, the relay contacts LS, the outputs ti and t2 of the amplifier and ground will. The potential at point b is thereby reduced so far that no more current through the transistors Q4 and Q5 of the relay circuit flows. As a result, the relay coil LC is de-energized and the relay contacts LS are opened, so that no more current through transistors Q6 and Q7 of the amplifier flows.

Even if the above-described abnormal condition no longer exists, the relay coil LC remains initially still de-energized, and the relay contacts LS remain accordingly open until the capacitor Cl is fully charged again. The transistors Q6 and Q7 of the amplifier thus remain temporarily ineffective, namely because the potential at point b remains lowered until the capacitor Cl is fully charged again, and the transistor q4 in the meantime does not have the predetermined feedback voltage is applied. The transistors Q4 and Q5 and thus also the relay coil LC remain ineffective until the capacitor C1 is fully charged. As soon the charging of the capacitor Cl is complete, lies

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also the feedback voltage again on transistor Q4 and the relay coil LC is energized again, from which the closing of the contacts LS between amplifier and loudspeaker SP results. In the absence of abnormal conditions, the loudspeaker will now operate again. Kick. Again abnormal conditions occur, the above-described process is repeated.

Monitoring of the voltage fluctuations is also according to the invention at point P of the amplifier with the aim of the output stage transistors 0.6 and Q7 as well as the loudspeaker It is intended to shield SP from voltage fluctuations. The transistor Q2 of the DC voltage detector circuit responds to positive deviations in the voltage, to negative ones Deviations of the transistor QJ. The transistor Q8 takes effect as soon as the transistor Q3 responds and calls a short circuit out, which discharges the capacitor Cl of the relay circuit.

It is now assumed that the potential at point P fluctuates in the negative direction. The transistor Q & of the detector circuit is then excited in a corresponding manner in order to reduce the voltage potential at point a, which is

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stood Ro in negative territory was held in positive Convict area. Once transistor Q8 is on applied in this way with the predetermined feedback voltage the discharge of the capacitor Cl via the mentioned, from the capacitor Cl, the resistor R9, The collector and emitter of transistor Q8 and the short-circuit formed earth are discharged.

When the potential in point b is ^{lowered, the transistors ei 2} ! - and 0.5 of the relay circuit become non-conductive, thus the relay coil LC is de-energized. The relay contacts LS are opened accordingly and the loudspeaker SP is disconnected from the amplifier. This circuit protects both the loudspeaker SP and the transistors Q.6 and 0.7

As explained above, the relay contacts LS then remain open until the capacitor C1 is fully charged again, even if the normal operating conditions are already present again. In the meantime, the transistors Q6 and 0.7 remain ineffective. If the potential fluctuations persist at point P, the transistors ^ 2, Qj5 and q8 react to it in the sense of a continuous opening of the relay contacts LS.

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In the circuit in FIG. 2, one of the transistors *, namely transistor Q5 of the relay circuit, is omitted. Ir. In this case, the rapid discharge of the capacitor C1 following the opening of the switch SVJ1 (FIG. 1) is brought about by the diode D1. If the switch SWl is closed, the described functions of the capacitor Cl are controlled by the diode Dl.

To the base of transistor Q4 of the relay circuit is a Avalanche diode D2 connected so that the excitation of the relay coil LC begins via the transistor Q4 as soon as the Charging of the capacitor Cl by the voltage present at the outputs C and D of the transformer increases the potential im Point b corresponds to the sum of the breakdown voltage of the avalanche diode D2 and the feedback voltage of the transistor q4. Since the size of the resistor Rio can be significantly reduced in this way, a current of such magnitude can the base of the transistor Q, 4 applied to its unaffected Ensures switching function. In addition, the capacitance of the capacitor Cl can be designed to be smaller will.

In Figure J5, the overload detection circuit is made up of transistors ^ l and Q9 and formed by a thjrristor QIo. Will

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the transistor Ql conducts when an overcurrent occurs, the transistor Q9 also becomes conductive with the result that on voltage is present at both ends of the resistor Rl4. The thyristor QIo made conductive in this way triggers the discharge of the capacitor Cl via that formed by the capacitor Cl, the resistor Rio, the thyristor QIo and ground Short circuit out. Because of this, the voltage at the point P is rapidly lowered so that the transistor Q4 is non-conductive from which the de-excitation of the relay coil LC results. The relay contacts LS are thus in turn in the sense a separation of the loudspeaker SP to the amplifier opened.

A resistor RI5 of such a size is provided here, that when the thyristor QIo is conductive, a current that maintains the conductive state of the thyristor flows. Another Resistor Rio protects the thyristor QIo and the Transistors Q2 and Q8 in the rapid discharge of the capacitor Cl. Since the thyristor QIo, provided that it is once conductive remains in this state, a switch SW ^ (Figure J5) should be provided to return the thyristor to its initial state transfer back. That can be done, however also by turning off the main switch.

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It goes without saying that constructive or circuitry Modifications of the protective circuit according to the invention which can be implemented on the basis of the known prior art appear to fall within the scope of the invention.

In Figure 4 is a modified DC voltage detector circuit intended. For the purpose of regulating the voltage level to a level that will make transistor QJ5 conductive, are the transistor an avalanche diode D3 and a variable Assigned to resistor R17. If there is a positive voltage at point P of the amplifier, transistor Q2 conductive, whereby the relay circuit is influenced in the sense of an opening of the relay contacts LS. In a corresponding way a negative voltage at point P makes transistors Q3 and 0.8 conductive, which in turn conduct the relay circuit affect LS in the sense of an opening of the relay contacts. If the one ensuring the conductive state of the transistor Q2 Voltage is, for example, + 0.62 volts, the conductive state of the transistors 03 and 0.8 by a from the avalanche diode D3 and the variable resistor R17 evoked voltage of --0.62 volts.

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Claims (1)

Applicant: Beltek Corporation 13-17,2 chome, Nishi-Kojiya, Otaku, T ο k γ ο / Japan B 250 patent claims Protective circuit for electroacoustic devices which have an amplifier equipped with transistors and a loudspeaker, characterized in that they are made of the following electrical components 1. Relay contacts between loudspeaker and amplifier output, 2. a relay coil assigned to the relay contacts and transistors for monitoring the relay coil having relay circuit, 5. one connected to the transistors of the relay circuit, a delay circuit containing a capacitor, which only excites the relay coil after a specified time after the closing of the switch allows, 309886/0963 ft 4. an overload detector circuit also equipped with transistors, the transistors of which are connected to the amplifier between the output of the amplifier and a final stage transistor of the amplifier, and which, if necessary, respond to the flow of an increased current through the final stage transistor which forms the discharge of the component of the delay circuit Capacitor trips,
whereby the relay coil is de-energized in the sense of an opening of the relay contacts, which then up to
be held in the open position to fully recharge the capacitor. 2. Protection circuit for electroacoustic devices, which have an amplifier equipped with transistors and a loudspeaker have, characterized in that it consists of the following electrical components 1. a pair of relay contacts between loudspeaker and Output of the amplifier, 2. a relay coil assigned to the relay contacts and transistors for monitoring the relay coil having relay circuit, 309886/0963 3. one connected to the transistors of the relay circuit a delay circuit containing a capacitor, the excitation of the relay coil only after a given tent after closing the switch, 4. a DC voltage detector circuit also equipped with transistors, whose transistors are connected to the output of the amplifier, and if necessary respond to voltage fluctuations at the amplifier output that cause the component to discharge trigger the capacitor forming the delay circuit, causing the relay coil to open the relay contacts are de-energized, which then takes place until the capacitor is fully recharged be held in the open position. Protection circuit for electroacoustic devices, which have an amplifier equipped with transistors and a loudspeaker have, characterized in that it consists of the following electrical components 1. Relay contacts between loudspeaker and amplifier output, 309886/0963 2. a relay coil assigned to the relay contacts and transistors for monitoring the relay coil having relay circuit, 5. one connected to the transistors of the "relay circuit, a delay circuit containing a capacitor, the excitation of the relay coil only after allows a specified time after the closing of the switch, 4. an overload detector circuit also equipped with transistors, its transistors with the amplifier between the output of the amplifier and connected to a final stage transistor of the amplifier and which may respond to the flow of an increased current through the output stage transistor, which triggers the discharge of the capacitor forming part of the delay circuit, whereby the relay coil is de-energized in the sense of an opening of the 'relay contacts, which then up to be held in the open position again to fully recharge the capacitor. 3098 8 6/0963 5. a DC voltage detector circuit also equipped with transistors, whose transistors are connected to the output of the amplifier, and if necessary respond to voltage fluctuations at the amplifier output that cause the component to discharge trigger the capacitor forming the delay circuit, whereby the relay coil in the sense of an opening the relay contacts are de-energized, which are then used until the capacitor is fully recharged in held in the open position. • 4. Protective circuit according to Claims 2 and J5, characterized in that that the DC voltage detector circuit at least one for positive deviations in the voltage on Amplifier output and at least one other for negative deviations in the voltage at the amplifier output having responsive transistor. 309886/0963 Empty soap