US3544720A - Protective circuit for loudspeaker - Google Patents

Protective circuit for loudspeaker Download PDF

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Publication number
US3544720A
US3544720A US810706A US3544720DA US3544720A US 3544720 A US3544720 A US 3544720A US 810706 A US810706 A US 810706A US 3544720D A US3544720D A US 3544720DA US 3544720 A US3544720 A US 3544720A
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voltage
terminal
loudspeaker
switch
bilateral
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US810706A
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Sidney A Corderman
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MCINTOSH LAB Inc
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MCINTOSH LAB Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/007—Protection circuits for transducers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
    • H02H9/041—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage using a short-circuiting device
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/52—Circuit arrangements for protecting such amplifiers

Definitions

  • Transistor power amplifiers commonly are connected directly to a loudspeaker. They are operated push-pull, one transistor being connected to a positive supply and the other to an equal negative supply. If a transistor shorts, on either side, one side of the power supply or the other is connected directly to the loudspeaker, through the shorted transistor. Under these conditions sufficient current flows to the loudspeaker to destroy or seriously damage the loudspeaker and may cause the speaker cone to catch fire. A simple fuse does not provide adequate protection because it acts too slowly, and a supplementary rapidly acting device is therefore needed. According to the present invention, solid state devices are utilized for the purpose, which are connected directly to the loudspeaker system and which are capable in response to control voltage of either polarity of firing and conducting full load current around the loudspeaker to ground.
  • FIG. I is a schematic circuit diagram of a system according to the invention.
  • FIG. 2 is a schematic circuit diagram of a modification of the system of FIG. 1.
  • the output terminal 14 is connected directly to an anode I of triac TR and via a 1K resistance 16 to the gate electrode of triac TR, anode 2 of which is grounded.
  • C constitutes a low pass filter so that the audio voltage across the $88 or bilateral switch S is always zero, absent d.c. voltage, since one side of S is connected to the junction of C and R and the other side to the terminal 14 via small resistance (1K) 16.
  • T, and T shorts, high d.c. voltage from either terminal 11 or 12 will be applied to one side of S and the other side will be at ground voltage via resistance R, and the SBS will fire.
  • the $38 is a silicon planar monolithic integrated circuit having the electrical characteristics of a bilateral thyristor, but which switches rapidly at :8.v. It is normally supplied with a gate lead, not used in the present application.
  • a triac TR is connected between terminal 14 and ground, and has a gate electrode connected directly to the ungrounded side of S. So long as S is unfired, there is no net gating voltage. When S fires, one side of TR is at supply voltage and the gate electrode, which is on that side, is brought to ground via S and R. TR then fires and having fired remains fired, shorting the loudspeaker L to ground.
  • the terminal 14 is connected to one side of TR, the other side of which is grounded.
  • Resistance R is connected to one side of C, the other side of which is grounded, and S is connected between the junction of C and R and the gate electrode of TR.
  • Resistance 16 is connected in shunt to TR.
  • TR is normally unfired, and CR provides a low pass filter which blocks audio frequencies, so that both sides of S are normally at ground potential. If a transistor shorts out, high d.c. voltage is applied to one side of S, which fires, causing d.c. current flow in resistance 16. The resulting d.c. voltage across resistance 16 is applied to the gate electrode of TR, causing it to fire. The resistance 16 also prevents triac turn on due to rate-effect. R is selected to allow adequate triac gate current to assure turn on, and C is then designed in view of the value of R to provide the desired filter characteristics.
  • the triac is an ac. switch, i.e., a bidirectional triode thyristor which may be gate triggered from a blocking to a conducting state for either polarity of applied voltage, and is roughly equivalent to two SCRs connected in inverse parallel. Once fired, it remains fired until its primary circuit is opened or primary current reduced to zero, i.e., the gate electrode controls firing but not defiring.
  • Fuses F, and F will blow after the triac has fired, because fuses are slowly acting devices.
  • the system thus provides rapidly acting protection, operation pending blowing of fuses, which are slow acting.
  • a solid state protective circuit for an audio speaker connected between a terminal and ground comprising:
  • said triac having a gate electrode means connecting said bi lateral solid state switch in series with said gate electrode;
  • an audio filter connected, arranged, and adapted to supply only d.c. voltage across said bilateral solid state switch and to prevent access to said bilateral solid state switch of ac. voltage in the audio frequency range.
  • a protective circuit for a transistor audio power amplifier having one transistor connected to a positive voltage terminal and another transistor connected to a negative voltage terminal, and a speaker connected to a terminal at the junction of said transistors, comprising:
  • an audio filter having a cutoff at the lowest audio frequency of the audio frequency band passed by said audio power amplifier and connected, arranged, and adapted to maintain substantially zero voltage across bilateral voltage sensitive switch in response to said audio frequency band at said terminal but full d.c. voltage in response to d.c. voltage at said terminal.
  • said filter is a low pass filter having a series resistance and a shunt capacitor connected between said terminal and one side of said bilateral voltage sensitive switch, the other side of said bilateral voltage sensitive switch being connected to said gate electrode.
  • said filter includes a capacitor connected between said terminal and one side of said bilateral voltage sensitive switch, a resistance connected between said terminal and the other side of said bilateral voltage sensitive switch, said gate electrode being connected directly to said other side of said bilateral voltage sensitive switch, a resistance connecting said other side to ground, and a direct connection to ground from said terminal via the anodes of said solid state switch.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Description

United States Patent Inventor Sidney A. Corderman Binghamton, New York 810,706
March 26, 1969 Dec. 1, 1970 McIntosh Laboratory, Inc. Binghamton, New York a corporation of Delaware Appl. No. Filed Patented Assignee PROTECTIVE CIRCUIT FOR LOUDSPEAKER 7 Claims, 2 Drawing Figs.
US. Cl. 179/1; 307/93, 307/914, 307/248; 323/22 Int. Cl. H04r 3/00; H02h 3/20; GOSf 1/60 Field of Search 179/1 (A), 1, 1(SW); 307/248, 299, 93, 9 4, 100; 330/144; 323/22, 66.9
AMP
[56] References Cited UNITED STATES PATENTS 3,058,010 10/1962 S. C. Rockafellow 307/248 3,206,695 9/1965 E. Y. Bennett, Jr. 307/93X 3,218,542 11/1965 V. L. Taylor 323/22 Primary Examiner- Kathleen I-l. Claffy Assistant Examiner-Charles W. Jirauch Attorney-Hurvitz, Rose & Greene ABSTRACT: A protective circuit for a transistor power amplitier which connects both positive and negative voltages directly to a loudspeaker, in which a voltage sensitive bilateral switch is connected to the speaker terminal in series with an ac. filter, to act as a switch, sensitive to voltage of either polarity above a predetermined value, and which when fired fires a triac connected directly across the speaker.
LOUD
SPEAKER PA'TENTED 0501 I970 LOUD I SPEAKER ANDDE l [K GATE muons 2 TR 0. us
- lll SIDNEY HCORDERNHN M 6a 0 ATTORNEY PROTECTIVE CIRCUIT FOR LOUDSPEAKER BACKGROUND OF THE INVENTION Transistor power amplifiers commonly are connected directly to a loudspeaker. They are operated push-pull, one transistor being connected to a positive supply and the other to an equal negative supply. If a transistor shorts, on either side, one side of the power supply or the other is connected directly to the loudspeaker, through the shorted transistor. Under these conditions sufficient current flows to the loudspeaker to destroy or seriously damage the loudspeaker and may cause the speaker cone to catch fire. A simple fuse does not provide adequate protection because it acts too slowly, and a supplementary rapidly acting device is therefore needed. According to the present invention, solid state devices are utilized for the purpose, which are connected directly to the loudspeaker system and which are capable in response to control voltage of either polarity of firing and conducting full load current around the loudspeaker to ground.
SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic circuit diagram of a system according to the invention; and t FIG. 2 is a schematic circuit diagram of a modification of the system of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Tenis an amplifier circuit antecedent to an output stage consisting essentially of two series connected NPN transistors T, and T The collector of T, is connected via a fuse F, to a positive voltage supply terminal 11. The emitterof T is connected via a fuse F to a negative voltage supply terminal 12. The emitter of T, is connected via a very small resistance 13 to output terminal 14. The collector ofT, is similarly connected. The amplifier configuration is wholly conventional. A loudspeaker L is connected between terminal 14 and ground.
The output terminal 14 is connected directly to an anode I of triac TR and via a 1K resistance 16 to the gate electrode of triac TR, anode 2 of which is grounded. C constitutes a low pass filter so that the audio voltage across the $88 or bilateral switch S is always zero, absent d.c. voltage, since one side of S is connected to the junction of C and R and the other side to the terminal 14 via small resistance (1K) 16. However, if either T, and T shorts, high d.c. voltage from either terminal 11 or 12 will be applied to one side of S and the other side will be at ground voltage via resistance R, and the SBS will fire.
The $38 is a silicon planar monolithic integrated circuit having the electrical characteristics of a bilateral thyristor, but which switches rapidly at :8.v. It is normally supplied with a gate lead, not used in the present application.
A triac TR is connected between terminal 14 and ground, and has a gate electrode connected directly to the ungrounded side of S. So long as S is unfired, there is no net gating voltage. When S fires, one side of TR is at supply voltage and the gate electrode, which is on that side, is brought to ground via S and R. TR then fires and having fired remains fired, shorting the loudspeaker L to ground.
In FIG. 2, the terminal 14 is connected to one side of TR, the other side of which is grounded. Resistance R is connected to one side of C, the other side of which is grounded, and S is connected between the junction of C and R and the gate electrode of TR. Resistance 16 is connected in shunt to TR.
In operation, TR is normally unfired, and CR provides a low pass filter which blocks audio frequencies, so that both sides of S are normally at ground potential. If a transistor shorts out, high d.c. voltage is applied to one side of S, which fires, causing d.c. current flow in resistance 16. The resulting d.c. voltage across resistance 16 is applied to the gate electrode of TR, causing it to fire. The resistance 16 also prevents triac turn on due to rate-effect. R is selected to allow adequate triac gate current to assure turn on, and C is then designed in view of the value of R to provide the desired filter characteristics.
The triac is an ac. switch, i.e., a bidirectional triode thyristor which may be gate triggered from a blocking to a conducting state for either polarity of applied voltage, and is roughly equivalent to two SCRs connected in inverse parallel. Once fired, it remains fired until its primary circuit is opened or primary current reduced to zero, i.e., the gate electrode controls firing but not defiring.
Fuses F, and F will blow after the triac has fired, because fuses are slowly acting devices. The system thus provides rapidly acting protection, operation pending blowing of fuses, which are slow acting.
While the is system is applied to protection of a loudspeaker, it is applicable to any type of load.
lclaim:
1. A solid state protective circuit for an audio speaker connected between a terminal and ground, comprising:
a bilateral solid state switch;
a triac connected between said terminal and ground;
said triac having a gate electrode means connecting said bi lateral solid state switch in series with said gate electrode; and
an audio filter connected, arranged, and adapted to supply only d.c. voltage across said bilateral solid state switch and to prevent access to said bilateral solid state switch of ac. voltage in the audio frequency range.
2. A protective circuit for a transistor audio power amplifier having one transistor connected to a positive voltage terminal and another transistor connected to a negative voltage terminal, and a speaker connected to a terminal at the junction of said transistors, comprising:
a bilateral gate electrode controlled solid state switch connected across said speaker;
a bilateral voltage sensitive switch connected between said terminal and said gate electrode; and
an audio filter having a cutoff at the lowest audio frequency of the audio frequency band passed by said audio power amplifier and connected, arranged, and adapted to maintain substantially zero voltage across bilateral voltage sensitive switch in response to said audio frequency band at said terminal but full d.c. voltage in response to d.c. voltage at said terminal.
3. The combination according to claim 2, wherein said filter is a low pass filter having a series resistance and a shunt capacitor connected between said terminal and one side of said bilateral voltage sensitive switch, the other side of said bilateral voltage sensitive switch being connected to said gate electrode.
4. The combination according to claim 2, wherein said filter includes a capacitor connected between said terminal and one side of said bilateral voltage sensitive switch, a resistance connected between said terminal and the other side of said bilateral voltage sensitive switch, said gate electrode being connected directly to said other side of said bilateral voltage sensitive switch, a resistance connecting said other side to ground, and a direct connection to ground from said terminal via the anodes of said solid state switch.
5. A solid state protective circuit for a transistorized audio power amplifier having a speaker connected directly to a power output transistor, of said power amplifier, said transistor normally providing only audio frequency signal to said speaker and providing only high d.c. voltage to said speaker on short circuiting of said transistor, comprising:
a voltage sensitive normally open solid state switch;
6. The combination according to claim 5, wherein said filter means is a low pass audio filter connected in series with said switch.
7. The combination according to claim 5, wherein said switch is an ac. switch and said gate controlled switching device is a triac, and said dc. voltage can be of either polarity.
US810706A 1969-03-26 1969-03-26 Protective circuit for loudspeaker Expired - Lifetime US3544720A (en)

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Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3731153A (en) * 1970-08-27 1973-05-01 Sansui Electric Co Protective device for loudspeaker
US3784840A (en) * 1972-12-21 1974-01-08 Klh Res Dev Corp Solid state remote power switch
US3925708A (en) * 1974-03-25 1975-12-09 Andrew V Picciochi Safety means for audio speakers
US3980930A (en) * 1975-05-01 1976-09-14 Rca Corporation Protection circuit
US3992677A (en) * 1974-04-30 1976-11-16 Sony Corporation Muting circuit
US4010402A (en) * 1974-05-21 1977-03-01 Sony Corporation Load protective circuit
US4023074A (en) * 1975-11-21 1977-05-10 Electrohome Limited Loudspeaker protection network
FR2359532A1 (en) * 1976-07-20 1978-02-17 Cit Alcatel Balanced load protection circuit - is controlled from pilot network and parallel nominal load connected across supply
US4208594A (en) * 1978-04-03 1980-06-17 Honeywell Inc. Power monitor for use in starting and stopping a digital electronic system
US4296278A (en) * 1979-01-05 1981-10-20 Altec Corporation Loudspeaker overload protection circuit
EP0147818A2 (en) * 1983-12-21 1985-07-10 FASE S.p.A. Electronic circuit for protection of productive systems coupled to a power supply
US4538296A (en) * 1983-07-22 1985-08-27 Short Robert S Sound inhibitor for audio transducers
US4644294A (en) * 1984-01-23 1987-02-17 SGS Componenti Elettronici S.p.A. Device for protecting a push-pull output stage against a short-circuit between the output terminal and the positive pole of the supply
US4944015A (en) * 1988-04-29 1990-07-24 Juve Ronald A Audio compression circuit for television audio signals
US4975963A (en) * 1983-08-01 1990-12-04 Zvie Liberman Muting circuit
US5237421A (en) * 1990-08-27 1993-08-17 Thomson Consumer Electronics, Inc. Shutdown system in a television receiver
US5548650A (en) * 1994-10-18 1996-08-20 Prince Corporation Speaker excursion control system
US5548810A (en) * 1994-03-30 1996-08-20 Safe Pursuit, Inc. Hands-free two-way radio communication system
US6351544B1 (en) 1999-12-10 2002-02-26 Harman International Industries Incorporated Regressively hinged spider
US6563926B1 (en) * 1999-07-27 2003-05-13 Nortel Networks Limited Resetting surge protection in telephone line interface circuits
US6665415B1 (en) 1999-09-09 2003-12-16 Harman International Industries, Incorporated Loudspeaker overcurrent protection
US6885745B1 (en) 1998-12-17 2005-04-26 Nortel Networks, Ltd. Voltage and protection arrangement for a telephone subscriber line interface circuit

Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3731153A (en) * 1970-08-27 1973-05-01 Sansui Electric Co Protective device for loudspeaker
US3784840A (en) * 1972-12-21 1974-01-08 Klh Res Dev Corp Solid state remote power switch
US3925708A (en) * 1974-03-25 1975-12-09 Andrew V Picciochi Safety means for audio speakers
US3992677A (en) * 1974-04-30 1976-11-16 Sony Corporation Muting circuit
US4010402A (en) * 1974-05-21 1977-03-01 Sony Corporation Load protective circuit
US3980930A (en) * 1975-05-01 1976-09-14 Rca Corporation Protection circuit
US4023074A (en) * 1975-11-21 1977-05-10 Electrohome Limited Loudspeaker protection network
FR2359532A1 (en) * 1976-07-20 1978-02-17 Cit Alcatel Balanced load protection circuit - is controlled from pilot network and parallel nominal load connected across supply
US4208594A (en) * 1978-04-03 1980-06-17 Honeywell Inc. Power monitor for use in starting and stopping a digital electronic system
US4296278A (en) * 1979-01-05 1981-10-20 Altec Corporation Loudspeaker overload protection circuit
US4538296A (en) * 1983-07-22 1985-08-27 Short Robert S Sound inhibitor for audio transducers
US4975963A (en) * 1983-08-01 1990-12-04 Zvie Liberman Muting circuit
EP0147818A3 (en) * 1983-12-21 1985-08-07 Fase Spa Electronic circuit for protection of productive systems coupled to a power supply
EP0147818A2 (en) * 1983-12-21 1985-07-10 FASE S.p.A. Electronic circuit for protection of productive systems coupled to a power supply
US4644294A (en) * 1984-01-23 1987-02-17 SGS Componenti Elettronici S.p.A. Device for protecting a push-pull output stage against a short-circuit between the output terminal and the positive pole of the supply
US4944015A (en) * 1988-04-29 1990-07-24 Juve Ronald A Audio compression circuit for television audio signals
US5237421A (en) * 1990-08-27 1993-08-17 Thomson Consumer Electronics, Inc. Shutdown system in a television receiver
US5548810A (en) * 1994-03-30 1996-08-20 Safe Pursuit, Inc. Hands-free two-way radio communication system
US5548650A (en) * 1994-10-18 1996-08-20 Prince Corporation Speaker excursion control system
US6885745B1 (en) 1998-12-17 2005-04-26 Nortel Networks, Ltd. Voltage and protection arrangement for a telephone subscriber line interface circuit
US6563926B1 (en) * 1999-07-27 2003-05-13 Nortel Networks Limited Resetting surge protection in telephone line interface circuits
US6665415B1 (en) 1999-09-09 2003-12-16 Harman International Industries, Incorporated Loudspeaker overcurrent protection
US6351544B1 (en) 1999-12-10 2002-02-26 Harman International Industries Incorporated Regressively hinged spider

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