US3549808A - Protective circuit for speaker windings - Google Patents
Protective circuit for speaker windings Download PDFInfo
- Publication number
- US3549808A US3549808A US673543A US3549808DA US3549808A US 3549808 A US3549808 A US 3549808A US 673543 A US673543 A US 673543A US 3549808D A US3549808D A US 3549808DA US 3549808 A US3549808 A US 3549808A
- Authority
- US
- United States
- Prior art keywords
- speaker
- circuit
- loudspeaker
- output
- windings
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/50—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the appearance of abnormal wave forms, e.g. ac in dc installations
-
- 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
Definitions
- This invention relates to a circuit for protecting a loudspeaker and, more particularly, to a protective circuit that will prevent damage to a loudspeaker from overload currents resulting from a unique set of conditions.
- a particularly vexing problem that arises in the driving of loudspeakers occurs in the situation where the final amplifier stage, i.e. the stage just preceding the speaker, is directly and conductively connected to the speaker. This contrasts with the more common situation where the output arrangement involves transformer coupling.
- Such direct connection is a well-known useful and economic expedient for the purpose of providing a very simple output arrangement in, for example, a radio or television receiver.
- the failure of the amplifying device results in the power supply voltage being applied to the, speaker winding.
- the power supply conventionally takes the formof batteries or other DC supply. Since the speaker winding has a low impedance to direct current it will be damagedby the resultant excessive current unless it is protected.
- the failure referred to above of the amplifying device would be, for instance, the case where the device shorts out.” In that event, the normally high im 'pedance afforded by the amplifying device, such as the high impedance normally present at the output of a transistor, for example, would be eliminated and thereby the speaker would receive substantially the full power supply voltage.
- the protective device In a context or environment where the final stage of the amplifier is in the form of a push-pull circuit, as is common arrangement today, the protective device must protect against overload currents of either polarity.
- a pushpull circuit will be set forth hereinafter, this particular form being a complementary push-pull transistor circuit, but it will be evident that other push-pull circuits, as well as single device output stages, are similarly amenable to control by the circuit of the present invention.
- the present invention provides as its principal feature a circuit that substantially instantaneously responds when a condition arises such that the direct voltage supply would be applied to the loudspeaker due to failure of the amplifying output stage.
- the circuit is such that it does not respond to the normal alternating signal currents that are meant to flow to the loudspeaker.
- the present invention provides a solution to a unique problem present with direct-connected loudspeakers.
- the circuits operation is for all practical purposes instantaneous in preventing harm that might result from the application of the full voltage supply to the speaker windings. It thus sharply contrasts with slow acting protective devices previously known in the art.
- FIG. 1 is a circuit diagram illustrating one embodiment of invention incorporated in a typical "f the circuit of the present push-pull circuit.
- FIG. 2 is an alternative embodiment of the protective circuit in accordance with the present inve'ntion.
- transistor push-pull circuit in which the unique protective arrangement of the present invention i's jembodied.
- the circuit has been selected' toshow a'complementary (NPN and PNP) form of push-pull operation.
- the transistor 10 is a PNP transistor and transistor 12 is an NPN transistor.
- This configuration that is, complementary push-pull, is, of course, well-known in the art.
- the direct conductive connection to the speaker at the output of this push-pull configuration is also, per se, well-known.
- the transistors 10 and 12 which are opposite polarity transistors, have their emitters connectedto their"respective oppositely polarized power supplies, shown as batteries 14 and 16. Thence, the transistors 10 and 12 are connected in common to the load; that is, to the speaker 18 which serves as the only load in the output circuit.
- the novel circuit means in accordance with the present invention is shown within the box designated 20.
- the elements within the box 20 are thus interposed between the final amplifying stage and the loudspeaker 18.
- the protective means generally designated 20, consists of a relay which, as shown has its coil S1 connected in series with a resistor R1. Together, these two elements are connected across the output terminals.
- the coil S1 is shown schematically, the relay is of the nonpolarized variety, that is to say, it will respond equally well to. currents of opposite polarity to perform its intended function. I 1
- a capacitor C1 is connected in parallel with the relay wind ing S1.
- This capacitor C1 is a nonpolarized type.
- the relay in the protective circuit has a contact K1 which is connected in series with the speaker 18. This contact K1 is normally closed but operates in realizing the intended objective of the protec tive circuit, so as to open the output connection the loud-.
- An arc-suppressing capacitor C2 is connected in shunt with the relay contact terminals.
- the normal operation of the circuit of FIG. 1 is such that alternating output signals, in the form of audio frequency signals, which result from theapplication of input signals to the bases of transistors 10 and 12, are applied to the load, i.e. the loudspeaker 18, which is connectedin common to these push-pull transistor stages.
- the resulting alternating output currents are bypassed around the relay winding 81 through the capacitor C1. This is done in order that there be no spurious operation, that is, energization of the relay with consequent opening up of the speaker circuit when, in fact, no danger is present. 7
- the capacitor C1 and the resistance R1 are judiciously selected so as to present sufficient impedance to alternating signals of the lowest frequency and the maximum amplitude which are intended to be supplied to the speaker. Thus, under the normal conditions, there will be no interference with the listening enjoyment.
- the resistance of R that is, of the resistor in series with the relay coil 51, depends on the relay sensitivity, and should be made substantially equal to the resistance of the relay coil itself. It will be understood that the resistance of R1 is effectively acting as part of an RC circuit which determines the lowest frequency passed to the speaker and also as a current limiter for the relay.
- FIG. 2 there is illustrated an alternative embodiment of the protective circuit of the present invention.
- electronic solid-state components rather than electromechanical components, such as a relay, are employed.
- a device sometimes called a triac or thyristor, well known to those versed in the art, is connected to serve as the protective element which absorbs the current that would normally damage the speaker winding.
- a triac or thyristor well known to those versed in the art
- the resistor R1 and a nonpolarized capacitor C1 are again connected across the output terminals of the amplifier.
- the control device 30 is shown connected to the protective device 32.
- One terminal of the device 30 is connected to the gate 32a of the device 32 and the other end of the device 30 is connected to the common junction of the RC circuit formed by the resistor R1 and the capacitor C1.
- the device 32 has its output elec trodes 32b and 32c connected across the speaker winding.
- the device 30, which is a two terminal device, may take the form of a so-called four layer diode and, more particularly, such a diode having the property that its VI characteristic exhibits breakdown in both the forward and reverse bias states. Effectively, then, the impedance of such a device goes to substantially zero when a predetermined critical voltage is exceeded in either direction.
- An alternative form for such device 30 is that it may be constituted simply of two diodes, of the type shown in U.S. Pat. No. 2,789,254, connected in series and oppositely poled.
- the usual alternating currents that are normally present are bypassed by the capacitor C1, so as to have no effect on the operation of device 30.
- the device 30 immediately breaks down upon reaching its critical voltage.
- This critical voltage is, of course, chosen to be less than the supply voltage.
- the critical or breakdown voltage for device 30 is chosen to be of the order of 8 volts, while the supply voltage has a value, for example, of 36 volts. At breakdown the impedance of device 30 goes to a value of substantially zero.
- a biasing current flows through the gate 32a of the device 32 of a sufficient value to cause that device to assume an extremely low impedance output state, being effectively a short circuit. This means that the potentially damaging current from the DC supply is bypassed through the output of device 32, rather than flowing through the windings of speaker 18.
- a fuse be incorporated in the output circuit so that the aforenoted short" across the device 32 will result in blowing the fuse.
- the fuse is not absolutely necessary and may be omitted since the devices 30 and 32 and the resistor R1 are capable of withstanding the current values involved.
- FIG. 2 is capable of protecting the speaker windings regardless of the polarity of DC voltage that is sought to be applied to these windings. This is so because both of the devices 30 and 32 are able to respond to absorb the potentially damaging current regardless of the applied polarity. It will be understood, of course, that the nature of the device 32 must be such that, in the illustration of FIG. 2, the polarity of current must be similar to that of the direction of conduction through the output terminals 32b and 32c.
- the device 32 is selected to have those modes of operation such that, for example, when a positive battery potential is sought to be applied to the point above resistor R1, the current flow will be into the gate 320 of the device 32, and this will comport with the current flow through device 32 in a direction from electrode 32b to electrode 320.
- breakdown to the low impedance state at these output electrodes is accomplished through the medium of the gate control current rather than being provided directly by the DC voltage applied to the output electrodes of device 32.
- What has been provided by the present invention is an ex tremely simple and effective protective means which operates quickly and efficiently to protect a loudspeaker from the dangers presented by the application of the full direct voltage of the power supply. This is accomplished in such a way that the dynamic range and fidelity of the loudspeaker is not impaired and thus the listening enjoyment is in nowise diminished.
- a protective circuit interposed between said final amplifier stage and the loudspeaker, said protective circuit comprising a controlling means which is unresponsive to the normal alternating currents flowing to said loudspeaker but which responds in the event of failure of said amplifier device to the consequent imposition of said direct voltage supply by preventing excessive current flow to said speaker due to such imposition; said protective circuit further comprising a resistor and a capacitor in series, both being connected across the output terminals of the final amplifier stage; and further comprising first and second devices, the first device having the property that its voltage-current characteristic exhibits breakdown in both the forward and reverse bias states, said second device including a gate, one end of said first device being connected to the common junction between said resistor and said capacitor, the other end thereof being connected to said gate of said second device, said second device having its output terminals
- the first device comprising a four layer diode and the second device comprising a thyristor.
- a circuit comprising a loudspeaker and an amplifier stage directly and conductively connected-thereto, said loudspeaker being the only load for said amplifier stage; a direct current power supply connected to said amplifier such that, upon failure of said amplifier, said direct current power supply has its full value applied to said speaker, said circuit further comprising protective means instantaneously operating in response to such failure to prevent excessive current flow to said speaker, said means being unresponsive otherwise so as not to interfere with the flow of signal currents to said speaker; said protective means comprising a resistor and a capacitor in series, both being connected across the output terminals of said amplifier stage; and further comprisingfirst and second devices, the first device having the property that its voltagecurrent characteristic exhibits breakdown in both the forward and reverse bias states, said second device including a gate, one end of said first device being connected to the common junction between said resistor and said capacitor, the other end thereof being connected to said gate of said second device, said second device having its output terminals across said speaker and being operative responsive to the breakdown of said first device to provide a low impedance across
Description
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US67354367A | 1967-10-09 | 1967-10-09 |
Publications (1)
Publication Number | Publication Date |
---|---|
US3549808A true US3549808A (en) | 1970-12-22 |
Family
ID=24703075
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US673543A Expired - Lifetime US3549808A (en) | 1967-10-09 | 1967-10-09 | Protective circuit for speaker windings |
Country Status (1)
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US (1) | US3549808A (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2133639A1 (en) * | 1971-04-16 | 1972-12-01 | Stanton Magnetics | |
US4359626A (en) * | 1980-03-18 | 1982-11-16 | Potter Bronson M | Electric blanket heating control with capacitance sensing |
US20060222185A1 (en) * | 2005-04-05 | 2006-10-05 | Ultimate Ears, Llc | Headset visual feedback system |
US9450636B2 (en) | 2014-12-30 | 2016-09-20 | Motorola Solutions, Inc. | Intrinsically safe audio power current circuit and device using same |
-
1967
- 1967-10-09 US US673543A patent/US3549808A/en not_active Expired - Lifetime
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2133639A1 (en) * | 1971-04-16 | 1972-12-01 | Stanton Magnetics | |
US4359626A (en) * | 1980-03-18 | 1982-11-16 | Potter Bronson M | Electric blanket heating control with capacitance sensing |
US20060222185A1 (en) * | 2005-04-05 | 2006-10-05 | Ultimate Ears, Llc | Headset visual feedback system |
WO2006107464A2 (en) * | 2005-04-05 | 2006-10-12 | Ultimate Ears, Llc | Headset visual feedback system |
WO2006107464A3 (en) * | 2005-04-05 | 2007-11-15 | Ultimate Ears Llc | Headset visual feedback system |
US8077872B2 (en) * | 2005-04-05 | 2011-12-13 | Logitech International, S.A. | Headset visual feedback system |
US9450636B2 (en) | 2014-12-30 | 2016-09-20 | Motorola Solutions, Inc. | Intrinsically safe audio power current circuit and device using same |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: SECURITY PACIFIC FINANCE CORP., A CORP. OF DE, CAL Free format text: SECURITY INTEREST;ASSIGNORS:SUPERSCOPE, INC. A CA CORP.;SUPERSCOPE TAPE DUPLICATING PRODUCTS, INC., A CA CORP.;MARANTZ PIANO COMPANY, INC., A VA CORP.;AND OTHERS;REEL/FRAME:003950/0705 Effective date: 19811223 Owner name: SECURITY PACIFIC FINANCE CORP. 10 SOUTH LAKE AVE, Free format text: SECURITY INTEREST;ASSIGNORS:SUPERSCOPE, INC. A CA CORP.;SUPERSCOPE TAPE DUPLICATING PRODUCTS, INC., A CA CORP.;MARANTZ PIANO COMPANY, INC., A VA CORP.;AND OTHERS;REEL/FRAME:003950/0705 Effective date: 19811223 |
|
AS | Assignment |
Owner name: DYNASCAN CORPORATION, A CORP. OF DE Free format text: RELEASED BY SECURED PARTY;ASSIGNOR:SECURITY PACIFIC FINANCE CORP., A CORP. OF DE;REEL/FRAME:005852/0823 Effective date: 19910923 |