WO2007062686A1 - Thermal protection circuit for an crt amplifier - Google Patents

Thermal protection circuit for an crt amplifier Download PDF

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Publication number
WO2007062686A1
WO2007062686A1 PCT/EP2005/056341 EP2005056341W WO2007062686A1 WO 2007062686 A1 WO2007062686 A1 WO 2007062686A1 EP 2005056341 W EP2005056341 W EP 2005056341W WO 2007062686 A1 WO2007062686 A1 WO 2007062686A1
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WO
WIPO (PCT)
Prior art keywords
clipping
thermal protection
protection circuit
circuit
signal
Prior art date
Application number
PCT/EP2005/056341
Other languages
French (fr)
Inventor
Thomas Dett
Bernd Fey
Original Assignee
Tte Germany Gmbh
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Tte Germany Gmbh filed Critical Tte Germany Gmbh
Priority to PCT/EP2005/056341 priority Critical patent/WO2007062686A1/en
Publication of WO2007062686A1 publication Critical patent/WO2007062686A1/en

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Classifications

    • 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
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/447—Indexing scheme relating to amplifiers the amplifier being protected to temperature influence
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/552—Indexing scheme relating to amplifiers the amplifier being made for video applications

Definitions

  • the present invention is related to a thermal protection circuit according to the preamble of claim 1.
  • Thermal protection circuits of this kind are used for amplifiers of cathode ray tubes, e.g. for CRT amplifiers.
  • the request for higher resolutions (HDTV) for CRT displays requires stronger CRT amplifiers.
  • the CRT amplifiers have to provide a high beam current at high picture frequencies. This request results in a high power dissipation of the CRT amplifiers for large picture areas at a high bandwith.
  • Thermal protection circuits are needed to reduce the chip temperatures of the CRT amplifiers. Large heatsinks for the CRT amplifiers output stages are no longer needed.
  • a thermal protection circuit of the prior art which is shown in figure 1, controls a temperature of an amplifier A for a cathode ray tube CRT by modifying an input signal S.
  • Temperature detection means TD of the thermal protection circuit detect values, which are related to the chip temperature of the amplifier A.
  • the values can be generated by the chip temperature itself or by the dissipated power, which can be measured by an integration of the supply current.
  • the supply current increases with the current consumption, when the amplifier A is driven at a full picture high frequency signal.
  • the thermal protection circuit further comprises temperature controlling means TC and signal modifying means B with switching means SW and a slew rate reduction circuit SR.
  • the temperature controlling means TC are connected to the slew rate reduction circuit SR due to the switching means SW.
  • the detected temperature is controlled by modifying the input signal S with the slew rate reduction circuit SR.
  • the signal modifying means B only modify high level and high frequency contents of the input signal S.
  • the thermal protection circuit is only active for the high level contents of the high frequency part of the input signal S.
  • the chip temperature is too high, only the high level contents are reduced. Low level, high frequency contents are not modified. They remain unchanged.
  • the modification of the input signal S, by an inventive thermal protection circuit is non-linear. It enables a significant increase in picture performance, especially in the picture sharpness, even when the thermal protection circuit is active. Large, heavy and expensive heatsinks, e.g, cooling elements, are avoided.
  • the invention is very useful for amplifiers with a high bandwidth output.
  • the signal modifying means B can comprise clipping means CL, which clip the high level amplitudes of the high frequency contents of the input signal S.
  • the signal modifying means B can further comprise providing means FP, which provide the clipping means CL with the high frequency contents of the input signal S.
  • the providing means can comprise frequency detection means and switching means .
  • the providing means can comprise a high pass filter circuit HP.
  • the modifying means B can comprise a providing circuit Bl with a high pass filter circuit HP as providing means FP, with a low pass filter circuit LP and with an adding circuit AD.
  • the signal modifying means B can comprise an integrated clipping circuit B2, which integrates the clipping means CL and the temperature controlling means TC. Clipping levels U c i, U c h of this clipping means can be determinded by the detected temperature. - A -
  • the integrated clipping circuit B2 can comprise two clipping transistors in a push-pull arrangement, which are controlled by the clipping levels U c i, U C h
  • the temperature detection means TD can comprise a resistor, which is thermally coupled to the amplifier A.
  • figure 1 a simplified diagram of a thermal protection circuit of the prior art, an amplifier and a cathode ray tube, figure 2, a simplified diagram of a thermal protection circuit of the first embodiment, an amplifier and a cathode ray tube, figure 3, a simplified diagram of a thermal protection circuit of the second embodiment, an amplifier and a cathode ray tube, figure 4, a simplified circuit diagram of the thermal protection circuit of the second embodiment, an amplifier and a cathode ray tube, figure 5, a simplified diagram of a transfer function U out (Ui n ) of the thermal protection circuit of the prior art, which is generated for a high frequency signal, figure 6, a simplified diagram of a transfer function U out (Ui n ) of the thermal protection circuit of the first and second embodiments of the invention, which is generated for a high frequency signal, figure 7, simplified input signal S with high frequency, with a high level and with a low level and signals Sm, which are modified by the thermal protection circuit of the prior art, figure 8, simplified input signals S
  • the thermal protection circuit for an amplifier A for a cathode ray tube CRT of the prior art is shown in figure 1.
  • the thermal protection circuit comprises temperature detection means TD, temperature controlling means TC and signal modifying means B.
  • the signal modifying means B have switching means SW and a slew rate reduction circuit SR. By the switching means SW, the temperature controlling means TC are connected to the slew rate reduction circuit SR of the signal modifying means B.
  • the temperature of the amplifier A is detected by the detection means TD.
  • the temperature controlling means TC control the switching means SW in a way that the input signal S is modified by the slew rate reduction circuit SR.
  • the temperature of the amplifier A is controlled by modifying an input signal S.
  • the input signal S is modified in a way, that the bandwidth of its high frequency contents is reduced.
  • the reduction is independent of the level of the input signal S, e.g. of its amplitude.
  • the modification of the high frequency contents of the signal S are shown as modified signals Sm in figures 5 and 7.
  • a thermal protection circuit of the first embodiment of the invention corresponds to that of the prior art in that, it comprises temperature detection means TD, temperature controlling means TC and signal modifying means B with switching means SW. It is shown in figure 2.
  • the signal modifying means B only modify high level and high frequency contents of the input signal S. Therefore the signal modifying means B comprise clipping means CL, which clip the high level amplitudes of the high frequency contents of the input signal S.
  • the signal modifying means B further comprise providing means FP, which are connected with the switching means SW and which provide the clipping means CL with the high frequency contents of the input signal S.
  • the providing means B comprise frequency detection means and switching means .
  • the temperature of the amplifier A is detected by the detection means TD.
  • the temperature controlling means TC control the switching means SW and, as a result, the providing means FP. If there are any high frequency contents, they are conducted to the clipping means CL. As a result the high level, high frequency contents of the input signal S are modified by the clipping means CL in a way, that its amplitudes are reduced.
  • the modification of the high frequency contents are shown as modified signals Sm in figures 6 and 8.
  • thermal protection circuit of the second embodiment of the invention corresponds to a thermal protection circuit of the first embodiment in all ways, except for the following features:
  • the signal modifying means B comprise a providing circuit Bl and an integrated clipping circuit B2, which is coupled to the temperature detection means TD.
  • the clipping circuit B2 integrates the clipping means CL and the temperature controlling means TC.
  • the clipping circuit B2 further integrates the switching means SW.
  • the providing circuit Bl comprises the providing means PR, which are generated by a high pass filter circuit HP, a low pass filter circuit LP and an adding circuit AD.
  • the input signal S is led to the high pass filter circuit HP and to the low pass filter circuit LP.
  • the high pass filter circuit HP is generated by a capacitor CBOOl, which is coupled in series, and an emitter follower circuit of a transistor TBOOl.
  • This circuit comprises a voltage divider with to resistors RBOOl and RB002 at the base of the transistor TBOOl and an emitter resistor RB003.
  • the input signal S is taken off with a high input resistance and its high level contents are delivered with a low output resistance to the clipping circuit B2.
  • the emitter of the transistor TBOOl is coupled to a resistor RB004 of an entrance step of the clipping circuit B2.
  • the entrance step further comprises a frequency compensation circuit with a resistor RB005 and a capacitor CB002, which are coupled in series to each other and in parallel to the resistor RB004.
  • the resistor RB004 is coupled to two clipping transistors TB002 and TB003 in a push-pull arrangement. Specifically, the resistor RB004 is coupled to the connected emitters of the clipping transistors TB002 and TB004.
  • the clipping transistors TB002 and TB003 are arranged in emitter follower circuits, which comprise resistors RB005 and RB006.
  • the clipping transistor TB002 is a npn-transistor . When necessary it clips the amplitude of the negative part of the high frequency contents of the signal S.
  • the clipping transistor TB003 is a pnp-transistor . When necessary it clips the amplitudes of the positive part of the high frequency contents of the signal S.
  • the clipping transistors TB002 and TB003 are controlled by clipping levels U c i, U C h ⁇ e.g. by the voltages U c i, U C h at their bases.
  • the clipping level U c i which controls the clipping of the negative part of the high frequency contents of the signal S, is generated by a low level generation circuit.
  • This circuit comprises a diode DBOOl and a resistor RB007, which are coupled in series to each other and to the base of the clipping transistor TB002.
  • the diode DBOOl only conducts a positive voltage.
  • the resistor RB007 limits the current of the base of the clipping transistor TB002.
  • the circuit further comprises a capacitor CB004, which is coupled parallel to the base and sinks high frequency interferences.
  • the circuit further comprises a transistor TB004 in a collector circuit.
  • the transistor TB004 is a pnp-transistor, whose emitter is coupled to a resistor RB006. The emitter of the transistor TB004 is also coupled to the base of the clipping transistor TB002.
  • the low level generation circuit is coupled to the temperature detection means TD.
  • the base of the transistor TB004 is coupled to a resistor R # , which is a PTC- resistor.
  • the PTC-resistor R# is one of two resistors, R-& and RB012, of a voltage divider of the temperature detection means TD.
  • the resistor R# is thermally coupled to the amplifier A.
  • the clipping level U C h r which controls the clipping of the positive part of the high frequency contents of the signal S, is generated by a high level generation circuit.
  • This circuit comprises a diode DB002 and a resistor RB008, which are coupled in series to each other and to the base of the clipping transistor TB003.
  • the diode DB002 only conducts a negative voltage.
  • the resistor RB008 limits the current of the base of the clipping transistor TB003.
  • the circuit further comprises a capacitor CB003, which is coupled parallel to the base and sinks high frequency interferences.
  • the circuit further comprises a transistor TB005 in an emitter circuit.
  • the transistor TB003 is an npn-transistor, whose collector is coupled to a resistor RB009.
  • the collector of the transistor TB004 is also coupled to the base of the clipping transistor TB003.
  • the circuit further comprises a voltage divider with resistors RBOlO and RBOIl, which is coupled to the base of the transistor TB003, and a resistor RB0012, which is coupled in series to the base.
  • the resistors RBOlO, RBOIl and RB012 specify an operation point of the clipping resistor TB005.
  • the high level generation circuit is also coupled to the temperature detection means TD. Specifically, the base of the transistor TB005 is coupled to the resistor R # .
  • the high frequency contents of the input signal S is clipped.
  • a modified signal with a clipped voltage Uhf C is generated.
  • the clipping circuit B2 further comprises a capacitor CB032, which blocks the DC-parts of the clipped signal, and an emitter follower circuit of a transistor TB0032.
  • This circuit comprises a voltage divider with two resistors RB042 and RB043 at the base of the transistor TB032 and an emitter resistor RB034.
  • the clipped signal is taken off with a high resistance and is matched to a signal with low frequency contents of the input signal S, which is generated by the low pass filter circuit LP. Specifically, it is delivered with a low resistance to the adding circuit AD.
  • the low pass filter circuit LP is generated by a capacitor CBOOl and an emitter follower circuit of a transistor TB031.
  • the capacitor CBOOl is coupled in parallel to the base of the transistor TB032.
  • the emitter follower circuit comprises a resistor RB031, which is coupled in series to the base of the transistor TB032, and an emitter resistor RB033.
  • the input signal S is taken off with a high input resistance and its low level contents are delivered with a low output resistance to the adding circuit AD.
  • the adding circuit AD comprises a resistor RB037 for the low frequency contents of the input signal S, a resistor RB036 for its high frequency, clipped contents and a common base circuit of a transistor TB033.
  • the adding circuit AD further comprises a capacitor CB035, which is coupled in series to the resistor RB036 and which blocks the DC-parts of the high frequency contents of the signal S.
  • the adding circuit comprises a frequency compensation circuit with a resistor RB035 and a capacitor CB033, which are coupled in series to each other and in parallel to the resistor RB036.
  • the common base circuit with the transistor TB033 comprises an emitter resistor RB038, a collector resistor RB039, a voltage divider with two resistors RB040 and RB041, which is coupled to the base, and a capacitor CB034.
  • the capacitor CB034 is coupled parallel to the base and sinks high frequency interferences.
  • the collector of the transistor TB033 is coupled to the negative input of the amplifier A. Uiow is a low supply voltage of 12 V for the thermal protection circuit.
  • the temperature of the amplifier A is detected by the PTC-resistor R#.
  • the increasing voltage U# at the resistor R# increases the clipping level U c i and decreases the clipping level U C h-
  • the clipping levels U c i, U C h are determined by the detected temperature.
  • the two clipping transistors TB002 and TB003 becomes conductive and, as a result, the negative and the positive amplitudes of the high frequency contents of the signal S are clipped.
  • the clipped high frequency contents and the low frequency contents of the signal S are added in the adding circuit AD and generate the modified signal S M .
  • This signal S M is led to the amplifier A. Only the high level contents of the high frequency part of the input signal S are reduced. The low level, high frequency contents of the signal S remain unchanged.
  • the modification of high frequency contents of the signal S are shown in as modified signals Sm in figures 6 and 8.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Abstract

A thermal protection circuit controls a temperature of an amplifier (A) by modifying an input signal (S). Such a thermal protection circuit is used for a CRT amplifier and comprises temperature detection means (TD), temperature controlling means (TC) and signal modifying means (B). The signal modifying means (B) modify, as an inventive feature, only high level and high frequency contents of the input signal (S).

Description

Thermal Protection Circuit for an CRT Amplifier
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention is related to a thermal protection circuit according to the preamble of claim 1. Thermal protection circuits of this kind are used for amplifiers of cathode ray tubes, e.g. for CRT amplifiers. The request for higher resolutions (HDTV) for CRT displays requires stronger CRT amplifiers. The CRT amplifiers have to provide a high beam current at high picture frequencies. This request results in a high power dissipation of the CRT amplifiers for large picture areas at a high bandwith. Thermal protection circuits are needed to reduce the chip temperatures of the CRT amplifiers. Large heatsinks for the CRT amplifiers output stages are no longer needed.
DESCRIPTION OF THE PRIOR ART
A thermal protection circuit of the prior art, which is shown in figure 1, controls a temperature of an amplifier A for a cathode ray tube CRT by modifying an input signal S.
Temperature detection means TD of the thermal protection circuit detect values, which are related to the chip temperature of the amplifier A. The values can be generated by the chip temperature itself or by the dissipated power, which can be measured by an integration of the supply current. The supply current increases with the current consumption, when the amplifier A is driven at a full picture high frequency signal. The thermal protection circuit further comprises temperature controlling means TC and signal modifying means B with switching means SW and a slew rate reduction circuit SR. The temperature controlling means TC are connected to the slew rate reduction circuit SR due to the switching means SW. The detected temperature is controlled by modifying the input signal S with the slew rate reduction circuit SR.
The disadvantage of this modification of the input signal S is, that its bandwidth is reduced independently of its amplitude. This is shown in figures 5 and 7. In addition, high frequency, low level signals are attenuated. The details of the pictures become smoother than desired.
SUMMARY OF THE INVENTION
It is therefore desirable to develop a thermal protection circuit according to the preamble of claim 1, which avoids this disadvantage.
According to the invention this can be achieved by the features of claim 1. The signal modifying means B only modify high level and high frequency contents of the input signal S.
As a result, the thermal protection circuit is only active for the high level contents of the high frequency part of the input signal S. When the chip temperature is too high, only the high level contents are reduced. Low level, high frequency contents are not modified. They remain unchanged. This is shown in figures 6 and 8. The modification of the input signal S, by an inventive thermal protection circuit, is non-linear. It enables a significant increase in picture performance, especially in the picture sharpness, even when the thermal protection circuit is active. Large, heavy and expensive heatsinks, e.g, cooling elements, are avoided. The invention is very useful for amplifiers with a high bandwidth output.
Possible advantageous developments of the invention are specified in the dependent claims.
The signal modifying means B can comprise clipping means CL, which clip the high level amplitudes of the high frequency contents of the input signal S.
The signal modifying means B can further comprise providing means FP, which provide the clipping means CL with the high frequency contents of the input signal S.
The providing means can comprise frequency detection means and switching means . Alternatively, the providing means can comprise a high pass filter circuit HP.
The modifying means B can comprise a providing circuit Bl with a high pass filter circuit HP as providing means FP, with a low pass filter circuit LP and with an adding circuit AD.
The signal modifying means B can comprise an integrated clipping circuit B2, which integrates the clipping means CL and the temperature controlling means TC. Clipping levels Uci, Uch of this clipping means can be determinded by the detected temperature. - A -
The integrated clipping circuit B2 can comprise two clipping transistors in a push-pull arrangement, which are controlled by the clipping levels Uci, UCh
The temperature detection means TD can comprise a resistor, which is thermally coupled to the amplifier A.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in more detail using two embodiments, which are illustrated in the figures together with an example of the prior art.
It shows : figure 1, a simplified diagram of a thermal protection circuit of the prior art, an amplifier and a cathode ray tube, figure 2, a simplified diagram of a thermal protection circuit of the first embodiment, an amplifier and a cathode ray tube, figure 3, a simplified diagram of a thermal protection circuit of the second embodiment, an amplifier and a cathode ray tube, figure 4, a simplified circuit diagram of the thermal protection circuit of the second embodiment, an amplifier and a cathode ray tube, figure 5, a simplified diagram of a transfer function Uout (Uin) of the thermal protection circuit of the prior art, which is generated for a high frequency signal, figure 6, a simplified diagram of a transfer function Uout (Uin) of the thermal protection circuit of the first and second embodiments of the invention, which is generated for a high frequency signal, figure 7, simplified input signal S with high frequency, with a high level and with a low level and signals Sm, which are modified by the thermal protection circuit of the prior art, figure 8, simplified input signals S with high frequency, with a high level and with a low level and signals Sm, which are modified by the thermal protection circuit of the first and second embodiment of the invention.
DETAILED DESCRIPTION OF A PRIOR ART
A thermal protection circuit for an amplifier A for a cathode ray tube CRT of the prior art is shown in figure 1. The thermal protection circuit comprises temperature detection means TD, temperature controlling means TC and signal modifying means B. The signal modifying means B have switching means SW and a slew rate reduction circuit SR. By the switching means SW, the temperature controlling means TC are connected to the slew rate reduction circuit SR of the signal modifying means B.
While in operation, the temperature of the amplifier A is detected by the detection means TD. When the detected temperature is greater than a setpoint, the temperature controlling means TC control the switching means SW in a way that the input signal S is modified by the slew rate reduction circuit SR. As a result, the temperature of the amplifier A is controlled by modifying an input signal S.
The input signal S is modified in a way, that the bandwidth of its high frequency contents is reduced. The reduction is independent of the level of the input signal S, e.g. of its amplitude. The modification of the high frequency contents of the signal S are shown as modified signals Sm in figures 5 and 7.
DETAILED DESCRIPTION OF A FIRST EMBODIMENT OF THE INVENTION
A thermal protection circuit of the first embodiment of the invention corresponds to that of the prior art in that, it comprises temperature detection means TD, temperature controlling means TC and signal modifying means B with switching means SW. It is shown in figure 2.
As an inventive feature, the signal modifying means B only modify high level and high frequency contents of the input signal S. Therefore the signal modifying means B comprise clipping means CL, which clip the high level amplitudes of the high frequency contents of the input signal S. The signal modifying means B further comprise providing means FP, which are connected with the switching means SW and which provide the clipping means CL with the high frequency contents of the input signal S. The providing means B comprise frequency detection means and switching means .
While in operation, the temperature of the amplifier A is detected by the detection means TD. When the detected temperature is greater than a setpoint, the temperature controlling means TC control the switching means SW and, as a result, the providing means FP. If there are any high frequency contents, they are conducted to the clipping means CL. As a result the high level, high frequency contents of the input signal S are modified by the clipping means CL in a way, that its amplitudes are reduced. The modification of the high frequency contents are shown as modified signals Sm in figures 6 and 8. DETAILED DESCRIPTION OF A SECOND EMBODIMENT OF THE INVENTION A thermal protection circuit of the second embodiment of the invention, which is shown in figures 3 and 4, corresponds to a thermal protection circuit of the first embodiment in all ways, except for the following features:
The signal modifying means B comprise a providing circuit Bl and an integrated clipping circuit B2, which is coupled to the temperature detection means TD. The clipping circuit B2 integrates the clipping means CL and the temperature controlling means TC. The clipping circuit B2 further integrates the switching means SW.
The providing circuit Bl comprises the providing means PR, which are generated by a high pass filter circuit HP, a low pass filter circuit LP and an adding circuit AD. The input signal S is led to the high pass filter circuit HP and to the low pass filter circuit LP.
The high pass filter circuit HP is generated by a capacitor CBOOl, which is coupled in series, and an emitter follower circuit of a transistor TBOOl. This circuit comprises a voltage divider with to resistors RBOOl and RB002 at the base of the transistor TBOOl and an emitter resistor RB003. The input signal S is taken off with a high input resistance and its high level contents are delivered with a low output resistance to the clipping circuit B2.
The emitter of the transistor TBOOl is coupled to a resistor RB004 of an entrance step of the clipping circuit B2. The entrance step further comprises a frequency compensation circuit with a resistor RB005 and a capacitor CB002, which are coupled in series to each other and in parallel to the resistor RB004. The resistor RB004 is coupled to two clipping transistors TB002 and TB003 in a push-pull arrangement. Specifically, the resistor RB004 is coupled to the connected emitters of the clipping transistors TB002 and TB004. The clipping transistors TB002 and TB003 are arranged in emitter follower circuits, which comprise resistors RB005 and RB006.
The clipping transistor TB002 is a npn-transistor . When necessary it clips the amplitude of the negative part of the high frequency contents of the signal S. The clipping transistor TB003 is a pnp-transistor . When necessary it clips the amplitudes of the positive part of the high frequency contents of the signal S. The clipping transistors TB002 and TB003 are controlled by clipping levels Uci, UCh^ e.g. by the voltages Uci, UCh at their bases.
The clipping level Uci, which controls the clipping of the negative part of the high frequency contents of the signal S, is generated by a low level generation circuit. This circuit comprises a diode DBOOl and a resistor RB007, which are coupled in series to each other and to the base of the clipping transistor TB002. The diode DBOOl only conducts a positive voltage. The resistor RB007 limits the current of the base of the clipping transistor TB002. The circuit further comprises a capacitor CB004, which is coupled parallel to the base and sinks high frequency interferences. The circuit further comprises a transistor TB004 in a collector circuit. The transistor TB004 is a pnp-transistor, whose emitter is coupled to a resistor RB006. The emitter of the transistor TB004 is also coupled to the base of the clipping transistor TB002.
The low level generation circuit is coupled to the temperature detection means TD. Specifically, the base of the transistor TB004 is coupled to a resistor R#, which is a PTC- resistor. The PTC-resistor R# is one of two resistors, R-& and RB012, of a voltage divider of the temperature detection means TD. The resistor R# is thermally coupled to the amplifier A.
The clipping level UChr which controls the clipping of the positive part of the high frequency contents of the signal S, is generated by a high level generation circuit. This circuit comprises a diode DB002 and a resistor RB008, which are coupled in series to each other and to the base of the clipping transistor TB003. The diode DB002 only conducts a negative voltage. The resistor RB008 limits the current of the base of the clipping transistor TB003. The circuit further comprises a capacitor CB003, which is coupled parallel to the base and sinks high frequency interferences. The circuit further comprises a transistor TB005 in an emitter circuit. The transistor TB003 is an npn-transistor, whose collector is coupled to a resistor RB009. The collector of the transistor TB004 is also coupled to the base of the clipping transistor TB003.
The circuit further comprises a voltage divider with resistors RBOlO and RBOIl, which is coupled to the base of the transistor TB003, and a resistor RB0012, which is coupled in series to the base. The resistors RBOlO, RBOIl and RB012 specify an operation point of the clipping resistor TB005.
The high level generation circuit is also coupled to the temperature detection means TD. Specifically, the base of the transistor TB005 is coupled to the resistor R#.
At a junction point, between the resistor RB004 and the emitters of the clipping transistors TB002 and TB003, the high frequency contents of the input signal S is clipped. A modified signal with a clipped voltage UhfC is generated.
The clipping circuit B2 further comprises a capacitor CB032, which blocks the DC-parts of the clipped signal, and an emitter follower circuit of a transistor TB0032. This circuit comprises a voltage divider with two resistors RB042 and RB043 at the base of the transistor TB032 and an emitter resistor RB034. The clipped signal is taken off with a high resistance and is matched to a signal with low frequency contents of the input signal S, which is generated by the low pass filter circuit LP. Specifically, it is delivered with a low resistance to the adding circuit AD.
The low pass filter circuit LP is generated by a capacitor CBOOl and an emitter follower circuit of a transistor TB031. The capacitor CBOOl is coupled in parallel to the base of the transistor TB032. The emitter follower circuit comprises a resistor RB031, which is coupled in series to the base of the transistor TB032, and an emitter resistor RB033. The input signal S is taken off with a high input resistance and its low level contents are delivered with a low output resistance to the adding circuit AD.
The adding circuit AD comprises a resistor RB037 for the low frequency contents of the input signal S, a resistor RB036 for its high frequency, clipped contents and a common base circuit of a transistor TB033. The adding circuit AD further comprises a capacitor CB035, which is coupled in series to the resistor RB036 and which blocks the DC-parts of the high frequency contents of the signal S. Additionally, the adding circuit comprises a frequency compensation circuit with a resistor RB035 and a capacitor CB033, which are coupled in series to each other and in parallel to the resistor RB036. By joining the low frequency contents and the high frequency contents of the signal S together, the two resistors RB036 and RB037 are coupled to the emitter of the transistor TB033.
The common base circuit with the transistor TB033 comprises an emitter resistor RB038, a collector resistor RB039, a voltage divider with two resistors RB040 and RB041, which is coupled to the base, and a capacitor CB034. The capacitor CB034 is coupled parallel to the base and sinks high frequency interferences. The collector of the transistor TB033 is coupled to the negative input of the amplifier A. Uiow is a low supply voltage of 12 V for the thermal protection circuit.
While in operation, the temperature of the amplifier A is detected by the PTC-resistor R#. When the detected temperature becomes greater than a setpoint, the increasing voltage U# at the resistor R# increases the clipping level Uci and decreases the clipping level UCh- As a result, the clipping levels Uci, UCh are determined by the detected temperature. The two clipping transistors TB002 and TB003 becomes conductive and, as a result, the negative and the positive amplitudes of the high frequency contents of the signal S are clipped. The clipped high frequency contents and the low frequency contents of the signal S are added in the adding circuit AD and generate the modified signal SM. This signal SM is led to the amplifier A. Only the high level contents of the high frequency part of the input signal S are reduced. The low level, high frequency contents of the signal S remain unchanged. The modification of high frequency contents of the signal S are shown in as modified signals Sm in figures 6 and 8.

Claims

Claims
1. Thermal protection circuit for controlling a temperature of an amplifier by modifying an input signal (S) , which comprises temperature detection means (TD) , temperature controlling means (TC) and signal modifying means (B) , characterised in that the signal modifying means (B) modify only high level and high frequency contents of the input signal (S) .
2. The thermal protection circuit according to claim 1, characterised in that the signal modifying means (B) comprise clipping means (CL) , which clip the high level amplitudes of the high frequency contents of the input signal (S) .
3. The thermal protection circuit according to claim 2, characterised in that the signal modifying means (B) further comprise providing means (FP) , which provide the clipping means with the high frequency contents of the input signal (S) .
4. The thermal protection circuit according to claim 3, characterised in that the providing means (FP) comprise frequency detection means and switching means .
5. The thermal protection circuit according to claim 3, characterised in that, the providing means (FP) comprise a high pass filter circuit (HP) .
6. The thermal protection circuit according to claim 5, characterised in that the signal modifying means (B) comprise a providing circuit (Bl) with a high pass filter circuit (HP) as providing means (FP) , with a low pass filter circuit (LP) and with an adding circuit (AD) .
7. The thermal protection circuit according to one of the claims 2 to 6, characterised in that the signal modifying means (B) comprise an integrated clipping circuit (B2), which is coupled to the temperature detection means (TD) and which integrates the clipping means (CL) and the temperature controlling means (TC) in a way, that clipping levels (Uci, UCh) are determined by the detected temperature .
8. The thermal protection circuit according to claim 7, characterised in that the integrated clipping circuit (B2) comprise two clipping transistors (TB002, TB003) in a push-pull arrangement, which are controlled by the clipping levels (Uci, UCh) •
9. The thermal protection circuit according to one of the claims 1 to 8, characterised in that the temperature detection means (TD) comprise a resistor (R#) , which is thermally coupled to the amplifier (A) .
PCT/EP2005/056341 2005-11-30 2005-11-30 Thermal protection circuit for an crt amplifier WO2007062686A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2005/056341 WO2007062686A1 (en) 2005-11-30 2005-11-30 Thermal protection circuit for an crt amplifier

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2005/056341 WO2007062686A1 (en) 2005-11-30 2005-11-30 Thermal protection circuit for an crt amplifier

Publications (1)

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WO2007062686A1 true WO2007062686A1 (en) 2007-06-07

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0344545A2 (en) * 1988-05-31 1989-12-06 Yamaha Corporation Temperature compensation circuit in a negative impedance driving amplifier
EP0399276A2 (en) * 1989-05-22 1990-11-28 STMicroelectronics S.r.l. Circuit for limiting temperature without distortion in audio power amplifiers
EP1111775A1 (en) * 1999-12-20 2001-06-27 Ecler Laboratorio de Electro Acustica S.A. Power stage

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0344545A2 (en) * 1988-05-31 1989-12-06 Yamaha Corporation Temperature compensation circuit in a negative impedance driving amplifier
EP0399276A2 (en) * 1989-05-22 1990-11-28 STMicroelectronics S.r.l. Circuit for limiting temperature without distortion in audio power amplifiers
EP1111775A1 (en) * 1999-12-20 2001-06-27 Ecler Laboratorio de Electro Acustica S.A. Power stage

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