Abstract: A transimpedance pre-amplifier is used in connection with optical detectors and is designed to obtain low noise, low distortion and flat frequency response simultaneously. The amplifier design accomplishes low distortion and flat frequency response over a wide range of input signals by designing the pre-amplifier circuitry in such a manner as to compensate for the phase shift introduced by a feedback network connected across the input and output of the amplifier. This adjustment allows the feedback network to be of such a value as to effectively control any thermal noise introduced by the feedback resistor-input capacitance system. This compensation for the phase shift allows the phase margin and therefore stability to be controlled by means of the load impedance on the output transistor of the amplifier circuit.

Abstract: Apparatus for electronically protecting output transistors of electronic amplifiers against thermal overload, overcurrent, overvoltage, and second breakdown mechanism. An analog multiplier circuit, together with a novel circuitry for deriving the instantaneous voltages across, and the currents through, each of the output transistors, is used to obtain the instantaneous power dissipation in the transistors. A thermal sensor, the electrical signal of which is used as an additional variable in the multiplication, yields the thermal derating necessary for the transistors, and an integrating time constant used to weigh the output signal of the multiplier, takes into account the time derating of the transistors.

Abstract: Secondary surge protection means for equipment connected to transmission lines, for example line-powered amplifiers interconnecting T1 or T1C telephone lines, includes two diode bridges and a pair of surge diverters. One diode bridge has its cathode/anode nodes connected one to each conductor of an incoming transmission line. The other diode bridge is connected in like manner to an outgoing transmission line. Each surge diverter interconnects the anode/anode node of one bridge and the cathode/cathode node of the other bridge. When a surge on one line causes the voltage across one or other diverter to exceed a predetermined threshold, the diverter conducts, shunting the surge past the amplifier to dissipate in the other line. The two transmission lines may be coupled to the input and output, respectively, of one amplifier, or to the input of one amplifier and the output of a different, oppositely connected amplifier.

Abstract: Disclosed is a regulator circuitry (stabilizer) for controlling the output of an RF generator according to a programmable input signal. A power stage is responsive to the selected value of the programmable input signal to drive the RF generator at the desired power level. A forward power feedback control circuit monitors and controls the power output stage so that the desired RF output level is maintained at a constant level. In this particular mode of operation, RF output power is maintained constant and therefore independent of variations in gain due to temperature changes and other parameters which could effect the overall transfer function of said generator (and including mismatch of the generator into the load).

Abstract: In a signal amplifying apparatus which is provided with a amplifier, a feedback circuit having its input connected via a CR circuit to the output of the amplifier and its output connected to the input of the amplifier, a first terminal connected with the output of the amplifier for connection with a first cord connected with the input of a load, and a second terminal connected with the input of the feedback circuit for connection with a second cord connected with the input of the load, there are provided means for detecting whether the second cord is connected with the second terminal, and connecting means for connecting the output of the amplifier directly to the input of the feedback circuit by the detected output from the detecting means without passing through the CR circuit.

Abstract: The disclosed RF imbalance detector detects degradation in the performance of either a first or a second radio frequency amplifier and includes a means for monitoring the output of the radio frequency amplifiers. A comparator compares the two monitored outputs and provides a third signal which is converted into a usable signal that represents any RF imbalance between the amplifiers.

Abstract: Transistor switching means in which a principal transistor (T.sub.5) feeds into a load (R.sub.c) when a control signal saturates a control transistor (T.sub.1), a resistance bridge (R.sub.3,R.sub.4) fed by a source (V.sub.AL) then polarizing the base of the principal transistor (T.sub.5).An auxiliary transistor (T.sub.3 a) has its base coupled to the collector of the transistor (T.sub.5) by means of a diode (D.sub.2 a) and one of the two polarization resistances (R.sub.10 -R.sub.11). When the collector-emitter voltage of the principal transistor becomes too strong as a result of a short-circuit in the load, the auxiliary transistor (T.sub.3 a) is saturated and blocks the principal transistor (T.sub.5).Application to detectors of the type having an electro-luminescent diode excited by pulses; these pulses, applied to the auxiliary transistor (T.sub.3 a) block it momentarily in order to ensure the re-setting of the circuit when the overload has disappeared.

Abstract: An AC transistor switch is provided with simple, accurate and fast overcurrent protection circuitry. A pair of transistors are connected in anti-series across an AC load line, and each transistor has an anti-parallel diode therearound conducting current in the alternate half cycles. Comparator means senses current flow through the diodes and is responsive to given threshold overload current to turn off the transistors. Voltage sensing means is referenced to a common point between the series connected transistors and senses the voltage at each main terminal relative to the common point to thus sense the voltage drop from the common point across each diode to its respective main terminal for sensing current flow through the respective diode.

Abstract: A protective current mirror, with a reflection ratio greater than one, is connected as the active load of an input differential amplifier of a power amplifier. This mirror is provided in addition to the usual current mirror which has its output connected to the drive transistor of the output power amplifier stage. The protective mirror senses the imbalance due to a voltage peak which occurs at an inverted input of the input differential amplifier at the very beginning of the descending portion of a sawtooth input signal ramp voltage and the protective mirror operates a protective transistor which is connected to the base of the power amplifier drive transistor so as to keep one power transistor of the final power amplifier stage in its inactive state. Protection of the output power transistor occurs before the output of the power amplifier has reached its maximum voltage level.

Abstract: A two signal amplifying system is constructed of first and second BTL amplifiers each including a phase splitter and first and second push-pull output circuits. In each of the first and second push-pull output circuits, output transistors are connected between a power source and output terminals, and detectors for detecting the operating states of said transistors are connected with the output transistors constituting the aforementioned first and second push-pull output circuits, respectively. The outputs of those two detectors are fed to a control circuit. The output of the control circuit renders the two output transistors nonconductive in case at least one of the two output transistors deviates from a predetermined operating range.

Abstract: A line driver circuit having a protective circuit against excess currents, which includes a protective transistor for limiting the output current of an output-stage emitter-follower transistor. A detecting means for detecting the output current of the emitter-follower transistor and a pull-up transistor for pulling up the base potential of the protective transistor are provided. Before the output current becomes too large, the detecting means detects the output current to turn on the pull-up transistor. Then the base potential of the protective transistor is pulled up to turn on the protective transistor. As a result the base current of the emitter-follower transistor is decreased, so that the emitter-follower transistor is protected from being thermally destroyed.

Abstract: A protective circuit for a class B OTL circuit such as a vertical deflection circuit and a sound output circuit of a television set. The protective circuit comprises a first voltage comparator circuit having one input terminal applied with a detection signal in the form of an average voltage of an output signal of the OTL circuit and the other input terminal applied with a first reference voltage, and a second voltage comparator circuit having one input terminal applied with the detection signal and the other input terminal applied with a second reference voltage which is different from the first reference voltage. Either one of the voltage comparator circuits is operated when the output terminal of the OTL circuit is short-circuited to either the power supply voltage line or earth.

Abstract: A protecting arrangement is dislcosed for multiple loads supplied from a single DC power source. Each load is monitored by a separate protection circuit. Detection of an over-current condition associated with one of the loads will cause the associated protection circuit to assume a non-conducting state and provide a visual indication of same. Periodically enabled common reset means are provided to restore conduction to non-conducting protection circuits following removal of the cause of over-current.

Abstract: A power amplifier which has a muting circuit bringing the power amplifier into a muting condition when an excessively large input signal is applied. The power amplifier comprises a preamplifying stage and a power amplifying stage. The preamplifying stage includes at least one transistor for driving the power amplifying stage. The collector of the transistor is coupled to one power source terminal. The emitter of the transistor is coupled to the other power source terminal through an electronic switch, and to the first power source terminal through a resistor. The electronic switch selectively connects the emitter of the transistor to one of the power source terminals.

Abstract: An audio amplifier having an auxiliary terminal for connection of a feedback line to the grounded terminal of a loudspeaker and including a circuit for protection against voltage overload on the amplifier and loudspeaker if the auxiliary terminal is inadvertently connected to the ungrounded terminal of the loudspeaker, or in case of malfunction of the feedback circuit. The protection circuit includes a signal generator activated by the closing of a power switch for producing a check signal for circuiting through the terminals of the loudspeaker to the auxiliary terminal and a controller sensitive to the voltage at the auxiliary terminal for controlling a switch for disconnecting the feedback line, if the voltage at the auxiliary terminal exceeds a predetermined value.

Abstract: A conduction limit protective arrangement for a power transistor switch regulated by a train of control pulses is disclosed which automatically changes the conduction limit as a function of the voltage, current, and temperature conditions to which the switch is subjected so that it is within its safe operating area limits at all times, thereby permitting the switch to carry maximum current while being fully protected at all times.

Abstract: An intermodulation distortion limiter controls the ratio of average power to peak envelope power in the output of a linear power amplifier and this protects against excess non-linearity by reducing the drive power when the ratio exceeds a similar ratio associated with the incoming RF signal.

Abstract: An audio amplifier having an auxiliary terminal for connection of a feedback line to the grounded terminal of a loudspeaker and including a circuit for protection against voltage overload on the amplifier and loudspeaker if the auxiliary terminal is inadvertently connected to the ungrounded terminal of the loudspeaker, or in case of malfunction of the feedback circuit. The protection circuit includes a signal generator activated by the closing of a power switch for circuiting a check signal through the terminals of the loudspeaker to the auxiliary terminal and a controller sensitive to the voltage at the auxiliary terminal for controlling a switch for muting the output of the amplifier if the voltage at the auxiliary terminal exceed a predetermined value.

Abstract: A protection device for a power output circuit, designed such that the device protects the power output circuit from damage due to output overloads and simultaneously eliminates the power dissipation of the protected device, thereby conserving power and eliminating unnecessary heating of both the protected device and adjacent components. The protection device includes a comparator for comparing the voltage at the input to the power output circuit with the voltage at the output of the power output circuit. If the power output circuit has a unity voltage gain, its voltage output equals its voltage input under normal operating conditions but its voltage output becomes lower than its voltage input under overload conditions. The comparator is arranged to inhibit the power operation of the power output circuit and reduce its power dissipation to zero when the input voltage of the power output circuit exceeds the output voltage thereof by a specified value, that is, under overload conditions.

Abstract: A multistage radio frequency (RF) signal power amplifier is described that utilizes microstrip transmission line techniques for realizing essentially all of the matching circuitry for each stage of amplification. The power amplifier includes a variable gain predriver, a driver amplifier and a pair of paralleled final amplifiers, all of which are intercoupled by microstrip coupling circuitry. A power detector senses the magnitude of the final amplifier output and provides a forward power signal having a magnitude proportional thereto. A power output regulator is responsive to the forward power signal for providing a drive signal for varying the gain of the predriver amplifier to maintain the magnitude of the final amplifier output at a preset magnitude. The RF signal power amplifier further includes spurious signal suppression circuitry coupled to the output of the driver amplifier and final amplifiers for suppressing spurious signals generated by regenerative modes of oscillation occurring therein.

Abstract: A power output circuit is provided which is protected against latching due to voltage pulses developed by an inductive load. The circuit comprises a transistor constructed on a monolithic integrated circuit chip including a grounded semiconductor substrate of one type conductivity, and including collector and emitter regions of opposite type conductivity located on the substrate and containing opposite type conductivity modifiers. The collector and emitter regions are separated by a base region of one type conductivity, and the collector region is coupled to the inductive load. A fourth region of one type conductivity, containing one type conductivity modifiers is located on the substrate in galvanic contact with the collector region. A resistive impedance is coupled between the fourth region and a source of reference potential, and a capacitor is coupled between the fourth region and the source of reference potential.

Abstract: A signal-muting circuit, applied to a bridge amplifier comprises two amplifying means, performs signal-muting by shorting the input terminals of non-reversible buffer amplifiers forming the final stage of each amplifying means. Non-reversible amplifiers and said non-reversible buffer amplifiers in the amplifying means have the same voltage gain respectively.

Abstract: A protection circuit which may be used, for example, in an audio amplifier to protect the output drive transistor against conditions of excessive power dissipation. The circuit includes apparatus for monitoring the product of output current and output voltage across the protected transistor and applying a feedback signal to reduce the power dissipation if a predetermined limit is exceeded. Specifically, a representation of the product of the output voltage and output current is obtained by providing a current proportional to each and passing such current through a respective semiconductor junction to produce a logarithmically related voltage. The logarithm of the power product is obtained by summing the logarithmic voltages developed across each respective semiconductor junction.

Abstract: To protect a discrete electronic component such as a bipolar transistor or a field-effect transistor against destructive current surges, one or two ancillary transistors are formed in the same semiconductor body which has a major portion thereof overlain by an output electrode constituting a variable-voltage terminal connected to a load. This major portion, acting as the collector of the bipolar transistor (or of two such transistors in a Darlington configuration) or as the drain of the FET to be protected, also forms the collector of each ancillary transistor whose emitter is grounded through a constant-current generator or through a resistor.

Abstract: A protection circuit for a transmitter amplifier which provides power leveling and controls transmitter output power as a function of the ratio of reflected power to forward power. The circuit senses forward power level and develops a first voltage which is compared with the reference voltage to provide a control voltage which controls the power developed by the transmitter amplifier. Reflected power is sensed and a second voltage is developed which is compared to a portion of the first voltage and causes a reduction in the reference voltage when the reflected power to forward power ratio exceeds a predetermined level.

Abstract: Short-circuit protection of the load of an output amplifier by means of a non-linear coupling between the output and a d.c. bias point of the amplifier.

Abstract: A current limiting circuit is provided wherein the monitored voltage is applied to the base of first and second transistors, the first transistor having a substantially larger emitter area than the second transistor. Impedance means are connected to the emitters of the first and second transistors such that they function in conjunction with the emitter area ratio causing the current flowing through the first transistor to be higher than that flowing through the second transistor at low base voltages, while at higher base voltages the current flowing through the second transistor is higher than flowing through the first transistor. At some intermediate voltage the current flowing through both the first and second transistors is equal. This property may be used, for example, in a voltage regulator so as to divert base drive current from the output transistor at the point where the first and second currents are equal.

Abstract: A protection circuit for an output transistor includes a transistor having two discrete emitter regions and which is responsive to both the voltage across the protected transistor and its drive current to provide both short circuit and overcurrent protection for the output transistor.

Abstract: This invention relates to a loudspeaker protection device which disconnects the drive unit, or units, of the loudspeaker from an amplifier when the voltage across, or the current through, the drive unit, or one of the drive units, exceeds a predetermined level. The protection device includes a bistable device comprising a complementary pair of transistors arranged to be changed from the reset state to the set state when the voltage on an input terminal exceeds a predetermined level. The transistors are arranged to be both non-conductive when the device is in the reset state and both conductive when the device is in the set state. When the transistors are conductive, the collector current of one of them flows through the coil of an electromagnetic relay having normally closed contacts in the output circuit of the amplifier.

Abstract: A circuit for a switch which receives an input from a sensor head (18) such as a proximity sensor, limit switch, or other type of condition-responsive sensor. In its most complex form the circuit includes a power supply/regulator (24), an output load current source (12), an output load current sink (14), input logic (16) to receive the signal from the sensing head, a selector (10) to determine whether the source and sink will be normally open or normally closed, and a device (26) for checking the outputs for faults and indicating the presence of such. Other circuits include certain combinations of these parts or variations of these parts.

Abstract: A transistor push-pull output stage, particularly for pulse shapers having inverse feedback from the output to the input, as well as a high-resistance input and a low-resistance output is disclosed. In testing components of data technology, short circuits in the component should not lead to the destruction of the output stage of the testing apparatus. To this end, the invention provides that a field effect transistor is employed in each push-pull stage as the input transistor, the field effect transistor respectively driving the parallel connection of a plurality of output transistors by way of an emitter follower stage. The bases of the output transistors are driven by way of a constant current source which is switched off given overvoltage of the output. The transistors and the push-pull stages are complementary to one another. In addition, a structure is provided for the power supply which is driven as a function of the voltage shift and of the pulse basic voltage of the signal.

Abstract: A solid-state, multistage temperature controller for automatically controlling the operation of fans to maintain the temperature of an associated engine within preselected limits.

Abstract: A circuit arrangement is provided which prevents latching in a power amplifier or supply. A power output transistor drives an inductive load, which is coupled in parallel with the collector-to-emitter path of the transistor. A first diode is coupled between the transistor and a point of reference potential, and is in series with the collector-to-emitter path of the transistor and poled to be of like polarity to the base-emitter junction of the transistor. A capacitor is coupled in parallel with the first diode, and a second diode is coupled in parallel with the inductive load and is poled in an opposite sense to the first diode. The second diode is chosen to have a voltage drop such that a negative voltage impulse from the inductive load will be clipped at a voltage which is the difference between the voltage drops of the first and second diodes.

Abstract: A protected transistor in an electronic circuit receives base drive current and has its collector-emitter path coupled to a source of collector-emitter potential and to a load. Overcurrent protection therefor is provided by a first, complementary conductivity type transistor connected base to emitter and emitter to base with the protected transistor, and thermally coupled thereto, to develop a collector current responsive to the collector-emitter current of the protected transistor. A comparator provides an overcurrent indication whenever the collector current of the first transistor exceeds a predetermined level. The overcurrent indication prevents further increase in the base drive current to the protected transistor. A further feature of the invention reduces the predetermined level in response to increasing collector-emitter potential of the protected transistor.

Abstract: Sense voltages representative of transmitter power and the temperature of the transmitter output stage are summed and fed to the input of a high gain amplifier. The output of the amplifier provides bias to the transmitter driver stage and, thus, controls the total transmitter developed power. The resulting overall feedback system provides precise transmitter power control and output stage thermal protection.

Abstract: An output from an OCL type power output circuit is applied to a loudspeaker load through a switching means such as a relay. A first detector circuit and a second detector circuit detect a first operating status (e.g., output d.c. level) and a second operating status (e.g., output current level of an output transistor) of the OCL type power output circuit, respectively. The detection output signals of the first detector circuit and the second detector circuit are respectively applied to a first detecting transistor and a second detecting transistor. In the normal operation status of the OCL type power output circuit, the first detecting transistor and the second detecting transistor are respectively biased into "on" states by the first detector circuit and the second detector circuit so as to permit predetermined currents to flow. When the first and second detecting transistors are in their "on" states they control a driving transistor into an "on" state.

Abstract: Electronic logic circuitry operates to detect and correct a short circuit condition, be it a short to system ground or supply voltage, in a circuit output. In one application, the short protection circuitry is incorporated into a high power CMOS driver. If the circuit output is shorted to ground, the short is detected and a signal is fed back to the input. This feedback signal forces the output to ground thus eliminating the excessive current flow. Conversely, if there is a short to supply voltage, V.sub.DD, a signal is fed back to the input that forces the output to supply voltage V.sub.DD, again eliminating the excessive current flow.

Abstract: A circuit is described for protecting a semiconductor junction device such as a transistor against damage from high voltage transients that can be produced by kinescope arcing in a television receiver. The protected device is coupled to a circuit point at which the transients can appear. The protection circuit comprises a normally nonconductive protection transistor with a collector coupled to a source of operating potential, a base coupled to a source of threshold conduction bias reference voltage, and an emitter connected to the circuit point at which high voltage transients are likely to appear. The base bias of the protection transistor is determinable independent of the bias of the protected device, and the protection circuit is connected to the protected device with substantially zero voltage offset between the circuit point and the protected device.

Abstract: A loudspeaker protection circuit senses an overload condition caused by an improper input signal or a fault within the amplifier by sensing a DC or infrasonic signal applied to the loudspeaker. The time between zero (axis) crossings of the amplifier output signal, which are related to the lower frequency components of the signal, are detected. If the period of time between zero crossings exceeds a predetermined time limit, the supply of the amplifier output signal to the loudspeaker is interrupted. In order to prevent false tripping of the circuit by normal conditions, the circuit only responds to signals exceeding a predetermined voltage level.

Abstract: A solid-state overload protection circuit for protecting a multiple-stage compound transistor power amplifier. The overload protection circuit includes a current-limiting circuit for sensing or limiting the current during an overload condition. The current-limiting circuit includes a transistor which conducts to limit the current in the output stages of the multiple-stage power amplifier. A monitoring circuit including a timing circuit, a comparator, and a switching transistor monitors the duration of the overload condition and disables the input stages of the multiple-stage power amplifier when a prolonged overload condition persists.

Abstract: A low pass filter is connected to a junction of a direct-coupled amplifier. The amplifier has a single-ended push-pull output stage consisting of two output transistors and series-connected two resistors. The output transistors are connected to a positive and negative d-c power sources, respectively. The series-connected two resistors are interposed between the two output transistors and defines an intermediate point therebetween at which substantially zero d-c voltage prevails when the amplifier is functioning normally. The junction of the amplifier, to which the low pass filter is connected, is between one of the output transistors and the series-connected resistors. The low pass filter is supplied with the voltage at the junction and applies its output to following isolating means. The means responds to the output of the low pass filter for isolating the intermediate point from a load device connected thereto.

Abstract: Disclosed is a means for reducing leakage current associated with a path used to couple a high impedance sensor to a detector as, for example, in coupling a smoke-sensitive ionization chamber to an integrated circuit smoke detector chip. A unity gain amplifier is provided which receives a detection voltage signal from the sensor and generates an output guard voltage which tracks the detection voltage signal. The output guard voltage is used to bias the voltage of the areas surrounding the path used to conduct the detection voltage signal. The effect of undesirable leakage paths that may exist between the detection voltage signal conduction path and surrounding areas is reduced by minimizing the voltage across the leakage paths, thus maintaining a high impedance value associated with the detector input.

Abstract: Circuitry for controlling the power output of an R.F. generator for regulating the forward power transmitted into a load of varying impedance, such as an R.F. sputtering target, and for limiting reflected power to a safe predetermined level. Forward power is controlled by circuitry that compares the voltage across the target with a predetermined reference voltage and the amplified output is applied to the signal generator control circuitry. Reflected power is measured by a sensor that outputs a proportional D.C. signal that is compared with a predetermined threshold voltage. Whenever the reflected power signal exceeds this threshold, it removes the effect of the target voltage input signal so that the amplified control signal to the R.F. generator is a function only of the reflected power.

Abstract: A power amplifier having first and second amplifiers each including an output stage consisting of series connections of collector-emitter paths of first and second output transistors connected between power supply terminals is disclosed. Each first and second transistor is driven alternately in response to an input signal fed through an input terminal, and each output transistor is provided with an over-current detector circuit. Protective circuits are responsive to the detection outputs of the detector circuits to protect the corresponding output transistors. The output terminals of the power amplifier are respectively connected to the common junction of the first and second output transistors of the first and second amplifiers, and a load such as a speaker is connected between the output terminals. Circuits are provided to apply the outputs of the over-current detector circuits in one amplifier to the corresponding protective circuits in the other amplifier, and vice versa.

Abstract: The output derived from an electric circuit such as an OCL type power amplifier circuit is delivered to a load such as a speaker, through a switching means such as a relay. When the operation of the electric circuit has come out of a predetermined range of operation, the switching means is operated to break the connection between the electric circuit and the load. A detection circuit for detecting the operation of the electric circuit includes a detecting transistor constructed in a semiconductor integrated circuit. The detecting transistor is connected at its base to the input terminal for external connection of the semiconductor integrated circuit, so as to receive a signal representative of the operation state of the electric circuit. The detecting transistor is so biased as to allow a predetermined electric current to flow therethrough, when the electric circuit is operating within the predetermined range of operation.

Abstract: A circuit employing parallel power transistors intended to share the load current, includes a separate current sensing resistor for each transistor and independently operating protection circuits controlled by the voltage drop across the associated sensing resistor to limit the current in each power transistor to a safe level. The protection circuits each include zener diodes and resistors connected to vary the current limit in accordance with the voltage across the power transistors.

Abstract: A power transistor in the final stage of an IC amplifier feeding a reactive load, such as a loudspeaker, has an emitter resistor connected across the input of a heat-sensitive monitoring transistor by way of a diode in bucking relationship with its base/emitter path, the monitoring transistor being part of a protective circuit which reduces the input signal to the power amplifier in the event of an overload. The monitoring transistor is separated from the power transistor, on the silicon chip of the amplifier, by a distance so chosen that an overload raising the temperature of the power amplifier will significantly reduce the operating threshold of the monitoring transistor only if the overload persists for a minimum period on the order of one millisecond.

Abstract: A first resistor and a second resistor are connected in series across the collector and emitter of a transistor that is to be protected thereby to detect a voltage across the collector and emitter thereof, as well as to detect a collector current or an emitter current thereof, and a third resistor is connected to be collector or the emitter of the transistor that is to be protected. A detector transistor is driven by a voltage produced across the second and third transistors. A fourth resistor is connected between the collector and the base of the detector transistor, one end of the fourth resistor connected to the base of the detector transistor being connected to a constant-current circuit, and the other end of the fourth resistor connected to the collector of the detector transistor being connected to the base of a control transistor. The emitter of the control transistor is connected to the collector or the emitter of the transistor that is to be protected via the third resistor.

Abstract: A bilateral repeater for communication transmission lines is described in which the opposite directions of transmission are separated by frequency bands for amplification. The repeater is powered from a power conversion unit energized from the line potential. The repeater includes three-electrode gas tube breakdown devices connected across the repeater for each conductor of the transmission line. The third electrodes in the gas tubes are cross-connected together with no ground connection.

Abstract: A protective circuit for a push-pull power amplifier comprises a load current-detecting resistor connected between the emitters of two transistors jointly constituting the power amplifier, a switch connected between an intermediate point on the load current-detecting resistor and the ground to shut off load current, a load resistance-detecting circuit for detecting the resistance of the load, and a driving circuit for causing the switch to be opened by an output from the load resistance-detecting circuit when the resistance of the load falls below a prescribed level. The load resistance-detecting circuit includes means for drawing out a first signal from one end of the load current-detecting resistor and, means for drawing out a second signal with lower potential than the first signal from the other end of the detecting resistor.