Abstract: A device load variation protection circuit connected to an output side of a device to protected the device from a variation in a load includes a detection circuit, a protection load, and a switch. The detection circuit detects the variation in the load. The protection load is connected to the output side of the device so as to be switchable between connection and disconnection. The switch switches between connection and disconnection of the protection load on the basis of a detection result from the detection circuit.
Abstract: The present invention teaches a variety of high VSWR mismatch output stages and methods for protecting output stages during high VSWR operation. To accomplish these goals, the present invention teaches absorbing reverse base current arising at the base of the power transistor of the output stage. In one embodiment, a variable impedance device such as a transistor is coupled to the base of the power transistor such that when the base-emitter voltage exceeds a predefined voltage, the variable impedance device goes into a low impedance mode and absorbs a portion of the base current. In another embodiment, feedback control circuitry is incorporated into the output stage bias circuitry in order to control the total base current.
Abstract: In a display signal amplifier arrangement, a current-sensing circuit (S) measures a supply current of an amplifier (A) to obtain a control signal (CTRL) for a bandwidth-reducing circuit (BRC) preceding the amplifier (A), where the bandwidth-reducing circuit (BRC) adaptively attenuates a high-frequency part of the display signal in dependence upon the supply current.
Abstract: In an arrangement for protecting the output transistors in a power amplifier against temperatures exceeding a predetermined first temperature value, a temperature sensor is provided adjacent to the output transistors to sense their temperature and influence the power amplifier when the first temperature value is reached. The temperature sensor is adapted to vary the driving current of the power amplifier inversely proportional to the temperature of the output transistors for temperature values between the first temperature value and a predetermined higher temperature value.
Abstract: A protective circuit in a power amplifier is adapted, by limiting the maximum output current of the power amplifier and by quickly recharging compensating capacitors in the power amplifier, to limit the amount and duration of the power drain in the power amplifier upon over-excitation of the power amplifier.
Abstract: A sensor of instantaneous power which is dissipated through a power transistor of the MOS type connected between the output terminal of a power stage and ground. It comprises a MOS transistor having its gate terminal connected to that of the power transistor, source terminal connected to ground, and drain terminal connected to a circuit node which is coupled to the output terminal by means of a current mirror circuit which includes a resistive element in its input leg. Connected to the circuit node is the base terminal of a bipolar transistor which is respectively connected, through a diode and a constant current generator between the output terminal and ground.
Abstract: A method for improving linear modulation compensation at the antenna terminals of an RF device in order to react to high voltage standing wave ratio variations is disclosed. In the present RF transmitters, such as portable radios, when transmission voltage standing wave ratio varies such that the linearization of its modulation technique is adversely affected, the dynamic accommodation of the variations in voltage standing wave ratio can be imposed on the output of the RF power amplifier to ensure that linearization is not lost. Specifically, the reverse power signal from the power amplifier can be detected and used to calculate a standing wave control signal. The standing wave control signal is provided to a step attenuator which attenuates the output of the power amplifier in an amount commensurate with the amount of reverse power signal at the output of the power amplifier. By adding attenuation in response to increases in reverse power signal, the linearity of the modulation being used can be controlled.
Abstract: In a differential amplifier, when an output node of an output buffer circuit is short-circuited to a high potential supply node, the difference between the potential at an output node of an amplifying circuit and the potential at the output node of the buffer circuit becomes so great as not to be produced in normal operation. A short-circuit protection circuit detects such a state and interrupts or limits a base current supplied to an output transistor of an output pull signal generating circuit, suppressing the flow of excess current into the output node of the buffer circuit.
February 3, 1998
Date of Patent:
May 18, 1999
Mitsubishi Denki Kabushiki Kaisha, Mitsubishi Electric Engineering Co., Ltd.
Abstract: A device for limiting the output current of an operational amplifier of the type including an output stage having an output transistor, including circuitry for limiting the biasing current of a differential input stage of the operational amplifier to a value determined by a measurement resistor connected between the output transistor and an output terminal of the operational amplifier.
Abstract: A current steering circuit diverts bias current from a differential current summing amplifier's front end when the differential input exceeds a safe threshold level, thus preventing the amplifier's output stage from being overdriven. Diverting the front end's bias currents also turns off transistors within the amplifier's front end and thus protects the front end from damage which may otherwise result from excessive input signals.
April 14, 1997
Date of Patent:
January 12, 1999
Hieu M. Le, Lloyd F. Linder, Erick M. Hirata, Benjamin Felder, Roger N. Kosaka, Donald G. McMullin, Kelvin T. Tran
Abstract: In a protection circuit for an audio amplifier, a power relay is provided on a primary side of a power source of the audio amplifier. When a power switch has instructed power-on, a drive power is supplied from an auxiliary power source to the power relay by an instruction given by a control section which is supplied with an operating power thereby to turn on the power relay. A primary voltage is thereby supplied to the power source to set the audio amplifier to a power-on state. When the audio amplifier is in the power-on state, an excess current flowing in an output stage of a power amplifier and dc voltage occurring in an output signal line of the power amplifier and, if necessary, an abnormal voltage occurring in the power source are detected and the power relay is cut off by an instruction from the control section when either one of the abnormalities takes place whereby a primary side of the power source is accurately cut off when an abnormality has occurred.
Abstract: A power amp module protecting apparatus of a mobile wireless phone having: a power supply unit for supplying driving power to a power amp module; a switching unit, connected between the power supply unit and an overcurrent detector, for performing a switching action in accordance with a logic level of a switching control signal output from a controller and a logic level of an overcurrent detecting signal from the overcurrent detector; the overcurrent detector, connected between the switching unit and the power amp module, for outputting an overcurrent detecting signal having a high logic level in response to the detection of an overcurrent from the power supply unit; and the controller for outputting the switching control signal to switch on the switching unit when no overcurrent is detected, for maintaining the switching unit in an off state in response continued receipt of the overcurrent detecting signal of high logic level output from the overcurrent detector and outputting the switching control signal to
Abstract: A power amplifier circuit drives a load with a convergence correction current which is proportional to a convergence correction voltage waveform that is applied to the power amplifier circuit. A predriver stage of the power amplifier circuit comprises first and second transistors in a push-pull configuration. First and second voltage divider networks bias emitter electrodes of the first and second transistors, respectively, so that a common-mode current flow between the first and second transistors is limited. The first and second voltage dividers also protect the first and second transistors, respectively, from damage caused by thermal runaway.
Abstract: In a hybrid matrix amplifier array (100), the amplitude of each of a plurality of input signals is measured (132-136, 202). In response to the signal amplitude measurements, an overload condition that will result in an amplifier overload in said hybrid matrix amplifier array is estimated (204, 206, 138). In response to the estimation of the overload condition, the signal amplitude of at least one of the plurality of input signals is modified to prevent the overload condition in the hybrid matrix amplifier array. An overload condition may be estimated if the sum of the amplitudes of the input signals exceeds a threshold (206). In one embodiment, all input signals are modified by proportionately reducing the amplitude of each of the plurality of input signals (304).
Abstract: An overdrive circuit having a first current source which supplies an overdrive current and a second current source which supplies an ordinary current smaller than the overdrive current. A first circuit operates the first current source that supplies the overdrive current for a predetermined time period after the start of current supply. A second circuit stops the action of the first current source after the predetermined time period has passed and drives the second current source to supply the ordinary current as the driving current.
Abstract: A direct current voltages detecting circuit is provided for monitoring output voltage of the power amplifier. A direct current signal is produced when a direct current voltage is detected. A cutoff circuit responds to the direct current signal and renders an output stage of the power amplifier a cutoff state. A failure determining circuit is provided to respond to the direct current signal and to produce an abnormality signal. In response to the abnormality signal, a power supply cutoff circuit operates to cutoff a power supply of the power amplifier.
Abstract: An ESD protection circuit for a BICMOS IC device protects NMOS transistors (Q2) of internal CMOS gates (G2) from ESD events at a high potential power rail (VCC). Specifically the ESD protection circuit protects NMOS pulldown transistors coupled between a pullup bipolar emitter follower transistor (Q5) and the low potential power rail (GND). A PMOS current control transistor (QPESD) is coupled with primary current path between the high potential power rail (VCC) and the bipolar emitter follower transistor (Q5) for controlling current flow through the emitter follower transistor. An RC time constant circuit (R10,C1) is coupled between the high potential power rail (VCC) and low potential power rail (GND). The RC time constant circuit is constructed with a time constant for following power up events but not for following the faster ESD events at the high potential power rail.
Abstract: An abnormal transmission stopping circuit for use in a transmitter including a base band signal processing circuit, an amplitude modulator which modulates the amplitude of a carrier signal in accordance with a base band signal, and a transmission amplifier which amplifies a signal modulated by the amplitude modulator. The stopping circuit includes an electric current detecting circuit which detects a power supply current to the transmission amplifier, and a comparator which generates and supplies a transmitting function stopping signal to the base band signal processing circuit when the detected power supply current exceeds a threshold value.
Abstract: Power amplifiers, which include a feedback element, may be protected from excessive operating power levels by adjusting the feedback element to reduce the drive signals to the power elements. This is accomplished by sensing the output power of the power amplifier to produce a sensing signal. When the sensing signal exceeds a predetermined threshold, a feedback element is adjusted to produce an increased feedback signal. The increased feedback signal is subtracted from an input signal, thus decreasing the drive signal. With the drive signal reduced, the output power is reduced proportional to the adjustment of the feedback element.
Abstract: In an antenna supervising apparatus for supplying a multiplexed signal comprised of a plurality of carrier wave signals respectively outputted from a plurality of transmitters through a transmission line to an antenna, a directional coupler detects progressive signals of the multiplexed signal to the antenna and the reflected signals thereof from the antenna, and a band-pass filter respectively filters the progressive signal and the reflected signal of one carrier wave signal preselected among those of the detected multiplexed signal. Further, a detector respectively detects the filtered progressive signal and the filtered reflected signal of the one carrier wave signal, and a micro processing unit calculates a standing wave ratio with respect to the preselected one carrier wave signal based on the detected signals.
Abstract: An RF transmitter protection circuit for providing protection to a power amplifier includes circuitry for sensing the presence of an input excitation signal applied to the input of the power amplifier. Circuitry is provided for monitoring an output signal generated by the power amplifier at the output of the power amplifier and for generating a signal proportional to the output signal. Circuitry is further provided for applying the signal generated by the monitoring circuit to the input of the power amplifier in response to a loss of input signal detected by the sensor.
Abstract: An audio amplifier (100) switches between a pulsewidth-modulated (PWM) mode to an analog mode when required in order to reduce unwanted EMI when the signals being reproduced fall within a predetermined threshold range such as when reproducing low amplitude signals. Amplifier (100) includes both a pulsewidth-modulator (114) and a low-level analog amplifier (126) coupled to a speaker bridge circuit. When controller (106) determines that the input signal (102) is at a predetermined level, controller (106) selectively applies to the load (164) an analog signal instead of the PWM signal, this provides for improved dynamic range and reduced amplifier produced EMI.
Abstract: A power amplifying unit implemented with a power amplifying module and connectable to a transmitter/receiver of a mobile radio telephone apparatus. A DC current amplifier is connected to a control voltage terminal included in the PA module. Different voltages generated by individual power source circuits are selectively applied to the DC current amplifier. The unit is operable with any of one of various PA modules, each requiring a particular voltage to be applied to a control voltage terminal thereof.
Abstract: This invention provides an automatic current interruption to protect the audio power amplifier circuitry when current conditions above the capacity of the power amplifier are encountered. The circuit monitors the current supplied to the power amplifier and utilizes a transistor to interrupt power amplifier output. Power output is latched in its interrupted state until reset and is capable of quickly and effectively shutting down power supply output.
Abstract: Phase and amplitude modifications in repeatable RF pulses at the output of a high power pulsed microwave amplifier are made utilizing a digital feed-forward correction system. A controlled amount of the output power is coupled to a correction system for processing of phase and amplitude information. The correction system comprises circuitry to compare the detected phase and amplitude with the desired phase and amplitude, respectively, and a digitally programmable phase shifter and attenuator and digital logic circuitry to control the phase shifter and attenuator. The Phase and amplitude of subsequent are modified by output signals from the correction system.
Abstract: A circuit and method for protecting a transistor during operation transistor's BV.sub.CEO by limiting the reverse base current. The reverse base current is used to adjust the applied base-emitter voltage. Limiting the reverse base current keeps the collector and emitter currents within safe limits and thus extends the safe operating area of the transistor. The invention finds application as an overvoltage sensor and transistor protector circuit and is particularly applicable to implementation in an integrated circuit. The circuit may be combined with circuits for the protection of a transistor against excessive current and temperature in a high voltage linear regulator.
Abstract: A power control circuit for use in radio transmitters such as portable telephone sets includes a power amplifier for amplifying the power of a transmission signal to obtain an output signal; control circuits for controlling the amplitude of the signal output by the power amplifier; a limiter for partially limiting the amplitude of the signal from the power amplifier in order to obtain a limited signal; a multiplication circuit for multiplying the limited signal from the limiter and part of the signal from the power amplifier in order to acquire a multiplied signal; a low-pass filter for extracting a DC component of the multiplied signal from the multiplication circuit; and a comparison circuit for comparing the DC component from the low-pass filter with a reference voltage in order to obtain a comparison output.
Abstract: A power supply circuit provides power to an antenna amplifier (4) of a vehicle radio via the antenna bushing (A) and the antenna cable (6). The circuit is resistant to short-circuits and has a pair of signal terminals (K2, K3) from which information, about the type of attached antenna and about its operating state, can be picked up.
Abstract: The protection circuit includes a micro strip line whose length is equal to a fourth of the wavelength of an amplification signal frequency on a board and whose one side is connected to the input side of a low noise amplifier, a diode whose one side is connected to the other side of the micro strip line and whose other side is grounded, and a capacitor which is connected to the point where the micro strip line is connected to the diode and whose impedance is sufficiently small at the amplification signal frequency. In this configuration, the diode has virtually no effect to the amplification signal component because the impedance of the protection circuit for the amplification signal frequency viewed from the contact point becomes sufficiently high. In addition, for static electricity charged on the antenna connected to the input terminal, the diode is virtually connected directly to the input side of the low noise amplifier because the micro strip line is almost zero in resistance.
Abstract: A protection circuit for an audio output channel of a television receiver includes a detector which detects the presence of either or both of (1) a sustained DC component applied to the loudspeaker form the audio power amplifier, (2) and the loss of a supply voltage for the power amplifier. The presence of a of a sustained DC component can damage the loudspeaker. The loss of a supply voltage of the power amplifier can damage the power amplifier and can also result in the application of a sustained DC amplifier and can also result in the application of a sustained DC component to the loudspeaker. For example, the loss of the negative supply voltage of a power amplifier incorporated in an integrated circuit results in the removal of potential from the substrate which otherwise serves to electrically isolates various semiconductor devices supported by the substrate.
May 13, 1991
Date of Patent:
June 29, 1993
Thomson Consumer Electronics, Inc.
Robert E. Morris, Jr., Mark R. Anderson
Abstract: An amplifier protector and method for preventing power overload of a power amplifier and destruction of transmission circuitry and printed wiring board. The protector continually monitors the peak forward and reflected voltages of the transmitter output which are proportional to the forward and reflected power. An associated processor determines whether the forward voltage is below a threshold voltage which indicates a circuit malfunction. If the circuit malfunction is detected, the processor via an automatic level control circuit turns off the power amplifier in a timely fashion to prevent damage to the transmission circuitry.
Abstract: An AC power amplifier is disclosed for amplifying an AC input signal while limiting the current drawn by the amplifier. The amplifier includes at least one transistor having an input circuit for receiving an AC input signal as well as a DC bias voltage and an output circuit connected to the DC voltage source for drawing current therefrom during conductive periods of the transistor. The transistor exhibits the characteristic of being nonconductive when the AC input signal together with the DC bias voltage are less positive than a DC threshold voltage level and is conductive when the AC input signal and the DC bias voltage are together more positive than the DC threshold voltage level whereupon DC current is drawn by the output circuit from the DC voltage source. The DC current is sensed and a sense signal is provided having a magnitude in accordance therewith.
Abstract: An RF power amplifier system is disclosed having a modulated voltage supply and fault monitoring thereof. The modulated DC voltage supply receives an input voltage as well as a modulating signal, such as an audio signal, to provide a modulated voltage which has been amplitude modulated in accordance with the amplitude variations of the modulating signal. Circuitry is provided for providing a variable reference signal which has a magnitude that varies with that of the modulating signal. A fault comparator compares the modulated signal with the variable reference signal and provides a fault signal dependent upon the comparison.
Abstract: An amplifier circuit in which a first amplifier (A1) and a second amplifier (A2) are protected against short-circuits by a protection apparatus which includes a first device (M1), a second device (M2), a third device (M3) and a protection device (B). For this purpose the first device and the second device generate four signals (s1, s2, s3, s4) related to an equal number of currents (i1, i2, i3, i4), which currents are related to a first or a second load current in the first amplifier or in the second amplifier. In order to control the protection device (B), the third device generates at least two control signals (r1, r2) related to the signal currents (s1, s2, s3, s4), use being made of the equality of the load currents in the absence of short-circuits.
July 3, 1990
Date of Patent:
March 17, 1992
U. S. Philips Corporation
Hendrik Boezen, Pieter Buitendijk, Rudolf W. Mathijssen
Abstract: An adaptive power amplifier system for use with VSWR loads includes an adaptive power supply that indirectly monitors the power dissipated by a RF power amplifier and adapts bias conditions of solid state components in the RF power amplifier to protect the components from excessive power dissipation typically experienced with VSWR loads, even while maintaining full forward power output.
Abstract: An RF power amplifier having amplifier protection is presented wherein an RF source supplies an RF input signal to an actuatable RF power amplifier having an on condition and an off condition for, when on, normally receiving and amplifying the input RF signal to provide an amplified output RF signal. RF current and RF voltage in the output circuit are detected. A first signal is provided from the RF current and exhibits a fixed amplitude but a frequency and phase corresponding with that of the RF current. A second signal is provided of the fixed amplitude and which corresponds in frequency and phase with the RF voltage. The first and second signals are compared so as to provide a phase signal having a magnitude dependent upon the phase difference between the first and second signals. This phase signal is then compared with a reference to provide a turn-off signal in dependence upon the comparison for purposes of actuating an RF power amplifier to its off condition.
Abstract: A transmitter, with an inphase input for receiving an inphase baseband input signal, and a quadrature input for receiving a quadrature baseband input signal, comprises a modulator, coupled to the inphase and quadrature inputs, for modulating the inphase and quadrature baseband signals to provide a modulated radio-frequency signal and a linear amplifier, coupled to the modulator, for amplifying the modulated radio-frequency signal to produce an output signal. Oscillation detector means are coupled to receive the output signal, for detecting oscillation, and for producing an error signal as a result of the oscillation. The transmitter also comprises means for reducing the open loop gain of the feedback loop, disposed between the inphase and quadrature inputs and the modulator. The means for reducing the open loop gain reduces the open loop gain of the transmitter to less than one, in response to the error signal.
Abstract: A levelling control arrangement for an RF transmitter circuit which additionally compensates for filter ripple, i.e. frequency dependant power variations caused by the filter disposed between a transmitter amplifier and an antenna. The forward and reflected power is sampled by a dual directional coupler between the amplifier and the filter. Signals V.sub.fwd and V.sub.rev are thus obtained indicative of the forward and reflected power levels respectively. The reflected signal V.sub.rev is subtracted from the forward signal V.sub.fwd at comparator and the difference signal V.sub.diff is compared with a reference signal Vref at comparator to produce a signal V.sub.c which is used to control the gain of the amplifier in such manner that the power developed by the amplifier increases as the signal V.sub.rev increases and vice versa. To protect against excessive reflected power levels a limiter may be included which causes the power developed by the amplifier to be reduced only if V.sub.
Abstract: A power amplifier provided with overload protection responsive to the impedance of a load falling below a threshold value having a pair of power output devices connected to the load and driven through a balanced operational amplifier and transistor couplers. The operational amplifier has opposed voltage supply inputs, and each is connected through a first resistor to a voltage source and to the load through a pair of diodes connected in series opposition and a second resistor, and the junction between the diodes is connected to the base of one of the transistor couplers. A fault condition causes current to flow through the diodes lowering the potentials of the voltage supply inputs and the bias on the transistor couplers.
Abstract: The amplifier includes a bridge circuit having an input circuit adapted for connection across a DC voltage source and an output circuit connected across a load. The bridge circuit includes first and second transistors for, when on, connecting the DC voltage source across the load for DC current flow therethrough in a first direction and third and fourth transistors for, when on, connecting the DC voltage source across the load for DC current flow therethrough in a second direction. The transistors are controlled by an RF signal so that they turn on and off at a frequency dependent upon that of the RF signal such that current flows from the DC source alternately in the first and second directions through the load.
Abstract: A gate drive circuit for an insulated gate bipolar transistor initially drives the gate to a first voltage potential which causes the transistor to partially turn on. A sensor detects when the transistor saturates, at which point the gate drive voltage is increased to increase the conductivity of the transistor and reduce its saturation voltage drop. If, however, a load coupled to the transistor is short circuited, the transistor will never reach saturation and will remain partially turned on at a point where it has increased short circuit current handling capability. In addition, once the transistor has been fully turned on, should a short circuit load condition occur, the transistor will drop out of saturation causing the drive circuit to reduce the gate voltage to increase the short circuit current handling capability of the transistor.
Abstract: An RF power amplifier having improved amplifier protection. An RF source provides an RF signal to be amplified. The amplifier includes a bridge circuit having an input circuit adapted for connection across a DC voltage source and an output circuit connected across a load. The bridge circuit includes first and second transistors for, when on, connecting the DC voltage source across the load for DC current flow therethrough in a first direction and third and fourth transistors for, when on, connecting the DC voltage source across the load for DC current flow therethrough in a second direction. The transistors are controlled in response to the RF signal so that they turn on and off at a frequency dependent upon that of the RF signal and such that current flows from the DC source alternately in the first and second directions through the load. An amplifier control serves to apply a reverse bias to the second and fourth transistors to prevent them from conducting current until receipt of a turn on signal.
Abstract: An adaptive thermal protection method and arrangement for a power amplifier by remote sense is disclosed which maximizes the amount of output power from electronic equipment such as a radio frequency (RF) power amplifier, having a finite heat sink and operating intermittently over a period of time. This method and apparatus utilizes a remote temperature sensor and knowledge of the on/off, or key/dekey times in conjunction with a stored, predetermined thermal model to adjust the operating power level to a maximum permissible point within a range of operating power levels such that the projected temperature of the power amplifier does not exceed a preset limit. In so doing, the apparatus and method combines the advantages of thermal protection and power maximazation and effects gradual changes in the operating power level by adapting to variable environmental and operational conditions.
Abstract: A circuit for protecting a switching transistor connected between a direct-current voltage source and an inductive load has a voltage-limiting element connected between the source and the transistor for switching the transistor when the voltage of the source exceeds a predetermined limit, elements for deriving from the voltage-limiting element a control signal when the source voltage exceeds the predetermined limit, and a variable pulse-width modulator connected to a control input of the transistor and receiving the signal from the means. The modulator decreases pulse width when the source voltage exceeds the limit.
December 13, 1988
Date of Patent:
December 26, 1989
Lenze GmbH & Co. KG Aerzen
Heinz-Dietmar Karl, Manfred Tinebor, Josef Lackhove
Abstract: A detection circuit for detecting the failure or disconnection of a sense line in an audio processing system that provides an audio output signal that drives the input of an audio power amplifier. The audio power amplifier drives a speaker. The audio processing system includes an input for receiving a first feedback signal on a sense line from the output of the power amplifier. The audio processing system is responsive to the first feedback signal to control the amount of power provided to the input of the power amplifier and thus to the speaker. The detection circuit also receives the first feedback signal. The detection circuit further receives a second feedback signal from the output of the audio processing system prior to the input of the power amplifier. The magnitude of the second feedback signal is compared to the magnitude of the first feedback signal to determine whether the sense line is providing the first feedback signal from the output of the power amplifier.
Abstract: An overload protection circuit for a disableable amplifier includes a sensing resistor connected to provide indication of the current supplied to the amplifier and includes logic circuitry for producing a disabling control signal for a selected time interval following detection of the overload condition of the amplifier.
Abstract: An output transistor (T.sub.1) is to be protected from damage due to excessive currents. This transistor supplies a current (I.sub.o) to a load (3) and is driven by a driver transistor (T.sub.2). The base-emitter junction of a current-sensing trnsistor (T.sub.3) is connected in parallel with that of the output transistor (T.sub.1). The collector current of transistor (T.sub.3) is a measure of the current (I.sub.o) of the output transistor (T.sub.1). A current generator (5) supplying a reference current (I.sub.ref) is coupled to the collector of the current-sensing transistor (T.sub.3). If the collector current of the current-sensing transistor exceeds the reference current (I.sub.ref) the protection circuit is activated so that the driver transistor is bottomed via an emitter-follower (T.sub.4). The base current of transistor T.sub.1 is thereby limited. Thus, the output current of the output transistor is limited to a maximum value which is substantially equal to the product of the reference current (I.sub.
Abstract: Differentially-connected pairs of JFETs on an IC chip are protected from ESD events by connecting respective discharge control resistors to the drains of the JFETs in such a manner as to be in series with any flow of current through either JFET.
Abstract: A preferred embodiment of a thermal protection circuit for a piezoelectric speaker includes a PTC resistor connected in series with the speaker and a second PTC nonlinear resistive element, such as a light bulb, connected in parallel with the resistor. This protects the speaker from failure due to overheating caused by excessive drive signals without causing audio distortion during infrequent excessive drive signals of a short duration.
Abstract: A device for protecting an integrated circuit against overload and short circuit currents. The integrated circuit functions such that it is alternatingly switched to an ON or an OFF state, and when in the ON state a supply current (I.sub.M) is amplified by a Darlington-connected transistor step (Q.sub.20,Q.sub.21) and is supplied to the output (OUT) of the circuit across a load resistor (R.sub.LOAD). For an OFF state of the integrated circuit no current is led to the output (OUT). A protective circuit (S) comprising a detection resistor (R.sub.SENSE) is connected in series with said load resistance (R.sub.LOAD). The protective circuit also includes a differential step (D) for sensing a voltaqge (V.sub.SENSE) across the detection resistor (R hd SENSE) and a thyristor (T). Short circuit or overload on the output (OUT) causes an overcurrent to pass through said transistor step (Q.sub.20,Q.sub.21) and through the detection resistor. The increasing voltage (V.sub.