USRE28432E - Signal source - Google Patents

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Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
  • H03F3/21—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only
  • H03F3/217—Class D power amplifiers; Switching amplifiers
  • H03F3/2178—Class D power amplifiers; Switching amplifiers using more than one switch or switching amplifier in parallel or in series

Definitions

• An audio frequency amplifier useful to DC in which a pulse-width modulated signal is formed from the audio frequency signal.
• Each excursion of the pulse-width signal is cut in half with respect to time by an appropriately timed square-wave and plural logic gates.
• the resulting waveforms are passed without distortion by pulse transformers.
• Plural rectifiers and low-pass filters re-form the pulse-width modulated signal.
• This signal is impressed upon switching power transistors.
• These give a greatly amplified power output, which is the same type of amplitude-varying waveform as the input audio signal, upon the current flowing through a small choke to the load.
• the load may have any phase angle without incurring distortion of the output waveform.
• Half-bridge, quarterbridge, full-bridge, and plural phase embodiments are described.
• This invention relates to linear audio frequency power amplifiers wherein the incoming signal is converted to a pulse-width modulated signal, amplified, and then reconverted to a signal of varying amplitude.
• Circuits of this type are to be found in the art; see applicants US. Pat. No. 3,400,334, issued Sept. 3, 1968.
• the apparatus thereof produces a sawtooth waveform to accomplish chopping.
• Short pulses are passed through pulse transformers in the amplifying process.
• Certain floating (ungrounded) power supplies were required.
• Reactive loads caused serious distortion of the output waveform.
• Additional active elements silicon-controlled rectifiers
• Inverters to provide lightweight apparatus for converting DC power to typically 400-cycle sine wave AC, may employ pulse-width modulation; but that art appears to require high voltage ratings on transistors and cannot approach 100 percent modulation in practice.
• the input signal to be amplified and a triangular waveform are combined in a comparator to give a corresponding pulse-width signal of constant amplitude.
• Each such pulse is sliced in half as to time duration by a square wave applied to plural logic gates.
• Each series of halfduration pulses is applied to a separate pulse transformer.
• the maximum duty cycle of any transformer for 100 percent modulation of the initial pulse-width Signal is thus only 50 percent, because only half-duration pulses pass through each of the transformers. Accordingly, low frequencies including DC, may be amplified with fidelity.
• All power supplies may be grounded at one terminal.
• FIG. 1 is a schematic diagram of the input stages of the Class D" linear audio amplifier according to this invention.
• FIG. 2 is a schematic diagram of a half-bridge embodiment of the gating, transformer and power stages of the amplifier.
• FIG. 3 shows time-related electrical waveforms that are present at various points in the apparatus.
• FIG. 4 is a schematic diagram of a full-bridge embodiment of the invention, showing the transformer connections and the power amplifier.
• FIG. 5 shows an inverted phase embodiment of the full-bridge.
• FIG. 6 is the schematic diagram of a quarter-bridge embodiment.
• FIG. 7 is the schematic diagram of a two-phase halfbridge embodiment.
• FIG. 8 is the schematic diagram of a three-phase halfbridge embodiment.
• schematically illustrated element 1 is a signal source, such as a microphone, audio generator, function generator, or an equivalent source of amplitude-varying signals typically in the audio frequency range. In a practical embodiment this source may provide a voltage output of 1 volt.
• a dual transistor 2 is employed to raise the impedance of the input circuit of the whole device to efficiently operate comparator amplifier 3.
• the right-hand base of what may be an RCA-type CA3018 dual transistor is tied to ground through resistor 26, typically of 5,000- ohms resistance.
• the left-hand base of element 2 is used as the summing point for the signal from signal source 1 and a triangular waveform.
• Resistor 18, 10,000 ohms decouples the signal source from the summing point and resistor 17, of equal resistance, decouples the source of triangular waveform.
• the two emitters are connected to the differential inputs of comparator 3, individually through resistors 36 and 37, each of 47 ohms.
• the two emitters are further connected to battery 31 through resistors 27 and 28, each of 1,000 ohms. Feedback is provided for the comparator by resistor 29, of 10,000 ohms.
• An energizing bias is provided for the emitters of transistor 2 and for comparator 3 by battery 31, of negative 6 volts, or by an equivalent power supply. Note that the positive terminal thereof is connected to ground in accordance with the feature of this invention which allows power supplies to be grounded at one terminal. Similarly, battery 30 provides positive 12 volts to further energize comparator 3 and transistor 2. Resistor 25, ohms, and Zener diode 32, of 6-volts rating, are connected in series from the positive terminal of battery 30 to ground. Both collectors of dual transistor 2 are connected to the junction between the resistor and the diode to thereby be fed with a constant voltage.
• Comparator 3 may be a Motorola MC 1710 CG integrated circuit operational amplifier of the difierentialinput single-ended output type. Its function is to transition its output from one state (positive) to another state (negative) whenever the input voltage to it transitions from negative to positive. The impedance of the source driving this type of comparator must be low. Dual transistor 2 provides this.
• the feedback for the comparator through resistor 29 is from the output to the noninverting input. This provides positive feedback and a hysteresis efiect. Thus, upon switching from one state to the other, the comparator acts like a Schmidt trigger and remains in the new state until the input is reduced a finite amount.
• Element 4a is one section of a hexagon inverter integrated circuit in a typical embodiment. This may be a Motorola-type MC 789 P integrated circuit. It is used to provide an inverted output from comparator 3, as compared with its input. Other sections of the inverter integrated circuit are 4b, 4c, 4d and 4e, which are used elsewhere in the input stages of FIG. 1, as will be later described. A direct output passes from FIG. 1 to FIG. 2 from comparator 3 via conductor 19, while an inverted output similarly passes via conductor 20.
• Unijunction transistor 5 a GE Dl3Tl, is connected as an oscillator.
• the anode is connected to a 6-volts positive source of energizing power through resistor 38, of 10,000 ohms; while the cathode is connected to a 6-volts negative source through resistor 34, of 100 ohms.
• the anode gate terminal of the transistor is directly grounded.
• Capacitor 6, of 470 picofarads (pf), is connected from the anode to signal ground, and causes the frequency of oscillation to be 100 kilohertz.
• Flip-flop 7 is of the JK variety, and may be an integrated circuit-type MC 787 P.
• the 100 kHz. pulses from the cathode of transistor 5 are fed through capacitor 33, of 5,000 pf., and in shunt to resistor 35, of 100 ohms, to the input of flip-flop 7.
• the common terminal thereof is connected to ground and the power supply terminal is connected to plus 6 volts.
• the inverted output is fed to inverter 4b to amplify the signal to about a 4-volt peakto-peak amplitude in order to properly feed integrator 8, an MC 1435 P integrated circuit.
• Flip-flop 7 divides the frequency of oscillator 5 in half and provides an accurately symmetrical square wave at each of its outputs.
• the second output of the flip-flop is taken through resistor 21, 100 ohms, which, in conjunction with capacitor 22, of 800 pf., connected between the resistor and ground, provides a time delay for the square wave transitions.
• This output passes through amplifiers 4c and 4d to sharpen the transitions of the square wave from the rounding thereof brought about through the functioning of delay filter 21, 22.
• a typical delay obtained is of the order of 0.2 microsecond (,usec.) and is required .to match the delay caused by integrator 8 and the positive feedback around high speed comparator 3.
• the positive feedback for hysteresis causes about 0.1 sec.
• inverter 4d passes from the schematic diagram of FIG. 1 to FIG. 2 via conductor 23 and the inverted phase of the same is provided by inverter 4e. This is forwarded via conductor 24.
• Integrator 8 includes subsidiary apparatus for accomplishing the integration function.
• the input arrives via capacitor 9, of 0.05 mfd., isolation and gain-reducing potentiometer resistor 10, of 6,800 ohms, in series with the capacitor and also in series with resistor 15, of 100 ohms, to ground.
• Resistor 10 connects to the inverting input of the MC 1435 P integrated circuit and resistor is shunted across both inputs.
• a low-pass filter comprised of series-connected resistors 12 and 13, both of 5,000 ohms resistance, with capacitor 14, of 0.2 mfd., connected to the junction between the two resistors and ground. This filter is also connected to the output of integrator 8 and reduces the DC offset of integrator 8.
• Capacitor 16 is connected between the stabilizing terminals, tocontrol the AC rollofi frequency.
• Shunt resistor 15 controls the DC gain.
• Power is supplied to integrator 8 by a connection from the upper power supply terminal thereon to the positive 6-volt supply provided by Zener diode 32, and by a connection from the lower power supply terminal thereon to the negative 6-volt supply 31.
• the output of the integrator an accurate triangular waveshape, proceeds fro-m the output terminal thereof through isolating resistor 17, of 10,000 ohms, to the first base of dual transistor 2, for mixing with the input signal from source 1 for processing by comparator 3.
• FIG. 2 We now turn to FIG. 2 to consider a typical apparatus and mode of operation to utilize the functioning of the apparatus of FIG. 1.
• the two phase-opposed square waves from amplifiers 4d and 4e, which appear on output conductors 23 and 24, respectively, are used in FIG. 2 to control gates which split the outputs on conductors 19 and 20 exactly in half.
• Such a current is easily and faithfully transformed by realizable transformers. It is then recombined to provide percent modulation; i.e., DC, if required.
• High eificiency results in this type of what may be termed a Class D amplifier.
• the isolation of the out put from the input afforded by transformer coupling is considered a useful characteristic in many applications.
• the inputs to FIG. 2 from FIG. 1 pass to a plurality of gates, 39a, b, c, d; which are separated into a first series, 39a & c, and a second series, 39b & d, to distinguish the related apparatus with which each series is associated.
• Each gale is typically a NAND gate having two inputs, in total, such as the Motorola MC 717 P, a quad two-input gate.
• Conductor 19 is connected to the first inputs of gates 39a & b.
• Conductor 20 is connected to the first inputs of gates 39c & d.
• Conductor 23 is connected to the second inputs of gates 39b & c.
• Conductor 24 is connected to the second inputs of gates 39a & d.
• the pulse-time modulated pulse carrying the signal to be amplified is present on conductor 19, while the square wave which has a transition exactly half way between the start and the finish of the pulse on conductor 19 is present on conductor 23.
• the first half of the pulse on conductor 19 passes through gate 39a, and the second half of that pulse passes through gate 3%.
• the output of gate 39a is connected to the base of emitter-follower transistor 40, a Motorola MP8 6514.
• Resistor 77 100 ohms, is connected to the emitter and also to the negative terminal of battery 31a, or equivalent, which provides an operating voltage of 6 volts.
• Battery 31a may be combined with battery 31 of FIG. 1, in practice.
• the collector of transistor 40 is con nected to Zener diode 32a, which maintains a positive 6- volt supply from resistor 25a and 12-volt battery 30a.
• the emitter of transistor 40 is connected to the base of transistor 41 through resistor 81, of 100 ohms.
• Transistor 40 provides a slight negative bias to the base of transistor 41 when gate 39a is off and a positive bias to the same when gate 39a is on.
• Transistor 41 may be an RCA 2N5262 and is connected to the primary winding of pulse transformer 42, having typically a 2 to 1 stepdown ratio.
• the second terminal of the primary is connected to the positive terminal of battery 30a for energizing the transistor, the emitter of which is connected directly to ground.
• Transformer 42 is of the first type, characterized by having plural secondaries; in this case, two.
• Secondary 43 feeds current of positive polarity into diode 44, this diode being composed of four GE-type DA 1704 diodes in parallel, and also into filter network 45, 46 & 47.
• Inductor 45 may have an inductance of 0.02 microhenries (,ul'l.) and inductor 46 of 0.007 ah,
• capacitor 47 has a capacitance of 0.05 mfd.
• These elements comprise a low-pass filter having a cutoff frequency above the frequency of the pulse-width modulated signals.
• Secondary 48 of transformer 42 provides a negative voltage of the order of 6 volts to the emitter of transistor 49, an RCA 2N5262.
• the base of this transistor is connected to capacitor 50, of 3,000 pf. capacitance, the other terminal of which is connected through resistor 50a, of 100 ohms, to the lower terminal of transformer 56 secondary 56b.
• Transistor 49 also has a resistor 50b, of 100 ohms, connected between emitter and base; the emitter also being connected to the lower terminal of secondary 48.
• the second half of the waveform pulse on conductor 19 passes through gate 39b, transistors 51 and 52' transformer 53, and from secondary 54 thereof through diode 55, which diode is the same type of component as diode 44.
• Transformer 53 is different from transformer 42, in that transformer 53 is of the second type having only one secondary.
• the performance of the two secondaries 43 and 54 is the same, the additional secondmy 48 on transformer 42 does not affect the performance of its secondary 43.
• the cathodes of diodes 44 and 55 are connected together and to filter 45, 46 & 47. This results in the front half and the rear half of the pulse originally on conductor 19 being combined in time sequence. Thus, the original pulse of full duration is restored. Passing through resistor 85, having a small fraction of an ohm resistance, the pulse passes on through the apparatus on conductor 64.
• the waveform on conductor 20 which is an inversion of the waveform on conductor 19, passes through gates 39c & d. It is also split in half as a matter of time duration. This is accomplished by the square waveforms present on conductors 23 and 24, which enter gates 39c and 39d, respectively.
• Transistors 73 and 75, resistor 83, and transformer 56 are the equivalent of previously described elements 40, 41, 81 and 42, respectively, as are transistors 74 and 76, resistor 84, and transformer 57 the equivalents of elements 51, 52, 82 and 53, respectively.
• the corresponding connections are also the same.
• Diodes 58 and 59 are the equivalents of diodes 44 and 55, respectively, and filter 60, 61 & 62 is the equivalent of filter 45, 46 & 47.
• each of transistors 40, 51, 73 & 74 are connected to sources of actuating power in the same way and to input and output circuits in an equivalent way.
• Transistors 41, 52, 75 & 76 are also connected to a source of actuating power and to ground in the same way and to input and output circuits in an equivalent way.
• the same polarity (direction of winding) of the several primaries and secondaries of transformers 42, 53, 56 & 57 is indicated by the dots at the ends of the windings.
• a companion transistor 49a complements transistor 49, as do the components associated with each.
• the relative symmetry of essentially all of the electronic circuit of FIG. 2 will be noted.
• the power transistors are 67 and 68. These may be single, relatively high power transistors for each of these opposed active elements, or they may each be a plurality of essentially normal output power transistors in parallel. In a practical embodiment this has reached a total of 56 RCA 2N5262 transistors for each of entities 67 and 68. With such an arrangement a corresponding number of 56 resistors 85 and 86 feed transistors comprising the generic transistor 67, and similarly for resistors 87 and 88 for generic transistor 68. Each individual transistor 6 has two resistors individually connected to its base. A typical resistance for each individual resistor is ohms.
• the base of power transistor 67 is connected to conductor 64 for suitable actuation by the circuits previously described.
• the input circuit to transistor 67 is completed through conductor 63, which connects to the emitter of the transistor.
• the base of power transistor 68 is connected to conductor 66 and the emitter to conductor 65.
• the output circuit of these transistors includes battery 69, or equivalent DC power supply, such as a rectifierfilter or a fuel cell, which has a voltage of the order of 20 volts.
• the negative terminal thereof is grounded and the positive terminal is connected directly to the collector of transistor 67
• the output circuit also includes a companion battery, or equivalent, with the positive terminal grounded and the negative terminal connected directly to the emitter of transistor 68.
• the emitter of transistor 67 and the collector of transistor 68 are connected together and to one terminal of reactor 71, typically having an inductance of 50 ,uh.
• the other terminal of the reactor is connected to load 72 and the second terminal of the load is connected to ground.
• a fast recovery diode 89 such as a GE DA 1702, is connected between emitter and collector of power transistor 67, and individually if this be composed of a plurality of transistors.
• the cathode of the diode is connected to the collector of the transistor.
• the diode specified is particularly suited for a large plurality of paralleled power transistors comprising transistor 67, one diode across each. If
• Reactor 71 typically has an iron core.
• FIG. 3 is employed in tracing the operation of the circuits.
• Waveform 1' represents a typical input waveform, having time as the abscissa and variation of amplitude as the ordinate. With the time scale chosen substantially three-fourths of one cycle of a sinusoidal waveshape having a frequency of the order of 4,000 hertz is shown. Substantially any waveshape can be handled by the apparatus, and at different frequencies, particular lower, than the frequency specified.
• the upper frequency limit of the apparatus is set by the inductance value of reactor 71. This value is determined by the ripple current considered allowable in any application of the amplifier, and by the oscillator frequency, this being 100,000 hertz in the examples that have been given.
• the upper frequency limit may be raised by employing transistors having faster switching characteristics.
• the higher cost of such transistors may bar their use in commercial apparatus, but the future is expected to raise both the technical and the economic limits that might be a bar to increasing the upper frequency limit of the amplifier.
• Waveform 8 is the triangular Waveform appearing at the output of integrator 8, having a frequency of the order of 50 kilohertz (kHz.).
• Waveform 19' is the output from comparator 3, at conductor 19 in FIG. 1, and results from the summing of waveforms 1' and 8.
• Waveform 19' is actually the inverse, phase shifted of the combination of waveforms 1' and 3. This is due to the, phase inversion of the comparator operational amplifier.
• the conversion from amplitude to pulse-width variations results in pulses of long duration with short intervals between them for representing positive peaks of the amplitude variation, pulses of duration equal to the intervals between them for zero amplitude, and pulses of the output of square wave producing flip-flop 7 after a delay is introduced as required and the waveform has been sharpened to have needed rectangularity by inverters 4c and 4d.
• This waveform is precisely timed to split each pulse waveform 19' in half according to the process of this invention. This relation will be seen by vertically com paring waveforms 19' and 23, any corresponding point representing the same instant of time for both waveforms. Note that the halving occurs whether the pulse width of Waveform 19 is large or small.
• Waveform 39a is the output of NAND gate 39a. This represents NOT (19 and NOT 23'), as shown by the logic term at the left of the waveform in FIG. 3.
• Waveform 39b is similarly the output of NAND gate 3%, and this is NOT (19' and 23').
• Waveform 39c is the output of gate 390, and this is NOT (NOT 19 and 23-).
• Waveform 39d is the output of gate 39d and is NOT (NOT 19' and NOT 13).
• the power output circuit of FIG. 2 has opposed active elements, transistors 67 and 68. Since these transistors operate in the switching mode, they alternately connect positive power supply 69 or negative power supply 70 through reactor 71 to load 72. This switching is accomplished with the base drive signals supplied by conductors 64 and 66.
• Waveform 71 is the voltage present at reactor 71 and waveform 72 is the smoothed voltage at load 72.
• the filtering effect of the reactor reproduces the original amplitude-varying waveform, though at a greatly increased power level, as desired.
• dual transistor 2 is employed to reduce the effect of temperature drift. It is not connected as a differential amplifier, but as two emitter-followers. Both sections of the transistor are on the same chip of semiconductor material and in the same metal can. The base of the right-hand transistor section is tied to ground through resistor 26. The emitter of that section serves merely as a reference for one input of comparator 3.
• Silicon transistors have been recited as typical herein, but those of Germanium, Gallium Arsenide, etc. could be used, including those of the field-effect type.
• the requirements are rapid switching (in the nanosecond range), adequate current-carrying capacity, capability of turning off current without punch-through, low forward voltage drop when conducting, and low leakage current when not conducting.
• the Beta of each must meet an average value. A spread of as much as 3 to 1 in value is satisfactory.
• the base current of each is limited by base resistors 85 or 87, and individual resistors are provided for each of the paralleled transistors. A limiting value of 35 milliarnperes (ma) for each of the RCA 2N5262 transistors specified is typical. With this base current no transistor will carry more than 3 amperes. Since the transistors are either on or off, this is still within the dissipation rating and the rating to run off this current at rated voltage without punch-through or secondary breakdown. The nominal current is 1 ampere per transistor.
• Diodes 44 and 55 are preferably of the fast type.
• the former When the quarter cycle of current carried by diode 44 ceases and diode 55 starts passing current, the former must surely be off, otherwise the latter will feed unwanted current in the reverse direction through the former. This results in a large glitch, a steep return to the axis of the waveform, in the waveform supplied to the bases of the power transistors 67 and 68, and an unwanted distortion in the output of the amplifier with increased dissipation in the power transistors.
• Each of diodes 44 and 55 carry 35 ma. per power transistor, and for this base current rating typically a considerable number of power transistors are paralleled. Small glass high-speed computer-type diodes are satisfactory.
• the time to have the diode take over carrying current should be 50 nanoseconds (ns.) or less for desired eificiency and performance.
• Such diodes are commercially available and the external wiring is kept short and otherwise of low inductance. Where paralleled power transistors are employed, one diode is used for each power transistor.
• reactor 71 Although the functioning of reactor 71 is significant in the operation of the amplifier of this invention, its effect is at frequencies very much above the audio frequencies typically amplified. With the typical value of inductance of 50 #11. its reactance at 3,000 Hz. is only 1 ohm; thus it has negligible inductive reactance at the upper audio frequencies normally amplified. It is at the commutating frequency of 50,000 Hz. and at spike harmonics thereof, which are many times higher in frequency, that the reactor exerts significant inductive effect.
• capacitor 50 which is connected to the base of transistor 49, charges rapidly when transistor 41 is turned on. This momentarily and quickly turns on transistor 49, which in turn acts to turn off power transistor 68 by reversing the base current thereof. A corresponding effect takes place on the other side of the amplifier involving transistor 49a and transistor 67.
• a power efiiciency of 93.5 percent was accomplished in the amplifier proper. Additional losses occurred in the power supply, so that the overall efficiency was 90 percent. This is high; however, as compared with an efficiency of 4-0 percent for a Class A amplifier and of 60 percent for a Class B amplifier, such as are normally employed for audio frequency amplification.
• the square wave from flipflop 7 is not equally above and below the zero volt DC axis. It is desirable that the triangular waveshape 8 in FIG. 3 be centered on the zero axis. Accordingly, blocking capacitor 9 is employed. Resistors 12 and 13 provide feedback for the integrator, with the alternating current component of the signal bypassed to ground through capacitor 14. This leaves an active AC amplifier arrangement, with capacitor 11 the feedback integrating capacitor, and the mean value of the output at the zero axis.
• Resistor 15 is of low value, ohms, and with resistor 10 forms a voltage divider of large ratio since the value of resistor 10 is typically 6,800 ohms.
• the value of resistor 15 determines the fine structure of the triangular waveshape. If it is too small the peaks of the waveshape are rounded. If it is too large, overshoot spikes result. However, once the proper value has been chosen for the circuit, other integrated circuit elements can be substituted for integrator 8, as for circuit repair, and the triangular waveshape remains proper.
• NAND gates have been shown in the embodiment described, it is also possible to use OR, NOR or AND gates instead. Appropriate change in the logic is made.
• Gates 39a, b, c, d shown are of nominal power output. Associated transistors, such as 40 and 41 for gate 39a, are employed to increase the power level of the signals involved for driving the transformers, as transformer 42. With gates of higher power now obtainable, each of the transistors exemplified by transistor 40 may be omitted. With still higher power gates, both transistors 40 and 41 may be omitted.
• the output voltage is made to be a faithful, but amplified, copy of the input voltage regardless of the phaseangle of the load in this amplifier by arranging the output circuit so that the output voltage is independent of the output current.
• FIG. 4 shows the alteration of FIG. 2 required to modify the apparatus thereof of a half-bridge embodiment to a full-bridge embodiment.
• the input stages of FIG. 1 are unaltered, as are gates 39a, etc., transistors 40, 41, etc., as well as all of the transformers, such as 42, the corresponding rectifiers 44, 55, 58 & 59, and the outputs at conductors 63, 64, 65, & 66.
• the modification takes the form of an additional set of transformers and rectifiers, giving four more output conductors 63a, 64a, 65a & 66a. These connect to an additional pair of power transistors 67a & 68a, and feed an equivalent load 91 through an additional reactor 71a.
• FIG. 2 the transformers, rectifiers, filters and associated elements are contained within a dotted rectangle M.
• This group of apparatus is identified as a modulator.
• this same modulator M is implied by the upper rectangle M, with the incoming and outgoing conductors shown.
• a duplicate modulator Ma is shown below modulator M, with the input connections to the transformers being in parallel to the corresponding input connections of upper modulator M.
• the output conductors are the same and are identified with the subscript a.
• FIG. 5 shows an alternate embodiment in connecting the drive apparatus to the bases of the power transistors in the full-bridge arrangement.
• This employs two modulators, M and Ma, as before, but these are separately driven out of phase rather than in phase as in FIG. 4.
• the input stages according to FIG. 1 are also duplicated. One of these is fed out of phase in FIG. 5. They are identified as I and la, respectively.
• Signal source in FIG. 5 is the same as signal source 1 in FIG. 1; being a microphone, audio generator, etc.
• the output thereof feeds directly into input stages I, as before. However, this output also passes through resistor 92, of 10,000 ohms, to the base of a phase-inverting transistor 93, an NPN-type 2N395 8A.
• the emitter thereof is given a negative bias by battery 94, or equivalent, through resistor of 5,000 ohms.
• the collector is connected to load resistor 96, of 5,000 ohms, and is given a positive bias by battery 97.
• Conductor 98 conveys the thus phase-reversed signal to the input of a duplicate of the input apparatus of FIG. 1; i.e., to a resistor 18a, which is the equivalent of resistor 18 in FIG. 1.
• outputs from input stages I pass into modulator M through conductors 19, 20, 23 & 24, as aslo shown in FIG. 1 in detail.
• the otuts from input stages 1a pass into modulator Ma through conductors 19a, 20a, 23a & 24a.
• output conductors 63', 64, 65 & 66 from modulator M connect to emitter and base of transistor 67 and to emitter and base of transistor 68, respectively. This is according to FIG. 4, and this portion of the whole circuit has not been redrawn in FIG. 5.
• the output conductors from modulator Ma are inverted in order with respect to those of modulator M because phase inverter 93 is present in front of modulator Ma. That is, conductors 65a & 66a connect to base and emitter of transistor 67a in FIG. 4, and conductors 63 and 64a connect to emitter and base of transistor 68a, respectively.
• FIG. 6 illustrates a quarter-bridge embodiment. This is a simplification over the half-bridge embodiment detailed in FIG. 2. Only half of all the apparatus shown in that figure is employed. Likewise, per in FIG. 1, only three outputs, conductors 19, 23 & 24, are used in the simplified version Ib of the input stages. These three inputs enter simplified modulator Mb, which has only two gates 39a and 39b, two transformers 42 and 53, one filter 45, 46 & 47, and two output conductors 63 and 64.
• these conductors connect to emitter and base, respectively, of single transistor 67.
• Reactor 71 is connected to the emitter and to load 72, while the second terminal of the load is connected to the negative terminal of battery 69.
• the cathode of diode 89 is connected to the emitter of transistor 67, while the anode is connected to the second terminal of the load.
• the current does not reverse in the load, thus the different connection of the diode.
• modulator Mb receives an input signal in only one polarity and the signal output varies from zero in the positive direction only.
• This embodiment is suited for supplying power to a DC motor in which reversing polarity is not required.
• FIG. 7 illustrates a two-phase half-bridge embodiment. This roughly follows the full-bridge embodiment of FIG. 4, but there are differences, as will become apparent.
• two singal sources are employed, having at any instant of time the same frequency but different phase, say 90 different.
• the two sources might be connected in some manner to retain the same frequency and diiference of phase, but these are not requirements for the functioning of this embodiment.
• source 1 having a phase timing of A is connected to input stages I, from which emerge four outputs, 19, 23, 20, & 24. These enter modulator M, and therefrom emerge outputs 63', 64, 65 & 66.
• Conductor 63 connects to the emitter of transistor 67 and conductor 64 to the base thereof.
• Conductor 65 connects to the emitter of transistor 68 and conductor 66 to the base thereof.
• transistors 67a & 68a occupy reversed positions from those occupied in FIG. 4. This change occurs because in a full-bridge circuit opposite corners switch together. In a two-phase embodiment opposite corners switch from diiferent modulators 90 apart in time. Notwithstanding, conductor 63a connects to the emitter of transistor 67a and conductor 64a to the base thereof, while conductor 65a connects to the emitter of transistor 68a and conductor 66a to the base thereof.
• two loads 72 and 72a are to be found at the output. These are symmetrically connected, with one terminal of each connected to the common, signal ground, point between the two power supplies, the positive one 69 and the negative one 70.
• the second terminal of load 72 is connected to reactor 71, while the second terminal of load 72a is connected to reactor 71a.
• These reactors typically have an inductance value of 50 uh each. Diodes 89, 90, 89a & 90a reverse bias each of the four power transistors -in the same manner and for the same reason as in FIG. 4.
• the second phase signal originates in source 1a at a phase B, and enters input stages 1a which has outputs 19a, 23a, 20a, & 24a, similar in nature to the corresponding apparatus for phase A.
• Modulator Ma accepts the above outputs and has outputs 63a, 64a, 65a & 66a, which connect to the power output stages as has been described.
• FIG. 8 illustrates a three-phase half-bridge embodiment. It is suited to operate from a three-phase input signal and deliver power to a three-phase load.
• FIG. 7 The structure of FIG. 7 is followed by extending it to one more phase, with a typical phase relation of 120, but not necessarily so.
• Three signal sources 1, 1a & 1b are of the same frequency but of different phases, and these originate the signal inputs to be amplified.
• the phases of the sources are, A, B & C.
• Each source is connected to a corresponding input stages entity I, la & Ib, each of which has outputs corresponding to those on conductors 19, 23, 20 and 24.
• These outputs enter modulators M, Ma & Mb, each of which has outputs corresponding to those on conductors 63, 64, 65 & 66.
• Each of these connect to a pair of power transistors corresponding to transistors 67 & 68 in the manner that has been repeatedly recited.
• Three pairs of power transistors are provided, one pair for each phase, and having differentiating subscripts.
• Each power transistor is shunted by a diode as before.
• the three-phase load has separate phases 99, 99a & 99b, and is shown delta connected.
• a connection from the common connection between the emitter of transistor 67 and the collector of transistor 68 passes through reactor 71 and to the connection between loads 99 and 99b.
• a similar connection from between transistors 67a and 68a passes through reactor 71a and to the connection between loads 99 and 99a.
• a further similar connection from between transistors 67b and 68b passes through reactor 71b and to the connection between loads 99a and 99b.
• each reactor has a typical value of 50 h.
• Power supplies 69 and 70 are connected in series without any external midconnection.
• the positive terminal of supply 69 connects to the collectors of transistors 67,
• Diodes 89, 89a & 89b are reverse bypass connected across transistors 67, 67a and 67b; while diodes 90, 90a & 90b are similarly connected across transistors 68, 68a & 68b.
• a Y connected three-phase load may be energized by connecting it to the three reactors 71, 71a & 7113, instead of to the delta configuration shown.
• the extremities of the Y are connected to the reactors; the common center of the Y connects to the second terminal of each load. If the Y load is nonsymmetrical the common center (neutral) is connected to the interconnection between power supplies 69 and 70.
• Typical load impedances for the several embodiments are as follows.
• a high power loudspeaker or with a group of the same, including those for underwater sound, will be understood.
• a dependable variable speed power drive is provided, as for a drill press, which may be programmed as to speed of rotation with time by programming the oscillator as to frequency as a function of time.
• the same control is possible for the known vibra tion exciter, or shaker.
• a tractive motor for railways or for other vehicles may be of the rugged induction or synchronous-type and still be controlled as to speed of rotation by suitably controlling the frequency of the input to the amplifier It is in this type of service that the twoor three-phase embodiments would be expected to find application.
• the invention is operative if this is other than exact; say, instead of /2, /2.
• the requirement is that long pulses be essentially halved. This is accomplished with the division.
• a short pulse might not be divided and go only through one transformer, as 42, with no pulse at all through the companion transformer, as 53, the output would be proper.
• the term half as used throughout this specification and claims is also to be interpreted as approximately hal
• base filters, as 45, 46 and 47 are desirable
• An electrical amplifier comprising;
• a. comparator apparatus having feedback to form a pulse-width modulated signal (19') from an amplitude-varying input signal (1') and a triangular wave amplitude-varying signal (8),
• first and second series of gating means (39a & c; 39b & d) connected to said comparator means, each said series supplied with a square wave signal (23 or 20') time related to said triangular wave signal to alternately pass said pulse-width modulated signal in successive halves of the duration of each pulse width,
• a plurality of low-pass filters (45, 46, 47; 60, 61, 62) equal in number to the number of said gating means insaid first series, each said filter connected to secondaries of both a first and a second type transformer,
• a power amplifier having at least two active elements (67 & 68) in opposed groups, and an output
• a comparator (3) connected to said source of triangular waveform and receiving said amplitude-varying input signal (1) to give an amplitude transition each time said triangular waveform becomes greater or less in amplitude that the amplitude of said input signal
• each of said gating means (39a, b, c, d) is a NAND gate, having an input from plural said comparator related outputs.
• each of said low-pass filters includes;
• each of said opposed active elements (67, 68) is a switching-type transistor
• connection (par. j) from the output of said power amplifier to said load (72) includes;
• said'first and said second series of gating means each have two gating means
• a. a second comparator apparatus (1a) to form a pulsewidth modulated signal from a second amplitudevarying input signal
• a linear AC-DC signal amplifier comprising:
• modulating means includes a triangular waveform input for adding to said signal to be amplified to form said first train of width-modulated pulses.
• said combining and amplifying means includes a switching amplifier and a low pass filter input to the amplifier for remvving frequency components above the frequency of the signal to be amplified.
• An amplifier comprising:
• means including a square wave signal said square wave signal having polarity transition exactly halfway between the leading and trailing edge of each pulse of said train of pulse width-modulated signal for biseoting each pulse of said pulse train and separately passing the bisected portions;
• Means for amplifying an amplitude-varying signal comprising:
• gating means including a square-wave input signal having polarity transitions exactly halfway between the leading and trailing edges of each pulse of said pulse-width-varying signal connected to the output of said pulse-width-varying signal forming means, to halve and separate each pulse of said pulse-widthvarying signal with respect to time duration;
• filter means for filtering the pulsed output of said conveying means
• An improved AC-DC amplifier comprising:
• first and second gating means controlled by a control signal synchronized with said high frequency modulation signal for alternately passing successive halves of each pulse of said train of pulses forming first and second trains of successive half pulses;
• inductance means for converting the amplified and reassembled pulse-width modulated signal to an amplified reproduction of said incoming signal.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Amplifiers (AREA)
• Control Of Direct Current Motors (AREA)
• Inverter Devices (AREA)

Abstract

Description

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• 1969
  • 1969-11-14 US US876771A patent/US3579132A/en not_active Expired - Lifetime
• 1970
  • 1970-07-10 FR FR7025735A patent/FR2071620A5/fr not_active Expired
  • 1970-07-15 GB GB3433470A patent/GB1319288A/en not_active Expired
  • 1970-10-12 DE DE2050002A patent/DE2050002C3/en not_active Expired
• 1973
  • 1973-02-28 US US33685373 patent/USRE28432E/en not_active Expired

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