Патент USA US3070766код для вставки
Dec. 25, 1962 M. FISCHMAN 3,070,756 AMPLITUDE STABILIZED SAWTOOTH CURRENT GENERATOR Filed May 7, 1959 ‘ . 2 Sheets-Sheet 1 =="-—20 + 22 A - --—/9 _ V‘! ; zfi T 26/ $ . -5 b'ASEM/I. § ' 5 1-200 % “2 3 -/ 8 -z -4 —e cozucmk V0175 BYILLA‘G‘IIM ', ATTORNEY’ ii a. a 337,756 ‘ . V Patented Dec. 25, 1962 2 3,070,756 The condenser 30 is connected as shown between the base 8 and the conductor 18 which may be maintained at Martin Fischman, Wantagh, N.Y., assignor to Sylvania a low A.C. potential or grounded by the action of large bypassing condenser 19, insofar as the generated oscilla tions are concerned. Resistor 32 in series with the yoke 2 is a monitoring resistance from which a sampling voltage may be derived by way of lead 34 for test and adjustment AMPLETUDE gTABILHZED SAWTOOTH (INT GENERATQR Electric Products line, a corporation of Delaware Filed May 7, 1959, Ser. No. 811,649 5 Qlaims. (Ci. 331-109) purposes. My present invention relates to a generator of electrical Transistor T2 serves to maintain the average current 10 through the entire circuit constant. Transistor T2 is currents of sawtooth waveform. In the generation of linear sawtooth currents in de?ec provided with an emitter electrode 40, a base electrode 42, tion coils that are primarily inductive, a problem arises in and a collector 44. Emitter 40 is connected to ground connection with maintaining the sawtooth amplitude in through a resistor R3 thus providing degeneration in the dependent of the sawtooth frequency. For example, when emitter circuit. The voltage applied to the base 42 with laboratory Oscilloscopes are supplied with de?ecting cur rents from conventional sawtooth generators, undesirable respect to emitter 40 of transistor T2, is controlled by a changes in de?ection of the oscilloscope beam take place at different frequencies, requiring time consuming re Resistor R2 as shown, is in series with resistors R5 and R4, the series combination of resistors R2, R5 and R4, being connected between the negative terminal 22 of power supply 24 and ground. adjustment or use of different scales and calibrations.‘ It is, therefore, an object of my present invention to provide a sawtooth current generator in which the peak to peak values of the sawtooth current waveforms gen erated are maintained constant over a range of operating l. u".1 tap 46, adjustably connected along and to resistor R2. If desired, modulating voltages such as voltages from a commercial 60 cycle source 53 may be introduced be tween the base 42 and emitter 40 by means of a trans frequencies. Another object of my invention is to pro former 50 connected as shown. The primary winding 51 vide a new, effective and relatively inexpensive amplitude 25 of transformer 50 is connected to the 60 cycle source 53 stabilized sawtooth current generator. and the secondary winding 52 of transformer 50 is, as Brie?y, my invention makes use of a transistorized illustrated, connected in series with base 42 and the tap 46 sawtooth generator connected to an inductive load such connected to resistor R2. ' The operation of my improved sawtooth generator may that currents of sawtooth form are caused to flow in the inductive load. By means of a current regulating transis 30 be followed and understood more readily by considering tor circuit, average current through the entire system is the system ?rst, without reference to the amplitude stabil ization feature. Referring to FIG. 1 (assuming point A maintained constant. As a result, when changes in fre to be grounded) it can be seen that transistor T1 provides quency are made, automatic, compensating voltage varia regenerative feedback from emitter 4 to base 8. The feed tions take place across the inductive load in such a way that the peak to peak ?ow therethrough is independent of back is of a magnitude sufficient to cause the transistor the frequency of operation. to operate in the saturation region of its characteristic. In this condition the transistor voltages remain practically in an equilibrium state due to the lack of dynamic gain FIG. 1 is a wiring diagram of an amplitude stabilized of the transistor in the saturation region for an interval 40 corresponding to the forward scan of the cycle. FIG sawtooth generator according to my present invention; URES 2B, F, G, and H show this equilibrium state of the FIG. 2 illustrates de?ection generator waveforms and voltages on the transistor elements during this interval. are used herein by way of explanation of the operation of The duration of this interval depends on the time required my present invention; and My invention will be described in greater detail, herein after, with the aid of the accompanying drawing wherein: FIG. 3 is an illustration of characteristic curves of a transistor showing the relationship of collector current to collector voltage at different base currents. In my invention, as illustrated in FIG. 1, currents of sawtooth form are caused to ?ow in'the inductive load here indicated as a coil 2, usually the de?ecting yoke for a cathode ray tube. In accordance with my present inven tion the peak to peak value of this current ?ow through coil 2 is maintained constant over a desired operating range of sawtooth wave frequencies. The sawtooth currents through the'load 2 are generated by the transistor generator comprising the transistor T1 having an emitter-electrode 4, a collector 6 and a base 8. for the collector current, starting from zero current, to reach the sharp knee in the collector characteristic for the ?xed base current that is applicable. When the knee is reached the rate of change of col lector current decreases and the ‘ transformer voltages start to drop resulting in decreased base drive. This 50 process occurs quite rapidly, due to the 'fact that the op erating point is now out of the saturation region and the regenerative feedback of the circuit results in rapid cut off of the transistor. The transformer voltage swings through approximately a half cycle of oscillation deter 55 mined by the effective inductance and capacity of the cir cuit and the transistor loading including the internal re sistance and capacitance of the transistor, whereupon the oscillation is arrested when the transistor turns-on and Regeneration is provided by means of the autotransformer AT having its upper or high potential terminal 10 connect the next period of forward scan is initiated by the turn ed to the base 8 by way of the variable resistor R1. An 60 on of the transistor. intermediate point 12 of the autotransformer AT is con During the forward scan interval both junctions of nected by way of conductor 14 to the emitter of transistor the transistor are forward biased. Low voltage drops T1. The lower terminal 16 of autotransformer AT is con therefore exist across the junctions of the transistor result nected by way of conductor 18 and bypass condenser 20 to the collector 6 of transistor T1. A negative voltage 65 ing in an e?icient switch that connects the supply voltage --V across the de?ection yoke 2 and the emitter tap 12 of —V is applied to the collector 6, this voltage being derived the transformer AT. The base current or drive is deter~ from the negative terminal 22 of a power supply 24, here mined by the voltage between the emiter 4 and the illustrated as a battery, grounded at its lower terminal 26. stepped-up end 10 of the transformer AT and the value “Shunting the terminals 22, 26 of battery 24 is a bypass of R1, the frequency control resistance. This resistance .condenser 25. The value of the voltage applied to col 70 is high in comparison-to the base to emitter resistance lector 6 is adjusted to a suitable value by adjustment of of the transistor T1, ‘under this operating condition. Dur ' the source voltage 24. ~-ing the forward ‘scan intervaL-the' base ‘current-is fairly 3,070,756 4 3 the yoke inductance and T is the duration of the sawtooth constant ‘since the voltages referred to above, the emitter voltage and the voltage at the high end 10 of the auto transformer, are practically constant. The waveform of or time of one cycle of the sawtooth waveform. The average value of the sawtooth current drawn by transistor T1 is approximately Ipp/ 2 if the ratio of trace to retrace time is large as is usualy the case. In accordance with my invention, I provide a transistor T2 to maintain the base current of the transistor during the forward scan interval is shown in FIG. 2-1. With the 1:3 autotrans former used in the circuit of FIG. 1, a simple approxima .tion for the base current useful for practical purposes is: the average current through the circuit constant. By maintaining the average current constant, the peak to peak current will likewise remain constant and desired 10 stabilization ensues. Transistor T2 is connected with its In the foregoing equation, E is the voltage across the emitter grounded through a resistor R3; emitter degen lower section 12-16 of transformer AT, and is substantial eration being provided by resistor R3 and the low base 2E Ib-fR1 ly equal, during saturation, to —-V. resistance of transistor T2. The high dynamic collector Estimated and measured values of base current at the resistance thus obtained maintains the collector current end of .the forward scan interval indicate a value of ap 15 practically independent of the collector voltage. Under proximately 4 ma. Referring now to the collector char these conditions the collector current of T2 will be ?xed acteristics of FIG. 3, it can be seen that the transistor by its base bias permitting the voltage drop across the will be in the saturation region for collector currents up scanner circuit to vary in accordance with Formula 1 to 200 ma. with a 4 ma. base drive provided that the while maintaining the average current through the entire collector to emitter voltage is small. The emitter voltage 20 circuit constant. Thus for a given DC. current deter waveform of FIG. 26 shows a .collector to emitter drop mined by the bias of transistor T2 adjustments of the fre of about .4 volt near the end of the forward scan interval. quency of the scanner will result in automatic compensat FIG. 2E shows that the collector current increases to a ing variations in the voltage E across yoke 2 with the re maximum value of 200 ma. corresponding to the knee in sult that Ipp remains independent of the frequency of the the collector'characteristic for a base drive of 4 ma. 25 scanner. For example, at higher frequencies the volt The locus of the operating point of the transistor then age across the yoke 2 will rise, thereby maintaining the falls out of the saturation region terminating the forward peak to peak current through the yoke of unchanged value. The peak to peak scanning current will be ‘in The duration of the forward scan may be estimated dependent of the characteristics of T1, the value of the with reasonable accuracy provided some simplifying as 30 yoke inductance, the sup-ply voltage V and will in fact sumptions are made with regard to the circuit. The tran be determined solely by the collector current of tran sistor and yoke inductance may be simpli?ed to a series sistor T2. inductance-resistance LR circuit and the ‘response to a The stabilization of the collector current of T2 may be step voltage E of 5 volts calculated. The total series re accomplished by emitter degeneration by the inclusion of sistance R3 is 35 resistor R3 in the emitter circuit. The potentiometer Ohms R2 serves as an amplitude control by establishing the DC. Collector to emitter resistance _ _______ __, _________ __ 2 operating current in the collector circuit of transistor T2 Yoke resistance __ 5 and hence the peak to peak sawtooth current of transis Monitor resistance ___________________________ -_,.; 1 tOl‘ T1. Modulation of the sawtooth current can be accom 8 40 plished by applying a modulating signal to the base circuit The parallel combination of the 1 millihenry yoke of T2, as explained, by use of a source 53 and transformer and transformer is 900 microhenrysl The collector cur 50. The emitter degeneration serves to establish a linear relationship between the modulated sawtooth cur 45 rent and the modulating signal. Table 1, below, indicates the amplitude variations as a function of frequency with and without the stabilization and the time required to reach a collector current .of 200 circuit and indicates a measure of improvement obtained ma. may be calculated from with my present invention. 50 Table 1 scan interval. . Without Stabilizer (Point A Frequency, kc. 55 ' grounded) , With stabi liner Peak to Peak Yoke Peak to Current, ma. Peak Yoke Current, ma. =43 microseconds now to FIG. 2E, it can be seen that the’ duration of the forward scan interval as shown by the waveform is close to this value. The frequency of oscil 60 Referring lation is conveniently controlled by the resistance R; in the base-emitter circuit. Increasing the value of R1 re duces the base current and therefore locates the knee in 8 ' 16 ______________________________________ __ ‘32 240 ,180 175 180 70 180 I claim as my invention: 1. In combination a ?rst transistor having a base, an emitter and a collector; an autotransformer; a resistor the collector characteristic at a reduced current. The connecting one end of said autotransformer to the base of ‘period of forward scan is reduced in response to an in 65 said ?rst transistor; a connection from the emitter of crease of the frequency controlling resistance in the base said ?rst transistor to an intermediate point on said auto vemitter circuit. transformen'an inductor having one end connected to Undesirable changes in de?ection with changes in fre the emitter of said ?rst transistor, means connecting the quency of the de?ecting currents is due to the fact that other end of said autotransformer to the other end of the peak to peak current is a function of the saw-tooth 70 said inductor; a ?rst condenser connected between the ‘duration in accordance with the approximation base of said ?rst transistor and the other end of said auto ET transformer; a second condenser connected between the 11:11:? Wk}??? (.1 ) collector of said ?rst transistor and the other end of said 15 ill? V91tag6 across the yoke or inductance, L is 75 autotransformer; a unidirectional power supply; a second 3,070,758 5 transistor having a base, an emitter and a collector; means for connecting the collector of said second transistor to the other end of said autotransformer, means for connect 6 4. A stabilized sawtooth generator as de?ned in claim 3 wherein said current regulating means comprise a sec ond transistor having its collector-emitter circuit con nected in series with said inductive load and further in ing said power supply between the collector of said ?rst transistor and the emitter of said second transistor, and 5 cluding biasing means coupled between the base and means for biasing the base of said second transistor with emitter of said second transistor, said biasing means respect to its emitter so as to cause constant average cur controlling the average value of the current through said rent to ?ow through said ?rst transistor whereby sawtooth inductive load. current pulses ?owing through said inductor will have a 5. A stabilized sawtooth generator as de?ned in claim relatively constant peak to peak value over a range of 10 4 wherein modulation means responsive to an applied operating frequencies. signal is coupled to said biasing means, said modulation 2. In combination, a generator adapted for providing means modulating the current through said inductive load a sawtooth current to an inductive load, current regulat in accordance with said applied signal. ing means coupled in series with said inductive load, and means coupling said series connected current regulating 15 References Cited in the ?le of this patent means and said inductive load across the output of said sawtooth generator, said current regulating means main UNITED STATES PATENTS taining the average current through said inductive lo-ad constant. 2,847,569 Finkelstein __________ __ Aug. 12, 1958 3. A stabilized sawtooth generator comprising a tran 2,891,192 Goodrich ___________ __ June 16, 1959 sistor having an emitter, a base, and a collector, regen 2,897,429 Jochems ____________ __ July 28, 1959 erative feedback means connected betwen the base and 2,939,040 Isabeau ____________ __ May 31, 1960 emitter of said transistor; an inductive load connected to the emitter of said transistor; current regulating means OTHER REFERENCES connected in series with said inductive load; and means 25 “Feedback-Stabilized Transistor Ampli?er,” by Slaugh adapted for connecting a voltage source between said ter in Electronics, May 1955, pages 174-175. current regulating means and the collector of said tran ‘Electronics, by Herzog, May 1, 1959, pages 52—53. sistor.