US2927247A

US2927247A - Transistor neon driver

Info

Publication number: US2927247A
Application number: US744978A
Authority: US
Inventors: Robert B Hennis
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1958-06-27
Filing date: 1958-06-27
Publication date: 1960-03-01
Anticipated expiration: 1977-03-01

Description

March 1, 1960 Filed June 27, 1958 FIG. 1

P 4.7 K 0b IN N R. B. HENNIS .2 Sheets-Sheet 1 TYPE 14 INVENTOR ROBERT B. HENNIS ATTORNEY March 1, 1960 R. B. HENNIS TRANSISTOR NEON DRIVER 2 Sheets-Sheet 2 Filed June 27, 1958 Nd E 2 1 A 2 S 25:: Z 55 x;

United. States Patent TRANSISTOR NEON DRIVER Robert B. Hennis, Poughkeepsie, N. assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Application June 27, 1958, Serial No. 744,978

5 Claims. (01. 315-135 This invention relates to indicator circuits and more specifically to improved transistor circuits for controlling or driving visual signal devices or neon indicators to indicate electrical conditions in other circuits.

In the transistor circuits which are replacing vacuum tube circuits in modern day electronic equipment, the operating potentials are at a' relatively low level. The potentials needed to operate commercially available neon indicator lamps are at a higher level. The use in a conventional transistor circuit of a potential high enough to operate a neon indicator lamp, might subject the transistor to a potential high enough to cause punchthrough. When punch-through occurs, the transistor no longer functions to produce normal transistor action.

Another difficulty encountered in the design of a transistor circuit for operating a neon indicator is the fact that commercially available neon lamps have a wide range of firing and extinguishing potentials.

The invention makes use of a pulsating DC. or A.C. voltage on one terminal of a neon for varying the potential at the terminal by an amount greaterthan the difference between the minimum extinguishing voltage and the maximum firing voltage of neons. The other terminal can then be placed at either of two D.C. levels, one of which does not allow the varying DC. potential across the terminals of the neon to reach the minimum firing voltage, so as to maintain the neon in its ofi condition, and the other of which shifts the reference of this varying DC. potential so that the latter scans from below the minimum extinguishing voltage to above the maxi mum firing voltage of commercial neons and the neon flickers to appear lit to the eye.

It is an object of this invention to provide an improved transistor circuit for reliably operating a neon indicator lamp.

Another object of the invention is to provide a transistor circuit for reliably operating a neon glow lamp without subjecting the transistor to unduly high potentials.

Still another object of the invention is to provide a transistor circuit which can operate reliably to fire a neon lamp for the full range of firing and extinguishing voltages of commercially available neon lamps.

A further object of the invention is to provide a scanning voltage which varies an amount greater than 'the difierence between the minimum extinguishing voltage and the maximum firing voltage of neons.

A still further object of 'the invention is to provide a means for effectively shifting the reference level of the varying potential across a neon lamp from a position where the voltage peak does not reach thefiring potential of the neon to a position where the peak voltage is greater than the maximum firing voltage and the minimum potential is lower than the minimum extinguishing point of commercially available neon lamps.

Another object of the invention is to provide a trausistor operated neon lamp indicator wherein'the'voltages 2,927,247 Patented Mar. 1, 196i} cially available neon lamps, and yet never apply greater are high enough to operate inthe' iull'rangepfcomrnerthan the punch-through voltage to the transistor.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which discloses, by way of example, the principles of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is a circuit diagram of the preferred embodiment of the invention. t Fig. 2 illustrates the voltage conditions in the circuit 0E Fig. 1 when the neon is not firing.

Fig. 3 illustrates the voltage conditions in the circuit of Fig. 1 when the neon is firing.

Before describing the invention it is necessary to understand some of the operating characteristics of present day commercially available transistors and neon lamps.

It is well known in the art that a neon lamp will not fire to light up until the firing voltage of the neon lamp is reached. Once the neon fires, it operates as a constant voltage device and will continue to remain lit until the extinguishing voltage, which is substantially lower than the firing voltage, is reached. Different neon lamps manufactured under the same type designation may have different firing and extinguishing voltages. For any particular type designation of neon, there is a fairly well defined range of firing and extinguishing voltages. ,For example, in the NE- type neon, which is utilized in the preferred embodiment of the invention, the firing voltage for the different neons may vary from a minimum of 65 volts to a maximum of 90 volts. The extinguishing voltage may vary from a minimum of 53 volts to a maximum somewhere below the firing point of the particular neon. The average firing voltage for an NE-75 is approximately volts and the average extinguishing voltage is 60 volts.

In the commercially available junction transistors, which are best suited for the operation of the preferred embodiment of the invention, the operating voltage usually placed at the collector of the transistor ranges between 5 and 20 volts. While there is no reason for going higher in a normal circuit design, these transistors are generally capable of operating with a collector voltage of 45 volts. This voltage is too low to operate the neon lamps. If voltages of greater than 45 volts are used, the problem of punch-through arises.

If the collector voltage of a transistor is increased sufficiently to cause the depletion region of the collector to move entirely through the base region and at some point contact the emitter region, a relatively low resistance path between the emitter and collector is established. This phenomenon is known as punch-through breakdown, and is more fully described in the Handbook of Semiconductor Electronics by L. P. Hunter, published in 1956 by McGraw Hill. When punch-through occurs, transistor action is lost.

A transistor indicator circuit is shown in the patent to J. C. Logue et al., in Patent 2,772,410, issued November 27, 1956. The present invention, which is an improvement on that patent, has a circuit which is operative for the full range of commercially available neons rather than for hand picked neon lamps.

One of the problems which is encountered in the circuit of the type shown in the Logue et al. patent is the reverse current which flows between the base and the collector through the collector resistor during cut ofi time. This current, known as ICQ eifectively operates to produce a voltage drop across the collector resistor. This condition acts to make a lower voltage available for operating the neon as will be more fully described hereinafter. It is to be understood that this I varies substantially with changes in temperature and from transistor to transistor in commercially available transistors, and so it is necesto take into account theworst conditions. That is,

if there is a low I' there is a larger voltage applied at sistor circuitincluding an IBM type I4QPNP' junction I transistor having an emitter electrode 102, a base electrode 10b and a collector electrode 100. Thecollector electrode is connected through a 39K ohm resistor $2 to a source of '43 voltsD-E. 13 and the collector elecwhichis connected to a pulsating source of DC. The waveformfor the pulsating source is shown inl-Figs; 2

drops to O. The neon remain in this unlit condition "until terminal 18 again goes above +3-7 volts so that there is 80 volts across the, neon and it again fires. The operation then continues irr the same manner as previously described. The preferred source used for the pulsating DC. voltage, which is applied to terminal '18 is a 60 cycle input, which'atter being put through a full wave rectifier, beco E s-a: 1'20 cycle Wave. Thus,

' the neon would-"go on orice for each cycle of the 120 trade-10c isalso connected oranges 150K ohm resistor .14 and a neon glow discharge lamp16 to a' terminal 18,

and- 3', and varies from-'0 volts to +57 volts DLC. F'This may be a well known type of waveform generated in a full wave rectifier whichhas no filter at its output. The base 10b is connected through a 4.7K ohm resistor 20' to an input terminal IN, and also through a 18K ohm resistor-22 to a source of +10 volts D-.C. -24.

The indicator circuit ofthe invention is ordinarily uti-- lized to indicate the-stateof other transistor circuits-as described in Logue et a1; patent. found in the output of transistors, especially trigger cir-' cuits, well known in the art varies from O to 5 volts; The neo11= lamp of the invention will glow to indicate when the output of the transistor circuit to which it is' connected is at 0 volts, andwill' not glow' when the out.

put of the-transistor circuit is at +5 volts.

When the input signal from-a previous transistor stage" goes'to 5 volts, the voltage at the ;base 10b of the driving' transistor 10 starts to go negative, and the transistor 10 conducts current from the emitter 102: t'o-the-col-lector 10c. When the driving transistor 10 conducts current, the collector 100 goes to approximately ovens. With The voltage levels;

0 volts on the collector 19c, theneon 16 is efiectively in I acircuit from the collector ltl'c-through the 150K. ohm v resistor and the neon 16 to the terminal -18.

It can'be seen from 'Figs. 1 and 2; that th'ere will be no current flowing through the neon, assuming first that there is 0 volts on the terminal 18' and 0 volts at the collector 10c, terminal =18 varies from-O to -|-57 volts and thus, the voltage across the neon varies n m mini' mum of '0" volts toa maximum or 57 volts. 'Since this maximum voltage-is not "enough to fire a NIB-75', even one at the'lowes'tend of the range with-a firing voltage V of 65 volts, the neonswill definitely not be-fired.

When 0' volts are applied at input-terminal the

resistors

20 and 22 act as a voltage divider and approximately +2 volts are applied to the'base'Illb of the driving transistor -10. This positive voltage on the base of a PNP transistor will cut it OE. With no current flowing from the emitter to the collector of the driving transistor 10, the neon 16 is 'etl'ectively in a: circuit from the terminal 1 3 through the 39K resistor, the ISOK ohm resistor and the neon-1 6' to thet'erminal 181' v Fig; 3 illustrates the pulsating voltage on terminal -18 and there'is a constant source of -43 voltsat terminal 13. Taking the average firing voltage of*80- volts: as the firing voltage, Fig. 3- indicates that when-the voltage across the neon is 80 volts, the neon will fire. --'Fhe voltageacross the neon almost immediately drops to avoltage-just above the extinguishing voltage, intheexample, approximately 60 volts; Even though the voltage at" team-ariscontinues to rise, the neon hasqa constant drop-of approximately 60 volts across it. When-"however, the voltage at terminal18 goes below +1 7 volts (assumin'gpan average extinguishing voltage of 6 0 volts), the

neon ,i's'exti s gh an th vo taseastos it inalusistely cyclewave. It. thus flickers on and oh at a cycle rate is. fast enough so'that it appears-to be lit to the normal eye. 7 a V v t The importance of a pulsating DC. voltage or varying voltage on terminal 18 may' be understood an analysis is made of a circuitwhich does notuse the. pulsating DC. current. As has been hereinbefore. described, the

voltage at terminal 13 is limit'e'dto about 45 volts because of the possibility of transistor punch-through. The

voltageon terminal 18', if it is to "be' D.C;, is limited because it must below enough to provide an extinguishing v'enagewhenme collector of the transistor I 0 'is' at "0 volts. In addition, since the neon must ;be fired when the transistor 10 is cut off, the factor caused by I must be taken into account. 1'5 flows through resistorIZ and produces'a voltage" drop which may be as high as 10 volts. This further limits: the potential available to the neon because" it produces aminepositive point at the collector than 5t 3"volts." The voltage across the neon available for firing is the: sum of the'potential at terminals 18 and 13' minus thevoltage drop "du'e to 1 6.

By using the"pulsating" D.C; voltage at terminal 18, the voltage can be made to-rise high enough to produce firing and low" enough to provide extinguishing. The amount of DC. voltage necessary at terrnihal 13 then becomes amount which is' high enough to. shift the pulsating no: voltage at 'terminal' ltltrom just below the extinguishing'point to justabove' the firing point. Therefore, this D.C. voltage does not have to be made so high, as to cause punch-through of the transistor.

The pulsating P.C.- voltage must vary so that'the difference betweenits-'m'inimum point'andfits. maximum point is slightly more than the difiere'nce between the minimum extinguishing voltage and maximum firing voltage.- It may be understood 'that'thi s p'uls'atin'g DlC. voltage maybe an A6; ol-za' esuperimposed on a= D.C; ,voltagein a well known manner. It can beunder'stood that with this circuit, ifa neon burns 1 out, it can'gbe replaced from commercially available stock without worrying about read 'u'sting circuitv'al'ues;

While there have been shown and describedv and pointed out the -fundame1ital novel feat'ur es of the invention as applied to a preferred embodiment; it will be understood that various omissions and substitutions and, changes in the forum and details of the": deviceillust r'ated 'ahdin its operation may be mad'e' by those skilled" in the art without departing from the spirit'lof the inyenti'on. -It is the intention therefore, tobe limited only as indicated by the scope of the ifollowing claims:

1. Visual signal apparatus comprising in' combination, .aglowdis charge-lamp having a'-"firing potential and an extinguishingpotential within a predetermined range of values, a; source ofpotential connected to one terminal of said glow lampxwhich varies periodically'hy'an amount greater than saidtcpredetermined range, .and means for applying a; unidirectional .potential to; the other .terminal of said glow vlamp,,saidcmeans including, means to vary the potential at s'aid otherdterminal between two fixed Po i ev a r 2 Ni e ana am swin i -ti combination, ingia filing. potential andan in zi praete nae'd range of I V I I conne'cted to one terminal of sa dlglo'w lampfwhich periodically an amount guishing potential and the maximum firing potential, and means for applying a unidirectional potential to the other terminal of said glow lamp, said means including means to vary the potential at said other terminal between a first fixed potential level which provides a maximum difie ence of potential at the terminals of the glow lamp of less than the minimum firing potential and a second fixed potential level which provides a difference of potential at the terminals of the glow lamp which varies from a value greater than the maximum firing potential to less than the minimum extinguishing potential.

3. Visual signal apparatus comprising in combination, a transistor having an output electrode, load circuit means connected to said output electrode including a load resistor and a first source of unidirectional electrical energy in series, means for indicating an electrical condition in said load circuit means comprising a glow discharge lamp having a firing potential and an extinguishing potential within a predetermined range of values, and an energizing circuit for said lamp including, in series, said load resistor, said lamp and a source of periodically varying electrical energy having a polarity opposite to that of the potential drop across said resistor produced by the current flowing through said output electrode and varying an amount greater than the diflference between the minimum extinguishing potential and the maximum firing potential of said predetermined range.

4. Visual signal apparatus comprising in combination, a glow discharge lamp having a firing potential and an extinguishing potential within a predetermined range of values, a first source of unidirectional potential connected to one terminal of said glow lamp, the potential of said first source varying periodically an amount greater than the difference between the minimum extinguishing potential and the maximum firing potential of said predetermined range, an energizing circuit for said lamp including in series, a second source of unidirectional potential, a

load resistor, and a transistor, said load resistor and the output electrode of said transistor being connected to the other terminal of said lamp, and means for selectively operating said transistor to produce current flow through said load resistor, said operation of said transistor providing at the output electrode two fixed levels of potential, a first fixed level when current is flowing which provides a maximum difference of potential across the glow lamp of less than the minimum firing potential and a second fixed level when no current is flowing which provides a difference of potential at the terminals of the glow lamp which varies from a value greater than the maximum firing potential to less than the minimum firing potential.

5. Visual signal apparatus comprising a glow discharge lamp having a firing potential and an extinguishing potential within a predetermined range of values, an energizing circuit for said lamp including a resistor and a source of periodically varying electrical energy in series, said source having a potential which varies an amount greater than the difierence between the minimum extinguishing potential and the maximum firing potential of said predetermined range, and means for controlling the potential across the lamp including circuit means for conducting a current through said resistor to produce a potential drop thereacross of a polarity and magnitude effective to reduce the maximum potential available at the lamp below the potential required to fire the lamp, and means for selectively stopping the current conduction through said circuit means to shift the potential available at the lamp so that it varies between the minimum extinguishing voltage and maximum firing voltage of said predetermined range.

References Cited in the file of this patent UNITED STATES PATENTS 2,772,410 Logue et al. Nov. 27, 1956