[1]Un'l't,ed Stei.,.,-tes Po,- ,cen-,t @Of-ace 390769135 3,076,135 POVIIEP" SUPPLY Cil".CUIT P,07,)ert P. F."rnswerth, Los Anuales, aud Leonard Azar, Culver City, assigners to HL,-@hes Aircraft Company, Culver City, CUIL'., a of Delaware Filed Sept. 29, 1953, Ser. No. 765,693 11 Claims. (Cl. 323-22) 'Eh-is inventioti relates to power sui)plies and particularly to a direct-current power supply utilizing a fast acting overload protec.'ion circliit. 1-ii th(- prior art, D.C. (direct current) power supplies were used -in coiinectio-@i with vacuum tubes and delivered relatively high output voltages and could op--rate wilh r.Iatively high output impedances. However, with transistor cire-,iitry, power suppl-les may be required to s,,ipply rela'Lively low ou@,put voltages while supplying current of 25 amperes or more. The oL,Lput impedance of th-@ power supply may be req-uired to be less than 10-3 ohms. These rroblems h,@)ve been solved by utilizing power supplies ,,vith h3gh power transistors for regulation and low forv@ard resistance diodes for rect;fication. T@ic lo-,v output impedance from these power supplies ha.- created new probleirs, the most formidable one bein.a thE,@'L of protec',ir@g the power supply and the load against shoi-t-c,'rcuits or accidental overloads. During a shortcircuit Ir accidcntal overload condition, destruction of the trans;s'Lo@-s ar@d rectifiers of the power supply as well as Llestruction of the tra-@isistor cireiiitry being suppl@'@ed with l,ower occurs at a fast rat.,. The time required for destruction may be in the order of 100 microseconds under severe conditio-@is. Conve-itional fuses or mechanical disconnections req,.,ire 20 to 30 milliseconds to open, which op-- rationisfartooslowtoprotectirans;s',ors. Som,-eleetronic d-scornect eirciiitry of the prior art samples si.-nal current iii a regulator loop a-,id provide ttirn-off- of the stipply when the si.-nal c,-lrrent reaches a preset value. The ,@@hortcoming of this system is thet the si.-nal current is related to the Ioad ci-irr-.nt by the gain of one or more stages of th.- s,,ipply, which gain is dependent upon ageing and temperature o-.@ the circuit elements, as well as upon sui)ply voltages. Thus, the turn-off current is variable and changes uider these conditions so as to not colisistently disconn-@-.t the power suoply at a Lixed inaximtim load current. Also, some conventional power supplies having automati.- turii-oft characteristics follow a turn-off path which although allowing them to turn on under full load after removal of a short circuit condition, will also allow them to exceed max-imum dissipations under partial short circuit. Other conventional power supplies follow a palh vjhich allows them to turn completely off when qn overload condition occurs under full '@oad but reqiiires partial removal of th.- full load to turn o-@i after the overload or short circuit conditioii has been corrected. These turno@n and turn-ot characteristics may result from the nonlinear,.ti.-s of 'the system colpponents. A system which would provi,,Ie fast operating overload protection, that would provide overl.oad protection at a fixed maxiiniiin load current ir,.dependcr@t of the gain of the circuit elements, apd which would turn both completely off and co-,upletely on whe-@i a short circuit condition occurs and is removed at full load, would have wide use, espec@'@ally with tr@,ns;stor circuitry. It is, tl-.Irefore, an obj,-ct of this invention to provide a p,ower supply which rapidly d,.sconnects from its load upon the occurrence of a short circuit or an overload condition. It is a flirther object of this invention to provide a transistor power supply wh-@ch turns off under an overload conditioii and turns on upon removal of the overload condition at a corsistent maxiinlm load current val-ae, ind-.pendent of temperature and agein.- of the ampl:@fying eler-.qents in the eircu:it. It is a still further object of this invention to provide a fast actilig power supply utilizing transistors which will not only completely disconnect the source from the load during an overload conditioii when operating at full rated power but will return to supplyin- full rated power upon removal of the overload condition' Another object of this invention is to provide a tran10 sistor power supply having a simplified overload protection circuit for prctectiiig both the power supply and the supplied c-ircui,ry, ar@d which operates to disconnect the power supply at a predetermined rated current indep,-ndent of changes of characterislics of 'Lhe transis'Lor due to age15 ing and temperature. According to one feature of this invention, a pow,-r supply receives unregulated direct clrrent vol'age f-,-or@l a transformer and rec'Lifler arran.cement, and supplies it to a load throli.-h a series cor@nected re.-ulatin.-, or con'trol, 20 transistor which varies in static imp-,dance in response to changes of i'ts base current. A voltag-@ comparator ineluding a first differential amplifier and a voltage divider both connected across the load, is utilized to control a current signal in respoilse to changes in t'hp- load voltage 25 or potential difference. A s,-cond differential amplifier is connected to the bas-. of the control transistor and is connected to the first difereiitial ampliper for resi)ondinto the changes of the current signal to maintain thp. constant load vol'Lage. An overload control circuit is pro30 vided includiiig a resistor connect-,d from a terminal of the control transistor and in series with the load to form a first voltage divider and including a second voltage divider cor@nected from the saine terminal of the control transistor to tne other side ol' the load. A signal-formin35 transistor is connected between the first apd the second volta-e dividers so as to respond to a predetermiped poiarity of pote-ilial d:iffe.-enc-, indicatin- maxin-ium r,,t d load. The signal formir@g trans-stor is conncct,-d to shunt out the current from the first differen'lial amplifi,-r in 40 response to the predeermined polarity wliich in ti-irn biases tne regulatin,@ transistor oi,,t of conduction to effectively discoilnect the soiirce -Liom the load. A leakage path across the control trarzsistor maintains this disconnected condition by supplying a s-,iiall current through the 45 first and second voltage dividers. When the overload condition is rertioved the potential difference b-.tween the first and second voltage dividers retur-@is to a polarity to bias the signal-forming 'Lrarsistor otit olconduction, thus 50 allowing tie voltao,e comparator cireliit to contin-Lie its regulating operation at any load up to maximum load. The novel featlires of this invention, as -,vell as @he invention icself, both as to its orga-@i-lzatioii -@nd method.o'@ operation, will best be undcrstood from the accompanying 55 description, tak.-n in connect-io-ii vvith the accomoanyiiig drawir@gs, in which: FIG. I is a schematic dia.-ram of ,he power supply circuit of this inventioil; and FIG. 2 is a graph to illiis'Lrate the operation of 'Lhe 60 circuit of FTG. 1. Referring first to FIG. 1, a schemat;c circuit dia-ram is shown of the power supply circuit in'cluding the @overload i)rotection arrangement of ttiis invention. The power supply o'l tnis invention receives unre.-Ulated voltage, which may be -32 vol'Ls, from an unre-ulated voltage 65 source 20 comprisir@g a transform@ er and all,eriiating current voltage source 22 coiinected to a termiral 25 wh,ch rnay be at ground potentiv.1 ard a rectifier 24 connected to the transformer and vol'ta.-e source 22. The unregulated voltage source 20 supplies power through a regulat:ln,- 7 trans-stor 26 of a re.-Ulating element circuit 32 to a load 34, which may include a r,- sistor RL, and is cor.,nected io the terminal 25 through a ground lead 103. The regi@.-
[2]3,078,135 3 lating element circuit 32 also includes a driver transistor 38. The regulatin,a transistor 26 which may be of the PNP t@,pe has a base 44, an emitter 42 ard a collector 40, and the driver transistor 3:8 which may be of the NPN typ.- has a base 50, an emitter 48, and a collector 46. 5 The collector 40 of the regulating transistor 26 is connected to the rectifier 24 and the base 44 of the regulating transistor 26 is connected to the collector 46 of the driver transistor 33. The emitter 43 of the driver transistor 33 is connected to ' h,e collector 40 of the - regulating transistor 10 26 to provide a r-,turn pach for current from the base 44 of the regula'Ling transistor 26, as will be explaitied subsequently. A leakage resistor 54 is connected between the collector 40 and the emitter 42 of the - reg@lating transistor 26 and, as vii'il be explained bereinafler, passes a current 15 to maintain the circuit disconnected during an overload c,ondition. The base 50 of the driver transistor 38 is connected to a current-amplifier circuit 60 which utilizes a differential amplifier for controlling the current passed into the 20 base 50 of the driver trans;stor 39@. The differential amplifier includes a transistor 64 and a transistor 66 both of which may be of the PNP type. The transistor 64 has a base 68, an emitter 70, and a collector 72, and the transistor 66 has a base 74, an eraitter 76, and a collector 25 78. The collector 72 of the transistor 64 is connected to the base 50 of the transistor 33 and the collector 78 of 'Lhe transistor 66 is connected to the collector 40 of the re,-Ulating transistor 26. A biasing resistor 80 is connected between the collector 72 of the - transistor 64 and 30 the collector 78 of the transistor 66 to provide a leakage current pa'th from the base 50 of the transistor 33 when the transistor 38 is biased out of conduction, as will be explailled subsequently. The emitters 70 and 76 of the transistors 64 and 66 are connec'Led by way of a current- 35 limiting resistor 32 to a lead 84. The lead 84 is conn,.cted to a terminal 88 which may be connected to a +15 voltage unregulated source (not shown), ivhich provides a bias for maintaining operation of the circuit during an overload condition. The base 68 of the transistor 64 is 40 connected to a lead 90 and the base 74 of the transistor 66 is connected to a lead 92 through which leads, control current passes, as will be explained - subsequently. Thus, the ctirrent amplifier circuit 60 is connected for controlEng the regula4liiig element circuit 32. 45 The current ampliiier circliit 60 is - controlled by an overload control circuit 94 and a voltage comparator circuit 96. The overload control circuit 94 includes a resis+,Oi- RI having one end connected to a junction loo which, in tutn, is connected to the emitter 42 of the regii- 50 lating transistor 26. 'Me other end of the resistor RI is cornected through a lead 102 to the resistor RL of the load 34. The load current IL is indicated by an arrow 101. The resistor RI in combination with the resistor l@L ol the load 34 provides a first voltage divider, as W: 55 @ll be explained subsequently. The junction 100 is also connected through a lead 103 to a resistor R2 which in turn is connected to one end of a resistor R3 by way of a lead 106. The other end of the resistor R3 iS connected to the ground lead 108. The lead 102 is connected to the 60 cathode of a diode 112 which has its anode connected to one en ' d of a resistor 114 by lead 116. The other end! of the resistor 114 is connected to the lead 94. . A s;gnal transistor 117 which may be of the NPN type has a base 110, an emitter 120, and a collector 122 with 65 the base 118 connected to the lead 116 and the emitter 120 connected to the lead 106. As will be exiolained subsequently, the difference in potential drop across the 0 resistor R, and the diode. 112 and across the resistor R2' 7 which potential difference appears between the leads 116 an.d 106, determi es whether transis p tor 117 is biased into conduction. The collector 122 of the transistor 117 is connected to the base a26 of a transistor 124, which may be of the PNP type, The transistor 124 has an eipitter 75 4 128 wliich is connected to the lead 84 and has a collector 130 which is connected to the lead 90 at a junction 132. Thus, it can be seen that current passes into the junction 132 either from the transistor 124 or .4rom the transistor 64 of the current amplifier circuit 60. The lead 103 is also connected to the base 44 of the regulating transistor 26 by way of a biasing resistor l@36 which acts to j)ass leakage current from the base 44 to maintain the regulating transistor 26 biased when in its nonconducting stat.,, as will be explained subsequently. The voltage comparallor circuit 96 inellides transistors 138 and 146 arranged as a second differential amplifier circuit. The transistors 138 and 146 may be of the PNP type. The transistor 138 has a base Ig,',O, an emitcer 142, and a collector 144, and the transistor 146 has a base 148, and emitter 150, aiid a collec*or 152. The collector 144 of the transistor 138 is connected to the lead 102 by way of a biasing resistor 156 aiid the collector ISZ of the transistor 146 is connected to the lead 102 by way of a biasing resistor 158. The emitters 142 and 150 of the transistors 138 and 146 are connected to ground lead 103 by way of a current limiting resistor 159. The base 148 of the transistor 146 is connected to a lead 162 by way of a,n imped,ance-matching resistor 164. The lead 162 is connected to the ground lead 108 by way of a resistor 166 and is connected to the cathode of a diode 168, which may be a Zener type diode. The anode of the diode 168 is connected to the lead 102 to provide a potential to the base 148 of the transistor 146 wi'iich foliows the variation of the load potential on the lead 102. It is to be noted that th-- resistor 164 is utilized to match the impedance out of the base 148 of the trarsistor 146 to the impedance out of th@D base 140 of the transistor 133. The base 140 of the transistor 138 is connected by a variable tap 172 to a resistor 174, one end of wbich is connected to the lead 102 by way of a resistor 176 and the other end of which is connected to ground lead 108 by way of a resistor 178. The resistors 174, 176, and 178 thus are a voltage d-1vider of the potential difi-erence across.the load 34 for dividing out a potential to control the conduction of the transistor 138. The collector 144 of the transistor 138 is connected to the lead 92 which, in turn controls the conduction of the transis@,or 66, as will be explained subsequently. The coilector 152 of the, transi@tor 146 is connected to a lead 182 which, in turn is connected to the junction 132 for receiivng current from either the transistor 64 during normal regulation or from the transistor 124 during an overload condition, as will@ also be explained subsequently. A capacitor loo is coupled across the leads 102 and 108 to stabilize the circuit for providing a low otitput impedance to si.-nals on the lead 102 at a frequency above the frequency response of the transistors in the circuit, as ;s well known in the art. The operation of the voltage regulator of this invention, includes both normal voltage regulation of the load voltage on the lead 102 to maintain a regulated voltage and overload protection during operation when, for example, a fault such as a short circuit of the load 34 occurs. During normal regulation, the regulating circuit con-Lrols the current through the series element which is the transistor 26, to correct variations of the regulate,d potential on the lead 102 caused either by voltage fluctuations of the source 20 or by small variations of the effective resistance of the load 34. A rise of pote-Titial on the collector 40 from a positive-going fluctuation of the unregtilated potential from source 20, decreases the em;tter to qollector potential of the regulating transistor 26 apd at the - - value, of, the current determined by the potential qii the base 44, results in a smatt decrease in collector qurrent. This decrease of collector current is accompanied by a de . crease of the current passing through load k,, which results in a rise in potential on the lead 102. This rise in potential, is sensed by t P, volt?,ge comparator
[3]3,076,135 5 circuit 96 and, as will be described, acts to lower the potential o-@i base 44. This cor@dition decreases the static impedance of the transistor 26 to sli.-htly increase the load current so as to iiicrease the pote-.itial drop across the resistor RL and to res' ore ta-. regiilated potential on 5 the lead 102. A decrease of t@he effective value of the resistor RL also causes aTi increase of potential on the lead 102. It is to be noted that 'this condition causes onl@y a small increase of collector curreiit of '@he regulating trarsistor 26 10 as determine by the Dotent;al on the base 94. The increase of potential on the- lead 102 is sensed by t@ie voltage comparator cirellit 96 aiid, as will be described, acts to lower the potential on the base 4A of the i-e,,-Lilating transistor 26 so as to decrease tli-- static ir@rpedance of 15 the transistor 26 a,@id to iii,-rease +lie currcit irom emitter 42 to collector 40 a reciuired amouiit. Tiiis increase of collector current increas-es t'@ie curreilt passii,- throu @-h the load RL and caises a fall in po@lential on the lead 102, thus restoring ffic regulated pc)tential on the lead 102. 20 The operation of the volta.-c comparator circuit 96 -and the c,,irrent amilifier circuit 60 durin.@ iiorrilal voltage regulation will now be described. During normal volta.-C regul,ition, the transistor 117 is biased out of condu--tion to iiiterrupt the current path throu.-h tlie transistor 1,2A ' to the junction 132. Thus, the poter@tial deveioped on t-he collector 152 of the transistor 1-46 from c,,irrent passi-iig through the transistor 14,6 and ,lie resistor 153 is impressed through the 1--ad 182 to th.- base 63 to control , of the transistor 64. Aii increase (positive- 00 goin-) of potential at the base 148 of fne trins-istor 146 1 ftlin the lead 102 results in a decrease of potential on the collector 152 of the transistor 146. Tlais decrease (neaative-- oing) of pote--qtial is ;Mpressed on the base 68 35 to increase the conduction o.L the traiisistor 64, and to iTi,crease the potent;al on ta-, base 50 of th,- trans;slor 3'-. The transistor 38 is thus biased into further conduction and the potential on the base 44 of the transistor 26 is decreased to i-@icrease t'-ric emitter to collector curent 40 through the transistor 26. The potential impressed on tfie base l,' oiL the transistor 138 is also delernined by the load polential on the lead 102, wbich potential acts to va-Y tiie current passed from the emitter 142 to the collector 144 of ttic 45 transistor 138. An iicrease of poter-ttial on the base 14@9 results in an increq-@.e of i)oteiitial ol the collector 14@4 of the transistor 139 becalse of tlae dii-ierencial - ainplifier action, Ps vv-111 be descr;bed, ,Tvhich pat,-nL-lat is impressed on the bas-, 74 of the transistor 66 to decrease its cor.- 0 dtiction. '@hus, the po@eiitials on the collectors and 152 are impressed ti@irough the leads 92 and 182 to tne bases 7,@l, and 69 -of the trans;stors 66 and 64. The d-f,erential air@ptifier arrang-,meiit is utilized so that cha?lges o'L gain cl-iaracterist,'@cs of tlp- transistors 64,, 55 66, la38 aiid 146 h,?,ve a very small effect on the r--gulating act;on. A subslantially co-Tistant cutrrerit passas througli the current lirnitin.- resisto,: '-,59 and throti@.,@ the parallel resistors !56 -ciid 153. ;-hus, changes of t'ac gain characteris@@ics d@,ic 'to ag-.in.@ orter@iperature 60 ' @C - enan- s, for example, of the trat,-,s-istors 138 and @,4@6 has a relatively srnall effec', on the diiierence in potential wii the collectors 14.4 and 152. The dif@er-@-,lce i-ii ro,-@ntial on the leads 92 and -ig2 -is the valve whicii controls thf,@ amc)unt of cor@duc'-on of t'pe trans;stors 66 and 61 and, 65 in turn, the impedance of the r-,,-ulatin.- trans,'stor 26. The current-1:1 @ni'L:@ng res;s-Lor 82 passing a cons@alit current into ihe iransistgrs 64 and 66 of the first diflerent,'al amplifier circuit, cancels chan,@es of -ain characte,,:isties of the transistor.- C-4 and 6@u' in a similar mannor. Thi-is, 70 the differential amplifier arran.-er.-i@-nts ol trans-stors 139, 146, 64 and 66 is utilized to provide reliable regulation independent of temperature chan.-es or ageing of the transistors, for example. (B the potential on fne lead 102 is regulated to -25 volts by 'Lhe act,on of a servo loop includir@- a voltage comparator 96 a@id the palh to 'the base 4-/i of the regulat-in-, transislor 26. An increase of potenlia'i on the lead lo@@ resultin- from a voltage variation of the source 20 or a small decrease in the vallic ol' tiie load 34 impedance, as discussed, im-oresses the increase of potenlial throueh the corstant vofLa@@, Zener diode 168 to deve'op across the resislor 166 for appliec,,! ' -ion to the base 149 of the transistor 140, as a pol,-.qlial incre,@is-@ subslartially s,.milar in amplitude to t'@ie iii.-rease o@i 'tr@e lead 102. -,tlie transistor 146 is thus bias@-d so as to decrease its co3lduction and this decreascd current fiow tTi.-oL,(,,h the resistor 153 results in a decrease of the poteiit;al on the collector 152, which decrease is impressed on the bas-6'a of the transistor 64 to ir@crease its cor@L@uclicii. At the sarrie time, a small incrce-,se o'L po',en,@ial is impressed on the base 1-40 of ',he trans,'@stor 133 I@rom@ t.qe taD 172. However, because of the 'arge decrease of current ro-ag@l the transistor 146 and t@.rou,-.h the res,"stor '@153, the ciirren'l- passi-.i@., Larou,-h the transistor 133 is increased. This increase oi. current results from the ciifferential ictioii of a constaiit current passin- through the c,,irrent l imiti-@i.resistor !59. Thus, ther,- is an inereas-. o@ r pot-@-@itial on 2') the collector 144. of the tr,,ins;stor l@S whici-i is imprcss-,d on the base 74 of the transistor 66 to bias ii ful-tlic,- otit of conduction. As a result of th,s actioii, the rot-,ntial on the collector 72 of the 'Lransis@'r 64 i, inllre-ased calse of the decrease of poLent@,,il o-.i th-, bas- C-IC, to bias tfie transistor 33 into ftirfiier condl,,clion and to decrease the potent-'@al o@..-i t,ic base 4e@ o-f 'the traiisistor 26. L-i response to the d.crease or pote-ntial on 'Llie base 4A, the static impedaiice of tiie tra@siscor 26 is decreased and iiic--reased ctir@-ent passes ',hrougli 'Lhe load RL tO dec,--,ase the po,ential on 'he I-,ad 1-@C,2 so as to correc, the ori.ainal ris-- in potentip,]. It is to be noted iliat this op-,ration is continuous, Also, -,i potential decrease on the leacl 1!@32 is corrected iii a siniilar but oriposite manner. I%Tow that th(@ normal regulatiqf, Pc"ion of tb-- inower sapply has been eyi)lained, the action of the ov-erload control ei,:cult 94 resultiig frgni an o-ver',Oad cond'@tioil such as a shori c,@rci-liL of t@ie load 34, will bt- describ--d. 'TLhe ratio ol. the value of resistor k@l to thit of the r-@sisto.- RL of the I.oad 34. to the ratio of the value of resistor R2 tO t'-pat ot the resistor R@, is the relat-on which determires the conditio-ii vihen an overload coiidicion, such as a short eircuil, of the load 34 is present. It is to be nolerl th,,i@ a short circuit cl@- fne load 3.,l r,-stiits i-ii the resista-@ic' c RL being e@f.Lectively redticed in value and a currer@t !L lar-,-r thaii ra'@ed curretit being supplied. Th,- transistor@ li7 is biased out of conduction during the :io-@-inai regula'tir@.- aclion @,T@'ren t.qe veita.-c drop across the resis@or R, is less thar. the voltaq-- drop across the resistor R@,. 1-iowever, wh,,n !he voltag-- drop acro@.s the resi.@tor 1-1,1 '@s -reater tnaii 'ine vol@afe drop across the resistor R2, result@ng frora a n-iaximuril load etirrent passin.- throlgh tbe' resistor RI a,.id the jur.--tion 10rj, 'he trans,stor 117 is biased into cor@dlictioii. Up-der thes-, conditions, the rat;o of RI 'LO RL iS - reater th-,n the ratio of R2 to R3 iiidic,,lting a decrease of the eff-ective value of ffie lopd resistor RT,. The minimum effective loa,-i r,- si@,tanc@, RL(,,ii,,i) iS equal to R,R, R, lliiis, t@ie maxinium clrrent LT w h i c h i s e q i l - a , @ . t o R L ( m i n ) may be expressed as foilows: T During the regula'cing operation of the po@ver suT)Ply, 75 wh.-re Eo is coual to the potent:ial on the lead 102 which
[4]is the regulated voltage for determining the maxinuin load current at which the overload control circuit 94 beegr.ies op-.rative. When the load current IL increases above Li-- rnaximum rated value so that the vcita.-a drop across the resistor Pl is greater than the voltage drop across R2, the transistor 117 is biased into full conduction. Thus, the transistor 124 is biased inlo conduction, passing current from the emitter 128 to the collector 130 and into the junction 132 and to the lead 132. The positive potential from the lead 04, is impressed throli,@h the transistor 124 and upon the base 68 of the transistor 64 to bias it out of conductio-ii. When thetransistor 64 is biased out of coilduction, Lhe driver transistor 33 is biased out of conduction and, in turn, the regulating transistor 26 is biased out of conduction to d,-velop a high impedance to flow of load current IL. Thus, the source 20 is cilectivelyclisconnected fror@i the load 34 under this overload condition. The foregoing overload condition Nvith the transistor 117 b-ased in a co,,idtictive state is rnaintained by a small current flow through the leakage resistor 5-It or by a small leakage current through the transistor 26. It is to be noted that wlien tne transisl@or 26 is of a type with a small leakage current, the leakage resistor 5,@, is not required. This leaka,-e current i)asses from the resistor RL through the resistor RI as well as through the resistors R3 and R2 to th., jililction 100 to maintain a potential diference from the base 113 to the emitter 120 of the signal transistor 117. T@@e poteiitial drop across the resistor RI is -reater than the drop across the resistor R2 because of their relative values. -Ihe base 1110 of the transistor 117 is biased by current passin,a from the +15 volt unregulated sol,rce at the terminal 88 throligh the resistor 114, thriou,-h the diode 112 a-@id throu-h the leaka.-C resistor 5@'. It is to be noted that ctirrent through the resistor II&, acts to maiiitain the diode 112 forward bia.@ed during both norrilal regulation and an overload condifion. Also, the transistor 124 is biased into conductio@i duri,-ig an overload condition by the +15 volt potential from the terminal 88 to apply ti-.e biasing potential to the junction 132 and the base 68 of the transisior 64. Thiis, the + 15 volt tei-minal 88 is required to iraintain the transistors 117 and 124 biased in conduction duriiig an overload condition. The transistor 117 and the diode 112 are of similar type riiaterials, so that an increase in impedance characteristics of the diode 112 and the traiisis+or 117 frori terrperature chan,@es, fOT exam-ole, is similar. Thi-is, an increase of impedance characteristics resulting in an increased poLential di?Lerer@ce for biasing the transistor 117 into conduction is ciiicelled by a@i increase of potential drop across the diode 112. Therefore, the ratio of potential drop across tLe resistors R, and R2 for biasing the transis'or 117 into conduction remaips constant a-@id the maximum load curren" IL at which the ovcrload protection circuit becomes op-,rative remains constant. When the load 34 rettirns to a condition such that there is a volta.-e drop across resistor RL iildicating a required load currcpt of maximum load current or less to cause a clecreased voltage Eo to be impre,,@sed o-ti the lead 102, t@e potential drop across resistor RI wi'll be less than the potential drop across the resistor r'2- Ti%us, the trans@stor 117 is biased o,,it of c6-.idvcLion, the transistor 124 is biased out of conduction, and the trans-@stor 64 is biased into conduction to c,,ttise the, '@ransistors 33 and 26 to be biased into conduction. Thits, the normal regulating action of the volta.-e c,Qmparator circuit 96, as i)rei?iousi@ described, willcontinue. N@lihile it will be understood that the eirciiit specification of the power supply of the inve-@ition may vary according to the desi.-n of any partic-Lilar application, the following circuit specifications for a power supply ar@- i@leluded, by way of example only, siitable to supply a regtjlated volta e of -25 volts at a maxL@Tium load current of I amppre to a gt-ounded load from a -32 volt unregulated source: Transistor 26. Delco (GM) --------------- 2NI73 Transis,or 33, Sylvania ----------------- -- 2NI42 Transistor 64, General Electric ------------- 2NI23 Tra-ilsistor 66, General Electric ------------- 2NI23 Transistor 117, General E.ectric ----------- 4JD4A5 Transistor 124, Phileo -------------------- T 1275 Transistor 133, Hu,,hes ------------------- HA-7550 10 Transistor 1,96, Hughes ------------------- I-IA-7550 'Ferniinal 88 ---------------------- volts-- +15 Resistor 1,76 ---------------------- ohms-- 2,000 Resistor C-0 ----------------------- do ---- 100 P@,esisto@- 82 ----------------------- do ---- 10,000 I'll) ikesistor @' 32@ ---------------------- do ---- 1 0 Resistor RI ----------------------- do ---- 2 Resistor R2 ----------------------- do ---- 9(9 Resistor R3 ----------------------- do ---- 11,300 -Pesistor RL(,,,i,,) ------------------- do ---- 25 20 '@esistor 114 ---------------------- do ---- 39,000 Resistor 156 ---------------------- do ---- 5,110 Resistor 153 ---------------------- do ---- 5,110 -p --------------- 8,060 @,esistor 159 - ------ do ---- Resistor 16,tl ---------------------- do ---- 560 25 R-,sistor 166 ---------------------- do ---- 1,690 Resistor 174 ---------------------- do ---- 200 Resistor 176 --------- ---------- do ---- 750 Resistor 173 ---------------------- do ---- 1,580 ('apacitor 180 -------------- r@iicrofarads-- 350 30 iode 112, I-luglies ----------------------- 6,007 Diode 168, Hoftman --------------------- IN 430A It is to be rioted that although 'the power supply has been described as supplying negative potentials relative to 35 grour@d potential, it may be easily arran,@ed to supply positive polential relative to ground potential by reversing all voll'ages and changi.,ig tile transistor types. Referrin.- now to FIG. 2, which is a graph of load _poter,.tial versus loid current, as well as referr;ng to F@1G. 40 1, the operation of the voltage regillator will be explained in further detail. The constant regulator dissipation line lgd, is shown to indicate the power cap-,tbilities of the regulating transistor 26. The regulated potential is shown as -25 volts, and the maximum load current is shown 4,5 as 1 amp-@re which is equal to E,R2 Rq Thus, the voltage regulator can operate anyvhere on a 50 -25 volt line 189. When an overload condition ocetirs at the rqa,-@imum load current of 1 ampere, ti@e return path of the load potential Eo and the load current IL is shown by the turn-off curve 186 which is a straight line. This straight line results fro@n the linear re'ation 55 between the resistors RI, R2 and R3 in relation to the voltage Eo and ground potential. The slope Eo IL 60 of the turn-off line nlay be expressed by the following relation when the transistor 117 is biased into conduction upon the occurrence of an overload condition: El- RI R3 IL- RI 65 Thus, the return path of the load current and the load volta,-e is determined only by the values of the resistors RI, R2 and R3 -in the two voltage div,@'der circuits. This linear turn-oif curve 136 allows the volta,@e re,- Ulator to 7o turii completely off when an ove.-load condition at maximum load current occurs and to tum completely on to supply max,.rrium load upqn removal of the overload condition. The operation of the circuit when turning on to supply a load wh;.-h is less than maximum is shovin by 75 a line 190. It, is@ to be noted thit coiiveii'lonti voltage
