US2624869A - Regulated power supply - Google Patents

Description

jan. 6, 1953 H. L. KNOEBEL 2,624,859

REGULATED POWER SUPPLY Filed June 13, 1951 ro nc L/ms (//a v) 70 rusa Hure/95 @Wawy Patented Jan. 6, 1953 REGULATED POWER SUPPLY Haines L. Knoebel, Philadelphia, Pa., assigner to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application June 13, 1951, Serial No. 231,387

Claims.

TheV invention herein described and claimed' relates to regulated power supplies and in particular to a power supply having an extended range of regulation. The term power supply is employed throughout this specicationto denote a local system forV deriving a D.C; supply voltage (i. g. B+) from an A.C. power line.

In some localities, notably foreign countries, regulation of power line voltage is relatively poor and as loads are added to or removed from the distribution system line voltages varyl over wide ranges. For example, in many foreign countries iti is not unusual for the line voltage of a nominal 11G-volt A.C; power line to vary overalrange: of from 90 to 130 volts; sometimes, the

variation rangei's even wider.

It is, of coiu'se, well known to include at the lo-l cal power supply a regulator circuit to' maintain substantially constantl the D.C. voltage derived from the A.-C. line voltage. However, the conventional regulator circuit is unable to maintain regulation over a range of line voltages as wide as may be encountered' in foreign countries.

In those cases where line voltages are subject to variation beyond the limits of the conventional regulator circuit, the prior art has employed a relayor other electrically operated switch whereby when the line voltage. increases to a predetermined value tlie relay operates and a reducd portion of the line voltage is impressed upon the rectifier, or alternatively, a reduced portionl of the rectied voltage is applied to the regulator circuit. However, prior-art power supplies of this type have not been entirely satisfactory due to the fact that, after an increase in line voltage has actuated the relay, when the line volt-` agethereafter decreases the relayv does not release soon enough to avoid having the power supply fall out of regulation. For, a relay willv ordinarily not release until the coil current has decreased to a value substantially less thanv the pull-in value. This is due to residual magnetism and to the increase which occurs in the magnetic ux when the reluctance of theY magnetic circuit is reduced by the closing of the air.-

gap. The release value may, for example, be of the order of twenty per cent or so of the pullin value. In addition, the release valuev seems to vary from relay to relay and from operation tov operation. It is generally conceded, then, that while relays will pull in at a predetermined definite value of coil current, they cannot be depended upon to release at a predetermined def,- inite value.

In view of the above, it isl the primary object of the present invention to provide a regulated power supply capable of maintaining a source of substantially constant D.-C. voltage at the local equipment despite wide variations in A.C. line voltage.

The foregoing object is achieved by means of a regulated power supply which includes an electrically operated relay for limiting the range of the voltages applied to the regulator circuit, preierably by limiting the range of line volta es applied' to the rectifier. The prior-art diiculties with respect to release of relay are overcome, accordi-ng to the present invention, by means responsiveV to an early indication that the power.

supply is falling or is about to` fall out oi regulaation for effecting positive release ofl the relay, thereby to apply an increased voltage to the regulator circuit, as by applying an increased portion of line voltage across the power-supply transformer. Thus, the power supply is prevented from falling out of regulation at a supply voltage which, if applied in full, is well within the range of the regulator circuit.

The invention will be most readily understood from a consideration of the following detailed description of a preferred embodiment illustrated in the accompanying single figure of drawing.

Referring now to the drawing, there is shown a regulated power supply particularly adapted for use in a modified domestic television receiver intended for use in foreign countries or other localities where the A.C. line voltage is subject to wide variations. Included in the power supply are the power transformer Id, the double-diode rectifiers I I and I2, the lter capacitors I3 and I4, and the choke I5. comprise the normal unregulated power supply of a conventional domestic television receiver and function in Well known manner to derive from the A.C. line voltage an unregulated positive D.C. supply voltage, B+, which appears at leadv I6. In the circuit shown in the drawing, this voltage is used to supply the R.F. chassis of the television receiver.

ForI use in foreign countries, the television receiver should have a regulated power supply, and to compensate for the voltage drop across the regulator circuit', the circuit shown in the drawing includes a voltage booster comprising the power transformer I'I, the diode rectiiiers I? and I9, and the lter capacitor 20. These elements function to develop an additional positive D..-C. voltage which, when added tothe unregulated D.,C:. supply voltage, B+, produces a These elements boosted unregulated D.C. supply voltage, B-l--1'-, on lead 2|. It is to be understood, of course. that so far as the present invention is concerned, a singl-e rectifier circuit could be employed and that the booster arrangement shown in the drawing is merely used to avoid replacing transformer Ill with a transformer of larger rating when modifying the television receiver for foreign use.

The regulator circuit is comprised of the parallel-connected triodes 22, 23 and 24, the pentode 25, the gas tube 25, the potentiometer 21, and the various associated resistance and capacitance elements shown in the drawing identified by reference numerals 28 to 34. Three parallel-connected tubes (22, 23, 24) are used in lieu of the single tube found in the more conventional circuit to increase the current capacity of the regulator.

The regulator circuit functions to maintain a substantially constant positive D.C. voltage. B+, on lead 35 in a manner which is largely conventional and need be but briefly described. When variations occur in the unregulated B+-I- voltage appearing on lead 2I in-phase variations tend to appear on the cathode lead 35 and at the grid of tube 25. The cathode potential of tube 25 is, however, held substantially constant by the action of the gas tube 26 which maintains a substantially constant voltage drop thereacross even though the current through the tube 23 varies over a relatively wide range. Thus, when the potential at the grid of tube 25 varies, the grid-to-cathode potential of the tube varies and so does the plate current through the tube. The plate potential of tube 25 then varies in the opposite direction. and so do the grid potential of the parallel-connected tubes 22, 23, 24. Thus, when the plate potential of tubes 22, 23, 24 varies, the voltage drop across these three tubes varies in such direction as to prevent any change in their cathode potential. It will be seen, then, that the potential on lead 35 remains constant despite variations in the B-I--I- voltage on lead 2 I. This assumes, of course, that the A.C. line voltage does not drop to such an extent that the regulator circuit is unable to imainain regulation.

To widen the range over which the A.C. line voltage may deviate without having the power supply fall out vof regulation, an automatic switching arrangement is provided comprising a relay 36 controlling a pair of switches 54 and 55, and, in accordance with the present invention, a relay-release control circuit comprised of the tubes 3l, 38, 39 and the various resistance and capacitance elements associated therewith identied by reference numerals 45 to 48 and connected as shown in the drawing. Tube 31 functions as the relay-release control tube. Tube 38 functions as an amplifier of a control signal which is derived from the regulated B-I- lead 35 as will later be described. Tube 39 functions as a dioderectifier` of the amplified control signal to produce a negative D.C. control signal which is then applied to the grid of the relay-release control tube 31.

As will be seen from the drawing, relay-release control tube 31 is connected in series with the coil of relay 35, fixed resistor I, and variable resistor 52, between the unregulated B-llead I6 and ground. An anti-chatter resistor 53, discussed more fully later, shunts the relay coil when the relay is not in actuated condition.

The operation of the automatic switching arrangement, including the means added by the present invention, may be most readily understood iii) by assuming certain values of voltages for discussion purposes. Assume that the A.C. line voltage is nominally 110 volts but is subject to wide variations and that it is desired to provide a regulated power supply capable of maintaining the derived D.C. supply voltage substantially constant over a range of A.C. line voltages extending from to 145 volts. Assume an instant when the line voltage is low, say about 90 volts. The D.C. current through the coil of relay 35 is then insufficient to operate the relay, and relay switch arms 54 and 55 are then at positions l and 3, respectively. Observe that with switch arm 55 at position 3, the voltage-dropping resistor 5l, which is series-connected in the lead from the line plug 58 to the parallel-connected transform ers I0 and I1, is shorted out. Thus the full A.C. line voltage is applied to the primaries of the transformers. The variable resistor 52 in the relay circuit is so adjusted that when the A.C. line voltage rises to a predetermined Value, say 120 volts, the current through the relay coil increases suiciently to actuate the relay and switch arms 54 and 55 then move to positions 2 and 4, respectively. When this occurs, the voltagedropping resistor 51 is no longer shorted and a voltage drop, say of 10 volts, occurs thereacross, Thus, when relay 36 operates, the A.C. voltage impressed upon the primaries of the parallelconnected transformers I0 and Il drops suddenly, in the present example by 10 volts, from 120 Volts to volts.

Though not a part of the improvement contributed by the present invention, it may be helpful at this point to discuss briey the manner in which resistor 53 functions to prevent relay chatter. When the relay starts to operate and the relay switch arms 54 and 55 break contact at positions I and 3, respectively, the line voltage impressed upon the primaries of transformers I Il and I1 drops suddenly, as just mentioned hereinabove, and as a result a sudden decrease occurs in the unregulated D.C. voltage on lead I6. Hence, in the absence of resistor 53, as soon as the relay began to operate, the current through the relay coil would decrease and the switch arms, instead of continuing on to the operate positions 2 and 4, would return to the release positions I and 3. Thus, the relay contacts would chatter. However, with a resistor 53 of suitable value connected as shown in the drawing, when the switch arm 54 breaks contact at position I, the resistive shunt across the relay coil is removed and all of the current owing in the relay circuit now ows through the coil, whereas prior to the opening of the contacts at position I, only a portion of the total relay-circuit current passed through the coil. Hence, by effecting an increase in the relay-coil current in lieu of the decrease which would otherwise occur when the relay began to operate, the resistor 53 prevents contact chatter.

Returning now to the discussion of the operation of the automatic switching arrangement shown in the drawing, if after the relay has operated the line voltage continues to rise, the voltage impressed upon the primaries of transformers IQ and I 'I will continue to be less than the actual A.C. line voltage by the amount of voltage drop in resistor 5l. In the exemplary case being discussed, if the A.C. line voltage should rise to 145 volts, the drop in resistor 5l may be of the order of 25 volts, and the voltage impressed upon the primaries of transformers IB and il will be about volts.

It will be seen, then, that if the line voltage assessor should rise from a low of 90 volts to a high of 145v transformers lil and Il will rise from 90 volts to' only about 120 volts, due to the action of the automatic switching arrangement described thus far, and the requirements imposed upon the regulator portion of the power supply will be no greater than they would be if the line-voltage variations themselves were from 90 volts to 12o volts.

Thus far we have considered how the automatic switching system operates when the line voltage increases. Consider now what happens when the line voltage decreases, say from a high Value oi 145 volts down to a low value or" Si) volts. It will be recalled that, in the illustrative situation being discussed, when the rising line voltage reached 120 volts, the current through the relay coil became sufficient to operate the relay. However, as stated previously hereinabove, before relay 3E will rele-ase, the current through the relay coil must decrease to a value substantially lower than that which caused the relay to operate. Hence, in the absence of the means provided by the present invention, the probability would be that, as the line voltage decreased from a high value, relay 3S would hold too long in the actuated position. In other words, there would be the danger that before the relay released, and before the voltagedropp-ing resistor was shorted out, the line voltage would drop to such an extent that the unregulated D.C. voltage on lead 2| would fall to such a low value 'that the regulator circuit would be unable to maintain regulation of the D.C. voltage on lead The above danger is obviated, in accordance with my invention, by the provision of means which, in response to an early indication that the power supply is falling or is about to fall out of regulation, effects positive release of relay 36, thus snorting out the voltage-dropping resistor 5l and increasing the amount of line voltage applied to the power supply circuit. The indication to which the relay-release control means is responsive is a signicant increase in hum or ripple voltage. For, I have observed that so long as regulation is maintained, the amount of ripple appearing on the regulated B+ lead 35 is `very small but that, when the power supply starts to fall or is about to fall out oi regulation, the ripple f voltage increases very appreciably, even before there is any change in the measured D.C. voltage on the regulated B+ lead. ln a particular for example, with a regulated D.C. voltage of 315 volts on B+ lead the root-mean-square value of hum or ripple voltage appearing on the lead, during regulation, was less than @.l volt. However, when the power supply was about to fall out of regulation, the root-mean-sduare value of ripple voltage rose rapidly to 5.0 voltsA though the D.C. voltage still measured 315 volts as before. The present invention takes advantage of this observed phenomenon, and uses the hum or ripple voltage to trigger relay 35 into the released condition.

n the arrangement shown in the drawing, the ripple voltage appearing on the regulated B+ lead l5 is applied by way of RC network 4%, to the grid of amplifier tube 313 whose plate voltage is supplied from lead 2i, and the amp-lined ripple signal developed on the plate of tube is applied by way of RC network di, i3 to the rectifier tube 39 which is shown to be a triode connected as a diode. Rect/incr and iilter dil, il! function to produce a negative D.C. control signal which is applied to the control grid of the relay-J release control tube 31. The substantially constant positive voltage developed across the gas regulator tube 26 is applied to the screen grid of the tube 3l by way of resistor 4Q. During regulation, the ripple voltage is small, the negative D.C. signal applied to the control grid of tube 3l is small, and tube 3l conducts. When, however, the power supply is about to fall out of regulation, the ripple voltage increases in a substantial and significant manner, and the negative D.C. control signal developed on the grid ofr relay-release control tube 3l is sufiicient to cut the tube off. When this occurs, the current in the relay coil is suddenly reduced to zero and relay 36 releases. Switch arms 54 and 55 thereupon return to positions I and 3, respectively, and the voltage-dropping resistor El is shorted out. The full line voltage is now applied across the primaries of transformers le and Il, and the unregulated D.C. voltage appearing on lead 2| is suddenly increased to a value which is within the limits of the regulator circuit. Thus, regulation maintained.

Component values for a typical system f been shown in the drawing. It is to be understood, of course, that the values shown are merely illustrative and not limiting.

In a particular case, a system employing values similar to those shown in the drawing developed about 75 volts D.C. at the grid of relay-releasev control tube 3l with about 2.0 Volts input to the grid of amplifierv tube 3S. Only about 3G Volts D.C. was required to out tube 3l off.

The point at which the relay pulls in is,` of course, largely determined by the total impedance of the series-connected components of the relay circuit, which is adjustable by means of the variable resistor 52. It is advantageous to keep the impedance of relay-release control tube 'i low, relative to the other relay-circuit series impedances, so that tube variations and aging effects are minimized. In the particular case referred to above, the voltage drop across relay-release conu trol tube :il at the time the relay operated was only about iifty volts.

Also, since the relay circuit loads the power supply, the current drawn by the relay circuit should be kept low. In the particular case being discussed, the total current in the relay circuit was 30 milliamperes. This was deemed to be a good compromise between relay cost and extra load.

The particular system above referred to is also designed to have the relay pull in at a line voltage about 10` volts higher than the line voltage at which the power supply would fall out of regulation. More particularly, the relay pulls in when the line voltage reaches 120 volts, and, with the relay in the operated condition, the power supply starts to fall out of regulation when the line voltage drops to volts. A voltage difference of this order of magnitude is desirable in order to prevent relay chatter and hunting in the event the line voltage hovers about the relay pull-in v-alue.

It is to be understood that, instead of being connected in the primary side of the transformers, the series voltage-dropping resistor 51 and the snorting-out relay switch 55 could be connected in the unregulated B-l--ilead 2l. This alternate arrangement is, however, less satisfactory than that shown in the drawing since the tube heaters, which are fed directly from the secondary of the power transformer, would then anar-,sea

7"- be subjected to the full range of line-voltageV variations. in the drawing, limits the range of the voltage variations in the heater circuit as well as on the unregulated B+ lead 2 I.

It should valso be understood that, instead of,

employing a series voltage-dropping resistance, the portion of line voltage applied to the transformer primary could be varied by switching between primary taps. However, in this case, there is a momentary loss of regulated B| during relay operation. In the arrangement shown and described, using a series voltage-dropping resistor, there is no loss of regulation as the shunt across the resistor is removed or connected.

. VHaving described my invention, I claim:

1. A power supply for deriving a regulated D.C. voltage from an A.C. line whose line voltage is subject to relatively wide variation, said power supply comprising: rectifier means; means for applying at least a portion of said A.C. line voltage to said rectifier means to develop an unregulated D.-C. voltage; a regulator circuit for deriving a regulated D.C. voltage from said un-v regulated D.-C. voltage; a relay operative in response to an increase in said line voltage for effecting a decrease in the unregulated voltage applied to said regulator circuit; and means responsive, when said line voltage decreases, to an increase in the ripple component of said regulated voltage for releasing said relay to increase the unregulated voltage applied to said regulator circuit, thereby to prevent said power supply from falling out of regulation.

2. Apparatus Ias claimed in claim 2 characterized by the fact that said means responsive to an increase in the ripple component of said regulated voltage for releasing said relay comprises a normally conductive control tube connected in series with said relay, and A.C. coupling and rectifying means for applying rectified ripple voltage to the grid of said control tube to cut said control tube off when said ripple voltage increases to a predetermined value.

3. A power supply for deriving a regulated D.C. voltage from an A.-C. line whose line voltage is subject to relatively wide variation, said power supply comprising: rectifier means; means for applying at least a portion of said A.C. line voltage to said rectifier means to develop an unregulated D.C. voltage; a regulator circuit for deriving a regulated D.C. voltage from said unregulated D.C. voltage; a relay operative in response to an increase in said A.-C. line voltage for eiecting a reduction in the portion of said line voltage applied to said rectifier circuit; and meansresponsive to an increase in the ripple component of said regulated D.C. voltage for releasing said relay to increase the portion of said A.C. line voltage applied to said rectifier The preferred arrangement, shown.

8. means, thereby to prevent said powerv supply from falling out of regulation when said line voltage decreases to such -an extent that said regulator circuit is unable to maintain regulation of said reduced portion thereof.

4. Apparatus as claimed in claim 3 characterized by the fact that said means responsive to an increase in the ripple component of said regulated voltage for releasing said relay comprises a normally conductive control tube connected in series with said relay, and A.-C. coupling and rectifying means for applying rectied ripple voltage to the grid of said control tube to cut said control tube off when said ripple voltage increases to a predetermined value.

5. A power supply for deriving a regulated D.C. voltage from an A.C. line whose line Voltage is subject to relatively wide variation, said power supply comprising: rectifier means; means for applying at least a portion of said A.-C. line voltage to said rectifier means to develop an unregulated D.C'. voltage whose value tends to vary in accordance with variations in said line voltage; a regulator circuit; means for applying said unregulated D.C. voltage to said regulator circuit to derive a regulated D.C. voltage; switching means responsive to an increase in said unregulated D.C. voltage beyond a predetermined upper control limit of said regulator and operative to reduce to a substantially lower base value the unregulated D.C. voltage applied to said regulator circuit; and means effective when said unregulated lower-base-value D.C. voltage decreases to a value substantially equal to a lower control limit of said regulator circuit for operating said switch means to increase to a sub- .stantially higher basey value the unregulated D.C. voltage applied to said regulator circuit, said last-named means being responsive to an increase in the ripple component of said regulated D.C. voltage.

HAINES L. KNOEBEL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,117,138 Bock May 10, 1938 2,207,259 Koch July 9, 1940 2,299,942 Trevor Oct. 27, 1942 2,301,343 Tarr Nov. 10, 1942 2,431,994 Dibrell et al Dec. 2, 1947 2,434,069 Goldberg Jan. 6, 1948 2,440,275 Kelly Apr. 27, 1948 2,511,850 Hoag June 20, `1950 2,556,129 Wellons June 5, 1951 2,573,744 Trucksess Nov. 6, 1951

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