US3462643A

US3462643A - Switching type voltage and current regulator and which can include voltage doubling means for a load

Info

Publication number: US3462643A
Application number: US627479A
Authority: US
Inventors: Carl R Turner; Peter Schiff
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1967-03-31
Filing date: 1967-03-31
Publication date: 1969-08-19
Anticipated expiration: 1986-08-19
Also published as: GB1218931A; FR1563295A; DE1763064A1

Description

Aug.A 19, 1969 C. R. TURNER ETAL CAN INCLUDE VOLTAGE DOUBLING MEANS FOR A LOAD Filed March 3l, 1967 Q N1 w@ A A Sv N. .W 1 A Nw uw Nm s wm Nw mmh WSN QN mw N .i

United States Patent O U.S. Cl. 315-101 8 Claims ABSTRACT F THE DISCLOSURE For certain types of electrical loads, the voltage must be a maximum at turn on. Current flow to the load must be limited to a maximum value during the warm-up period and, after the warm-up period is over, a regulated voltage which is less than the maximum voltage must be supplied for continued operation of the load. A regulated voltage supply of the switching type, which provides such output voltages and which limits the maximum current flow is disclosed.

Background of the invention Certain electrical loads, notably mercury arc lamps, require a high voltage to cause them to strike or start, and a regulated voltage of about half the striking voltage during normal operation. Furthermore, such loads require several minutes for warm-up to operating temperature. During the warm-up period, the current flow through the load may be excessively high and the voltage drop across the load may be quite low. In accordance with known installations for operating mercury vapor lamps, a ballast inductor is used with an alternating current supply. Therefore, twice each cycle, the mercury arc lamp goes on or is struck and goes off again, whereby a stroboscopic effect is produced. This stroboscopic effect makes the mercury arc lamp, which has the advantage of providing high intensity light at greater efficiency than an incandescent lamp and which also has the great advantage of providing a lamp life many times longer than the life of the incandescent lamp, unsuitable for various applications such as motion picture projection. Furthermore, unless several mercury arc lamps are used and apparatus is provided to cause the several lamps to produce their light in outof-phase relation whereby the stroboscopic effect is minimized, such lamps cannot be used for viewing sporting events or for lighting the stage while making motion pictures or when recording or broadcasting television programs. Furthermore, the necessary ballast inductos are heavy, bulky and expensive.

It is an object of this invention to provide an improved power supply that may advantageously be used to supply loads of the nature of mercury arc lamps.

It is a further object of this invention to provide an improved combination of a power supply and a mercury arc lamp in which the stroboscopic effect is eliminated.

It is still a further object of this invention to provide an improved power supply for a load such as a lmercury arc lamp that is lighter and less bulky, and that can be made more inexpensively than known power supplies using ballast inductors.

Summary of the invention In accordance with the invention, a rectified current and voltage regulator of the switching type is provided whose output is a regulated direct current voltage at or slightly less than the peak voltage of an alternating current input therefor. In addition, the regulator provides pulses of direct current voltage which are substantially higher in value than the peak voltage of the alternating current sup Patented Aug. 19, 1969 ply and further includes a current sensing means which takes over control of the output current during the time that the load draws an excess of current. Such a regulator is particularly adaptable for operation with a mercury arc lamp in that, while it provides the required starting or striking voltage for such a lamp, the excessive current drawn during the warm-up period of the lamp is reduced by the regulator to a safe value. The voltage supplied by the regulator to the lamp during normal operation is of 0 a regulated value near the peak value of the alternating current supply, whereby nearly the full voltage of the source is available for operating the lamp and losses in the regulator are reduced, resulting in high operating eiciency of the regulator. Furthermore, since a constant direct voltage is applied to the lamp, there is no stroboscopic effect. Also, since the regulator includes small electronic components, the bulk and the weight of the regulator are reduced compared to known regulators. Additionally, the regulator can be made by integrated circuit techniques, further reducing the bulk and the cost of the regulator. In fact, the bulk and the weight of the regulator can be so greatly reduced that the regulator can be built into the neck of the mercury are lamp, or into the socket into which the mercury arc lamp is inserted.

Brief description of the drawings The invention may be better understood upon reading the following description in connection with the accompanying drawing in which FIGURE l is a circuit diagram of a regulator in accordance with this invention, this figure also showing a mercury arc lamp load for the regulator and FIGURES 2 and 3 are curves useful in explaining the operation of the embodiment of this invention shown in FIGURE 1.

Description of the preferred embodiment Turning first to FIGURE l, an alternating current sup ply (not shown) is connected between the input terminals 10 of the regulator to be described. One of the terminals 10 is connected to one diagonal connection 11 of a rectifier bridge 12 through a surge reducing resistor 14. The opposite diagonal terminal 13 of the bridge 12 is connected directly to the other one of the input terminals 10. The rectifying bridge 12 is so poled that one of the remaining terminals 15 is negative with respect to its opposite terminal 36. The terminal 15 is connected to the emitter of a NPN voltage and current regulating transistor 16. The collector of the transistor 16 is connected to one terminal of the primary winding 18 of a transformed 20. Since, as will be explained, the transformed 20 operates at several thousand cycles per second, it is quite small and light even though, for purposes of efficiency a powdered iron core, not shown, may be provided for the transformer 20. the other terminal of the primary winding 18 is connected to a terminal 22 of a mercury arc lamp 24.

The base of the transistor 16 is connected through a bias resistor 26 to the bridge terminal 15, and the base is also connected directly to the emitter of a combined voltage and current regulating and control NPN transistor 28. The collector of the transistor 28 is connected to a tap 30 on the winding 18, for a purpose to be described. The base of the transistor 28 is connected directly to the collector of a NPN control transistor 32 and through a bias resistor 34 and Zener diode 40 in` series to the terminal 36 of the bridge 12. The emitter of the transistor 32 is connected directly to the emitter of the transistor 16. Also, a low frequency filter capacitor 42 is connected between the terminals 15 and 36 of the bridge 12.

The -base of the transistor 32 is connected through two series-connected resistors 44 and 46 and the secondary winding 48 of the transformer 20 to the bridge terminal 15. A protective rectifying diode 50 is connected between the junction of the resistors 44 and 46 and the terminal 15, the diode 50 being poled so that its cathode is connected through resistor 44 to the base of transistor 32. The base of the transistor 32 is also connected through a resistor 52 to the collector of a PNP transistor 54. A current sensing resistor 55 and a voltage divider cornprising two series connected resistors 56 and 58 are connected in series between the terminal 22 of the lamp 24 and the terminal 36 of the bridge 12. A capacitor 80 is connected across the series combination of resistors S6 and 58. The base of the transistor 54 is connected to the junction 77 of the resistors 56 and 58. The emitter of the transistor 54 is connected directly to the emitter of a PNP transistor 60, and through a `resistor 72 to the terminal 3-6. The collector of the transistor 60 is connected to the terminal 36 through a resistor 62 and a potentiometer 64 in series. The collector of the transistor 60 is also connected directly to the junction of the resistor 34 and the Zener diode 40. The movable contact of the potentiometer 64 is connected to the base of the transistor 60.

A half-wave voltage doubling circuit comprising a capacitor 74 and a rectifying diode 87 are connected in series between terminals 13 and 36 of the bridge 12 through the resistor 55. The diode 87 is poled to have its cathode connected to a terminal 78 of the mercury arc lamp 24 and to the capacitor 74. The capacitor 80 is a relatively small filter capacitor as will be explained. A diode rectifier 82 is connected between the collector of transistor 16 (junction S1) and the junction 76 of the diode 87 and resistor 55, the rectier 82 being poled for conventional current to iiow from the junction 81 to the junction 76.

The mercury arc lamp 24 is a known article of commerce. The lamp 24 comprises a glass outer envelope 91 having a neck 83, and a fused quartz inner envelope 84, which is supported within but spaced from the outer er1- velope 82. The neck 83 through which run conductors which are connected to the

lamp terminals

22 and 78 may be shaped to fit an Edison socket. A small quantity of mercury (not shown) is provided in the envelope 84. Also, two spaced electrodes 86 and 88 are provided in the envelope 84. These electrodes 86 and 88 are connected respectively to the

terminals

78 and 22. A starting electrode 90, whose tip is spaced from but is near to the electrode 86, is also positioned in the envelope 84. This starting electrode 90 is connected through a current limiting resistor 92 to the terminal 22.

The operation of the mercury arc lamp 24 is explained by reference to FIGURES 2 and 3. When a voltage supply s connected across the

terminals

22 and 78 of the mercury arc lamp 24, the voltage and current go from the zero point shown in FIGURE 2 to the strike point A along a curve such as the curve shown. Then, while the current increases from point A to the point B, the voltage decreases to about a tenth of its value at the point B as compared to the point A. T-he current drawn by the lamp increases very rapidly from the point A to the point B, and then the current continues to increase until the point C is reached without much change in voltage. However, when the point C is reached, the normally used ballast means takes control and the current and voltage drop along the line D to the operating point E of the lamp, the voltage at the point E being about half the voltage at the point A. It will be noted that a voltage A which is about twice the voltage of the operating voltage E is required for starting the mercury are lamp. It will also be noted that during the portions B to C of the start cycle of the lamp 24, t-he current drawn by the lamp increases to a high value and with very little increase of voltage thereacross, whereby the current drawn by the lamp unless limited to a safe value, will destroy the lamp or the supply or both. Furthermore, as is understood, the voltage applied to the lamp, and therefore the current through the lamp must be kept substantially constant during the operation of the lamp to keep the light supplied thereby substantially constant.

FIGURE 3 illustrates the desired relationship between the current and volt-age of a mercury are lamp as the lamp warms up. When the supply voltage is applied across the input terminals of the lamp at the beginning of the warm-up period, that is at time zero, the voltage rises to a high value G before there is an appreciable current liow. When the mercury arc lamp strikes, the current increases rapidly and the voltage decreases rapidly. At some point such as H, the current flow must be controlled to prevent destruction of the lamp, or the supply, or both. As the warm-up period continues, the voltage increases and the current decreases in a gradual manner. The voltage of the operation point I of the lamp is about half of the peak voltage G of the lamp or about where the dotted line F in FIGURE 3 crosses the voltage line. It will be noted that the voltage across the lamp is quite low and that the current through the lamp as indicated by the curves of FIGURE 2 is quite high during this warm-up period which may take several minutes. During this warmup period, control of the voltage across the lamp will not control the current flow through the lamp and therefore, the current ow to the lamp 24 must control the regulator.

The described regulator must lirst provide a high voltage to start the lamp 24. Secondly it -must act as a ballast means or current limiting means during the warm-up period of the lamp 24 to prevent the current flow through the lamp 24 from destroying the lamp 24 or from destroying the source, and finally the regulator must act to keep the voltage applied to the lamp 24 at its operating value. The starting operation of the regulator is described first.

When the alternating current supply (not shown) is `connected between the terminals 10, a surge of current will ow by way of the rectifying bridge 12 into the capacitor 42 through the surge limiting resistor 14. This current surge will be limited to a safe value by the surge resistor 14. The capacitor 42 acts as a low frequency filter, whereby a direct voltage having a small ripple component will appear across the terminals 15 and 36. Furthermore, when the terminal 11 is positive with respect to the terminal 13, the capacitor 74 will charge up by way of the rectifier 87, and when the terminal 11 is negative with respect to the terminal 13, the voltage on the capacitor 74 will be added to the voltage across the terminals 15 and 36. The junction point of the rectifier diode 87 and the capacitor 74 will therefore exhibit a fluctuating voltage at the frequency of the alternating current source on top of the above-mentioned filtered direct current voltage. The peak voltage at the point 85 with respect to the terminal 15 is high enough to strike or start the mercury arc lamp 24 once each cycle of the alternating current applied across the input terminals 10. This voltage is applied between the

terminals

78 and 22 of the lamp 24 to start it. As will be explained, once the lamp 24 is started, the high voltage appearing at the point 85 is not used.

The operation of the regulator during the warm-up period is now described.

Negative voltage is applied to the emitter of the transistor 16 due to its connection to the terminal 15, and a less negative voltage is applied to the base of the transistor 16 and to the emitter of the transistor 28 due to the voltage drop across the bias resistor. The bias current so applied to the transistor 16 is such as to cause the transistor 16 to operate in saturation. Due to the connection of the emitter of the transistor 28 through the resistor 26 to the terminal 15, and to the connection of the base of the transistor 28 to the positive terminal 36 through the bias resistor 34 and Zener diode 40, and further due to the voltage drop n the portion of the winding 18 that is connected between the collector of the transistor 16 and the collector of the transistor 28, the transistor 28 is also biased to saturation. Therefore, the transistors 16 and 28 share the current flow to the terminal 22. Current also flows from the terminal through the transistors 16 and 28, the resistor 34 and the Zener diode 40 in series to the terminal 36 whereby a standard voltage is set up across the Zener diode 40. Due to the connection of the junction of the Zener diode 40 and the resistor 34 to the collector of the transistor 60, this standard voltage is applied as a supply voltage for the transistor 60. Also a portion of this standard voltage is selected by manipulation of the slider of the potentiometer 64, and the current flow resulting from this voltage portion is applied as a control current between the base and the emitter of the transistor 60 in a circuit including the bias resistor 72. A predetermined portion of the voltage appearing across the lamp terminals 22 and 78 (less about half a volt drop in the rectifier diode 87) appears at the junction 77 of the resistors 56 and 58. This bias voltage appearing at the junction 77 is applied to the base of the transistor 54 in series with the voltage appearing across the resistor 55 (as will be explained) and with the voltage appearing across the resistor 72. Due to the operation of the common bias resistor 72 in the bias circuit of the two transistors 54 and 60 the transistor 54 is blocked or conductive, depending on whether the bias applied between its base and its emitter is above or below a certain value.

During the Warm-up period, that is from the time corresponding to the point H to about the time corresponding to the point I in FIGURE 3, the current flow drawn by the lamp 24 is very high and the voltage across the lamp 24 is very low. The current drawn by the lamp 24 flows through the current sensing resistor 55 and the voltage drop developed across this resistor 55 due to this current flow is applied between the base and the emitter of the transistor 54 in a direction to render it conductive. If the current through the resistor 55 is above a predetermined maximum value, the transistor 54 becomes conductive. A path for base current for the transistor 32 now exists through the conductive transistor 54, and the transistor 32 becomes conductive. Upon becoming conductive, the transistor 32 shunts the resistor 26 causing the base and the emitter of the transistor 16 to be at the same potential whereby the transistor 16 is not conductive. When the transistor 16 is not conductive and the transistor 32 is conductive, there is no emitter current for the transistor 28, whereby the transistor 28 also becomes nonconductive. Current flow through the primary winding 18 is blocked by this blocking of the transistors 16 and 28. However, by its inductive effect a voltage is induced in the winding 18 in a direction tending to keep the current lowing through the winding 18 in the same direction. The current so produced flows through the diode 82 into the lter capacitor 80. As the current in the winding 18 reduces, a current is developed in the secondary winding 48 which is applied in a direction to keep the transistor 32 (now conductive) in its conducting state as long as current in the winding 18 decreases. Since the current ilow through the transistors 16 and 28 is blocked, the current supply to the load, which flows through the current sensing resistor 55, is reduced to a point where the bias current for the transistor 54 is not suicient to keep the transistor 54 conductive, and it becomes non-conductive. As the current in the transformer primary 18 drops to zero, the transistor 32 also becomes non-conductive. The transistors 16 and 28 become saturated. Current builds up in the primary winding 18. During current buildup in the winding 18, the voltage induced in the winding 48, which is applied between the base and emitter of the transistor 32 (now blocked) is in such a direction as to keep the transistor 32 blocked while current builds up in the winding 18. Soon (during the warm-up period) the current ow through the current sensing resistor 55 is such as to cause the transistor 54 to become conductive again and a new cycle begins. Therefore, during the warm-up period, the current ow through the current sensing resistor 5S keeps the maximum current ow to the lamp 24 down to a safe maximum value.

When the warm-up period is over, the current taken by the lamp 24 is so low that the current sensing resistor 55 alone does not control the operation of the regulator and the voltage across the load comprising the lamp 24 rises to the point where the voltage regulating function of the described regulator also affects its regulating characteristics. The voltage regulating function operates as follows: When the voltage at the point 77 is above a predetermined value, the transistors 54 and 32 are both conductive and the transistors 16 and 28 are both blocked and current flow into the capacitor 80 ceases. When the voltage at the point 77 is below the said predetermined value, as when the load has drawn current from the lrer capacitor 80 sufficiently to reduce the voltage thereacross below a predetermined minimum value, the voltage at the junction 77 is too low to render the transistor 54 conductive. When the transistor 54 is not conductive, the transistor 32 is also blocked and both transistors 16 and 28 are conductive at saturation as noted above. 'Ihat is, after the warm-up period is over, the operation of the described regulator is the same as described above except that the turn on and off of the transistor 54 is controlled by the current sensed by the resistor 55 and by the voltage across the capacitor 80 (a portion of which appears at the junction 77).

The elements are so chosen that, during the warm-up period and the run period of the regulator, the frequency of the change of conductance of the transistors 16 and 28 is about five thousand cycles per second. The capacitor 80 acts as a filter element for the voltage appearing across the terminals of the lamp 24. The lter capacitor 80 need not be very large to provide a well ltered voltage to the load, due to the high frequencies involved. The fluctuating high starting voltages appearing across the

terminals

22 and 78 are applied between the main electrode 86 and the starting electrode through the current limiting resistor 92. When an arc is struck between the electrodes 86 and 90, ionized mercury vapor in the envelope 84 will heat up while its pressure will rise and the ionizing mercury vapor will surround both of the main electrodes 86 and 88. The high voltage peaks will be applied continuously between the

terminals

22 and 78. However these voltage peaks will be short-circuited between the electrodes 86 and 90 after the arc is struck. The current limiting resistor 92 will prevent the running current, taken by the mercury arc lamp 24, from being short-circuited between the electrodes 86 and 90.

The regulated voltage supply described may be used as a supply Wherever a regulated voltage is required and particularly where a high starting voltage is required and where a current overload is to be guarded against, as with mercury arc lamps and with fluorescent lamps.

Modications of the described regulator will occur to persons skilled in the art. For example the capacitor 74 and the diode 87 may be omitted whereby the described regulator may be used to provide voltage regulated current for other types of loads which do not require high starting voltages, but where protection against a short circuit is required. Or, the resistor 55 may be omitted, whereby, within limits, the regulator will provide a voltage regulated output current without control of the amount of current flowing. Or, the potentiometer -resistors 56 and 58 may be omitted and the base of the transistor 54 may be connected through a coupling resistor (not shown) and the current sensing resistor 55 and the biasing resistor 72 in series to the emitter thereof, whereby a constant current will be supplied by the regulator. Also, the high voltage, necessary to start the mercury arc lamp 24 may be obtained by adding an additional secondary winding on the transformer 20. Therefore, the above description is to be taken as illustrative and not in a limiting sense.

What is claimed is:

1. An electronic regulator comprising a pair of input terminals to be connected across a source of unregulated direct current, a current control element having a control electrode, a transformer having a primary and a secondary wind- 'Inga a connection between one of said pair of input terminals through said current control element and said primary winding in series to one of a pair of output terminals,

a connection between the remaining input terminal and the remaining output terminal,

means including a connection to said control electrode to vary the conductance of said current control element between full conductance and a blocked condition in accordance with the condition of the current and voltage applied between said output terminals,

said means comprising two transistors each having a base and a pair of main electrodes, means including a resistor for applying a voltage which is a measure of the voltage between the output terminals between the base and a main electrode of one of -said transistors,

means for providing a standard voltage,

means including a -resistor `for applying a voltage which is a measure of said standard voltage between the -base and a main electrode of the other of said transistors and for applying an operating voltage between the main electrodes of said other transistor,

said connection to said control electrode extending from the other main electrode of said one transistor, and

means including a connection between said secondary winding and said control electrode which tends to keep said conductive element conductive while current increases in said primary winding and which tends to keep said conductive element blocked while current decreases in said primary winding.

2. The electronic 'regulator as recited in claim 1 in which a mercury arc lamp is connected across said output terminals.

3. The regulator in accordance with claim 1 in which a shunt path comprising said primary winding and a rectifier element in series is connected across said output terminals, said rectifier being poled for conduction of a current produced in said primary winding upon reduction of the conductance of said current control element.

4. The regulator in accordance with claim 1 in which said means to vary the conductance of said current control element includes said voltage standard means and current sensing means which provides a voltage drop depending on the magnitude of the current ow to said output terminals, and means to compare the voltage provided by said current sensing means and the voltage of said voltage standard means.

5. The regulator in accordance with claim 1 in which said means to vary the conductance of said current control element includes said voltage standard means and a current sensing means which provides a voltage drop dependent in amplitude on the current flow to said output terminals and also means to compare the sum of the voltage across said output terminals and the voltage provided by said current sensing means with the voltage of said voltage standard means.

6. An electronic regulator comprising a rectifier having a pair of input terminals to which an alternating current may be applied and a pair of output terminals across which a direct voltage will appear,

a voltage doubler including said rectifier,

a current control element having a control electrode,

a transformer having a primary and a secondary winda connection through said current control element and said transformer primary winding in series between one of said output terminals of said rectifier and a first load terminal,

a second connection between the other output terminal of said rectifier and another load terminal,

means to apply the voltage provided by said voltage doubler across said load terminals,

means connected to the control electrode of said current control element and responsive to the current and voltage condition at said load terminals to vary the conductance of said current control element between full conductance and fully blocked condition, and

means including a connection between said secondary winding and said control electrode which tends to keep said current control element fully conductive while current through said primary winding is increasing and which tends to keep said current control element fully blocked while current through said primary winding is decreasing.

7. A current and voltage responsive regulator comprising a rectifier bridge having a pair of input terminals to which an alternating current supply may be connected and a pair of output terminals at which a direct voltage appears,

a transistor having a pair of main electrodes and a control electrode,

a transformer having a primary winding and a secondary winding,

a load having a pair of terminals,

means for providing a voltage which is a measure of the voltage appearing across said load terminals,

means to compare said measure voltage with a standard voltage,

a connection from one of said pair of rectifier output terminals through the main electrodes of said transistor and through said primary winding to one of said pair of load terminals,

means to apply a current to said control electrode in a direction to turn said transistor ofi when said measure voltage is greater than said standard voltage,

means responsive to the voltage induced in said secondary winding when the current in said primary winding is increasing to tend to render said transistor conducting, and to tend to render said transistor non-conducting when the current in said primary winding is decreasing,

a rectifier diode and a capacitor connected in series between an input and an output terminal of said rectifer bridge, said rectifier element being poled in the direction so that a doubled voltage appears between an output terminal of said bridge and the junction of said capacitor and said rectifier diode,

and a circuit connection between said junction and the other of said load terminals.

8. The current and voltage responsive regulator 0f claim 7 in which a mercury arc lamp is connected across said load terminals.

References Cited UNITED STATES PATENTS 3,238,415 l/1966 Turner 315-311 X 3,368,139 2/1968 Wuerflein 323-22 3,371,269 2/1968 Wattson 323-22 JAMES W. LAWRENCE, Primary Examiner E. R. LA ROCHE, Assistant Examiner U.S. Cl. X.R.