US3500127A

US3500127A - Switching type voltage and current regulator and load therefor

Info

Publication number: US3500127A
Application number: US686163A
Authority: US
Inventors: Peter Schiff
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1967-11-28
Filing date: 1967-11-28
Publication date: 1970-03-10
Anticipated expiration: 1987-03-10
Also published as: FR1597625A; NL6816964A; DE1811526A1; GB1229256A

Description

March 10, 1970 P. SCHIFF 3,

SWITCHING TYPE VOLTAGE AND CURRENT REGULATOR AND LOAD THEREFOR Filed Nov. 28, 1967 2 1 s NU 5 u, 55 g a o g Q L PETEZ EgZfFF United States Patent Oil ice 3,500,127 Patented Mar. 10, 1970 US. Cl. 315-224 9 Claims ABSTRACT OF THE DISCLOSURE A switching type of voltage regulator including a series switching element and a voltage comparator is dis closed in which the drive current for the series switching element is derived by transformer coupling to the load and in which the voltage across the load, which is to be regulated, is measured by and is applied to the voltage comparison means by transformer coupling to the load. Also, a voltage which is the measure of the current flowing into the load is applied to the voltage comparator whereby the regulator provides a negative voltage to current output characteristic which causes proper operation of a load of the mercury arc lamp type.

BACKGROUND Certain electrical loads, notably mercury arc lamps, require a high voltage to cause them to start and a regulated voltage of about one-half of the starting voltages during normal operation. Furthermore, such loads require several minutes for warm up to operating temperatures. During the Warm up period, the current flow through the load will be excessively high and the voltage drop across the load may be quite low. In accordance with known installations for operating mercury arc lamps, a ballast inductor is used with an alternating current supply. Therefore, twice each cycle, the light produced by the mercury arc lamp goes on 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 incandescent lamp, unsuitable for various applications such as motion picture projection. Furthermore, unless several mercury arc lamps are provided and an apparatus is used to cause the several lamps to produce their light in out of phase relation, whereby the stroboscopic efiect is minimized, such lamps cannot be used for viewing sporting events or for lighting the stage while making motion pictures or recording or broadcasting television programs. Furthermore, the necessary ballast inductors are heavy, bulky and expensive.

An electronic type of regulating power supply that will cause the mercury arc lamp to start and that will apply a properly regulated voltage and current to the mercury arc lamp may be used as a supply therefor. A standard 135 volt mercury arc lamp requires about 270 volts for starting. An AC. 110 volt source has a peak voltage of about 155 volts, which will not cause a 135 volt mercury arc lamp to start. Therefore a voltage step up means must be incorporated in the electronic type of regulating power supply to make it possible to operate a 135 volt lamp from a 110 volt source. If an A.C. source of 200 or more volts is used to supply the regulator, therefore insuring that the regulator will start the mercury arc lamp, the control circuits for the regulating or switching element comprising part of the voltage regulator will be subjected to high line voltages and the forward drive bias for the regulating element may be obtained from the high voltage source. Under these conditions, the

losses in the control circuits for the regulating element will be very high or a regulating element with very high current gain, which may be expensive, must be provided.

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 a mercury arc lamp.

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 eifect is eliminated.

SUMMARY OF THE INVENTION In accordance with the invention, a current and voltage regulator of the switching type including a switching element is provided which includes a current sensing means and a voltage sensing means, the current sensing means taking control of the output current during the time that the loads draws an excessive current. The circuit is so arranged that the control circuits for the switching element are not subjected to a high supply voltage, whereby low voltage control elements may be used, and the current losses of the control circuit are reduced and also whereby it is not necessary to use a switching element that exhibits high current gain, Furthermore in accordance with the invention, a voltage which is a measure of the output voltage of the described regulating power supply means is obtained from the load by transformer means for comparison with a load standard comprising part of the regulator.

This invention will be better understood upon reading the following description in connection with the accompanying drawing in which- FIGURE 1 is a circuit diagram of a circuit including the inventive current and voltage regulator and FIGURE 2 is a curve which is useful in explaining the operation of the circuit of FIGURE 1.

An AC. power supply (not shown) which may be 200 volts or higher, is connected across input terminals 10. The input terminals of a rectifying bridge 12 are connected across the terminals 10 in series with a surge current limiting resistor 14. A filter capacitor 16 is connected across the positive and the negative terminals 18 and 20 respectively of the bridge 12.

The terminal 20 is connected by way of a current sensing resistor 22 to the emitter of a NP'N transistor 24 whose collector is connected through the primary winding 26 of a three winding iron or ferrite core transformer 28 to a terminal 30 of a mercury arc lamp 32. The other terminal 34 of the lamp 32 is connected directly to the positive terminal 18 of the rectifying bridge 12. The mercury arc lamp 32 comprises the load for the discolsed regulator. The transistor 24 acts as the regulating or switching element for the regulator that supplies current to the lamp 32.

The mercury arc lamp 32, which is an article of commerce, includes a glass envelope 35. The envelope 35 contains a quartz enclosure 36 which, in turn includes two main electrodes 38 and 40 and a starting electrode 42. The envelope 36 also contains a small amount of liquid mercury and a gas at a low pressure (not shown). The electrode 38 is connected to the terminal 34 and the electrode 40 is connected to the terminal 30. The starting electrode 42 is connected through a current limiting resistor 44 to the terminal 30. The terminals 30 and 34 may be formed to fit an Edison socket as illustrated in FIGURE 1.

The operation of the standard mercury arc lamp is explained in connection with FIGURE 2. When a properly ballasted power supply is connected across the terminals 30 and 34 of the lamp 32, the ionization point A is reached in a fraction of a second. At this point A, the gas in the enclosure 36 ionizes and the mercury in the enclosure 36 begins to vaporize and the gas pressure in this enclosure builds up while the lamp 32 warms up. During this time, the current taken by the lamp 32 increases and the voltage thereacross decreases along the line from the point A to the point B of FIGURE 2. where, after the point B is reached, the current increases very rapidly and the voltage changes very little. The warming up period continues from about the point B' to about the point E along a line such as the line D and takes about three to four minutes. At about point C, the ballast means takes, control and prevents further increase in current. Due to operation of the ballast means, the voltage across the lamp increases as the current therethrough decreases to the stabilized operating point E. As will be pointed out, the described regulator performs the function of the ballast means for the load thereon comprising the lamp 32.

The described voltage regulator includes a Zener diode 46 and a resistor 48 which are connected in series in the order named across the terminals 20 and 18. The Zener diode 46 produces a standard voltage in a known manner. A potentiometer 50 and a resistor 52 are connected across the Zener diode 46, whereby an adjustable portion of the standard voltage appears at the slider of the potentiometer 50. The slider of the potentiometer 50 is connected to the base of an NPN transistor 54. The emitter of the transistor 54 is connected to the emitter of a second NPN transistor 56. The junction of the emitters of the transistors 54 and 56 is connected by way of a common resistor 58 to the negative terminal 20. The collectors of the transistors 54 and 56 are connected together through a resistor 60. The base of the transistor 56 is connected through a biasing resistor '62 and the current sensing resistor 22 to the terminal 20. The base of the transistor 56 is also connected to the junction of two resistors 64 and 66 which are connected serially across the resistor 48.

A voltage which is a measure of the voltage across the load 32 is developed in a secondary winding 68 of the transformer 28. The secondary winding 68 is connected between the emitter of the transistor 24 and the anode of a rectifying diode 70. The cathode of the diode 70 is connected through a resistor 72 to the base of the transistor 56 and to one electrode of a storage capacitor 74 whose other electrode is connected to the terminal 20 through the resistor 22. Therefore, the voltage that is applied between the base and emitter of the transistor 56 is the sum of two voltages, one of which is the voltage drop exhibited by the current sensing resistor 22 which is a measure of the current flowing to the load, and the other is a voltage appearing across the capacitor 74 which is the measure of the voltage applied to the load. These two voltages are compared in the differential amplifier 61 which includes the two transistors 54 and S6 and their biasing and input connection, with the standard voltage applied to the base of the transistor 54. The differential voltage provided by the differential amplifier '61 appears across the resistor 60.

The connection of the base of the transistor 56 to the junction of the resistors 64 and 66 tends to reduce the effect of variation in input voltage, applied to the terminals 10, on the output voltage of the regulator applied to theload 32. While the input voltage varies, the voltage across the Zener diode 46 varies very little. Therefore, the voltage variation across the resistor 48 is almost equal to the voltage variation of the input voltage applied to the terminals 10. A predetermined portion of this voltage variation appears at the junction of the resistors 64 and 66, and this portion is applied to the base of the transistor 56 in a manner to overcome the effect on the output voltage of a variation in the input supply voltage.

The base of a PNP transistor 76 is connected to the collector of the transistor 56, and the emitter of the transistor 76 is connected to the collector of the transistor 54. The collector of the transistor 76 is connected to the base of a NPN transistor 78 and, through a resistor 81 W and the resistor 22, to the terminal 20. The emitterof the transistor 78 is connected directly to the terminal 20 through the resistor 22 and the collector of the transistor 78 is connected through a high value resistor 80, in the order of 100,000 ohms, to the'terminal 18. The collector of the transistor 78'is also connected directly to the base of the'switching transistor 24 and to one terminal of a resistor 82 whose other terminal is connected to the emitter of the transistor 76. A second secondary winding 84 of the transformer 28 is connected between the emitter of the transistor 24 and the base of the transistor 24 by way of a resistor 85 and the resistor 82 in series. A diode 86, poled to be conductive in the direction towards the base of the transistor 24, is connected in shunt with the resistor 85. The anode of a protective diode 88 isconnected to the emitter of the transistor 24 and the cathode of the diode 88 is connected to the base of thetransistor 24. A filter capacitor 92 which may be quite small compared to' the capacitor 1'6 is connected across the terminals 30 and 34 of the load 32. The anode of a cummutating diode 90 is connected to the collector of the transistor 24 and the cathode of the diode 90 is connected to the terminal 18.

When, at turn-on, an AC. voltage of 200 or more volts is applied to the input terminals 10, a voltage of about 280 or more volts appears across the terminals of the bridge 12. The capacitor 16 is very quickly charged to this voltage, the surge resistor 14 keeping the capacitor charging rate, at turnon, down to a safe value. The Zener diode 46 breaks down, whereby a standard voltage is applied to the base of the transistor 54. A very small current flows into the base of the transistor 24 and out the emitter thereof through the high resistor whereby the transistor 24 is sufficiently conductive at turn-on for starting the regulator. Current flows through the current sensing resistor 22, through the emitter to collector path of the switching transistor 24, and through the primary winding 26 of the transformer 28 and between the electrodes 42 and 38 of the load 32. The gas in the enclosure 36 is ionized and the operation of the lamp 32 is represented by the point A in FIGURE 2. While at turn-on, current flows in the lamp 32 between the electrodes 38 and 42, after the lamp is started, current flows in the lamp 32 between the electrodes 38 and 40 due to the action of the current limiting resistor 44. Due to the small amount of current flow through the load 32 at the point A the voltage applied to the base of the transistor 56 by the voltage drop in the resistor 22 is low. At turn-on, the current in the transformer primary winding 26 increases. While current is increasing in the transformer primary 26, the voltage induced in the transformer secondary 68 is negative on the anode of the diode 70 and no current is stored in the capacitor 74, and no voltage is applied to the base of the transistor 56 at turn-on due to voltage induced in the transformer secondary 68. The voltage induced in the secondary 84, while current is increasing in the primary winding 26, is in such a direction as to provide drive current for the transistor 24 by way of the parallel combination of the resistor and the diode 86 in parallel, and in series with the resistor 82. The diode 86 is conductive for current induced in the winding 84 while the current in the winding 26 is increasing. This drive current tends to fully saturate the transistor 24 as long as current in the winding 26 is increased.

The current in the primary winding 26 reaches a maximum value and decreases. The voltages induced in the coils 68 and 84-reverse. The current induced in the coil 68,. while the current in the coil 26 is decreasing, is in a direction to charge the capacitor 74 through the diode 70 and is a measure of the voltage across the load 32. Therefore, the capacitor 74 is charged, while the current in the coil 26 is decreasing to a voltage which is the measure of the voltage appearing across the load 32. The capacitor 74 discharges through the resistors 72 and 62 in series. Therefore the voltage applied to the base of the transistor 56 is proportional to the sum of the voltages appearing in the resistor 22 due to the current flowing therethrough to the load 32 and the voltage produced in the resistor 62 due to the voltage applied to the load 32.

The voltage induced in the coil 84 is in a direction to block the transistor 24 when the current in the primary winding 26 is reducing The rectifying diode 86 is poled in a direction to stop current flow of this blocking current, however, it is a slow acting diode and also it has capacity, whereby a slug of blocking current is applied to the base of the transistor 24 at the moment that current starts to decrease in the primary winding 26 whereby the transistor 24 is turned off more quickly than if the diode 86 were a fast acting diode. The flow of blocking current is through the resistor 85 as long as the diode 86 assumes its rectifying function. As long as the current in the winding 26 decreases, blocking current is applied to the base of the transistor 24. The diode 88 prevents negative voltage from being applied to the emitter of the transistor 24 with respect to its base due to the operation of the coil 84 and therefore acts to protect the transistor 24 against such voltages.

The transistor 24 changes its condition from saturation to blocking very quickly and therefore the transistor 24 is either blocked or saturated whereby the losses therein are low. Also, the frequency of operation of the switching transistor 24 may be very high, that is in the order of several thousand cycles per second, and is determined by the characteristics of the circuit elements including the transistor 24, the inductance of the winding 26, the setting of the potentiometer 50 and on the load 32. Due to the high frequency of switching of the transistor 24, the filter capacitor 92 may be quite small compared to the filter capacitor 16 which filters a much lower frequency current. The diode 90 permits the back voltage induced in the coil 26 when the transistor 24 is blocked to flow into the load 32 and protects the blocked transistor 24 from this high voltage that is induced in the winding 26 when the transistor 24 is blocked. The voltage that is induced in the coil 84 when it is in the direction to saturate the transistor 24, also acts as a supply current for the transistors 54, 56 and 76, whereby these transistors are supplied from the load side of the transistor 24. The transistor 78 is supplied by the base drive for the transistor 24 from the secondary'winding 84. Since the emitter to base connection of the transistor 24 is connected across the emitter to collector connection of the transistor 78 the voltage across the transistor 78 is very low.

As noted above, a voltage which 'is proportional to the current drawn by the load 32 and a voltage which is proportional to the voltage applied to the load 32 are applied to the transistor 56. The current flowing in the resistor 60 is then determined by the relative magnitudes of the voltages applied between the base and emitter of the transistor 56 and the standard voltage applied between the base and emitter of the transistor 54. The resistor 60 acts as a threshold device for the transistor 76. That is, if the transistor 56 were leaky, the transistor 76 may be on at all times. The resistor 81 acts as a threshold device for the transistor 78 in a similar manner in case the transistor 76 is leaking. The transistor 76 and 78 and their connections comprises a current amplifier. The transistor 78 shunts all or none of the drive current away from the transistor 24, depending upon the control voltage applied to the transistor 56, whereby the duty cycle of the transistor 24 is changed in a direction to regulate the current and voltage applied to the load 32.

When the operation of the lamp 32 has arrived at a point such as the point C of FIGURE 2, the described circuit acts as a ballast means, that is, the voltage in the emitter to base circuit of the transistor 56 is such as to limit the current and the voltage applied to the lamp 32, and the lamp current and voltage are made to follow the portion D of the curve of FIGURE 2 to the stabilized operation point E. It will be noted that no auxiliary means are needed to supply starting potential to the lamp 32 even though the voltage at the starting point A is more than twice the voltage at the operating point E. It will also be noted that the drive current for the switching transistor 24 and the operating current for the differential amplifier 61 and for the amplifying transistors 76 and 78 are supplied from the load side of the transistor 24, and that only the small starting current for the transistor 24 that flows through the resistor 80 is provided from the source side of the transistor 24. It will further be noted that the control elements for the transistor 24 are operated at a much lower voltage than the rectified A.C. supply voltage, whereby only the switching transistor 24 need be subjected to the high voltage rectified A.C. supply.

Modifications of the described regulator will occur to persons skilled in the art and therefore the above description is to be taken as illustrative and not in a limitmg sense.

What is claimed is:

1. An electronic regulator comprising,

a pair of terminals to be connected across a source of unregulated direct current,

a current control element having a control electrode,

a transformer having a primary winding and at least one secondary winding,

2. 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,

a voltage standard means,

means including said secondary winding to measure the voltage across said output terminals,

means to compare the voltages provided by said voltage standard means and said voltage measuring means to provide a control voltage, and

means responsive to said control voltage provided by said voltage comparison means to control the conductance of said current control element in a manner tending to regulate the voltage appearing across said output terminals.

2. The invention as expressed in claim 1 in which said transformer has said one and a second secondary winding and in which means including a connection of said second secondary winding to said control electrode are provided to vary the conductance of said current control element between full conductance and a blocked condition, whereby the current through said primary winding increases and decreases, said means responsive to said control voltage provided by said voltage comparison means varying the duty cycle of said current control element.

3. The invention as expressed in claim 2 in which said second secondary winding applies operating voltages to said voltage comparison means.

4. The invention as expressed in claim 1 in which said means including said secondary winding to measure the voltage across said load terminals comprises a rectifying element and a capacitor in series, said rectifier being poled to cause charging of said capacitor while the current passing through said primary winding is decreasing and in which means are provided for applying the voltage across said capacitor to said voltage comparing means.

5. A regulator comprising,

a pair of input terminals to which an unregulated direct voltage may be applied,

a pair of output terminals across which a load may be connected,

a current control element having main electrodes and a control electrode,

a transformer having a primary winding and at least one secondary winding,

a connection from one of said input terminals through the main electrodes of said current control element and through said primary winding to one of said output terminals,

a connection between said remaining input and output terminals,

means for causing the conductance of said current control element to vary whereby the current flowing through said primary winding also varies,

means to provide a voltage which is a measure of the voltage across said output terminals comprising said secondary winding, a rectifying diode, and a capacitor connected in series, said diode being poled to cause charging of said capacitor when current in said primary winding is decreasing, and

means to apply the voltage produced by said voltage measuring means to said control electrode in a manner to tend to regulate the voltage across said output terminals.

6. The invention as expressed in claim 5 in which said last mentioned means includes means to produce a standard voltage and means to compare said voltage produced by said voltage measuring means with said standard voltage.

7. The invention as expressed in claim 5 including means to provide a voltage which is a measure of the amount of current taken by the load that is connected across said output terminals and in which said last mentioned means includes means to produce a standard voltage and means to compare said voltage produced by said voltage measuring means and said voltage produced by said means to produce a voltage which is a measure of the current taken by the load with said standard voltage.

8. The invention as expressed in claim 5 in which said transformer has a second secondary winding and in which said last mentioned means includes means to produce a standard voltage and means to compare said voltage produced by said voltage measuring means with said standard voltage, said comparing means requiring operating current and in which means are provided to supply the required operating current to said comparing means including said second secondary winding.

9. The invention as expressed in claim 5 in which said transformer has a second secondary winding and in which said last mentioned means includes means to produce a standard voltage and means to compare said voltage produced by said voltage measuring means with said standard voltage, said comparing means requiring operating current and in which means are provided to supply operating current to said comparing means including said second secondary winding, and in which a mercury arc lamp is connected across said output terminals.

References Cited UNITED STATES PATENTS 3,290,583 12/1966 Sinclair 307-252 3,311,814 3/1967 Clilfgard 307297 3,368,139 2/1968 Wuerfiein 307-297 3,383,584 5/1968 Atherton 3234 3,396,326 8/1968 Kisrow 323-22 JERRY D. CRAIG, Primary Examiner US. Cl. X.R.