US1849103A - Alternating current rectifier - Google Patents

Description

March 15, 1932. R. H. MAXSON ALTERNATING CURRENT RECTIFIER Filed May 4, 1925 ?atented (l5,

- attain -BOL a. .s mon- 1- ron, wrscoivsm; ASSIGNOB. '10 ran nmrcx conrona- TIQN, OF MTG]; WISCONSIN, A OOBIQBATION OF DELAWARE AL ATING CURRENT RECTIFIER Application filed May 4,

This invention relates to alternating current rectifiers. It will be explained as embodied in a rectifier particularly adapted for supplying high- 5 pressure mercury arc lamps, such as are use in light therapy, withunidirectional current from an alternating current source.

Mercury arc lamps such as are used 1n light therapy for the production of act1nic or ultraviolet light rays, ordinarily require a series ballast resistance whose function is to limit the current flow during the starting period when the voltage drop across the lamp is relatively low. After the vapor pressure in the lamp has increased and a cond1tion of equilibrium or stability is reached, this ballast resistance may be used to adjust the arc voltage. Heretotore rectifiers have been employed which utilize vacuum tube or electronic I valves, each of which comprises in general an evacuated or low ressure' inertgas filled vessel ortube containing two electrodes, i. -e., an anode and a heated cathode. These valves, under proper operating condi- Lions, permit current to flow through them in (tune direction, but prevent the passage of current in the reverse direction. Consequently, by a proper arrangement of transformer windings and valves, both waves of the alterec, nating current may berectified to produce a pulsating unidirectional-current. These current ulsations fall to zero twice for each alternatlng current cycle, and since the arc lamp will not operate if the current falls below a certain minimum value, it has been the practice to em lay a reactance or inductive resistance in t tance, when the current is flowing to the lamp, causes the. current pulsations'to lag behind the voltage pulsations, and the-current may be prevented from fallinfil below the critical value for the lamp. other words the react-ance serves to smooth but or straighten the unidirectional current waves.

To supply rectified or unidirectional current to a mercury arc therapeutic lamp at a typical voltage of approximately 7 5 volts and l amperes, it has been the practice to locate the ballast resistance in the transformer 85 secondary or lamp circuit, that is, on the load e lamp circuit. This reac-- 1925. Serial no. 27,673.

side of the transformer, as distinguished from its line side. In order to overcome the voltage drop in the ballast resistance and reactance, it is necessary for the rectifier to ded liver about 120 D. C. volts in order to provide the volts across the lamp terminals- The electronic valve ordinarily employed will not operate satisfactorily when the voltage across or between its electrodesis much in excess of 75 volts. Therefore it has been the practice to employ two valves in series to rectify each half-Wave or cycle in order to obtain the desired 120 volts. Thus, four valves have been required, and because the ballast resistance is located in the transformer secondary or lamp circuit, it has been necessary with the arrangement heretofore used. to

make the transformer large enough to carry M the energy loss of'the ballast resistance and cathode excitation in addition to its load current.

. One of the objects of this invention is to provide an improved rectifier.

Another object is to provide an improved electronic valve type of rectifier particular- 1y adapted for supplying mercury arc therapy lamps with unidirectional current from an alternating current source.

Another object is to provide a relatively inexpensive rectifier.

Another objectis to provide a rectifier requiring a smaller number of valves than have been necessary heretofore.

Another object is to provide a rectifier wherein the capacity or size of the transformer may be reduced.

Another object is to provide a rectifier which is eificient and relatively simple.

' Other objects and advantages will hereinafter appear.

Anembodiment of the invention particularly adapted for use in light therapy is diagrammatically shown in the accompanying drawing.

In the drawing a typical air cooled highpressure mercury arc therapeutic lamp 5 is arranged to receive unidirectional current from an alternating current su ply line 6. The details of the lamp need not be described because such lamps are well-known in the contacts with the anode, thus completin the circuit-and causing the current to start owing. Then the tube is tilted back. a ain to separate the mercury from the ano eand.

thus strike or draw the arc.

The improved rectifier has a transformer provided with a primary winding IOVand asecondary composed of two main sections 11 and 11' and two exciting sections 12 and 12'. A variable resistance 13 is located in the transformer primary circuit to maintain the voltage across the primary winding at the roper value and to act as ballast resistance or the lamp. The inner ends of the transformer secondary sections 11 and 11' are connected to one terminal of the lamp through a reactance 14. This reactance serves in the usual way to smooth out the waves of the pulsating rectified or unidirectional current and prevent the same from falling so low that the arc will go out or become unstable. The outer ends of the main secondary sections 11 and 11 are connected to the cathode exciting or heating circuits of electronic valves 15 and 15', respectively. Each of these valves comprises an evacuated or low pressure inert gas filled vessel-or tube containing two electrodes. The operation of the valve is dependent upon the heating of the cathode or negative electrode. The cathode 16 of valve. 15 is heated or excited by current from exciting secondary 12, and the cathode 16' of valve 15' is excited or heated by current from exciting secondary 12'. The anodes or positive electrodes 17 and 17 of valves 15 and 15', respectively, are connected to the cathode terminals of the mercury arc lamp.

. For the production of 4% am res of cur-- rent at a normal rating vo tage of approximately 75 D. are lamp terminals from a line voltage. of 110 volts A. (3., good results have been obtained by winding the transformer primary with 87 turns of #18 B. & S. gauge wire, and each of the main secondary sections with 112 turns of #15 B. & S. gauge wire. Thus, when the bal ast resistance is adjustedto provide about 85 volts across the primary, the voltage across the two main sections of the secondary will be about 219 :volts A. C. or a rectified voltage of about 75 volts. Each of the cathodeexciting sections of the secondary is.

wound with two turns of B. & S. gauge wire which will provide a maximum of about Woks across each cathode at no; load.

e operation of the rectifier is as follows:

The alternating voltage impressed upon the primary windin induces an alternatinglpotential across a of the sections or 'ngs alternating current directional current, t e frequency being twice' volts at the mercury nuance qo f the secondary. Since the excitation of .v the valve cathodes is dependent entirely upon the heati efiect of the current flowi therethrou h, t e current induced in exciting secondaries I2 and 12'.is not rectified but flows through the respective cathode filaments as alternating current. The heating of the cathodes renders the valves operative to permit current to flow therethrough from the anode to the cathode, although current is still prevented from flowing in the opposite direction as long as the voltage impressed across the electrodes does not exceed their break-down value, which ordinarily is about 75 volts. Consequently, during one-half wave of the alternatin voltage induced in the main seconary sections 11 and 11', current will flow, for example, from the common point between the main secondary sections throu h the reactance 14 and lamp 5 and throug valve from its anode 17 to its cathode 16, and thence to the outer end of secondary section 11. During this half-wave, however, valve 15' prevents current from flowin in the opposite direction. On the next hal -wave, current flows from the point between the main secondary sections through reactance 14 and lamp 5 and through valve 15' from its anode 17' to its cathode 16 and thence to the outer end of secondary section 11'. Valve 15 pmvents the flow of current in the opposite direction during this. half-wave. Thus the rgovides a pulsating unithe frequency of t e alternating current. The volta e across the electrodes of the electronic va ves during all load conditions is suficiently limited to prevent injury thereto or interfere with their valve action. When i the 'arcis not burning, however, and cons'equently the only current flowing in the pri, mary circuit is that drawn by the exciting secondaries, the voltage across the valve electrodes mag be sufliciently high to'cause the valvesto reak down or pass current in the wrong direction. It has been discovered that this breaking down under no load conditions canbe eliminated by putting a small load on the valves. A voltmeter V connected across the, leads to the mercury arc lamp has been found to afford sufiicient load under ordinary conditions. I

The improved rectifier permits the elimination of two of-the valves which are essential to the prior rectifiers andyet the voltage impressed across their electrodes maybe kept at safe values. Since the ballast resistance is located onthe line side instead of the lamp or load side of the transformer, the transformer does not have'tosupply the energy lost in their resistance during operation. Al-

so the current required to excite the valve cathodes is reduced becausethe number of valves is reduced. Consequently, the capaci ty and size of thetransformer may be matearc lamp and each permitting only alternate half-v current are needed. However,

rially reduced. It has been found that for the ordinary therapeutic mercury arc lamp the size of the transformer may be reduced in the neighborhood of 35%. Another feature of advantage is that the maximum voltage is impressed upon the valve cathodes or filaments before the load, i. e., the lamp, is turned on, but drops to a relatively low value as soon as current is flowing trodes. Thus the maximum voltage is impressed at a time when the to a relatively low value after the current between the electrodes is flowing and when only a relatively low exciting current is required.

Although a rectifier employing only a pair of valves has been described in detail, it will be understood that a greater number may be used when higher voltages of unidirectional the ratiobetween the number of valves used in my rectifier and the rectifier heretofore used will remain the same. That is for a given voltage my rectifier will require only half as many valves as the prior rectifiers.

I claim: I g I l. The combination of a mercury arc vacuum tube having a relatively low resistance at starting and a high resistance when normally operating, a valve for rectifying each half-Wave of an alternating current source, a transformer and ballast resistance in the primary circuit thereof for limiting the 'alternating voltage impressed from the source upon the valves and automatically varying the voltage impressed on the tube as the resistance thereof changes, and a reactance interposed between the tube and the transformer to lessen the tube.

2. In combination a high pressure mercury having an anode and a cathode, a pair of valves connected to the lamp cathode and each permitting. only alternate halfwaves of alternating current to pass therethrough to the lamp, a transformer having a primary winding for connection to an alternating current source and" a secondary winding which is connected at a different point to each valve to the lamp anode, the transformer servin to reducethe voltage of the induced hal waves to a valve within the rectifying range of the valves, and'a ballast resistance in the circuit between the transformer primary and the source. v

3. In combination a high pressure mercury arc lamp having an anode and a cathode,

a pair of valves connected to the lamp cathode waves of alternating current to pass therethrough to the lamp, a transformer having a primary winding for connection to an altprnating current source and a secondary between the valve elec-- valve is supposed. to pick up or being rectifying, but falls.

the amount of the fluctua-' 'tions of unidirectional current impressed on and at a common point waves to a value within the safe rectifying range of the valves, a ballast resistance in the circuit between the transformer primary and the source, and means for preventing the breaking down of the valves when the same are subjected to voltage while the lamp is extinguished.

4. In combination a high pressure mercury arc lamp having an anode and a cathode, a pair of valves connected to the lamp cathode and each ermittingonly alternate half- Waves of a ternating current to pass'therethrough to the lamp, atran'sformer having a primary winding for connection to an alternating current source and a secondary winding which is point to each valve and at a common point to the lamp anode, the transformer acting to reduce the voltage of the induced half-waves to a value within'the safe rectifying range of the valves, a ballast resistance in the circuit between the transformer primary and the source, and a relatively small load permanently in circuit'between the valves and the lamp to prevent excessive "voltage being applied to the valves when the lamp is not in service.

In witness whereof I ROLLAND H. MAXSON.

connected at a different hereunto subscribe my name this 27th day of "April, 1925'.

Images