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Lfchnical In~ormation Srvic, Oak Ridg6, f~nnesr~e
UNITED STATES ATOMIC ENERGY COMMISSION
CONTINUOUSLY VARIABLE 1VAGNET
JL~L jS1 I:i
;3 G I
W. D. Schultz
March 8, 1951
Carbide and Carbon Chemicals Company
Reproduced direct from copy
as submitted to this office.
Work performed under
Contract No. W-7405-eng-26
PRINTED UN USA
PRICE 5 CENTS
ASSAY LABORATORY DEPARTMENT
CONTINUOUSLY VARlIABLE MVAGNETP POW~ER SUPPLY
The need for continuously scanning the mass spectra in the mass
spectrometer has led to the development of a variable m~agnet power
supply which will deliver from 0 to 500 milliamperes to a magnet
of 1100 ohms resistance. The supply is a continuously variable,
electronic, degenerative regulator which will regulate better than
one part in 5000 throughout the range. Line voltage fluctuations of
f 10 volts have no effect on the output of the supply.
OPERA TI ON:
The power supply is actually two electronic degenerative regulators.
One of the circuits provides a constant voltage for the bias supply
used in the main regulator. The positive side of the bias regulator
is necessarily at ground potential to supply a negative bias for V3
(See Figure 1). TChe grid of V1 sees about one-half of any D.C, voltage
chage n he utpt f the bias regulator. Since the voltage gain of
the 6SJ7 is about 400(1 hna1 eompaela sueacag
of 1 millivolt in the output will cause a change of about 0.2 volts on
the grid of the 67T6. This high gain combined with the adjustment of the
proper screen potential on V1 produces a 300 volt output in which there
is no detectable ripple nor any detectable variation in D.C. level, The
adjustnent of this screen potential is made with ao oscilloscope connected
across the bias supply to detect the point of minimum supply fluctuation.
The regulator proper consists of six 807's in parallel to pass the magnet
current. These tubes were selected because of their low cost and high
voltage handling capacity. The average plate dissipation for each 807
is 10 watts with a maximum of 20 watts at full supply current of 500
milliamperes. At zero current, 800 volts appear across the 807's. The
supply originally contained twRo 829's as series regulators, but difficulty
was experienced when high frequency oscillations tended to develop due
to the common screen grid connection in each tube. Also, these oscilla-
tions were probably due to the screen-to-cathode bypass capacitor built
into the 829. A cost comparison also shows that six 807's cost less than
one-half of the cost of tw~o 829's.
The 807's are controlled by a 63J7 using a 10 mnegohn plate load, The
output as observed on an oscilloscope shows no ripple and less than.
one millivolt fluctuation in the D).C. level. The supply can have either
positive or negative regulation depending upon thre adjustment of R2*
The adjustment of the supply is as follows:
1. Connect magnet or inductive dummy load and oscilloscope across
the supply output.
2. With R4 set counter-olockwise, adjust R3 for zero current.
3. Advance R to full clockwise and adjust R2 to allow load
current o 500 milliamperes. (Caution: Care must be used
in setting R3 and R2 since there are two possible adjustments
of these controls. The wrong adjusthnent will be indicated by
instability in supply output and the, positioning of the con-
tact arm of R3 too near one end of the potentiome~ter.)
4. Return R4 to its counter-olockwise position and readjust R3
for zero current.
5. Repeat steps 3 and 4 until the range of 0 to 500 milliamperea
is covered by the helipot control.
6. Connect a voltmeter to the supply output and note the voltage
at 500 milliamperes output.
7. Break the connection between the supply and the load, and note
the voltage change on ~the output voltmeter. If any change is
observed, correct for the change by rotating R2 a small amount.
Continue this adjustment until a decrease of fran 1 to 5 volts
is noted in the 550 volt output when the load is placed on the
8. The oscilloscope signal should show very little fluctuation
at this point. Further minor adjustment of R2 and R3 may be
necessary to obtain the best supply regulation.
An alternate method for supply adjustnant can also be followed,ie:
1. Set R4 midway between clockwise andl counter-clockwise stops
2. Adjust R2 and R3 for best regulation as shown on an
oscilloscope with an output current of between 220 to
3. Adjust R6 an~d R7 for proper zero current position and full
range of 500 milliamperes at maximun control position. (R4)
The supply is constructed on two separate chassis as indicated by the
separate schematic diagrams Figure 1 and Figure 2. Figure 2 is the
diagram of the high voltage rectifier supply which has a D.C. output
of 800 volts at 500 milliamperes, This high voltage is dbosen to give
the best possible regulation in the range in which the regulator is
intended for use. This range is around a load current of 400 milli-
asperes. At this current, a voltage of 350 volts appears across the
807 regulators, and by experiment, the best regulation occurs between
200 and 500 milliamperes of load current, It was thought that it
might be advisable to include a switch for cutting out 3 or more of the
807's for better regulation in -the low current range. This idea was
discarded because of the possibility of overload should the supply be
run at high currents with the 807's out of the circuit. Regulation at
low currents is more than adequate for stable operations of the mass
It is intended that -this regulator be used with a motor driven poten-
tiometer (R4)* The mechanism for driving the potentiometer was not
completed at the time of the writing of this report. The heart of
the drive will be a Brown 2-phase balancing motor to give variable
speed and reversibility.
The author wishes to thank Mr. E. S. Lewis and NW. Do L. Glovier for
their assistance in the construction and testing of this equipment,
(1) G. E. Hamilton and T. M~aiman: Voltage Regulated Power Supplies,
Part II, Communications, December,
1945, P. 70.
MOI ') OE
END OF DOCUMENT
UNIVERSITY OF FLORIDA
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