United States Patent (19)
`Allison
`
`3,919,616
`11)
`(45) Nov. 11, 1975
`
`CONSTANT VOLTAGE POWER SUPPLY
`Inventor: Joseph M. Allison, Wesleyville, Pa.
`Assignee: General Systems, Erie, Pa.
`Filed:
`Dec. 6, 1972
`Appl. No. 312,709
`
`54)
`(75)
`73
`22)
`21
`
`(52
`(51)
`58
`
`56)
`
`U.S. Cl....................... 320/35; 320/39; 32.3/68;
`320/31
`Int. Cl.......................... H02) 7/10; G05F 1158
`Field of Search............. 32O/39, 40, 31, 32, 35,
`320/36; 322/28: 32.3/68
`References Cited
`UNITED STATES PATENTS
`10/1970 Rutherford et al................... 322/28
`1 1/1970
`Young.....................
`... 322/28
`1/1971
`Ebbinge et al................... 320,139 X
`
`3.535,616
`3,538,421
`3,553,565
`
`
`
`Prinary Evanliner-J. D. Miller
`Assistant Evanliner-Robert J. Hickey
`
`ABSTRACT
`57
`A constant voltage, current limited power supply pri
`marily intended for use as a single cell, nickel cad
`mium battery charger. The nickel cadmium cell has a
`temperature characteristic of approximately minus 1.1
`mV/F. The system disclosed herein also has substan
`tially this same temperature characteristic due to tak
`ing advantage of the intrinsic temperature characteris
`tic of a forward-biased base-emitter junction of a sili
`contransistor. A forward-biased base-emitter junction
`is used as a system voltage reference and the Voltage
`feedback arrangement permits the output voltage to
`be substantially above the reference voltage without
`reflecting a magnified voltage characteristic at the
`output.
`
`1 Claim, 4 Drawing Figures
`
`T4
`CURRENT
`SOURCE
`
`Exhibit 1033 - Page 1 of 6
`
`

`

`U.S. Patent Nov. 11, 1975
`
`sheet 1 of 2
`
`3,919,616
`
`COMPARATOR
`
`NPUT
`
`CONTROLLER
`
`FG. 1
`
`ERROR AMR
`T4, T3, T2
`
`
`
`
`
`T4
`CURRENT
`SOURCE
`FG.3
`
`Exhibit 1033 - Page 2 of 6
`
`

`

`U.S. Patent Nov. 11, 1975
`
`Sheet 2 of 2
`
`3,919,616
`
`
`
`
`3,919,616
`
`
`
`
`
`
`
`U.S.PatentNov.11,1975
`
`Sheet2of2
`
`Exhibit 1033 - Page 3 of 6
`
`

`

`3,919,616
`
`CONSTANT VOLTAGE POWER SUPPLY
`
`5
`
`()
`
`GENERAL STATEMENT OF INVENTION
`A constant voltage (current limited) power supply is
`disclosed which is intended to be used as a single cell
`battery charger primarily for a nickel cadmium cell.
`The nickel cadmium cell has a temperature character
`istic (dv/dT) of approximately minus 1.1 millivolt per
`degree Fahrenheit. The charger should also have this
`same characteristic. The system disclosed herein
`achieves the desired temperature characteristic by tak
`ing advantage of the intrinsic temperature characteris
`tic of a forward-biased base-emitter junction of a sili
`contransistor. A forward-biased base-emitter junction
`is used as the system voltage reference and the voltage
`feedback arrangement permits the output voltage to be
`Substantially above the reference voltage without re
`20
`flecting a magnified dVie/dT at the output. The output
`voltage is given by the following equation:
`V = W + kV,
`where k is a constant less than 1, so that
`
`d
`l
`
`clue
`all
`
`--
`
`kgl.
`l
`
`2
`GENERAL DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a functionally equivalent block diagram of a
`circuit of a conventional battery charger.
`FIG. 2 shows a hypothetical circuit that has three
`components removed but otherwise is identical to the
`circuit according to the invention.
`FIG. 3 shows a simplified diagram of the circuit ac
`cording to the invention.
`FIG. 4 shows a schematic wiring diagram of a power
`Supply circuit according to the invention.
`DETAILED DESCRIPTION OF THE DRAWINGS
`Now with more particular reference to the drawings,
`FIG. 1 shows a functionally equivalent block diagram
`of a battery charger. In the schematic diagram of FIG.
`4, the controller is identified as transistor T1. The error
`amplifier consists of transistor stages T2, T3, T4 and
`TS. The reference is identified as the base-to-emitter
`voltage of transistor T5, that is, the so-called cut-in or
`barrier voltage of the base-emitter junction of transis
`tor TS. Transistor TS serves the multiple functions of
`reference, comparator, and first stage of the error am
`plifier. All the essential elements of a feedback control
`system have been identified, that is, FIG. 1 shows the
`reference, comparator, and first stage of the error am
`plifier but it does not show the function of transistor
`stage T7 or Zener diode ZD1. Transistor T7 and Zener
`diode ZD1, along with the associated bias elements,
`serve to implement a desired temperature coefficient of
`the output voltage. Transistor T7, resistors R11, R12,
`Zener diode ZD1 diodes RD2, RD3, RD5, and RD6,
`and capacitor C2 are the temperature compensating
`elements. Without any constraints on temperature co
`efficient of output voltage, there components would be
`unnecessary and therefore undesirable.
`The manner in which transistor T7, resistors R11,
`R12, Zener diode ZD1, diodes RD2, RD3, RD5, and
`RD6, and capacitor C2 influence the temperature coef.
`ficient of the output voltage can be explained by analyt
`ically examining a hypothetical system which has these
`components removed but is otherwise identical to the
`actual system in all other characteristics. Then examine
`the system after inserting the transistor T7, resistors
`R11, R12, Zener diode ZD1, diodes RD2, RD3, RD5
`and RD6, and capacitor C2.
`FIG. 2 is a hypothetical workable system identical in
`all respects to that shown in FIG. 4 except the above
`mentioned temperature compensating elements are de
`leted. This hypothetical system has a temperature coef
`ficient much different from the circuit shown in FIG. 4.
`The presumption of a workable system that has this
`same low output impedance as the system shown in
`FIG. 4 requires that R1 and R2 of FIG. 2 be chosen
`such that the base current of TS (IB5 in FIG. 2) is very
`small in comparison with the bleeder current I of
`FIG. 2. With this presumption, the following approxi
`mate relationship holds in the limit as the gain of the
`error amplifier increases without bound:
`
`30
`
`Since k is less than , the first term predominates and
`the rate of change of output voltage with respect to
`temperature is given by:
`dVofall is proportional to dViefall is proportional to
`-l. 1 millivolts per degree Fahrenheit.
`The constant voltage, current limited power supply
`disclosed herein contains a voltage reference with
`which the system output voltage is compared. The dif
`ference signal produced at a comparator is amplified
`and applied to a series controller transistor in a manner
`which minimizes the error and hence tends to maintain
`a constant output voltage under the influence of vary
`ing load current and A.C. input voltage.
`OBJECTS OF THE INVENTION
`It is an object of the invention to provide a circuit for
`charging a battery wherein the output voltage of the
`circuit has substantially the same temperature charac
`teristic as the temperature characteristic of the battery.
`50
`Another object of the invention is to provide an im
`proved constant voltage power supply circuit.
`Another object of the invention is to provide a power
`supply voltage, wherein the intrinsic temperature char
`acteristic of a forward-biased base-emitter junction of
`an electronic valve is used as a system voltage refer
`ence to control the output voltage to have substantially
`the same temperature characteristic as the temperature
`characteristic of the battery.
`With the above and other objects in view, the present
`invention consists of the combination and arrangement
`of parts hereinafter more fully described, illustrated in
`the accompanying drawings and more particularly
`pointed out in the appended claims, it being under
`stood that changes may be made in the form, size, pro
`portions, and minor details of construction without de
`parting from the spirit or sacrificing any of the advan
`tages of the invention.
`
`35
`
`40
`
`45
`
`55
`
`60
`
`R
`- he
`R - R
`Rl
`R. Y.
`R2
`ht.
`
`Exhibit 1033 - Page 4 of 6
`
`

`

`3,919,616
`4
`3
`A 7.5 volt Zener diode is used for ZD1 in the circuit
`The rate of change of output voltage with respect to
`shown in FIG. 4. Assuming an output voltage of 1.5 volt
`temperature is found by differentiating the above equa
`and solving Eq. 4 for the ratio R1/(R1 + R2):
`tion for output voltage with respect to temperature. As
`suming that the resistances of R1 and R2 are indepen
`dent of temperature:
`
`5
`
`o
`
`hi.
`
`Eq. 2
`
`all,
`all
`
`R - R.
`R2
`
`dur:
`all
`
`Substituting this number into Eq. 5:
`
`A typical output voltage in practice for the circuit is 1.5
`volts at 70 Fahrenheit. V at 70 F. is about 0.58 volt
`for the transistor used in the circuit shown in FIG. 4.
`Solving the equation for the ratio, (R1 + R2/R2:
`
`15
`
`R - R.
`R
`
`l. 5
`().5 8
`
`(h
`
`Inserting this number into Eq. 2:
`
`Eq. 6
`
`clu -
`
`dT
`
`all re
`T
`
`().
`
`al
`all
`
`dV/dTV, for the 7.5 volt Zener is 0.05% per Centi
`grade at 5 milliamps of bias current (from Ref. 1, pp.
`144). So that dV/dT is +1.8 millivolts per degree Fahr
`enheit and dVie/dT is -1.28 millivolts per degree Fahr
`enheit, as already mentioned in reference to FIG. 2.
`Substituting these numbers into Eq. 6:
`
`al, -- T. 3.6
`
`clhi.
`
`-H = -1.28 + 0.12(1.8) = -1.1 mV/F. at 70° F (Q.E.D.)
`
`2 5
`
`dVhealTis, from Ref. 1, pp 131, -2.3 millovolts per de
`gree Centrigrade = -1.28 millovolts per degree Fahr
`enheit at room temperature for the silicon transistor.
`The rate of change of output voltage with respect to
`temperature is therefore:
`
`30
`
`Eq 3
`
`d
`all
`
`= 2.6 (-1.8) = -3.3 mVf F. at 7() F.
`
`35
`
`It has thus been shown that the power supply shown
`in FIG. 4 has the desired temperature coefficient of
`output voltage -1.1 millivolts per degree Fahrenheit at
`room temperature. Reference to Eq. 6 shows that this
`temperature characteristic is only mildly dependent on
`dV/dI at the nominal output voltage of 1.5 volts.
`The Zener is supplied current from a source transistor
`stage T7. The current supplied by T7 is temperature
`dependent but since the Zener voltage is weak function
`of Zener voltage (see Eq. 4 with V = 1.5 and V. = 7.5)
`the temperature dependency of the current through
`transistor T7 has very little influence on the tempera
`ture coefficient of output voltage. The function of T7 is
`40
`to stabilize the Zener bias current against unregulated
`supply voltage variations. It can further be stated that
`dViefdI is indeed a very weak function of temperature
`(Ref. 1, pp 131) so that dWo/all is virtually a constant
`-l. 1 millivolts per degree of Fahrenheit over a wide
`range of temperatures, which is a desirable characteris
`tic. Experimental measurements have verified this con
`clusion: The temperature characteristic has been dem
`onstrated in the laboratory to be a constant -1.1 milli
`volts per degree of Fahrenheit over the temperature
`range -20° to 85° Centigrade.
`The Ref. 1 referred to above is Electronic Devices and
`Circuits, Millman and Halkias; McGraw-Hill, 1967.
`In the circuit shown an A.C. line is connected to the
`primary winding of the transformer 10 which has a sec
`ondary winding 11 having its outer terminals connected
`to the full wave rectifier 12 made up of diodes RD1,
`RD2, RD3 and RD4. The output of the full wave recti
`fier 12 is connected to lines 14 and 15. Lines 14 and 15
`are connected to capacitors C1 and C2 which are con
`nected in series with each other. The junction 16 of ca
`pacitors C1 and C2 is connected to line 17 which is
`connected to the center tap of the secondary winding
`11. Line 15 is connected to diode RD6 and to resistor
`RD12. Line 14 is connected to the emitter of transistor
`T4 to the resistor R5 and to resistor R9 and to the Zener
`diode ZD1 and capacitor C5.
`What is claimed is:
`
`The desired temperature coefficient at room tempera
`ture is -1.1 millivolt per degree F. It will now be shown
`that the insertion of the missing elements results in the
`desired temperature characteristic. A simplified dia
`gram of the circuit of FIG. 4 is shown in FIG. 3.
`Assuming that the base current IB5 is much smaller
`than the bleeder current It:
`V = V -- ILR
`Where the bleeder current It is constrained by the
`Zener diode ZD1 to obey the relationship:
`
`I. F
`
`.
`R - R2
`
`Inserting this into the expression for output voltage:
`
`Eq. 4
`
`=
`
`i.
`
`R
`R1 + R.
`
`''
`
`45
`
`Taking the derivative with respect to temperature, as
`suming that the resistances of R1 and R2 are constant
`with temperature:
`
`60
`
`clo
`alT
`
`dihe
`all
`
`d
`lT
`
`Exhibit 1033 - Page 5 of 6
`
`

`

`3,919,616
`5
`1. A power supply circuit for charging a battery hav
`a transistor,
`ing a temperature-voltage coefficient comprising
`said transistor having a base, an emitter, and a collec
`a voltage supply,
`a reference means connected to said voltage supply
`said base of said transistor being connected to said
`for controlling the voltage of said supply,
`Zener diode,
`said reference means having a temperature coeffici
`means for connecting said base emitter Voltage to a
`ent similar to the said temperature coefficient of
`battery to be charged,
`said battery being charged,
`said transistor and said Zener being so connected that
`output means connected to said voltage source, a
`said output voltage is equal to said base emitter
`current source connected to said reference means, 10
`said current source being independent of the voltage
`voltage plus a constant times said Zener Voltage and
`of said battery being charged,
`said constant is equal to or less than one.
`a Zener diode comprising said reference,
`
`6
`
`-
`
`tor,
`
`5
`
`5
`
`40
`
`50
`
`60
`
`65
`
`Exhibit 1033 - Page 6 of 6
`
`