US 3403264 A
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Sept. 24, 1968 4 6 2, w A B 4", M D 3 O M L L S m. w\\ n H w m E R H 5 I 6 w m w A M I OLl\ W F .L 2 5m 7 R R p G A 0 e A L T s T U A A d MG 6 L E U M ul\ R J m i I F R F E G n mil/m V ML MI POWER SOURCE CLASS 8 AUDIO AMPLIFIER HORIZONTAL DEFLEC I'ION CIRCUIT VOL I AGE RE GULA TOR IN VENTOR. JAMES A. RONBACK United States Patent 3,403,264 VOLTAGE REGULATOR FOR MULTIPLE LOABS James A. Rollback, Kitchener, Ontario, Canada, assignor to Eiectrohome Limited, Kitchener, Ontario, Canada Filed Sept. 28, 1965, Ser. No. 490,892 9 Claims. (Cl. 30732) This invention relates to voltage regulation. More particularly, this invention relates to the voltage regulation of an arbitrary load when it is one of a number of loads connected in parallel, at least one of the other loads being variable. This invention also relates to the voltage regulation of an arbitrary load supplied with DC. power from a DC. power source which supplies the arbitrary load and other loads in a television receiver, at least one of the other loads being variable.
It is often desired to supply power from a power source through a voltage regulator to two or more loads. If one of these loads is variable, however, and the current demanded by the load is increased, the output voltage of the voltage regulator will decrease as the demand for additional current is met. This decrease in the output voltage of the voltage regulator is due to the increased voltage drop across the voltage regulator caused by a larger current passing through the internal resistance of the voltage regulator to meet the increased current demand of the variable load.
Conventional, simple voltage regulators have what is commonly termed a drooping characteristic, i.e., a graph showing output voltage of the regulator plotted against output current thereof will be a substantially straight line exhibiting a slowly decreasing output voltage with increasing output current over the operating range of the voltage regulator. Stated in another way, the voltage regulation achieved with such a voltage regulator is not perfect. This presents a substantial problem in a television receiver, for example, where it is desirable to be able to feed fixed and variable loads from a single DC. power source. As an example, in a television receiver that includes a Class B push-pull audio amplifier and a horizontal deflection circuit, it is desirable to employ a single DC. power source for both circuits. However, for proper operation of the horizontal deflection circuit, which is a substantially fixed load, a well regulated B+ is required, since, as B-ldecreases, the picture size also decreases. On the other hand, a Class B push-pull audio amplifier has varying current requirements with varying signal input. Changes in the current drawn by the amplifier will cause variation in the DC. output voltage, 3+, of the voltage regulator, because the voltage regulation of the regulator is not perfect. Consequently B+ for the horizontal deflection circuit will vary with the aforementioned undesirable consequences.
In accordance with this invention, there is provided a circuit which will maintain the voltage supplied to an arbitrary load at a substantially constant value, while also supplying the varying current requirements of a variable load. This is achieved, in accordance with this invention, by sensing and supplying to a voltage regulator a signal that is not just the output voltage of the regulator, as has been done in the past, but which includes a component indicative of the current drawn by only the variable load.
This invention will become more apparent from the following detailed description, taken in conjunction with the appended drawings, in which,
FIGURE 1 is a block diagram illustrating this invention, and
FIGURE 2 is a diagram, partly in block form, showing how this invention may be applied in a television receiver.
3,403,264 Patented Sept. 24, 1968 Referring to FIGURE 1, there is shown a power source 10, which may be A.C. or D.C., but which will be considered as a DC. power source, that produces an unregulated and partially filtered DC. voltage, and which may be of any known type, a conventional voltage regulator 11 having an output terminal 12, two loads designated load A and load B, the former being variable and the latter being substantially fixed, and a resistor R1. Load A requires good voltage regulation, whereas load B does not.
DC. power from DC. power source 10 is supplied via a conductor 13 from the output terminal 14 of DC. power source 10 to the input terminal 15 of voltage regulator 11. A regulated DC. voltage is supplied to the input terminal 16 of load B via a conductor 17 connected between output terminal 12 of voltage regulator 11 and input terminal 16. Resistor R1 is connected between output terminal 12 of voltage regulator 11 and the input terminal 18 of load A, and the DC. current supplied to load A passes through resistor R1. The DC. voltage at the terminal 19 of resistor R1 is equal to the difference between the DC. output voltage V of voltage regulator 11, which voltage appears at output terminal 12, and the voltage drop I RI across resistor R1 caused by the passage through resistor 21 of the DC. current I to meet the demands of load A. The voltage at terminal 19 is fed back to voltage regulator 11 via a conductor 20 and results in variations in the internal resistance of voltage regulator 11 that are such as to maintain V substantially constant while I varies.
How this is achieved may best be explained in connection with FIGURE 2 in which the same reference numerals as used in FIGURE 1 indicate the same components as designated FIGURE 1, and wherein load A is a Class B push-pull audio amplifier 21 of a television receiver, while load B is the horizontal deflection circuit 22 of the television receiver. Loads 21 and 22 have signal input terminals 21a and 22a respectively.
Before a description of FIGURE 2 is commenced, however, it should be noted that if power source 10 is an A.C. power source, resistor R1 could be a capacitor or an inductance coil dependent on the nature of load A. In other words, if a DC. voltage is being supplied to load A and regulated, resistor R1 must be a DC. impedance. If an A.C. voltage is being supplied to load A and regulated, resistor R1 could be replaced by an A.C. impedance such as a capacitor or an inductance coil.
Voltage regulator 11 of FIGURE 2 is conventional in nature and includes two transistors TR1 and TR2 of different conductivity type, resistors R2 and R3, a Zener diode D1 and a potentiometer P1 having a slider 23.
Input terminal 15 is connected to the emitter electrode of transistor TR2, while the collector electrode thereof is connected to output terminal 12. Resistor R2, which merely provides a path for starting current, and which performs no function when voltage regulator 11 is operating, is connected between the emitter and collector electrodes of transistor TR2.
The collector electrode of transistor TR1, which may be referred to as the error signal amplifying transistor, since this is the function performed thereby, is directly connected to the base electrode of transistor TR2, which may be referred to as the series regulating transistor. The emitter electrode of transistor TR1 is connected through resistor R3 to ground. The base electrode of transistor TR1 is directly connected to slider 23 of potentiometer P1, the latter component being connected between output terminal 12 of voltage regulator 11 and ground.
Zener diode D1 is connected via conductor 20 and a conductor 24 between terminal 19 and the emitter electrode of transistor TR1. In the past no resistor R1 has r 3 been provided, and Zener diode D1 has been connected to output terminal 12.
For purposes of discussion it will be assumed that it is desired to maintain the DC. output voltage V of voltage regulator 11 at output terminal 12 at ten volts, and that the Zener voltage (drop across Zener diode D1) is seven volts. Under normal operating conditions, the voltage drop across resistor R3 then will be threevolts, and slider 23 will be set so that the voltage drop between slider 23 and ground will be just slightly greater than three volts.
Suppose now that load 21 demands additional DC. current. The additional DC. current to meet this demand will flow from D.C. power source through voltage regulator 11 and resistor R1 to load 21, and voltage V will decrease relative to ground, say to nine volts, because of the increased voltage drop across voltage regulator 11 due to the larger current now passing through the voltage regulator. If Zener diode D1 were connected to output terminal 12, the resultant decrease in V to nine voltts would cause the impedance of transistor TR2 to decrease, because the base to emitter voltage of transistor TR1 would increase, since the voltage drop across Zener diode D1 is fixed at seven volts and the change in voltage across resistor R3 (one volt) would be greater than the change in voltage between slider 23 and ground, thus causing transistor TR1 to draw more current, and thus causing V to increase, but, because of the drooping characteristic of voltage regulator 11, V would not return to the value it had prior to the increase in current delivered to load 21. However, in accordance with this invention, the voltage which is sensed and fed back to voltage regulator 11 is not just the DC. output voltage V thereof, but
where 1 is the D.C. load current supplied to load 21. This voltage obviously is less (relative to ground) than V so that in this case the error signal, which is the base to emitter voltage of transistor TR1, is larger (relative to ground) than the error signal which results when Zener diode D1 is connected to output terminal 12 and includes a component that is dependent on the magnitude of the current drawn by load 21 alone.
The increase in the base to emitter voltage of transistor TR1 which results under the foregoing conditions causes the internal impedance of regulator 11 (the emitter to collector resistance of transistor TR2) to decrease, and to decrease more so than if Zener diode D1 has been connected to output terminal 12. This has the effect of returning V to its original value, while also permitting load 21 to draw the larger current demanded. By proper selection of resistor R1, which generally will be quite small in value, say of the order of one ohm, the voltage regulation of voltage regulator 11 can be made almost perfect over a definite operating range. It is even possible by varying the value of resistor R1, to cause overcompensation.
Those skilled in the art will appreciate that other voltageregulators than the one illustrated may be used in the practice of this invention, and vacuum tube type voltage regulators may be employed. Other reference voltage sources such as a battery may be employed in place of the Zener diode. It also will be apparent that this invention may be used with more than one variable load to compensate for the undersirable effects on one arbitrary load that otherwise would be caused by variations of the variable loads.
While a preferred embodiment of this invention has been disclosed herein, those skilled in the art will appreciate that changes and modifications may be made therein without departing from the spirit and scope of this invention as defined in the appended claims.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. In combination, a power source for producing a voltage and current; a first load, said first load being variable and demanding varying amounts of said current from said power source; a second load; a voltage regulator for maintaining the voltage supplied to said second load from said voltage regulator substantially constant during variations in the current demanded by said first load, said voltage regulator having first and second input terminals and an output terminal; means connecting said power source to deliver power to said first input terminal; means connecting said output terminal to said second load to deliver a regulated voltage thereto; and means connecting said output terminal to said first load to deliver power thereto, said last-mentioned means including an impedance connected in series between said output terminal and said first load, said second input terminal being connected between said impedance and said first load to supply a signal to said voltage regulator to increase the internal resistance thereof in response to an increase in said signal and to decrease the internal resistance thereof in response to a decrease in said signal.
2. The invention according to claim 1 wherein said impedance is a resistor.
3. The invention according to claim 2 wherein said signal is the difference between the voltage appearing at said output terminal and the voltage drop across said resistor due to passage through said resistor of the current supplied to said first load from said output terminal.
4. The invention according to claim 1 wherein said voltage regulator includes first and second transistors each having a base electrode, a collector electrode and an emitter electrode, a source of reference voltage, a first resistor and a potentiometer having a slider, means connecting said potentiometer between said output terminal and a reference potential, means connecting said first resistor in series between said emitter electrode of said first transistor and said reference potential, means connecting said source of reference voltage between said second input terminal and said emitter electrode of said first transistor and in series with said first resistor, means connecting said slider and said base electrode of said first transistor, means connecting said emitter electrode of said second transistor and said first input terminal, means connecting said collector electrode of said second transistor and said output terminal, and means connecting said collector electrode of said first transistor and said base electrode of said second transistor.
5. The invention according to claim 1 wherein said source of reference voltage is a Zener diode.
6. The invention according to claim 5 wherein said impedance is a resistor.
7. The invention according to claim 6 wherein said signal is the difference between the voltage appearing at said output terminal and the voltage drop across said resistor due to passage through said resistor of the current supplied to said first load from said output terminal.
8. In a combination, a power source for producing a voltage and current; a first load, said first load being vari-- able and demanding varying amounts of said current from said power source; a second load; a voltage regulator for maintaining the voltage supplied to said second load from said voltage regulator substantially constant during variations in the current demanded by said first load, said voltage regulator having an input terminal and an output terminal; means connecting said power source to deliver power to said input terminal; means connecting said output terminal to said second load to deliver a regulated voltage thereto; and means including an impedance connecting said output terminal to said first load to deliver power thereto; said voltage regulator including means connected between said first load and said impedance for sensing a first voltage that varies in accordance with the voltage supplied to said first load, means connected to said output terminal for sensing a second voltage that varies in accordance with the voltage supplied to said second load, means for deriving an error voltage from said first and second voltages, and means for varying the in- References Cited ternal resistance of said voltage regulator in accordance UNITED STATES PATENTS W1th variations in said error signal, said internal resistance increasing in response to increases in said first and 1,414,248 4/1922 Armor 30732 second voltages and decreasing in response to decreases 5 2307217 1/1943 Hansen in said first and second voltages.
9. The invention according to claim 8 wherein said ROBERT SCHAEFER P'lmary Exammer' impedance is a resistor. H. J. HOHAUSER, Assistant Examiner.