US 3747008 A
A power supply producing a bi-polar reference voltage uses a constant votage element, such as a zener diode, in a negative feedback loop from the reference voltage output of an amplifier to the input of another amplifier in a two amplifier system. This negative feedback loop permits the establishment of a reference voltage output lower in magnitude than the voltage of the constant voltage element.
Description (OCR text may contain errors)
United States Patent [191 Zaretsky [111 3,747,008 [451 July 17, 1973 REFERENCE POWER SUPPLY HAVING AN OUTPUT VOLTAGE LESS THAN ITS CONTROL ELEMENT Inventor: Leo G. Zaretsky, San Diego, Calif.
Assignee: Control Data Corporation,
Minneapolis, Minn. Filed: Dec. 23, 1971 Appl. No.: 211,499
US. Cl 330/110, 323/23, 330/69, 330/148 Int. Cl. H03! H36 Field of Search 330/9, 30 R, 69, 330/100, 110, 148; 323/23 References Cited UNITED STATES PATENTS 7/1971 Gordon 340/347 AD 3,133,242 5/1964 Harries 323/22 Primary Examiner-Roy Lake Assistant Examiner-James B. Mullins Attorney-William J. McGinnis, Jr. et al.
 ABSTRACT A power supply producing a bi-polar reference voltage uses a constant votage element, such as a zener diode, in a negative feedback loop from the reference voltage output of an amplifier to the input of another amplifier in a two amplifier system. This negative feedback loop permits the establishment of a reference voltage output lower in magnitude than the voltage of the constant voltage element.
7 Claims, 1 Drawing Figure 20 out PAINTED- 3,747. 008
/4 20 ouf REFERENCE POWER SUPPLY HAVING AN OUTPUT VOLTAGE LESS THAN ITS CONTROL ELEMENT BACKGROUND OF THE INVENTION This invention relates to reference power supplies employing constant voltage or current control elements as a standard for regulation of output values. More particularly, this invention relates to a negative feedback circuit containing a constant voltage control element which provides a bi-polar output voltage less in magnitude than that of the constant voltage element.
Although constant voltage elements, such as zener diodes, have been used in feedback loops, no known prior art power supply produces an output voltage less than the zener diode voltage without the use of a voltage divider or inverting amplifier. Either of these techniques tend to make the power supply stable. It has also been difficult to build stable bi-polar reference supplies because of constant current requirements for the reference element and the temperature coefficient of the reference element. It is well known in the electronic art that the zener elements in the 6.4 and 9.4 voltage range can provide extremely low temperature coefficients. Therefore, it is desirable to design reference supplies utilizing these reference elements. It is clear that a stable bi-polar reference supply producing voltages less than the constant voltage element would be desirable.
SUMMARY OF THE INVENTION A reference voltage supply is provided using a constant voltage element as a standard, which has a voltage greater in magnitude than the output reference voltages which the supply may produce.
In one embodiment of the invention, a pair of amplifiers are cascaded together, the output of the first connected to the input of the second and the output of the second to the input of the first. The amplifiers are connected so that a phase reversal occurs between the positive input of the first amplifier and the output of the second amplifier. The outputs of the first and second amplifiers are the reference voltage outputs of the supply. They generally are equal but opposite in polarity. A constant voltage element, such as a zener diode, as illustrated in this embodiment of the invention, is connected between the reference voltage output of the second amplifier and the input of the first amplifier so as to provide a negative feedback loop within the system. In the present embodiment of the invention, the gain of the second amplifier remains at a fixed value while the gain of the first amplifier is adjusted within predetermined limits to provide a bi-polar output voltage which varies from a fraction of the reference element voltage to the maximum amplifier output voltage. The gain of the second amplifier can also be varied. If it is varied, however, reference voltages of opposite polarities but unequal valuewill result. With this method the output of the first amplifier can be adjusted to almost zero volts. Anyone skilled in the state of the arts of circuit design can find a multitude of other uses. Inverting the zener polarity will change the polarities at the outputs of the first and second amplifiers. The circuit configuration is such that the zener diode carries a constant current which contributes to a highly stable circuit.
IN THE FIGURES The single FIGURE is an electrical schematic diagram of one embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGURE illustrating one form of the invention, the positive output of a first amplifier I0, indicated symbolically, is connected through a re sistor 12 to the positive input of an amplifier 14, also indicated symbolically. Both amplifiers are of a conventional type having a high impedance input, low impedance output, and very high gain. Of course, additional circuits or amplifiers may be connected between amplifiers l0 and 14 to improve stability or improve accuracy of output voltage control without departing from the inventive concept.
The minus input of amplifier 10 is connected to one end of resistor 16 and to variable resistor 18 which, in turn, is connected to the positive output of amplifier 10. It is well understood in the electronics art that resistors 16 and 18 determine the gain of the amplification stage, and as will be seen, adjustment of variable resistor 18 therefore allows adjustment of the reference voltage outputs provided at terminals 20 and 21, 20 from the minus output of amplifier l4 and 21 from the plus output of amplifier 10. The zener diode can be inverted in this circuit to produce opposite polarities at output terminals 20 and 21.
A positive source voltage is provided at terminal 22 and current flows through resistor 24 to the positive output of amplifier 10. Also connected to the positive output of amplifier 10 is a feedback resistor 26 which is connected with the positive input to amplifier 10. Resistor 26 provides the constant voltage element with a constant current which is stable within the same limits as the output voltages. By maintaining the power dissipation essentially constant in the constant voltage element, circuit stability is improved.
A constant voltage element 28, which is shown in the FIGURE as a zener diode, in this form of the invention, is connected in a negative feedback loop from the positive input of amplifier 10 to the negative output of amplifier 14. It has been found that a temperature compensated zener diode will work quite well in this form of the circuit. Resistor 30 connects the minus output of amplifier 14 with a negative source voltage at terminal 32.
The other end of resistor 16 is connected with the anode of the'zener diode as shown in the FIGURE for this form of the invention. This arrangement of resistor 16 provides an additional feedback path which tends to increase the stability of the circuit with respect to changes in component values. By selecting values correctly the other end of resistor 16 may also be connected to ground potential, in other forms of the invention, with acceptable regulation but slightly decreased stability.
A negative feedback resistor 34 is connected from the positive input of amplifier 14 to the output of that amplifier. For purposes of explaining the circuit, the voltage of the constant voltage element 28 is shown at terminals 36, 36 as voltage V,.
The gain of the amplifier stage incorporating amplifier 14 may be set at unity in order to provide equal but opposite polarity reference voltages. This gain is set by than V,.
Circuit elements which have been found to work in this embodiment of my invention are: zener voltage 6.2 volts, supply voltages equal to plus and minus volts respectively,resistor 12 resistor 34 10 K ohm, resistor 16 6.2 K ohm, resistor 18 3.8 K ohm, and resistor 26 500 ohms. Reference output voltages are approximately plus and minus 5 volts.
1. A power supply for producing a reference voltage comprising:
first and second amplifiers each having input and an output;
said first amplifier being responsive to an input voltage to produce an output voltage having the same polarity as said input voltage, said second amplifier being responsive to said output voltage to produce said reference voltage at its output, said reference voltage having a polarity opposite to that of said output voltage;
a negative feedback loop connecting the output of said second amplifier to the input of said first amplifier, said feedback loop including a zener diode so disposed and arranged that the more negative of said input voltage and said reference voltage appears at its anode and the more positive of said input voltage and said reference voltage appears at its cathode; and
a voltage source connected to the output of said second amplifier through a resistance, said source providing a voltage having the same polarity as said reference voltage.
2. The power supply of claim 1 and further comprising means for controlling the gain of at least one of said amplifiers within predetermined limits.
3. The power supply of claim 1 wherein said reference voltage is of negative polarity and wherein the anode of said zener diode is connected to the output of said second amplifier and wherein the cathode of said zener diode is connected to the input of said first amplifier.
4. The power supply of claim 3 wherein the output of said first amplifier is connected through a resistance to a voltage source of positive polarity and further comprising means for controlling the gain of at least one of said amplifiers, whereby the reference voltage output of said power supply may be varied in bi-polar fashion about a zero voltage.
5. The power supply of claim 3 wherein the gain of said first amplifier is controlled by a variable resistor connected between the output of said first amplifier and a second input of said first amplifier having an opposite polarity to said first-named input, said first amplifier having an additional feedback loop in the form of a resistor connected between said second input and the anode of said zener diode.
6. The power supply of claim 5 wherein the output of said first amplifier is connected through a resistance to a voltage source of positive polarity.
7. The power supply of claim 6 further including a further feedback loop in the form of a resistor connected between the cathode of said zener diode and the output of said first amplifier.