US 3829717 A
Description (OCR text may contain errors)
United States Patent [191 Harrison Aug. 13, 1974 REFERENCE VOLTAGE COMPENSATION FOR ZENER DIODE REGULATION CIRCUIT  Inventor: Clarence E. Harrison, Madison Heights, Mich.
 Assignee: Ford Motor Company, Dearborn,
 Filed: Jan. 29, 1973  App]. No.: 327,279
 US. Cl 307/297, 307/237, 307/310, 307/318  Int. Cl. H03k 1/14  Field of Search 307/318, 310, 297, 237
 References Cited UNITED STATES PATENTS 2,905,835 9/1959 Wray 307/318 3,114,872 12/1963 Allard 1.
3,156,832 11/1964 Mollinca 3,192,441 6/1965 Wright .1
3,227,942 l/l966 Bunch .1
3,289,050 11/1966 Duval 3,317,817 5/1967 Gershen 3,320,493 5/1967 Culbertson....
3,374,361 3/1968 Callis 3,445,664 5/1969 Martens 307/310 OTHER PUBLlCATIONS Smith, Reference Voltage With Adjustable Temperature Coef." Vol. 9, No. 12, March 1967 of IBM Tech. Bull. Pages 1808-1809.
Learned Zener Diodes Application Notes Motorola Semiconductor December 1960 AN 103 3 pages.
Primary Examiner.lohn S. Heyman Attorney, Agent, or FirmRobert A. Benziger; Keith L. Zerschling 5 7 ABSTRACT A circuit is disclosed for providing a constant regulated voltage to a load in conjunction with a first stage zener diode regulation circuit. The circuit compensates for regulated voltage variations incident to zener diode internal resistance by applying the zener diode regulation voltage to a voltage divider which goes to ground and using the voltage differential between the intermediate junction of the voltage divider resistances and the anode of the zener diode and by further communicating the anode of the zener diode to ground through an additional, compensating, resistance. The value of this resistance may be determined by multiplying the internal resistance of the zener diode by the ratio of the resistance of the voltage divider from the intermediate junction to ground divided by the resistance from the intermediate junction to the cathode of the zener diode.
8 Claims, 3 Drawing Figures PATENTEDAus 13 I974 lllll REFERENCE VOLTAGE COMPENSATION FOR ZENER DIODE REGULATION CIRCUIT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is related to the field of circuitry for providing regulated voltages to utilization means. More particularly, the present invention is related to that portion of the above noted field in which a circuit including a zener diode member is connected to a DC power supply to provide a constant voltage DC source for a load.
2. Description of the Prior Art The prior art generally teaches that a zener diode operated in the breakdown region will provide a virtually uniform voltage drop between its cathode and anode terminals. The prior art makes use of this fact to provide constant DC voltage sources of known voltage levels by either (1) using a suitably sized zener diode member to directly provide the desired voltage or (2) by taking a convenient zener diode member having a known voltage drop capability and placing this device in parallel with a voltage divider network having a pair of resistances sized to provide the desired differential between their voltage junction and the anode of the zener diode member. The prior art circuits have typically connected the anode of the zener diode member and the low voltage portions of both the voltage divider means and the load to a common potential with a current limiting resistance in series between the zener diode member and a primary source of DC voltage. However, it is well known that zener diodes operated in the breakdown region exhibit a small amount of internal resistance which may be, for example, on the order of about ohms for zener diodes having breakdown voltage of about 10 volts or less. The cost of zener diode members is frequently dependent upon how small the internal resistance value may be. For example, a zener diode having an internal resistance on the order of about 2 ohms will be more expensive than a zener diode member having an internal resistance on the order of about 10 ohms for zener diodes having the same voltage breakdown characteristic. As a result of this internal impedance or resistance, the voltage drop across the zener diode will vary in proportion to current flow through the device which may be caused by voltage variations in the associated source. In the application of such a regulating circuit to, for example, an automotive electrical system powered by the normally provided battery, fluctuation in the voltage of the primary source, the battery, would cause a fluctuation in the regulated voltage.
In automotive electrical systems wherein the regulated voltage is used to energize a sensor such as a thermistor which may be monitoring, for example a critical engine parameter for the purpose of engine control or for the purpose of exhaust emission reduction, fluctuation in a regulated voltage value may readily result in false readings or false control signals which would be considered deleterious to the operation controlled or monitored by the associated sensor. It is, therefore, a specific object of the present invention to provide electrical circuitry for generating a constant voltage which does not fluctuate in the presence of fluctuations of the primary or energizing voltage. More specifically, it is an object of the present invention to provide electrical circuitry for association with a primary source of electrical energy which primary source may demonstrate a significant variation in the voltage potential for providing a constant reference voltage. It
is a further object of the present invention to provide such a circuit which is capable of offsetting the effect of reference voltage variations induced by the internal resistance of the zener diode. More specifically still, it is an object of the present invention to provide such a circuit in which relatively inexpensive zener diode members (that is zener diode members having relatively high amounts of internal resistance when operated in the breakdown region) may be used while a constant reference voltage is being generated.
SUMMARY OF THE PRESENT INVENTION The circuit of the present invention provides a resistive voltage divider interconnecting the cathode of the zener diode member to the electrically negative primary voltage supply terminal and having a terminal for connection to the electrical load. The anode electrode of the zener diode member is also provided with means for connection with the electrical load and a compensating resistive member interconnects the anode electrode of the zener diode member with the electrically negative terminal of the primary source. The resistive value of the compensating resistance is determined by multiplying the internal resistance of the zener diode member by the ratio of the resistance in'the voltage divider between the terminal and the electrically more negative terminal of the primary voltage supply divided by resistance of the voltage divider network between the terminal and the cathode of the zener diode member.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the voltage characteristic of the zener diode operated in the breakdown region.
FIG. 2 illustrates a prior art form of the voltage regulator containing a zener diode member.
FIG. 3 illustrates the circuit of the present invention in a preferred schematic.
DETAILED DESCRIPTION OF THE DRAWING Referring now to FIG. I, a graph is shown illustrating a typical voltage and current characteristic for a zener diode operating in the breakdown region. Voltage across the zener diode is graphed on the horizontal axis while current flow through the zener diode is graphed on the vertical axis. When operated in the breakdown region, the cathode of the zener diode is biased to an electrically more positive value than is the anode of the zener diode member. Current flow through the diode from the cathode to the anode is graphed in FIG. 1 as positive current flow. For voltages impressed across the zener diode member having values less than the V value, the zener diode will act as a true diode and will block current flow therethrough. In an ideal zener diode, the voltage potential difference between the anode and cathode electrodes will not increase above the V value for increasing current flow through the zener diode member. This is illustrated by the dashed vertical line identified as IDEAL in FIG. 1. In actual practice however, there will be a slight increase in the voltage potential difference between the anode and cathode electrodes for increasing current flow through the zener diode member resulting from internal resistance of the zener diode member. This is denoted by the solid line curve identified as ACTUAL in FIG. 1. The angle at which the ACTUAL curve departs from the vertical varies from one zener diode member to another only as their internal resistances may vary with this deviation angle becoming very small in more expensive zener diode members.
Referring now to FIG. 2, the prior art voltage regulation technique utilizing a zener diode member is illustrated. According to the prior art, a primary power source having a terminal denoted as B-lwould be connected to a current limiting resistor 12 with the other lead of the current limited resistor 12 connected to the cathode electrode 14 of a zener diode member 10. The anode electrode 16 of the zener diode member 10 will be communicated back to the electrically negative lead of the primary power supply through, for example, a common ground connection as illustrated. As illustrated, the zener diode member 10 is comprised of an ideal zener diode 18 in series with a resistance 20 illustrative of the internal resistance of commercially available zener diode members. The resistive value of the resistance 20 may be on the order of, for example, about 10 ohms for breakdown voltages on the order of 10 volts. Other values of internal resistance and breakdown voltage are often encountered.
The primary power supply whose terminal is designated as B-lmay be, for example, a source of DC voltage having a value which may range over a relatively wide region. Zener diode members are available rated at a variety of voltage differentials, a typical example of which would be MZ 1,000-12, available from Motorola Semiconductor Products, Inc., having a voltage differential or breakdown voltage of 9.1 volts nominal. In this arrangement, the current limiting resistance 12 would operate to provide for dissipation of the B+ voltage down to the zener diode voltage and would insure that the current flow through the zener diode member did not reach a value sufficiently large to destroy the device.
In order to provide a regulated output voltage at a fixed value, and without requiring specially fabricated zener diode members, a voltage divider network comprised of a pair of resistances 22 and 24 would be connected in parallel with the zener diode member 10. Resistance means 22 and 24 would then be sized to provide at their intermediate junction 26 a voltage potential with respect to the ground or common terminal of the power supply which is equal to the desired regulated voltage. This voltage could then be applied to a load which may be for example a temperature sensing thermistor 28. According to the prior art, the anode electrode of zener diode member 10, and the low voltage sides of the resistive voltage divider and the load element would all be connected or communicated directly to the low voltage terminal of the primary power supply as, for example, through a common ground connection as illustrated in FIG. 2. In the application of this type of voltage regulation circuit to a primary power supply which demonstrates a significant variation in the potential between its output terminals, as for example the battery commonly used in an automotive electrical system, the voltage fluctuations occurring at the B+ terminal with respect to the common ground would result in significant voltage fluctuation appearing at the intermediate terminal 26 which could readily induce the aforementioned false signals from the sensor or control device represented in this case by the load thermistor 28.
Referring now to FIG. 3, a circuit illustrating the present invention is shown and will be described. For purposes of comparison, the various elements within the FIG. 3 circuit which have direct counterparts in the FIG. 2 circuit bear identical numbers. In the FIG. 3 circuit, the low voltage lead of the load represented by thermistor 28 is connected to the anode electrode 16 of the zener diode member 10 while the low voltage side of the voltage divider resistances 22 and 24 is connected to the common ground. The anode electrode 16 of the zener diode member 10 and the low voltage side of the load 28 are communicated to the common ground through compensating resistance 30. In order to illustrate the operation of the present invention, the current flow through the zener diode is given as 1 the current flow into the high voltage branch of the voltage divider means is given as l the voltage appearing at the cathode of the zener diode 10 is given as V and the current flowing through the load is given as I Writing equations for the circuit of FIG. 3
V V +I R (I 1,) R
where V; is the breakdown voltage rating of the zener diode member 10, and
VL u u 24) V IL) 30 where V is the voltage across the load, the regulated voltage value, and I is very much less than 1 as is normally the case.
Substituting Equation (1) into Equation (2) yields VL W; z 20 IL) 30] u/ 22 24) IL) 30 However, for most, if not all, practical applications of constant voltage to sensory or control elements is the load, the zener current will be very much larger than the load current so that Equation (3) reduces to VL z 20 30) u/ 22 24) 30 Differentiating Equation (4) with respect to the zener current, 1 yields the change in the regulated or load voltage as a function of zener current. The resultant equation is L z 20 30) u/ 22 24) 30 Setting Equation (5) equal to zero expresses the desired situation of the regulated or load voltage being constant for changing zener current so that R30 R30 (RM/R22 R24) R20 (R24/R22 R24) Solving Equation (6) provides the equation expressing the necessary value of R for Equation (5) to be satisfied. This value is I claim:
1. A constant voltage source circuit for association with a DC voltage power supply having a pair of supply terminals and producing a first potential therebetween, comprising in combination:
a limit resistor having a pair of leads connected by one of said pair of leads to one terminal of the power supply;
a zener diode having a cathode electrode and an anode electrode, connected by one of said electrodes to the other of said pair of limit resistor leads, adapted to provide a second potential at said one electrode;
voltage divider means interconnecting said other limit resistor lead and the second terminal of the power supply and having an intermediate terminal for connection to one side of a load operative to reduce said second potential to a third potential for energizing the load; and
a compensating resistor having a pair of leads, one of said pair of leads connected to the other electrode of said zener diode and the other of said pair of leads connected to the other terminal of the power supply, said one lead connectable to the other side of the load whereby variations in the regulation provided by the zener diode and caused by the zener diode internal resistance may be compensated.
2. The voltage source circuit of claim 1 wherein the compensating resistor has a value equal to the internal resistance of the zener diode multiplied by the resistive value of the portion of the voltage divider means interconnecting the intermediate terminal and the power supply other terminal, and divided by the resistive value of the portion of the voltage divider means interconnecting the intermediate terminal and said limit resistor other lead.
3. In a constant voltage source of the type having a zener diode connected to a supply and providing a regulated voltage and a voltage divider receiving the regulated voltage and reducing it to a desired value for application to a load, the improvement comprising a compensating resistor electrically connected in series with the zener diode and connectable in series with the load whereby the series combination of the zener diode and the compensating resistor are electrically in parallel with the voltage divider, and the series combination of the load and the compensating resistor will be electrically in parallel with a portion of the voltage divider.
4. The improvement of claim 3 wherein the compensating resistor, R has a value determined by the expression 1 U u R11) where R is the internal resistance of the zener diode,
' R is the resistance of the portion of the voltage divider a current limiting resistance means having a pair of leads, one of said pair of leads communicating with said first terminal;
a compensating resistance means having a pair of leads, one of said pair of compensating resistance leads communicating with said second terminal;
a zener diode having a cathode and an anode, said cathode being connected to said limiting resistance means other lead and said anode being connected to said compensating resistance means other lead; and
a voltage divider having first and second interconnected resistance means, a pair of leads and an intermediate terminal, one of said pair of leads being connected to said cathode and the other of said pair of voltage divider leads communicating with the power supply second terminal;
said intermediate terminal being connectable to one side of a load for providing a source of voltage to the load, the other side of the load being connectable to said anode electrode of said zener diode whereby the load will receive a constant voltage differential between said intermediate terminal and said zener diode anode.
6. The constant voltage source of claim 5 wherein said compensating resistance means has a resistive valve substantially equal to the internal resistance value of the zener diode multiplied by the resistive value of the portion of the voltage divider interconnecting the intermediate terminal with the power supply second terminal and divided by the resistive value of the portion of the voltage divider interconnecting the intermediate terminal with the cathode electrode of the zener diode.
7. ln an electrical system of the type having a rechargeable battery with electrically positive and electrically negative terminals for providing a source of electric energy and wherein the electric potential difference between said terminals may vary, a circuit connected to the battery for providing a constant regulated voltage supply independent of battery potential difference variations comprising in combination:
a curent limiting resistance means having a pair of lea s;
a compensating resistance means having a pair of leads;
a zener diode having an anode electrode and a cathode electrode, said zener diode current limiting resistance means and compensating resistance means interconnected in series relationship between the battery positive and negative terminals; and
a voltage divider means having first and second interconnected resistance means, said first resistance means having a lead connected to said cathode electrode and said second resistance means having a lead communicating with the battery negative terminal, and an intermediate terminal intermediate said first and second resistance means connectable to a load the other side of the load being connectable to said zener diode anode electrode whereby the load will receive a constant voltage differential between said intermediate terminal and said zener diode cathode electrode.
8. The constant voltage source of claim 7 wherein said compensating resistance means has a resistive value substantially equal to the internal resistance value of the zener diode multiplied by the resistive value of the portion of the voltage divider interconnecting the intermediate terminal with the battery electrically negative terminal and divided by the resistive value of the portion of the voltage divider interconnecting the intermediate terminal with the cathode electrode of the zener diode.