GB2046483A

GB2046483A - Voltage regulator

Info

Publication number: GB2046483A
Application number: GB8010904A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1979-04-06
Filing date: 1980-04-01
Publication date: 1980-11-12
Also published as: JPS55138119A; DE3013285A1; FR2453447A1

Abstract

A voltage regulator includes resistors R5, R10 and transistors Q1, Q2 forming a negative feedback arrangement that maintains an output voltage across terminals 12, 13 at a desired magnitude despite change in the input voltage across terminals 10, 11. The resistors are selected to cause the output voltage to track the changes with temperature of the base to emitter voltage of a transistors Q6. <IMAGE>

Description

SPECIFICATION Improved voltage regulator This invention relates to a voltage regulator, and particularly to a voltage regulator for use with a relatively low and variable source voltage over a range of temperatures.

Electronic circuits, such as paging radio receivers, must frequently be operated with a single cell battery which has an open circuit voltage ranging from 1.3 to 1.55 volts, depending on the type of battery. In order to obtain as much use as possible from the battery, the electronic circuits should be capable of operating with as low a voltage as possible, for example 1.1 volts. With such a low operating voltage, the circuits are, for all practical purposes, limited to no more than one solid state device junction voltage drop (about 0.65 volt for silicon) between the battery terminals.

A primary application of the present invention is to provide an improved voltage regulator circuit for use with a single cell battery.

An aim of the invention is to provide a circuit that delivers a regulated output voltage for a relatively wide range of suply voltages and temperatures.

The invention provides a voltage regulator circuit that can be partially realized in integrated circuit form to take advantage of certain temperature characteristics and mass production techniques.

Some electronic circuits requiring a regulated voltage are sensitive to temperature changes, and particularly to the change in the base to emitter voltage V(BE) caused by changes in temperature. Generally, this voltage changes by approximately -2 millivolts (MV) per degree centigrade (C), where the minus sign indicates that the base to emitter voltage changes in a direction opposite to the change in temperature. For a V(BE) of 650 MV at 25"C, the V(BE) becomes 652 MV at 24"C and 648 MV at 26"C. These changes can adversely affect the operation of some transistor circuits, particularly those operating at a relatively low voltage.

Accordingly, another general object of the invention is to provide a new and improved voltage regulator circuit that provides an output voltage that varies as a function of temperature.

Another feature of the invention is to provide a regulated output voltage that tracks or follows the voltage between a transistor base and emitter as it changes with temperature.

In the illustrated regulator there is an output transistor connected between a source voltage terminal and a regulated voltage terminal. The conduction of the output transistor, and hence the output voltage magnitude, is determined by a voltage sensing resistor network and control transistors connected in a negative feedback arrangement. One of the resistors of the network is provided on an integrated circuit with a selected magnitude and a positive temperature coefficient, and another resistor of the network is provided outside of the integrated circuit with a selected magnitude and a substantially negative temperature coefficient. The selected resistors cause the regulated output voltage magnitude to follow or track the base to emitter voltage of a transistor or solid state junction as that voltage varies with temperature.A circuit that requires very little current is also provided to start and stop the operation of the new voltage regulator circuit.

The structure and operation of the invention, may be better understood from the following description given in connection with the accompanying drawing, in which: Figure 1 shows a schematic diagram of a preferred embodiment of a voltage regulator in accordance with the invention; and Figure 2 shows graphs for illustrating the operation of the regulator of Figure 1.

In Figure 1 it is assumed that a source of unregulated voltage, such as a battery, has its positive and negative terminals connected to the input terminals 10, 11 respectively. The positive terminal 10 is connected through the emitter-collector path of an output transistor 06 to a positive output terminal 12, and the negative terminal 11 is connected directly to a negative output terminal 13. If desired, the negative terminals 11, 15 may be connected to a point of reference potential or yround as shown. The output terminals 12, 13 provide a regulated voltage output, and may be shunted byafiltercapacitorC1.A portion of the voltage regulator is preferably realized as an integrated circuit 14which is represented by the dashed line rectangle.The other portions of my regulator which are not part of the integrated circuit are outside the dashed line rectangle.

Conduction from the emitter to collector of the output transistor 06 is controlled or determined by a sensor transistor 01 whose base is connected to the junction of two resistors R5, R10 connected in series between the terminals 12, 13. The resistor R5 is on the integrated circuit 14, but the resistor R10 is external to the integrated circuit 14. The resistor R5 has a positive temperature coefficient (which on an integrated circuit is typically about 2500 parts per million per degree C), but the external resistor 910 has a substantially flat or zero temperature coefficient. The collector of the sensor transistor Ol is connected to the base of a control transistor Q2.A bias resistor R4 is connected from the terminal 12 to the base of the transistor 02. The collector of the transistor Q2 is connected to the base of the output transistor 06. The transistors Q1, 02 and the resistors R5, R10 form a negative feedback circuit that determines the amount of conduction through the output transistor 06, and provide the desired regulation. If the voltage at the terminal 10 increases, the transistor 01 conducts harder, and this causes transistor 02 to conduct less, which in turn lowers the conduction through the transistor Q6 to prevent the output voltage at the terminal 12 from increasing. If the voltage at the terminal 10 decreases, the transistor Q1 conducts less, and the transistors Q2, Q6 conduct more to maintain the output voltage at the terminal 12 at the desired level.

The voltage regulator is turned on and off by a switch S1 whose movable contact (or signal source if desired) is connected to the base of a switching transistor Q5. The transistor OS has two collectors (a structure obtainable in integrated circuits). Its base is connected through a resistor R1 to the positive terminal 10. When the switch arm is in the position shown to turn the regulator on, the base of the transistor OS is connected to ground to turn the transistor OS off. In the off condition, its two collectors can have positive voltages determined by circuit values. One collector is connected to the resistor R4 which provides bias for the base of the control transistor 02.The other collector of the transistor Q5 is connected to the base of a start transistor 03, and is also connected to the junction of a bias resistor R2 and the collector of a lock-out transistor Q4. The base of the lock-out transistor Q4 is biased by two resistors R6, R7 which are connected in series between the output terminals 12, 13.

When the regulator is turned off, the movable arm of the switch S1 is moved to the off-contact which is floating or not provided with any voltage. The switching transistor OS is rendered conducting by the current supplied through the resistor R1. This maintains the starting transistor 03 turned off. Similarly, this also maintains the control transistor Q2 turned off so that no voltage is provided at the terminals 12, 13.

When the regulator is turned on, the movable arm of the switch S1 is connected to the on-contact. This turns the transistor OS off, so that the voltages at its two collectors can take whatever level is determined by the regulating circuit. In this condition, the voltage provided by the bias resistor R2 turns the transistor 03 on. Conduction of the transistor Q3 draws some base current in output transistor Q6 through the resistor R3 so as to provide an output voltage at the terminal 12. As this voltage builds up, the control transistor Q2 is turned on so as to provide another path for base current in the output transistor 06.Eventually, the voltage builds up sufficiently so that the current through the transistor Q6 and the regulated output is under the control of the transistors 01, 02. As this output voltage builds up, it reaches a point where it turns the lockout transistor 04 on. This turns the start transistor 03 off, so that base current in the output transistor no longer flows through the start transistor Q3, but only flows in the control transistor 02. Hence, the output voltage is only controlled by the transistors 01, Q2. This provides a new and improved arrangement for starting the regulator circuit, and then removing the starting portions of the circuit so that regulation is only in accordance with the output voltage.This has the additional advantage of providing regulator bias from the regulator output, thus eliminating variations in regulated voltage due to bias variations.

As mentioned earlier, the resistor R5 has a positive temperature coefficient, and the resistor R10 has a substantially zero temperature coefficient. Proper selection of the ratios of the magnitudes of the two resistors R5, R10, provides an output voltage V(OUT) at the terminals 12, 13 which follows or tracks the base-emitter voltage V(BE) of the sensor transistor 01 as that voltage changes with temperature. This selection is explained in connection with the graphs of Figure 2 which show these voltages as a function of temperature. The base-emitter voltage V(BE) of the transistor 01 is assumed to be 650 millivolts (MV) at 25"C, and has a temperature coefficient of -2.00 MV per degree C. These changes in V(BE) with respect ro temperature are shown by the graph 20.The point 21 shows a V(BE) of 650 MV at 25-C; the point 22 shows a V(BE) of 652 MV at 24"C; and the point 23 shows a V(BE) of 648 MV at 250C. Corresponding V(BE'sYwould be presented for other temperatures farther above or below the illustrated temperatures between 24vC and 26"C.

It is assumed that an output voltage V(OUT) of 900 MV at 25"C is desired. To obtain this, the resistors R5, 910 would be designed (assuming negligible base current) with the relation: V(OUT) ~ V(BE) (Formula 1) R5+R10 - R10 A reasonable value obtainable for resistor R5 in the integrated circuit 14 is 7500 ohms. With V(OUT) of 900 MV and V(BE) of 650 MV, Formula 1 determines that the resistor R10 must be 19500 ohms. The resistor 910 is external to the integrated circuit 14so that it can be trimmed to the desired value.As the temperature changes, V(BE) and hence V(OUT) also change. However, V(OUT) changes to a greater extent because of the ratio effect of the resistors R5, R10. If the magnitude of the resistors R5, R10 changes very little with temperature, the values of V(OUT) for different temperatures can be calculated with Formula 1, using V(BE's) of 650, 652 and 648 MV. The results are illustrated by the dashed line graph 30 in Figure 2. The point 31 shows a V(OUT) of 900 MV at 25CC; the point 32 shows a V(OUT) of 902.77 MV at 24-C; and the point 33 shows a V(OUT) of 897.23 MV at 26"C. Thus, V(OUT) varies at -2.77 MV per degree C while V(BE) varies at -2.00 MV per degree C.For this reason, the resistor R5 is provided in integrated circuit form so that the temperature variation of resistor R5 offsets this excessive change in V(OUT). A typical or nominal temperature coefficient for integrated circuit resistors in 2500 parts per million per degree C. If, in accordance with the invention, the resistor R5 is made to be as near a selected value as possible (for example 7500 ohms), and the resistor R10 trimmed to provide the desired output (for example 900 MV at 25'C, then the voltage V(OUT) will follow or track the V(BE) very closely with temperature changes. If the resistor R5 has a magnitude of 7500 x .0025 or 18.75 ohms for each degree C the temperature varies from 253C. Thus, the resistor R5 would be approximately 7481.25 ohms at 24"C and 7518.75 ohms at 260C. With Formula 1, this would provide V(OUT) of 902.14 MV at 240C and V(OUT) of 897.86 at 260C. These values are shown as points 41,42 respectively on graph 40. Thus, in accordance with the invention, the change in V(OUT) is reduced from approximately -2.77 MV per degree C to approximately -2.14 MV per degree C, a value which very nearly tracks or follows the -2.00 MV per degree C of the base-emitter voltage of a transistor.This close tracking is very desirable in low voltage circuits requiring a regulated voltage to operate transistors over a wide temperature range.

A regulator in accordance with Figure 1 and as explained above was constructed with the following values: ResistorR1 Trimmed to 47,000 ohms Resistor R2 100,000 ohms Resistor R3 7,000 ohms Resistor R4 6,200 ohms Resistor R5 7,500 ohms Resistor R6 20,000 ohms Resistor R7 100,000 ohms Resistor R10 Trimmed to 19,500 ohms to provide V(OUT) of 900 MV Capacitor Cl 2 microfarads This circuit provided a regulated output voltage of 900 MV at 25 C to within t3MV for unregulated input voltages between 1.5 and 1.1 volts.The output voltage V(OUT) tracked or followed changes in V(BE) very closely for tem peratu res between + 50"C and -10"C. If the resisto r R5 is divided into a resistor i nside the integrated circuit 14 and a resistor outside the integrated circuit 14, it is possible to exactly compensate to the 2MV"C V(BE) variation. This was not done because it requires another pin on the integrated circuit 14; the 2MV"C is not exact or constant; and the coefficient and value of the inside resistor R5 varies considerably from lot to lot and is not constant with temperature or voltage.

This voltage regulator circuit can be constructed in mass production using integrated circuit techniques. A computer analysis indicates that with the values chosen, the output voltage V(OUT) would vary no more than 10 MV from the ideal compensation curve for all reasonable variations in the resistor R5 value and temperature coefficient. The regulator has improved temperature characteristics, and reliably starts and stops reliably. The regulator requires very little operating current, thus saving drain on the supply battery, a critical item for small personal electronic equipment. Persons skilled in the art will appreciate that many modifications may be made without departing from the spirit and scope of the invention. NPN and PNP type transistors may be substituted, and different voltages may be provided for regulation, and different regulated output voltages may be provided, as described.

Claims

1. An improved voltage regulator circuit comprising: a. first and second input terminals and first and second output terminals; b. an output transistor having an emitter and collector connected between said first input terminal and said first output terminal, and having a base electrode; c. means connecting said second input terminal to said second output terminal; d. a voltage sensitive network having first and second resistors connected in series between said first and second output terminals, said first and second resistors having different temperature coefficients; e. and means including a transistor network connected between said voltage sensitive network and said base electrode of said output transistor in a negative feedback arrangement.

2. The improved voltage regulator of claim 1 wherein said temperature coefficient of said voltage sensitive network is opposite in sign to the temperature coefficient of said transistor network, whereby said regulated output voltage at said output terminals substantially tracks the temperature coefficient of said transistor network.

3. The improved voltage regulator of claim 1 or claim 2 wherein said first resistor of said voltage sensitive network and said transistor network are in integrated circuit form, and wherein said second resistor of said voltage sensitive network is external to said integrated circuit.

4. The improved voltage regulator of claim 1 or claim 2 and further comprising a start circuit connected to said base electrode of said output transistor and to said transistor network for alternatively rendering said output transistor and said transistor network non-conductive or for rendering said output transistor and said transistor network conductive.

5. The improved voltage regulator of claim 3 and further comprising a start circuit connected to said base electrode of said output transistor and to said transistor network for alternatively rendering said output transistor and said transistor network non-conductive or for rendering said output transistor and said transistor network conductive.

6. The improved voltage regulator of claim 4 wherein the connection between said start circuit and said base electrode of said output transistor is rendered inoperative in response to the presence of a regulated output voltage.

7. The improved voltage regulator of claim 5 wherein the connection between said start circuit and said base electrode of said output transistor is rendered inoperative in response to the presence of a regulated output voltage.

8. An improved circuit for providing a control output voltage that has a selected magnitude at a selected temperature, and that tracks the base-emitter voltage change of a solid state device with temperature comprising: a. first and second input terminals, and first and second output terminals; b. an output transistor having an emitter, a collector, and a base; c. means connecting said emitter and collector of said output transistor between said first input terminal and said first output terminal; d. first and second resistors connected in a voltage sensing circuit between said first and second output terminal; e. a negative feedback arrangement comprising at least one transistor having a control electrode and output electrodes; f. means connecting said control electrode of said one feedback transistorto the junction of said first and second resistors;; g. means connecting one of said output electrodes of said one feedback transistor to said base of said output transistor to provide negative feedback thereto in response to the voltage at said first output terminal; h. said first and second resistors having magnitudes selected to provide the desired voltage at said first output terminal as a function of the base-emitter voltage of said one feedback transistor, and said first resistor having a positive temperature coefficient to at least partially offset the negative temperature coefficient of said base-emitter voltage of said one feedback transistor.

9. The improved circuit of claim 8 wherein said first resistor and said one feedback transistor are in integrated circuit form, and wherein said output transistor and said second resistor are separate components.

10. The improved circuit of claim 8 or claim 9 and further comprising a start circuit having a start transistor connected to said output transistor and to said one feedback transistor to selectively render said output transistor conductive in response to an input signal, to render said start transistor inoperative in response to a voltage at said first ouput terminal, and to render said output transistor non-conductive in response to removal of said input signal.

11. An improved circuit for producing a selected output voltage at a selected temperature despite changes in an input voltage comprising: a. first and second input terminals, and first and second output terminals; b. an output transistor having an emitter, a collector, and a base; c. means connecting said emitter and collector of said output transistor between said first input terminal and said first output terminal; d. means connecting said second input terminal to said second output terminal; e. first and second resistors connected in series between said first output terminal and said second output terminal; f. a sensing transistor having an emitter, a collector, and a base; g. means connecting said emitter and collector path of said sensing transistor between said base of said output transistor and said second output terminal;; h. and means connecting said base of said sensing transistor to the junction of said first and second resistors whereby said sensing transistor provides negative feedback to said base of said output transistor as a function of the voltage across said first and second resistors; i. said first and second resistors having selected magnitudes that provide the desired voltage at said first output terminal as a function of the junction voltage of said sensing transistor, and said first resistor having a positive temperature coefficient that at least partially offsets the negative temperature coefficient of said junction voltage.

12. The improved circuit of claim 11 and further comprising a start transistor having an emitter, a collector, and a base, means connecting said emitter and collector of said start transistor between said base of said output transistor and said second output terminal, and means connecting said base of said start transistor to said first output terminal to render said start transistor non-conductive in response to a voltage of predetermined magnitude at said first output terminal.

13. The improved circuit of claim 11 or claim 12 wherein said first resistor, said sensing transistor, and said start transistor are in integrated circuit form, and wherein said output transistor and said second resistor are external components.

14. A voltage regulator substantially as described herein with reference to the accompanying drawings.