GB1603469A

GB1603469A - Voltage regulating circuits

Info

Publication number: GB1603469A
Application number: GB2432878A
Authority: GB
Original assignee: FLEXDRIVE INSTR Pty Ltd
Current assignee: FLEXDRIVE INSTR Pty Ltd
Priority date: 1978-05-22
Filing date: 1978-05-30
Publication date: 1981-11-25
Also published as: AU4660479A

Description

(54) VOLTAGE REGULATING CIRCUITS (71) We, FLEXDRIVE INSTRUMENTS PTY. LTD., a company incorporated under the laws of the State of Victoria, Australia, of 390 Mount Alexander Road, Ascot Vale, 3032, Victoria, Australia, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement :- This invention relates to voltage regulating circuits and in particular, but not exclusively, to such circuits in which at least part thereof comprises a semiconductor device.

According to the present invention there is provided a voltage regulating circuit having: a transistor forming a series regulating element, the emitter electrode of said transistor being coupled to a first input terminal of the circuit and its collector electrode being coupled to an output terminal of the circuit, a first resistor providing a current source connected between said first input terminal and one terminal of means for providing a reference voltage less than an input voltage to be supplied to said first input terminal, another terminal of said reference voltage providing means being connected to a second input terminal of the circuit; A differential amplifier means comprising first and second transistors, said first transistor of the amplifier means having its collector electrode connected to the base electrode of said transistor forming said regulating element and its emitter electrode connected to a current sink and its base electrode coupled to said one terminal through a base resistor, said second transistor of said amplifier means having its emitter electrode connected to said current sink and its collector electrode connected to said output terminal and to said one terminal through a bias resistor; and a voltage divider means connected be- tween said output terminal and the other terminal of said means for providing a reference voltage said voltage divider means comprising a first and a second divider resistor the junction between which is connected to the base electrode of said second transistor of said amplifier means; whereby said differential amplifier means compares the reference voltage to the voltage developed at the junction between said divider resistors, and reduces or increases current flowing through said regulating element thereby respectively reducing or increasing the voltage at said output terminal such that the voltage at said output terminal is maintained at substantially a constant value.

The circuit may be designed for use as a voltage regulator for automotive application, such as for controlling a voltage applied to a bimetal gauge. In such application, the voltage applied to the input terminal normally will be in the range of + I IV to + 16V, with the output voltage controlled at lOV generally being required.

The means for providing a reference voltage may be a transistor used as a zener diode such as to utilize its reverse emitter collector breakdown voltage as the reference voltage.

A silicon transistor having a breakdown voltage of approximately 5V to 8V is preferred.

The circuit may at least in part be provided by a semiconductor device. In such form of the invention, the device most conveniently is a thick film structure or a monolithic structure.

Where the circuit is based on a thick-film device, rather than built from discrete components, the device may incorporate all components. However, where the device is a monolithic structure it normally will not include the regulating element, due to difficulties in effecting heat dissipation from the latter. Additionally, a monolithic device normally will not include the voltage divider means, due to it generally being necessary to adjust the ratio of the resistors of the divider means to a precise value, such as by trimming one or both of the resistors. Finally, as will be appreciated, it generally is impractical to include the capacitor, if required, in a monolithic semiconductor device, due to the level of capacitance required to prevent unwanted high frequency oscillation.

Particularly where based on a thick-film device, the circuit may form part of a unit including a metallic body providing a heat sink for the circuit. The metallic body may define a recess having a base surface on which the circuit is mounted in heat exchange relation.

Thus, according to a preferred feature of the invention, there is provided a circuit according to the invention comprising a semiconductor device at least partly constituting the circuit and a metallic body providing a heat sink for the device, the metallic body defining a recess having a base surface secured to the device, in heat exchange relation, over a first major surface thereof, the periphery of the recess on each of a pair of opposed sides of the device being bounded by a respective flange which projects beyond a second major surface of the device remote from the first major surface.

The metallic body may be relatively large in area in comparison with the semiconductor device. In one form, it may be of channel section to accommodate such relation in a relatively small volume; the body for example being formed from metal sheet. The flanges may be stepped in end profile, each comprising for example a first portion with its width dimension extending from the base to beyond the second major surface of the device, and a second portion projecting from the inner portion laterally of the device. The rigidity of the metallic member may be increased by the outer edge of each second flange portion being turned to define a rib.

In an alternative form, the metallic body may have a substantially rectangular wall defining the base; with a side flange projecting from each edge thereof beyond the second major surface of the device.

Conveniently, the major dimensions of the semi-conductor device are such that its area is substantially less than that of the base of the recess. Thus, where the metallic member is of channel form, the web thereof may be of a length approximately twice the corresponding dimension of the device; although it is desirable that the perspective dimensions across the web are comparable to optimise protection for the device by the opposed flanges being in close proximity thereto.

The relatively greater dimensions of the base of the recess also is desirable so that there can be fitted thereto connecting means spaced from the device. The connecting means may comprise lugs integral with the body and projecting therefrom for engagement with a convenient mounting structure.

The device may be protected by a suitable covering, for example, by means of a layer of an epoxy resin.

In order that the invention may be more readily understood, description will now be directed to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram of a regulator circuit embodying the invention; Figure 2 is a schematic circuit diagram of a modified regulator circuit; Figure 3 and 3A, respectively, is a plan view and an end elevation of a voltage regulator structure; and Figure 4 and 4A, respectively, is a plan view and an end elevation of a modified voltage regulator structure.

With reference to Figure 1, the circuit includes a pass or series regulator element in the form of a transistor Q4, the emitter and collector of which are connected to input and output terminal pins 1, 3 respectively of the circuit. A voltage divider, provided by resistors Rl, R2, is connected between the pin 3 and a circuit earth terminal pin 2.

The circuit also includes, between its pins 1 and 2, a resistor R3 in series with means, in the form of a transistor Q1, for providing a reference voltage at a point A. Q 1 is used as a zener diode, utilizing its reverse emitter collector breakdown voltage to provide a reference voltage at A, and has its collector connected to earth and its emitter connected to the resistor R3.

Additionally, the circuit includes a differential amplifier, consisting of transistors Q2 and Q3. The emitters of Q2 and Q3 are connected to the pin 2 via a current sink resistor R6, with their bases being connected via a resistor R5 to A and to a voltage point B, respectively, and their collectors connected to the base of Q4 and the pin 3, respectively.

When battery voltage is applied to the pin 1, a starting current flows through the resistors R3 and R4. The voltage at the emitter of Q I rises to establish the reference voltage at A which, in the example illustrated of a silicon transistor (BC 548), will be approximately 8 volts. As a result of current flow through R5, the transistor Q2 turns"on"and this causes Q4 to turn"on"An output voltage now appears at the pin 3. This voltage is divided between the resistors RI and R2 and applied to the transistor Q3.

The transistors Q2 and Q3 of the differential amplifier compare the 8 volt"reference" voltage at the emitter of Q I with the sensed output voltage at the base of Q3. If the output voltage rises above 10 volts more current flows in Q3 which in turn reduces current in Q2 which reduces current in Q4.

This has the effect of lowering the output voltage.

If the output voltage drops below 10 volts then the reverse set of conditions apply.

The resistor R2 is trimmed to set the output voltage to 10 volts 1%.

Short circuit output current is limited by R6.

The resistor R5 provides current limiting in the event of reverse breakdown of Q2 or Q4 caused by high voltage transients, while a capacitor C I is included to eliminate unwanted high frequency oscillation.

As indicated, Ql is used as a zener diode.

By this arrangement, rather than one incorporating a conventional zener diode, protection against reverse connection of battery terminals is achieved.

In the above form with the transistors of the type indicated and the resistors and the capacitor of the indicated values, the circuit can accommodate as input the normal car battery operating voltage range of + 11 to 16 volts, with a surge maximum of 60 volts.

Also in the arrangement of Figure 1, an output of 10 volts 1% is obtained with an output current maximum of 500 m A; the precision of the output voltage being achieved by the precise values selected for R I and R2 for a given form of Q 1. It therefore is necessary to trim R I and R2 such as by means of a laser or abrasive trimmer to within precise tolerances.

In the alternative circuit of Figure 2 a similar arrangement is shown, with transistors Q2 to Q5 corresponding in function to the transistors Q I to Q4 of Figure 1. However, in this instance, the reference voltage established at A by the transistor Q2 is 5 volts. Additionally, the base of the transistor Q3 of the differential amplifier is connected to A via a voltage divider, comprising resistors R5 and R5A.

An additional modification is the provision of temperature compensation means in the circuit of Figure 2. This is provided by means of a diode connected in parallel with the resistor R4 and having its cathode connected to the collector of the transistor Q5. The diode preferably is provided by a transistor Ql which, as shown, has its basecollector junction short-circuited.

The capacitor Cl is shown in broken outline. This is to indicate that, as with Figure 1, the capacitor can be omitted since the unwanted high frequency oscillations that may be encountered where the circuits are made of discrete components generally are not encountered with semi-conductor devices.

As in the arrangement of Figure 1, an output of 10 volts ! % is obtained but, in this case, with an output current maximum of 400 m A. The precision of the output voltage, as in Figure 1, is achieved by the precise values selected for RI and R2 for a given form of Q2.

The circuits of Figures) and 2 may be built from discrete components. Preferably, however, they comprise a thick film semiconductor device or are based on a monolithic semi-conductor device. In the latter case, the resistors Ri and R2, capacitor Cl and transistor Q4 of Figure 1, or the transistor Q5 of Figure 2, do not form part of the monolithic device, as discussed in the forego ing.

The circuits are designed for use as a regulator to replace mechanical switching regulators that normally are used with bi metal gauge systems, and offers a number of advantages in reliability and life expectancy over the mechanical type. In addition to precision in maintaining the output voltage and high surge voltage handling capacity the device and, hence, a gauge system used therewith, is protected against reverse polar ity connection of the input power source.

Moreover, the device is short circuit pro tected and protected against earth lead re moval.

With reference to Figures 3 and 3A, there is shown a voltage regulator structure which includes a thick film semiconductor device 10 mounted within a recess 11 of a metallic heat sink member 12. The device 10 comprises a ceramic substrate on which is built a circuit as shown in Figure I or 2; the terminal pins I, 2 and 3 corresponding to the input, earth and output terminal pins of such circuit.

As is most clearly apparent from Figure 3A, the recess in which the device 10 is mounted is provided by the member 12 being of channel section, defined by a base 14 and opposed, stepped flanges 16. The device is mounted with its substrate secured in face to face contact with the recess base in heat exchange relation therewith, with the flanges projecting upwardly beyond, and diverging slightly from the device a substantial distance in relation to the thickness of the later and then diverging laterally therefrom. The outer edge 17 of each flange projects upwardly from the device to increase the rigidity of the member 12.

At each end of the base 14, a central portion thereof is bent away from the device 10 to provide a lug 18. The latter provide means by which the structure may be mounted on a support, the lugs being benda ble after insertion in apertures of the support.

As indicated by the shaded area shown in Figure 3, a protective covering is provided over the recess base to encapsulate the device 10. The covering may be of a suitable electrically insulating material, such as an epoxy resin.

With reference to Figures 4 and 4A, there is shown a voltage regulator or device 50 mounted within a recess 51 of a metallic heat sink member 52. The regulator or device 50 comprises a ceramic substrate on which is built a circuit as shown in Figure I or 2; the terminal pins 4,5 and 6 corresponding to the input, earth and output terminal pins of such circuit.

The recess 51 in which regulator 50 is mounted is provided by the member 52 having a rectangular base 54 from each edge of which a respective side flange 56 extends.

The regulator 50 is mounted with its sub strate secured, by a major face thereof, in face to face contact with the base 54 so as to be in heat exchange relation with the member 52. The flanges 56 project beyond, and provide protection for, the regulator; with one of the flanges being discontinuous along its length to allow a marginal portion of the regulator. substrate and the pins 4,5 and 6 to project beyond the base 54 for access.

Corners of the base 54 are cut-away to avoid zones of heat concentration. Additionally, the ends of adjacent flanges are spaced apart to improve connection cooling.

At each end of the base, a respective flange provides a lug 58 which projects in the direction of the pins 4,5 and 6. The lugs provide means by which the structure may be mounted on a support, the lugs being bendable after insertion in apertures of the support.

Also, a hole 60 is provided at each end of base 54, each on a respective side of the regulator; the holes providing alternative means by which the structure may be secured to a support, such as by screws.

As indicated by the shaded area in Figure 4, a protective covering is provided over the recess base to encapsulate the device 50.

Again, the covering may be an epoxy resin or other suitable electrically insulating material.

As indicated above, the circuit provides protection against earth lead removal and polarity reversal of the input power source. It also is short circuit protected. These advantages are of particular importance in use of the circuit as an automotive voltage regulator.

A further important advantage, particularly in automotive use, is that the circuit is operable with quite small voltage differentials between its input and output. Thus, in contrast to commercial regulators, it is able to maintain an output volage of up to 10 volts with a car battery operating voltage as low as I I volts.

Claims

Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the ambit of the invention as defined by the appended claims.

WHAT WE CLAIM IS : 1. A voltage regulating circuit having; a transistor forming a series regulating element, the emitter electrode of said transistor being coupled to a first input terminal of the circuit and its collector electrode being coupled to an output terminal of the circuit, a first resistor providing a current source connected between said first input terminal and one terminal of means for providing a reference voltage less than an input voltage to be supplied to said first input terminal, another terminal of said reference voltage providing means being connected to a second input terminal of the circuit; a differential amplifier means comprising first and second transistors, said first transistor of the amplifier means having its collector electrode connected to the base electrode of said transistor forming said regulating element and its emitter electrode connected to a current sink and its base electrode coupled to said one terminal through a base resistor, said second transistor of said amplifier means having its emitter electrode connected to said current sink and its collector electrode connected to said output terminal and to said one terminal through a bias resistor; and a voltage divider means connected between said output terminal and the other terminal of said means for providing a reference voltage, said voltage divider means comprising a first and a second divider resistor the junction between which is connected to the base electrode of said second transistor of said amplifier means; whereby said differential amplifier means compares the reference voltage to the voltage developer at the junction between said divider resistors, and reduces or increases current flowing through said regulating element thereby respectively reducing or increasing the voltage at said output terminal such that the voltage at said output terminal is maintained at substantially a constant value.
2. A circuit according to claim 1, including a substrate on which said regulating element, voltage divider means, means for providing a reference voltage, and said differential amplifier means are built, said circuit comprising a thick film integrated circuit.
3. A circuit according to claim 1, including a substrate on which said means for providing a reference voltage and said differ- ential amplifier means are built to comprise a monolithic integrated component of said circuit.
4. A circuit according to any one of claims 1 to 3, wherein said means for providing a reference voltage is a transistor used as a zener diode such as to utilize its reverse emitter-collector breakdown voltage as the reference voltage.
5. A circuit according to claim 4, wherein the transistor used as a zener diode is a silicon transistor.
6. A circuit according to claim 5, wherein a capacitor is connected between the collector and base electrodes of the transistor which forms the regulating element thereby to eliminate unwanted high frequency oscillation in the circuit.
7. A circuit according to claim 6, wherein said base resistor limits current flow in the event of reverse breakdown of one of the transistors of the differential amplifier means.
8. A circuit according to any one of claims I to 7, including temperature compensation means.
9. A circuit according to claim 8, wherein the temperature compensation means comprises a diode connected in parallel with said bias resistor and having its cathode connected to the collector of said transistor forming the regulating element.
10. A circuit according to clam 9, wherein the diode comprises a transistor having its base-collector junction short-circuited.
11. A circuit according to any one of claims I to 10 comprising a semi-conductor device at last partly constituting the circuit and a metallic body providing a heat sink for the device, the metallic body defining a recess having a base surface secured to the device, in heat exchange relation, over a first major surface thereof, the periphery of the recess on each of a pair of opposed sides of the device being bounded by a respective flange which projects beyond a second major surface of the device remote from the first major surface.
12. A circuit according to clam 11, wherein said metallic body is formed from metal sheet.
13. A circuit according to claim 11 or 12, wherein the metallic body is of channel section, said recess being defined between side flanges of the section with the base surface of the recess being defined by a web portion of the section extending between said side fanges.
14. A circuit according to clam 13, wherein said flanges are of stepped profile when viewed from an end of said section, that is longitudinally of the section, each flange having a first longitudinal portion having its width dimension extending from the web portion of the section beyond said second surface of the device, and a second longitudinal portion having its width dimension extending laterally outwardly from the first portion from the edge of the latter remote from the web portion.
15. A circuit according to claim 14, wherein each said second flange portion has a strengthening rib extending therealong, such as of the edge thereof remote.
16. A circuit according to claim 11 or claim 12, wherein said metallic body has a substantially rectangular wall defining said base, with a respective side flange projecting from each edge of said wall beyond the second major surface of the device.
17. A circuit according to claim 16, wherein corner portions of said wall are cutaway and the ends of adjacent side flanges are spaced to avoid zones of heat concentration at said corners.
18. A circuit according to any one of claims I I to 17, wherein the projection of the device onto the base. of the recess is substan tially less than the area of the base.
19. A circuit according to clam 18, wherein said flange at each side of said opposed pair thereof is in close proximity to a respective edge of the device, the length of the recess in the direction of longitudinal extent of the flanges being approximately twice the corresponding dimension of the device.
20. A circuit according to any one of claims I1 to 19, wherein the device is provided with a protection covering, such as of an epoxy resin.
21. A circuit according to any one of claims 11 to 20, including connecting means for mounting the unit for use.
22. A circuit according to claim 21, wherein said connecting means comprises at least two lugs of which a respective one projects from the base at each of opposed sides of said device.
23. A voltage regulating circuit substan tially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.
24. A voltage regulating circuit substan tially as herein described with reference to Fig. I or Fig. 2, as modified by Figures 3 and 3A or Figures 4 and 4A, of the accompany ing drawings.