Direct-current stabilizer

Abstract: A direct-current stabilizer (5) includes a n-p-n transistor (Tr₃), and a control terminal (CNT₁) to which a control voltage (V c ) for driving the transistor (Tr₃) is applied. The value of the control voltage (V c ) is determined so that a voltage applied to the base of the transistor (Tr₃) is not lower than the sum of the emitter voltage (V₀(V₀₂)) and the base-emitter voltage. With this structure, since the transistor (Tr₃) is driven by the control voltage (V c ) of a value different from that of the input voltage (V IN ), it is possible to limit the input voltage (V IN ) to a low value, allowing the difference between the input voltage (V IN ) and the output voltage (V₀(V₀₂)) to be minimized. Moreover, it is possible to switch the output of the direct-current stabilizer (5) by connecting to the control terminal (CNT₁) a control transistor (Tr₂) for switching the application of the control voltage (V c ) to the control terminal (CNT₁) between on and off. Furthermore, when the control terminal (CNT₁) is connected to the input terminal (V IN ), the transistor (Tr₃) is driven by the input voltage (V IN ). Therefore, the direct-current stabilizer (5) is used in the same manner as a conventional direct-current stabilizer is used.

Description: FIELD OF THE INVENTION The present invention relates to a direct-current stabilizer including an n-p-n transistor for controlling an output voltage. BACKGROUND OF THE INVENTION In general, a direct-current stabilizer is used to supply a DC voltage necessary for electronic devices. For example, a so-called dropper-type direct-current stabilizer which outputs a stabilized voltage by decreasing an input voltage is commonly used because it has low noise and is easy to design. The following description discusses such direct-current stabilizers. As illustrated in Fig. 19, in a direct-current stabilizer, for example, when an input voltage applied to an input terminal IN reaches a predetermined level, an actuator 81 starts operating and a reference voltage circuit 82 generates a reference voltage. An output voltage V O delivered to an output terminal OUT is divided by resistors R 81 and R 82 . The difference between the resulting voltage and the reference voltage is amplified by a differential amplifier 83. The differential amplifier 83 controls the base current of a transistor Tr 81 through a transistor Tr 82 by adjusting an output according to the difference. The transistor Tr 81 is an n-p-n transistor for controlling output, and stabilizes the output voltage V O by controlling the base current. The output voltage V O is applied to a load 84. The output characteristics of the output voltage V O is improved by a capacitor C 81 connected to the output terminal OUT in parallel with the load 84. When the collector current of the transistor Tr 81 is increased by a short circuit or overload, the voltage drop in a resistor R 83 connected to the emitter of the transistor Tr 81 becomes significant. Then, the base-emitter voltage of a transistor Tr 83 for controlling current is significantly increased. This causes the transistor Tr 83 to be switched on, and the base currents of the transistors Tr 82 and Tr 81 to be limited. Consequently, the collector current of the transistor Tr 81 is limited, and the transistor Tr 81 is protected from an overcurrent. Another direct-current stabilizer shown in Fig. 20 includes a p-n-p transistor Tr 84 for controlling output. Similar to the above-mentioned n-p-n transistor, with the p-n-p transistor Tr 84 , the reference voltage circuit 82 generates a reference voltage with the operation of the actuator 81, an output voltage is divided by the resistors R 81 and R 82 , and a difference between the divided voltage and the reference voltage is amplified by the differential amplifier 83. The base current of the transistor Tr 84 is controlled by the output of the differential amplifier 83 through a transistor Tr 85 as driver, and thereby stabilizing the output voltage V O . When the collector current of the transistor Tr 84 is increased by a short circuit or overload, the collector current of the transistor Tr 85 is also increased. The base-emitter voltage of a transistor Tr 86 for controlling current is increased by a resistor R 84 which is connected in series with the emitter of the transistor Tr 85 . This causes the transistor Tr 86 to be switched on, and the base currents of the transistors Tr 85 and Tr 84 to be limited. As a result, the collector current of the transistor Tr 84 is limited and the transistor Tr 84 is protected from an overcurrent. However, since the former direct-current stabilizer uses the n-p-n transistor Tr 81 to control the output voltage, the collector-emitter voltage drops significantly, causing considerable losses and poor efficiency. On the other hand, the latter direct-current stabilizer uses the p-n-p transistor Tr 84 for controlling the output voltage so as to reduce the losses by minimizing the potential difference between the input voltage and the output voltage. However, such a direct-current stabilizer also has the following problem. The p-n-p transistor usually can not produce a direct current gain that the n-p-n transistor of the same chip size produces. Therefore, in order to produce a direct current gain similar to the gain of the n-p-n transistor of the same rating, it is necessary to increase the size of chip, resulting in an increase in costs. Moreover, the direct-current stabilizer using a p-n-p transistor presents the following structural problem. A direct-current stabilizer shown in Fig. 21 has a structure where a transistor section 91 as a transistor for controlling an output voltage and an IC section 92 for controlling the transistor are vertically arranged on a single chip. More specifically, such a direct-current stabilizer has a complicated structure where an n + buried layer 94 and a p + buried layer 95 are formed in this order on a p-type substrate 93. In addition, there is a need to provide a p-well region 96 to form the p-n-p structure. Therefore, the number of wafer processes in manufacturing is increased, resulting in an expensive chip. Furthermore, an increase in the number of heat treatment processes causes the diffused layers 97 to 100 to expand, thereby increasing the area and costs of the chip. A direct-current stabilizer shown in Fig. 22 has a structure where a transistor section 101 as a transistor for controlling output voltage and an IC section 102 for controlling the transistor are laterally arranged on a single chip. In such a direct-current stabilizer, an emitter diffused layer 104, a base diffused layer 105 and a collector diffused layer 106 are formed in a cross direction on an n-type epitaxial layer 103. This arrangement causes the chip to have an increased area, resulting in an increase in costs. The characters (B), (C) and (E) in the drawing represent the base, collector and emitter, respectively. US-A-4 950 975/WO 88/06757 discloses a direct current stabiliser according to the preamble of claim 1 or claim 2. The biasing voltage applied to the base of the control transistor is derived from the input voltage in a preliminary stage of the direct current stabiliser. A first aspect of the present invention provides an integrated direct-current stabiliser comprising: an input terminal for receiving an input supply voltage; and an n-p-n control transistor whose base current is controlled on the basis of an output voltage of said direct-current stabiliser, for reducing an input voltage and maintaining the output voltage at a predetermined value; characterised in that the stabiliser further comprises: a control terminal provided separately from said input terminal, for controlling biasing of the base of said control transistor independently of said input voltage and for supplying to the base of said control transistor a control voltage which is not lower than a sum of the emitter voltage and the base-emitter voltage of the control transistor; and in that it further comprises an n-p-n transistor having a collector connected to said control terminal, said n-p-n transistor and said control transistor being a Darlington pair. A second aspect of the present invention provides an integrated direct-current stabiliser comprising: an input terminal for receiving an input supply voltage; and an n-p-n control transistor whose base current is controlled on the basis of an output voltage of said direct-current stabiliser, for reducing an input voltage and maintaining the output voltage at a predetermined value; characterised in that the stabiliser further comprises: a control terminal provided separately from said input terminal, for controlling biasing of the base of said control transistor independently of said input voltage and for supplying to the base of said control transistor a control voltage which is not lower than a sum of the emitter voltage and the base-emitter voltage of the control transistor; and in that it further comprises a p-n-p transistor having an emitter connected to said control terminal, said p-n-p transistor and said control transistor being a Darlington pair. In a preferred embodiment the integrated direct-current stabiliser further comprises: a differential amplifier for controlling the base current of said control transistor in accordance with said output voltage so that said control transistor maintains said output voltage at the predetermined value; and wherein the control terminal is adapted to supply to the differential amplifier a source voltage such that the differential amplifier applies to the base of said control transistor a voltage which is not lower than a sum of the emitter voltage and the base-emitter voltage of the control transistor. In a preferred embodiment, the differential amplifier and said n-p-n transistor are directly connected to said control terminal, the withstand voltages of the differential amplifier and the n-p-n transistor are higher than a withstand voltage of said input terminal, and the base of said n-p-n transistor is connected to an output of said differential amplifier. In a preferred embodiment the differential amplifier and said p-n-p transistor are directly connected to said control terminal, the withstand voltages of the differential amplifier and the p-n-p transistor are higher than a withstand voltage of said input terminal, and the base of said p-n-p transistor is connected to an output of said differential amplifier. In a preferred embodiment the integrated direct-current stabiliser further comprises current limiting means for limiting a flow of a current from said control terminal. In a preferred embodiment the current limiting means limits a flow of the current into a source input of said differential amplifier. In a preferred embodiment the withstand voltage of the control terminal is greater than the withstand voltage of the input terminal. In a preferred embodiment the control terminal is placed adjacent to the input terminal. In a preferred embodiment the control terminal is connectable to an ON/OFF circuit for applying or for not applying a voltage. The direct-current stabilizer having such characteristics brings the following advantages (A) to (D). (A) Since the withstanding voltage of the control terminal is higher than that of the input terminal, it is possible to apply a voltage higher than the input voltage to the control terminal without increasing the withstanding voltages of other terminals including the input and output terminals which require a change according to the input voltage. Namely, the control transistor is driven by a voltage having a value different from that of the input voltage. (B) The input voltage is used for driving the control transistor by connecting the control terminal to the input terminal. Since such a direct-current stabilizer functions in the same manner as a conventional direct-current stabilizer using an n-p-n transistor, it is used for various purposes. (C) The control terminal and the input terminal are easily connected to each other by placing the control terminal adjacent to the input terminal. (D) The output of these direct-current stabilizer is externally switched between on and off by controlling the application of voltage to the control terminal by means of the ON/OFF circuit. For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a circuit diagram schematically showing a structure of a regulator IC according to a first comparative example. Fig. 2 is a circuit diagram showing a structure of a power source system incorporating the regulator IC of Fig. 1. Fig. 3(a) is a front view showing an internal structure of the regulator IC of Fig. 1. Fig. 3(b) is a side view showing an internal structure of the regulator IC of Fig. 1. Fig. 4 is a vertical section showing part of a structure of a transistor chip and an IC chip in the regulator IC of Fig. 3. Fig. 5 is a circuit diagram showing a structure of switching the output of the regulator 10 of Fig. 1. Fig. 6 is a circuit diagram showing a structure of the regulator IC of Fig. 1, wherein a control terminal and an input terminal are connected. Fig. 7 is a circuit diagram schematically showing a structure of a regulator IC according to a second comparative example. Fig. 8 is a circuit diagram of a regulator IC of the present invention, having a Darlington pair of an n-p-n transistor and a control transistor. Fig. 9 is a circuit diagram of a modified example of the regulator IC of Fig. 8, having Darlington pair of a p-n-p transistor and a control transistor. Fig. 10 is a circuit diagram schematically showing a structure of a regulator IC according to a third comparative example. Fig. 11 is a circuit diagram showing the actuation of the regulator IC of Fig. 10 with a control voltage as an example. Fig. 12 is a circuit diagram showing switching off the output of the regulator IC of Fig. 10 as an example. Fig. 13 is a circuit diagram showing the actuation of the regulator IC of Fig. 10 with an input voltage as an example. Fig. 14 is a circuit diagram of a modified regulator IC of Fig. 10, wherein a current limiter is placed in a position located between a control terminal and a differential amplifier and between the control terminal and a driving circuit. Fig. 15 is a circuit diagram of a modified regulator IC of Fig. 10, wherein a current limiter is placed between a control terminal and a differential amplifier. Fig. 16 is a circuit diagram of a modified regulator IC of Fig. 10, wherein a current limiter is placed between a control terminal and a driving circuit. Fig. 17 is a circuit diagram schematically showing a structure of a regulator IC according to a fourth comparative example. Fig. 18(a) is a front view showing an internal structure of the regulator IC of Fig. 17. Fig. 18(b) is a side view showing an internal structure of the regulator IC of Fig. 17. Fig. 19 is a circuit diagram showing a structure of a conventional direct-current stabilizer using an n-p-n control transistor. Fig. 20 is a circuit diagram showing a structure of a conventional direct-current stabilizer using a p-n-p control transistor. Fig. 21 is a vertical section showing a structure of a vertically constructed chip of a conventional direct-current stabilizer using a p-n-p control transistor. Fig. 22 is a vertical section showing a structure of a laterally constructed chip of a conventional direct-current stabilizer using a p-n-p control transistor. DESCRIPTION OF THE EMBODIMENTS The following description discuses a first comparative example with reference to Figs. 1 through 6. As illustrated in Fig. 2, a power source system of this comparative example includes a line filter 1, a bridge rectifier 2, a control IC 3 for controlling switching, a photocoupler 4 for insulation, and a regulator IC 5 as a direct-current stabilizer. The power source system also has a transistor Tr 1 for switching, a high frequency transformer T, a transistor Tr 2 for controlling ON/OFF switching, smoothing capacitors C 1 to C 3 , diodes D 1 and D 2 as rectifiers, and a resistor R 1 . In this power source system, line noise is removed from a 100 V alternating current by the line filter, and the resulting alternating current is rectified and smoothed by the bridge rectifier 2 and the capacitor C 1 to produce a DC voltage. The DC voltage is changed into pulse form when the transistor Tr 1 is switched between on and off by the control IC 3. The voltage pulses thus obtained are transmitted through the high frequency transformer T toward the outputs, and rectified and smoothed by a circuit formed by a diode D 1 and a capacitor C 2 and a circuit formed by a diode D 2 and a capacitor C 3 , respectively, to produce two DC voltages. The DC voltage output from the diode D 1 is fed back as an output voltage V O 1 , through the photocoupler 4 to the control IC 3. The output voltage V O 1 also goes through the resistor R 1 and is input to a control terminal CNT 1 of the regulator IC 5. On the other hand, the DC voltage output from the diode D 2 is input to the input terminal IN of the regulator IC 5. In the regulator IC 5, an input voltage supplied to the input terminal IN from the diode D 2 is controlled by driving a transistor Tr 3 , to be described later (see Fig. 1), with the output voltage V O 1 , and a stabilized output voltage V O 2 is produced. The output of the regulator IC 5 is switched between on and off by starting or stopping applying the voltage to the transistor Tr 3 . The application of the voltage is started or stopped by switching the transistor Tr 2 as an ON/OFF circuit between on and off in accordance with an ON/OFF control signal supplied from an external source. As illustrated in Fig. 1. the regulator IC 5 includes the input terminal IN connected to an external device, an output terminal OUT, a ground terminal GND, and the control terminal CNT 1 . The regulator IC 5 also includes the transistor Tr 3 , resisters R 2 to R 4 , a differential amplifier 6 and a reference voltage circuit 7 as essential components for the direct-current stabilizer. The base of the transistor Tr 3 as an n-p-n control transistor is connected to the output terminal of the differential amplifier 6, and connected through the resistor R 2 to the control terminal CNT 1 as a first control terminal. The collector of the transistor Tr 3 is connected to the input terminal IN, while the emitter thereof is connected to the output terminal OUT. The withstanding voltage of the control terminal CNT 1 is higher than those of other terminals IN, OUT and GND. Therefore, for example, the control terminal CNT 1 has an insulating layer with a thickness greater than those of the insulating layers on other terminals, IN, OUT and GND. Placed between the output terminal OUT and the ground terminal GND are the resisters R 3 and R 4 which are connected in series and form a voltage divider. The junction between the resistor R 3 and R 4 is connected to the negative input of the differential amplifier 6. The reference voltage circuit 7 is placed between the input terminal IN and the ground terminal GND. The reference voltage circuit 7 is a circuit for generating a predetermined reference voltage according to the input voltage. For example, a fixed voltage element such as a Zener diode, and a fixed voltage circuit are used as the reference voltage circuit 7. The reference voltage circuit 7 is connected to the positive input of the differential amplifier 6 and supplies a predetermined voltage thereto. The positive source input of the differential amplifier 6 is connected to the input terminal IN, while the negative source input thereof is connected to the ground terminal GND. The differential amplifier 6 controls the emitter voltage or the output voltage of the regulator IC 5 by controlling the base current of the transistor Tr 3 , so that the feedback voltage divided by the resistors R 3 and R 4 becomes equal to the reference voltage of the reference voltage circuit 7. In the regulator IC 5, a current limiter 8 as current limiting means is placed between the control terminal CNT 1 and the resistor R 2 . The current limiter 8 limits an increase in the power consumption by limiting the current flowing from the control terminal CNT 1 to the base of the transistor Tr 3 to a predetermined value. The regulator IC 5 with such a circuit structure includes a transistor section 9 and an IC section 10 manufactured as a single chip as shown in Figs. 3(a) and 3(b). The transistor section 9 is the transistor Tr 3 produced in chip form. The IC section 10 is formed by integrating on a single chip all the above-mentioned elements and circuits, except for the transistor Tr 3 . The transistor section 9 and the IC section 10 are die-bonded onto a metal frame 12 at a solder junction 11. A near central portion of one edge of the metal frame 12 is elongated to form an outer lead frame 13 as the ground terminal GND. In Figs. 3(a) and 3(b), an outer lead frame 14 as the output terminal OUT is formed in parallel with and on the left side of the outer lead frame 13, while an outer lead frame 15 as the input terminal IN and an outer lead frame 16 as the control terminal CNT 1 are formed in parallel with and on the right side of the outer lead frame 13. The metal frame 12 is fixed to an inner lead frame 17. A contact section 9a of the transistor section 9, which functions as a collector, is connected to the outer lead frame 15, and a contact section 9b thereof functioning as an emitter is connected to the outer lead frame 14. A contact section 10a of the IC section 10 to be grounded is connected to the metal frame 12, and a contact section 10b thereof to which a control signal is input is connected to the outer lead frame 16. These connections are made by wire bonds using metal wires 18. The chips 9 and 10, the metal frame 12 and the inner lead frame 17 as well as one end of each of the outer lead frames 13 to 16 are covered with a package 19. The package 19 is made from a coating resin, such as an epoxy resin, and formed by transfer-molding for example. The sectional structure of the transistor section 9 and the IC section 10 is discussed below. As illustrated in Fig. 4, in the transistor section 9, an n+ buried layer 21 and an n-type epitaxial layer 22 as the collector are formed on a p-type substrate 20. Further, a base diffused layer 23, an emitter diffused layer 24 and a collector layer 25 are formed on the epitaxial layer 22. The IC section 10 has a portion where a base diffused layer 27, an emitter diffused layer 28 and a collector layer 29 are formed on an n+ buried layer 26 and the n-type epitaxial layer 22 over the p-type substrate 20. The epitaxial layer 22 includes isolation diffused layers 30 to 33 so as to separate the transistor section 9 and the IC section 10 from each other. The operation of the regulator IC 5 of such a structure is discussed below. As illustrated in Figs. 2 and 5, a control voltage V C derived from an output voltage V O 1 is applied through the resistor R 1 to the control terminal CNT 1 . When the transistor Tr 2 is switched off, the control voltage V C is applied to the control terminal CNT 1 . On the other hand, when the transistor Tr 2 is switched on, no control voltage V C is applied to the control terminal CNT 1 . The value of the control voltage V C is set so that a voltage, which is not lower than the sum of the emitter voltage of the transistor Tr 3 , i.e., the output voltage V O (V O 2 ) of the regulator IC 5 and the base-emitter voltage, is applied to the base of the transistor Tr 3 . In the case when the output voltage V O of the regulator IC 5 is 5 volt, the control voltage V C is set to a value which meets the requirement, for example, around 10 volt. When the transistor Tr 2 is switched off and the control voltage V C is applied to the control terminal CNT 1 , the transistor Tr 3 is biased and switched on. At this time, the output voltage V O appearing at the emitter is divided by the resistors R 3 and R 4 to produce a feed back voltage. The feed back voltage is applied to the differential amplifier 6, and the reference voltage generated by the reference voltage circuit 7 is also applied thereto. The differential amplifier 6 controls the base current of the transistor Tr 3 according to the difference between the feedback voltage and the reference voltage. Thus, the transistor Tr 3 controls an input voltage V IN so as to produce the output voltage V O of a value which is determined by the dividing rate of the resistors R 3 and R 4 and by the reference voltage. When the transistor Tr 2 is switched on by an ON/OFF control signal, no control voltage V C is applied to the control terminal CNT 1 , thereby switching off the transistor Tr 3 . This causes the output of the regulator IC 5 to be switched off. Namely, the output of the regulator IC 5 is switched between on and off by switching the transistor Tr 2 between on and off. As described above, in the regulator IC 5, the transistor Tr 3 is activated upon the application of the control voltage of a predetermined value to the control terminal CNT 1 . Unlike a regulator IC which uses the input voltage V IN to drive the transistor Tr 3 , the regulator IC 5 does not require a high input voltage V IN . For example, when the output voltage V O is 5 volt, the input voltage V IN is set to around 5.5 volt in anticipation of a lowering of the collector-emitter voltage of the transistor Tr 3 . It is therefore possible to reduce the losses of the regulator IC 5 to a large degree. Moreover, since the n-p-n transistor Tr 3 which has a smaller chip size and is inexpensive to manufacture is used, the low-cost regulator IC 5 is obtained. Furthermore, since the regulator IC 5 includes the current limiter 8 for limiting a current delivered from the control terminal CNT 1 , it is possible to restrict the power consumption of the regulator IC 5. Since the withstanding voltage of the control terminal CNT 1 is higher than those of other terminals IN, OUT and GND, the regulator IC 5 is protected from the control voltage V C . In addition, it is possible to switch the output of the regulator IC 5 between on and off by connecting the transistor Tr 2 to the control terminal CNT 1 . In the regulator IC 5 since the input terminal IN and the control terminal CNT 1 are located adjacent to each other as shown in Fig. 3, the input terminal IN and the control terminal CNT 1 are easily connected as shown in Fig. 6. With this arrangement, since the input voltage V IN is applied to the control terminal CNT 1 , the transistor Tr 3 is driven by the input voltage V IN like in a conventional regulator IC. Namely, the regulator IC 5 is used even in a power source system with a single output. Consequently, by providing the control terminal CNT 1 , the low-cost general-purpose regulator IC 5 achieving a reduction in the losses is obtained. The following description discusses a second comparative example with reference to Fig. 7 and embodiments of the invention with reference to Figs 8 and 9. The components having the same function as the components described in the first comparative example will be designated by the same code and their description will be omitted. A direct-current stabilizer is shown in Fig. 7 as a regulator IC 41 having a control terminal CNT 2 . The withstanding voltage of the control terminal CNT 2 as a second control terminal is higher than those of other terminals IN, OUT, and GND. The control terminal CNT 2 is connected through the current limiter 8 to the positive source input of the differential amplifier 6. The control terminal CNT 2 is connectable to a transistor, not shown, like the transistor Tr 2 in the first embodiment (see Fig. 5). Connecting the control terminal CNT 2 to the transistor allows the output of the regulator IC 41 to be switched between on and off. In an actual IC package, the control terminal CNT 2 is located adjacent to the input terminal IN. The operation of the regulator IC 41 having such a structure is discussed below. In the regulator IC 41, the control voltage V C is applied to the control terminal CNT 2 . The effective variations in the output voltage of the differential amplifier 6 are determined by the power source voltage, i.e., the control voltage V C . Namely, the value of the control voltage V C is set such that the differential amplifier 6 applies to the base of the transistor Tr 3 a voltage not lower than the sum of the emitter voltage and the base-emitter voltage. When the control voltage V C is applied to the control terminal CNT 2 , the transistor Tr 3 is biased and switched on, so that the output voltage V O is delivered to the output terminal OUT. Then, the base current of the transistor Tr 3 is controlled by the differential amplifier 6 according to the feedback voltage produced by dividing the output voltage V O with the resistors R 3 and R 4 and the reference voltage of the reference voltage circuit 7. Consequently, the transistor Tr 3 controls the input voltage V IN to produce the output voltage V O of a constant value which is determined by the dividing rate of the resistors R 3 and R 4 and the reference voltage. As described above, in this regulator, since the control voltage V C of value different from that of the input voltage V IN is used as a power source for the differential amplifier 6, the low-cost regulator IC 41 having reduced losses like the above-mentioned regulator IC 5 is obtained. Modified examples of the regulator IC 41, which form embodiments of the invention, are shown as regulators IC 42 and 43 in Figs. 8 and 9. The regulator IC 42 includes an n-p-n transistor Tr 4 . The emitter of the transistor Tr 4 is connected to the base of the transistor Tr 3 , forming a Darlington pair. The collector of the transistor Tr 4 is connected to the control terminal CNT 2 and the base thereof is connected to the output terminal of the differential amplifier 6. Since the transistors Tr 3 and Tr 4 of the regulator IC 42 form a Darlington pair, the regulator IC 42 is capable of supplying an output current greater than that of the regulator IC 41. However, the voltage necessary for driving the transistor Tr 3 includes the base-emitter voltage of the transistor Tr 4 . Therefore, the base-emitter voltage is needed to be considered when determining the value of the control voltage V C . On the other hand, the regulator IC 43 includes a p-n-p transistor Tr 5 instead of the transistor Tr 4 . The transistors Tr 3 and Tr 5 form a Darlington pair. Since the transistor Tr 5 is a p-n-p transistor, the regulator IC 43 is designed so that the differential amplifier 6 draws a current from the base of the transistor Tr 5 . Namely, the positive input of the differential amplifier 6 is connected to the junction of the resistors R 3 and R 4 , and the negative input is connected to the output of the reference voltage circuit 7. Like the regulator IC 42, the regulator IC 43 with such a structure is capable of supplying high output currents. The following description discusses a third comparative example with reference to Figs. 10 to 16. The components having the same function as the components described in the first comparative example will be designated by the same code and their description will be omitted. A direct-current stabilizer includes a regulator IC 51 shown in Fig. 10. The regulator IC 51 has a control terminal CNT 3 and a driving circuit 52. The withstanding voltage of the control terminal CNT 3 as a third control terminal is higher than those of other terminals IN, OUT, and GND. The control terminal CNT 3 is connected to the positive source input of the differential amplifier 6 and the source input of the driving circuit 52. The control terminal CNT 3 is connectable to a transistor, not shown, like the transistor Tr 2 in Fig. 5. Connecting the control terminal CNT 3 to the transistor allows the output of the regulator IC 51 to be switched between on and off. In an actual IC package, the control terminal CNT 3 is located adjacent to the input terminal IN. The driving circuit 52 is a circuit including an active element which is activated by the control voltage V C applied to the control terminal CNT 3 , and drives the transistor Tr 3 under the control of the differential amplifier 6. The operation of the regulator IC 51 having such a structure is discussed below. In the regulator IC 51, the control voltage V C is applied to the control terminal CNT 3 . The value of the control voltage V C is set such that the driving circuit 52 applies to the base of the transistor Tr 3 a voltage which is not lower than the sum of the emitter voltage and the base-emitter voltage. When the control voltage V C is applied to the control terminal CNT 3 , the transistor Tr 3 is biased and switched on, so that the output voltage V O is delivered to the output terminal OUT. Then, the base current which is supplied from the driving circuit 52 to the transistor Tr 3 is controlled by the differential amplifier 6 according to the feedback voltage produced from the output voltage V O and a reference voltage. Consequently, the transistor Tr 3 controls the input voltage V IN to produce the output voltage V O of a constant value which is determined by the dividing rate of the resistors R 3 and R 4 and the reference voltage. As described above since the control voltage V C of a value different from that of the input voltage V IN is used as a power source for the driving circuit 52, the low-cost regulator IC 51 having reduced losses like the regulator IC 5 is obtained. An application of the regulator IC 51 to a practical circuit is described below. As illustrated in Fig. 11, the regulator IC 51 includes an actuator 53 and an overcurrent limiter 54 which are not shown in Fig. 10. The actuator 53 activates the reference voltage circuit 7 when the input voltage V IN reaches a predetermined value. The overcurrent limiter 54 limits the collector current of the transistor Tr 3 by limiting the base current thereof, thereby protecting the transistor Tr 3 from the overcurrent. As described above, in the regulator IC 51, when the control voltage V C is applied to the control terminal CNT 3 , the transistor Tr 3 controls the input voltage V IN and produces the output voltage V O of a predetermined value. The output voltage V O is then applied to a load 55. The output characteristic of the output voltage V O is improved by a capacitor C 4 . When the control terminal CNT 3 is grounded as illustrated in Fig. 12, the output of the regulator IC 51 is switched off. The switching of the output may be performed by means of a transistor as mentioned above. In the regulator IC 51, on the other hand, as illustrated in Fig. 13, when the control terminal CNT 3 is connected to the input terminal IN, the transistor Tr 3 is driven by the input voltage V IN via the driving circuit 52. Therefore, the regulator IC 51 functions in the same manner as a conventional regulator IC using an n-p-n transistor. With this structure, the regulator IC 51 is used in a system having a single power source. Modified examples of the regulator IC 51 are shown as regulators IC 56, 57 and 58 in Figs. 14 to 16. In the regulator IC 56, the current limiter 8 is placed in a position which is located between the control terminal CNT 3 and the differential amplifier 6 and between the control terminal CNT 3 and the driving circuit 52. In the regulator IC 57, the current limiter 8 is placed between the control terminal CNT 3 and the differential amplifier 6. In the regulator IC 58, the current limiter 8 is placed between the control terminal CNT 3 and the driving circuit 52. By providing the current limiter 8, the current flowing from the control terminal CNT 3 to the differential amplifier 6 and to the driving circuit 52 is limited to a predetermined value, thereby restricting an increase in the consumption of power. The following description discusses a fourth comparative example with reference to Figs. 17 and 18. The components having the same function as the components described in the first and third comparative examples will be designated by the same code and their description will be omitted. A direct-current stabilizer is a regulator IC 61 shown in Fig. 17. The regulator IC 61 is constructed by adding a reset signal generating circuit 62 to the regulator IC 51 shown in Fig. 10. The regulator IC 61 is therefore provided with a reset terminal R for outputting a reset signal. The reset signal generating circuit 62 is connected to the output terminal OUT, and generates a reset signal when it detects an output voltage V O lower than a predetermined level. The reset signal is supplied to the reset terminal R and then transmitted to essential external devices. For example, in the case where this direct-current stabilizer is used in a power source for a resettable electronic circuit such as microcomputer, when the output V o drops, the reset signal prevents a runaway of the electronic circuit. As illustrated in Figs. 18(a) and 18(b), the regulator IC 61 includes a transistor section 63 and an IC section 64 formed on a signal chip. The transistor section 63 is the transistor Tr 3 in chip form. The IC section 64 is formed by integrating the above-mentioned elements and circuits except for the transistor Tr 3 on a single chip. The transistor section 63 and the IC section 64 are fixed onto a metal frame 66 by die bonds at a solder junction 65. A central portion of one edge of the metal frame 66 is elongated to form an outer lead frame 67 serving as the ground terminal GND. In Figs. 18(a) and 18(b), outer lead frames 68 and 69 are formed in parallel with and on the left side of the outer lead frame 67, while outer lead frames 70 and 71 are formed in parallel with and on the right side thereof. The outer lead frame 68 next to the outer lead frame 67 serves as the output terminal OUT, and the outer lead frame 69 next to the outer lead frame 68 serves as the reset terminal R. The outer lead frame 70 next to the outer lead frame 67 serves as the input terminal IN, and the outer lead frame 71 next to the outer lead frame 70 is the control terminal CNT 3 . In the transistor section 63, a contact section 63a as the collector is connected to the outer lead frame 70, while a contact section 63b as an emitter is connected to the outer lead frame 68. In the IC section 64, a contact section 64b to be grounded is connected to the metal frame 66, a contact section 64b to which a control signal is input is connected to the outer lead frame 71, and a contact section 64c for outputting a reset signal is connected to the outer lead frame 69. These connections are made by wire bonds using metal wires 72. Portions of the metal frame 66 on which the transistor section 63 and the IC section 64 are mounted and one end of each of the outer lead frames 67 to 71 are covered with a package 73. The package 73 is made from a coating resin, such as an epoxy resin, and formed by transfer-molding for example. Similar to the regulator IC 52, in the regulator IC 61 having the above-mentioned structure, since the control voltage V C having a value different from that of the input voltage V IN is used as a power source for the driving circuit 52, the low-cost regulator IC 61 having reduced losses is obtained. Moreover, since the regulator IC 61 generates the reset signal, it is applicable to resettable electronic circuits such as a microcomputer applied systems. The invention being thus described, it will be obvious that the same may be varied in many ways within the scope of the following claims.

Claims: An integrated direct-current stabiliser comprising: an input terminal (IN) for receiving an input supply voltage; and an n-p-n control transistor (Tr 3 ) whose base current is controlled on the basis of an output voltage of said direct-current stabiliser, for reducing an input voltage and maintaining the output voltage at a predetermined value; characterised in that the stabiliser further comprises: a control terminal (CNT 2 ) provided separately from said input terminal, for controlling biasing of the base of said control transistor independently of said input voltage and for supplying to the base of said control transistor a control voltage which is not lower than a sum of the emitter voltage and the base-emitter voltage of the control transistor; and in that it further comprises an n-p-n transistor (Tr 4 ) having a collector connected to said control terminal, said n-p-n transistor and said control transistor being a Darlington pair. An integrated direct-current stabiliser comprising: an input terminal (IN) for receiving an input supply voltage; and an n-p-n control transistor (Tr 3 ) whose base current is controlled on the basis of an output voltage of said direct-current stabiliser, for reducing an input voltage and maintaining the output voltage at a predetermined value; characterised in that the stabiliser further comprises: a control terminal (CNT 2 ) provided separately from said input terminal, for controlling biasing of the base of said control transistor independently of said input voltage and for supplying to the base of said control transistor a control voltage which is not lower than a sum of the emitter voltage and the base-emitter voltage of the control transistor; and in that it further comprises a p-n-p transistor (Tr 5 ) having an emitter connected to said control terminal, said p-n-p transistor and said control transistor being a Darlington pair. An integrated direct-current stabiliser as claimed in claim 1 or 2 and further comprising: a differential amplifier (6) for controlling the base current of said control transistor in accordance with said output voltage so that said control transistor maintains said output voltage at the predetermined value; and wherein the control terminal (CNT 2 ) is adapted to supply to the differential amplifier a source voltage such that the differential amplifier applies to the base of said control transistor a voltage which is not lower than a sum of the emitter voltage and the base-emitter voltage of the control transistor. An integrated direct-current stabilizer according to Claim 3 when dependent upon Claim 1, wherein said differential amplifier and said n-p-n transistor are directly connected to said control terminal, the withstand voltages of the differential amplifier and said n-p-n transistor are higher than a withstand voltage of said input terminal, and the base of said n-p-n transistor is connected to an output of said differential amplifier. An integrated direct-current stabilizer according to Claim 3 when dependent upon Claim 2, wherein said differential amplifier and said p-n-p transistor are directly connected to said control terminal, the withstand voltages of the differential amplifier and said p-n-p transistor are higher than a withstand voltage of said input terminal, and the base of said p-n-p transistor is connected to an output of said differential amplifier. An integrated direct-current stabiliser according to claim 3, and further comprising current limiting means (8) for limiting a flow of a current from said control terminal. An integrated direct-current stabiliser according to claim 6, wherein the current limiting means limits a flow of the current into a source input of said differential amplifier. An integrated direct-current stabiliser according to any preceding claim wherein the withstand voltage of the control terminal (CNT 2 ) is greater than the withstand voltage of the input terminal (IN). An integrated direct-current stabiliser according to any preceding claim wherein the control terminal (CNT 2 ) is placed adjacent to the input terminal (IN). An integrated direct-current stabiliser according to any preceding claim wherein the the control terminal (CNT 2 ) is connectable to an ON/OFF circuit for applying or for not applying a voltage.

Inventors: HACHIMURA KENJI, MATSUMURA TSUNEO, SUZUKI TOMOHIRO, HACHIMURA, KENJI, MATSUMURA, TSUNEO, SUZUKI, TOMOHIRO
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1993
Main classification: G05F1
IPC codes: G05F1